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 (ZrO2). 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 ZrO2 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 ZrO2 at different annealing temperatures were observed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The ZrO2 thin film achieved a better thermal stability after high temperatures annealing. Moreover, the MOS-HEMTs with ZrO2 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 nicker noise measurements showed that ZrO2 MOS-HEMT had a higher output power at high input swing and low surface density. Therefore, ZrO2 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. (C) 2012 Elsevier Ltd. All rights reserved.