Characteristics of GaAs DCFL MESFET's and inverters exposed to high energy neutrons

This paper reports on a systematic investigation of the effects of high-energy neutrons on GaAs metal-semiconductor field effect transistors (MESFET's) and direct coupled FET logic (DCFL) gates. Measurements were made of the threshold voltage shifts and the transconductance and saturation current degradation of GaAs enhancement and depletion mode MESFET's, which comprise the DCFL logic gates, at neutron fluences ranging from 5 x 1013 - 2 x 1015 n/cm2 (E>keV). DCFL inverter characteristics were measured and successfully simulated with simulation program with integrated circuit emphasis (SPICE) using device parameters extracted from the neutron damaged FET's. Ring oscillator measurements were made to determine the effects of high-energy neutrons on the frequency performance of DCFL circuits. Measurements confirm that propagation delays scale inversely with the device transconductance. The results of this investigation are useful in predicting how GaAs IC's, fabricated using DCFL logic, will perform in a high-energy neutron environment