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Stable and fast-switching thin-film transistors and circuits incorporating 5-nm-thick amorphous-InGaZnO (a-IGZO) active layers are demonstrated, and their dependence on channel length is studied. Turn-on voltage shifts in the positive gate voltage direction as the channel length increases. A low area density of defects in the bulk a-IGZO, which is ultrathin, results in good stability under positive bias stress, whereas interdiffusion of electrons/electron donors from the highly doped source and drain regions to the channel edges results in the dependence of turn-on voltage on channel length. Stable operation of an 11-stage ring oscillator is achieved with a propagation delay time of ∼97 μs/stage due to reduced gate-to-drain overlap capacitance and parasitic resistances. Index Terms-Amorphous InGaZnO (a-IGZO), inverter, ring oscillator, thin-film transistor (TFT), ultrathin.

This article presents the design and fabrication process of a two-dimensional hydrogenated amorphous silicon (a-Si:H) n-i-p photodiode array, developed for low light level sensor applications. Utilization of the single a-Si:H switching diode for signal readout enables simpler device design and fabrication. Since the sensing and switching diodes are formed simultaneously by dry etching the a-Si:H layers deposited over the whole area, the number of masks required in lithography was reduced to six. A significant reduction of the leakage current has been achieved by tailoring defects at the i-p interface and optimizing the plasma processing conditions. Details of device fabrication along with results of the sensor array performance are presented.

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Because of the inherent desired material and technological attributes such as low temperature deposition and high uniformity over large area, the amorphous silicon (a-Si:H) technology has been extended to digital X-ray diagnostic imaging applications. This paper reports on design, fabrication, and characterization of a MIS-type photosensor that is fully process-compatible with the active matrix a-Si:H TFT backplane. We discuss the device operating principles, along with measurement results of the transient dark current, linearity and spectral response.