Temperature dependence of locked mode in a Single-Electron Latch

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Temperature dependence of locked mode in a
Single-Electron Latch
Alexei O. Orlov Department of Electrical
Engineering University of Notre Dame, IN, USA
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Notre Dame research team

• Experiment
• Dr. Ravi Kummamuru
• Prof. Greg Snider
• Prof. Gary Bernstein
• Theory
• Mo Liu
• Prof. Craig Lent
• Supported by DARPA, NSF, ONR, and W. Keck
  Foundation

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Outline of presentation

• Introduction
• Power Gain in nanodevices
• Clocked single-electron devices
• Bistability for memory
• Experiment and simulations
• Temperature dependence of bistability and
  hysteresis loop size
• Summary and conclusions

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Problems shrinking the current-switch
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How to make a power amplifier using quantum wells?
Keyes and Landauer, IBM Journal of Res. Dev. 14,
152, 1970
1
0
Clock
0
Clock Applied
Input Removed
Small Input Applied
0
but Information is preserved!
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Quantum-dot Cellular Automata
Old Paradigm
New Paradigm
Current switch
Tunneling between dots
Polarization P 1 Bit value 1
Neighboring cells tend to align. Coulomb coupling
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Clocking for single-electron logicQuantum-dot
Cellular Automata and Parametrons
Semiconductor dots (QCA) Clocking achieved by
modulating barriers between dots
Metallic or molecular dots (parametron)
Clocking achieved by modulating energy of third
state directly

• Clocked QCA Lent et al., Physics and
  Computation Conference, Nov. 1994
• Parametron Likharev and Korotkov, Science 273,
  763, 1996

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Metal dot fabrication process
2nd evaporation
1st evaporation

• Aluminum Tunnel junction technology combining E
  beam lithography with a suspended mask technique
  and double angle evaporation
• Oxide layer between two layers of Aluminum forms
  tunnel junctions.

NanoDevices Group
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Ultra-sensitive electrometers for QCA

• Sub-electron charge detection is needed
• Single-electron transistors are the best choice

SET electrometers can detect 1 of elementary
charge.
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Single-Electron Latch a Building Block Layout
And Measurement Setup
The third, middle dot acts as an adjustable
barrier for tunneling
Electrometer
1mm
MTJmultiple tunnel junction
SEM Micrograph of SE latch
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Animated three-dot SE latch operation
(0,0,0) neutral
(0,0,0) ? (0,-1,1) switch to 1
(0,-1,1) storage of 1
(0,0,0) ? (0,-1,1) back to neutral
Bit can be detected
D2
D1
D3

-VCLK
VCLK0

• Clock signal gtgt Input signal
• Clock supplies energy, input defines direction of
  switching
• Three states of SE latch 0 , 1 and
  neutral

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Experiment Single-Electron Latch in Action

• Weak input signal sets the direction of switching
• Clock drives the switching

T100 mK
Input
Clock
Switch to 0
Hold 1
Switch to neutral
Switch to neutral
Hold 0
Switch to 1

• Bistable Switch Inverter demonstrated
• Memory Function demonstrated

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How temperature affects bistability?

• 2 level switch with memory there must be a
  Hysteresis
• SEL operates fine _at_ T100 mK
• Charging energy consideration EC10 kT , EC 0.8
  meV (9.3 K)
• What is the highest operating temperature?
• Zero K calculations were performed before
• Korotkov et al. (1998)
• Toth et al. (1999)

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Sweeping input bias
Assume Coulomb barrier is the same for hops
between adjacent dots
Equilibrium Border
VD1(mV)
D1
VIN-
VIN
VCLK0
2.5
5
0
VIN(mV)
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How bistabile behavior scales with temperature?

• Thermal energy surmounts Coulomb barrier
• Hysteresis loop shrinks and then disappears

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Hysteresis loop change with Temperature
T320 mK
T160 mK
Calculations performed using time dependent
master equation for orthodox theory of Coulomb
blockade
T90 mK
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Bistability area vs kT

• Relative loop size DV/V0
• Calculations represent ensemble averaging
  averaging over multiple scans
• At T gt300 mK no bistability is observed
• Bistability disappears for kTW/30, where W is
  Coulomb barrier
• At Tgt0 (DV/V0 )gt1, it means that system becomes
  multistable

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Summary Conclusions

• Temperature dependence of bistable switching in
  Single-Electron Latch is studied experimentally
• Theoretical calculations using time-dependent
  master equation are performed
• Hysteresis loop size vs temperature is studied
• Bistability disappears as kT reaches EC/30
• For 300K operation W30 kT1 eV
• The real world applications can be implemented
  using molecular assembly line once technology
  becomes available

Molecular Single-Electron Latch
Metal-dot Single-Electron Latch
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Measured and calculated charging diagrams

• Charging diagram is a 3D plot (gray scale map) of
  dot potential vs input and clock bias
• White is positive, black is negative
• Calculated data are superimposed with measured

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Single-Electron Latch in Action

• Two electrometers are used
• Both are connected to end dots