Enhanced gallium arsenide metal-semiconductor field effect transistors designed for high temperature operation

An enhanced gallium arsenide (GaAs) metal-semiconductor field effect transistor (MESFET) has been developed which demonstrates the capability of operating at temperatures greater than 350°C. At elevated temperatures, the semi-insulating substrate of traditional GaAs MESFETs begins to conduct significant amounts of current. These leakage currents degrade device performance by introducing inter-device leakage paths (through pad and interconnect metal) and intra-device leakage paths (between the source and drain). Through modifications to a standard MESFET process, the inter-device leakage paths have been virtually eliminated, and the intra-device leakage has been reduced to a level where the high temperature MESFETs developed for this investigation have shown an order-of-magnitude improvement in switching characteristics over conventional MESFETs at 350°C. These modifications include the introduction of a silicon nitride insulating layer between the metal layers and the substrate (to reduce inter-device conduction), the addition of an aluminum arsenide (AlAs) high resistivity buffer layer on the substrate (to reduce intra-device conduction), and the replacement of the standard source/drain metal contacts with a refractory high temperature ohmic metal system (to improve long-term reliability). Thus, with relatively minor modifications to a standard MESFET process, it has been demonstrated that high temperature MESFETs can be fabricated which possess the characteristics desired in future avionics systems where high temperature operation is required (i.e., smart-skins, and engine sensors/controllers)