High thermal stability and low hysteresis dispersion AlGaN/GaN MOS-HEMTs with zirconia film design

Gate structure of AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) on silicon substrates has been developed using electron-beam evaporated high-permittivity (high-k) zirconium oxide layer (ZrO ₂). As a gate insulator, this structure has been investigated and compared with the conventional GaN HEMTs. From the measured capacitance-voltage (C-V) curve, the dielectric constant of ZrO ₂ was 20.7 and the voltage shift of C-V hysteresis phenomena can be reduced to 7.2 mV after high temperatures annealing. The crystalline structures of ZrO ₂ at different annealing temperatures were observed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The ZrO ₂ thin film achieved a better thermal stability after high temperatures annealing. Moreover, the MOS-HEMTs with ZrO ₂ gate insulator layer markedly improved its gate leakage current and microwave performances. The device linearity was also improved due to its flat and wide transconductance (g _m) distribution which was analyzed by polynomial curve fitting technique. Load-pull and flicker noise measurements showed that ZrO ₂ MOS-HEMT had a higher output power at high input swing and low surface density. Therefore, ZrO ₂ was a potential candidate high-k material for the gate insulator on GaN-based MOS-HEMT for it exhibited a better thermal stability and reliability at high power applications.