Q. Lee

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f/sub max/ and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 1.1 THz. f/sub max/ will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f/sub T/. The substrate transfer process provides microstrip interconnects on a low-/spl epsiv//sub r/ polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz.

Submicron transferred-substrate heterojunction bipolar transistors

We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors (HBTs). Devices with 0.4-/spl mu/m emitter and 0.4-/spl mu/m collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 820 GHz. The high f/sub max/, results from the scaling of HBTs junction widths, from elimination of collector series resistance through the use of a Schottky collector contact, and from partial screening of the collector-base capacitance by the collector space charge.

A>400 GHz f/sub max/ transferred-substrate heterojunction bipolar transistor IC technology

We report transferred-substrate AlInAs/GaInAs bipolar transistors. A device having a 0.6 /spl mu/m/spl times/25 /spl mu/m emitter and a 0.8 /spl mu/m/spl times/29 /spl mu/m collector exhibited f/sub /spl tau//=134 GHz and f/sub max/>400 GHz. A device with a 0.6 /spl mu/m/spl times/25 /spl mu/m emitter and a 1.8 /spl mu/m/spl times/29 /spl mu/m collector exhibited 400 GHz f/sub max/ 164 GHz f/sub /spl tau//. The improvement in f/sub max/ over previous transferred-substrate HBTs is due to improved base Ohmic contacts, narrower emitter-base and collector-base junction areas, and slightly reduced transit times. The transferred-substrate fabrication process provides electroplated gold thermal vias for transistor heat-sinking and a microstrip wiring environment on a low dielectric constant polymer substrate.

66 GHz static frequency divider in transferred-substrate HBT technology

We report a 66 GHz emitter coupled logic (ECL) 2:1 static frequency divider using InAlAs/InGaAs transferred-substrate HBTs. To our knowledge this is the fastest static divider reported in any semiconductor technology.

Submicron transferred-substrate heterojunction bipolar transistors with greater than 8000 GHz f/sub max/

We report submicron transferred-substrate AlInAs/GaInAs heterojunction bipolar transistors. Devices with 0.4 /spl mu/m emitter and 0.9 /spl mu/m collector widths have 17.5 dB unilateral gain at 110 GHz. Extrapolating at -20 dB/decade, the power gain cut-off frequency f/sub max/ is 820 GHz.

80 GHz distributed amplifiers with transferred-substrate heterojunction bipolar transistors

We report distributed amplifiers with 80 GHz bandwidth, 6.7 dB gain and /spl sim/70 GHz bandwidth, 7.7 dB gain. These amplifiers were fabricated in the transferred-substrate heterojunction bipolar transistor integrated circuit technology. Transferred-substrate HBTs have very high f/sub max/ (>400 GHz) and have yielded distributed amplifiers with record gain-bandwidth product.

A 277-GHz f/sub max/ transferred-substrate heterojunction bipolar transistor

We report a AlInAs-GaInAs transferred-substrate heterojunction bipolar transistor (HBT). The transferred-substrate process permits fabrication of narrow and aligned collector-base and emitter-base junctions, reducing the collector-base capacitance and increasing the device f/sub max/. A device with aligned 0.7-/spl mu/m emitter and 1.6-/spl mu/m collector stripes has extrapolated 277 GHz f/sub max/ and 127 GHz f/sub /spl tau//, respectively.

Transferred-substrate heterojunction bipolar transistor integrated circuit technology

Using substrate transfer processes, we have fabricated heterojunction bipolar transistors with 0.4 /spl mu/m emitter-base and collector-base junctions, minimizing RC parasitics and increasing f/sub max/ to 820 GHz, the highest yet reported for a transistor. The process provides microstrip interconnects on a low-/spl epsiv//sub /spl tau// polymer dielectric with a electroplated copper ground plane and substrate. Substrate thermal resistance is reduced 5:1 over InP. Important wiring parasitics, including wiring capacitance, ground via inductance, and IC-package ground-return inductance, are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz, master-slave flip-flops operable at over 48 GHz, and 50 GHz AGC/limiting amplifiers. Current efforts include further improvement in bandwidth, development of power devices, and demonstration of more complex mixed-signal ICs.

Deep submicron transferred-substrate heterojunction bipolar transistors

Using e-beam lithography and combined reactive-ion and wet-chemical etches, we have fabricated transferred-substrate heterojunction bipolar transistors (HBTs) with 0.2 μm emitter and 0.6 μm collector widths and a measured DC current gain of 14. Devices with 0.4 μm emitter and 1.0 μm collector widths obtain record 500 GHz f/sub max/ value.

A transferred-substrate HBT wide-band differential amplifier to 50 GHz

Differential amplifiers are used in automatic gain control amplifiers and limiting amplifiers in fiber-optic receivers. Here we present a differential amplifier fabricated in the transferred-substrate heterojunction bipolar transistor (HBT) integrated circuit technology. The amplifier has a gain of 11 dB and the 3-dB bandwidth is greater than 50 GHz. Two gain stages with DC interstage coupling are used. Biasing is through active current mirrors and a single negative power supply. A bandwidth of 50 GHz is the highest bandwidth ever reported for a broad-band differential amplifier in any technology.