Radiation effects on n-channel polycrystalline silicon thin-film transistors

Abstract

The radiation effect on the n-channel polycrystalline silicon (polysilicon) thin-film transistors has been investigated. It is found that for an unhydrogenated device, the irradiation of Co60 with a total dose of 1 Mrads caused a negative threshold-voltage (Vth) shift and a slight subthreshold-swing (S) degradation, while for a hydrogenated n-channel device, the same irradiation results in a positive Vth shift and a serious S degradation. It is also found that the radiation hardness of the hydrogenated devices can be improved somewhat by a simple irradiation-then-hydrogenation treatment.

Effects of x-ray irradiation on polycrystalline silicon, thin-film transistors

“…In general, the measured effects of radiation on ELA poly-Si TFTs in the present study are more significant than effects observed in earlier studies on SPC poly-Si TFTs 25 and a-Si TFTs. 21 For example, 4%-5% reductions in mobility were found for the ELA poly-Si TFTs after ϳ1 kGy, while similar percentage reductions were observed for SPC poly-Si and a-Si TFTs only after receiving much higher doses ͑several kilograys and more than 20 kGy, respectively͒.…”

“…The effects of radiation of various types of solid-phase crystallized ͑SPC͒ poly-Si TFTs at a single dose ͑equivalent to ϳ10 000 Gy͒ has been reported in an earlier study by Yang et al 25 However, poly-Si TFTs fabricated by ELA, the presently preferred method, 9,26 exhibit significantly different structure ͑i.e., much larger grain size͒ and better properties ͑e.g., higher mobility and sharper turn on͒. It is therefore interesting to examine the radiation-induced effects on ELA poly-Si TFTs, which are critical to the above-mentioned applications, but are still largely unknown.…”

Hydrogenated n-Channel Low Temperature Polycrystalline Silicon TFTs as Ultraviolet Dosimeters

“…The positive shift of Vth and degradation of eff and SS should be caused by the generation of additional defect traps in the poly-Si channel and at the poly-Si/SiO2 interface. For n-channel devices, these traps are generally acceptor-like and thus negatively charged after band bending, which lead to the positive Vth shift [10], [22]. The eff drop can be explained by the enhancement of grain boundary barrier height of LTPS-TFT channel by UV irradiation.…”

“…In this work, we investigate this idea by irradiating hydrogenated n-channel LTPS-TFTs with UV light to a cumulative dose of 16 J/cm 2 . Some reports showed that hydrogenated TFT devices are more vulnerable to irradiation [10], [11], because the silicon hydrogen bonds (Si-H) are easily broken during irradiation. The application of MOSFET dosimeter is based on converting the threshold voltage shift (Vth), induced by radiation, into the radiation dose (D).…”

Defect generation in non-nitrided and nitrided sputtered gate oxides under post-irradiation Fowler–Nordheim constant current stress

“…There is significant interest for implementation of thin film transistors (TFTs) in irradiation environment [1][2][3][4]. Generally, there is insufficient research in this direction, including gate insulator which is the most sensitive component of TFTs [5,6].…”