Radiation and Spontaneous Annealing of Radiation-sensitive Field-effect Transistors with Gate Oxide Thicknesses of 400 and 1000 nm

Abstract

We investigated the influence of gamma radiation of 50 Gy(H 2 O) on radiation-sensitive p-channel metal-oxide-semiconductor field-effect transistors with an Al gate (RADFETs) with gate oxide thicknesses of 400 and 1000 nm and gate voltages of 0 and 5 V. The obtained results showed that the sensitivity S at a given gate voltage increases with the square of the gate oxide thickness. After irradiation (IR), spontaneous annealing (SA) was performed at room temperature without voltage at the gate. We present the behaviors of fixed traps and switching traps, determined by the midgap technique, and that of fast switching traps, determined by the charge-pumping technique, during IR and SA. A very important characteristic of dosimetric transistors is fading, which represents the recovery of the threshold voltage of the irradiated RADFETs during SA. The maximum fading is about 15% after 9100 h, except for the RADFETs with a gate oxide thickness of 1000 nm and a gate voltage of 5 V, for which it is about 30%. A fitting equation for fading was proposed, which fitted the experimental fading values very well.

Fading of pMOS dosimeters over a long period of time

“…It was also shown [6] that S is proportional to t ox 2 (S ∼ t ox 2 ), which can be seen in Table 1. Namely, for a given V G,i , S 1000 /S 400 ≈ 6.25 = 2.5 2 .…”

“…It is shown [6] that ΔN ft decreases, but ΔN st increases during SA. At the beginning of SA, the small negative fading, as a consequence of a greater increase in STs than a decrease in FTs, can be seen in Figure 1 for two transistor types.…”

“…The results of IR are presented in reference [6]. It is shown that ΔV T is linear with D for used dose of 50 Gy (ΔV T = S⋅D, where S is the sensitivity of pMOS dosimeters; see Table 1).…”

“…In reference [6], the fading up to 9100 h (about 1 year) is investigated (as shown in Figure 1). Fading saturation was assumed and fading was well fitted by the proposed function [6].…”

“…In reference [6], the fading up to 9100 h (about 1 year) is investigated (as shown in Figure 1). Fading saturation was assumed and fading was well fitted by the proposed function [6]. However, further examination of the fading for 10 years shows a different behaviour, as also shown in Figure 1.…”