On the Vertical Fin Field-Effect Transistor in Gallium Nitride: Experimental Realization and Evaluation of the Frequency Capability for High-Power, High-Frequency Applications

Compared to the currently deployed lateral gallium nitride (GaN) high-electron-mobility transistor (HEMT), a vertical transistor concept would enhance the current handling capability and improve thermal management. While research on vertical transistors in GaN has focused on high-power switching applications, there has been limited exploration of their potential use as radio-frequency (RF) power amplifiers.
This work experimentally assesses the frequency capability of the vertical fin field-effect transistor (FinFET) in the GHz regime. It develops a process capable of manufacturing RF-compatible FinFETs on a wafer scale. Furthermore, two assumed drawbacks of the vertical FinFET concept are successfully addressed: the use of electron beam lithography for structuring sufficiently narrow fins and the limited yield due to high device complexity. Small-signal analyses for devices consisting of up to 100 fins are presented, achieving cut-off frequencies beyond 10 GHz. The limitations of the concept in terms of gate capacitance and resitance are analysed. Ultimately, this work provides estimations for achievable maximum frequencies of oscillations for the vertical GaN FinFET concept.