DUAL-GATE MULTIPLE-QUANTUM-WELL (MQW) HETEROJUNCTION FIELD-EFFECT TRANSISTORS (HFETS) FOR ACTIVE PHASE SHIFTERS

We present a theoretical evaluation of the potential of dual-gate GaAs / AlGaAs multi-quantum-well heterojunction field effect transistors ( MQWHFETs) for active phase shifters in the frequency range 4-60 GHz. T he computer-aided design program TOUCHSTONE was used to study the phas e-shift characteristics. The transmission phase of a dual-gate MQWHFET mostly depends on variation of the gate source capacitances C-gs1, C- gs2, and the transconductance g(mo2) with gate bias rather than on oth er intrinsic elements. Limited gate-bias ranges in the active regions of the device operation result in a quasi-linear phase shift for analo g applications. For digital applications, a maximum differential phase shift of 36, 51, 63, and 105 degrees at f = 12, 20, 30, and 60 GHz, r espectively, was obtained by switching both control gate biases discre tely. Compared to a single-gate device, a dual-gate MQWHFET shows an i ncrease in differential phase shift by 9-90% from 12-60 GHz. Furthermo re, a dual-gate device provides extra possibilities by varying differe nt geometrical and structural parameters that influence the phase-shif t and the gain characteristics. The use of different gate lengths give s a flat gain in the active regions. Using the same layer structure wi th different recess depths under the two gates results in a greater ph ase shift. (C) 1996 John Wiley & Sons, Inc.