Design of 1.2 kV Power Switches With Low Using GaN-Based Vertical JFET

Two novel gallium nitride-based vertical junction FETs (VJFETs), one with a vertical channel and the other with a lateral channel, are proposed, designed, and modeled to achieve a 1.2 kV normally OFF power switch with very low ON resistance (R_ON). The 2-D drift diffusion model of the proposed devices was implemented using Silvaco ATLAS. A comprehensive design space was generated for the vertical channel VJFET (VC-VJFET). For a well-designed VC-VJFET, the breakdown voltage (V_BR) obtained was 1260 V, which is defined in this study as the drain-to-source voltage at an OFF-state current of 1 μA · cm^-2 and a peak electric field not exceeding 2.4 MV/cm. The corresponding R_ON was 5.2 mΩ · cm². To further improve the switching device figure of merit, a merged lateral-vertical geometry was proposed and modeled in the form of a lateral channel VJFET (LC-VJFET). For the LC-VJFET, a breakdown voltage of 1310 V with a corresponding R_ON of 1.7 mQ · cm² was achieved for similar thicknesses of the drift region. This paper studies the design space in detail and discusses the associated tradeoffs in the R_ON and V_BR in conjunction with the threshold voltage (V_T) desired for the normally OFF operation.