Abstract
MOSFET can operate as a radiation detector mainly in high-energy photon beams that are normally used in cancer treatments. In general, such an electronic device can work as a dosimeter from the threshold voltage shift measurements. The purpose of this paper is to show a new way for measuring the dose response of MOSFETs when they are under an X-ray beam generated from a 100-kV potential range, which is normally used in diagnostic radiology. Basically, the method consists of measuring the MOSFET drain current as a function of the radiation dose. For this type of device, it has to be biased with a high-value resistor aiming to see a substantial change in the drain current after it has been irradiated with an amount of radiation dose. Two types of n-channel devices were used in the experiment: a signal transistor and a power transistor. The delivered dose to the device was varied, and the electrical curves were plotted. In addition, a sensitivity analysis of the power MOSFET response was made by varying the tube potential of about 20%. The results show that both types of devices have very similar responses, and the shift in the electrical curve is proportional to the radiation dose. Unlike the power MOSFET, the signal transistor does not provide a linear function between the dose rate and its drain current. We have also observed that the variation in the tube potential of the X-ray equipment produces a very similar dose response.
Highlights
MOSFET has been used for many years as a radiation detector mainly in high-energy photon beams, which are normally used in cancer treatments
The purpose of this article is to show a new way for measuring the dose-response of typical MOSFETs when they are under X-ray beam generated from 100kV potential, that is, an energy range which is normally used in diagnostic radiology
Unlike the known conventional method for measuring the radiation dose, from the threshold voltage measurements, this paper brings an innovative measurement process, which consists of evaluating the drain current of the MOSFET
Summary
MOSFET has been used for many years as a radiation detector mainly in high-energy photon beams, which are normally used in cancer treatments. The MOSFETs are being used to measure the dose in X-ray beams of the diagnostic radiology energy range. Notice that the drain current depends on the resistor value, i.e., the saturation point can be changed. If we choose another resistor with the thousand times lower value, the saturation point naturally goes to ID=50 mA at VGS=2.9 V. As it will be seen later, there are some considerations that must be taken into account both in the choice of MOSFET bias, type of transistor, and the spectrum of radiation to be measured
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