I Presentation of MIEC - Context and Definition

I Presentation of MIEC - Context and Definition

Author :Benjamin Meunier

Supervisors :Geoffrey W. BurrKumar Virwani

II Impedance Spectroscopy- Method description

III Results Presentation- Impedance Models- Complementary

studies

Conclusion

Impedance spectroscopy of Cu-containing Mixed Ionic

Electronic Conduction (MIEC) material 09-19-12



III Results Presentation- Impedance Models- Complementary studies

Conclusion

Outline




Conclusion

Outline

Outline

OutlineI Presentation of MIEC

Context: Flash NAND Limitations

6/14/123Source : Objective-Analysis (Understanding the NAND Market) K.Kim and J.Choi, Conference 2006

Scaling Barrier

n+ n+p-type

silicon wafer

Floating gate

Control gate

Tunneling oxide

Dielectric ONO

Oxide sidewall (→ 40nm node )

It starts to be hard to keep shrinking flash devices

NAND Unlike to match HDD $/GBBit line

NOR NAND

Word line20

04

2000

$ 103

$ 101

$ 10-1

Price per Gigabyte

2012

2008

Bigger Capacity = Less Endurance

Endurance loss

Voltage

Voltage

Voltage

0 1

10 0111 00

Dis

trib

uti

on

s of

cells

000001

010011

111110 100

101

SLC100K cycles

MLC10K cycles

TLC1K cycles

Non – Volatile Memory : candidate devicesPhase Change Memory (PCM) Resistive RAM

BEC

HfOx

“Oxygen exchange layer”

(Ti,Zr,Hf,La)

VO VO

VO

VO

VOVO

VO VO

VOVO

VOVO

VO

VOVOVOVOVOVOVOVO

VO VO

VOVO

VO

O2-

O2-

O2-

Overall Vision: 3Dmulti-layer Storage class

memory

6/14/124

• ON state: high currents PCM needs ~ 107 A/cm2 @ 30 nm CD

• OFF state: low leakageto enable large & efficient arrays

• Back-End-Of-the-Line compatible (< 400oC processing)

for stacking above metal wires

• Bipolarity: to access bipolar RRAM (more reliable than uni-polar RRAM)

Access Device specifications

Conventional silicon diodes do not meet

all these requirements!

NVM – non-volatile memory

ND – ‘Novel Diode’ access device

Mixed Ionic-Electronic Conduction (MIEC)-based access device

Source : G. W. Burr, VLSI paper 2012

IV : General behavior – Double Diode

6/14/125

MIEC theory is an area of active research

We assume a n-doped semiconductor behavior because of the Cu+ ions (donors)

Two Schottky junctions

L

MIECmetal metal

Ec

Ev

IV measurements : first characterization110 nm

110 nm

50 nm

70 nm70 nm

< 10 pA leakage

< 10 pA leakage

30 nm

30 nm

TEC Voltage (V)

TEC Voltage (V)

Curre

nt

(A)

Curre

nt

(A)

IV : Details of the Different States

6/14/126

Source : I. Riess, J. Phys. Chem. Solids, vol.47, no.2, p129-138 (1986)

1

2ntanh

βqVI

2

3

Jtun Jtun

1 OFF State : Equilibrium large barrier for holes → accumulation tunneling current due to the electrons

2 ON State : lowest barrier → hole injection

3 Saturation Current only limited by space-charge effects

++

+

+

+ n depending of the defect model

Prediction from electronic transport equations :

Solid-state model :

I-V : Voltage Margin and Yield

6/14/127

Voltage Margin @ 10 nA

92 % : 1.35 V +/- 0.18 V

100 % > 0.48 V

Voltage (V)

Voltage Margin =1.5V

Sufficient for cross-point arrays of HfO2

RRAM

0 2 4 6 8 10 12 140

2

4

6

8

10

14

12

um

um

Volta

ge m

arg

in @

1

0nA

Previous Results

6/14/128

100% Yield :

Source : G. W. Burr, VLSI paper 2012

Endurance :




Conclusion

Outline I Presentation of MIEC - Context and Definition

Outline

I Presentation of MIEC II Impedance Spectroscopy

ZMIEC

50 nm

110 nm

6/14/1210

Impedance : MIEC – expectations

Voltage (V)

Va

exp behavior of the current and single-sine → need small Va

- Amplitude- Phase

Sample

ω+ωtωZP=tS sin0

mm

m +mωA+ sin

tN+

6/14/1211

Impedance : BioLogic SP-300

Generator

ωtP=tP sin0

ωtsin

ωtcos

∫

∫

ωRe

ωIm

Frequency Response Analysis (FRA) :

Generation of Perturbation and Reference SignalResponse of the sample :

- Transfer Function- Harmonics of non-

linearity - Noise coefficient

Homodyne detection (lock-in)

In the frequency domain :Real and Imaginary parts function of the frequency

tω0sin

+tωZ 0sin

02ω

03ω...V

I

Same electrical behavior→ Different physical phenomena

Equivalent circuits :

- Physical intuition/model must be involved - Different sets of measurements in different conditions

Solutions :

6/14/1212

Impedance : Example and Limitation

C

R s

R p

Bode Diagram of R+R/C

ps R+Rlog

sRlogCR=f

pcutoff

1

sp R+R

p

ss R

R+R 1

2

1

p

s

R

R+C

OR

ZMIEC

50 nm

110 nm

6/14/1213

ZMIEC

50 nm

110 nm

Impedance : First measurement

Ctip Ctip

Like 1st order behavior→ Same if withdraw the tip

6/14/1214

First tests : Adopted Solution

110 nm 200 um

AFM Testing Probe

Preliminary tests :

1) Resistance device

2) Capacitance device

3) MIEC top gold electrode (before and after annealing)

Resistance Sample :

6/14/1215

The force that must be applied to assure good contact with the sample without damage.

Need to add serial resistance in order to avoid explosion

Test the regularity of the results

50.92 Ohms

Rsample

= 20.6 +/- 0.5 Ohms

Au

TiN

Si

Au

SiNx

TiN

Si

6/14/1216

We cannot see the cutoff frequency50 M

Ohm

s

Capacitance Sample :

Cut-off frequency

We can see the cutoff frequency

Capacitance Sample :

6/14/1217

Capacitance (pF

)

Area (um2)

C = a x S + b

St

=C 0r b = C//

parasitic capacitance

t=a r 0

b ≈ 20 pF23 /2.88e μmpF=a

8.77=r

Method Dielectric Constant

b-Si3N4 exp.1 8.4 - 8.66

b-Si3N4 DFT2 8.191T. Goto and T. Hirai, J. Mater. Sci. 24, 821 (1989) and references therein.2 D. Fischer et all. , Phys. Rev. Lett. 92, 236405 (2004).

C// : same order of magnitude than C

tip (ie. slide 15)

The characterization of the apparatus is done

let's do IS of MIEC device

Au

SiNx

TiN

Si


Conclusion



Outline

II Impedance SpectroscopyIII Results Presentation

Measurements : First results

6/14/1219

Phase Diagram Phase (degree) vs frequency (Hz)

MIEC Impedance : Band Diagram–based model

6/14/1220

22j12j

22j1

22j1

Debionelcontionel

Deb

ionDeb

el

s CπfR+RπfC+R+R

Cπf+

RC

πf+R+R=Z

CDeb

CDeb

Rio

n

Rel

Ccont

CDeb

/2R

ion

Rel

Ccont

Rs

Electrical model Impedance Equation

Ccont

: Due to the metal contactR

el : Tunneling electrons generating a current

Rion

: Resistance due to the ionsC

Deb : proportional to (λ

D)-1 which correspond to the 0-charged region close to contact

Rs : Serial resistance added in order to reduce the current flowing through the device.

+ fix the high frequency impedance

Source : A. Leshem, E. Gonen and I. Riess, Nanotechnology 22 (2011) 254024

Measurements : First Analysis

6/14/1221

Bode Diagram

0.2 V

- 0.2V

- 0.4 V

Rel

Rion

CDeb

Ccont

Rs

Low frequency :

Z = Rs + R

el

High frequency :

Rs

Z = Rs

Rs

= 100 Ω

Ccont

~ 3 nF

Rel

~ kΩ

CDeb

~ nF

Rion

~ kΩ

Summarize of the results :

CDeb

Rion

Rel

Phase Diagram

Measurements : Matching with the model

6/14/1222

CDeb

/2R

ion

Rel

Ccont

Rs

Phase Diagram Phase (degree) vs frequency (Hz)

Theory : Relaxation Process

6/14/1223Source : E. Barsoukov and J. R. MacDonald, Impedance Spectroscopy, Second Edition, Wiley (2005) p30-34

P

tt = 0s

P∞

Ps

P'(t)

Polarization (P) :- Ps : long time polarization

E=P ss 10

- P∞ : high frequency polarization E=P 10

0

0

0 ω+ss

Pω+

ω+s

P=sf=tPL s

j=dPdt and E

s=EL

1

0

000 ω+s

sωs

l

S=

EL

jL

l

S=Y s

lS=C /01 lS=C s /02

τ=ω=RC 102

C2

Equivalent circuit :For a constant electric field :

C1

R

2

21 1 Cj+

RCj+Cj=

u

i=y

Theory : Electrolyte Model

6/14/1224

i

iii

ii νqccD=j

Current through an electrolyte :

Chemical Electrical

We can neglect the concentration gradient.Correct assumption for High Frequency

Ref : Jonscher [1977, 1980] ; Almond and West [1983a, b], Almond et al. [1982, 1983, 1984]

0j+σ=σΣ

“[…] the origin of the frequency dependance of the conductivity [is] due to relaxation of the ionic atmosphere after the movement of the particles. “

With : j+

Δ+=

1

Deriving from the previous relations

Conductivity when several relaxation process are involved :

∑i=1

n

C i

C 1

C n

R1

Rn

Rtot

Jonscher :

Almond and West :

Results : Effect of Bias 30nm

6/14/1225

Applied Voltage

Voltage

+ 0.5V

- 0.5V

6/14/1226

120 nm

90 nm

60 nm

Results : Effect of Thickness

-0.2V 0.2V

Summarize : Promising but …

6/14/1227

Au

MIEC

TiN

Si

Au

MIEC

TiN

Si

Unexplained asymmetry

Explore transient/higher frequency behavior.

Add circuit elements that match empirical “turn-on” behavior.

Measure transient current directly.

Connect Impedance Spectroscopy to device modelling. Much additional work will be required before a complete understanding

CDeb

/2R

ion

Rel

Ccont

Rs

To Do List : for future experiments

6/14/1228

AFM measurement with the same sample (IV not the same than small MIEC samples)

Effect of post-annealing

Gold diffusion upon anneal? → SIMS?

Effect of electrode material

Evolution of frequency shape from negative to positive …

Temperature dependance

before annealing

after annealing

Au TEC

Cu TEC




Outline

Conclusion

II Impedance SpectroscopyIII Results PresentationConclusion

Impedance Spectroscopy performed on MIEC devices

New IS setup established, independent of C-AFMLarge-area MIEC samples allow measurement of sample

impedance rather than “tip” impedance.

Impedance Spectroscopy spectra matched to RC circuits from MIEC literature, at multiple bias conditions

Fitting procedure developed for circuit parameter extractionIntroduced extensions to existing circuit modelsShowed connection between circuit models & relaxation

processes

Preliminary experiments performed vs. thickness, top-electrode material, and anneal conditions

Numerous future experiments identified and initiated

Conclusion

Thanks for your attention

Acknowledgements :

Rohit Shenoy, Alvaro Padilla, Bulent N. Kurdi, for their involvement and interest.

Luisa Bozano, Carl Larson and Spike Narayan without whom I would never have been here

Liz Fedde, Jane Frommer, Leslie Krupp, Larissa Clark for their help and advice

Amy Bowers, Mark Jurich, Bill Risk and all those who have contributed to the achievement of these results

Documents

I Presentation of MIEC - Context and Definition