Introduction
Wireless real-time radiation sensors networks offer the general public and those that work in high radiation areas greater protection against radiation hazards. Combined with real-time localized and global heat mapping of radiation levels, these radiation networks will help give government and environmental agencies the ability to understand the radiation landscape and respond quickly to radiation changes before they become life-threatening. Low-cost, low-power and no-power radiation sensors, also known as RADFETs (radiation field effect transistors) or dosimeters, are necessary for the implementation of these networks. The RADFET is unique because it does not need a power source to detect radiation. It is also unique in that it records the amount of actual radiation exposure and, as a non-volatile analog memory device, stores the level of radiation exposure as a change in threshold voltage. RADFETs are relatively simple circuits, consisting of only a PMOS transistor. The LS 3N163 PMOS (P-Channel) MOSFET transistor can be used to design RADFETs to meet different design requirements like cost, sensitivity, linearity, and power. The ability to optimize a RADFET for these different design requirements give network designers the ability to construct wireless radiation sensor networks that can also be optimized for cost and performance on a wide scale. Radiation detector principles PMOS MOSFET radiation detectors work on the principle that electron-hole pairs form when radiation or an ionizing particle strikes the MOSFET. This in turn results in shifts to the threshold voltage and drain current parameters of the MOSFET device. Because the change in threshold voltage with radiation exposure is highly linear in a PMOS device, PMOS devices such as the LS 3N163 are commonly used as a radiation detector. In a typical application, the LS 3N163 is operated in unbiased mode (no-power mode) and exposed to radiation. The change in threshold voltage is then measured and the corresponding radiation exposure level determined. In another application, where higher levels of sensitivity are needed, the LS 3N163 is operated in biased mode (power mode).