Advanced Semiconductor Devices

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• Advanced Semiconductor Devices
• Y-BRANCH SWITCH
• (YBS)
• Anubhav Khandelwal

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OUTLINE

• INTRODUCTION Need for efficient electronic
  switches
• YBS
• Principle of operation
• Ballistic Transport
• Characteristics
• Fabrication
• YBS as efficient switch
• APPLICATIONS
• Theoretical Predictions
• Demonstrated devices
• Diodes
• Transistors
• Schmitt Trigger
• Logic Gates NAND
• SUMMARY

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Need for efficient electronic switches

• Problem of switching bottleneck in modern
  communications network

• Need
• Ultra-fast switching
• High packing density
• Low power dissipation

YBS be the solution?
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YBS Principle of OperationAssuming Ballistic
transport
For a YBS manufactured by etching through a
GaAs/AlGaAs 2DEG, with ns41011 cm-2 and Li
200 nm, ?Vs 1 mV
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YBS Ballistic Transport

• Ballistic Transport
• Branch width lt Electron free wavelength

(1)
(1) PHYSICAL REVIEW B, Vol. 62, No.24, 15
DECEMBER 2000-II
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YBS Characteristics

• For symmetric YBS, applying V and V to VL and
  VR will always result in negative Vc
• For asymmetric YBS, Vc is negative for lVl
  greater than certain threshold

(1)
2. (Theoretically) Possible to achieve gain
without external biasing due to self coupling
between the branches.
(1) PHYSICAL REVIEW B, Vol. 62, No.24, 15
DECEMBER 2000-II
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YBS Fabrication
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YBS as efficient switch

• Speed
• Small capacitance of central branch and small
  contact resistance (few kOs).
• Switching at 50GHz has been
  demonstrated.
• Theoretically, self coupling in gateless YBS
  result in switching at THz range
• 2. Size
• YBS with sub-100nm thick branches demonstrated.
  With branched nanowires, can go down further.
• 3. Switching energy
• Fundamental limit for switching (single mode
  coherent transport) is not Thermally limited in
  YBS
• Switching voltage in FET is Thermally limited

(1) APL VOLUME 83, NUMBER 12 22 SEPTEMBER 2003
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ApplicationsTheoretical predictions
Rectifier
Second and higher harmonic generator

• VC as a function of VL
• Diode if VR0V
• Transistor if VR is varied

Logic AND
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Reversible logic using YBS

• Minimum energy dissipation due to information
  erasure is
• Currently, much more than kT being dissipated

IRREVERSIBLE LOGIC e.g. NAND

• Ideally, avoid information erasure by zero energy
  dissipation
• Practically, always some energy dissipation
  but

REVERSIBLE LOGIC
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Reversible logic using YBS
Erik Forsberg, INSTITUTE OF PHYSICS PUBLISHING,
Nanotechnology 15 (2004) S298S302
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YBS as Diode Transistor

• Diode VR 0V
• - VLlt0V, VC follows
• VL linearly
• VLgt0V, VC saturates
• Triode VC as a function
• of VL for different values
• of VR
• Note Room temperature
• operation demonstrated on
• YBS etched on GaInAs/InP
• Heterostructure

H. Q. Xu, I. Shorubalko, D. Wallin, I. Maximov,
P. Omling, L. Samuelson, and W. Seifert IEEE
ELECTRON DEVICE LETTERS, VOL. 25, NO. 4, APRIL
2004
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YBS as Schmitt-Trigger

• SEM image of a YBS together with a schematic view
  of the measurement setup. A bistable mode of
  operation was realized by coupling the left
  branch to the right sidegate, i.e., VgrVbl . All
  voltages are related to ground
• Measurement setup in combination with the
  equivalent circuit of the YBS (shaded area)

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Schmitt-Trigger characteristics
Demonstration of the bistable switching
characteristic in feedback mode for Vbias2.0 V.
The hysteretic loop both for Vbl and Vbr is shown
vs the voltage Vgl applied to the left sidegate.
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Logic Gates using YBS NAND
(a) SEM image of a NAND logic gate realized by
integration of a TBJ with a point contact and the
circuit setup for characterization.
(b) Measured output voltage V and the
corresponding input voltages V (dashed line) and
V (solid line), for the NAND logic gate at room
temperature. V 10V and R2.3M. The applied
logic low and high inputs were set to 0 and 1.5
V, respectively, and the measured logic low and
high outputs were set to 0.8 and 3.2 V. (c)
Experimental truth table for NAND logic gate
H. Q. Xu, I. Shorubalko, D. Wallin, I. Maximov,
P. Omling, L. Samuelson, and W. Seifert IEEE
ELECTRON DEVICE LETTERS, VOL. 25, NO. 4, APRIL
2004
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SUMMARY

• Principle of operation, fabrication and
  characteristics of YBS
• YBS as efficient electronic switch for high
  speed, low power operations like in
  communications networks
• YBS as diode, transistor, schmitt trigger, NAND
• Reversible logic possible through YBS