Transferred-substrate HBTs Research Articles

Submicron InP-based HBTs for Ultra-high Frequency Amplifiers

Transistor bandwidths are approaching terahertz frequencies. Paramount to high speed transistor operation is submicron device scaling. 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. We have fabricated HBTs with narrow collector junctions using a substrate transfer process. HBTs with submicron collector junctions exhibit extremely high fmaxand high gains in mm-wave ICs. Transferred-substrate HBTs have obtained record 21 dB unilateral power gain at 100 GHz. Recently-fabricated devices have shown unbounded unilateral power gain from 40-110 GHz, and fmaxcannot be extrapolated from measuremente. However, these devices exhibited high power gains at 220 GHz, the frequency limit of presently available microwave network analyzers. Demonstrated amplifier ICs in the technology include reactively tuned amplifiers at 175 GHz, lumped and distributed amplifiers with bandwidths to 85 GHz, and W-band power amplifiers.

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 f max and high gains in mm-wave ICs. Logic gate delays are primarily set by depletion-layer charging times, and neither fτ nor f max 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 f max is 1.1 THz. Transferred-substrate HBTs have obtained 295 GHz f τ . 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.

Transferred-substrate HBTs with 254 GHz f τ

The authors report the simultaneous achievement of record current gain cutoff frequency f/sub /spl tau// and high power gain cutoff frequency f/sub max/ in a transferred-substrate HBT. The device parasitics are examined, and inferences made about the relative value of various approaches toward further improvements in f/sub /spl tau// and f/sub max/. Transferred-substrate HBTs with record f/sub /spl tau// of 254 GHz are reported.

170 GHz transferred-substrate heterojunction bipolartransistor

The authors report transferred-substrate HBTs with an fmax of 170 GHz and fτ of 120 GHz. Devices scaled to deep submicrometre dimensions should obtain an fmax of ~500 GHz.