| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 98 === We demonstrate the use of native GaAs and InGaP oxides as gate insulators in the fabrication of InGaP/InGaAs pseudomorphic high electron mobility transistors (pHEMTs) that are characterized through the liquid phase oxidation (LPO) method. The liquid phase oxidation system is simple, low-cost, and near temperature (30-70℃); it also does not require the use of extra energy to form a native oxide layer in comparison with the other oxidation systems.
In this work, the high electron mobility transistors are fabricated with gate geometry 1×100 (μm)2. Compared with the conventional pHEMTs, InGaP oxide is used as the gate insulator for MOS-pHEMT applications in the DC measurements. The maximum drain current density is found to be 126 mA/mm at the gate-to-source voltage of 2 V, representing an improvement of about 50%. Meanwhile, the extrinsic transconductance is 118 mS/mm, representing an improvement of about 32%. The maximum turn-on voltage is 1.05 V, and the breakdown voltage is -23.65 V. The gate leakage current density can be improved about 1640 times at VGD=-7.8V.
GaAs oxide is used as the gate insulator for MOS-pHEMT applications. The maximum drain current density is at 310 mA/mm at the gate-to-source voltage of 2 V; this represents an improvement of about 269%. The extrinsic transconductance is 186 mS/mm, which represents an improvement of about 108%. The sub-threshold swing is 106 mV/decade, which improved by about 58%. The maximum turn-on voltage is 0.9 V, and the breakdown voltage is -29.3 V. The gate leakage current density can be improved by about 781 times at VGD=-7.8V.
The surface roughness of the gate interface influenced the DC and microwave performances. In the DC performances, the rougher surface caused a decrease in breakdown voltage and an increase in leakage current. Meanwhile, in the microwave performances, the rougher surface caused an increase in gate resistance.
The cut-off frequencies and the maximum oscillation frequencies of MOS-pHEMTs with GaAs oxide are 45.73 and 20.26 GHz, indicating an improvement of about 27% and 81%, respectively.
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