Microwave Modeling And Parameter Extraction For HEMTs

With the explosive development of wireless communication industry, GaN high electron mobility transistors, as the third-generation of microwave active devices, have a huge advantage in operational frequency, gain and efficiency. Therefore they are widely used in microwave integrated circuits design. For improving circuit design success rate, reducing the design cycle time and the time to market, validated and accurate HEMT models are needed. The parameter extraction and modeling of HEMT is studied in this paper. Based on this research topic, the following research results achieved have been listed:1) An improved small-signal equivalent circuit parameter extraction method for HEMTs is proposed. This method overcomes the limit of traditional small-signal modeling parameter extraction methods that the gate-source and gate-drain of HEMT are symmetrical device structure. The new method deduces the computational formulas between parasitic parameters and scaling factors through the test S-parameters under two bias voltage conditions. Based on the new method, the relationship between gate width of HEMT and small-signal equivalent circuit parameters is studied in the thesis;2) A semi-analytical parameter extraction procedure of small-signal model is proposed for the AlGaN/GaN HEMT small-singal modeling to fulfill the increasing of parasitic elements for distribution effect. The method combines the test structure approach, optimum numerical method and pinch-off condition approach to get the accurate physical small-signal model parameters. Sensitivity of intrinsic parameters is also studied based on the semi-analytical parameter extraction method.3) A STATZ-based large-signal equivalent circuit model of AlGaN/GaN HEMT is proposed. The new large-signal model takes nonlinear relationship between drain-source current and gate-source voltage into account. Polynomial and exponential function are used to describe the nonlinear relationship. Parameter extraction technologies of improved CURTICE model for current model and capacitance model of AlGaN/GaN HEMT are researched in this thesis, and the advantage to this approach is that it combines the features of two-order CURTICE model and TOM III model. Finally, the accuracy of commonly used large-signal models of microwave commercial software is also compared in the thesis;4) The noise parameter extraction technology is studied based on 50Ω noise-figure measurements. The advantages of PUCEL noise model and POSPIESZALSKI noise model are used to research the effect of the gate-drain distance on the high frequency performance, noise performance and intrinsic parameters for AlGaN/GaN HEMTs. Finally, a low noise amplifier is designed with the proposed noise model of AlGaN/GaN HEMT and the measuring environment is introduced.