DC and RF performance of HR Si(111)-based AlGaN/GaN MIS-HEMT with a symmetrical multi-finger grid array structure for 5G N28 700MHz low-bias-control applications

Abstract

HR Si(111)-based AlGaN/GaN metal insulator semiconductor high electron mobility transistor (MIS-HEMT) for 5G mobile communication at N28 700 MHz band is proposed in this paper. The device is ingeniously designed with a symmetrical dual-column multi-finger grid array structure. In addition, the device is designed with an MIS gate with a 6 nm SiN dielectric film to suppress the leakage current and a source field plate to suppress the current collapse effect. The fabrication process of the device is studied in detail, including the epitaxial surface treatment, F ion implantation isolation, ohmic contact, electron beam lithography gate process, surface passivation, and source field plate. A device with a gate length of 0.25 μm, gate-source space of 1 μm, a gate width of 1200 μm (the number of gate fingers is 12 with a single-finger gate width of 100 μm), and source field plate length of 0.2 μm is fabricated successfully. Results of electrical tests show that the HEMT device has a threshold voltage of about −7.5 V, a low knee voltage of about 4 V, a high saturation drain current density of 750 mA/mm, and a gate leakage current as low as less than 160 pA at the gate bias of 0 V. At the frequency band of 703–803 MHz, with low bias control of 10 V, the S21 of HEMT is about 5.923–7.261 dB, the gain flatness is 1.338 dB, the current gain is about 27.3 dB, and the stability factor is more than 1. This device would be a good candidate for future 5G low-frequency and low-voltage-control applications.