Characteristics of GaAs heterojunction FETs (HFETs) and source follower FET logic (SFFL) inverters exposed to high energy neutrons

GaAs heterojunction field-effect transistors (HFETs) and inverters and ring oscillators comprising HFETs have been exposed to neutron fluences of 5*10/sup 13/ n/cm/sup 2/ to 1*10/sup 15/ n/cm/sup 2/ to evaluate the characteristics of HFET integrated circuits in a high-energy-neutron environment. The HFETs exhibited preirradiation transconductances of approximately 120 mS/mm and threshold voltages of -0.82 V. The degree of transconductance degradation is similar to that observed in ion-implanted GaAs MESFETs, but the magnitude of the HFET threshold shift is significantly smaller. The neutron-induced threshold shift in GaAs HFETs has been modeled, including the effect of pinning the Fermi level at the semi-insulating boundary. Neutron bombardment of source-follower FET logic (SFFL) inverters and ring oscillators results in a reduction in high noise margin and an increase in low noise margin with 35% reduction in ring oscillator frequency at 1*10/sup 15/ n/cm/sup 2/. These results indicate that more complex HFET SFFL circuits should remain functional at high neutron fluences.<
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