SUMMARYA self-consistent numerical transport model based on the hydrodynamic equations obtained from Boltzmann's transport equation (BTE) is presented. The model includes both the temporal and spatial variation in electron velocity. A parallel implementation of the solution method, using FDTD techniques, is illustrated. Numerical results for a GaAs MESFET device are generated using this complete hydrodynamic model (CHM) and compared with results obtained from the more commonly used energy or simplified hydrodynamic model (SHM). The results indicate that for short gate-lengths (less than 0·5 m) the two models lead to different DC steady-state results which in turn lead to different microwave small-signal models for the device.

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In conventional microwave transistors, the gain and output power are significantly reduced by gate ohmic resistance and phase cancellation. The air-bridged gate (ABG) transistors overcomes both problems by providing larger gate cross section along the propagation direction of the signal, and keeping both the input and output signals in phase along the device width. The performance of the air-bridged and conventional transistor is evaluated from both dc and radio-frequency (RF) points-of-view. A full hydrodynamic transport model, which accurately describes the electron dynamics in short channel devices, is used in the dc analysis. For RF analysis, a full-wave model, capable of capturing all important high-frequency effects, such as wave-particle interactions and traveling-wave effects, is implemented. This model is based on the coupling of the hydrodynamic transport equations with Maxwell's equations. Results related to the traveling-wave effects in conventional and ABG devices, such as phase mismatch and gain reduction at high frequencies, are illustrated. From these results, we show that the ABG metal-semiconductor fieldeffect transistor (MESFET) has superior performance at very high frequency as compared to conventional planar MESFET's.

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