Device Isolation by Plasma Treatment for Planar Integration of Enhancement/Depletion-Mode AlGaN/GaN High Electron Mobility Transistors

Abstract

We demonstrate a new planar fabrication technology for integrating enhancement/depletion (E/D) mode AlGaN/GaN high electron mobility transistors (HEMTs) using fluoride plasma treatment techniques. The CF4 plasma treatment is used in two separate steps to achieve two objectives: 1) active device isolation; and 2) threshold voltage control for the E-mode HEMT formation. Compared with the devices formed by standard mesa etching, the HEMTs by planar process have comparable DC characteristics, with no obvious difference in device isolation. By using the planar process, the E/D-mode HEMTs are integrated on the same chip, and a direct-coupled FET logic inverter and a 17-stage ring oscillator are fabricated. When the supply voltage is 4.5 V, the ring oscillator yields a frequency of 146 MHz, corresponding to a propagation delay of 201 ps/stage.