In this article, we present an analysis of the gate degradation induced by long-term forward gate stress in GaN-based power HEMTs with p-type gate, controlled by a Schottky metal-retracted/p-GaN junction. In particular, time-dependent gate breakdown and threshold voltage instability are investigated as function of different geometries, gate biases, and temperatures. The introduction of a gate metal retraction (GMR) process step improves the device lifetime because it suppresses the onset of the leakage current flow occurring at the gate edges for relatively high gate voltage. However, biasing GMR p-GaN HEMT at VG > 8 V and T > 80 °C, a new degradation mechanism shows up, possibly altering the lifetime even at low VG operation. Main results in this article demonstrate that although at high VG and high T, a localized degradation effect ascribed to the device isolation region is responsible for time-dependent gate breakdown, thanks to GMR higher operating voltages compatible with ten-year continuous operation is attained. Finally, the longer device lifetime at moderate VG values brought by GMR allows evaluating the threshold voltage instability for long stress times (≈112 h) at relatively high VG and high T, leading to the observation of a saturation of the long-term positive threshold voltage shift and providing additional information about the underlying physical degradation mechanisms. Overall, the saturated 0.65-V AVTH under worst-case condition (VG = 7 V at 150 °C, i.e., correspondingto ten-year lifetime) reveals a reliable and fairly stable technology with respect to forward gate stress.

中文翻译：

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具有栅极金属回缩功能的 p-GaN HEMT 的栅极可靠性


在本文中，我们分析了由肖特基金属缩回/p-GaN 结控制的 p 型栅极基功率 HEMT 中长期正向栅极应力引起的栅极退化。特别是，随时间变化的栅极击穿和阈值电压不稳定性作为不同几何形状、栅极偏置和温度的函数进行研究。栅极金属回缩 （GMR） 工艺步骤的引入延长了器件的使用寿命，因为它抑制了相对较高的栅极电压下栅极边缘发生的泄漏电流的开始。然而，在 VG > 8 V 和 T > 80 °C 下偏置 GMR p-GaN HEMT 时，出现了一种新的退化机制，即使在低 VG 操作下也可能改变寿命。本文的主要结果表明，尽管在高 VG 和高 T 下，归因于器件隔离区域的局部退化效应是导致随时间变化的栅极击穿的原因，但由于 GMR 实现了与十年连续运行兼容的更高工作电压。最后，GMR 在中等 VG 值下带来的较长器件寿命允许在相对较高的 VG 和高 T 下评估长应力时间 （≈112 h） 的阈值电压不稳定性，从而观察到长期正阈值电压偏移的饱和，并提供有关潜在物理退化机制的其他信息。总体而言，在最坏情况下（150 °C 时 VG = 7 V，即对应于 10 年的使用寿命）下的饱和 0.65 V AVTH 显示出一种可靠且相当稳定的正向栅极应力技术。