We have developed a new, zone-based compact physics-based AlGaN/GaN heterojunction field-effect transistor (HFET) model suitable for use in commercial harmonic-balance microwave circuit simulators. The new model is programmed in Verilog-A, an industry-standard compact modeling language. The new model permits the dc, small-signal, and large-signal RF performance for the transistor to be determined as a function of the device geometric structure and design features, material composition parameters, and dc and RF operating conditions. The new physics-based HFET model does not require extensive parameter extraction to determine model element values, as commonly employed for traditional equivalent-circuit-based transistor models. The new model has been calibrated and verified. We report very good agreement between simulated and measured dc and RF performance of an experimental C-band microwave power amplifier. 1. Introduction AlGaN/GaN heterojunction field-effect transistors (HFETs) are promising RF transistors for use in high-power and high-frequency circuit applications. These HFETs possess a combination of high current density capability and high breakdown voltage due to the desirable physical properties of the materials, such as high critical electric field for breakdown, high electron mobility and saturated carrier velocity, high carrier density in the channel, lower dielectric constant compared to the conventional materials, and high thermal conductivity. These parameters permit the HFET to operate at high RF voltage and current, which results in high power operation at high frequency [1, 2]. The technology for fabricating devices and circuits in AlGaN/GaN is developing rapidly [3–6] and this rapid development is creating a need for improved device models. RF power amplifiers based on AlGaN/GaN HFETs are now commercially available from several companies, including Nitronex, RFMD, and TriQuint. However, to date, no commercially available HFET model for use in harmonic-balance circuit simulators exists that can predict the large-signal RF operation of an HFET or an MMIC before the active device is fabricated, characterized, and fitted. The basic structure for an HFET is shown in Figure 1. The dc and RF performance of the transistor varies with the physical dimensions and material properties. However, the sensitivity of RF power performance to the physical parameters will vary, depending upon the particular parameter, and variations in some parameters (e.g., the gate length, ) have a more significant effect upon device performance than others. These
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