Evaluation and MHz Converter Application of 1.2-kV Vertical GaN JFET

Abstract

The 1.2 kV vertical GaN fin-channel junction field-effect transistor (JFET) is an emerging industrial device with low specific <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>-resistance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub>), normally-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> operation, and avalanche capability. This article reports the first comprehensive evaluation of 1.2 kV, 75 mΩ gallium nitride (GaN) JFET in converter applications. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i>-interface gate driver is optimized through the double-pulse test (DPT). To quantify the device's conduction loss, an in-situ measurement of dynamic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> is performed in a continuous DPT at steady-state. The vertical GaN JFET shows no dynamic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> issue. Subsequently, a GaN JFET-based half bridge is evaluated in a zero-voltage-switching (ZVS) buck converter under various frequencies, duty cycles, and load conditions. For comparison, similarly-rated SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> and Si IGBT are tested in the same converter. Benefitting from the lowest output capacitance and output charge, the GaN JFET requires a short deadtime and enables MHz operation in the 800-V ZVS buck converter. The GaN converter achieves a maximum efficiency of 97.7% at 1 MHz and 98.0% at 500 kHz and shows a general advantage in frequency and efficiency compared to the same converters based on SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> and Si IGBT. In addition, under the operational driver condition, the 1.2 kV GaN JFET shows a long short-circuit withstanding time of over 40 μs at 800 V. These results provide key reference for the application of 1.2 kV GaN JFETs and suggest that a GaN device with proper designs can achieve excellent stability and robustness.