THRESHOLD VOLTAGE TRIMMING OF GaAs MESFETS
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Method for adjusting the threshold voltage of GaAs MESFET devices, particularly for MESFET fabrication processes, that allows characterization of the FET channel prior to device completion. Trimming is accomplished by controlled and, where needed, repeated removal of thin surface layers of the MESFET channel using oxidation and subsequent oxide etching until the desired threshold voltage is obtained. The threshold voltage of MESFETs is determined by the amount of charge in the channel. By removing part of the channel, the threshold becomes more positive. This can be achieved by first exposing the implanted GaAs channel surface to a microwave oxygen plasma (2.4 GHz), thereby oxidizing a thin surface layer. Subsequently, the oxide is removed in a wet chemical etch process (HCl).