1. 1999 IEEE Symposium on Indium Phosphide & Related Materials
Transferred-Substrate Heterojunction Bipolar Transistor Integrated Circuit Technology
M Rodwell , Q Lee, D Mensa, J Guthrie, Y Betser, S Jaganathan, T Mathew, P Krishnan, S Long University 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 )

2. 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 . . .

3. Scaling for THz device bandwidths

5. Current-gain cutoff frequency in HBTs
Collector velocities can be high: velocity overshoot in InGaAs Base bandgap grading reduces transit time substantially RC terms quite important for > 200 GHz ft devices

6. Excess Collector-Base Capacitance in Mesa HBTs
base contacts: must be > 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

8. Transferred-Substrate HBTs: A Scalable HBT Technology
Collector capacitance reduces with scaling:
Bandwidth increases rapidly with scaling:

9. 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

12. 50 mm transferred-substrate HBT Wafer: Cu substrate

13. AlInAs/GaInAs graded base HBT- 2 1 . 5 3 4 6 D i s t a n c e , Å C o l l e c t o r d e p l e t i o n r e g i o n E m i t t e r S c h o t t k y c o l l e c t o r G r a d e d b a s e
Band diagram under normal operating voltages V
= 0.9 V
, V
= 0.7 V ce be
• 400 Å 5E19 graded base ( D E
= 2kT), 3000 Å collector g

14. Transferred-Substrate Heterojunction Bipolar Transistor
Device with 0.6 µm emitter & 1.8 µm collector
extrapolated fmax at instrument limits, >400 GHz
(?)
0.25 µm devices should obtain >1000 GHz fmax

15. Submicron Transferred-Substrate HBT
0.4 mm x 6 mm emitter, 0.4 mm x 10 mm collector

16. Emitter Profile: Stepper Device
0.5 mm emitter stripe
0.15 mm e/b junction

17. Transferred-Substrate HBT: Stepper Lithography
0.4 mm emitter, ~0.7 mm collector

18. DC characteristics, stepper device
We=0.2 X 6 mm2
Wc=1.5 X 9 mm2
b=50

19. Given high fmax, vertical scaling exhanges reduced fmax for increased ft

20. Transit times: HBT with 2kT base grading
2000 Å InGaAs collector 400 Å InGaAs base, 2kT bandgap grading

21. 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 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: ~ Gb/s
160 Gb/s needs ~350 GHz ft, 500 GHz fmax

22. Transferred-Substrate HBT ICs: Key Features
100 GHz clock-rate ICs will need:
very fast transistors
short wires –> high IC density –> high thermal conductivity
low capacitance wiring
low ground inductance –> microstrip wiring environment
Transferred Substrate HBT ICs offer:
800 GHz fmax now , > 1000 GHz with further scaling GHz ft now, >300 GHz with improved emitter Ohmics
copper substrates / thermal vias for heatsinking
low capacitance (= 2.5) wiring

23. THz-Bandwidth HBTs ??? Transistor with 500 GHz ft, 1500 GHz fmax 2 4 1
deep submicron
transferred-substrate
regrown-base HBT 2 4 1 5 3
1) regrown P+++ InGaAs extrinsic base --> ultra-low-resistance
2) 0.05 µm wide emitter --> ultra low base spreading resistance
3) 0.05 µm wide collector --> ultra low collector capacitance
4) 100 Å, carbon-doped graded base --> 0.05 ps transit time
5) 1kÅ thick InP collector --> 0.1 ps transit time.
Projected Performance:
Transistor with 500 GHz ft, 1500 GHz fmax

24. The wiring environment for 100 GHz logic

25. 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

26. Ground Bound Noise in ADCs
digital
sections
input
buffer
ground return
currents L
ground D V in
bounce
noise
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

27. Microstrip IC wiring to Eliminate Ground Bounce Noise
Transferred-substrate HBT process provides vias & ground plane.

28. Power Density in 100 GHz logic
Transistors tightly packed to minimize delays 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 < 100 mm Replace semiconductor with metal ® copper substrate

29. Transferred-Substrate HBT Integrated Circuits
11 dB, 50+ GHz AGC / limiting amplifier
47 GHz master-slave flip-flop
10 dB, 50+ GHz feedback amplifier
7 dB, 5-80 GHz distributed amplifier

30. Transferred-Substrate HBT Integrated Circuits
multiplexer
16 dB, DC-60 GHz amplifier
W-band VCO
2:1 demultiplexer (120 HBTs)
6.7 dB, DC-85 GHz amplifier
Clock recovery PLL

31. Darlington Amplifier - 360 GHz GBW
15.6 dB DC gain
Interpolated 3dB bandwidth of 60 GHz
360 GHz gain-bandwidth product

32. 6.7 dB, 85 GHz Mirror Darlington Amplifier
6.7 dB DC gain
3 dB bandwidth of 85 GHz
ft-doubler (mirror Darlington) configuration

33. Master-Slave Flip-Flops
CML: 47 GHz
ECL: 48 GHz

34. 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. Rodwell University of California, Santa Barbara
IEEE RFIC’99, Anaheim, California

35. Fiber Optic ICs (not yet working !) PIN / transimpedance amplifier
CML decision circuit
AGC / limiting amplifier

36. Delta-Sigma ADC In Development (300 HBTs)

37. 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 > 800 GHz
fast flip-flops, 85 GHz amplifiers, ...
Future:
0.1 mm HBTs with fmax > 1000 GHz
100 GHz digital logic ICs --> DACs, DDS, ADCs, fiber