Ingaas inp dhbts demonstrating simultaneous f t f max 460 850 ghz in a refractory emitter process
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InP and Related Materials 2011. InGaAs/InP DHBTs demonstrating simultaneous f t / f max ~ 460/850 GHz in a refractory emitter process. Vibhor Jain , Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell ECE Department, University of California, Santa Barbara, CA 93106-9560

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Vibhor Jain , Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell

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Ingaas inp dhbts demonstrating simultaneous f t f max 460 850 ghz in a refractory emitter process

InP and Related Materials 2011

InGaAs/InP DHBTs demonstrating simultaneous ft/fmax ~ 460/850 GHz in a refractory emitter process

Vibhor Jain, Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell

ECE Department, University of California, Santa Barbara, CA 93106-9560

Miguel Urteaga

Teledyne Scientific & Imaging, Thousand Oaks, CA 91360

D Loubychev, A Snyder, Y Wu, J M Fastenau, W K Liu

IQE Inc., 119 Technology Drive, Bethlehem, PA 18015

[email protected], 805-893-3273


Outline

Outline

  • Need for high speed HBTs

  • HBT Scaling Laws

  • Fabrication

    • Challenges

    • Process Development

  • DHBT

    • Epitaxial Design

    • Results

  • Summary


Why thz transistors

Digital Logic for Optical fiber circuits

THz amplifiers for imaging, sensing, communications

High gain at microwave frequencies precision analog design, high resolution ADC & DAC, high performance receivers

Why THz Transistors?


Vibhor jain evan lobisser ashish baraskar brian j thibeault mark rodwell

We

Wbc

Tb

Tc

(emitter length Le)

Bipolar transistor scaling laws

To double cutoff frequencies of a mesa HBT, must:

Keep constant all resistances and currents

Reduce all capacitances and transit delays by 2

Epitaxial scaling

Lateral scaling

Ohmic contacts


Base access resistance

We

Wbc

Wgap

Base Access Resistance

  • Surface Depletion

  • Process Damage

 Need for very small Wgap

  • Small undercut in InP emitter

  • Self-aligned base contact


Base emitter short

Base-Emitter Short

Undercut in thick emitter semiconductor

Helps in Self Aligned Base Liftoff

InP Wet Etch

Slow etch plane

Fast etch plane

  • For controlled semiconductor undercut

    • Thin semiconductor

      To prevent base – emitter short

    • Vertical emitter profile and line of sight metal deposition

    • Shadowing effect due to high emitter aspect ratio


Composite emitter metal stack

Composite Emitter Metal Stack

W emitter

TiW

W

Erik Lind

Evan Lobisser

TiW emitter

  • W/TiW metal stack

  • Low stress

  • Refractory metal emitters

  • Vertical dry etch profile


Vertical emitter

Base Metal

SiNx

TiW

BCB

100nm

W

FIB/TEM by E Lobisser

Vertical Emitter

Vertical etch profile

Low stress

High emitter yield

Scalable emitter process


Narrow emitter undercut

Dual SiN sidewall

Controlled InP undercut

Mo contact

InGaAs cap

InP emitter

50nm

Narrow BE gap

FIB/TEM by E Lobisser

Narrow Emitter Undercut


Process flow

Process flow

Mo contact to n-InGaAs for emitter

W/TiW/SiO2/Cr dep

SF6/Ar etch

SiNx Sidewall

SiO2/Cr removal

InGaAs Wet Etch

Second SiNx Sidewall

InP Wet Etch

Base Contact Lift-off

Base and collector formed via lift off and wet etch

BCB used to passivate and planarize devices

Self-aligned process flow for DHBTs


Epitaxial design

Epitaxial Design

Vbe = 1 V, Vcb = 0.7 V, Je = 24 mA/mm2

Thin emitter semiconductor

 Enables wet etching


Vibhor jain evan lobisser ashish baraskar brian j thibeault mark rodwell

Results - DC Measurements

Common emitter I-V

@Peak ft,fmax

Je = 19.4 mA/mm2

P = 32 mW/mm2

BVceo = 3.7 V @ Je = 10 kA/cm2

β = 20

Base ρsh = 710Ω/sq, ρc < 5Ω·µm2

Collector ρsh = 15 Ω/sq, ρc = 22Ω·µm2

Gummel plot


1 67 ghz rf data

1-67 GHz RF Data

Ic = 11.5 mA

Vce = 1.66 V

Je = 19.4 mA/mm2

Vcb = 0.7 V

Single-pole fitto obtain cut-off frequencies


Vibhor jain evan lobisser ashish baraskar brian j thibeault mark rodwell

Parameter Extraction

Jkirk = 23 mA/mm2 (@Vcb = 0.7V)


Vibhor jain evan lobisser ashish baraskar brian j thibeault mark rodwell

Equivalent Circuit

Rex < 4 Wmm2

Hybrid-p equivalent circuit from measured RF data


Tem wide base mesa

TEM – Wide base mesa

High Ac / Ae ratio (>5)

High Rex . Ccb delay

Low ft

0.2 mm

220 nm


Summary

Summary

  • Demonstrated DHBTs with peak ft/ fmax = 460/850 GHz

  • Small Wgap for reduced base access resistance  High fmax

  • Narrow sidewalls, smaller base mesa and better base ohmics needed to enable higher bandwidth devices


Vibhor jain evan lobisser ashish baraskar brian j thibeault mark rodwell

Thank You

Questions?

This work was supported by the DARPA THETA program under HR0011-09-C-006.

A portion of this work was done in the UCSB nanofabrication facility, part of NSF funded NNIN network and MRL Central Facilities supported by the MRSEC Program of the NSF under award No. MR05-20415


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