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. 2023 Apr 6;23(7):3771.
doi: 10.3390/s23073771.

General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams

J A Moreno-Pérez  1 , I Ruiz-García  1 , P Martín-Holgado  2 , A Romero-Maestre  2 , M Anguiano  3 , R Vila  4 , M A Carvajal  1
Affiliations

General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams

J A Moreno-Pérez et al. Sensors (Basel). .

Abstract

A commercial pMOS transistor (MOSFET), 3N163 from Vishay (USA), has been characterized as a low-energy proton beam dosimeter. The top of the samples' housing has been removed to guarantee that protons reached the sensitive area, that is, the silicon die. Irradiations took place at the National Accelerator Centre (Seville, Spain). During irradiations, the transistors were biased to improve the sensitivity, and the silicon temperature was monitored activating the parasitic diode of the MOSFET. Bias voltages of 0, 1, 5, and 10 V were applied to four sets of three transistors, obtaining an averaged sensitivity that was linearly dependent on this voltage. In addition, the short-fading effect was studied, and the uncertainty of this effect was obtained. The bias voltage that provided an acceptable sensitivity, (11.4 ± 0.9) mV/Gy, minimizing the uncertainty due to the fading effect (-0.09 ± 0.11) Gy was 1 V for a total absorbed dose of 40 Gy. Therefore, this off-the-shelf electronic device presents promising characteristics as a dosimeter sensor for proton beams.

Keywords: dosimetry; general purpose MOSFET; proton beams.

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Conflict of interest statement

The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Tandem accelerator (left), and experimental setup showing the irradiation chamber, the reader unit, and the control computer (right).
Figure 2
Figure 2
(a) Two MOSFET samples placed on the holder. (b) Detail of the housing modification showing the silicon die of the MOSFET. (c) Silicon die image obtained with the profilometer SNeox.
Figure 3
Figure 3
Sensor module configurations at different states: (a) Storage mode. (b) Sensing mode. (c) Readout of VS. (d) Readout of VF.
Figure 4
Figure 4
Measurement chronogram: In blue the source voltage is displayed; in green the gate voltage of the MOSFET; in red the gate voltage of the JFET_GD and, in yellow, the gate voltage of the JFET_SD.
Figure 5
Figure 5
(a) Source voltage (black dots) of sample #4 biased by an external voltage of 1 V and VF in mV (grey dots), during six irradiation shoots and rest periods. (b) Accumulated source voltage shift as a function of the accumulated dose (empty symbols) and line showing the least squared linear fitting. The sensitivity per irradiation shot is shown by solid symbols.
Figure 5
Figure 5
(a) Source voltage (black dots) of sample #4 biased by an external voltage of 1 V and VF in mV (grey dots), during six irradiation shoots and rest periods. (b) Accumulated source voltage shift as a function of the accumulated dose (empty symbols) and line showing the least squared linear fitting. The sensitivity per irradiation shot is shown by solid symbols.
Figure 6
Figure 6
Average sensitivity as a function of the bias voltages (coverage factor k = 1). Symbols represent experimental data and the line indicates linear fitting.
Figure 7
Figure 7
Source voltage increment during three irradiation shots of three samples biased at different gate voltages.
Figure 8
Figure 8
Fading quantified as the difference between the value of Vs at the end of the irradiation at 40 Gy and the value of the source voltage 5 min later. The coverage factor is k = 1. The symbols represents experimental data and the line indicates linear fitting.
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