Nanoscale switching in resistive memory

structures

D. Deleruyelle, C. Dumas, M. Carmona, Ch. Muller

IM2NP – UMR CNRS 6242

& Institut Carnot STAR

Polytech’ Marseille, Université de Provence

IMT Technopôle de Château–Gombert

13451 Marseille Cedex 20

e–mail: christophe.muller@im2np.fr

Innovative Memory Technologies – 06.21.2010

Minatec – Grenoble – France

Partners in EMMA* project

• MDM (Milano – Italy)

S. Spiga, A. Lamperti, and M. Fanciulli

• Numonyx (Milano – Italy)

I. Tortorelli, R. Bez

• IMEC (Leuven – Belgium)

R. Müller, L. Goux, D.J. Wouters

*Emerging Materials for Mass storage Architectures

FP6 IST no. 33751

Outline

1. Context

2. Nanoscale switching in CuTCNQ-based

memory structures

3. Nanoscale switching in NiO film on top of

pillar bottom electrode

4. Summary

Outline

1. Context

2. Nanoscale switching in CuTCNQ-based

memory structures

3. Nanoscale switching in NiO film on top of

pillar bottom electrode

4. Summary

Key players on resistive systems

Materials

Logical states

Nanothermal

• Transition metal

oxide (TMO)

• Chalcogenide

nanowires for

PCM

High resistance Low resistanceTypes

Nanomechanical

• Suspended CNT

• Nanowires

• Nanorods

Nanoionic

• Organic

complex

• Oxide

• Chalcogenide

"1""0"

Latest ITRS classification (partial)

Fujitsu (TiO2) Samsung (NiO)

Hynix (TiO2) Spansion (Cu2O)

Matsushita (FeOx)

Fujitsu (Ti doped NiO)

Nanothermal devices (TMO)

Qimonda

Nanoionic devices

• Ionic transport combined with redox process in a solid electrolyte

o Anions (e.g. O2–)

Memristor (HP), CMOx™ (Unity),…

o Cations (e.g. Ag+)

CBRAM (Qimonda, NIMS, Adesto,…)

4F2/8 bits = 0.5F2

HP

Unity

NIMS

Adesto

Outline

1. Context

2. Nanoscale switching in CuTCNQ-based

memory structures

3. Nanoscale switching in NiO film on top of

pillar bottom electrode

4. Summary

• Copper-tetracyanoquinodimethane

• CuTCNQ may grow in small dimension

via holes

o High density & low cost memory

devices

• Gas/solid reaction or growth in solution

• Bipolar resistive switching

Metal organic complex CuTCNQ

Demolliens et al., J. Cryst. Growth, submitted

Pt (BE)

HfO2 (switching layer)

CuTCNQ

nanowires

Au (TE)

• CuTCNQ nanowires grown on 3 nm thick HfO2 "switching layer" (SL)

o Copper transport within HfO2 switching layer

Creation/dissolution of conductive bridges

o Improved electrical performances

CuTCNQ nanowires on HfO2 layer

Muller et al., Solid-State Electronics, Submitted

Switching characteristics

• Bipolar resistance switching (RS)

o Clockwise on pad-size devices

o Anticlockwise at nanoscale

• At nanoscale, RS governed by a nano-gap between AFM tip and

CuTCNQ nanowires

Cu (BE)

Au

An additional proof…

• Complementary C-AFM experiments performed on

CuTCNQ(nanowires)/Cu(BE) (without oxide switching layer)

• Basic local memory operations achieved under bias voltage

o Set/Reset/ReadMuller et al., Solid-State Electronics, Submitted

Redox process

CuTCNQ

Nano-gap

CuCu

CuCu

Cu+ Cu+

CuTCNQ

Nano-gap

CuCu

CuCu

Cu+ Cu+

Cu+

CuTCNQ

Nano-gap

= SLtCF tSL

VTop

• Equivalent resistance of the stack

• Transport of Cu+ ions governed by drift-diffusion mechanism

with

VTop

VBottom

RSL

RCuTCNQ

RTOT = RSL + RCuTCNQ RSL = SL

tSL – tCF

SSL

J(x,t) = qµCu+[Cu+] – DCu+

[Cu+]

x

Einstein relationship and

continuity equation+

Modeling

CuCu

CuCu

Cu+

Actual nanoionic device

• Satisfactory agreement

between AFM measurements

and model

• This model can be transposed

to copper transport within

HfO2 switching layer

• Oxidation process at CuTCNQ surface

o Cu Cu+ + 1e–

Transport of Cu+ ions from CuTCNQ to AFM tip

• Reduction process at AFM tip

o Cu+ + 1e– Cu

Growth of conductive filaments from AFM tip

to CuTCNQ surface

Redox set

operation

HRS LRS

Deleruyelle et al., Appl. Phys. Lett., vol. 96, no. 26, pp. 263504(1-3), 2010

Outline

1. Context

2. Nanoscale switching in CuTCNQ-based

memory structures

3. Nanoscale switching in NiO film on top of

pillar bottom electrode

4. Summary

Memory devices

Si

SiO2

NiO

Pt

CoSi2Si3N4

Pt

BE

TE

W-plug

Si

SiO2

NiO

CoSi2Si3N4

Electrical characterization on

conventional probe station

Conductive AFM (C-AFM)

measurements

ALD

Spiga et al., Proc. of MRS Spring Meeting, 2009

Demolliens et al., IEEE Proc. of Int. Memory Workshop, 2009

Silver pasteAFM tip

SiO2W

(180 nm)

PtNiO

Si3N4

CoSi250 nm

Microstructure

200 nm

AFM topography

Imprint of

underlying W-plug

TEM cross-section

• Bending of NiO film due to a dishing of

W-plugs during CMP process

Program

Set & Reset

Read

B-doped

diamond Pt-Ir

Experimental protocol

• No conductive spots in initial state

o High resistance state

• Gradual appearance and growth of highly conductive regions

(around 20 to 30 nm) when increasing programming bias

o Emulation of forming/set operation

Forming/set operation

1.5 µm

Initial state VProg = 1 V VProg = 2 V VProg = 3 V

VRead = 1 mV

Superimposition of topography and current mapping

• Dissolution of conductive filaments at high voltage

o Reset operation achieved!

• Some residual conductive regions still remain after local reset

Reset operation

1.5 µm

Initial state VProg = 5 V VProg = 4.5 V

Superimposition of topography and current mapping

VRead = 1 mV

Retention

1.5 µm

2 days 13 days 21 days

Superimposition of topography and current mapping

30 days

VRead = 1 mV

• Initial forming and read of programmed area

• Some conductive filaments remain after 30 days

o Retention demonstrated at nanoscale

• Decrease of filament diameter in time

Actual nanothermal device

• Initial insulating state

• LRS: multiple conductive regions within NiO film

• HRS: only few residual conductive filaments after reset

Outline

1. Context

2. Nanoscale switching in CuTCNQ-based

memory structures

3. Nanoscale switching in NiO film on top of

pillar bottom electrode

4. Summary

Memory cell

structure

Polarity of

switching

Switching

classification

Basic

mechanism

Size

limits

Reset

operation

NiO

deposited

on top of

pillar W

electrode

Unipolar Nanothermal Filamentary

Filament

diameter

(20 nm)

Joule effect

enabling

filament

dissolution

CuTCNQ-

based

memory

elements

Bipolar Nanoionic Filamentary

Area

around

tip

Redox

process

• Switching demonstrated at nanoscale in both systems!

o Scalabilty conditioned by a tight control of filaments…

Summary

Thank you for your attention