Performance improvement of Al0.3Ga0.7N/AlN/GaN HEMTs using Nitrogen pre-treated Si3N4 passivation

In the present study, new process of N-2 pre-treated (NP) Si3N4 passivation on Al0.3Ga0.7N/AlN/GaN HEMTs (High Electron Mobility Transistors)has been developed and its impact on DC and RF performance of HEMTs has been investigated. Additionaly, this study reveals the beneficial effects of NP passivation on RF performance in comparison to w/o NP passivation. The physical role of NP passivation is explained through extraction of small signal model parameters. NP Si3N4 passivation layer was deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) technique and was analysed using analytical techniques like X-ray Photoelectron Spectroscopy (XPS), High Resolution X-Ray Diffraction (HR-XRD), Ellipsometry & Fourier Transform Infrared Spectroscopy (FTIR). After NP passivation, devices exhibited better DC/RF characteristics. For a device, with gate-length of 0.25 mu m, drain current density (Idss) increased from 747 to 876 mA/mm and the peak transconductance(g(m)) increased from 192 to 236 mS/mm. The cut-off frequency (Ft) increased from 28.6 to 49.5GHz, maximum frequency oscillation (Fmax)increased from 27.2 to 42.5GHz&maximum available gain @ 8GHz increased from 11 dB to 15 dB for w/o NP passivation and with NP passivation respectively.