D. Mensa

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.

SCALING OF InGaAs/InAlAsHBTs FOR HIGH SPEED MIXED-SIGNAL AND mm-WAVE ICs

High bandwidths are obtained with heterojunction bipolar transistors 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 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 fmax and high gains in mm-wave ICs. Logic gate delays are primarily set by depletion-layer charging times, and neither fτ nor fmax is indicative of logic speed. For high speed logic, epitaxial layers must be thinned, emitter and collector junction widths reduced, current density increased, and emitter parasitic resistance decreased. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency fmax is 1.1 THz. Transferred-substrate HBTs have obtained 295 GHz fτ. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz, 66 GHz master-slave flip-flops, and 18 GHz clock rate Δ-Σ ADCs.

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.

250 nm InP DHBT monolithic amplifiers with 4.8 dB gain at 324 GHz

An indium-phosphide (InP) double-heterojunction bipolar transistor (DHBT) based common-base monolithic power amplifier has been fabricated and has a measured small signal gain of 4.8 dB at 324 GHz. This is the highest frequency DHBT MMIC amplifier reported to date. The submillimeter-wave power amplifier MMIC incorporates microstrip transmission lines on a 10-μm thick layer of BCB dielectric. The thick BCB layer provides mode-free low-loss millimeter-wave transmission lines without requiring a thin fragile InP substrate and through-wafer VIAs as with conventional microstrip placed directly on the semiconductor substrate. The single-stage power amplifier has a compact size of only 0.124 mm2 and a measured saturated output power of 1.3 milliWatts with a dc input power of 1.4 V at 12 mA. These results demonstrate the capability of 250nm InP DHBT technology to enable power amplifiers for submillimeter-wave applications.

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.

Advanced InP DHBT process for high speed LSI circuits

We report on the development of an advanced InP double heterojunction bipolar transistor (DHBT) technology that utilizes electroplated device contacts and dielectric sidewall spacers to form a self-aligned base-emitter junction. These processes permit aggressive scaling of the transistor, while achieving high levels of yield and manufacturability. HBTs with 0.5 mum emitter junction widths have been demonstrated with an ft/fmax of 405/390 GHz and a common-emitter breakdown voltage BVCEO >4 V. Large-scale direct digital synthesizer (DDS) circuits have been fabricated operating at clock rates up to 24 GHz.

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.