A radiation-resistant readout integrated circuit for focal plane arrays was studied to improve the reliability of infrared
image systems operating in a radioactive environment, such as in space or in the surroundings of a nuclear reactor. First,
as radiation-hardened NMOSFET structure, which includes a layout modification technique, was proposed. The readout
integrated circuit for infrared focal plane arrays was then designed on basis of the proposed NMOSFET layout.
Commercial 0.35 um process technology was used to fabricate the proposed unit NMOSFET and the designed readout
integrated circuit which is based on the proposed NMOSFET. The measured electrical characteristics of the fabricated
unit NMOSFET and readout integrated circuit are in good agreement with the simulated results. For verification of the
radiation tolerance, the fabricated chip was exposed to 1 Mrad (Si) of gamma radiation, which is high enough to
guarantee reliable usage in space or in a very harsh radiation environment. While exposed to gamma radiation, the
fabricated chip was connected to a power supply (3.3 V) for testing under the worst conditions. After being exposed to
1 Mrad of gamma radiation, the unit NMOSFET showed only a slight increment of a few picoamperes in the leakage
current, and the designed readout integrated circuit showed little change at an output voltage of less than 10% of a proper
output voltage. The changes in the characteristics of the unit NMOSFET and the designed readout infrared integrated
circuit are at an allowable level in relation to process variation.