Design of 1.2 kV Power Switches With Low R_ ON 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 (RON). 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 (VBR) 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-2and a peak electric field not exceeding 2.4 MV/cm. The corresponding RONwas 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 RONof 1.7 mQ · cm2was achieved for similar thicknesses of the drift region. This paper studies the design space in detail and discusses the associated tradeoffs in the RONand VBRin conjunction with the threshold voltage (VT) desired for the normally OFF operation.