Characteristics of GaAs MESFET inverters exposed to high energy neutrons

Abstract

GaAs MESFET circuits were exposed to high-energy neutrons with fluences ranging from 1*10/sup 14/ n/cm/sup 2/ to 2*10/sup 15/ n/cm/sup 2/. The reflections of discrete transistors, inverters, and ring oscillators were characterized at each fluence. While the MESFETs exhibit significant threshold voltage shifts and transconductance and saturation current degradation over this range of neutron fluences, an improvement in the DC characteristics of Schottky diode FET logic (SDFL) inverters was observed. This unusual result has been successfully simulated using device parameters extracted from FETs damaged by exposure to high-energy neutrons. Although the decrease in device transconductance results in an increase in inverter gate delay as reflected in ring oscillator frequency measurements, it is concluded that GaAs ICs fabricated from this logic family will remain functional after exposure to extreme neutron fluences. This is a consequence of the observed improvement in inverter noise margin evident in both measured and simulated circuit performance. >