18 MV-Harici Demet ile RadFET Radyasyon Sensörü Performansının Değerlendirilmesi

Abstract

Lineer hızlandırıcıdan yayılan 18 MV’luk X-ışınları ile ışınlanan RadFET’lerin radyasyon cevapları, eşik voltaj kaymaları ve tuzak yoğunlukları üzerinden incelenmiştir. Işınlamadan önce ve sonra eşik voltajları ölçülerek karşılaştırılmıştır. Çeşitli teknikler kullanılarak kapı oksitinde ve oksit/silikon arayüzeyinde hesaplanan tuzak yoğunlukları değerlendirilmiştir. ΔVth – D grafiği, yaklaşık 2 Gy’e kadar mükemmel doğrusallık göstermiştir. RadFET’in radyasyon cevabı, elektrik alan perdelemesi tarafından uyarılan oksit tuzak yüklerinin artmasıyla 2 Gy sonrasında doğrusallıktan sapmaya başlamıştır. Deneysel sonuçlar, RadFET’ler için verilen fit fonksiyonuyla iyi bir uyum içindedir. Işınlama sonucunda oluşan sabit ve anahtarlama tuzakları incelenmiştir. Sabit tuzakların yoğunluğu, anahtarlama tuzaklarının yoğunluğundan önemli bir miktar daha yüksek olarak bulunmuştur. Sıfır kapı voltajı altında ölçülen eşik voltajlarından yüzde zayıflama aralığı %0.004 – %1.235 olarak hesaplanmıştır.

Keywords

• RadFET,Radyasyon Cevabı,Radyoterapi

EVALUATION OF THE RadFET RADIATION SENSOR PERFORMANCE IN 18 MV-EXTERNAL BEAM

Abstract

The radiation response of RadFET irradiated with 18 MV X-rays emitted from a linear accelerator was examined on threshold voltage shifts and trap densities. The measured threshold voltages were compared before and after irradiation. Trap densities calculated using various techniques in the gate oxide and oxide/silicon interface were interpreted. The ΔVth – D graph showed excellent linearity of up to just about 2 Gy. The RadFETs response to radiation started to deviate from linearity after 2 Gy due to increasing oxide trapped charges induced by electric field screening. The experimental outcomes are in good accordance with the fitting function given for RadFETs. Fixed and switching traps formed by irradiation were investigated. The density of the fixed traps was significantly higher than the density of the switching traps. From the threshold voltages measured under zero gate voltage in a certain time interval, the percentage fading range was calculated as 0.004-1.235%.

Keywords

• RadFET,Radiation Response,Radiotherapy

References

1. Andjelkovic, M.S., Ristic, G.S. and Jaksic, A.B. (2015) Using RADFET for the real-time measurement of gamma radiation dose rate, Measurement Science and Technology, 26, 025004. doi: 10.1088/0957-0233/26/2/025004
2. Brugler, J.S. and Jespers, P.G.A. (1969) Charge pumping in MOS devices, IEEE Transactions on Electron Devices, 16, 297-302. doi: 10.1109/T-ED.1969.16744
3. Fröhlich, L., Casarin, K., Quai, E., Holmes-Siedle, A., Severgnini, M. and Vidimari, R. (2013) Online monitoring of absorbed dose in undulator magnets with RADFET dosimeters at FERMI@Elettra, Nuclear Instruments and Methods in Physics Research A, 703, 70-79. doi: 10.1016/j.nima.2012.11.021
4. Groeseneken, G., Maes, H.E., Beltran, N. and De Keersmaecker, R.F. (1984) A reliable approach to charge-pumping measurements in MOS transistors, IEEE Transactions on Electron Devices, 31, 42-53. doi: 10.1109/T-ED.1984.21472
5. Holmes-Siedle, A. and Adams, L. (1986) RADFETs: a review of use of metal/oxide/silicon devices as integrating dosimeters, Radiation Physics and Chemistry, 28, 235-244. doi: 10.1016/1359-0197(86)90134-7
6. Holmes-Siedle, A., Ravotti, F. and Glaser, M. (2007) The dosimetric performance of RadFETs in radiation test beams, IEEE Radiation Effects Data Workshop, 42-57. doi: 10.1109/REDW.2007.4342539
7. Jaksic, A., Ristic, G., Pejovic, M., Mohammadzadeh, A. and Lane, W. (2002) Characterization of radiation response of 400 nm implanted gate oxide RADFETs, 23rd International conference on microelectronics, 727-730. doi: 10.1109/MIEL.2002.1003360
8. Kahraman, A., Kaya, S., Jaksic, A. and Yilmaz, E. (2015) A comprehensive study on the photon energy response of RadFET dosimeters using the PENELOPE Monte Carlo code, Radiation Effects and Defects in Solids, 170:5, 367-376. doi: 10.1080/10420150.2015.1010167

9. Lu, L., Wang, M. and Wong, M. (2011) A new observation of the Elliot curve waveform in charge pumping of poly-Si TFTs, IEEE Electron Device Letter, 32, 506-508. doi: 10.1109/LED.2010.2104311
10. Martinez-Garcia, M.S., Torres del Rio, J., Palma, A.J., Lallena, A.M., Jaksic, A. and Carvajal, M.A. (2015) Comparative study of MOSFET response to photon and electron beams in reference conditions, Sensors and Actuators A, 225, 95-102. doi: 10.1016/j.sna.2015.02.006
11. McWhorter, P.J. and Winokur, P.S. (1986) Simple technique for separating the effects of interface traps trapped-oxide charge in metal-oxide-semiconductor transistors, Applied Physics Letters, 48, 133-135. doi: 10.1063/1.96974
12. O’Connell, B., Kelleher, A., Lane, W. and Adams, L. (1996) Stacked RADFETs for increased radiation sensitivity, IEEE Transactions on Nuclear Science, 43, 985-990. doi: 10.1109/23.510744
13. O’Connell, B., McCarthy, C., Lane, B. and Mohammadzadeh, A. (1999) Optimised stacked RADFETs for micro-gray dose measurement, Fifth European Conference on Radiation and Its Effects on Components and Systems, 101-105. doi: 10.1109/RADECS.1999.858553
14. Paulsen, R.E., White, M.H. (1994) Theory and application of charge pumping for the characterization of Si-SiO2 interface and near interface oxide traps, IEEE Transactions on Electron Devices, 41, 1213-1216. doi: 10.1109/16.293349
15. Pejovic, M.M., Pejovic, M.M. and Jaksic, A.B. (2012) Contribution of fixed oxide traps to sensitivity of pMOS dosimeters during gamma ray irradiation and annealing at room an elevated temperature, Sensors and Actuators A, 174, 85-90. doi: 10.1016/j.sna.2011.12.011
16. Pejovic, M.M. (2017) Process in radiation sensitive MOSFETs during irradiation and post irradiation annealing responsible for threshold voltage shift, Radiation Physics and Chemistry, 130, 221-22. doi: 10.1016/j.radphyschem.2016.08.027
17. Ristic, G., Golubovic, S. and Pejovic, M. (1996) Sensitivity and fading of pMOS dosimeters with thick gate oxide, Sensors and Actuators A, 51, 153-158. doi: 10.1016/0924-4247(95)01211-7
18. Ristic, G.S. (2009) Thermal and UV annealing of irradiated pMOS dosimetric transistors, Journal of Physics D: Applied Physics, 42, 135101. doi: 10.1088/0022-3727/42/13/135101
19. Ristic, G., Vasovic, N.D., Kovacevic, M. and Jaksic, A.B. (2011) The sensitivity of 100 nm RADFETs with zero gate bias up to dose of 230 Gy(Si), Nuclear Instruments and Methods in Physics Research Section B, 269, 2703-2708. doi: 10.1016/j.nimb.2011.08.015
20. Ristic, G.S., Andjelkovic, M. and Jaksic, A.B. (2015) The behavior of fixed and switching oxide traps of RADFETs during irradiation up to high absorbed doses, Applied Radiation and Isotopes, 102, 29-34. doi: 10.1016/j.apradiso.2015.04.009
21. Stamenkovic, Z., Vasovic, N.D. and Ristic, G.S. (2014) Automatic and reliable electrical characterization of MOSFETs, IEEE 17th International Symposium on Design and Diagnostics of Electronic Circuits & Systems. doi:10.1109/DDECS.2014.6868804
22. Vasovic, N.D. and Ristic, G. (2012) A switching system based on microcontroller for successive applying of MGT and CPT on MOSFETs, Measurement, 45, 1922-1926. doi: 10.1016/j.measurement.2012.03.011
23. Yilmaz, E., Kahraman, A., McGarrigle, A.M., Vasovic, N., Yegen, D. and Jaksic, A. (2017) Investigation of RadFET response to X-ray and electron beams, Applied Radiation and Isotopes, 127, 156-160. doi: 10.1016/j.apradiso.2017.06.004