Characteristics of GaAs buffered FET logic (BFL) MESFETs and inverters exposed to high-energy neutrons

A systematic investigation of the effects of high-energy neutrons on GaAs metal-semiconductor field-effect transistors (MESFETs) and buffered FET logic (BFL) gates has been carried out. Discrete transistors, inverters, and ring oscillators were characterized and modeled as a function of neutron fluence. Measurements were made of the threshold voltage shifts, the transconductance degradation, and saturation current degradation of GaAs depletion mode MESFETs, which comprise the BFL logic gates, irradiated with neutron fluences ranging from 5×10¹³ n/cm² to 2×10¹⁵ n/cm² (for particle energies above 10 keV). The threshold voltage was found to shift positively by 0.45 V, the transconductance decreased to 3%, and the saturation current to 1% of their unirradiated values at the highest neutron fluence (2×10¹⁵ n/cm²). The BFL inverter characteristics were measured and successfully simulated with SPICE using device parameters extracted from the neutron-damaged FETs. Ring oscillator measurements were made to determine the effects of high-energy neutrons on the frequency performance of BFL circuits. The ring oscillator frequency decreased to 9% of its unirradiated value at the highest neutron fluence