Submicron gate Si3N4/AlGaN/GaN-metal-insulator-semiconductor heterostructure field-effect transistors

We present the characteristics of a quarter-micron gate metal-insulator-semiconductor heterostructure field-effect transistor (MISHFET) with Si3N4 film as a gate insulator. A detailed comparison of the MISHFET and an identical geometry RFET shows them to have the same radio frequency (RF) power gain and cut-off frequency, while the MISHFET has much lower gate-leakage currents and higher RF powers at operating frequencies as high as 26 GHz. The MISHFET gate-leakage currents are well below 100 pA at gate bias values from -10 V to +8V. At zero gate bias, the drain saturation current is about 0.9 A/mm and it increases to 1.2 A/mm at +8 V gate bias. The output RF power of around 6 W/mm at 40 drain bias was found to be frequency independent in the range of 2 to 26 GHz. This power is 3 dB higher than that from HFET of the same geometry. The intrinsic cutoff frequency is similar to63 GHz for both the HFET and the MISHFET. This corresponds to an average effective electron velocity in the MISHFET channel of 9.9 x 10(6) cm/s. The knee voltage and current saturation mechanisms in submicron MISHFETs and heterostructure field-effect transistors (HFET) are also discussed.