Display device

Abstract

A protective circuit includes a non-linear element, which further includes a gate electrode, a gate insulating layer covering the gate electrode, a pair of first and second wiring layers whose end portions overlap with the gate electrode over the gate insulating layer and in which a conductive layer and a second oxide semiconductor layer are stacked, and a first oxide semiconductor layer which overlaps with at least the gate electrode and which is in contact with side face portions of the gate insulating layer and the conductive layer of the first wiring layer and the second wiring layer and a side face portion and a top face portion of the second oxide semiconductor layer. Over the gate insulating layer, oxide semiconductor layers with different properties are bonded to each other, whereby stable operation can be performed as compared with Schottky junction. Thus, the junction leakage can be decreased and the characteristics of the non-linear element can be improved.

Description

TECHNICAL FIELD[0001]The present invention relates to a display device including an oxide semiconductor.BACKGROUND ART[0002]A thin film transistor formed over a flat plate such as a glass substrate is manufactured using amorphous silicon or polycrystalline silicon, as typically seen in a liquid crystal display device. A thin film transistor manufactured using amorphous silicon has low field effect mobility, but such a transistor can be formed over a glass substrate with a larger area. On the other hand, a thin film transistor manufactured using polycrystalline silicon has high field effect mobility, but a crystallization step such as laser annealing is necessary and such a transistor is not always suitable for a larger glass substrate.[0003]In view of the foregoing, attention has been drawn to a technique by which a thin film transistor is manufactured using an oxide semiconductor, and such a transistor is applied to an electronic device or an optical device. For example, Patent Doc...

AI Technical Summary

Benefits of technology

[0006]A thin film transistor in which a channel formation region is formed using an oxide semiconductor has characteristics as follows: the operation speed is higher than that of a thin film transistor including amorphous silicon and the manufacturing process is simpler than that of a thin film transistor including polycrystalline silicon. That is, the use of an oxide semiconductor makes it possible to manufacture a thin film transistor with high field effect mobility even at low temperatures of 300° C. or lower.

[0009]In a display device intended for a variety of purposes manufactured by stacking, in addition to an oxide semiconductor, an insulating film and a conductive film, an object of an embodiment of the present invention is to enhance the function of a protective circuit and stabilize the operation.

[0016]According to an embodiment of the present invention, a display device having a structure suitable as a protective circuit can be provided by forming the protective circuit with use of a non-linear element including an oxide semiconductor. In the connection structure between the first oxide semiconductor layer of the non-linear element and the wiring layers, the provision of the region which is bonded with the second oxide semiconductor layer, which has higher electrical conductivity than the first oxide semiconductor layer, allows stable operation as compared with the case of using only metal wirings. Accordingly, the function of the protective circuit is enhanced and the operation can be made stable.

Problems solved by technology

On the other hand, a thin film transistor manufactured using polycrystalline silicon has high field effect mobility, but a crystallization step such as laser annealing is necessary and such a transistor is not always suitable for a larger glass substrate.

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