Compensation-circuit to improve radiation-hardness in GaAs digital-circuits, based on X-ray studies

Earlier results have shown that GaAs devices do not exhibit appreciable degradation up to a radiation dose of nearly 10⁸ rad (GaAs). The results of this work suggest that GaAs devices and circuits are sensitive to radiation exposure at dose levels below 10⁸ rad(GaAs). Degradation was observed in E-MESFET and D-MESFET parameters and in circuit performance for devices which were designed and fabricated in a 1.2 μm GaAs process, when exposed to varying doses of 1.49 keV X-rays in the range 40-65 Mrad (GaAs). The degradation is attributed to the change in the properties of the MESFET channel region, caused by the transport of the atomic hydrogen from the passivation layer to the channel. A compensation circuit, based on the observed behavior of radiation effects on GaAs devices, has been designed to improve the radiation insensitivity of GaAs (E/D) based circuits under SPICE (Simulation Program with IC Emphasis) simulated conditions. Its usefulness is demonstrated through a DCFL inverter circuit up to nearly 10⁸ rad (GaAs) dose level. The results of this work can be used in the design of complex-function radiation-insensitive DCFL based circuits