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

Advanced Semiconductor Devices Y-BRANCH SWITCH (YBS) Anubhav Khandelwal. OUTLINE. INTRODUCTION –Need for efficient electronic switches YBS Principle of operation Ballistic Transport Characteristics Fabrication YBS as efficient switch APPLICATIONS Theoretical Predictions

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

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

  2. 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

  3. 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?

  4. YBS: Principle of OperationAssuming Ballistic transport LEFT RIGHT Li STEM Fundamental limit for switching: For a YBS manufactured by etching through a GaAs/AlGaAs 2DEG, with ns=4×1011 cm−2and Li ~ 200 nm, ΔVs ~1 mV

  5. VR=-VO VL=VO Classical: Ballistic: VC YBS: Ballistic Transport • Ballistic Transport – Branch width < Electron free wavelength (1) (1) PHYSICAL REVIEW B, Vol. 62, No.24, 15 DECEMBER 2000-II

  6. VR=-VO VL=VO VC YBS: Characteristics • For symmetric YBS, applying +V and –V to VL and VRwill always result in negative Vc For asymmetric YBS, Vcis 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

  7. YBS: Fabrication

  8. YBS as efficient switch • Speed • Small capacitance of central branch and small contact resistance (few kΩs). • 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

  9. ApplicationsTheoretical predictions Rectifier Second and higher harmonic generator • VC as a function of VL • Diode if VR=0V • Transistor if VR is varied Logic AND

  10. 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

  11. (b) (a) • A Fredkin or “Controlled Exchange” gate based on four YBSs • The corresponding truth table • A is the control, exchanging the inputs B and C if it is set to high. • Note: It is as universal as NAND/NOR Reversible logic using YBS Erik Forsberg, “INSTITUTE OF PHYSICS PUBLISHING, Nanotechnology 15 (2004) S298–S302”

  12. YBS as Diode & Transistor • Diode: VR = 0V • - VL<0V, VC follows • VL linearly • VL>0V, 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”

  13. 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., Vgr=Vbl . All voltages are related to ground • Measurement setup in combination with the equivalent circuit of the YBS (shaded area)

  14. Schmitt-Trigger characteristics Demonstration of the bistable switching characteristic in feedback mode for Vbias=2.0 V. The hysteretic loop both for Vbl and Vbr is shown vs the voltage Vgl applied to the left sidegate.

  15. 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 R=2.3M. 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”

  16. 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

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