Abstract
We investigate the origin of visible-light-induced instability in amorphous metal-oxide based thin film transistors (oxide-TFTs) for transparent electronics by exploring the shift in threshold voltage (Vth). A large hysteresis window in amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs possessing large optical band-gap (≈3 eV) was observed in a visible-light illuminated condition whereas no hysteresis window was shown in a dark measuring condition. We also report the instability caused by photo irradiation and prolonged gate bias stress in oxide-TFTs. Larger Vth shift was observed after photo-induced stress combined with a negative gate bias than the sum of that after only illumination stress and only negative gate bias stress. Such results can be explained by trapped charges at the interface of semiconductor/dielectric and/or in the gate dielectric which play a role in a screen effect on the electric field applied by gate voltage, for which we propose that the localized-states-assisted transitions by visible-light absorption can be responsible.
Highlights
Such results can be explained by trapped charges at the interface of semiconductor/dielectric and/or in the gate dielectric which play a role in a screen effect on the electric field applied by gate voltage, for which we propose that the localized-states-assisted transitions by visible-light absorption can be responsible
S.S = qKBT (Nttc + Dit) Cox log(e) where kB is the Boltzmann constant, T is the temperature, Cox is the capacitance per unit area of gate dielectric, Dit is the density of interfacial trap states, Nt is the density of bulk trap states and tc is the thickness
It must be noted that photo-induced hysteresis was not appreciably suppressed in amorphous indiumgallium-zinc-oxide (a-IGZO) TFTs encapsulated with a passivation layer of SiNx/SiO2, which is quite unlike results from reported papers.[18,19]
Summary
Outstanding electrical characteristics of metal-oxide semiconductor based thin-film transistors (oxide-TFTs) have been shown to be promising for various electronic applications requiring high field-effect mobilities, low threshold voltage, good on-off current ratio.[1,2,3,4] Significantly, low-temperature and large-area processes of oxide-TFTs compatible with flexible substrates have been of technical interest in next-generation electronics possessing excellent device uniformity and stability as contrasted with conventional TFTs consisting of hydrogenated amorphous silicon and polycrystalline silicon.[5,6,7,8,9]Since the major expectation of oxide-TFTs lies on photo-insensitivity which promotes the aperture ratio with high current driving capability, undesired variation in device key metrics under visible-light irradiation in oxide-TFTs leads to failure in overall system operations.[10,11,12,13] Most of reported papers have focused on the effect of ultra violet (UV) irradiation on device performance in amorphous oxide-TFTs.[10,11,12,13,14,15,16] the optical band transitions in metal-oxide semiconductor possessing the optical band-gap of around 3 eV are obviously expected in the UV spectrum. Visible-light-induced instability in amorphous metal-oxide based TFTs for transparent electronics
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