We propose an accurate FET model for microwave nonlinear circuit simulation, which has been modified from the Statz model. We have greatly enhanced the accuracy of both dc and capacitance expressions, especially in the knee voltage region where Ids begins to saturate. In the expression of dc characteristics, our model improves the accuracy by incorporating the drain-source voltage dependence of pinch-off voltage, the gate-source voltage dependence of knee voltage, and the non-square dependence of drain current against the gate-source voltage. The non-square-root voltage dependence of gate capacitances is considered as well. All modifications are simple and the parameter extraction is kept as simple as that of the Statz model. By using this model, good agreement has been obtained between simulated and measured characteristics of a GaAs FET. For the dc characteristics and the S-parameters, each of estimated error is within 5% and 10%. The model accuracy has been verified by comparison of simulated and measured results of power amplifier performances over a wide range of operating conditions.

A 60-GHz-band monolithic HEMT amplifier for which BCB thin film layers are adopted on GaAs substrate has been developed. The MMIC utilized a thin film microstrip line for the bias circuit and a coplanar waveguide for the RF circuit. The coplanar waveguide has the advantage of low loss, whereas the thin film microstrip line has the advantage of small size. Two different types of transmission lines were selected to coexist in the monolithic amplifier. As a result, the MMIC achieved high gain over a wider frequency range at a small size. This MMIC had a gain of over 15 dB in a frequency bandwidth of 11 GHz. In particular, the high-frequency characteristics of the transmission lines and the HEMTs were evaluated in detail for the conventional MMIC structure and the new MMIC structure. It was confirmed that this newly developed MMIC using BCB thin film layers is attractive for millimeter-wave applications.