A semiconductor radiation dosimeter fabricated in 8-inch process

The radiation-sensitive field effect transistors (RADFET) radiation dosimeter is a type of radiation detector based on the total dose effects of the p-channel metal−oxide−semiconductor (PMOS) transistor. The RADFET chip was fabricated in United Microelectronics Center 8-inch process with a six-layer photomask. The chip including two identical PMOS transistors, occupies a size of 610 µ m × 610 µ m. Each PMOS has a W / L ratio of 300 µ m/50 µ m, and a 400 nm thick gate oxide, which is formed by a dry-wet-dry oxygen process. The wet oxygen-formed gate oxide with more traps can capture more holes during irradiation, thus significantly changing the PMOS threshold voltage. Pre-irradiation measurement results from ten test chips show that the initial average voltage of the PMOS is 1.961 V with a dispersion of 5.7%. The irradiation experiment is conducted in a cobalt source facility with a dose rate of 50 rad(Si)/s. During irradiation, a constant current source circuit of 10 µ A was connected to monitoring the shift in threshold voltage under different total dose. When the total dose is 100 krad(Si), the shift in threshold voltage was approximately 1.37 V, which demonstrates that an excellent radiation function was achieved.