Review Article Ferroelectric Polymer Thin Films for ...downloads.hindawi.com/journals/jnm/2015/812538.pdf · Review Article Ferroelectric Polymer Thin Films for Organic Electronics

Review ArticleFerroelectric Polymer Thin Films for Organic Electronics

Manfang Mai12 Shanming Ke1 Peng Lin1 and Xierong Zeng12

1College of Materials Science and Engineering Shenzhen University Shenzhen 518060 China2Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong ProvinceCollege of Optoelectronic Engineering Shenzhen University Shenzhen 518060 China

Correspondence should be addressed to Shanming Ke smkeszueducn and Xierong Zeng zengxierszueducn

Received 2 January 2015 Accepted 23 March 2015

Academic Editor Edward A Payzant

Copyright copy 2015 Manfang Mai et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The considerable investigations of ferroelectric polymer thin films have explored new functional devices for flexible electronicsindustry Polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene (TrFE) are the most commonly used polymerferroelectric due to their well-defined ferroelectric properties and ease of fabrication into thin films In this study we reviewthe recent advances of thin ferroelectric polymer films for organic electronic applications Initially the properties of ferroelectricpolymer and fabrication methods of thin films are briefly described Then the theoretical polarization switching models forferroelectric polymer films are summarized and the switching mechanisms are discussed Lastly the emerging ferroelectric devicesbased on P(VDF-TrFE) films are addressed Conclusions are drawn regarding future work on materials and devices

1 Introduction

In recent years driven by the rapidly developingminiaturizedelectronics new organic devices based on polyvinylidenefluoride (PVDF) and its copolymer with trifluoroethylene(TrFE) thin films have attracted intensive research interestGenerally ferroelectrics exhibit a striking finite size effect[1] The switching time and the coercive field increase withdecreasing film thickness while reversely the remanent polar-ization and the phase transition temperature decrease withdecreasing thickness For applications which require low-voltage operation such as nonvolatile memories the ferro-electric films should be thin enough for low operation voltageat the same time they should have sufficient and stable ferro-electric properties to maintain the memory functionality

PVDF and its copolymer with TrFE are the representativeand the most important organic ferroelectric materials Theferroelectricity in PVDF and P(VDF-TrFE) originates frommolecular dipoles associated with electropositive hydrogenatoms and electronegative fluoride atoms which are switch-able upon an external field [2]They are promising candidatesfor the next generation nonvolatile high-density memoryapplications which can replace perovskite ceramics currently

used in the commercial ferroelectric random access memo-ries (FRAMs) [3ndash5] Their attractive advantages include lowtemperature processing low-cost solution processing out-standing chemical stability and nontoxicity [6] In the pastfew years there have been considerable research activitiesto combine P(VDF-TrFE) films as nonvolatile memory cellssuch as metal-ferroelectric-insulator-semiconductor (MFIS)diode [7ndash11] and ferroelectric-field-effect-transistor (FeFET)[12ndash15] The key issues for optimizing the memory perfor-mance including switching time switching voltage retentionand endurance still need to be overcome Recently PVDFand its copolymer find their new way for the emerging appli-cations in organic electronics such as negative capacitancedevices [16] organic photovoltaic cells [17] and multiferroictunnel junctions [18]

The discovery of Langmuir-Blodgett (LB) ferroelectricpolymer films in 1995 [19] led to investigation of ferroelectricproperties at the nanoscale For P(VDF-TrFE) films the fer-roelectricity and polarization switching have been found fortwo monolayers (119897 = 1 nm) [20] It opened the way for inves-tigation of finite size effect at the nanoscale Since then it hasbeen a subject of intensive study not only in theoreticalaspects but also in technical applications The results on

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2015 Article ID 812538 14 pageshttpdxdoiorg1011552015812538

2 Journal of Nanomaterials

FC

H

VDF TrFE

P

Figure 1 Schematic ofmolecular structure of P(VDF-TrFE) in the120573 phaseThepolarization direction points fromfluoride to hydrogen atoms

P(VDF-TrFE) LB films provide many new insights into thefundamental physics the existence of two-dimensional ferro-electrics with nearly absence of finite size effects on the bulktransition (a first order phase transitionwith a transition tem-perature nearly equal to the bulk value) [20] the transitionfrom extrinsic (switching with nucleation and domain wallmotion) to intrinsic (switching without domain) ferroelectricswitching in the context of Landau-Ginzburg mean-fieldtheory below a thickness of 15 nm [21] and so forth Howeverthere have been strong debates of the theoretical modelsused to explain the experiments Scott pointed out thatthe presence of two apparent phase transition temperaturesinterpreted as true two-dimensional surface ferroelectricityby the Moscow-Nebraska group instead can be explained bythe seminal Tilly-Zeks theory and its extension by Duiker tofirst order phase transition [22] Several groups spoke againstthe intrinsic nature of the switching as the experimentslack several key features of intrinsic switching [23ndash27]Lately theMoscow-Nebraska group demonstrated some newexperiment evidences to support their claim of domain-freeLandau switching in P(VDF-TrFE) LB films [28 29] as well asin ultrathin BaTiO

3films [30] suggesting that homogeneous

switching in ultrathin films is a common phenomenon forall ferroelectric materials Currently the explanations forthe switching behavior in P(VDF-TrFE) thin films are stillcontroversial

PVDF is a rich system for both practical applicationsand academic investigations including phase transition andswitching mechanism The main objective of this paper is toreview the current research status of ferroelectric polymerfilms with emphases on switching mechanism and ferro-electric devices based on P(VDF-TrFE) films particularlywith the thickness below one hundred nanometers Thedevelopment of ferroelectric polymer thin film devices willhave a significant impact on organic electronics

2 Ferroelectric Polymers

The piezoelectricity in poled PVDF was discovered in 1969[31] followed by the discovery of the pyroelectricity inPVDF in 1971 [32] However it was not until the late 1970sthat the ferroelectricity in PVDF was confirmed [33 34]

The distinguishing characteristics of PVDF and its copoly-mers include highly compact structure high chemical sta-bility large permanent dipole moment ease of fabricationand low annealing temperature which can be integratedwith other materials and processes for example siliconmicrofabrication

PVDF exhibit four polymorphic crystalline forms 120572 120573120574 and 120575 phases whose formations depend on crystallizationconditions electrical poling and mechanical drawing The120573 phase has an orthorhombic structure with an all-trans(TTTT) molecule conformation possessing a large sponta-neous polarization and is responsible for the ferroelectricand piezoelectric properties The dipoles in the 120573-PVDFextend from the electronegative fluoride atoms to the slightlyelectropositive hydrogen atoms perpendicular to the polymerchain direction producing a dipole moment of 7 times 10minus30 Csdotm(2Debyes) as shown in Figure 1 Recently 120575-PVDF is success-fully fabricated as an overlooked polymorph of PVDF pro-posed 30 years ago [35] The remanent polarization andcoercive field are comparable to those of 120573-PVDF and ofP(VDF-TrFE) while the thermal stability is enhanced due toits higher Curie temperature

The introduction of TrFE which has three fluoride atomsper monomer to copolymerize with PVDF can enhancethe all-trans conformation associated with the 120573 phase Thisis because the fluoride atom is larger than hydrogen atomand therefore it can induce a stronger steric hindrance [2]In addition the copolymer with TrFE can be annealed tomuch higher crystallinity than pure PVDF [36] The moststudied copolymers have a composition of P(VDF-TrFE7030) which has a maximum spontaneous polarizationaround 10120583Ccm2 [37] Another feature for the introductionof TrFE is that it can lower the phase transition temperature119879

119888

in the copolymers P(VDF-TrFE)withmolar ratios of 50ndash80of PVDF undergoes a clear ferroelectric-paraelectric phasetransition with a measurable Curie point The 119879

119888increases

with increasing PVDF content from 70∘C at 50mol to140∘C at 80mol The transition is an order-disorder typewhile the disorder is a random mixture of trans- and gauchecombinations in the conformation of the molecules More-over the transition tends to change from a first order to

Journal of Nanomaterials 3

a second order as the PVDF content decreases to a 5248composition with evidence of the disappearance of thermalhysteresis [38] In the bulk PVDF the phase transition is notaccessible with experiments because the melting temperatureof this ferroelectric polymer (sim170∘C) is lower than the pointof the possible phase transition 119879

119888 Until very recently a

first order ferroelectric phase transition in the Langmuir-Blodgett ultrathin PVDF films was observed for the first time[39]We have found the thickness interval where ferroelectricphase transition disappears and transition from ferroelectricto pyroelectric state takes place in PVDF Langmuir-Blodgettfilms and explain the shift of 119879

119888by the finite size effect at the

nanoscale using Landau-Ginzburg-Devonshire theory andthe Weiss mean field model [40]

3 Thin Films Fabrication

31 Spin Coating Conventionally ferroelectric thin films areprepared by solvent spinning method which is very attractivefor researchers due to its ease of processing and good qualityof film surface PVDF and its copolymers can be dissolvedin a variety of organic solvents for spin coating such as 2-butanone dimethylsulfoxide (DMSO) dimethylformamide(DMF) andmethylethylketone (MEK)The sample thicknesscan be controlled by varying the solution concentrations androtating speeds P(VDF-TrFE) films prepared by spin coatingconsist of both crystalline and noncrystalline regions [2]Uniform and compact ferroelectric films thinner than 60 nmare usually difficult to achieve by spin coating Lately with theimprovement of experimental conditions some groups canproduce ferroelectric copolymer films even down to 10 nmby spin coating [35 44 45] Li et al [46] reported thathomogeneous and smooth thin PVDF films can be preparedeither at low relative humidity or at high substrate temper-ature Figure 2 shows the surface morphology evolution ofPVDF thin films as a function of both relative humidityand substrate temperature At high relative humidity thefilm surface is porous and loose With decreasing humiditythe film becomes homogeneous and dense (Figure 2(a)) Onthe other hand (Figure 2(b)) fixing the relative humidity at25 the surface morphology of PVDF films is denser andsmoother as the substrate temperature is increased from20∘C to 100∘C The microstructure of PVDF thin films isdetermined by the phase separation mechanism

32 Langmuir-Blodgett Technique Two-dimensional ferro-electric polymer films can be fabricated by Langmuir-Blodgett (LB) technique which allows precise control of filmthickness down to one monolayer with high crystallinityThe principle of LB technique is the amphiphilic property ofmolecules which are composed of a hydrophilic part and ahydrophobic part [47] Amphiphilic molecules are trappedat the interface with one type of bonding being attracted topolarmedia such aswater and the other type of bonding beingmuch less water soluble The LB films are achieved throughsubsequent transfer of monolayers from gas-liquid interfaceonto a solid substrate The transfer can be done by eithervertical or horizontal dipping with the latter called horizontalLangmuir-Schaefer method as shown in Figure 3(a) [37]

Although P(VDF-TrFE) copolymer is not amphiphilic thelarge molecular weight of polymers with low solubility inwater can be dispersed to form a sufficiently stable layer onwater with a repeatable pressure area isotherm (Figure 3(b))which identifies the conditions forming closest packing of afilm of monolayer thickness [37] Good quality P(VDF-TrFE7030) LB films are deposited from a copolymer solution indimethylsulfoxide (DMSO) with concentration of 001 wtand target pressure of 3mNm [48 49]

Generally the as-prepared films need to be annealed closeto the crystallization temperature to increase the crystallinityIt is reported that the thermal annealing increases the filmsurface roughness [46] Alternately smooth PVDF thin filmscan be prepared using elevated substrate temperatures andapplying a short electrical pulse [35] Different materialshave served as electrodes for P(VDF-TrFE) films includingaluminum [20 50 51] platinum [52 53] gold [44 54 55]silver [54 56] copper [52] nickel [52] indium [45] sodium[57] and conducting PEDOTPSS copolymer [58] The mostcommonly used electrode is aluminum The advantages ofaluminum electrode are its low deposition temperaturechemical passivation and suppressing of charge injectionfrom themetal electrodeHowever the formation of the oxidelayer (Al

2O3) between the electrode and the ferroelectric film

inhibits fast switching of the films

4 Polarization Switching Mechanism

Theswitching behavior of ferroelectric polymer thin films hasbeen extensively investigated to understand the kinetics ofpolarization switching which is very critical for intentionaldesign and preparation of materials for various purposesDomain nucleation and domain wall motion mechanism forpolarization reversal was established early by Merz [59] andLittle [60] and later by Miller [61 62] and Fatuzzo [63] Thestudied ferroelectric material was barium titanate (BaTiO

3)

Numerous models have been proposed to quantify domainphenomena and their effects on ferroelectric switching Theclassical model to describe ferroelectric switching kineticsis the Kolmogorov-Avrami-Ishibashi (KAI) model [1 6465] which is based on the study of statistical behavior andthe probability of nucleation and growth of domains Analternative model is the nucleation-limited switching (NLS)model for thin films developed by Tagantsev et al [66 67]For P(VDF-TrFE) ultrathin films ferroelectric switchingmaynot include the usual nucleation and domain propagationprocesses Here the existing theoretical models for ferroelec-tric switching are summarized

41 Kolmogorov-Avrami-Ishibashi (KAI) Model Polarizationreversal in ferroelectrics proceeds by the nucleation ofreversed nuclei followed by the forward and sideways growthof the reversed areas as shown in Figure 4 [63] When afield is applied with the opposite polarity small nuclei ofdomain with reverse polarization direction appear usuallyat the interfaces or grain boundaries (Figure 4(a)) Eachnucleus grows parallel or antiparallel to the applied field untilit becomes a domain and reaches the opposite side (Fig-ure 4(b)) The domain formed in this way starts expanding


Top view Cross section20∘C

60

40

25

5

0

(a)

Top view Cross section

20∘C

25 humidity

40∘C

50∘C

90∘C

100∘C

(b)

Figure 2 Surface morphology evolution of PVDF thin films (a) Top view and cross section SEMmicrographs of PVDF thin films presentedas a function of the relative humidity between 0 and 60The films were deposited at room temperature 20∘CThe scale bars of 10 120583m and2 120583m are presented in the bottommicrographs (b) Top view and cross section SEMmicrographs of PVDF thin films presented as a functionof the deposition temperature between 20∘C and 100∘CThe relative humidity was fixed at 25 [46]

sideways (Figure 4(c)) After some time these domains arelarge enough to join each other and become coalescence(Figure 4(d))The above successive processes will repeat untilthe polarization is completely reversed in the whole sample

The Kolmogorov-Avrami-Ishibashi (KAI) model is appli-cable and very useful for analyzing the above switchingprocess in many materials including single crystals [66 68]as well as epitaxial thin film ferroelectrics [69] In the scopeof KAI model the ferroelectric media where the polarizationreversal takes place are infiniteThe reversed polarization119875(119905)and the switching current 119868(119905) can be written as

119875 (119905) = 21198751199041 minus exp [minus(

119905

1199050

)

119899

] (1)

119868 (119905) = 21198751199041198780

119899

1199050

(119905

1199050

)

119899minus1

exp [minus(119905

1199050

)

119899

] (2)

where119875119904is spontaneous polarization 119878

0is electrode area 119905

0is

switching time and 119899 can be an integer (120572-model or120573-model)or non-integer value (mixture of 120572-model and 120573-model)between 1 and 3 depending on the dimension of the systemA plot of the switching current profiles for different values of119899 according to (2) is depicted in Figure 5 The tick labels inthe axes would be different for a variation of parameters 119875

119904

1198780 and 119905

0in different samples Figure 5 shows qualitatively

different shapes of the switching currents For 119899 gt 1 there isa peak in the current transients For 119899 le 1 it is not possibleto identify a current maximum However there is no physical


HorizontalLB deposition

(a)

0

4

9

14

19

24

5 10 15

Expansion

Compression

Surfa

ce p

ress

ure (

mN

mminus1)

Area per molecular fragment (A2)

(b)

Figure 3 (a) Diagram of the Langmuir-Schaefer monolayer deposition method (b) Pressure-area isotherm of P(VDF-TrFE 7030) [37]

P

(a) (b)

(c) (d)

Ea

Figure 4 The evolution of the domain structure in ferroelectric during switching under an application of electric field (a) nucleation of newdomains (b) forward growth (c) sideways expansion and (d) coalescence after [63]

meaning in the framework of KAI model for an 119899 value lessthan 1 since the growth dimensionality could never be lessthan 1 Therefore a current maximum should always existin the switching transient when the sample is suppressedby a field above the coercive field in the framework of KAImodel Moreover KAI model describes a thermally activatedswitching

The KAI model assumes unrestricted domain growthin an infinite media Due to the simplified assumptions it

encounters problems when it comes to precisely describethe switching behavior in real finite ferroelectrics especiallyfor polycrystalline films and ceramics Therefore later onnew models are constructed to give a more realistic andappropriate description of polarization reversal

42 Nucleation-Limited Switching (NLS) Model Tagantsevet al [67] developed an alternative scenario of a nucleation-limited switching (NLS)modelwhich is successful to describe


0

Time (s)

n = 08

n = 1

n = 15

n = 2

n = 3

Switc

hing

curr

ent (

A)

Figure 5 Switching current profiles for 119899 with different values according to (2)

the switching kinetics in Pb(ZrTi)O3thin films This model

assumes that the film consists of many areas which switchindependently The switching in an area is considered to betriggered by an act of the reverse domain nucleation Theyused a distribution function of the switching times to describethe ensemble of the elementary regions In the frameworkof the NLS model the nucleation time is assumed to bemuch longer than the time of domain wall motion and adistribution of switching time is modified in the expressionof the time dependence of polarization written as [67]

119875 (119905) = 2119875119904int

infin

minusinfin

1 minus exp [minus(119905

1199050

)

119899

]119865 (log 1199050) 119889 (log 119905

0)

(3)

where 119865(log 1199050) is the distribution function for log 119905

0 It meets

the normalizing condition

int

infin

minusinfin

119865 (log 1199050) 119889 (log 119905

0) = 1 (4)

The value of 119899 is assumed to be 2 for thin film ferro-electrics and 3 for bulk ferroelectrics [67] The switchingdynamic extended in a wide time range can be describedin terms of this model with a simple shape of the spectrum119865(log 119905

0) Jo et al [70] suggested to use the Lorentzian dis-

tribution of log 1199050 which can account for variations in the

local electrical field related to the randomly distributed dipoledefects A Gaussian distribution can also be well adjusted tothe random electric field distribution suggested by Zhukovet al [71] Mao et al used the NLS model based on region-by-region switching to explain the switching kinetics ofP(VDF-TrFE) thin films which is successful to describe thepolarization reversal behavior in the time domain for samplesas thick as 100 nm [72]

Both KAI model and NLS model neglect the size ofnuclei and domains Fatuzzo [63] reported that the switchingcurrent maximum in time could be as broad as that of

a single relaxation process regardless of the domain growthdimensions if the size of nuclei is taken into considerationNumerical simulations in small systems using a local fieldmethod combined with dynamic Monte Carlo steps result ina monotonic decrease in the switching current [73]

43 The Weiss Mean Field Model One hundred years agoWeiss [74 75] proposed a model to describe phase transitionin ferromagnetic materials This model is actually a positivefeedback model The magnetic dipoles mutually evoke a fieldat the location of other dipoles which results in an alignmentof all dipoles into the same direction This local field whichis also called Weiss field is only defined at the location ofthe dipoles This model for magnetism was later applied toferroelectrics [76]

In dielectrics Lorentz [77] developed a similar local fieldmodel The local field at induced point dipoles for an infinitecubic lattice can be expressed as

119864loc = 119864119886+

119875

31205760

(5)

with 119864119886being the applied field and 119875 the polarization of

the matter Equation (5) illustrates that the local field viceversa produces the dipole moments at the lattice points Itis the superposition of the applied field and the dipolar fieldwhich is proportional to the polarization itself There aretwo types of dipoles permanent dipoles fluctuating thermallyactivated in double well potentials and induced dipoles Theinteraction between all these dipoles is considered withmeanfields averaged over all particular local fieldsThe double wellpotentials as shown in Figure 6 are characterized by theiractivation energy 120593

0and the distance between the wells 119897

[78] When no local field is present the double wells aresymmetrical and the dipoles are equally occupied in bothdirections The net polarization of the whole system is zeroWith a local field 119864loc acting at the permanent dipoles theoccupation changes and a net polarization results


minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0

Figure 6 Permanent dipoles are assumed to fluctuate thermally activated in double well potentials A local field shifts one well against theother redistributing the dipoles [78]

If only permanent dipoles are present the local fieldwithin the Weiss model is assumed to be similar to (5)

119864loc = 119864119886+ 120572119875 (6)

where 119875 is the macroscopic polarization which can bespontaneous below119879

119888or paraelectric above119879

119888120572 is a coupling

factor describing the strength of the interaction between thedipoles The model is a mean field approach It also containsmicroscopic elements including the properties of the doublewells with the magnitude of the fluctuating dipole momentsthe dipole densities and the coupling constant 120572 Thereforethe model can be considered as a link between phenomeno-logical descriptions and molecular modeling [78]

With the Weiss model several ferroelectric propertiescan be described that is ferroelectric hysteresis loop thetemperature dependence of the coercive field the Curie-Weiss law for the electrical susceptibility the buttery curvesof the susceptibility in an external field and a secondorder ferroelectric to paraelectric transition with its typicalprotraction in an applied electric field [78ndash80] It has beenshown that if additionally a strain in the material caused bythe piezoelectric effect that is by the polarization itself istaken into account a second order phase transition changesto a first order [81] In addition the appearance of a doublehysteresis close to the Curie temperature can be explained[82 83]

Lately Kliem and Kuehn [84] presented an analyticalapproach using the Weiss molecular mean-field model com-binedwith the fluctuation of dipoles in double-well potentialsto simulate the switching process with a maximum in theswitching current as observed by Merz The time-dependentswitching process and the static polarization hysteresis loopare simulated which are in good qualitative agreement withexperiments using the material parameters of P(VDF-TrFE)This theory is exact in the limit of infinite dimensions withhomogeneous state and single domain

44TheHomogenous Non-Domain Switching Recent studiesusing P(VDF-TrFE) copolymer Langmuir-Blodgett ultrathinfilms suggested that the switching kinetics in these filmsis different from the rules of nucleation and domain wallmotion (extrinsic switching) This type of switching is calledintrinsic switching which is defined by the absence of nucle-ation center and domain The distinction between domainnucleated and continuous intrinsic switching mechanisms

(a) Nucleated mechanism

(b) Continuous mechanism

Figure 7 Schematic of polarization evolution during switching ina uniaxial ferroelectric (a) Discontinuous nucleation and growthof inverted domains (b) Continuous uniform decrease of thepolarization magnitude through zero without domain formationArrows indicate the orientation and magnitude of polarization [85]

can be illustrated in Figure 7 [85] For intrinsic switching ithas a threshold field the intrinsic coercive field which is ashigh as 109 VmThe polarization switching exhibits a criticalbehavior characterized by a pronounced slowing just abovethe threshold field [86] In 2000Ducharme et al [21] reportedthat the intrinsic coercive field predicted by the Landau-Ginzburg theory of ferroelectricity was observed in P(VDF-TrFE) LB films below a thickness of 15 nm for the first timeThey found that with decreasing thickness the coercive fieldfirst increases and then saturates for samples thinner than15 nm to a value of 5MVcm which is in good agreementwith the theoretical intrinsic value

In intrinsic switching the dipoles in the systems arehighly correlated and tend to switch coherently or not at allIt can be described by Landau-Khalatnikov equations in thecontext of mean-field theory

120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)

where 119875 119866 119864 and 119879 are the polarization the free energy theelectric field and the temperature respectively 120585 is a dampingcoefficient and 119879

0is the Curie-Weiss temperature 120572 120573 and 120574

are constants assumed to be independent of temperature Byminimizing the free energy 119866 in (8) a steady state hysteresisloop119875(119864) can be derived as shown in Figure 8 [86]The solidlines in Figure 8(a) denote stable (AB andA1015840B1015840) ormetastable


(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10

Electric field EEc Time t120591

A B

C

O

12 106 102

00

10

A998400B998400

C998400

Figure 8 (a) The theoretical hysteresis loop 119875(119864) calculated from (7) and (8) for 119879 asymp 1198790 The solid lines represent stable or metastable states

and the dotted line denotes unstable states (b) Time evolution of the normalized polarization and current during switching at 119879 = 1198790for

several values of the normalized electric field The horizontal dashed lines connect corresponding points in (a) to states in (b) [86]

(BC and B1015840C1015840) minima in the free energy The dotted line(COC1015840) denotes unstable minima Starting from a stable stateB if an opposite electric field which has an amplitude lowerthan the coercive field is applied the polarization will remainin the metastable state (BC) and then return to its initial stateB after the field is removed On the contrary if a field largerthan the coercive field is applied the polarization will switchto the other state (A1015840B1015840) and remain in B1015840 when the fieldis suppressed The vertical dashed lines mark the limits ofthe quasi steady state hysteresis loop The evolution of thepolarization from a negative polarization state to a positivepolarization state in Figure 8(b) is obtained by numericalintegration of (7) There is switching only for 119864 gt 119864

119888 Any

field larger than 119864119888results in the same polarization value

The switching time 120591in in intrinsic homogenous switchingframe can be defined as the time needed by the polarizationfrom a stable state (eg +119875

119903) to cross the zero axis of

the polarization (eg BrarrO in Figure 8(a)) [23] From therelationship between the derivative of the polarization 119875 andthe free energy 119866 in (7) and (8) the reciprocal switching time120591in is found to have a square-root critical dependence of theform [86]

1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this

equation it can be seen that the switching time 120591in will goto infinity as the applied field 119864 approaches 119864

119888or the

temperature increases to 1198791 There is a true coercive field that

for fields below this value no switching should occur Inaddition the temperature dependence of switching processis different from a thermally activated behavior which has anexponential dependence

Followed by the observation of intrinsic switching inultrathin P(VDF-TrFE) LB films several groups arguedagainst the intrinsic nature of the switching [23ndash27] In [23]the authors found that the experiments lack several keyfeatures of intrinsic switching the coercive field does notsaturate with decreasing film thickness the electric fieldand temperature dependence of the switching time are notwell described by the intrinsic switching dynamics in (9)

the films have switching below the coercive field Naber etal [27] presented measurements using gold electrode forspin coated P(VDF-TrFE) films down to 60 nm A thicknessindependence of coercive field is found which leads to theconclusion that the thickness dependence of coercive field inLB films is due to the influence of the electrode interfacesVery recently the same group in [21] demonstrated newexperiment evidences to confirm the existence of intrinsicswitching kinetics in ultrathin ferroelectric copolymer films[28 29] They used piezoresponse force microscopy (PFM)to switch the sample at the nanoscale The dependence ofthe switching rate on voltage for a 54 nm thick film exhibitsextrinsic nucleation and domain growth kinetics without truethreshold coercive field and is qualitatively different fromthe behavior of an 18 nm thick film which exhibits intrinsicswitching kinetics with a true threshold coercive field Theabsence of top electrode on the sample can exclude the effectof electrode interface Intrinsic homogeneous switching isalso found in ultrathin ferroelectric BaTiO

3films [30] by

PFM and ultrathin epitaxial PbTiO3films [85] by in situ

synchrotron X-ray scattering measurements Consequentlythe authors claimed that homogeneous switching in ultrathinfilms is a commonphenomenon for all ferroelectricmaterials

The applicability of these models for PVDF and itscopolymer depends on the sample thickness morphologyexternal field and temperature Up to date the switchingprocess in P(VDF-TrFE) thin films is not fully understoodRecently thermal Barkhausen effect is observed in P(VDF-TrFE) copolymer films for the first time [87]The Barkhausenpulse is a microscopic phenomenon and can be a directway to prove the existence of domains The investigationof Barkhausen effect should be a new tool to distinguishdifferent switching mechanisms in ferroelectric materials inthe future

5 Applications

51 Nonvolatile Memories One of the most important appli-cations of P(VDF-TrFE) thin films is ferroelectric nonvolatilememory The principle of nonvolatile ferroelectric randomaccess memories (FRAMs) is based on the polarizationreversal by an external applied electric field The binary logic


Table 1 Comparison of the performances for different types of nonvolatile memories [41ndash43]

Type Areacell(normalized)

Read accesstime

Write accesstime

Energy per 32 bwrite

Energy per 32 bread Endurance

EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104

FRAMs 2ndash5 100 ns 100 ns 1 nJ 1 nJ gt1015

states ldquo1rdquo and ldquo0rdquo are represented by the nonvolatile storageof the positive or negative remanent polarization states Thenonvolatile property is due to the fact that the sample canhold the polarization state when the external field is removedCompared to other nonvolatile memories for example flashelectrically erasable and programmable read-only memories(EEPROM) FRAMs have faster write and read times lowerpower consumption and high write and read endurance Asummary of the performances for different devices is givenin Table 1 FRAMs can be applied in a variety of consumerproducts such as smart cards power meters printers videogames and radio-frequency identification (RFID) tags

The available commercial FRAMs are based on perov-skite-type ferroelectrics such as lead zirconium titanate (PZT)and strontium barium titanate (SBT) Researchers have over-come many difficulties including degradation and retentionBesides perovskites generally require high annealing temper-ature (gt400∘C) which is harmful to other components on thechip Therefore the perovskite memory chips require bufferlayers and complex mask sets [3 88] P(VDF-TrFE) copoly-mer is the promising material to replace perovskites whichhas attractive advantages the device can be achieved by low-temperature processing (lt200∘C) and solution-processingtechniques which would enable its use in ultra-low-costapplications the copolymer has outstanding chemical stabil-itywhich barely reacts to other components and it is nontoxic

There are three main memory elements based on fer-roelectric films metal-ferroelectric-metal (MFM) capacitormetal-ferroelectric-insulator-semiconductor (MFIS) diodeand ferroelectric-field-effect-transistor (FeFET) The MFMcapacitors can be connected to the transistors to integrateinto 1T1C (one-transistor-one-capacitor) or 2T2C (two-tran-sistor-two-capacitor) memory cells [89] The devices basedonMFM capacitors are destructive which require restorationby a rewriting cycle after a readout operation The MFISand FeFET devices are nondestructive with the ferroelectricpolarization state modulating the electrical conductance ofthe semiconductor channel and thus distinguishing two logicstates

MFIS devices based on P(VDF-TrFE) films have beeninvestigated by several groups [7ndash11] Earlier relatively thickP(VDF-TrFE) films (gt100 nm) with SiO

2buffer layer were

used resulting in a higher operation voltage (gt10V) Morerecently using sub-100 nm P(VDF-TrFE) films a plusmn3V CVloop with a memory window of 1 V was achieved in a stackconsisting of 10 nm SiO

2layer and 36 nm P(VDF-TrFE) LB

film [9] A plusmn4V loop with a large memory window of 29 Vwas obtained using a 3 nm Ta

2O5buffer layer and a 100 nm

P(VDF-TrFE) spin coated film [10] In [11] the authors

fabricated MFM and MFIS devices using epitaxially grownP(VDF-TrFE) thin films (20ndash30 nm) A memory windowof 24V with a plusmn5V loop was obtained in MFIS and theirprinted micropattern application was demonstrated All-organic FeFET devices based on P(VDF-TrFE) have beenreported in [5 12ndash15] High-performance solution-processedFeFETs were first reported in 2005 by Naber et al [13] usingP(VDF-TrFE) film as the gate insulator and MEH-PPV (poly(2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene)) as asemiconductorThe FeFETs have a long retention time (gtoneweek) with a stable 119868on119868off of 104 a high programmingcycle endurance (gt1000 cycles) and a short programmingtime of 03ms However with 60V operation voltages thedevices need to be scaled down To develop a storagemediumthat enables an independent tuning of the conductive andferroelectric properties Asadi et al used phase separatedfilms of P(VDF-TrFE) and the polymer semiconductor rir-P3HT (region-irregular poly(3-hexylthiophene)) to realizea nonvolatile resistive memory [90] The charge injectionof the electrode into the semiconducting phase is modifiedby the poling of the ferroelectric phase A rectifying diodewith a LiFAl top electrode and a silver bottom electrodecan be switched and read out nondestructively Retentionswitching time and cycle endurance of the blend devicesare comparable to those of the state-of-the-art polymerFeFETs Lately Gerber et al [15] fabricated FeFET withvery thin P(VDF-TrFE) films prepared by Langmuir-Blodgetttechnique The memory element consists of a 10 nm thickSiO2layer and a 35 nm thick P(VDF-TrFE) film which can be

operated at 4V The memory window can also be measuredusing a PtPVDFSiO

2p-Si gate MFIS stack diode with

device capacitance 119862 versus gate voltage 119881119892 as shown in

Figure 9 The high capacitance at negative gate bias is dueto accumulation while the low capacitance at positive gatebias arises from depletion The memory window increaseslinearly from 015 to 13 V as the amplitude of the gate voltagecycle increases from plusmn1 V to plusmn6V In contrast the memorywindow decreases with increasing temperature toward thephase transition temperature at a fixed gate voltage cycle(inset in Figure 9) The short retention time (lt10 s) is likelylimited by incomplete polarization saturation which can beimproved by further reducing the thickness of the oxidelayer so that its capacitance is at least ten times that of theferroelectric film

In spite of these efforts to commercialize P(VDF-TrFE)based nonvolatile memory devices there are two importanttechnical obstacles thatmust be overcome First an appropri-ate approach must be found to control switching dynamicsin the copolymer films Second the solution-processing


40

80

120

160

Capa

cita

nce (

pF)

minus8 minus6 minus4 minus2 0 2 4 6 8

30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)

Figure 9 Capacitance-voltage hysteresis loops of a PtPVDFSiO2p-Si gate MFIS stack diode measured with gate voltage sweeps over plusmn1

plusmn4 and plusmn6V at a rate of 005Vs The measurement frequency was 100 kHz The inset shows the width of the memory window as a functionof temperature for gate voltage sweeps over plusmn5V [15]

Gate

Source Drain

SiO2

P-Si

Body

Metal (Au)P(VDF-TrFE)

Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg

Figure 10 Investigated ferroelectric transistor Fe-FET and equivalent capacitive divider of gate potentials [94]

technology must be scaled up and incorporated into thesemiconductor-manufacturing process which is challengefor Langmuir-Blodgett technique [3]

52 Negative Capacitance Devices Conventional field-effecttransistors (FETs) require a change in the channel potentialof at least 60mV at room temperature to induce a change inthe current by a factor of 10 which is determined by the Boltz-mann limit Recently the concept of coupling the ferroelectriclayer to the channel of a field effect transistor for lowering thesubthreshold swing due to the negative capacitance effect isactively studied This concept is proposed by Salahuddin andDatta in 2008 [91] which opens a new route for the realizationof transistors with steeper subthreshold characteristics andthus enabling low power dissipationThe experimental valid-ity of Fe-FET with a sub-60mVdecade switching behavioris firstly demonstrated incorporating a thin P(VDF-TrFE)film into a gate stack [16] Later capacitance enhancement ismanifested in an epitaxially grown single crystalline bilayerconsisting of strontium titanate (SrTiO

3) as the dielectric and

lead zirconate titanate (PbxZr1minusxTiO3) as the ferroelectric athigher temperature [92] and in an epitaxially grown singlecrystalline bilayer of SrTiO

3and barium titanate (BaTiO

3) at

room temperature [93]

Figure 10 shows the device configuration of the negativecapacitance FET [94] The gate insulator consists of a layerof 40 nm P(VDF-TrFe) and a layer of a 10 nm SiO

2 The

ferroelectric negative capacitance can be stabilized by the in-series positive oxide capacitance The layer thicknesses andmaterial properties should be properly engineered so as tosuppress the hysteretic operation The gate structure acts asan internal voltage transformerThus a small voltage swing onthe gate electrode causes a larger change in the internal poten-tial barrier which gates the channel currentThe subthresholdswing value depends on the P(VDF-TrFE) thickness and thesize of the channel In this device (channel size of 50 120583m times

50 120583m) a subthreshold swing as low as 13mVdecade is mea-sured at room temperature which offers the possibility oflower voltage operation in electronic devices The challengesinclude successful integration of ferroelectricdielectric gatestacks onto FET structures especially for oxides and efficientdesigns to ensure hysteresis free operation [95] More worksneed to be done including temperature and interface effect onthe device performance

53 Photovoltaic Devices Recently it is reported that byusing a permanent electric field of an ultrathin layer of fer-roelectric P(VDF-TrFE) introduced at the interface between


+ + + + + + + +

+++

+ + ++ +

+++++++++++

minus minus minus minus minus minus minus minus

minus minus minus minus minus minus minus

minusminusminusminusminusminusminus

minus

ITO

Al Al

PolymerPCBMP(VDF-TrFE)

E

Figure 11 The structure of polymer photovoltaic devices with FE interfacial layers and a schematic diagram of electric field induced bythe polarized FE layer and the field-assisted charge extraction The right-hand panel illustrates the electric-field distribution and electronconduction through the P(VDF-TrFE) on the Al side [17]

the electrode and a semiconductor layer in an organic photo-voltaic (OPV) device the charge pair separation and chargeextraction efficiency can be increased and thus the powerconversion efficiency (PCE) is enhanced by up to 200 [1796] OPV devices have been intensively investigated duringthe last few years due to their promising application for futurelow cost and high performance energy sources The energyloss in OPV devices is mainly caused by the recombinationof electrons and holes in semiconducting polymer-fullereneblends To separate the electrons and holes and prevent theirrecombination by an external field is essential to increase theOPV efficiency A large internal electric field can be inducedby incorporating a ferroelectric layer thus eliminating theneed for an external field The device structure and workingprinciple of the OPV based on a P(VDF-TrFE) thin film areillustrated in Figure 11 The ultrathin ferroelectric layer wasprepared by Langmuir-Blodgett technique and inserted atthe interface of the organic semiconducting layer and metalelectrode which has a large polarization of the order of10 120583Ccm2 The ferroelectric layer can induce a high densityof charges at the FE-semiconductor interface which cannotbe compensated by the low-concentration free charges inorganic semiconductorsThebuilt-in electric field introducedby the P(VDF-TrFE) layer is derived as 119864 = 119889120590

1198751205760120576FE119871

with 120590119875being the polarization charge density 119889 the thickness

of the P(VDF-TrFE) layer 119871 the thickness of the polymersemiconductor layer and 120576FE the relative dielectric constantof the P(VDF-TrFE) layer A three monolayer (5 nm) P(VDF-TrFE) film can induce an internal built-in field as highas 50V120583m in a 150 nm P3HTPC

70BM layer and thus

suppresses the recombination in the device According to theabove derived equation the higher the built-in electric field isthe thicker the P(VDF-TrFE) layer is However the increaseof the P(VDF-TrFE) layer thickness also increases the contactresistance which would reduce device efficiency [17] Theauthors found that one or two monolayers of P(VDF-TrFE)were the optimum thickness range for P3HTPC

70BM to

achieve the highest efficiency

54Multiferroic Tunnel Junctions Incorporating P(VDF-TrFE)thin films in multiferroic tunnel junctions is also an emerg-ing application Ferroelectric polymer has a high electric

polarization and weakly binds to the metal ferromagnetswhich are favorable for use as barriers in multiferroic tunneljunctions Experimentally Mardana et al have demonstratedthat the use of P(VDF-TrFE) LB films can efficiently tailorthe interface magnetocrystalline anisotropy (MCA) of anadjacent ferromagnetic Co layer [18] In a wedge-shaped Cofilm of varying thickness overlaid with a P(VDF-TrFE) filmthe magnetic anisotropy of the Co films changes as muchas 50 when the ferroelectric polarization of the copolymeris switched from up to down The large mismatch in thestiffness coefficients between the copolymer and the metalferromagnet manifests that the magnetic changes are causedby the large electric field at the ferroelectricferromagnetinterface First-principles density functional calculations [9798] show that PVDF basedmultiferroic tunnel junctions havevery high tunability of the tunneling magnetoresistance andelectroresistance effects which are promising candidates forlogic andmemory applicationsMore experiment works needto be done

6 Summary and Outlook

Significant advances have been made on the developmentof ferroelectric devices based on PVDF and P(VDF-TrFE)thin films in the last ten years Still we are in the earlystages of commercialization of thin ferroelectric polymerdevices in organic electronics There remain some questionsabout the microscopic mechanisms of polarization reversalin ferroelectric polymer films Understanding of these issuesis critical The material quality in terms of processing andproperties could be evaluated and improved Future works toestablish a clear relationship between ferroelectric propertiesand device performance are required The prospects of fer-roelectric polymer devices are promising for microelectronicindustry

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper


Acknowledgments

This work was supported by the National Natural ScienceFoundations of China (nos 51302172 21405106 and 51272161)and the Science and Technology Research Items of Shenzhen(no JCYJ20140509172719306)

References

[1] C P de Araujo J F Scott and G W Taylor FerroelectricThin Films Synthesis and Basic Properties Gordon and BreachPublicher 1996

[2] T Furukawa ldquoFerroelectric properties of vinylidene fluoridecopolymersrdquo Phase Transitions vol 18 pp 143ndash211 1989

[3] S Ducharme T J Reece C M Othon and R K RannowldquoFerroelectric polymer Langmuir-Blodgett films for a nonvol-atile memory applicationsrdquo IEEE Transactions on Device andMaterials Reliability vol 5 no 4 pp 720ndash735 2005

[4] T Furukawa Y Takahashi and T Nakajima ldquoRecent advancesin ferroelectric polymer thin films for memory applicationsrdquoCurrent Applied Physics vol 10 no 1 pp e62ndashe67 2010

[5] R C G Naber K Asadi P W M Blom D M de Leeuw and Bde Boer ldquoOrganic nonvolatile memory devices based on ferro-electricityrdquoAdvancedMaterials vol 22 no 9 pp 933ndash945 2010

[6] M Poulsen and S Ducharme ldquoWhy ferroelectric polyvinyli-dene fluoride is specialrdquo IEEE Transactions on Dielectrics andElectrical Insulation vol 17 no 4 pp 1028ndash1035 2010

[7] T J Reece S Ducharme A V Sorokin and M Poulsen ldquoNon-volatile memory element based on a ferroelectric polymerLangmuir-Blodgett filmrdquo Applied Physics Letters vol 82 no 1pp 142ndash144 2003

[8] S H Lim A C Rastogi and S B Desu ldquoElectrical properties ofmetal-ferroelectric-insulator-semiconductor structures basedon ferroelectric polyvinylidene fluoride copolymer film gatefor nonvolatile random access memory applicationrdquo Journal ofApplied Physics vol 96 no 10 pp 5673ndash5682 2004

[9] A Gerber H Kohlstedt M Fitsilis et al ldquoLow-voltage oper-ation of metal-ferroelectric-insulator-semiconductor diodesincorporating a ferroelectric polyvinylidene fluoride copolymerLangmuir-Blodgett filmrdquo Journal of Applied Physics vol 100 no2 Article ID 024110 2006

[10] S Fujisaki H Ishiwara and Y Fujisaki ldquoLow-voltage oper-ation of ferroelectric poly(vinylidene fluoridetrifluoroethy-lene) copolymer capacitors and metal-ferroelectric- insulator-semiconductor diodesrdquo Applied Physics Letters vol 90 no 16Article ID 162902 2007

[11] Y J Park S J Kang Y Shin R H Kim I Bae and C ParkldquoNon-volatile memory characteristics of epitaxially grownPVDF-TrFE thin films and their printed micropattern applica-tionrdquo Current Applied Physics vol 11 no 2 pp e30ndashe34 2011

[12] R Schroeder L A Majewski and M Grell ldquoAll-organic per-manent memory transistor using an amorphous spin-cast fer-roelectric-like gate insulatorrdquo Advanced Materials vol 16 no 7pp 633ndash576 2004

[13] R C G Naber C Tanase P W M Blom et al ldquoHigh-per-formance solution-processed polymer ferroelectric field-effecttransistorsrdquo Nature Materials vol 4 no 3 pp 243ndash248 2005

[14] K N Narayanan Unni S Dabos-Seignon and J M NunzildquoImproved performance of pentacene field-effect transistorsusing a polyimide gate dielectric layerrdquo Journal of Physics DApplied Physics vol 38 no 8 pp 1148ndash1151 2005

[15] A Gerber M Fitsilis R Waser et al ldquoFerroelectric field effecttransistors using very thin ferroelectric polyvinylidene fluoridecopolymer films as gate dielectricsrdquo Journal of Applied Physicsvol 107 no 12 Article ID 124119 2010

[16] A Rusu G A Salvatore D Jimenez andAM Ionescu ldquoMetal-ferroelectric-metal-oxide-semiconductor field effect transistorwith sub-60mVdecade subthreshold swing and internal voltageamplificationrdquo in Proceedings of the IEEE International ElectronDevices Meeting (IEDM rsquo10) pp 395ndash398 December 2010

[17] Y Yuan T J Reece P Sharma et al ldquoEfficiency enhancement inorganic solar cells with ferroelectric polymersrdquo Nature Materi-als vol 10 no 4 pp 296ndash302 2011

[18] A Mardana S Ducharme and S Adenwalla ldquoFerroelectriccontrol of magnetic anisotropyrdquo Nano Letters vol 11 no 9 pp3862ndash3867 2011

[19] S Palto L Blinov A Bune et al ldquoFerroelectric Langmuir-Blodgett filmsrdquo Ferroelectrics Letters Section vol 19 no 3-4 pp65ndash68 1995

[20] AV BuneVM Fridkin SDucharme et al ldquoTwo-dimensionalferroelectric filmsrdquoNature vol 391 no 6670 pp 874ndash877 1998

[21] S Ducharme V M Fridkin A V Bune et al ldquoIntrinsic ferro-electric coercive fieldrdquo Physical Review Letters vol 84 no 1 pp175ndash177 2000

[22] J F Scott ldquoDomain wall kinetics nano-domain nucleationin lead germanate and Tilley-Zeks theory for PVDFrdquo Ferro-electrics vol 291 no 1 pp 205ndash215 2003

[23] H Kliem and R Tadros-Morgane ldquoExtrinsic versus intrinsicferroelectric switching experimental investigations using ultra-thin PVDF LangmuirndashBlodgett filmsrdquo Journal of Physics DApplied Physics vol 38 no 12 pp 1860ndash1868 2005

[24] A M Bratkovsky and A P Levanyuk ldquoComment on lsquointrinsicferroelectric coercive fieldrsquordquo Physical Review Letters vol 87 no1 Article ID 019701 2001

[25] R L Moreira ldquoComment on lsquointrinsic ferroelectric coercivefieldrsquordquo Physical Review Letters vol 88 no 17 Article ID 1797012002

[26] J F Scott M Dawber A Q Jiang and F D Morrison ldquoNewdevelopments in ferroelectric thin filmsrdquo Ferroelectrics vol 286no 1 pp 223ndash235 2003

[27] R C G Naber P W M Blom and D M De Leeuw ldquoCom-ment on lsquoextrinsic versus intrinsic ferroelectric switchingexperimental investigations using ultra-thin PVDF Langmuir-Blodgett filmsrsquordquo Journal of Physics D Applied Physics vol 39 no9 pp 1984ndash1986 2006

[28] R V Gaynutdinov S Mitko S G Yudin V M Fridkinand S Ducharme ldquoPolarization switching at the nanoscale inferroelectric copolymer thin filmsrdquo Applied Physics Letters vol99 no 14 Article ID 142904 2011

[29] RGaynutdinov S Yudin SDucharme andV Fridkin ldquoHomo-geneous switching in ultrathin ferroelectric filmsrdquo Journal ofPhysics CondensedMatter vol 24 no 1 Article ID 015902 2012

[30] S Ducharme V Fridkin R Gaynutdinov M Minnekaev ATolstikhina and A Zenkevich ldquoHomogeneous switching inultrathin ferroelectric BaTiO

3filmsrdquo httparxivorgabs1204

4792[31] H Kawai ldquoThe piezoelectricity of poly(vinylidene fluoride)rdquo

Japanese Journal of Applied Physics vol 8 no 7 pp 975ndash9761969

[32] J G Bergman Jr J H McFee and G R Crane ldquoPyroelectricityand optical second harmonic generation in polyvinylidenefluoride filmsrdquo Applied Physics Letters vol 18 no 5 pp 203ndash205 1971


[33] R G Kepler and R A Anderson ldquoFerroelectricity in poly-vinylidene fluoriderdquo Journal of Applied Physics vol 49 no 3p 1232 1978

[34] T Furukawa M Date and E Fukada ldquoHysteresis phenomenain polyvinylidene fluoride under high electric fieldrdquo Journal ofApplied Physics vol 51 no 2 pp 1135ndash1141 1980

[35] M Li H JWondergemM-J Spijkman et al ldquoRevisiting the 120575-phase of poly(vinylidene fluoride) for solution-processed ferro-electric thin filmsrdquoNature Materials vol 12 no 5 pp 433ndash4382013

[36] T Furukawa G E Johnson H E Bair and Y Tajitsu ldquoFerro-electric phase transition in a copolymer of vinylidene fluorideand trifluoroethylenerdquo Ferroelectrics vol 32 no 1 pp 61ndash671981

[37] LM Blinov VM Fridkin S P Palto A V Bune P A Dowbenand S Ducharme ldquoTwo-dimensional ferroelectricsrdquo Physics-Uspekhi vol 43 no 3 pp 243ndash257 2000

[38] V V Kochervinskii ldquoFerroelectricity of polymers based onvinylidene fluoriderdquo Russian Chemical Reviews vol 68 no 10pp 821ndash857 1999

[39] A R Geivandov S G Yudin V M Fridkin and S DucharmeldquoManifestation of a ferroelectric phase transition in ultrathinfilms of polyvinylidene fluoriderdquo Physics of the Solid State vol47 no 8 pp 1590ndash1594 2005

[40] MMai V Fridkin BMartin A Leschhorn andHKliem ldquoThethickness dependence of the phase transition temperature inPVDFrdquo Physica B Condensed Matter vol 421 pp 23ndash27 2013

[41] A Sheikholeslami and P G Gulak ldquoA survey of circuit innova-tions in ferroelectric random-access memoriesrdquo Proceedings ofthe IEEE vol 88 no 5 pp 667ndash689 2000

[42] G W Burr B N Kurdi J C Scott C H Lam K Gopalakr-ishnan and R S Shenoy ldquoOverview of candidate devicetechnologies for storage-classmemoryrdquo IBM Journal of Researchand Development vol 52 no 4-5 pp 449ndash464 2008

[43] M H Kryder and C S Kim ldquoAfter hard drivesmdashwhat comesnextrdquo IEEETransactions onMagnetics vol 45 no 10 pp 3406ndash3413 2009

[44] T Nakajima Y Takahashi S Okamura and T FurukawaldquoNanosecond switching characteristics of ferroelectric ultrathinvinylidene fluoridetrifluoroethylene copolymer films underextremely high electric fieldrdquo Japanese Journal of AppliedPhysics vol 48 no 9 Article ID 09KE04 2009

[45] K Muller D Mandal K Henkel I Paloumpa and DSchmeisser ldquoFerroelectric properties of spin-coated ultrathin(down to 10 nm) copolymer filmsrdquo Applied Physics Letters vol93 no 11 Article ID 112901 2008

[46] M Li I Katsouras C Piliego et al ldquoControlling themicrostruc-ture of poly(vinylidene-fluoride) (PVDF) thin films for micro-electronicsrdquo Journal of Materials Chemistry C vol 1 no 46 pp7695ndash7702 2013

[47] P Martin and M Szablewski Langmuir-Blodgett Troughs Oper-ating Manual Nima Technology 2002

[48] M Mai B Martin and H Kliem ldquoFerroelectric switching inLangmuir-Blodgett and spin-coated thin films of poly(vinylid-ene fluoridetrifluoroethylene) copolymersrdquo Journal of AppliedPhysics vol 110 no 6 Article ID 064101 2011

[49] M Mai B Martin and H Kliem ldquoPolarization relaxation andcharge injection in thin films of poly(vinylidene fluoridetriflu-oroethylene) copolymerrdquo Journal of Applied Physics vol 114 no5 Article ID 054104 2013

[50] B Xu C N Borca S Ducharme et al ldquoAluminum dopingof poly(vinylidene fluoride with trifluoroethylene) copolymerrdquoJournal of Chemical Physics vol 114 no 4 pp 1866ndash1869 2001

[51] B Martin MMai and H Kliem ldquoBroadband dielectric disper-sion in ferroelectric P(VDF-TrFE) copolymer filmsrdquo Physica BCondensed Matter vol 407 no 21 pp 4398ndash4404 2012

[52] F Xia and Q M Zhang ldquoInfluence of metal electrodes onthe ferroelectric responses of poly(vinylidene fluoride-trifluor-oethylene) copolymer thin filmsrdquo MRS Proceedings vol 7342003

[53] G Vizdrik and E Rije ldquoFast polarization switching and influ-ence of platinum electrodes in ultrathin langmuir films ofpoly(vinylidene fluoride-trifluoroethylene)rdquo Ferroelectrics vol370 no 1 pp 74ndash84 2008

[54] P K Wu G-R Yang X F Ma and T-M Lu ldquoInteraction ofamorphous fluoropolymer with metalrdquo Applied Physics Lettersvol 65 no 4 pp 508ndash510 1994

[55] G-D Zhu X-Y Luo J-H Zhang Y Gu and Y-L JiangldquoElectrical fatigue in ferroelectric P(VDF-TrFE) copolymerfilmsrdquo IEEETransactions onDielectrics and Electrical Insulationvol 17 no 4 pp 1172ndash1177 2010

[56] R C G Naber B de Boer P W M Blom and D M de LeeuwldquoLow-voltage polymer field-effect transistors for nonvolatilememoriesrdquo Applied Physics Letters vol 87 no 20 Article ID203509 2005

[57] B Xu J Choi C N Borca et al ldquoComparison of aluminumand sodium doped poly(vinylidene fluoride-trifluoroethylene)copolymers by x-ray photoemission spectroscopyrdquo AppliedPhysics Letters vol 78 no 4 pp 448ndash450 2001

[58] R C G Naber P W M Blom A W Marsman and D MDe Leeuw ldquoLow voltage switching of a spin cast ferroelectricpolymerrdquo Applied Physics Letters vol 85 no 11 pp 2032ndash20342004

[59] W J Merz ldquoDomain formation and domain wall motions inferroelectric BaTiO

3single crystalsrdquoPhysical Review vol 95 no

3 pp 690ndash698 1954[60] EA Little ldquoDynamic behavior of domainwalls in barium titan-

aterdquo Physical Review vol 98 no 4 pp 978ndash984 1955[61] R C Miller ldquoSome experiments on the motion of 180∘ domain

walls in BaTiO3rdquo Physical Review vol 111 no 3 pp 736ndash739

1958[62] R C Miller and G Weinreich ldquoMechanism for the sidewise

motion of 180∘ domain walls in barium titanaterdquo PhysicalReview vol 117 no 6 pp 1460ndash1466 1960

[63] E Fatuzzo ldquoTheoretical considerations on the switching tran-sient in ferroelectricsrdquo Physical Review vol 127 no 6 pp 1999ndash2005 1962

[64] A N Kolmogorov ldquoA statistical theory for the recrystallizationof metalsrdquo Izvestia Akademia Nauk USSR Serie Mathematicavol 3 pp 355ndash359 1937

[65] M Avrami ldquoKinetics of phase change I General theoryrdquo TheJournal of Chemical Physics vol 7 no 12 p 1103 1939

[66] A K Tagantsev L E Cross and J Fousek Domains in FerroicCrystals and Thin Films Springer New York NY USA 2010

[67] A K Tagantsev I Stolichnov andN Setter ldquoNon-Kolmogorov-Avrami switching kinetics in ferroelectric thin filmsrdquo PhysicalReview BmdashCondensedMatter andMaterials Physics vol 66 no21 Article ID 214109 2002

[68] S Hashimoto H Orihara and Y Ishibashi ldquoStudy on D-E hys-teresis loop of TGS based on the Avrami-type modelrdquo Journalof the Physical Society of Japan vol 63 no 4 pp 1601ndash1610 1994


[69] W Li and M Alexe ldquoInvestigation on switching kinetics inepitaxial Pb (Zr

02Ti08) O3ferroelectric thin films role of the

90∘ domain wallsrdquoApplied Physics Letters vol 91 no 26 ArticleID 262903 2007

[70] J Y Jo H S Han J-G Yoon T K Song S-H Kim and TW Noh ldquoDomain switching kinetics in disordered ferroelectricthin filmsrdquo Physical Review Letters vol 99 no 26 Article ID267602 2007

[71] S Zhukov Y A Genenko and H von Seggern ldquoExperimen-tal and theoretical investigation on polarization reversal inunfatigued lead-zirconate-titanate ceramicrdquo Journal of AppliedPhysics vol 108 no 1 Article ID 014106 2010

[72] D Mao I Mejia H Stiegler B E Gnade and M A Quevedo-Lopez ldquoPolarization behavior of poly(vinylidene fluoride-tri-fluoroethylene) copolymer ferroelectric thin film capacitors fornonvolatile memory application in flexible electronicsrdquo Journalof Applied Physics vol 108 no 9 Article ID 094102 2010

[73] M Kuehn and H Kliem ldquoThe method of local fields a bridgebetween molecular modelling and dielectric theoryrdquo Journal ofElectrostatics vol 67 no 2-3 pp 203ndash208 2009

[74] P Weiss ldquoSur la Rationalite des rapports des moments mag-netiques moleculaires et le Magnetonrdquo Archives des SciencesPhysiques et Naturelles vol 4 p 401 1911

[75] P Weiss ldquoSur la nature du champ moleculairerdquo Archives desSciences Physiques et Naturelles vol 37 p 201 1914

[76] J C Burfoot and G W Taylor Polar Dielectrics and TheirApplications Macmillan London UK 1979

[77] H A LorentzTheTheory of Dielectrics Teubner 1909[78] H Kliem M Kuehn and B Martin ldquoThe weiss field revisitedrdquo

Ferroelectrics vol 400 no 1 pp 41ndash51 2010[79] M Kuehn V M Fridkin and H Kliem ldquoInfluence of an

external field on the first order ferroelectric phase transitionrdquoFerroelectrics Letters Section vol 37 no 3 pp 55ndash59 2010

[80] M Kuehn and H Kliem ldquoPhase transitions in the modifiedweiss modelrdquo Ferroelectrics vol 400 no 1 pp 52ndash62 2010

[81] H Kliem ldquoStrain induced change from second order to firstorder ferroelectric phase transitionrdquo Ferroelectrics vol 425 no1 pp 54ndash62 2011

[82] H Kliem A Leschhorn and T Edtbauer ldquoA model for thedouble loop of ferroelectric polarization close to T

119862rdquo Journal

of Applied Physics vol 113 no 10 Article ID 104102 2013[83] M Mai A Leschhorn and H Kliem ldquoThe field and temper-

ature dependence of hysteresis loops in P(VDFndashTrFE) copoly-mer filmsrdquo Physica B Condensed Matter vol 456 pp 306ndash3112015

[84] H Kliem and M Kuehn ldquoModeling the switching kinetics inferroelectricsrdquo Journal of Applied Physics vol 110 no 11 ArticleID 114106 2011

[85] M J Highland T T Fister M-I Richard et al ldquoPolarizationswitching without domain formation at the intrinsic coercivefield in ultrathin ferroelectric PbTiO

3rdquo Physical Review Letters

vol 105 no 16 Article ID 167601 2010[86] G Vizdrik S Ducharme V M Fridkin and S G Yudin

ldquoKinetics of ferroelectric switching in ultrathin filmsrdquo PhysicalReview B vol 68 no 9 Article ID 094113 pp 1ndash6 2003

[87] M Mai and H Kliem ldquoObservation of thermal Barkhauseneffect in ferroelectric films of poly(vinylidene fluoridetrifluor-oethylene) copolymerrdquo Journal of Applied Physics vol 114 no22 Article ID 224104 2013

[88] MMort G SchindlerWHartner et al ldquoLow temperature pro-cess and thin SBT films for ferroelectric memory devicesrdquoIntegrated Ferroelectrics vol 30 no 1ndash4 pp 235ndash244 2000

[89] H Ishiwara M Okuyama and Y Arimoto Eds Ferroelec-tric Random Access Memories Fundamentals and ApplicationsSpringer Berlin Germany 2004

[90] K Asadi D M de Leeuw B de Boer and P W M BlomldquoOrganic non-volatile memories from ferroelectric phase-separated blendsrdquo Nature Materials vol 7 no 7 p 547 2008

[91] S Salahuddin and S Datta ldquoUse of negative capacitance to pro-vide voltage amplification for low power nanoscale devicesrdquoNano Letters vol 8 no 2 pp 405ndash410 2008

[92] A IslamKhanD Bhowmik P Yu et al ldquoExperimental evidenceof ferroelectric negative capacitance in nanoscale heterostruc-turesrdquo Applied Physics Letters vol 99 no 11 Article ID 1135012011

[93] D J R Appleby N K Ponon K S K Kwa et al ldquoExperimentalobservation of negative capacitance in ferroelectrics at roomtemperaturerdquo Nano Letters vol 14 no 7 pp 3864ndash3868 2014

[94] G A Salvatore D Bouvet and A M Ionescu ldquoDemonstrationof subthrehold swing smaller than 60mVdecade in Fe-FETwith P(VDF-TrFE)SiO

2gate stackrdquo in Proceedings of the IEEE

International Electron Devices Meeting (IEDM rsquo08) pp 1ndash4 SanFrancisco Calif USA December 2008

[95] S Salahuddin ldquoNegative capacitance in a ferroelectric-dielec-tric heterostructure for ultra low-power computingrdquo in Spin-tronics V vol 8461 of Proceeding of SPIE p 846111 2012

[96] Y Yuan P Sharma Z Xiao et al ldquoUnderstanding the effectof ferroelectric polarization on power conversion efficiency oforganic photovoltaic devicesrdquo Energy and Environmental Sci-ence vol 5 no 9 pp 8558ndash8563 2012

[97] P V Lukashev T R Paudel J M Lopez-Encarnacion SAdenwalla E Y Tsymbal and J P Velev ldquoFerroelectric controlof magnetocrystalline anisotropy at cobaltpoly(vinylidene flu-oride) interfacesrdquo ACS Nano vol 6 no 11 pp 9745ndash9750 2012

[98] J P Velev J M Lopez-Encarnacion J D Burton and E YTsymbal ldquoMultiferroic tunnel junctions with poly(vinylidenefluoride)rdquo Physical Review BmdashCondensed Matter and MaterialsPhysics vol 85 no 12 6 pages 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


FC

H

VDF TrFE

P

Figure 1 Schematic ofmolecular structure of P(VDF-TrFE) in the120573 phaseThepolarization direction points fromfluoride to hydrogen atoms

P(VDF-TrFE) LB films provide many new insights into thefundamental physics the existence of two-dimensional ferro-electrics with nearly absence of finite size effects on the bulktransition (a first order phase transitionwith a transition tem-perature nearly equal to the bulk value) [20] the transitionfrom extrinsic (switching with nucleation and domain wallmotion) to intrinsic (switching without domain) ferroelectricswitching in the context of Landau-Ginzburg mean-fieldtheory below a thickness of 15 nm [21] and so forth Howeverthere have been strong debates of the theoretical modelsused to explain the experiments Scott pointed out thatthe presence of two apparent phase transition temperaturesinterpreted as true two-dimensional surface ferroelectricityby the Moscow-Nebraska group instead can be explained bythe seminal Tilly-Zeks theory and its extension by Duiker tofirst order phase transition [22] Several groups spoke againstthe intrinsic nature of the switching as the experimentslack several key features of intrinsic switching [23ndash27]Lately theMoscow-Nebraska group demonstrated some newexperiment evidences to support their claim of domain-freeLandau switching in P(VDF-TrFE) LB films [28 29] as well asin ultrathin BaTiO

3films [30] suggesting that homogeneous

switching in ultrathin films is a common phenomenon forall ferroelectric materials Currently the explanations forthe switching behavior in P(VDF-TrFE) thin films are stillcontroversial

PVDF is a rich system for both practical applicationsand academic investigations including phase transition andswitching mechanism The main objective of this paper is toreview the current research status of ferroelectric polymerfilms with emphases on switching mechanism and ferro-electric devices based on P(VDF-TrFE) films particularlywith the thickness below one hundred nanometers Thedevelopment of ferroelectric polymer thin film devices willhave a significant impact on organic electronics

2 Ferroelectric Polymers

The piezoelectricity in poled PVDF was discovered in 1969[31] followed by the discovery of the pyroelectricity inPVDF in 1971 [32] However it was not until the late 1970sthat the ferroelectricity in PVDF was confirmed [33 34]

The distinguishing characteristics of PVDF and its copoly-mers include highly compact structure high chemical sta-bility large permanent dipole moment ease of fabricationand low annealing temperature which can be integratedwith other materials and processes for example siliconmicrofabrication

PVDF exhibit four polymorphic crystalline forms 120572 120573120574 and 120575 phases whose formations depend on crystallizationconditions electrical poling and mechanical drawing The120573 phase has an orthorhombic structure with an all-trans(TTTT) molecule conformation possessing a large sponta-neous polarization and is responsible for the ferroelectricand piezoelectric properties The dipoles in the 120573-PVDFextend from the electronegative fluoride atoms to the slightlyelectropositive hydrogen atoms perpendicular to the polymerchain direction producing a dipole moment of 7 times 10minus30 Csdotm(2Debyes) as shown in Figure 1 Recently 120575-PVDF is success-fully fabricated as an overlooked polymorph of PVDF pro-posed 30 years ago [35] The remanent polarization andcoercive field are comparable to those of 120573-PVDF and ofP(VDF-TrFE) while the thermal stability is enhanced due toits higher Curie temperature

The introduction of TrFE which has three fluoride atomsper monomer to copolymerize with PVDF can enhancethe all-trans conformation associated with the 120573 phase Thisis because the fluoride atom is larger than hydrogen atomand therefore it can induce a stronger steric hindrance [2]In addition the copolymer with TrFE can be annealed tomuch higher crystallinity than pure PVDF [36] The moststudied copolymers have a composition of P(VDF-TrFE7030) which has a maximum spontaneous polarizationaround 10120583Ccm2 [37] Another feature for the introductionof TrFE is that it can lower the phase transition temperature119879

119888

in the copolymers P(VDF-TrFE)withmolar ratios of 50ndash80of PVDF undergoes a clear ferroelectric-paraelectric phasetransition with a measurable Curie point The 119879

119888increases

with increasing PVDF content from 70∘C at 50mol to140∘C at 80mol The transition is an order-disorder typewhile the disorder is a random mixture of trans- and gauchecombinations in the conformation of the molecules More-over the transition tends to change from a first order to
















3)





60

40

25

5

0

(a)


20∘C

25 humidity

40∘C

50∘C

90∘C

100∘C

(b)




119875 (119905) = 21198751199041 minus exp [minus(

119905

1199050

)

119899

] (1)

119868 (119905) = 21198751199041198780

119899

1199050

(119905

1199050

)

119899minus1

exp [minus(119905

1199050

)

119899

] (2)



0is


119904

1198780 and 119905





(a)

0

4

9

14

19

24

5 10 15

Expansion

Compression

Surfa

ce p

ress

ure (

mN

mminus1)


(b)


P

(a) (b)

(c) (d)

Ea







0

Time (s)

n = 08

n = 1

n = 15

n = 2

n = 3

Switc

hing

curr

ent (

A)




119875 (119905) = 2119875119904int

infin

minusinfin


1199050

)

119899

]119865 (log 1199050) 119889 (log 119905

0)

(3)


0 It meets


int

infin

minusinfin

119865 (log 1199050) 119889 (log 119905

0) = 1 (4)









119864loc = 119864119886+

119875

31205760

(5)






minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0



119864loc = 119864119886+ 120572119875 (6)













120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)





(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


















3)





60

40

25

5

0

(a)


20∘C

25 humidity

40∘C

50∘C

90∘C

100∘C

(b)




119875 (119905) = 21198751199041 minus exp [minus(

119905

1199050

)

119899

] (1)

119868 (119905) = 21198751199041198780

119899

1199050

(119905

1199050

)

119899minus1

exp [minus(119905

1199050

)

119899

] (2)



0is


119904

1198780 and 119905





(a)

0

4

9

14

19

24

5 10 15

Expansion

Compression

Surfa

ce p

ress

ure (

mN

mminus1)


(b)


P

(a) (b)

(c) (d)

Ea







0

Time (s)

n = 08

n = 1

n = 15

n = 2

n = 3

Switc

hing

curr

ent (

A)




119875 (119905) = 2119875119904int

infin

minusinfin


1199050

)

119899

]119865 (log 1199050) 119889 (log 119905

0)

(3)


0 It meets


int

infin

minusinfin

119865 (log 1199050) 119889 (log 119905

0) = 1 (4)









119864loc = 119864119886+

119875

31205760

(5)






minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0



119864loc = 119864119886+ 120572119875 (6)













120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)





(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





60

40

25

5

0

(a)


20∘C

25 humidity

40∘C

50∘C

90∘C

100∘C

(b)




119875 (119905) = 21198751199041 minus exp [minus(

119905

1199050

)

119899

] (1)

119868 (119905) = 21198751199041198780

119899

1199050

(119905

1199050

)

119899minus1

exp [minus(119905

1199050

)

119899

] (2)



0is


119904

1198780 and 119905





(a)

0

4

9

14

19

24

5 10 15

Expansion

Compression

Surfa

ce p

ress

ure (

mN

mminus1)


(b)


P

(a) (b)

(c) (d)

Ea







0

Time (s)

n = 08

n = 1

n = 15

n = 2

n = 3

Switc

hing

curr

ent (

A)




119875 (119905) = 2119875119904int

infin

minusinfin


1199050

)

119899

]119865 (log 1199050) 119889 (log 119905

0)

(3)


0 It meets


int

infin

minusinfin

119865 (log 1199050) 119889 (log 119905

0) = 1 (4)









119864loc = 119864119886+

119875

31205760

(5)






minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0



119864loc = 119864119886+ 120572119875 (6)













120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)





(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





(a)

0

4

9

14

19

24

5 10 15

Expansion

Compression

Surfa

ce p

ress

ure (

mN

mminus1)


(b)


P

(a) (b)

(c) (d)

Ea







0

Time (s)

n = 08

n = 1

n = 15

n = 2

n = 3

Switc

hing

curr

ent (

A)




119875 (119905) = 2119875119904int

infin

minusinfin


1199050

)

119899

]119865 (log 1199050) 119889 (log 119905

0)

(3)


0 It meets


int

infin

minusinfin

119865 (log 1199050) 119889 (log 119905

0) = 1 (4)









119864loc = 119864119886+

119875

31205760

(5)






minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0



119864loc = 119864119886+ 120572119875 (6)













120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)





(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

Time (s)

n = 08

n = 1

n = 15

n = 2

n = 3

Switc

hing

curr

ent (

A)




119875 (119905) = 2119875119904int

infin

minusinfin


1199050

)

119899

]119865 (log 1199050) 119889 (log 119905

0)

(3)


0 It meets


int

infin

minusinfin

119865 (log 1199050) 119889 (log 119905

0) = 1 (4)









119864loc = 119864119886+

119875

31205760

(5)






minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0



119864loc = 119864119886+ 120572119875 (6)













120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)





(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




minus

minus

minus

minus

+

+

+

+

Δ120593

1205930

120001

Eloc = 0Eloc ne 0



119864loc = 119864119886+ 120572119875 (6)













120585119889119875

119889119905= minus

120597119866

120597119875 (7)

119866 = 120572 (119879 minus 1198790) 1198752+ 1205731198754+ 1205741198756minus 119864119875 (8)





(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

minus15

minus10

minus05

00

05

10

15

Pola

rizat

ionP

P0

Curr

ent

minus10minus10

minus05

00

0 10 20 30 4000

05

10

10


A B

C

O

12 106 102

00

10

A998400B998400

C998400





119888 Any





1

120591inasymp

1

1205910

(119864

119864119888

minus 1)

12

(1 minus119879 minus 1198790

1198791minus 1198790

)

12

(9)

where 1205910

asymp 631205741205851205732 and 119879 = 119879

0+ 312057324120574120572 From this


119888or the





3films [30] by




5 Applications





Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Read accesstime

Write accesstime



EEPROM 2 50 ns 10120583s 1 120583J 150 pJ gt106

Flash 1 50 ns 100 ns 2 120583J 150 pJ 104






2buffer layer were













40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




40

80

120

160

Capa

cita

nce (

pF)


30 40 50 60

T (∘C)

00

02

04

Mem

ory

win

dow

(V)

Vg (V)



Gate

Source Drain

SiO2

P-Si

Body


Cox

CferroCins_eq

VB

CS

ΨSN+ N+

Vg







3) at



2 The





+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




+ + + + + + + +

+++

+ + ++ +

+++++++++++




minus

ITO

Al Al


E



1198751205760120576FE119871



70BM layer and thus


70BM to









Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Acknowledgments


References




























































































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




























































119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




















119862rdquo Journal





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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