A DOSE-RATE INDEPENDENT PMOS DOSIMETER FOR SPACE APPLICATIONS

A dual-dielectric pMOS dosimeter (RADFET) has been recently designed a t Sandia. The RADFET consists of a thermally grown oxide and a CVD dep osited nitride. With a negatively applied bias, holes generated in the SiO2 transport to and are trapped at the SiO2/Si3N4 interface produci ng a measurable threshold-voltage shift. Because holes are trapped awa y from the Si/SiO2 interface, hole neutralization by tunneling and int erface-trap buildup are minimized resulting in little fade or annealin g 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(7) s at temperatures up to 100 degre es C. Within experimental uncertainty, no difference in RADFET output response at a given bias was observed over the dose rate range examine d and for 25 degrees C anneals. At an anneal temperature of 100 degree s 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 applicati ons.