In Situ Measurement and Physical Mechanism of Dynamic <i>R</i> <sub>ON</sub> in GaN-on-Si Monolithic Half-Bridge Power IC
Xin Yang, Hongchang Cui, Zineng Yang, Matthew Porter, Bin Lü, Yuhao Zhang
Abstract
Dynamic on-resistance (R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub>) is a critical stability concern for GaN high-electron mobility transistors (HEMTs). In GaN monolithic half-bridges on conductive Si substrate, the dynamic R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> of high-side (HS) device can be more severe than that of discrete HEMTs due to the back-gating effect. However, current evaluation methods typically apply a DC or pulsed substrate bias while keeping the HS device always ON, which differs from the application-use condition in power converters. This work proposes a new circuit method for accurate in-situ extraction of the dynamic R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> of a HS device in steady-state hard switching. The measured dynamic R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> is found to be nearly twice the value measured by conventional pulsed bias method. This suggests an interplay between the back-gating effect and the hard-switching stress to deteriorate dynamic R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub>. To validate this interplay effect, two buck converters are constructed based on a monolithic half-bridge and a discrete device-based half-bridge, respectively. We tune the converter loss to be dominated by the HS device by implementing a hard turn-on for the HS device and a zero-voltage-switching for the low-side device. A lower efficiency is observed in the monolithic half-bridge-based converter, and the dynamic R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> is verified to be higher than that obtained from pulsed bias method. The physical mechanism of this interplay phenomenon is also revealed. Overall, this work manifests the importance of dynamic R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> measurement of GaN-on-Si power IC under the practical switching conditions; the proposed circuit method provides a powerful tool for the evaluation and qualification of GaN monolithic half-bridge.