Polyimide passivated AlGaN-GaN HFETs with 7.65 W/mm at 18 GHz

Current metal-organic chemical vapor deposition-grown AlGaN-GaN heterojunction field-effect transistor devices suffer from threading dislocations and surface states that form traps, degrading RF performance. A passivation scheme utilizing a polyimide film as the passivating layer was developed to reduce the number of surface states and minimize RF dispersion. Continuous-wave power measurements were taken at 18 GHz on two-finger 0.23-μm devices with 2×75 μm total gate width before and after passivation yielding an increase from 2.14 W/mm to 4.02 W/mm in power density, and 12.5% to 24.47% in power added efficiency. Additionally, a 2×25 μm device yielded a peak power density of 7.65 W/mm at 18 GHz. This data suggests that polyimide can be an effective passivation film for reducing surface states.