Self-aligned ALD AlO_x T-gate insulator for gate leakage current suppression in SilVpassivated AlGaN/GaN HEMTs

摘要

A proof-of-concept metal-insulator-semiconductor (MIS) AlGaN/GaN high-electron mobility transistor (HEMT) that uses a self-aligned 10 nm AIO_X gate insulator and SiN_x passivation in the device access regions was investigated. Self-alignment of the gate insulator to metal was achieved by utilizing a sub-micron tri-layer photoresist pattern to lift-off sequentially-deposited AlO_x dielectric and Ni/Au gate metal layers. By keeping the temperature low (100 ℃) during the atomic-layer deposition (ALD) of AIO_x. reflow of the photoresist pattern was prevented, which maintained the integrity of its re-entrant profile. After lift-off, the resulting transistor gate had a T-shaped profile with AIO_x directly under the gate metal only. In a split wafer comparison, this experimental structure reduced reverse-bias gate leakage current after passivation by one to two orders of magnitude over Schottky gate devices. Plasma-enhanced chemical vapor deposition (PECVD) SiN_x passivation of the exposed AlGaN surface access regions of AIO_x-insulated gate devices was found to produce pulsed I-V improvements that are similar to those observed in passivated Schottky gate devices. This fabrication technique has been successfully used to demonstrate insulated gate devices with gate lengths (L_G) as short as 160 nm with f_T = 35 GHz and f_(max) = 77 GHz small-signal performance. Substantial output conductance andfTLc product roll-off were observed at short gate lengths for both AlO_x-insulated and Schottky gate devices.