Transferred-Substrate Heterojunction Bipolar Transistor Integrated Circuit Technology

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Transferred-Substrate Heterojunction Bipolar
Transistor Integrated Circuit Technology
1999 IEEE Symposium on Indium Phosphide Related
Materials

• M Rodwell , Q Lee, D Mensa, J Guthrie, Y Betser,
  S Jaganathan, T Mathew, P Krishnan, S
  LongUniversity of California, Santa Barbara
• SC Martin, RP Smith, NASA Jet Propulsion Labs
• Supported by ONR (M Yoder, J Zolper, D Van
  Vechten), AFOSR ( H Schlossberg )

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Why are HEMTs smaller faster than HBTs ?

• FETs have deep submicron dimensions.
• 0.1 µm HEMTs with 400 GHz bandwidths
  (satellites).
• 5 million 1/4-µm MOSFETs on a 200 MHz, 500 CPU.
• FET lateral scaling decreases transit times.
• FET bandwidths then increase.
• HBTs have 1 µm junctions.
• vertical scaling decreases electron transit
  times.
• vertical scaling increases RC charging times.
• lateral scaling should decrease RC charging
  times.
• HBT RTD bandwidths should then increase.
• But, HBTs must first be modified . . .

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Scaling for THz device bandwidths
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Current-gain cutoff frequency in HBTs
Collector velocities can be high velocity
overshoot in InGaAsBase bandgap grading reduces
transit time substantiallyRC terms quite
important for gt 200 GHz ft devices
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Excess Collector-Base Capacitance in Mesa HBTs

• base contacts must be gt 1 transfer length (0.3
  mm) sets minimum collector width sets
  minimum collector capacitance Ccb
• base resistance spreading resistance scales
  with emitter scaling contact resistance
  independent of emitter scaling sets minimum
  base resistance sets minimum RbbCcb time
  constant
• fmax does not improve with submicron scaling

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Transferred-Substrate HBTs A Scalable HBT
Technology

• Collector capacitance reduces with scaling
• Bandwidth increases rapidly with scaling

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Thinning base, collector epitaxial layers
improves ft, degrades fmax Lateral scaling
provides moderate improvements in fmax Regrowth
(similar to Si BJT !) should help
considerably Transferred-substrate helps
dramatically
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50 mm transferred-substrate HBT Wafer Cu
substrate
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AlInAs/GaInAs graded base HBT
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Band diagram under normal operating voltages
V
0.9 V
, V
0.7 V
ce
be
D
400 Å 5E19 graded base (
E
2kT), 3000 Å collector
g
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Transferred-Substrate Heterojunction Bipolar
Transistor
Device with 0.6 µm emitter 1.8 µm
collector extrapolated fmax at instrument limits,
gt400 GHz
(?)
0.25 µm devices should obtain gt1000 GHz fmax
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Submicron Transferred-Substrate HBT
0.4 mm x 6 mm emitter, 0.4 mm x 10 mm collector
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Emitter Profile Stepper Device
0.5 mm emitter stripe
0.15 mm e/b junction
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Transferred-Substrate HBT Stepper Lithography
0.4 mm emitter, 0.7 mm collector
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DC characteristics, stepper device
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Given high fmax, vertical scaling exhanges
reduced fmax for increased ft
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Transit times HBT with 2kT base grading
2000 Å InGaAs collector400 Å InGaAs base, 2kT
bandgap grading
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Why would you want a 1 THz transistor ?
Digital microwave / RF transmitters (DC-20
GHz) direct digital synthesis at microwave
bandwidths microwave digital-analog converters
Digital microwave / RF receivers delta-sigma
ADCs with 10-30 GHz sample rates 16 effective
bits at 100 MHz signal bandwidth ? Basic
Science 0.1 µm Ebeam device 1000 GHz
transistor (?) transistor electronics in the
far-infrared Fast fiber optics, fast digital
communications 200 GHz ft, 500 GHz fmax device
75-90 Gb/s 160 Gb/s needs 350 GHz ft, 500
GHz fmax
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Transferred-Substrate HBT ICs Key Features
100 GHz clock-rate ICs will need very fast
transistors short wires gt high IC density
gt high thermal conductivity low capacitance
wiring low ground inductance gt microstrip
wiring environment Transferred Substrate HBT ICs
offer 800 GHz fmax now , gt 1000 GHz with
further scaling 250 GHz ft now, gt300 GHz
with improved emitter Ohmics copper
substrates / thermal vias for heatsinking
low capacitance (??? 2.5) wiring
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THz-Bandwidth HBTs ???
deep submicron transferred-substrate regrown-base
HBT
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1
4
5
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1) regrown P InGaAs extrinsic base --gt
ultra-low-resistance 2) 0.05 µm wide emitter --gt
ultra low base spreading resistance 3) 0.05 µm
wide collector --gt ultra low collector
capacitance 4) 100 Å, carbon-doped graded base
--gt 0.05 ps transit time 5) 1kÅ thick InP
collector --gt 0.1 ps transit time. Projected
Performance Transistor with 500 GHz ft, 1500
GHz fmax
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The wiring environment for100 GHz logic
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Why is Improved Wiring Essential?
Wire bond creates ground bounce between IC
package
ground return loops create inductance
30 GHz M/S D-FF in UCSB - mesa HBT technology
Ground loops wire bonds degrade circuit
packaged IC performance
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Ground Bound Noise in ADCs
Ground bounce noise must be 100 dB below
full-scale input Differential input will partly
suppress ground noise coupling 30 to 40 dB
common-mode rejection feasible CMRR insufficient
to obtain 100 dB SNR Eliminate ground bounce
noise by good IC grounding
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Microstrip IC wiring to Eliminate Ground Bounce
Noise
Transferred-substrate HBT process provides vias
ground plane.
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Power Density in 100 GHz logic
Transistors tightly packed to minimize delays
105 W/cm2 HBT junction power density. 103
W/cm2 power density on-chip 75 C
temperature rise in 500 mm substrate. Solutions
Thin substrate to lt 100 mm Replace
semiconductor with metal copper substrate
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Transferred-Substrate HBT Integrated Circuits
47 GHz master-slave flip-flop
11 dB, 50 GHz AGC / limiting amplifier
10 dB, 50 GHz feedback amplifier
7 dB, 5-80 GHz distributed amplifier
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Transferred-Substrate HBT Integrated Circuits
W-band VCO
multiplexer
16 dB, DC-60 GHz amplifier
21 demultiplexer (120 HBTs)
6.7 dB, DC-85 GHz amplifier
Clock recovery PLL
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Darlington Amplifier - 360 GHz GBW

• 15.6 dB DC gain
• Interpolated 3dB bandwidth of 60 GHz
• 360 GHz gain-bandwidth product

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6.7 dB, 85 GHz Mirror Darlington Amplifier

• 6.7 dB DC gain
• 3 dB bandwidth of 85 GHz
• ft-doubler (mirror Darlington) configuration

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Master-Slave Flip-Flops
CML 47 GHz
ECL 48 GHz
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66 GHz Static Frequency Divider in
Transferred-substrate HBT Technology

• Q. Lee, D. Mensa, J. Guthrie, S. Jaganathan, T.
  Mathew, Y. Betser, S. Krishnan, S. Ceran, M.J.W.
  RodwellUniversity of California, Santa Barbara
• IEEE RFIC99, Anaheim, California

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Fiber Optic ICs (not yet working !)
PIN / transimpedance amplifier
CML decision circuit
AGC / limiting amplifier
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Delta-Sigma ADC In Development (300 HBTs)
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Transferred Substrate HBTs
An ultrafast bipolar integrated circuit
technology Ultrahigh fmax HBTs Low capacitance
interconnects Superior heat sinking, low
parasitic packaging Demonstrated HBTs with
fmax gt 800 GHz fast flip-flops, 85 GHz
amplifiers, ... Future 0.1 mm HBTs with fmax gt
1000 GHz 100 GHz digital logic ICs --gt DACs,
DDS, ADCs, fiber