The resistivity of an indium-gallium-zinc oxide (IGZO) thin film was found to depend on not only the conditions of its thermal annealing but also the oxygen-permeability of the cover film during the heat-treatment. Based on this observation, a technology for constructing a homojunction IGZO thin-film transistor (TFT) has been developed and demonstrated. In this device architecture, the junction and channel regions were capped respectively by impermeable and permeable covers. During a subsequent junction “activation” heat-treatment in an oxidizing atmosphere, the resistivity of the source and drain regions were greatly reduced; while the channel region, being exposed to the oxidizing atmosphere through the permeable cover, retained its highly resistive character. The permeable cover could serve additionally as an etch-stop during the removal of the impermeable cover over the channel region, thus preventing the region from being exposed to the etch.
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