常关型GaN基MISFET栅极可靠性和阈值稳定性研究

GaN基功率器件基于优越的材料特性在新一代高效率功率开关器件的竞争中极具潜力。但其应用受限于缺少具有大栅压摆幅、大栅极偏置安全工作范围和类似于Si基MOSFET的栅极结构和驱动方式的单芯片常关型器件。常关型GaN基MISFET是突破这个限制的富有吸引力的解决方案，但面临着栅极可靠性和阈值稳定性的挑战。目前研究发现LPCVD-SiNx栅介质在MISFET结构中展现了高击穿电场、长经时击穿（TDDB）寿命和较小的栅极偏置温度不稳定性（BTI）等优异特性。但要进一步提高MISFET的阈值稳定性和栅极可靠性以满足应用需求，依然存在亟待解决的问题，包括栅介质的体缺陷、高温反向偏置应力（HTRB)下的栅极稳定性、AC应力下阈值漂移和栅极击穿机理等。为推动这些方面的研究，本项目针对常关型MISFET结构提出增强阈值稳定性和栅极可靠性的技术方案，并结合实际应用在交流电应力下研究栅极退化机理。

Owing to the superior material properties, Gallium Nitride-based power device is a promising candidate for the next-generation high-efficiency power switching devices. However, the wide application of GaN-based power electronics is limited by the lack of a single-chip normally-off device, which has a large gate voltage swing, a large gate bias safe operating range, and especially, a gate structure and simple gate driver like that of a Si MOSFET. Enhancement-mode (E-mode) GaN-based Metal-Insulator-Semiconductor Field Effect Transistor (MISFET) is an attractive method to break this limit. However, threshold voltage stability and gate reliability are the major concerns in developing the E-mode GaN MISFETs. Recently, LPCVD-SiNx was demonstrated as a promising gate dielectric for the GaN MISFETs, which has a high breakdown electric field, long time-dependent dielectric breakdown lifetime and low gate bias temperature instability (BTI). However, to further improve the threshold voltage stability and gate reliability of MISFETs to meet the application requirements, there are still some challenges, including defects in the silicon nitride dielectric layer, high-temperature reverse-bias stress (HTRB) instability, mechanisms of threshold voltage shifts and gate breakdown under AC stress, and so on. To address these challenges, this project proposes gate dielectric treatment techniques and double-channel structure to enhance the threshold stability and gate reliability of the E-mode LPCVD-SiNx MISFET. The degradation mechanisms under AC stress will also be investigated to promote the establishment of an accurate lifetime model that is critical to the GaN power MISFET technology.