VDMOSFET as a prospective dosimeter for radiotherapy.

Performance of a commercial p-channel power vertical-double-diffusion metal-oxide-semiconductor field-effect transistors (VDMOSFETs) as a γ-radiation dosimeters were studied. The devices were irradiated with 60 Co to 10-50Gy at the gate biases ranging from 0 to 5V, and subsequent dosimetric signal fading was monitored during room-temperature storage without a gate bias for 100 days. A linear relationship was found between the threshold voltage shift and the radiation dose for all values of the gate bias. Furthermore, a power-law relationship between the radiation sensitivity and the gate bias during the irradiation was revealed. The radiation sensitivity of these devices is higher than that of RADFETs with 100-nm-thick oxide gate layers manufactured by the Tyndall National Institute in Cork, Ireland. Room-temperature signal fading for VDMOSFETs is similar to that for RADFETs, i.e., the threshold voltage shift decreases slowly. A continuous annealing of VDMOSFETs at 150°C for 27 days results in a significant decrease of the threshold voltage shift, especially during the first 7 days.