ON-CHIP P-MOSFET DOSIMETRY

On-chip p-FETs were developed to monitor the radiation dose of n-well CMOS ICs by monitoring threshold voltage shifts due to radiation induc ed oxide and interface charge. The design employs closed geometry FETs and a zero-biased n-well to eliminate leakage currents. The FETs are operated using a constant current chosen to greatly reduce the FET's t emperature sensitivity. The dose sensitivity of these p-FETs is about -2.6 mV/krad(Si) and the off-chip instrumentation resolves about 400 r ad(Si)/bit. When operated with a current at the temperature-independen t point, it was discovered that the pre-irradiation output voltage is about -1.5 V which depends only on design-independent silicon material parameters. The temperature sensitivity is less than 63 mu V/degrees C over a 70 degrees C temperature range centered about the temperature insensitive point.