Sensitivity of RADFET for gamma and X-ray doses used in medicine

Abstract

In this paper, the results of radiation sensitive field effect transistors (Al-gate p-channel metal-oxide-semiconductor field effect transistors) sensitivity to gamma and X-ray irradiation are presented. Radiation fields were created using 60Co source for three dose ranges (0-1 Gy, 0-5 Gy, and 0-50 Gy), as well as X-ray unit of 280 kVp spectrum for a single dose range from 0 to 5 Gy. The sensitivity was characterized by the threshold voltage shift, determined from reader circuit measurements, as a function of absorbed radiation dose. It was shown that for the three dose ranges of gamma radiation, as well as for the X-ray range from 0 Gy to 5 Gy there is approximately a linear dependence between threshold voltage shift DVT and radiation dose D. The application of positive bias of +5 V at the RADFET gate during irradiation, for these ranges of gamma radiation, also for X-ray dose range, leads to the increase in DVT and also, approximately a linear dependence between DVT and D, is established. Moreover, it was shown that the sensitivity of RADFET is much higher in the case of X-ray irradiation then in the case of gamma-ray irradiation for the same dose range. [Projekat Ministarstva nauke Republike Srbije, br. 171007]

Application of pMOS Dosimeters in Radiotherapy

“…This is a consequence of different photon energies which lead to ionization of SiO 2 molecules. Namely, X-ray photons energy of 140 keV lead to molecule ionization by both photo effect and Compton's effect, while gamma-ray photons with energies of 1.17 and 1.33 MeV lead to SiO 2 molecules ionization only by Compton's effect [38]. A direct change in Δ V T values is caused by a larger number of FT and ST, which are formed during X-ray irradiation compared to gamma-ray irradiation, the reason being the probability for molecule ionization by photoeffect is significantly higher than by Compton's effect.…”

“…Sensitivity represents threshold voltage shift Δ V T and radiation dose D ratio ( Δ V T / D ) and could be controlled by the gate bias during irradiation. It is well known [37,38] that an increase in sensitivity could be achieved with increase in gate bias during irradiation. In the case of positive gate bias, the sensitivity is higher, than in the case of negative gate bias and the lowest sensitivity being for zero gate bias [20].…”

“…In the case of positive gate bias, the sensitivity is higher, than in the case of negative gate bias and the lowest sensitivity being for zero gate bias [20]. Moreover, sensitivity increase can be achieved by increasing the gate oxide thickness [36][37][38][39] and by processing conditions which determine the FT density, their capture cross section and their location as well as the ST density [40].…”

“…Experimental data fitting using Eq. (2) Figure 9 shows the threshold voltage shift Δ V T as a function of radiation dose D for 1 μm gate oxide thickness pMOS dosimeters irradiated with gamma-rays which originates from 60Co and X-ray with energy 140 keV in dose range from 0 to 1 Gy for gate bias during irradiation 35,38]. Experimental results fitting using Eq.…”

Application of pMOS dosimeters in low-field mode for radiation dose measurements which could be used in radiotherapy

“…As for gate bias dur ing ir ra di a tion V irr > 0, a large number of holes will es cape the ini tial re-com bi na tion, further in creas ing the prob a bil ity of an in crease in pos itive trapped charge in the ox ide and in ter face traps which, there fore, leads to the in crease in DV T . It is shown [24][25][26] that pos i tive gate bias dur ing ir ra di ation leads to a more lin ear re sponse of MOSFET dosim e ters. More over, the sen si tiv ity of MOSFET dosim e ters can also be in creased with the in crease in ox ide layer thick ness [27,28].…”