Comparative Assessment of GST and GeTe Materials for Embedded

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2007

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Comparative Assessment of GST Comparative Assessment of GST and and GeTeGeTe Materials for Embedded Materials for Embedded Phase Change Memory DevicesPhase Change Memory Devices

L.Perniola, A.Fantini, M.Armand, J.F.Nodin, V.Sous a, A.Persico, C.Jahan, S.Maitrejean, S.Lhostis*, A.Rou le,

E.Gourverst, C.Dressler, G.Reimbold, B.DeSalvo, P.Mazoyer*, D.Bensahel*, F.Boulanger

CEA/LETI, Grenoble, France*St-Microelectronics, Crolles, France

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2007



PCM statePCM state --ofof --thethe --art (1/2)art (1/2)

For ePCM development goal:

128 Mb, 90 nm, Numonyx, VLSI 2006

512 Mb, 90 nm, SAMSUNG, IEDM 2006

SA

MS

UN

G

Num

onyx

1. Constant improvement of process integration ( companies)

… however data retention of GST demonstrated up 70°C – 85°C, despite process integration efforts

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For ePCM development goal:2. Phase-change material research

Strong research at material level is raised to enha nce device performance: best result with In-Ge-Te (@ 156 °C )

Hitachi, O-doped GST, IEDM 2005 Hitachi, InGeTe, IEDM 2007

PCM statePCM state --ofof --thethe --art (2/2)art (2/2)

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OutlineOutline

Introduction

Approach

Material Study

Electrical Characterization

Summary

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AppliedMethodology

CT200

24 26 28 30 32 34 36 38 40 42 44 46 48

Ge0.62Te0.38 (400°C)

Ge cubic (Fd-3m)αααα-GeTe rhombohedral (R3m)

Nor

ma

lized

inte

nsity

Ge0.76Te0.24 (400°C)Ge

0.76Te

0.24 (360°C)

Ge0.62

Te0.38

(250°C)

Ge0.5

Te0.5

(400°C)

2θθθθ (°)

Material research:Material research:From GST to GeTe

ApproachApproach

Test Test devicedevice fabricationfabrication :GST & GeTe

deposited by PVD

Electrical Electrical CaractCaract . & . & ModelingModeling

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

Programming Current [A]

Re

sist

anc

e [O

hm]

RESET-SET

SET-RESET

2D sim SET-RESET

2D sim RESET-SET

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0 2 4 6 8

Applied Voltage VA [V]

Cel

l Res

ista

nce

[Ohm

]

AVG - 500ns

AVG - 100ns

AVG - 50ns

AVG - 25ns

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OutlineOutline

Introduction

Approach

Material Study


Summary

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CT200

Material Material ResearchResearch

Incr

. Ge

%

Incr. Sb %

Automotive application requires amorphous stability at high temperature, primary focus on Crystallization Temp increase

GeTe is thus interesting as a possible host material

Ge2Sb2Te5 is the most studied PC alloy

Increasing Sb Content Faster Write Lower TC

Increasing Ge Content Higher TC

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InIn--Situ XRD on GeSitu XRD on Ge xxTeTe(1(1--x)x) samplessamples

24 26 28 30 32 34 36 38 40 42 44 46 48

Ge0.62

Te0.38

(400°C)

Ge cubic (Fd-3m)αααα-GeTe rhombohedral (R3m)

Nor

mal

ized

inte

nsity

Ge0.76

Te0.24

(400°C)Ge

0.76Te

0.24 (360°C)

Ge0.62

Te0.38

(250°C)

Ge0.5

Te0.5

(400°C)

2θθθθ (°)Stoichiometric

GeTe

IncreasingG

e content

Excess Ge will result in Cubic-Ge segregation

We need stoichiometric GeTe for a stable material

E. Gourvest et al., APL 2009

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Properties of asProperties of as --depdep GeTeGeTe and GST (1/3)and GST (1/3)

Resistivity and Reflectivity of GeTe, GeSbTe as a function of Temperature T

GeTe has:

Higher crystallization temperature Higher resistivity contrast Stable resistivity after cristallisation

25.00

50.00

75.00

20 60 100 140 180 220 260 300

Temperature [°C]

Ref

lect

ivity

[%]

GeTeGeSbTe

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

20 60 100 140 180 220 260 300

Temperature [°C]

Res

istiv

ity

[Ohm

*m]

GeTeGeSbTe

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Resistivity of GeTe, GeSbTe as function of time

Different shapes:Probably stronger growth process in GeTe

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

10 100 1000 10000Time [s]

Squ

are

Res

ista

nce

[Ohm

/sq]

GeTe 155 °C

GeTe 165 °C

GeTe 175 °C

GeTe

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

10 100 1000 10000Time [s]

Sq

uare

Res

ista

nce

[Ohm

/sq]

GST 125 °C

GST 130 °C

GST 135 °C

GST 140 °C

GeSbTe

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GST 50% fail

Ea = 3.13 eV

R2 = 0.996

Ea = 3.2 eV

R2 = 0.9927

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

1.0E+08

1.0E+09

24 25 26 27 28 29 30 31 32 33 34

1/KT [1/eV]

Fai

l Tim

e [s

]

75 °C107 °C

GeTe

GeSbTe

10 years

As-dep GeTe has higher 10-years fail temperature than GST


Fail Temperature Estimation (50% Fail Threshold)

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OutlineOutline

Introduction

Approach

Material Study


Summary

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Y Y’

Test Devices Test Devices -- ProcessProcess

Al - Line Al - Pad

SiO2

Si - Bulk

Al - Line Al - Pad

SiO2

Si - Bulk

Al - Line Al - Pad

SiO2

Si - Bulk

Al - Line

Al - Pad

SiO2

Si - Bulk

300 nm

Cross-bar resistor structure Memory Dot defined by W plug

300 nm CD size Active Stack

PC deposited by PVD

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Test Setup & SET/RESET WaveformsTest Setup & SET/RESET Waveforms

Flexible test setup allows for PULSED electrical measurements

ArbitaryWaveformGenerator

SemiconductorCharacterization

System

S

G

Oscilloscope

Activeprobe RF probe

TEBE

Ch1 SMU1

IEE

48

8

Switch

RL ~ 0 – 1K

50 Ω

ArbitaryWaveformGenerator

SemiconductorCharacterization

System

S

G

Oscilloscope

Activeprobe RF probe

TEBE

Ch1 SMU1

IEE

48

8

Switch

RL ~ 0 – 1K

50 Ω

Test Setup

0

0.5

1

1.5

2

2.5

3

20 40 60 80 100

Time [ns]V

olta

ge [

V]

V ProbeV Appl

VA (Applied)

VP (Probe)

Waveform readout

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Program Curves: Program Curves: GeTeGeTe and and GeSbTeGeSbTe (1/2)(1/2)

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0 2 4 6 8

Applied Voltage VA [V]

Cel

l Res

ista

nce

[Ohm

]

AVG - 500ns

AVG - 100ns

AVG - 50ns

AVG - 25nsGeSbTe

Program Curve vs Pulse Time

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6

Voltage on Probe [V]

Ce

ll C

urre

nt [m

A]

VTH ~1.5 VIRESET ~30 mA

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Data Retention: Data Retention: GeTeGeTe DevicesDevices

GeTe: Longer fail times at HT compared to GST

Room for improvement will probably come from optimi zed RESET procedure and optimized test device structure s

0.10

1.00

10.00

10 100 1000 10000 100000Time [s]

Nor

mal

ized

Res

ista

nce GeTe 120 °C

GeTe 175 °C

GeSbTe 120 °C

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OutlineOutline

Introduction

Approach

Material Study


Summary

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SummarySummary

Complete analysis is presented on GeTe compared with GST phase-change materials. The applied methodology spa ns through: Physico-chemical characterization Reflectivity and resistivity measurements on full-sheet samples Dynamic R-I on test devices

100~ 75 °C1E3145 °CGST

1000~ 107 °C1E5185 °CGeTe

RRES/ RSETMax Temp 10yρρρρam/ρρρρxlsTc

Material comparison in brief:

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THANK YOU FOR THANK YOU FOR YOUR ATTENTIONYOUR ATTENTION

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Program Algorithm for Pulsed Meas.Program Algorithm for Pulsed Meas.

Comparative Assessment of GST and GeTe Materials for Embedded

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