Augmentation and Assessment of a Universal FET I -V Model for Simulating GaN HEMTs

The ON-state I - V characteristics of gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are affected by the bias dependencies of four parameters, namely - virtual gate length, mobility, saturation velocity, and the channel-length modulation (CLM) parameter - this is in addition to the source/drain resistance, CLM, and self-heating which affect all FETs. The existing modeling approach involves developing an equation that includes all the above effects and then extracting all the equation parameters from measured I - V data. In this approach, at times, some effects need to be neglected in the quest for simplicity, and the values of some extracted parameters influence each other. To mitigate this problem, we propose a flipped modeling approach. Here, first, discrete data regarding the above four bias dependencies is extracted from the measured I - V curves using a universal FET model (UFM) which captures effects common to all the FETs. Next, the extracted data of each bias dependence is fitted using a simple equation with qualitatively correct behavior; these curve-fit equations are augmented to the UFM to complete the model. The CLM and saturation velocity data are extracted from the remnants of calibrated 2-D numerical simulations after turning off the virtual gate and self-heating effects. The parameter values of different devices and models are compared.