On the Combined Effect of Silicon Oxide Thickness and Boron Implantation Under the Gate in MOSFET Dosimeters

The metal-oxide-semiconductor field-effect transistor (MOSFET) can be used as a dosimeter. It is robust, lightweight, cost-effective, is able to operate in real time with and without external bias, and also has a very small sensitive volume. Therefore, it is particularly suitable for in vivo dosimetry in modern radiation therapy and also as a patient dosimeter in diagnostic radiology. MOSFET sensitivity to ionizing radiation can be tailored to a specific application or a dose range. This is done by fabricating the radiation-sensitive volume of different thicknesses, or alternatively, by adjusting the external bias applied on the gate during irradiation. However, increased sensitivity comes at the cost of reduction in the MOSFET’s lifespan. This article investigated a way to maximize sensitivity while minimizing the reduction in lifespan. The MOSFETs we considered had a sensitive volume of thickness 0.68 or 1.0 $\mu \text{m}$ and different boron implantations under the gate. We then irradiated the MOSFETs by applying different positive biases on the gate. We assessed linearity of the dose-response relationship and sensitivity in photon beams that were produced using a megavoltage medical linear accelerator (linac) and an orthovoltage X-ray tube.