Self-aligned ALD AlO x T-gate insulator for gate leakage current suppression in SiN x -passivated AlGaN/GaN HEMTs

• Published in: Solid-state electronics Vol. 54; no. 10; pp. 1098 - 1104
• Main Authors: Meyer, David J., Bass, Robert, Katzer, D. Scott, Deen, David A., Binari, Steven C., Daniels, Kevin M., Eddy, Charles R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2010
• Subjects: Breakdown; Gate leakage current; Insulated gate; MIS; Passivation; Pulsed I– V; Pulsed I– V; MIS; Gate leakage current; Breakdown; Insulated gate; Passivation
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2010.05.024

A proof-of-concept metal–insulator–semiconductor (MIS) AlGaN/GaN high-electron mobility transistor (HEMT) that uses a self-aligned 10 nm AlO 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 submicron tri-layer photoresist pattern to lift-off sequentially-deposited AlO x dielectric and Ni/Au gate metal layers. By keeping the temperature low (100 °C) during the atomic-layer deposition (ALD) of AlO 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 AlO 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 AlO 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 and f T · L G product roll-off were observed at short gate lengths for both AlO x -insulated and Schottky gate devices.