prof. jorge kittl, dept. of physics and...

Back end Memories

Prof. Jorge Kittl,

Dept. of Physics and Astronomy

Outline

Introduction

STT-RAM

RRAM Systems

o OXRAM

o CBRAM

o Mott

Summary

2 Prof. Jorge Kittl, KU Leuven - EPICO 2012, Buenos Aires, Argentina

DRAM

SRAM

Density, cost per bit - cross-talk for planar - complexity for 3D Eventually: # charges

Cost, complexity Need for high voltage

Scaling Limitations

Large cell size e.g. 6T Operating window shrinking

Increase capacity/wafer area, maintaining capacity per bit - Decrease EOT (k>100) - Increase Aspect Ratio (~100)

Rutile TiO2

Ti

SrO

STO

Fukuzumi et al., IEDM 2007 Jang et al., VLSI 2009

3D BiCS

Flash

Embedded NVM

NAND Flash

Memory Markets


DRAM

SRAM



Scaling Limitations



Retention:10 yr at 85C Density (3D BiCS) Cost per bit High bit rate (fast and/or low energy) Write energy: 100 FJ Multilevel cell

Retention:10 yr at >150C Integration compatibility with CMOS

Speed (<1 ns) Endurance: 1013-1015 cy Static leakage Low voltage

Speed (<30ns) Endurance: 1015 cycles Cost per bit Retention: 1s at 85 C Low voltage (<3V)

Key Requirements

Rutile TiO2

Ti

SrO

STO


3D BiCS

Flash

Embedded NVM

NAND Flash

Memory Markets


DRAM

SRAM



Scaling Limitations







Key Requirements

Rutile TiO2

Ti

SrO

STO


3D BiCS

Flash

Embedded NVM

NAND Flash

Memory Markets


DRAM

SRAM



Scaling Limitations







Key Requirements

Rutile TiO2

Ti

SrO

STO


3D BiCS

Flash

Embedded NVM

NAND Flash

Can different emerging memories

meet the specs for each market?

Can one emerging memory meet the

specs for all these markets?

Additional opportunities enabled by

emerging memories (new markets as

SCM)?

Memory Markets


Emerging “Back End” Memories

Amorphous Crystalline

High resistivity Low resistivity

Amorphous Crystalline

High resistivity Low resistivity

Crystalline

GST

Top

Electrode

Resistor

(heater)

Thermal

Insulator

(a/Xtalline

GST)

I

Bottom

Electrode

Data storage region


Memory state stored as resistance state

Can switch between different resistance states

by electrical pulses

Several emerging memories have resistance

switching behavior:

Phase change RAM (PC-RAM)

Spin torque transfer RAM (STT-RAM)

RRAM OXRAM

CBRAM

Performance Capacity Landscape

Conventional Memories


Need for Selector: Density Implications


Transistor as Selector: “1T1R”

PCM/1T1R

CBRAM/1T1R


STT-RAM/1T1R

Transistor as Selector: “1T1R”


OXRAM/1D1R

OTP/1D1R

2 Terminal Selector: “1D1R”


Selector: Density Implications

1T1R

2 terminal selector “1D1R”3D stacked

6F2 4 F2 (VFET)

DRAM replacement

NAND replacement

3D bit cost savings (BICS)


Outline

Introduction

STT-RAM

RRAM Systems

o OXRAM

o CBRAM

o Mott

Summary


STT-MRAM Mechanisms


Giant TMR in (Co)Fe/MgO/(Co)Fe (001) films


Giant TMR in FeCoB/MgO/FeCoB

polycrystalline films


MRAM Building Block: The MTJ


STT Induced Magnetization Reversal


STT-MRAM Endurance


Benchmarking - Memories


STT - Possible Applications


• Thermal Stability: DD= Energy/kT, E ~ V

• Write Current Density: Jc

• Stack Patterning• Stack Deposition

• TMR Ratio (Ion/Ioff)

• RA Variability

Technical Challenges


Perpendicular vs. in-plane STT-RAM


Retention (Thermal Stability)


Ic (Write Current)


Scaling Considerations


Perpendicular and Orthogonal MTJ


Perpendicular STT-RAM Scalability


In-Plane

Perpendicular

STT-RAM Status


Outline

Introduction

STT-RAM

RRAM Systems

o OXRAM

o CBRAM

o Mott

Summary


Switching

element:

Reset: thermal disruption of conductive path

Set and reset: ionic transport in opposite directions (according to field polarity)

RRAM polarity


Switching

element:

Reset: thermal disruption of conductive path

Set and reset: ionic transport in opposite directions (according to field polarity)

“gentler” “balanced”=> more reliable (e.g. higher endurance)

RRAM polarity


RRAM goals

Generate fundamental understanding of mechanisms

Develop materials, stacks to meet specs

DRAM/SRAM FLASH

Scalability 10 nm 10 nm

Density 1T1R 3D BICS

Speed 1-30 ns 30-100 ns

Endurance 1015 107

Retention 1s at 85 C 10 yr at 85C

WriteV < 3V < 3V

Roff/Ron > 102 >102

I < 107A/cm2 < 107A/cm2

Multilevel yes


RRAM goals



DRAM/SRAM FLASH



Speed 1-30 ns 30-100 ns

Endurance 1015 107


WriteV < 3V < 3V

Roff/Ron > 102 >102

I < 107A/cm2 < 107A/cm2

Multilevel yes

H.S.Yoon, et al., VLSI Tech. 2009

Need for integrated

selector functionality

(prevent sneak currents)


RRAM goals



Develop selector elements and cells with integrated

selector function

Generate understanding on array implications

DRAM/SRAM FLASH



Speed 1-30 ns 30-100 ns

Endurance 1015 107


WriteV < 3V < 3V

Roff/Ron > 102 >102

I < 107A/cm2 < 107A/cm2

Multilevel yes

H.S.Yoon, et al., VLSI Tech. 2009

Need for integrated

selector functionality


1D Filamentary

(narrow conduction path)

Local change in oxidation state (reduced state is more conductive)

Metal Oxides

TE

BE

metaloxide

reduced

Hf(Zr)Ox, NiOx, TiOx, TaOx...

Resistance Change Systems


Cation motion, Electrochemical metallization, metal bridge

Ag, Cu based (Chalcogenide or oxide glasses)

Cation Source (Ag+, Cu+ or...)

Cu+

Ag+

BE

ME

TA

LIC

FIL

AM

EN

T

1D Filamentary



Metal Oxides

TE

BE

metaloxide

reduced







Cu+

Ag+

BE

ME

TA

LIC

FIL

AM

EN

T

Interface barrier, Redox - vacancy

migration across interface

2D

Area Distributed

s/c Perovskites RE-CMO, Nb-STO....

TE

BE

exchange layer

O vacancy,...

perovskite

1D Filamentary



Metal Oxides

TE

BE

metaloxide

reduced




PCM; Electronic MIT

(Mott)



Oxides

VO2...

3D

Bulk Transition


Cu+

Ag+

BE

ME

TA

LIC

FIL

AM

EN

T



2D

Area Distributed


TE

BE

MITMIT

TE

BE

exchange layer

O vacancy,...

perovskite

1D Filamentary



Metal Oxides

TE

BE

metaloxide

reduced




Evidence of filamentary conduction in TMO

RRAM and of localized switching Switching parameters independent of:

Cell Area filamentary conduction Film thickness localized switching

Physical characterization HRTEM study of formed TiO2 films

Identification of

Magnelli phases Ti4O7

D. H. Kwon et al., Nanotechnology (2010)

IV fitting with QM model: conduction through a narrow constriction current controlled by tunneling through barrier within constriction Quantized conduction channels observed

anode

E0

E1

E2

cathode

x

y

E

EF

Parabolic

potential well

Potential

barrier

0.0

0.2

0.4

0.6

0.8

1.0

1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+0110-4 10-3 10-2 10-1 100 101

TiN/HfO2/Hf/TiN 1T1RVR

ese

t[V

] DC

Cell Area [µm2]

5 nm HfO2

10 nm HfO2

R. Degraeve et al., IEDM 2010


Filament = narrow ‘incision’ through insulator barrier

Model by parabolic potential well

o Discrete energy levels (=channels) in constriction

Add potential barrier inside constriction

ħωy

E0

E1

E2

x

y

E

anode

E0

E1

E2

cathode

x

y

E

EF

Quantum mechanical model of the IV characteristic through filament

Three parameters capture main features of a filament

Current through filament = conduction through saddle shaped potential well

2222

02

1

2

1, ymxmeVyxE yx - y determines constriction width

- low y wide constriction - high y narrow constriction x determines constriction length - low x long tunneling path - high x no tunnel barrier V0 determines nature of the constriction - V0<EF metallic - V0>EF still insulating barrier

4-Channel Quantization at 25oC

R. Degraeve et al, VLSI-TSA 2012

Conductive filament in TMO RRAM

Shimeng Yu et al.

Low Vo concentration: Trap Assisted Tunneling

(TAT), conductive filament: percolation path

High Vo concentration: change in band structure

leads to metallic behavior

IV still controlled by tunneling through

weakest link (constriction)


Filament formation and switching

05

10152025

0 20 40 60 80 100

Vfo

rmin

g(V

)

NiO thickness (nm)

~1.8MV/cm

+ +

+

++

++ ++

+

+ +

++

+++

++

++ +

++

+

+

Ni or Pt

TiN

Ni

TiN

Ni-rich filaments are formed

+ +

+

++

++ ++

+

+ +

++

+++

++

++ +

++

+

+

Ni or Pt

TiN

Ni

TiN

Formation of percolation path

Forming is film thickness dependent

Switching parameters independent of film thickness localized switching

0.0

0.2

0.4

0.6

0.8

1.0

1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+0110-4 10-3 10-2 10-1 100 101

TiN/HfO2/Hf/TiN 1T1RVR

ese

t[V

] DC

Cell Area [µm2]

5 nm HfO2

10 nm HfO2

Form Switching


Forming-less RRAM operation

Lee et al. IEDM 2008

RRAM forming-less cell: Vform~Vset (i.e. cycling without initialization) possible w. thin dielectrics

HfO2/Ti


Bipolar switching in HfO2/reactive metal system

RESET SET

ALD HfO2 10nm

PVD TiN 40nm

PVD TiN 30nm

PVD Hf 10nm

HfO2/Hf HfO2/Ti

Lee et. al, IEDM 2008

General trend: - Abrupt SET (runaway effect) - Gradual RESET (self-limiting)


Capping Layer Role

Hf-Capping: Hf/O XPS Profiles


O2- (Vo++) migration Local redox at active electrode

Switching mechanisms: Filamentary-Bipolar

VoO-2

0.01

0.1

1

10

100

-1 -0.5 0 0.5 1

NiOreduction

Reduction

Vo Vo

Vo

VoVoVo

VoVo

-1V “OFF” “ON” SET

Anodic Oxidation

Vo Vo

Vo

VoVoVo

VoVo

0.01

0.1

1

10

100

-1 -0.5 0 0.5 1

O2- driftoxidation

VoO-2

+1V “ON” “OFF”

NiO

RESET


O2- (Vo) drift Local redox at active electrode

VoO-2

0.01

0.1

1

10

100

-1 -0.5 0 0.5 1

NiOreduction

Reduction

Vo Vo

Vo

VoVoVo

VoVo

-1V “OFF” “ON” SET

Anodic Oxidation

Vo Vo

Vo

VoVoVo

VoVo

0.01

0.1

1

10

100

-1 -0.5 0 0.5 1

O2- driftoxidation

VoO-2

+1V “ON” “OFF”

NiO

RESET

STO (Waser et al.)

Switching mechanisms: Filamentary-Bipolar


Switching mechanisms: TiOx

Filament in reduced state corresponds to different TiOx phase

HRTEM study of formed TiO2 films

Identification of

Magnelli phases Ti4O7

D. H. Kwon et al., Nanotechnology (2010)


QM model and RESET

anode

E0

E1

E2

cathode

x

y

E

EF

x = describes the barrier shape y = describes the potential well V0=saddle point of the surface

Degraeve et al. IEDM 2010

10-7

10-6

10-5

10-4

Cu

rre

nt

(A)

0.60.40.20.0

Voltage (V)

reset

model


10-7

10-6

10-5

10-4

Cu

rre

nt

(A)

0.60.40.20.0

Voltage (V)

reset reset

y

x

2

4

6

1014

2

4

6

1015

pa

ram

ete

r

6

10-6

2 3 4 5 6

10-5

2

Current @ 0.2V (A)

x

y

RESET characterized by constriction narrowing

Main parameter change = change of y

RESET=constriction narrowing

V0 and x are nearly constant

model

I I I

RESET

HfSIO/FUSI


TiN\NiO\Ni cells: state conduction

1.E-08

1.E-06

1.E-04

1.E-02

0 0.5 1

LRS

HRS

1 Voltage to Ni (V)

Cu

rre

nt (

A) 2

83

4 ...

0

5

10

0 20 40

1.5MV/cm

tox (nm)

VF (V)

300x10-6

250

200

150

100

50

0

Curr

ent (A

)

0.50.40.30.20.10.0

Voltage (V)Voltage to Ni (V)

Cu

rre

nt (

A)

2 3 4

5 67

8

(c)ohmic

QM tunneling

5.E+13

5.E+14

0.E+00 2.E-05 4.E-05 6.E-05

x

y

Co

nst

rict

ion

p

aram

eter

s (H

z)Current (A)

(b)Gradual reset results in transition from ohmic- to QM-conduction

Corresponding to constriction narrowing (increase of wy )

(similar to NiSi\SiO\HfSiO\NiSi)

L. Goux et al., 2011 Symp. on VLSI Tech., 24 (2011)


NiO cells: Influence of anode material

5.E+13

5.E+14

0.E+00 2.E-05 4.E-05 6.E-05

x

yC

on

stri

ctio

n

par

amet

ers

(Hz)

Current (A)

(b)

Reset constriction is controlled by appropriate anode material

Blue circles: Pt anode

red squares: Ni anode

NiO thickness = 40nm

300x10-6

250

200

150

100

50

0

Cu

rre

nt

(A)

0.80.60.40.20.0

Voltage (V)

TiN\NiO\Pt(a)

Voltage to Pt (V)

Cu

rre

nt (

A)Same results with catalytic Pt anode

(reset is not due to Ni injection)

5 channels Ei+1-Ei=80meV



TiN\NiO\Ni cells: set/reset mechanisms

Forming: Percolation of oxygen species

+ +

+

++

++ ++

+

+ +

++

+++

++

++ +

++

+

+

Ni or Pt

TiN

+ +

+

++

++ ++

+

+ +

++

+++

++

++ +

++

+

+

Ni or Pt

TiN

(a) (b) (c)

dx

Ni or Pt

NiO1-x

NiOdy dy

Ni or Pt

NiO1-x

NiO

(d)+VRESET+VRESET

Reset: Local constriction narrowing

controlled by the anode (presumably at anode interface)

Set: Local percolation



Scaled TiN\NiO\Ni cells: anode engineering

Anode performances: Ni>Pt>NiPt>NiPtSi>TiN>TaN>Ti

stack Switching mode Ref.

Ni\NiO\Ni Non-polar

Pt\NiO\Pt Non-polar

Ni\NiO\TiN Unipolar

(Ni anode)

this

work

Pt\NiO\TiN Unipolar

(Pt anode)

TiN\NiO\TiN Super-linear LRS

NiPt\NiO\Ni Non-polar

NiPtSi\NiO\Ni Non-polar

Stack engineering: non-polar switching is

allowed provided both BE and TE have appropriate

catalytic properties

L. Goux et al., IEEE TED 56 (2009)

H. Akinaga et al., Proc. IEEE, 98 (2010); I.H. Inoue et al., Phys. Rev. B 77 (2008)



Scaled TiN\NiO\Ni cells: TEM/EELS

Pile-up of oxygen at the NiO\Ni interface after

reset switching

20 nm20 nm20 nm20 nm20 nm

TiN

NiONiTiN

PMD

~80nm

2

1

1.E+03

1.E+04

1.E+05

1 10 100

Voltage to Ni (V)

# switching cycles

Cu

rre

nt

(A)

HRS

LRS78.5

96.5

Ni

TiNNiO

NiONi

TiN

Ni

TiNNiO (a)

(b)

(e)

(c)

Re

sist

ance

(

)

0.E+00

5.E-05

1.E-04

0 0.5 1

10

100

1000

10 100 1000

ICOMP (A)

IRESET (A)(d)

0.E+00

3.E+06

5.E+06

0.E+00 4.E-08 8.E-08

0.E+00

5.E+05

1.E+06

0.E+00 4.E-08 8.E-08

0.E+00

1.E+05

2.E+05

3.E+05

0.E+00 4.E-08 8.E-08

TiNNiNiOTiN

1 2

Co

un

ts (T

i)C

ou

nts

(O)

Position (nm)

Co

un

ts (N

i)before reset

0.E+00

3.E+06

5.E+06

0.E+00 4.E-08 8.E-08

0.E+00

5.E+05

1.E+06

0.E+00 4.E-08 8.E-08

0.E+00

1.E+05

2.E+05

3.E+05

0.E+00 4.E-08 8.E-08

TiNNiNiOTiN

1 2

Co

un

ts (T

i)C

ou

nts

(O)

Position (nm)

Co

un

ts (N

i)after reset



Scalability of filament formation: filament formation depends

on local defects

Predictable area scaling for uniform distribution of defects (e.g.

amorphous material)

In crystalline material: grain size vs. cell size

Scalability of switching:

Good scalability (not much changes) expected down to scale of

filament (few nm)

Scalability to 10 nm!

Planarized BE

Implications of filamentary conduction, localized switching

HfO2-based 1T1R Govoreanu et al., IEDM 2011


10 nm RRAM Cell

Govoreanu et al., IEDM 2011


Variability:

Filament formed at defects...local atomic

configuration at constriction varies among filaments

(and for same filament with switching!)

Few atomic jumps may impact conduction of

narrow filament

Stochastic component (small numbers)

(however: “small number” stochastic variability

likely present for ANY technology when scaling

to nm range)

3000 /s

experiment

log(time)50x10-6

40

30

20

10

0

Cu

rre

nt (A

)

1.00.80.60.40.20.0

Voltage (V)

reset

0.0 0.2 0.4 0.6

Voltage (V)

Cu

rre

nt (

A

)

50

40

30

20

10

0



Retention: Few atomic jumps may impact conduction of narrow filament

variability of retention

Stronger (more conductive) filaments have better retention

Shimeng Yu, Y. Y. Chen, X. Guan, H.-S. Philip Wong, J. A. Kittl , Appl. Phys. Lett. 100, 043507 (2012)

MC simulations:



Switching voltage-pulse width trade-off

-9 -8 -7 -6 -50

0.2

0.4

0.6

0.8

1

Pulse duration, log(tp[s])

RE

set

vol

tage

, VR

E,S

et [V

]

T = 25C

0.5

1.0

1.5

2.0

2.5

1.00E-09 1.00E-08 1.00E-07 1.00E-06 1.00E-0510-9 10-8 10-7 10-6 10-5

Pulse Width [s]

Sw

itch V

oltage [V

]

Reset

Set

TiO2/Al2O3 Hf/HfO2

Shimeng Yu, Yi Wu, and H.-S. Philip Wong APL 98, 103514 (2011)

Exponential dependence of switching time on voltage

High speed (< 1 ns), low voltage switching achieved


Retention and endurance in HfO2-based RRAM

Retention: LRS failure thermally activated

Stronger (wider) filaments

better retention

10 yr at 85C spec

Ea consistent with ab-initio +

molecular dynamic simulations of

diffusion

107

106

105

104

1031E+3

1E+4

1E+5

1E+6

1E+7

1E+0 1E+1 1E+2 1E+3 1E+4 1E+5 1E+6 1E+7 1E+8 1E+9100 101 102 103 104 105 106 107 108 109

R (

ohm

)

Cycle #

Rete

ntion T

ime (

s)

1/kT

Endurance: 1010 cycles achieved


Retention and endurance in HfO2-based RRAM

Retention: LRS failure thermally activated

Stronger (wider) filaments

better retention

10 yr at 85C spec

Ea consistent with ab-initio +

molecular dynamic simulations of

diffusion

Rete

ntion T

ime (

s)

1/kT

Endurance: 1010 cycles achieved


IEEE Trans on Electron Dev. 59, 3243 (2012)

Endurance and balanced cycling

Prof. Jorge Kittl, KU Leuven - EPICO 2012, Buenos Aires, Argentina 70

Too strong Reset: LRS failure Too strong Set: HRS failure

IEEE Trans on Electron Dev. 59, 3243 (2012)

Improving cycling: Stack optimization (HfO2-based 1T1R)

1.E-091.E-081.E-071.E-061.E-051.E-04

-1.6 -1.2 -0.8 -0.4 0-1.6 -1.2 -0.8 -0.4 0

Voltage (V)

Cu

rre

nt (A

)

10-4

10-5

10-6

10-7

10-8

10-9 1.E-091.E-081.E-071.E-061.E-051.E-04

-1.6 -1.2 -0.8 -0.4 0-1.6 -1.2 -0.8 -0.4 0

Voltage (V)

Cu

rre

nt (A

)

10-4

10-5

10-6

10-7

10-8

10-9

Switching with:

Lower variability

Lower current

Larger R window

Standard stack Optimized stack


L. Goux et al, VLSI 2012

Controlling the constriction for improved switching


Optimized stack

L. Goux et al, VLSI 2012

Dynamic ‘Hour Glass’ Model for SET and

RESET in HfO2 RRAM


R. Degraeve et al., VLSI 2012


RESET in HfO2 RRAM






RESET in HfO2 RRAM

Transition line: equal probability of emisison between BR and C

PCM; Electronic MIT

(Mott)



Oxides

VO2...

3D

Bulk Transition


Cu+

Ag+

BE

ME

TA

LIC

FIL

AM

EN

T



2D

Area Distributed


TE

BE

MITMIT

TE

BE

exchange layer

O vacancy,...

perovskite

1D Filamentary



Metal Oxides

TE

BE

metaloxide

reduced




Operation

ON-switching:

Reduction @ cathode

Ag filament formation

Ag+ + e‘ Ag

OFF-switching:

Oxidation @ anode

Ag Ag+ + e‘

M. Faraday (1834)

Electrolyte

* amorphous GeSe2+x

and GeS2+x

* Disordered and amorphous

sulfides and oxides C. Schindler et al., IEEE T-ED, 54 (2007) 2762

CBRAM BASICS

79 Prof. Jorge Kittl, KU Leuven -

EPICO 2012, Buenos Aires,

Argentina

CBRAM STACKS Cations: Ag, Cu,... Insulators: Chalcogenides, Oxides

Decouple functionality, no phase separation better scalability

WRITE ERASE

Metal+

ions

e-

Ag-rich

precipitates

ElectrodeElectrode

ElectrodeElectrode

~20-

50 nm

K. Aratani et al., IEDM 2007 R. Muller et al. (imec)

oxides, few nm

M.Kozicki et al. IEEE Trans. On Nanotechnology 4(3), 331 (2005)

C.Schindler et al., IEEE TED 54(10), 2762 (2007) T.Sakamoto et al., VLSI 2007

- phase separation in switching layer

- percolation between conductive

metal-rich precipitates

- functionality divided by layer

- no phase separation



Argentina

Cu-BASED CBRAM UNDER STUDY

TECu-sourceCu+

Cu+

Cu+

Cu+

BE

Cell concept: engineered stack, separating functions by layers:

Cu-source and stack optimization

Combinatorial approach (e.g. Cu-Te composition)

A

B

AxBy

JORGE KITTL @ IMEC 2010 67

5

15

25

35

45

55

65

Te/(

Te+

Cu

)

Composition Cu-Te (XRF)

10 30 50 70

2theta

Crystallinity (XRD)

Cu

Cu

2Te

a

-Cu

Te

+ a

-Te

Cu-Te gradient

Cu

Te

IMEC partner conf idential – as listed in access slide

Mapping capabilities for composition, crystallinity, phase…



Argentina

L. Goux et al., Appl. Phys. Lett. 99, 053502 (2011), IMW 2011, VLSI 2012

COMBINATORIAL PVD OF Cux-Te1-x



Argentina

7.5

8

8.5

0

2

4

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Cell resista

nce

[Log(Ω)]

VFO

RM

ING (

V)

x in CuxTe1-x 1.E-12

1.E-08

1.E-04

0 2.5 5

x>0.7

Voltage (V)

Curr

ent

(A)

Cux-Te1-x COMPOSITION EFFECT: FORM

X>0.7: lower Vform

L. Goux et al., Appl. Phys. Lett. 99, 053502 (2011), IMW 2011, VLSI 2012 83 Prof. Jorge Kittl, KU Leuven -


Argentina

7.5

8

8.5

0

2

4

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Cell resista

nce

[Log(Ω)]

VFO

RM

ING (

V)

x in CuxTe1-x

x in CuxTe1-x

Form

ing

volt

age

(V)

Cell resistance (Ω

)

1030

5070

Intensity

2theta

Crys

tallin

ity(X

RD)

April

2010

1020304050607080

Te/(Te+Cu)

Comp

ositi

on

(XRF

) 30

50

Cu

Cu2Te

2()

Intensity (a.u.)

Cu2Te + CuCu2TeTe + CuTe

(a)

(b)

(c)

x=0.74x=0.67x=0.6x=0.35

amorphous Cu2Te-Crystal Cu inclusions

0.0E+00

5.0E+07

1.0E+08

1.5E+08

2.0E+08

2.5E+08

0

1

2

3

4

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Forming voltageresistance

1.E-12

1.E-08

1.E-04

0 2.5 5

x>0.7

V(V)

I(A)

1030

5070

Intensity

2theta

Crys

tallin

ity(X

RD)

April

2010

1020304050607080

Te/(Te+Cu)

Comp

ositi

on

(XRF

) 30

50

Cu

Cu2Te

2()

Intensity (a.u.)


a-Cu-Te Cu2-xTe

Cu CuTe

2 ()

Si Si Si

x<0.5 0.5<x<0.7 x>0.7

Cu-Cu Te-Cu

VF.Cu-Cu<VF.Te-Cu

Te-CuTe-Cu

VF.Te-Cu

Te-Cu

VF.Te-CuCu Cu Cu

Cu-Te phases require

larger energy for

Cu-filament formation

1.E-12

1.E-08

1.E-04

0 2.5 5

x>0.7

Voltage (V)

Curr

ent

(A)

Cux-Te1-x COMPOSITION EFFECT: FORM

X>0.7: lower Vform



Argentina

x in CuxTe1-x

Form

ing

volt

age

(V)

Cell resistance (Ω

)

1030

5070

Intensity

2theta

Crys

tallin

ity(X

RD)

April

2010

1020304050607080

Te/(Te+Cu)

Comp

ositi

on

(XRF

) 30

50

Cu

Cu2Te

2()

Intensity (a.u.)


(a)

(b)

(c)

x=0.74x=0.67x=0.6x=0.35


0.0E+00

5.0E+07

1.0E+08

1.5E+08

2.0E+08

2.5E+08

0

1

2

3

4

0.2 0.3 0.4 0.5 0.6 0.7 0.8


1.E-12

1.E-08

1.E-04

0 2.5 5

x>0.7

V(V)

I(A)

1030

5070

Intensity

2theta

Crys

tallin

ity(X

RD)

April

2010

1020304050607080

Te/(Te+Cu)

Comp

ositi

on

(XRF

) 30

50

Cu

Cu2Te

2()

Intensity (a.u.)


Cu2-xTe

Cu CuTe

2 ()

Si Si Si

x<0.5 0.5<x<0.7 x>0.7

Cu-Cu Te-Cu

VF.Cu-Cu<VF.Te-Cu

Te-CuTe-Cu

VF.Te-Cu

Te-Cu

VF.Te-CuCu Cu Cu

-10

-8

-6

-4

-2 -1 0 1 2 3

-10

-8

-6

-4

-2

-3 -2 -1 0 1 2

-10

-8

-6

-4

-2

-4 -2 0 2 4

(1) x=0.25

Curr

ent [L

og(A

)]Voltage to the Pt TE (V)

(2) x=0.57 (3) x=0.78

a-Cu-Te

Cux-Te1-x COMPOSITION EFFECT: SWITCHING x<0.5: volatile

forming 0.5<x<0.7: Ireset~Icomp

x>0.7: Ireset>>Icomp

Si n+

Al2O3 (3nm)

Pt (50nm)

CuxTe1-x (50nm)



Argentina

-10

-8

-6

-4

-2 -1 0 1 2 3

-10

-8

-6

-4

-2

-3 -2 -1 0 1 2

-10

-8

-6

-4

-2

-4 -2 0 2 4

3

4

5

6

7

8

0.2 0.4 0.6 0.8

-8

-6

-4

-2

0.2 0.4 0.6 0.8

x in CuxTe1-x

ICOMP=5A

ICOMP=100A

x in CuxTe1-x

(3)(2)(1)

RLR

S[L

og(

)]

I RESE

T[L

og(A

)]

(1) x=0.25

Curr

ent [L

og(A

)]

Voltage to the Pt TE (V)

(2) x=0.57 (3) x=0.78

Region (2): ICOMP allows

tuning IRESET and RLRS

Cu-Te bond

limits Cu injection

Te phase prevents

stable Cu filament

Volatile switch Optimum CBRAM (low I)

-10

-8

-6

-4

-2 -1 0 1 2 3

-10

-8

-6

-4

-2

-3 -2 -1 0 1 2

-10

-8

-6

-4

-2

-4 -2 0 2 4

3

4

5

6

7

8

0.2 0.4 0.6 0.8

-8

-6

-4

-2

0.2 0.4 0.6 0.8

x in CuxTe1-x

ICOMP=5A

ICOMP=100A

x in CuxTe1-x

(3)(2)(1)

RLR

S[L

og(

)]

I RESE

T[L

og(A

)]

(1) x=0.25

Curr

ent [L

og(A

)]

Voltage to the Pt TE (V)

(2) x=0.57 (3) x=0.78

Pure Cu phase excessive Cu injection

High I CBRAM Reset failuers

Cux-Te1-x COMPOSITION EFFECT: SWITCHING

-10

-8

-6

-4

-2 -1 0 1 2 3

-10

-8

-6

-4

-2

-3 -2 -1 0 1 2

-10

-8

-6

-4

-2

-4 -2 0 2 4

(1) x=0.25

Curr

ent [L

og(A

)]Voltage to the Pt TE (V)

(2) x=0.57 (3) x=0.78

x<0.5: volatile forming

0.5<x<0.7: Ireset~Icomp

x>0.7: Ireset>>Icomp

L. Goux et al., Appl. Phys. Lett. 99, 053502 (2011), IMW 2011, VLSI 2012



Argentina

1.E+03

1.E+05

1.E+07

1.E+09

0 1000 2000 3000 4000 5000

resistan

ce at 0.1V

(ohm)

# cycles

LRS

HRS

109

107

105

103

Resi

stan

ce a

t 0.1

V (ohm

)

# cycles

90nm CBRAM stack

1.E-07

1.E-06

1.E-05

1.E-04

-0.5 0 0.5

I (A)

Vte (V)

Thermal Budget: 200C,1h

Stack optimized to achieve stable low current cycling (<5 µA)

Further stack optimization for implementation into 1T1R, thermal budget 200oC

OPTIMUM Cu-Te COMPOSITION

Voltage (V)

Curr

ent (A

) (2) 0.5<x<0.7

-1.0 -0.5 0.0 0.51E-10

1E-9

1E-8

1E-7

1E-6

1E-5

Si n+

Al2O3 (3nm)

Pt (50nm)

CuxTe1-x (50nm)

L. Goux et al., Appl. Phys. Lett. 99, 053502 (2011), IMW 2011, VLSI 2012 87 Prof. Jorge Kittl, KU Leuven -


Argentina

Write speed: Voltage-time trade-off 90nm CBRAM stack

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

PW (sec)

Vre

set(V

)

drift-limited switching

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

I-V

Pulse width [s] 10-9 10-7 10-5 10-3 10-1

DC AC

V r

es

et

[V] 5

4

3

2

1

0

10ns@3V

Cu-Te

Al2O3

Exponential scaling of switching speed with operating voltage

5 ns switching achieved at low V

C. Schindler et al.,

APL (2009)

Cu15 nm SiO2

Ir

100ns@4V10s@3V

ion-transport

limited

Ag/GeS



Argentina

90nm CBRAM stack

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

PW (sec)

Vre

set(V

)

drift-limited switching

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

0

1

2

3

4

5

1.E-09 1.E-07 1.E-05 1.E-03 1.E-01

I-V

Pulse width [s] 10-9 10-7 10-5 10-3 10-1

DC AC

V r

es

et

[V] 5

4

3

2

1

0

10ns@3V

Cu-Te

Al2O3

Different regime at low V allowing read, helping disturb immunity

Reaction limited

C. Schindler et al.,

APL (2009)

Cu15 nm SiO2

Ir

100ns@4V10s@3V

Russo et al.,

TED (2009)

ion-transport

limited

Ag/GeS

Write speed: Voltage-time trade-off



Argentina

CBRAM Multi-Level Capability

Source: Qimonda

AgTa40 nm GeS2

W

Ag-based

AgTa/50 nm GeS2 (QIMONDA)

Cu/40 nm GeSe4 (ITRI)

Cu-based (IMEC)

CuTe/2 nm Gd2O3 (SONY)

Ag/Ge-Se (C. Schindler, 2008))

Cu/15 nm SiO2 (C. Schindler, 2008)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

-0.3 -0.2 -0.1 0 0.1 0.2 0.3Resis

tan

ce [

Oh

m]

107

106

105

104

103

LR1

LR2

LR3 HR

Cu-Te/Al2O3 (imec)

W, BE W, BE

Al2O3CuTeTE TEAlO, HfO

CuTe

W

AlO

Ti\CuTe

Pt=90nm

x

Large range of R possible: - HR limited by leakage: better insulating layer

and smaller cells larger HRS possible

- LR limited by low operation current

requirements (10 µA)

Multi-level capability (2 bits per cell,

4 levels, demonstrated) 90 Prof. Jorge Kittl, KU Leuven -


Argentina

CBRAM ENDURANCE

K. Aratani et al., IEDM 2007 R. Muller et al. (imec)

105

108

Cycling of individual cells up

to 1011 demonstrated

Considered as candidate for

DRAM replacement 91 Prof. Jorge Kittl, KU Leuven -


Argentina

CBRAM Scalability

Demonstration of the potential of the CBRAM technology on very small dimensions laying out a scalability path down to ~15nm

Source: Qimonda

Functionality down to 20 nm demonstrated



Argentina

1.E+03

1.E+05

1.E+07

1.E+09

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05

CBRAM RETENTION

W, BE W, BE

Al2O3CuTeTE TE

W CT (90nm)

select transistor

AlO

Cu-Te

Time [Log(sec)]

Res

ista

nce

[Lo

g(Ω

)]

LRS

HRS

@85C

1.E+03

1.E+04

1.E+05

1.E+06

0.1 1 10 100

Vbias = -0.1V

Time (sec)

Vbias = +0.1V Res

ista

nce

(Ω

) LRS

@85C

...however, sensitivity of

filaments to voltage disturb

Si n+

Al2O3 (3nm)

Pt (50nm)

CuxTe1-x (50nm)

State stability at 85C...

Time (sec) Res

ista

nce

(Ω

) @85C

LRS

HRS



Argentina

CBRAM CHALLENGES: THERMAL STABILITY AND RETENTION

High diffusivity metals used for fast switching (Ag,Cu)

with thermal budget, metal will tend to move leading to

challenges in:

Retention:

- dissolution of filament due to fast metal diffusion

Thermal stability (e.g. during processing)

- Excessive metal diffusion (shorts)

- Morphological degradation

- Phase separation (unacceptable for scaling)

- Adhesion issues



Argentina

ADDRESSING CBRAM CHALLENGES: THERMAL STABILITY AND RETENTION

x in CuxTe1-x

Form

ing

volt

age

(V)

Cell resistance (Ω

)

1030

5070

Intensity

2the

ta

Crys

tallin

ity(X

RD)

April

2010

1020304050607080

Te/(Te+Cu)

Comp

ositi

on

(XRF

) 30

50

Cu

Cu2Te

2()

Intensity (a.u.)


(a)

(b)

(c)

x=0.74x=0.67x=0.6x=0.35


0.0E+00

5.0E+07

1.0E+08

1.5E+08

2.0E+08

2.5E+08

0

1

2

3

4

0.2 0.3 0.4 0.5 0.6 0.7 0.8


1.E-12

1.E-08

1.E-04

0 2.5 5

x>0.7

V(V)

I(A)

1030

5070

Intensity

2theta

Crys

tallin

ity(X

RD)

April

2010

1020304050607080

Te/(Te+Cu)

Comp

ositi

on

(XRF

) 30

50

Cu

Cu2Te

2()

Intensity (a.u.)


Cu-Te Cu2-xTe

CuCuTe

x=0.75x=0.6x=0.35

2

()

Intensity (a.u.)


Cu-content

100 200 300 400 500 600 700 800 Temperature (oC)

2-T

he

ta (d

eg

) 20

25

30

35

200oC 200oC 200oC

IS-XRD

200oC 300oC

XRD

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

0 10 20 30 40

Inte

nsi

ty (C

ou

nts

/s)

Time (min)

Te

Cu

Al

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

0 10 20 30 40

Inte

nsi

ty (C

ou

nts

/s)

Time (min)

Te

Cu Al

200oC

Better morphology and thermal stability

by composition and stack optimization

Composition optimization Stack optimization (layers, alloying elements)

SIMS

200oC



Argentina

2D “Area Distributed” Systems



Argentina



Argentina

PCM; Electronic MIT

(Mott)


Ag, Cu based (Chalcogenide or oxide glasses

Oxides

VO2...

3D

Bulk Transition


Cu+

Ag+

BE

ME

TA

LIC

FIL

AM

EN

T



2D

Area Distributed


TE

BE

MITMIT

TE

BE

exchange layer

O vacancy,...

perovskite

1D Filamentary



Metal Oxides NiOx, HfOx, TiOx, TaOx...

TE

BE

metaloxide

reduced

Resistance Change systems


PCM; Electronic MIT

(Mott)



Oxides

VO2...

3D

Bulk Transition


Cu+

Ag+

BE

ME

TA

LIC

FIL

AM

EN

T



2D

Area Distributed


TE

BE

MITMIT

TE

BE

exchange layer

O vacancy,...

perovskite

1D Filamentary



Metal Oxides

TE

BE

metaloxide

reduced




VO2 VO2 changes from semiconducting to

metallic at 68oC

Structural/Mott transition

Phase transformation occurs by local

displacements (V-V bond dilation) on a

fs/ps time scale, followed by long-range

shear rearrangements on sub-ns

timescale.

Switching in ns time scales possible

Switching devices demonstrated (but

device operation required holding voltage)

low-temp phase

Monoclinic VO2

Tetragonal VO2

high-temp phase

Kim et al.

Local atomic displacement

Shear

P. Baum et al., Science, 318, 788 (2007)


VO2 potential applications

Volatile memory concept, Selector

Requires material with TC higher

than operating temperature range

Non-volatile memory concept

Wide bi-stable region spanning

operating range

R

TC

vola

tile

oper

atio

n

NV

Mop

erat

ion


0.001

0.01

0.1

1

10

Re

sis

tivity (

cm

)

12010080604020

T(°C)

Oct. 2010 Apr. 2010

VO2 Material development

PVD V + low PO2 oxidation

VO2~ 100nm

log(R48/R100)=3.71

Initial process:

PVD V + oxidation

New process: ALD VO2 (U.Gent, now

transferred to imec 300 mm)

42nm VO2

Precursor: ALVA= TEMAV As deposited oxide is amorphous Crystallization T ~550C

550°C

New process enables VO2 thickness scaling

below 50nm and in-situ doping of VO2

G. Rampelberg et al., Appl. Phys. Lett. 98, 162902 (2011)


2-terminal VO2 devices

• VO2 produced by sputtering 50nm V on

20nm SiO2 or Al2O3 + oxidation at 500 and

1Torr O2.

• 2-terminal devices are patterned with e-

beam lithography and metal lift-off.

10-4

10-3

10-2

10-1

100

101

Re

sis

tivity (

cm

)

100806040

Temperature (ºC)

10-3

10-2

10-1

100

Cu

rre

nt(

mA

)

-4 -2 0 2 4Applied voltage (V)

Metal

Metal

VO2

Devices display bipolar volatile switching.

I. Radu et al., 2011 SSDM


Switching mechanism

Switching likely

controlled by Joule

heating as the

switching field varies

with electrode

separation.

Steep decrease of ON

voltage with increasing

temperature.

Linear decrease of

power to turn on device

with increasing

temperature consistent

with Joule heating.

10

5

0Pow

er

(x10

-4W

)

60504030

Temperature (ºC)

1

0.5

0

Curr

ent

(mA

)

6420

Applied voltage (V)2

5ºC

60ºC

45ºC

35ºC

55ºC

0.8

0.6

0.4

0.2

0

EO

N/O

FF (

MV

/cm

)

1002 3 4 5 6

10002 3 4 5

Electrode separation (nm)

open symbol EON

closed symbol EOFF



Switching times

o Fast turn on in less than 20ns.

o Turn-off by heat dissipation.

o Current devices ~200ns.

o Turn-off time could be

engineered with device design

ON/ON ON/OFF

100ns 200ns



Endurance • ROFF/RON~100

• Stable over more than 1010 cycles (device still

working when endurance testing stopped).

4

102

2

4

103

2

4

104

R (

)

102 10

4 106 10

8 1010

cycle #



Volatile switching

Joule heating

induced switching in

2 terminal devices

Volatile, symmetric,

excellent cyclability

VO2 devices

Isothermal (68 )

retention time:

Excellent retention to 10

years within hysteresis

loop

4

102

2

4

103

2

4

104

R (

)

102 10

4 106 10

8 1010

cycle #

10-3

10-2

10-1

100

Cu

rre

nt(

mA

)

-4 -2 0 2 4Applied voltage (V)


Summary


Thank you for your attention

Gracias a Pablo y a todos los organizadores!


Thank you for your attention

Gracias a Pablo y a todos los organizadores!

Appl. Phys. Lett. 99, 053502 (2011) Appl. Phys. Lett. 100, 113513 (2012)

TECu-sourceCu+

Cu+

Cu+

Cu+

BE

90nm CBRAM stack

OPTIMUM Cu-Te COMPOSITION

Voltage (V)

Curr

ent (A

)

(2) 0.5<x<0.7

-1.0 -0.5 0.0 0.51E-10

1E-9

1E-8

1E-7

1E-6

1E-5

Si n+

Al2O3 (3nm)

Pt (50nm)

CuxTe1-x (50nm)

1st International Workshop on Resistive RAM


prof. jorge kittl, dept. of physics and...

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