III-Nitride Based High Electron Mobility Transistors for RF Applications

Rapid development of wireless communication systems, including the deployment of 5G networks, calls for robust electronic components that can efficiently support the transmission of increasingly high data rates with wider bandwidths and at higher frequencies. III-nitride based high electron mobility transistors are ideal candidates for such systems due to their wide/ultra-wide bandgaps, high carrier concentrations, as well as high carrier velocities. This work explores and evaluates two separate approaches to advance beyond the performance of the conventional GaN HEMT technology. Fabricated AlGaN channel HEMTs intended for RF power applications have been measured in DC and RF from 25 °C to 150 °C. Mobility, effective velocity, and fT have been extracted at all measured temperatures. The temperature sensitivities of mobility and velocity are modest compared to devices composed of Si, GaAs and GaN channel. Ferroelectric gated GaN HEMTs are explored as potential candidates for RF/mm-wave switch applications. Hf0.5Zr0.5O2 is implemented in the gate stack on a standard AlGaN/GaN HEMT structure to utilize ferroelectric polarization in addition to the spontaneous and piezoelectric polarization provided by AlGaN/GaN. Counter-clockwise hysteresis has been demonstrated in DC measurements. Switch figure of merit of 1-2.1 THz has been achieved from 10 MHz to 67 GHz, which is among the highest in single channel three-terminal devices to the best of our knowledge. Regrown n+ GaN has also been explored experimentally as a replacement for the alloyed source/drain ohmic contacts to improve on-resistance. Simulation based effort is presented to demonstrate a multichannel design for further on-resistance improvement.