THE EFFECT OF GATE-OXIDE PROCESS VARIATIONS ON THE LONG-TERM FADING OF PMOS DOSIMETERS

Radiation-sensitive field-effect transistors (RADFETs) have applicatio ns as integrating dosimeters in spacecraft, medicine and laboratories to measure the amount of dose absorbed from various radiation sources. The principal advantages that the RADFET has over more traditional fo rms of dosimeters is that it is small and provides continuous readout. However, all dosimetric media undergo some annealing or fading subseq uent to irradiation. Fading effects in PMOS dosimeters may be negative or positive, depending on the occurrence of reverse annealing. The ai m of this paper is to examine the effect of gate-oxide process variati ons on the long-term fading of the NMRC's PMOS dosimeter which has a d ry/wet/dry gate oxide. The necessity for this evaluation arises becaus e existing published results do not address the fading characteristics of dry/wet/dry oxides in the range 100-1000 nm. This paper clearly sh ows that for the NMRC's RADFET gate oxide an optimum set of processing conditions exists to minimize the dosimeter fading. The optimum proce ssing conditions for fade reduction are compared with those required t o maximize the radiation sensitivity of the dosimeter and the implicat ions of fading at high dosimeter operating temperatures are discussed.