On-chip p-MOSFET dosimetry [CMOS ICs]

On-chip p-FETs were developed to monitor the radiation dose of n-well CMOS ICs by monitoring threshold voltage shifts due to radiation-induced 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 temperature sensitivity. The dose sensitivity of these p-FETs is about -2.6 mV/krad(Si) and the off-chip instrumentation resolves about 440 rad(Si)/b. When operated with a current at the temperature-independent point, it was discovered that the preirradiation output voltage is about -1.5 V, which depends only on design-independent silicon material parameters. The temperature sensitivity is less than 63 μV/°C over a 70°C temperature range centered about the temperature-insensitive point