Nanoscale switching in resistive memory...
Transcript of Nanoscale switching in resistive memory...
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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
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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
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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
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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
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Key players on resistive systems
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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)
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Fujitsu (TiO2) Samsung (NiO)
Hynix (TiO2) Spansion (Cu2O)
Matsushita (FeOx)
Fujitsu (Ti doped NiO)
Nanothermal devices (TMO)
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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
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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
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• 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
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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
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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
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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
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Redox process
CuTCNQ
Nano-gap
CuCu
CuCu
Cu+ Cu+
CuTCNQ
Nano-gap
CuCu
CuCu
Cu+ Cu+
Cu+
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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+
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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
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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
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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
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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
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Program
Set & Reset
Read
B-doped
diamond Pt-Ir
Experimental protocol
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• 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
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• 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
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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
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Actual nanothermal device
• Initial insulating state
• LRS: multiple conductive regions within NiO film
• HRS: only few residual conductive filaments after reset
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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
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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
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Thank you for your attention