Semiconductor Energy Laboratory Co., Ltd.

Toshikazu Kondo

Hideyuki Kishida

Jun Koyama

Shunpei Yamazaki

Atsushi Umezaki

In a thin film transistor, an increase in off current or negative shift of the threshold voltage is prevented. In the thin film transistor, a buffer layer is provided between an oxide semiconductor layer and each of a source electrode layer and a drain electrode layer. The buffer layer includes a metal oxide layer which is an insulator or a semiconductor over a middle portion of the oxide semiconductor layer. The metal oxide layer functions as a protective layer for suppressing incorporation of impurities into the oxide semiconductor layer. Therefore, in the thin film transistor, an increase in off current or negative shift of the threshold voltage can be prevented.

Thin film transistor, method for manufacturing the same, and semiconductor device

An object is to reduce parasitic capacitance of a signal line included in a liquid crystal display device. A transistor including an oxide semiconductor layer is used as a transistor provided in each pixel. Note that the oxide semiconductor layer is an oxide semiconductor layer which is highly purified by thoroughly removing impurities (hydrogen, water, or the like) which become electron suppliers (donors). Thus, the amount of leakage current (off-state current) can be reduced when the transistor is off. Therefore, a voltage applied to a liquid crystal element can be held without providing a capacitor in each pixel. In addition, a capacitor wiring extending to a pixel portion of the liquid crystal display device can be eliminated. Therefore, parasitic capacitance in a region where the signal line and the capacitor wiring intersect with each other can be eliminated.

Display device having an oxide semiconductor transistor

A semiconductor device capable of simply performing power gating and a driving method thereof are provided. Power gating is started passively (automatically in the case of satisfying predetermined conditions). Specifically, the semiconductor device includes a transistor for selecting whether a power source voltage is supplied or not to a functional circuit. The power gating is started by turning off the transistor in the case where a voltage between a source and a drain is less than or equal to a predetermined voltage. Therefore, complicated operation is not needed at the time of starting power gating. Specifically, it is possible to start power gating without a process for predicting the timing at which an arithmetic operation performed in the functional circuit is terminated. As a result, it is possible to start power gating easily.

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Atsugi, Japan

Toshikazu Kondo