3B.2 Final.2025

Abstract
A fabrication process for encapsulating T-gates with a robust SiN/SiO2 airbox has been developed at HRL, allowing for further passivation layers to be deposited, without creating additional parasitic capacitances that would degrade radio frequency (RF) performance of devices. This process has been demonstrated and validated on HRL’s T3 GaN devices, maintaining fT/fMAX after SiN and SiO2 coverage of the entire transistor. This robust inorganic airbox can be either used to enable wafer-level passivation of inorganic materials for complex BEOL fabrication and/or addition of moisture barrier layers to improve device reliability – all without altering device performance.