Thin film transistor, method for manufacturing the same, and semiconductor device
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.
1. A semiconductor device comprising:
a gate electrode and a capacitor wiring over a substrate;
a gate insulating layer over and in contact with the gate electrode and the capacitor wiring;
an oxide semiconductor layer over the gate insulating layer;
a first electrode layer and a second electrode layer in electrical contact with the oxide semiconductor layer;
an interlayer insulating layer over the oxide semiconductor layer, the first electrode layer and the second electrode layer; and
a pixel electrode over the interlayer insulating layer and in direct contact with the second electrode layer,
wherein the capacitor wiring is overlapped with the first electrode layer and the pixel electrode.
2. The semiconductor device according to claim 1 , further comprising a metal oxide layer over the oxide semiconductor layer.
3. The semiconductor device according to claim 1 , wherein the gate electrode and the capacitor wiring contain copper.
4. A semiconductor device comprising:
a gate electrode and a capacitor wiring over a substrate;
a gate insulating layer over and in contact with the gate electrode and the capacitor wiring;
an oxide semiconductor layer over the gate insulating layer;
a first electrode layer and a second electrode layer in electrical contact with the oxide semiconductor layer;
an interlayer insulating layer over the oxide semiconductor layer, the first electrode layer and the second electrode layer; and
a pixel electrode over the interlayer insulating layer and in electrical direct contact with the second electrode layer,
wherein the capacitor wiring is overlapped with the first electrode layer and the pixel electrode, and
wherein the capacitor wiring extends beyond an end portion of the first electrode layer.
5. The semiconductor device according to claim 4 , further comprising a metal oxide layer over the oxide semiconductor layer.
6. The semiconductor device according to claim 4 , wherein the gate electrode and the capacitor wiring contain copper.