A Comprehensive Lifetime Model for Schottky-Type pGaN Gate of GaN HEMTs

A systematic time-dependent gate breakdown study was conducted on enhancement-mode GaN high-electron-mobility transistors (HEMTs) under various accelerated gate voltages and temperatures. Impact ionization (I.I.) was identified as the primary wearout mechanism responsible for pGaN gate breakdown failures. A comprehensive gate lifetime model, based on the I.I. mechanism, was developed to quantitatively model the voltage and temperature dependence of mean-time-to-fail (MTTF). Two distinct activation energies (E<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {a}}$ </tex-math></inline-formula>) were observed across different temperature ranges. At lower temperatures, the temperature dependent MTTF is primarily influenced by the temperature dependence of I.I. coefficients, resulting in a negative E<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {a}}$ </tex-math></inline-formula>. At higher temperatures, thermionic emission (TE) becomes the dominant conduction mechanism for the gate leakage current (I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {G}}$ </tex-math></inline-formula>). Consequently, I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {G}}$ </tex-math></inline-formula> increases exponentially with temperature, leading to considerably more hot electrons within the depleted pGaN gate layer, which accelerates the I.I. failure process. Therefore, the temperature dependence of I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {G}}$ </tex-math></inline-formula> dominates over the effect of I.I. coefficients, yielding a positive E<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {a}}$ </tex-math></inline-formula> at elevated temperatures.