| dc.description.abstract | In this paper, the analysis of variable temperature characteristics of GaN HEMTs with different substrates has been investigated, and divided into two parts: (1) variable temperature static characteristics and thermal resistance of GaN HEMTs with different substrates; (2) variable temperature dynamic characteristics of GaN HEMTs with different substrates.
This paper discusses GaN HEMTs with different substrates which use traditional Si substrates and QST substrates respectively. The advantage of QST substrate is that the coefficient of thermal expansion match GaN, and can grow a thicker buffer. Also, GaN-on-QST is more stable to operate at high temperature than is GaN-on-Si because of higher thermal conductivity. The temperature coefficients of two GaN HEMTs are obtained by variable temperature measurement, including on-resistance, maximum drain current, maximum transconductance, power, and leakage current. The results show that GaN-on-QST has lower temperature coefficients. The thermal resistance of two GaN HEMTs is extracted by drain current-voltage characteristics, and the thermal resistance of GaN-on-Si is lower. By Silvaco TCAD simulation, it can be found that GaN HEMTs with higher thermal resistance have higher junction temperatures due to weak heat dissipation.
The second part of the paper is to discuss the dynamic characteristics of these two GaN HEMTs. Using the soft and hard switching to evaluate dynamic on-resistance, GaN-on-QST has lower dynamic on-resistance in these two switching tests; for the consecutive switching, the pulse measurement is used to evaluate the dynamic off-current in the off-state. The GaN-on-Si dynamic off-current is higher than the static, due to the lowered conduction band in the gate region induced by hole injection from p-GaN, the electrons from the source are easily transported. Due to the high static off-current of GaN-on-QST, the injected hole is recombined with the high electron concentration resulting in lower dynamic leakage. The double pulse dynamic measurement is used to observe GaN HEMTs switching behavior, GaN-on-Si has better switching characteristics because of its lower capacitance. Both GaN HEMTs turn on characteristics degrade due to transconductance decreases, the capacitance decreases induced by higher temperature makes the GaN HEMTs turn on characteristics better. | en_US |