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: [email protected]
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
