Physical modeling and optimization of a GaN HEMT design with a field plate structure for high frequency application

In this paper, physical modeling of a GaN HEMT with a field plate structure is proposed, with the objective of providing the connection between the physical design parameters of the device (geometry, Al mole fraction, type of the field plate, etc) and on-resistance together with parasitic capacitances of the device. In this way, it is possible to optimize the design of a switching device for a particular application, which in our case is a high frequency DC DC converter for Envelope Tracking and Envelope Elimination and Restoration techniques. In this work, extrinsic models for output characteristics together with input, output and reverse capacitance of a depletion mode GaN HEMT with a field plate structure were obtained. The obtained physical model was implemented in a Simplorer simulation model of a high frequency buck converter and verified by the prototype that employed modeled GaN HEMT, operating at 7, 15 and 20MHz of switching frequency. Comparing to the measured efficiency curves, simulation results showed good agreement, especially in the low power range at high switching frequency, which are the operating conditions in our application.