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Abstract: We report on p-channel depletion mode organic inverter composed of two pentacene thin-film transistors (TFTs), which have different channel thickness each other. Adopting thin hydrophilic AlO x as dielectric, the 25nm-thin channel pentacene TFT showed lower threshold voltage (V TH) than that of 50nm-thick channel-TFT, while on hydrophobic poly-4-vinyphenol (PVP) dielectric the results became opposite. We utilized the different V TH caused by different channel thickness to operate the inverter that consists of driver- and load-TFTs. The 50nm-thick pentacene operated as the channel layer of driver-TFT on AlO x , but on PVP dielectric the 25nm-thin pentacene layer played as the driver channel. Maximum voltage gain of ∼22 under −8V supply voltage was achieved when the dielectric layer was optimized. [Copyright &y& Elsevier]

Abstract: We report on the surface-induced time-dependent instability of ZnO based thin-film transistors (ZnO-TFTs) with interdigitated source/drain (S/D) electrodes. As time elapsed, a considerable shift of threshold voltage (V T) was observed (by ~−16 V) from our TFT. Contact angle of de-ionized water on ZnO surface also changed from 30° to 110°, revealing time-dependent surface state change. According to X-ray photoemission spectroscopy (XPS) measurements, the Zn 2p3/2 core-level peak and the valence band maximum (VBM) of aged ZnO surface shifted to the higher binding energy by 0.3 eV, which implies a downward energy band bending of the ZnO back channel-surface. We conclude that without passivation layer any bottom gate ZnO-TFT meets the surface-induced electrical instabilities due to the time-dependent conductance of ZnO surface. [Copyright &y& Elsevier]

Abstract: We report on the fabrication of ultraviolet (UV)-sensing top-gate ZnO thin-film transistors (TFTs) with a poly-4-vinylphenol (PVP) polymer gate dielectric on glass substrate. Our top-gate ZnO-TFT showed a field-effect mobility of 0.05cm2/Vs, maximum saturation current of 0.11μA at a gate bias of 10V and an on/off ratio of ∼103 in the dark. Under UV illumination with a wavelength of 364nm the ZnO-TFT exhibited ∼4.7μA for a drain current (at the same gate bias of 10V), which is ∼50 times higher than without UV. Such photo-transistor action appeared more pronounced under a depletion regime of 0V gate bias and the photo-to-dark current ratio was more than about 104. By adopting this high UV-sensitivity, our inverter device with the top-gate ZnO-TFT and a load resistance well demonstrated its optical gating behavior. [Copyright &y& Elsevier]

Trap density of states (DOS) for two amorphous-InGaZnO thin-film transistors are measured by photoexcited charge-collection spectroscopy (PECCS); free charges trapped at a certain energy level are liberated by the corresponding energetic photons and then electrically collected at the source/drain electrodes. During this photoelectric process, the threshold voltage of TFT shifts and its magnitude provides the DOS information of charge traps. According to the PECCS analysis, the TFT with a channel deposited under high sputtering power appeared more stable than the other device prepared with low sputtering power, showing even less than \sim\!\!\10^10\ \cm^-2 as its totally integrated trap density. [ABSTRACT FROM PUBLISHER]

Abstract: Semi-transparent organic–inorganic hybrid photo-detector cells were fabricated on glass substrate, composed of pentacene/ZnO photodiodes and pentacene thin-film transistors (TFTs). Semi-transparent NiO x window with a large band gap of ∼4eV was used as an ohmic electrode on 50nm-thin pentacene channel in the TFT and simultaneously on the 150nm-thick pentacene layer, which is deposited on ZnO for p–n diode, to absorb visible and ultraviolet photons from pentacene and ZnO, respectively. Our photo-detector exhibited a minimum temporal response of ∼300ms for photo-induced output voltage at −1V input and −3V supply voltage. [Copyright &y& Elsevier]