Study of DC-Induced RF Performance Degradations in AlGaN/GaN HEMTs Through High-Temperature DC Stress

In this work, we investigate the RF performance degradations in AlGaN/GaN high-electron mobility transistors (HEMTs) subjected to high-temperature ON-state dc stress (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>DS</roman></sub> = 18 V, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>DS</roman></sub> = 300 mA/mm). The main focus was on the RF degradation mechanism analysis induced by merely dc stress for short gate-length devices targeting for millimeter-wave applications. Throughout the dc stress process, variations in device parameters were meticulously measured and extracted. It was noted that the device exhibited an increase in intrinsic gate capacitance and parasitic resistance, leading to the degradation in unit-current-gain cutoff frequency (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>T</roman></sub><roman xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">)</roman> and maximum oscillation frequency (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>MAX</roman></sub><roman xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">)</roman>. Investigation of the degradation mechanism was first conducted through the current transient measurement methodology and then analyzed by TCAD simulation. It is concluded that the additional acceptor-like traps generated in the AlGaN barrier tend to increase the net charge density leading to the increase of total gate capacitance as well as the decrease in the transconductance, which causes the severe degradations in the RF performance after stress. This analysis offers deeper insights into the primary mechanisms behind RF performance degradation induced by dc stress in GaN HEMTs operating at millimeter-wave frequencies.