A dose rate independent pMOS dosimeter for space applications

A dual-dielectric pMOS dosimeter (RADFET) has been recently designed at Sandia. The RADFET consists of a thermally grown oxide and a CVD deposited nitride. With a negatively applied bias, holes are generated in the SiO/sub 2/ transport and are trapped at the SiO/sub 2//Si/sub 3/N/sub 4/ interface producing a measurable threshold-voltage shift. Because holes are trapped away from the Si/SiO/sub 2/ interface, hole neutralization by tunneling and interface-trap buildup are minimized resulting in little fade or annealing of the RADFET output response. RADFETs were irradiated at dose rates from 0.002 to 50 rad(Si)/s with biases from -5 to -20 V. RADFETs were also annealed for times up to 10/sup 7/ s at temperatures up to 100/spl deg/C. Within experimental uncertainty, no difference in RADFET output response at a given bias was observed over the dose rate range examined and for 25/spl deg/C anneals. At an anneal temperature of 100/spl deg/C only a 20% decrease in RADFET output response was observed. These results show that Sandia's RADFETs exhibit little or no fade of their output characteristics and are ideal for low dose rate space applications.