Integration of enhancement and depletion‐mode AlGaN/GaN MIS‐HFETs by fluoride‐based plasma treatment

Abstract

AbstractEnhancement‐mode AlGaN/GaN metal–insulator–semiconductor HFETs (MIS‐HFETs) are demonstrated by combining CF4 plasma treatment technique and a two‐step Si3N4 deposition process. The threshold voltage has been shifted from –4 to 2 V using this technique. A 15 nm Si3N4 layer is inserted under the gate to provide additional isolation between the gate metal and AlGaN surface, which can lead to higher gate turn‐on voltage. The two‐step Si3N4 deposition process is developed to reduce the gate coupling capacitances in the source and drain access regions, while assuring the plasma‐treated gate region being fully covered by the gate electrode. The forward gate turn‐on voltage can be as large as 6.8 V. By tuning the plasma treatment parameters, the threshold voltage of the enhancement‐mode MIS‐HFETs can be raised to as high as 4.3 V. By integrating with depletion‐mode MIS‐HFETs, a direct‐coupled FET logic inverter has been fabricated, with logic low and high noise margins of 2.1 and 2 V. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)