| High electron mobility and saturation velocity enable AlGaN/GaN HEMT to be very attractive for millimeter wave study and applications. This work studies the equivalent circuit modeling in AlGaN/GaN HEMT. In the study of small signal equivalent circuit modeling, a small-signal model for AlGaN/GaN HEMT is provided, the parasitic parameters and intrinsic parameters are extracted. Through further analysis of the intrinsic parameters, the concept of mesa edge capacitance is proposed, and the specific physical model is given. In order to extract the mesa edge capacitance, a small-signal model considering mesa edge capacitance is provided. Through analysis of the intrinsic gate capacitances as a function of the gate widths, mesa edge capacitance are obtained.To verify the model and the method for mesa edge capacitance extraction, simulations for mesa edge capacitance are conducted. The good agreement between the simulation and measurement indicates that the model and the method for parameter extraction are reliable. The following conclusions are obtained by further analysis of mesa edge capacitance. Firstly, mesa edge capacitance accounts for a larger proportion in the total gate capacitance, which can be about 33.2%. Mesa edge capacitances results in a significant drop of frequency characteristics. Then, the effect is more serious in the shorter gate length devices. Mesa edge capacitance can be 71.5% in ultra-short 20 nm gate length device. Thus, reducing mesa edge capacitances is an effective approach to improve the frequency performance of millimeter-wave AlGaN/GaN HEMT.Based on the small signal equivalent circuit modeling in millimeter-wave AlGaN/GaN HEMT, the large signal equivalent circuit modeling is study. According to the DC characteristics of devices, the Curtice cube model is selected to fit the DC I-V characteristic and the model parameters are fitted successfully by Matlab. The model fitting results are in good agreement with the test results. |
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