Carbon-based Resistive Memory Resistive Memory ... Shmoo-plot of 40 nm diameter CC memory cell ... 0...
Transcript of Carbon-based Resistive Memory Resistive Memory ... Shmoo-plot of 40 nm diameter CC memory cell ... 0...
F. Kreupl et al. 1
Carbon-based Resistive Memory
Franz Kreupl, Rainer Bruchhaus+, Petra Majewski , Jan B. Philipp,
Ralf Symanczyk, Thomas Happ*, Christian Arndt*, Mirko Vogt*,
Roy Zimmermann*, Axel Buerke*, Andrew P. Graham*, Michael Kund
Qimonda AG,
+Qimonda North America, *Qimonda Dresden GmbH & Co. OHG [email protected]
F. Kreupl et al. 2
Outline of Presentation • Introduction and Motivation • Basic Switching in Carbon • Carbon Allotropes • Carbon Nanotubes • Graphene-like Conductive Carbon • Insulating Carbon • Conclusions
F. Kreupl et al. 3
Introduction and Motivation • Resistive Memories like
– Phase Change (GexSbyTez,.... ) – Nano-Ionic, (CBRAM-like, e.g. Ag2S, Ag-GeSe, Cu2S....) – Transition-Metal-Oxide ( NiO, TiO2,.....) are very promising memory technologies
• but are binary, ternary or even more complex materials: – what about scalability – how do they respond to volume/surface ratio – what about variability, if scaled
• Are there other, simpler materials available?
F. Kreupl et al. 4
Introduction and Motivation • The available current in a memory cell
is given by the select device (FET, diode) An upper limit may be estimated by:
j= e*Nd*vsat= e*1019*107 = 16 MA/cm2
• Typical currents in phase change
memories are ~10 MA/cm2 Are there options or materials
which enable switching at low currents (some µA)?
F. Kreupl et al. 5
Introduction: Carbon Memory sp3 sp2
I2 > I1
high conductance low conductance
I1
sp2 to sp3 conversion of disordered graphitic carbon (phase change of carbon) inherently scalable to atomic scale (no phases of different materials)
F. Kreupl et al. 6
Basic Switching in Carbon I1
TEM image by courtesy of J. Huang et al., Nano Letters 2006 Vol. 6, No. 8 pp. 1699-1705
• Current changes structure and resistance • Resistance changes by a factor of ~ 100 • High Low well known from e-fuses • New: switch to disorder by short pulse
I + -
F. Kreupl et al. 7
Short Laser Pulses on Graphite
Bonelli et al., Laser-irradiation-induced structural changes on graphite, Phys. Rev. B 59, 13513 (1999)
• Short laser pulse induces disorder (D-band) • D-band overlaps with sp3-peak at 1332 cm-1 • Diamond cubic phase observed by
e-beam diffraction Disordered, quenched state by short energy pulse
0 1000 2000 30000
5001000150020002500
Inte
nsity
(a.u
)
Raman shift cm-1 0 1000 2000 30000
500
1000
1500
Inte
nsity
(a.u
.)
Raman shift cm-1
pulse 20 ns
1580 cm-1 G=1580 D=1355
before after overtones
F. Kreupl et al. 8
3 ps Laser Pulse on Graphite
source: Anming Hu, PhD Thesis, U Waterloo, 2008
sp3 sp
632 nm 325 nm
sp3
• The shorter the laser pulse the more disorder Disordered, quenched state by short energy pulse
F. Kreupl et al. 9
Short Energy Pulses
• Fluence of the laser pulse at graphite ablation threshold =~ 285 mJ/cm2
Energy density (energy/volume) = 95 KJ/cm3 • Energy density for a wire subjected to a current:
E/V = j2ρt = 1GA/cm2 ·1mΩcm · 20 ns = 2 MJ/cm3
Disordered, quenched state by short current pulse
K. Sokolowski-Tinten et al., CLEO 2000
F. Kreupl et al. 10
Short Current Pulse
temperature distribution in carbon filament after 1 ns current pulse with 1.7 GA/cm2 : Tpeak ~ 3900 K; rapid cool down (0.05 ns)
carbon cell
F. Kreupl et al. 11
Carbon Nanotubes
• Nanotubes have a length dependent switching current • 25 nm long tubes need ~ 100µA @ 1.5 V
and have no phonon-limited transport • tubes > 200 nm need ~ 30 µA @ 4V (phonon-limited) Select device needs to handle ~ 30 µA and 4-8 Volt
0 1 2 3 40
20µ
40µ
60µ
80µ
100µ
200 nm 25 nm
voltage [V]
curre
nt [A
]
local modification of sp2 structure by
current pulse
F. Kreupl et al. 12
Carbon Nanotubes In vacuum ~ 12 µA current possible
Jin et al., nature 18 nanotechnology | VOL 3 | JANUARY 2008 |
on-state off-state 12 uA
switch on 6 uA, 1.6V
on-state
F. Kreupl et al. 13
Allotropes of Carbon (investigated)
• Carbon Nanotubes - sp2-type - difficult to integrate - high conductivity
• Graphene or Conductive Carbon - sp2-type - easy to integrate
- high conductivity
• Insulating carbon - sp3-type, diamond-like
- easy to integrate - high resistivity
graphene layers
SiO2
nanotube
source: J. Robertson
F. Kreupl et al. 14
Conductive Carbon (CC)
• Conductive Carbon is – graphene-like – easily deposited (CVD) – can be used as interconnect
material (highly conductive) – easy to pattern
SiO2
conductive carbon in via
R. Seidel. et al., Chemical Vapor Deposition Growth of Single-Walled Carbon Nanotubes at 600 °C and a Simple Growth Model J. Phys. Chem. B, (2004) G. Aichmayr et al., Carbon-high-k Trench Capacitor for the 40nm DRAM Generation, VLSI Technology, (2007)
F. Kreupl et al. 15
Conductive Carbon: Memory Cell
• Carbon memory cells with varying diameter
30 nm
F. Kreupl et al. 16
Conductive Carbon: Critical Current
• Critical current density of 350 MA/cm2 observed • Appropriate cell diameter ~ 6 nm for I < 100 µA Use spacer, cladding or self-assembled nano-pores
F. Kreupl et al. 17
Conductive Carbon (CC): Switching
• Shmoo-plot of 40 nm diameter CC memory cell smaller diameter, current compliance and optimized
pulses required
1 2 3 4 5 6 7 8 9 10 11 12102103104105106107108109
1010
Reset 1 Set 1 Reset 2
Resi
stan
ce (O
hm)
Pulse Amplitude (V) 1 2 3 4103104105106107108109
Resi
stan
ce (O
hm)
Cycle
Reset Set
5 ns reset 300 ns set pulse
F. Kreupl et al. 18
Insulating Carbon (IC): Memory Cell
• Insulating diamond-like carbon film • First switching occurs now from high to low state
F. Kreupl et al. 19
Insulating Carbon (IC): Critical Field
• Quasi-static switching curves determine critical field • Switching power is about 50µW with leakage currents. • Very low power levels: 5 µA @ 1.5 V (P= 7.5 µW)
350 nm wide
150 nm wide
F. Kreupl et al. 20
Ins. Carbon: Read Endurance & Speed
• Read endurance at 75 degree C: 2.3*1013 read cycles at 0.1 V.
• Switching speed is faster than 11 ns.
0 100 200 300 400 500 6000
2
4
switching event
11 ns
puls
e he
ight
(V)
t (ns)10M 100M 1G 10G 100G 1T 10T0
25p50p75p
9µ
10µon-state
off-state
re-adjustmentof the probes
curre
nt [A
] @ 0
.1 V
number of read cycles
F. Kreupl et al. 21
Insulating Carbon: Switching
• I(V) curves show similar behavior after pulses • Resistance level can be trimmed by individual
voltage pulses (multi-level capability)
0.02 0.04 0.06 0.08 0.10
10p
100p
1n
10n
100n
1µ
after 5 V 500 µs after 5 V 100 ns after 5 V 500 µs after 5 V 100 ns
curre
nt [A
]
Voltage [V]0 1 2 3 4 5 6 7 8
6k8k
10k12k14k16k18k20k22k
w=100 ns w=5 ns
Resi
stan
ce [Ω
]
Voltage [V]
F. Kreupl et al. 22
Insulating Carbon: Filament size
crater with ~10 nm diameter
10 V pulse evaporates metal filament ~ 10 nm @ 10 V use carbon as current spreader
F. Kreupl et al. 23
Conclusions • New carbon memory proposed based on
sp2 to sp3 conversion • Inherently fast: reset ~ ns, set ~ ns • Nanotubes need ~30 µA @ 8V • Graphene-like Conductive Carbon
needs pores < 6 nm • Insulating Carbon shows lowest switching
power: 5 µA @ 1.5 V (P= 7.5 µW) • Pulses and cell design needs to be optimized • Should also work with Fullerens, Graphene and
Diamonds
F. Kreupl et al. 24
Acknowledgement Qimonda Fab Dresden Roland Thewes, Werner Pamler, Walter Weber, Uli Klostermann, Klaus-Dieter Ufert, Henning Riechert Stanford University Questions?
Thank you!