Gate Oxide Reliability Issues of SiC MOSFETs Under Short-Circuit Operation

Silicon-Carbide (SiC) MOSFETs, due to material properties, are designed with smaller thickness in the gate oxide and a higher electric field compared to Si MOSFETs. Consequently, the SiC MOSFETs have a worse reliability which causes higher leakage currents during instantaneous abnormal operating conditions. This paper investigates the reliability issues of the SiC MOSFET gate oxide under standard short-circuit test conditions. In this paper, 1200-V SiC MOSFETs are newly modeled, and also their short-circuit sustainability (tolerance) have been studied at different drain–source and gate–source voltages. A hardware tester circuit was designed and developed to test the devices under such extreme circuit conditions. Then, the gate reliability of SiC MOSFET devices have been compared to that of Si power devices of similar ratings. The results reveal a higher reduction in the instantaneous gate–source voltage of SiC MOSFETs compared to that of Si devices under the same operating conditions. The gate–voltage reduction phenomenon results from the higher leakage currents through the gate. Furthermore, it was found that the gate–source voltage reduction during the test depends on the gate structures. The gate voltage reduction of SiC MOSFETs with planar gate is higher than that of MOSFETs with shield planar gate. As the pulse duration increases in short-circuit tests, the leakage current in the gate­source of SiC devices increases. The results show that even though the SiC MOSFETs are very capable of processing long pulses and high power in the drain–source, the gate–source side is highly degraded by these pulses in the test. Moreover, whenever a small number of the short-circuit tests are applied, the gate structure of SiC MOSFETs becomes broken while the drain–source is still able to block the dc-link voltage. The paper concludes that the short-circuit reliability of the gate was found to be worse compared with commercial Si devices with similar rating.

I. Introduction

The development of power semiconductor devices has always been a driving force for power electronic fields. For a long time, silicon-based power devices have dominated the power electronics semiconductor market and power system applications. Furthermore, silicon (Si) devices are widely used in the field of home appliance applications, power supplies, and information technology equipment. Therefore, the cost of Si MOSFETs has already stabilized with high operational reliability. However, market demands of higher voltage, power, and efficiency of emerging power electronic systems have been faced with performance limitation of Si material properties. SiC technology proposes a solution for many of the issues by superior material properties with regards to Si. After years of research on device physics and manufacturing technology, silicon-carbide (SiC) semiconductor devices for high-power applications have become commercially available as switching discrete devices such as Thyristors, JFETs, and MOSFETs [1]. The demand is strongly growing for these devices in high-voltage and high-temperature applications [2], [3] . SiC material offers a number of advantages compared to Si: SiC has ten times higher dielectric-breakdown field strength, three times the band gap, and three times the thermal conductivity [4] . These properties make SiC an attractive material that can far exceed the performance of their Si counterparts.