Small dose effect in RADFET with thick gate oxide

Svetlana M Pejović; Milić M Pejović; Miloš Živanović

doi:10.1016/j.apradiso.2019.06.034

Small dose effect in RADFET with thick gate oxide

Appl Radiat Isot. 2019 Oct:152:72-77. doi: 10.1016/j.apradiso.2019.06.034. Epub 2019 Jun 23.

Authors

Svetlana M Pejović¹, Milić M Pejović², Miloš Živanović³

Affiliations

¹ Clinic for Radiooncology, University of Saarland, Homburg, 66421, Germany.
² University of Nis, Faculty of Electronic Engineering, Aleksandra Medvedeva 14, 18000, Nis, Serbia. Electronic address: milic.pejovic@elfak.ni.ac.rs.
³ Vinca Institute of Nuclear Science, University of Belgrade, PO Box 522, 11001, Belgrade, Serbia.

PMID: 31280110
DOI: 10.1016/j.apradiso.2019.06.034

Abstract

In order to track "small dose effect" leading to stabilization of RADFETs with 1 μm thick oxide fabricated at Tyndall National Institute, Cork, Ireland irradiation was performed with gamma-rays in the radiation dose interval from 1 to 5 cGy, followed with room temperature annealing for the time of 28 days. Gate bias during irradiation was 0, 2.5 and 5 V. Threshold voltage shift ΔV_T determined from transfer characteristics in saturation were followed during irradiation and annealing. It was shown that there is significant increase in ΔV_T for 1 cGy radiation dose and those are 36.3, 43.3 mV and 45.7 mV for gate bias 0, 2.5 V and 5 V, respectively. For higher radiation doses ΔV_T also increases, however, such increase is much lower. RADFETs fading at room temperature lead to permanent decrease in ΔV_T and after 28 days the threshold voltage for devices is returned to virgin device value. Small dose effect is confirmed and radiation dose of at least 5 cGy is necessary for RADFET stabilization before their use in dosimetric application. After RADFETs stabilization they were irradiated in dose interval from 10 to 50 cGy with gate bias of 0, 2.5 and 5 V. It was shown that there is a linear dependence between ΔV_T and absorbed radiation dose D, for gate bias during irradiation 0, 2.5 and 5 V. Defects responsible for threshold voltage shift, formed during irradiation as well as their neutralization/compensation during annealing, are also discussed.

Keywords: Absorbed radiation dose; Gamma ray irradiation; RADFET; Room temperature annealing; Threshold voltage shift.