Abstract
The electrical properties of p-channel low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) under deep ultraviolet (UV) irradiation were studied. Characteristics including threshold voltage (Vth), hole field effect mobility (μeff) subthreshold swing (SS), and leakage current (Ioff) were investigated as a function of UV irradiation doses from 4 to 20 J/cm2. With an increase in UV irradiation dosage, the Vth shift of the TFT showed a turnaround effect, which first shifted to the positive direction and then shifted back to the negative direction after a UV irradiation dose of 16 J/cm2. The continuous degradation of SS and μeff was discovered with the enhancement of UV irradiation dose. To better understand the physical mechanisms underlying these characteristic changes, UV induced traps at poly-Si grain boundaries, traps at the poly-Si and gate oxide insulator (poly-Si/SiO2) interface, and trapped charges in the gate oxide were studied with a function of UV irradiation doses.
Highlights
In recent years, high-resolution flat panel displays (FPDs) have been in high demand in the market since it is predicted that over 1000 ppi displays will be used in the generation of smartphones and VR.1–3 According to Rayleigh’s equations, UV exposure light with shorter wavelengths will contribute to higher resolution
We systematically studied the effects of UV irradiation doses on the properties of p-channel low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs), including threshold voltage (Vth), hole field effect mobility, subthreshold swing (SS), and leakage current (Ioff)
At a UV irradiation dose of 20 J/cm2, the increase in UV induced poly-Si grain boundary traps resulted in the addition of gate-induced drain leakage (GIDL) current,14,15 which might exceed the effect of drain junction electric field reduction by the gate oxide trapped negative charges
Summary
High-resolution flat panel displays (FPDs) have been in high demand in the market since it is predicted that over 1000 ppi displays will be used in the generation of smartphones and VR. According to Rayleigh’s equations, UV exposure light with shorter wavelengths will contribute to higher resolution. According to Rayleigh’s equations, UV exposure light with shorter wavelengths will contribute to higher resolution. Using deep UV exposure light is one way to achieve high resolution while keeping a sufficient depth of focus (DOF).. For conventional FPD exposure tools, the high wavelength region (350–450 nm) is usually used as exposure light. Yabu et al reported that a resolution of 1.0 μm can be achieved with a sufficient DOF by using 290 nm UV as exposure light.. Since the wavelength of exposure light was reduced to the deep UV region, it is important to study the effect of deep UV irradiation on the electrical performance of p-channel LTPS TFTs. In this study, 290 nm UV light was chosen as the deep UV illumination source. Scitation.org/journal/adv at the poly-Si/SiO2 interface, and trapped charges in the gate oxide insulator
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