KIST Staff scientists visited two German leading institutes to forge future collaborations. This visit

was part of the Global KIST Program, which is intended to promote collaborative research with

world leading institutes. From March 21st to 25, eight KIST scientists visited the institute for applied

materials (IAM) at Karlsruhe Institute of Technology (KIT) and the Max Planck Institute for Steel

Research (MPIE). The visits were followed by two separate bi-lateral workshops between KIST and

KIT-IAM and between KIST and MPIE. The workshops brought together leading researchers from the

institutes to share common research interests and identify collaboration opportunities in the area of

nanostructured materials and next-generation power plant materials. The directors of MPIE and KIT-

IAM will visit KIST in May and July, respectively, to elaborate and develop a collaboration program.

1. Research Scientists

• Qualifications: Ph.D. degree in science and engineering fields

• Deadlines: Candidates who apply must submit their application packages during 5/16/2011~ 6/17/2011

• For more information, please visit website http://www.kist.re.kr or contact E-mail : recuit@kist.re.kr Tel:+82-2-958-6249

2. KIST Star Postdoctoral Program

• Qualifications: Ph.D. degree in science and engineering fields, Non-Korean citizenship

• Salary and benefit: 52 million won (approx. US$45,000) per year, Basic health insurance and workers’ compensation insurance ,

On-campus housing available on a “space available” basis (monthly rent: US$120-450)

• How to Apply: Applications are accepted year-round. Complete the online application form available at

www.kist.re.kr/en/cy/ns_view.jsp?content_id=17920 and email to starpostdoc@kist.re.kr

KIST held its 45th Anniversary Commemorative Ceremony on Thursday, February 10,

2011. Five hundred KIST members and distinguished guests, including members of

the National Assembly, high-ranking government officials, and ambassadors to Korea,

celebrated the KIST foundation day. President Kil-Choo Moon of KIST emphasized

KIST’s new vision in his speech, “KIST: At the forefront of Korea’s development

over the past half century, it will become the hope of the world with its own unique

development model, as well as a leading global institution that creates new history.”

KIST scientists visited German leading research institutes

Job openings at KIST

KIST Held Its 45th Anniversary Commemorative Ceremony

KISToday MaterialsMaterials Research Quarterly Magazine

Editor-in-ChiefDr. Seok-Jin Yoon sjyoon@kist.re.kr

Editors Dr. Insuk Choi insukchoi@kist.re.kr Dr. Ho Won Jang hwjang@kist.re.kr Dr. Heesuk Kim heesukkim@kist.re.kr Dr. Sang hoon Kim kim_sh@kist.re.kr Dr. Kwan Hyi Lee kwanhyi@kist.re.kr Dr. Jung Ah Lim jalim@kist.re.kr

Editorial OfficeMaterials Research Korea Instite of Science and TechnologyHwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, KoreaTel +82-2-958-5401 www.kist.re.kr

Materials Research News

KIST 50 years, Global Leading Institute for Future

Special Issue

Pushing the limits of thin films in solid oxide fuel cellsContribution

Spin Devices for Information Technology

Focus inDevelopment of nanostructured amorphous thick coatings by plasma sprayingComprehensive review of the stability of oxide thin film transistors for display applicationsSynthesis of ladder-like polysilsesquioxane with superior opto-/electronic propertiesUltrafast mode-locked lasers incorporating graphene

www.kist.re.kr/materials

Pantone : 1788C 2XProcess Color :Cyan 5%+Magenta 90%+Yellow 100%RGB : R 242+G 25KIST Red

KIST Dark Gray

Pantone : 423CProcess Color : Black 40%RGB : R 153+G 153+B 153KIST Gray

Pantone : 877CKIST Silver

Pantone : 873CKIST Gold

Pantone : 425C Process Color :Magenta 5%+Yellow 10%+Black 70%RGB : R 88+G 84+B 78

Thin film solid oxide fuel cell with graded nanostructure

Materials Research Quarterly Magazine No.2

APRIL

2011

12 K ISToday MATERIALS

500 nm

2 K ISToday MATERIALS APRIL 2011 3

>> Brain Science Institute

Mission : Brain disease treatment mechanisms, new drug development,

molecular-level mechanisms of brain cognitive function

>> Biomedical Research Institute

Mission : Development of artificial organs and human body parts,

development of human intention-oriented rehabilitation systems

>> Future Convergence Technology Research Division

Mission : Frontier research for the future, platform for multidisciplinary

core technologies in the material-, nano-, and bio-sciences, as well as in

the IT field

>> National Agenda Research Division

Mission : meet the challenges identified in the national agenda,

particularly relating to energy and environmental challenges, leadership

in research for global issues.

KIST Materials will broaden its coverage, expanding the former Materials

Research Division to cover material science and technology issues in all

research institutes and divisions at KIST.

We are pleased to announce the formation of the Future Convergence

Technology Research Division. This division encompasses the majority of

research centers formerly in the Materials Research Division. The division

is designed to achieve convergence among the nanotechnology (NT),

biotechnology (BT), and informational technology (IT) fields by fostering

multidisciplinary research. The division additionally provides a platform

for blending research approaches in the conventional technologies, which

will lead to the advancement of core technologies.

The division is formed from the NT-based Spin Device Research Center,

Nanomaterials Research Center, Nanophotonics Research Center,

Interfacial Engineering Research Center, high-Temperature Energy

Materials Research Center, and Nanohybrid Research Center, as well

as the IT-based Electronic Materials Research Center, Visual Media

Research Center, Computational Science Research Center, and BT-based

Biomolecular Functions Research Center. The division will act as an

integrating body in support of multidisciplinary research to strengthen the

nation’s competitiveness and support one of the world’s leading research

organizations in multidisciplinary research.

The principal research fields are as follows:

- Interfacial engineering for energy related and environmental materials

- Sustainable hybrid energy conversion materials and devices

- Next-generation oxide electronic materials and plasmonics

- Nanocarbon convergence materials and nanostructured hybrid smart

materials

- Nanomaterials and processing for softronics

- Biomarkers and clinical diagnostic-based OMICs, as well as novel drugs

based on chemical biology

- human–media interaction technologies for virtual reality, ubiquitous

computing, multimodal interactions, and 3D display

- Spin-based memory, communication, energy, and VLSI technologies

- Synthesis, functionalization, and hybridization of nanoparticulates

- Design, synthesis, and applications of nano-bio systems using atomic-

scale and massive computational methods

- Quantum functional optoelectronics based on nano/microstructures.

KIST Reorganization

>> Before >> After

KIST Reorganization

KIST underwent a major reorganization in March 2011

To better meet the growing demands for frontier research in support of global agendas, as well as to establish world class

research institutes in strategic research fields, KIST underwent a full-scale reorganization across the institute in March

2011. Two specialized research institutes were established, and five former research divisions were restructured to form

two new research divisions as follows;President

Vice President for Research

Convergence Research Division

Materials and Device Research Division

Robot and Systems Division

Energy and Environment Division

Bio and Medical Research Division

Technology Policy Research institute

Gangneung Branch

JeonbukBranch

KiST Europe

President

Brain Science institute

Biomedical Research institute

Vice President

Future Convergence Research Division

National Agenda Research Division

Technology Policy Research institute

Gangneung Branch

JeonbukBranch

KiST Europe

4 K ISToday MATERIALS APRIL 2011 5

surfaces cannot be avoided as long as porous electrodes are used

as deposition surfaces. Effective plugging via conformal deposition

technologies can mitigate the problems associated with pinholes.

Using these approaches, reliable gas-tight thin film electrolytes were

successfully obtained, and electrolyte layer thickness reductions

were satisfactorily achieved.

The second challenge was effectively addressed using composite

electrodes. Both the formation of nano-composite electrodes during

the deposition and the employment of a ‘template’ as a structural

support remarkably suppressed the degradation of the nano-porous

electrodes.These electrodes showed stabilities, in terms of structure

and performance, beyond those achievable using single-phase

nanoporous electrodes.

This work was based on highly reliable thin film technologies.

The structural requirements and high-temperature operation

of SOFCs raise several challenges to the use of thin films and

nanostructures for producing reliable thin film SOFCs (TF-SOFC). The

two main challenges have been: 1) to develop thin gas-impermeable

electrolytes over porous electrodes, and 2) to suppress the

intensive degradation of nanoporous electrodes at high operating

temperatures.

To address the first challenge, we employed two distinct approaches.

First, we developed nanostructured electrodes with transition

from dense to porous structures to form a surface beneath an

electrolyte layer. The electrolyte quality was not a major concern in

this case because dense thin film electrolytes were found to form

during deposition over the dense deposition surface. Secondly, we

‘plugged’ the pinholes of the electrolyte layer formed by the porous

deposition surface. The generation of pinholes at thin electrolyte

Solid oxide fuel cells (SOFCs) are fuel cells in which the electrolytes

and electrodes are composed of ceramic material (oxides). Recently,

SOFCs have attracted attention for their use in next-generation

power sources because they can be operated with a variety of fuels

other than pure hydrogen. SOFCs additionally yield the highest

energy conversion efficiencies of all fuel cell types. Traditional

SOFCs operate at high temperatures (≥ 800°C) to secure the oxygen

ion conductivity in ceramic electrolytes. high operating temperatures

promote reactions between the cell components and degrade the

long-term stability of the cell. Reducing SOFC operating temperatures

without compromising performance is an important goal in the

field. The need for improved low-temperature SOFC performances

by introducing thin electrolytes and nanostructured electrodes has

surged over the past several years both in conventional SOFCs for

high-capacity power generation and in micro-SOFCs for portable and

mobile power sources.

Special Issue Special Issue

Pushing the limits of thin films in solid oxide fuel cells

References• H.-S. Noh, J.-S. Park, H. Lee, H.-W. Lee, J.-H. Lee, J.-W. Son, Transmission electron microscopy study on microstructure and interfacial property of thin film electrolyte SOFC. Electrochem. Solid. St. Lett. 14 (2011) B26-B29.• C.-W. Kwon, J.-W. Son, J.-H. Lee, H.-m. Kim, H.-W. Lee, K.-B. Kim, High-performance micro-solid oxide fuel cells fabricated on nanoporous anodic aluminum oxide templates. Adv. Funct. mater.21 (2011) 1154-1159.

These efforts were key to achieving critical performance

advancements and significantly advanced SOFCs along the

commercialization pathway.

200 nm

HAADF

100 nm1 ㎛1 ㎛

The two main challenges have been: 1) to develop thin gas-impermeable

electrolytes over porous electrodes, and 2) to suppress the intensive degradation

of nanoporous electrodes at high operating temperatures.

Ji-Won SonPrincipal Research Scientist jwson@kist.re.kr

>> high Temperature Energy Materials

Fig. 1 First method to obtain gas-impermeable electrolyte: using dense to porous structural transition of electrode

Fig. 2 Second method to obtain gas-impermeable electrolyte: plugging pinholes in electrolyte deposited over porous electrode

Fig. 3 interpenetrating nano-composite electrode with structural stability

6 K ISToday MATERIALS APRIL 2011 7

Focus in Focus in

Comprehensive review of the stability of oxide thin film transistors for display applications >> Electronic Materials

Fig. 2 Stability of various oxide TFTs (BTS test): (a) Zr-in-Zn-O, (b) Hf-in-Zn-O, and (c) Al-in-Zn-Sn-O TFTs.

Fig. 1 A 70-inch 3D Ultra-Definition 240Hz LCD Display using oxide TFTs, manufactured by Samsung Electronics.

Oxide thin film transistors (TFT) have been steadily replacing

Si-based transistors over the past decade. Next-generation

displays, including ultra-definition (UD), 3D, and flexible

displays, require new materials with mobilitiesof 20–30 cm2/

Vs, much higher than those of Si-based transistors (less than

1 cm2/Vs). Using oxide TFTs, 70-inch UD 240Hz LCD displays

were developed in 2010. KIST has supported a research

program that focuses on various oxide semiconductors,

including Zn-Sn-O, In-Zn-O, Si-In-Zn-O, In-Ga-Zn-O, and hf-

In-Zn-O to develop oxide TFTs with performancesthat meet

the needs of next-generation displays.The stability of oxide

TFTs, which is a key issue in practical applications, has also

been studied.

The stability of oxide TFTs may be improved by developing

robust oxide channel layers and novel channel structures

or by using passivation layers. TFT stabilitiesare evaluated

using bias temperature stress (BTS) tests, which measure

the threshold voltage shift (ΔVth) under thermal and bias

conditionsover a period of time. The instability mechanisms

mainly arise from traps in or on the channel layer. Among

the various robust oxide materials, indium (In)-containing

Zn-O channel layers show high mobility, and other elements

may be added to improve the performance and enhance

the stability. Various oxide materials, including Zr-In-Zn-O,

hf-In-Zn-O, and Al-In-Zn-Sn-O, have been studied and have

shown good stability in BTS tests. Novel oxide channel layer

structures have been developed to enhance the performance

and long-term stability of oxide TFTs. Introduction of a

highlydoped buried layer into an amorphous indium-

gallium-zinc oxide (a-IGZO) TFT channel layer dramatically

improved the performance and prolonged the biasstability

without the need for high temperature treatments. To

eliminate environmental effects and improve stability,

various passivation layers have been studied. Recently, we

developed an amorphous hf-In-Zn-O TFT with an enhanced

stability, and we compared this TFT to the published

properties of other TFTs. New channel materials composed

of binary, ternary, and quaternary oxide materials have been

studied with different composition ratios, and element-

doped oxide materials, including doping with Al, N, and Mn,

have been studied for their stability enhancement properties.

At KIST, we combine fundamental and applied research

into new oxide semiconductors to improve TFT performance

and stability for next-generation display applications. high

mobilities and good stabilities have been achieved using

robust channel layers, such as hIZO and SIZO, with a buried

structure channel layer. Passivation layers, such as PMMA

and SiO2, prevent environmental effects and enhance device

stability. These advances in oxide semiconductorsenable the

development of future generation displays.

Sang Yeol LeePrincipal Researcherlsy@kist.re.kr

References• S. Y. Lee, et al., Appl. Phys. Lett. 98, 122105 (2011) • E. Chong, et al., Electrochem. Solid-State Lett. 14, H96 (2011) • E. Chong, et al., Appl. Phys. Lett. 96, 152102 (2010) • J. K. Jeonget al., Adv. mater. 21, 329 (2009)• J. K. Jeong et al., IEEE Electron Dev. Lett. 31, No. 2, 144 (2010)

Plasma spraying is a complex process that combines

several sequential steps: the injection of solid particles

into a high-temperature plasma flame (15,000 K), melting

and acceleration of the particles, and consolidation of

the sprayed molten droplets onto a substrate to form a

coherent coating. This process has unique advantages.

Few restrictions apply to the coating area, thickness, and

materials, and the method is cost-effective.

Recently, plasma-sprayed ceramic coatings, such as Al2O3

and Y2O3 have been applied on metal or ceramic parts

of semiconductor, LCD, LED, and solar cell fabrication

equipment including the PE-CVD coater and reactive ion

etcher because ceramic coatings have strong resistance

against plasma erosion and induces the harmful elements

or reaction products. however, it is difficult to fabricate ideal

ceramic coatings by plasma spraying because micro voids

and micro cracks inevitably form due to volume contraction

of the coating materials during the rapid quenching stages

of the process.

We designed new materials that include both metallic

elements (such as Al, Y, Zr) and non-metallic elements (such

as N, O) which easily formed in nanostructured amorphous

coatings with few microcracks and microvoids via plasma

spraying. The plasma-sprayed nanostructured amorphous

coatings was clearly showed a five-fold improvement in

plasma corrosion resistance, a

50-100% improvement in micro-

hardness, and a five- to ten-fold

improvement in wear resistance

compared to existing ceramic

coatings, such as Al2O3 and Y2O3.

The outstanding nanostructured

amorphous coatings manufactured

b y p l a s m a s p r a y i n g w e r e

successfully deployed on the

commercial scale in items that

include metal and/or ceramic

Fig. 2 Comparison of the wear properties of nanostructured amorphous and CNT-reinforced coatings.

Development of nanostructured amorphous thick coatings by plasma spraying >> Advanced Functional Materials

Fig. 1 Amorphous nanostructuring mechanism.

← Volum

e

Temperature →

(nano/amorphous)Solid

(crystalline) Solid

(amorphous) Liquid← Volum

e contraction →

New materialsHigh cooling rate

Melting Temperature

Wea

r rat

e, X

10-8

[Kg/

Nm

]

components in semiconductor equipment.

Furthermore, we developed methods for effectively adding

carbon nanotubes (CNTs) to nanostructured amorphous

coatings with minimal damage to the CNTs during the

high-temperature plasma spraying process. To do so, the

processing atmosphere was controlled to minimize the

oxygen present in the plasma jet. As a result, the micro-

hardness, elastic modulus and fracture toughness of the

coatings were dramatically improved upon addition of the

CNTs. The wear resistance of CNT-reinforced amorphous

coatings showed a ten-fold improvement over the bare

nanostructured amorphous coatings.

References• J. –h. Jeong et al., J. Phys. D: Appl. Phys. 42, 035104 (2009) • S. Lee et al., J. Electrochem. Soc.156, H612 (2009) • Z. Wu et al., Appl. Phys. Lett. 96, 133510-1 (2010) • J. Choi et al., Appl. Phys. Lett. 95, 081905-1 (2009) • J. -h. Jeong et al., Appl. Phys. Lett. 94, 011902-1 (2009) • Z. Wu et al., unpublished work • S. Lee et al., Appl. Phys. Lett. 92, 243507-1 (2008)

Fig. 3 Representative samples of commercialized semiconductor fabrication equipment parts with plasma sprayed nanostructured amorphous coatings.

Hyun Kwang SeokPrincipal ResearcherCenter for Biomaterialsdrstone@kist.re.kr

Eun Young ChoiResearch AssistantCenter for Biomaterials

Jeong HoonResearch AssistantCenter for Biomaterials

Fig. 3 Enhanced stability of a-HiZO TFT by KiST compare to other published results.

Stress Time (Hrs)

delta

Vth

(V)

0 5 10 15 20 25 30 35 40 45 50 55 60

10

8

6

4

2

0

ZnO (refAPL, 89, 263513)

a-HIZO at 350˚C

a-HIZO (refAdv. Master. 21, 329 2009)

VGS (V)

(a) Zr-In-Zn-O (c) Al-In-Zn-Sn-O

-8 -4 0 4 8 12

Gate Voltage (V)

(b) Hf-In-Zn-OCu

rren

t (A

)

I DS1/

2 [x10

-3A

1/2 ]

10-6

10-8

10-10

10-12

-10 0 10 20 30 40 0

1

0h60hLeakage

Gate Voltage (V)

Dra

in C

urre

nt (A

) VDS = 5.1V

VDS = 0.1V

10-4

10-5

10-6

10-7

10-8

10-9

10-10

10-11

10-4

10-6

10-8

10-10

10-12

10-14

-30 -20 -10 0 10 20 30 40

Before stressAfter 60hrs stress

I DS (

A)

0.09Nanostructured

AmorphousCoating (APS)

CNT-reinforcedAmorphous

Coating (APS)

CNT-reinforcedAmorphous

Coating (ECPS)

• Counter part : Ruby Ball• Load : 1,000gf• Sliding distance : 226.08m• Sliding rpm : 100rpm• Track diameter : 12mm

0.198590.08576

0.93429Five-fold

Ten-fold

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

8 K ISToday MATERIALS APRIL 2011 9

Focus in Focus in

Polysilsesquioxanes comprise a class of organosilicon polymers

of molecular formula (RSiO1.5)n. These unique materials exhibit a

plethora of advantageous properties, including excellent thermal

stability, easy processability, excellent mechanical strength,

chemical and oxidative resistance, and biocompatibility.

Equipped with an organic R functional group, these polymers are

physically and chemically mutable in ways not observed in other

organic–inorganic hybrid materials. Three structural classes of

polysilsesquioxanes have been identified: random branched,

polyhedral caged, and ladder-like. Of these classes, ladder-

like polysilsesquioxanes (LPSQs) give the largest number of

functional groups without the need for thermal curing processes.

however, synthetic difficulties have rendered these materials

problematic for industrial applications.

To take advantage of the superior properties of LPSQs, KIST

researchers at the Polymer hybrid Center have worked toward

the controlled facile syntheses of such materials. As shown

in Figure 1, a base catalyst was used in a controlled in situ

hydrolysis-condensation reaction to synthesize well-defined

ladder-like silsesquioxanes.

The introduction of carbazole moieties into LPSQs (PPCSQ)

enhanced the photoluminescence (PL) properties over its organic

analog, polyvinylcarbazole(PVK). The PL spectrum of PPCSQ,

shown in Figure 2(b), revealed two sharp peaks. Moreover, the

PL quantum yield of PPCSQ was twice that of PVK, even though

the UV-vis absorption intensity of PPCSQ was only 10% that of

PVK. These physical properties of the LPSQs were attributed to

the isolating effect of the rigid linear siloxane chain in the LPSQ

backbone, which afforded the carbazole moieties more degrees

Synthesis of ladder-like polysilsesquioxane with superior opto-/electronic properties >> Nano hybrid Materials

Fig. 1 Novel synthetic route to the ladder-like polysilsesquioxanes.

of freedom, as shown in Figure 2(a).

The isolating effects were unequivocally observed when PPCSQ

and PVK were incorporated into devices. Although fewer

carbazole moieties were present in PPCSQ, Figure 3 shows that

the material displayed a higher luminous efficiency compared

to devices fabricated from PVK. Compared with the organic

materials, PPCSQ exhibited far greater thermal stability (up to

400°C), with high transparency due to the inorganic siloxane

backbone.

Such excellent physical, optical, and thermal properties,

coupled with a facile synthetic method, will invariably facilitate

its use in a variety of industrial applications. This research was

recently published in the Journal of Materials Chemistry and

Macromolecular Research.

References• K. –Y. Baek et al., “High Photo- and Electroluminescence Efficiencies of Ladder-like Structured Polysilsesquioxane with Carbazole Groups”, J. mater. Chem. 20, 9852 (2010) • S. S. Hwang et al., “Synthesis and Characterization of Ladder-like Structured Polysilsesquioxane with Carbazole Group” macromol. Res, 19, 3 (2011)

Kyung-Youl BaekSenior Researcherbaek@kist.re.kr

Seung-Sock ChoiResearch Assistantxy7ab5@kist.re.kr

He Seung LeeResearch AssistantSeaung@kist.re.kr

Albert S. LeeResearch Assistantalbert.ss.lee@gmail.com

Seung Sang HwangPrincipal Researchersshwang@kist.re.kr

Fig. 3 Voltage–luminous efficiency of PPCSQ and PVK in an EL device.

VLum

inou

s ef

ficen

cy(C

d/A

)

Voltage0 1 2 3 4 5 6 7 8 9 10 11

10

9

8

7

6

5

4

3

2

1

0

PVKPPCSQ

100

90

80

70

60

50

40

30

20

10

0

Fig. 2 (a) isolated carbazole moieties tethered to ladder-like polysilsesquioxanes (b) UV-vis absorption and photoluminescence spectra of PPCSQ and PVK in solid thin films.

(a) (b)PVK

PPCSQ

Abs

. Nor

m.

PVKPPCSQ

300 350 400 450 500

Wavelength(nm)

1.0

0.8

0.6

0.4

0.2

0.0

PL intensity. Norm

.

Ultrafast pulsed lasers using passive mode-locking have been

rapidly developed over the past decade. A paradigm shift in

the field has been accelerated by the use of carbon nanotube

(CNT)-based devices to replace conventional semiconductor-

based saturable absorber mirrors (SESAMs). CNTs have several

advantages, including a nano-scale foot-print and extremely high

and fast optical nonlinear properties. Unfortunately, they require

bandgap tuning via control over their diameter and chirality,

along with requirements for a homogeneous dispersion in liquid

media. Quite recently, graphene, a 2-dimensional honeycomb

crystal structure of carbon atoms, has emerged as a promising

photonic material with notable advantages, such as (i) a broad

nonlinear operating spectral range covering the telecomm and

VIS bands, (ii) ultrafast recovery times, (iii) a saturable absorption

threshold lower than that of CNTs, and (iv) facilitated preparation

processes. In order for graphene to act as a nonlinear intensity

modulating component particularly in the high power regime,

direct interaction between graphene and the penetrating light

should be avoided to protect the thermally fragile nanostructures.

Researchers at KIST demonstrated a novel scheme in which the

evanescent field of a laser interacts with graphene to provide

mode-locking operation (see Fig. 1) [1,2]. Because only a small

portion of the propagating mode is involved in pulse formation,

graphene can guarantee the high-power operation with the

intracavity powers up to 21.41 dBm. The resultant graphene-

based mode-locked fiber laser has a center wavelength of 1561.6

nm, a spectral width of 1.96 nm, a repetition rate of 6.99 MHz,

and an estimated pulse duration of 1.3 ps. KIST researchers

also achieved the deformation-suppressed optical deposition

of graphene by co-dissolving polyvinyl acetate (PVAc) into

dimethylformamide (DMF). The PVAc played a critical role during

the deposition as a buffer medium to suppress the deformation

and/or distortion of graphene, which is closely correlated with its

nonlinearity [3]. Deposition of the graphene/PVAc composite on

an optical fiber by laser radiation proceeded via three correlated

mechanisms: optical trapping, thermally-induced convection flow,

and thermodiffusion. The preserved nonlinearity of graphene

successfully formed a 91.5-MHz (higher harmonic) pulsed laser.

A dramatically simplified but elegant graphene preparation

method based on mechanical exfoliation of bulk graphite using

a strip of scotch tape was employed to achieve ultrafast passive

mode-locking by the KIST researchers [4]. After verifying that the

chromatic dispersion in the multilayered graphene was negligible,

optical-intensity-dependent absorption modulation in a laser

cavity was demonstrated with a fundamental repetition rate of

10.92 MHz and a peak-to-background ratio of >40 dB at 1576 nm.

Ultrafast mode-locked lasers incorporating graphene >> Optoelectronic Materials

References• Y. W. Song, et al., “A graphene mode-locker for fiber lasers passively pulsed by evanescent field interaction,” Appl. Phys. Lett., 96, 051122 (2010). • Nature Photonics Research Highlight, “Graphene: under high energy,” Nature Photon., 4, 196 (2010). • Y. W. Song, et al., “Deformation-immunized optical deposition of graphene for ultrafast pulsed lasers,” Appl. Phys. Lett., 98, 021104 (2011). • Y. W. Song, et al., “multilayered graphene efficiently formed by mechanical exfoliation for ultrafast photonics,” Appl. Phys. Lett., 97, 211102 (2010).

Fig. 2 Conceptual explanation of the optical deposition setup and mechanism using PVAc-coated graphene.

Yong-Won SongSenior Researcherysong@kist.re.kr

DFBLaser EDFA ATT

Fig. 1 Fiber mode-locked laser setup and output laser pulse train. The schematic diagram illustrates that the guided mode in the fiber core can be broadened by removing the clad so that the evanescent field of the mode can interact with the graphene layer to form ultrafast laser pulses.

10/90Coupler

Graphenemode-locker

Isolator

Output

Out

put(

a.u.

)

SMFPC

Time Delay (nsec)-300 -400 0 400 300

HO-EDFA

GrapheneLayer

Evanescent field ofbroadened mode

Side-polishedfiber

Guided modeSMF

Core

→ OUTIN→

Fig. 3 AFM analysis of few-layered graphene prepared by mechanical exfoliation. The 3D image (left) and height analysis on selected regions (right) are presented.

10 K ISToday MATERIALS APRIL 2011 11

of MRAM: GMR, anisotropic magneto resistance (AMR), and

tunneling magneto resistance (TMR). GMR and AMR cells

are composed of metal structures characterized by a low

resistance change, which is not attractive for high-density

memory devices. however, TMR cells are composed of a

magnetic tunnel junction (MTJ) with two ferromagnetic layers

separated by a thin dielectric layer, which acts as a DRAM

capacitor. Recently, spin transfer torque MRAM (STT-MRAM)

has been extensively investigated to solve the high cell

writing current and large cell size problems posed by MRAM

devices. The MTJ structure includes two ferromagnetic layers

and an MgO tunneling barrier layer. Switching MTJ states

from antiparallel or “1” to parallel or “0” and vice versa is

performed by running a polarized electron current from the top

to the bottom of the MTJ and vice versa. The polarized current

transfers angular momentum to the spins in the magnetic free

layer, causing it to switch. The read operation of STT-MRAM

is essentially the same as that used with MRAM. The current

STT-MRAM technology has been picked up by leading memory

companies as a serious contender that may replace the

conventional DRAM technology. Several consortia, both local

and abroad, are competing for the potential market share,

including the Samsung-hynix STT-MRAM co-development

project launched in 2009. MRAM displays non-volatility,

endurance, speed, and density, and may potentially function as

a universal memory medium for a host of applications that rely

on embedded memory. Leading groups are now turning their

focus to spintronic VLSI applications, which integrate the MTJ

technology with the conventional CMOS technology to enable

high-performance programmable logic circuits.

a creative research field characterized by high risks and high

rewards. In 2009, the Center for Spintronics Research at KIST

first demonstrated the successful operation of a spin-FET,

the long sought-after goal of spintronics. The achievements

are scientifically noteworthy because spin-FETs rely on the

modulation of spin information. The spin-FET may be used as

an active device in switching and logic devices as well as in

non-volatile devices. Furthermore, it can potentially replace

conventional electronic devices.

The magnetic random access memory (MRAM) technology

combines a spintronic device with standard silicon-based

microelectronics to obtain a combination of attributes not

found in any other memory technology, such as dynamic RAM

(DRAM). MRAM utilizes the magnetization direction in the

free layer of a two-layer magneto resistive structure for data

storage and the resulting resistance difference for information

readout. Three physical effects are required for the realization

C oonventional semiconductor-based electronics that

rely only on charge properties are approaching their

physical size reduction limits due to the importance

of direct tunneling on the nanoscale. The field of spintronics

provides a double-edged sword that may provide a solution

to the scaling problems by relying on spin and its associated

magnetic moment. The technology benefits from other

properties of electron spin systems, such as the non-volatility

of electron spin, the high speed of transmittance, and the low

power consumption requirements of spintronic devices. These

provide a major driving force for the development of next-

generation electronic devices.

Among the spin technologies under development, two large

areas in the field are led by KIST.

Spin field effect transistors (spin-FETs), which are lateral

semiconducting channels with two ferromagnetic electrodes,

lie at the heart of spintronics applications. First proposed in

1990, demonstrations of spin-FETs have required good spin

injection and detection using ferromagnetic sources and

drains, as well as gate voltage control over the spin precession

of injected spins. Purely electrical (rather than optical) spin

injection and detection are necessary to implement spin-

FETs. The development of spin-FETs began in 2002, and

the program has constituted one of the largest spintronics

projects in the world, driven by KIST. The goal of the project

was to demonstrate operational spin-FETs, which had been

unsuccessful at that junction. The project was embedded in

Hyung-jun KimSenior researchermbeqd@kist.re.kr

Spintronics is an emerging technology that exploits both the fundamental electronic charge and the intrinsic spin of the electrons. A representative product was realized as a hard disk drive (HDD) in personal computers, which employs giant magnetoresistance (GMR) effect of 2007 Nobel Prize winner in physics.

Conventional CMOS

Fig. 1 MRAM

Fig. 2 Spin-FET

Contribution Contribution

Spin Devices forinformation Technology

Spin-VLSI

Leakage Current