Investigation on Output Capacitance Losses in Superjunction and GaN-on-Si Power Transistors

Abstract

Low ON-resistance of advanced superjunction (SJ) and GaN-on-Si transistors is of great importance in power converters, however, the anomalous loss in their output capacitance (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> ) severely limits their performance. In this work, we use an energy-oriented measurement technique providing high voltage swings, high frequencies, and high values of dv/dt, which unlike Sawyer Tower, works without any pre-assumptions about circuit model of the transistor under test. This measurement method just relies on a low-voltage dc supply without the need of a high-power RF amplifier. In contrast with previous studies, the method shows that the small-signal E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> of SJ devices is not necessarily different from the one measured at large-signal domain. However, the reported E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> in datasheets might correspond to the discharging cycle, which is considerably lower than the actual E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> needed to charge C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> . Measurements on enhancement-mode GaN-on-Si power transistors give insights on the possible relation between C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OSS</sub> -losses and dynamic R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> degradation, as the two main phenomena hindering the performance of GaN transistors at high switching frequencies. These results give useful guidelines in utilizing and optimizing power transistors, especially at high-frequency operation.