Display device and electronic device
A transistor whose channel region includes an oxide semiconductor is used as a pull down transistor. The band gap of the oxide semiconductor is 2.0 eV or more, preferably 2.5 eV or more, more preferably 3.0 eV or more. Thus, hot carrier degradation in the transistor can be suppressed. Accordingly, the circuit size of the semiconductor device including the pull down transistor can be made small. Further, a gate of a pull up transistor is made to be in a floating state by switching of on/off of the transistor whose channel region includes an oxide semiconductor. Note that when the oxide semiconductor is highly purified, the off-state current of the transistor can be 1 aA/μm (1×10 −18 A/μm) or less. Therefore, the drive capability of the semiconductor device can be improved.
1. A circuit comprising:
a first transistor;
a second transistor;
a third transistor;
a fourth transistor;
a fifth transistor; and
a sixth transistor,
wherein:
a first terminal of the first transistor is electrically connected to a first wiring;
a second terminal of the first transistor is electrically connected to a second wiring;
a first terminal of the second transistor is electrically connected to a third wiring;
a first terminal of the third transistor is electrically connected to a fourth wiring;
a first terminal of the fourth transistor is electrically connected to the third wiring;
a first terminal of the fifth transistor is electrically connected to the second wiring;
a second terminal of the fifth transistor is electrically connected to the third wiring;
a first terminal of the sixth transistor is electrically connected to the second wiring;
a second terminal of the sixth transistor is electrically connected to the third wiring;
a gate electrode of the first transistor is directly connected to a second terminal of the second transistor and a gate electrode of the fourth transistor;
a gate electrode of the second transistor is directly connected to a second terminal of the third transistor and a second terminal of the fourth transistor; and
a gate electrode of the third transistor is directly connected to the first terminal of the third transistor.
2. The circuit according to claim 1 , wherein a channel forming region of at least one of the first to sixth transistors includes an oxide semiconductor.
3. The circuit according to claim 1 , wherein carrier density of the channel forming region of at least one of the first to sixth transistors is less than 1×10 11 /cm 3 .
4. The circuit according to claim 1 wherein off-state current of at least one of the first to sixth transistors is 1 aA/μm or less.
5. A display device including the circuit according to claim 1 .
6. A semiconductor device comprising:
a first transistor;
a second transistor;
a third transistor;
a fourth transistor;
a fifth transistor; and
a sixth transistor,
wherein one of a source and a drain of the first transistor is electrically connected to a first wiring,
wherein the other of the source and the drain of the first transistor is electrically connected to a first gate signal line,
wherein one of a source and a drain of the second transistor is electrically connected to a second wiring,
wherein the other of the source and the drain of the second transistor is electrically connected to a gate of the first transistor,
wherein one of a source and a drain of the third transistor is electrically connected to the gate of the first transistor,
wherein a gate of the third transistor is electrically connected to a second gate signal line,
wherein one of a source and a drain of the fourth transistor is electrically connected to the gate of the first transistor,
wherein a gate of the fourth transistor is electrically connected to a third gate signal line,
wherein one of a source and a drain of the fifth transistor is electrically connected to a third wiring,
wherein the other of the source and the drain of the fifth transistor is electrically connected to a gate of the second transistor,
wherein a gate of the fifth transistor is electrically connected to the third wiring,
wherein one of a source and a drain of the sixth transistor is electrically connected to the second wiring,
wherein the other of the source and the drain of the sixth transistor is electrically connected to the gate of the second transistor,
wherein a gate of the sixth transistor is electrically connected to the gate of the first transistor,
wherein each of the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, and the sixth transistor comprises a gate electrode layer, a gate insulating layer over the gate electrode layer, an oxide semiconductor layer over the gate insulating layer, a source electrode layer over the oxide semiconductor layer, and a drain electrode layer over the oxide semiconductor layer,
wherein an oxide insulating layer is over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer,
wherein a protective insulating layer is over the oxide insulating layer,
wherein the oxide semiconductor layer comprises In, Ga, and Zn,
wherein the oxide insulating layer comprises oxygen and silicon, and
wherein the protective insulating layer comprises nitrogen and silicon.
7. The semiconductor device according to claim 6 , further comprising a seventh transistor,
wherein one of a source and a drain of the seventh transistor is electrically connected to the first gate signal line.
8. The semiconductor device according to claim 6 ,
wherein a clock signal is input to the first wiring.
9. The semiconductor device according to claim 6 ,
wherein a voltage is supplied to the second wiring.
10. A semiconductor device comprising:
a first transistor;
a second transistor; and
a third transistor,
wherein one of a source and a drain of the first transistor is electrically connected to a first wiring,
wherein the other of the source and the drain of the first transistor is electrically connected to a first gate signal line,
wherein one of a source and a drain of the second transistor is electrically connected to a gate of the first transistor,
wherein the other of the source and the drain of the second transistor is electrically connected to the first gate signal line,
wherein a gate of the second transistor is electrically connected to the first wiring,
wherein one of a source and a drain of the third transistor is electrically connected to the gate of the first transistor,
wherein the other of the source and the drain of the third transistor is electrically connected to a second gate signal line,
wherein each of the first transistor, the second transistor, and the third transistor comprises a gate electrode layer, a gate insulating layer over the gate electrode layer, an oxide semiconductor layer over the gate insulating layer, a source electrode layer over the oxide semiconductor layer, and a drain electrode layer over the oxide semiconductor layer,
wherein an oxide insulating layer is over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer,
wherein a protective insulating layer is over the oxide insulating layer,
wherein the oxide semiconductor layer comprises In, Ga, and Zn,
wherein the oxide insulating layer comprises oxygen and silicon, and
wherein the protective insulating layer comprises nitrogen and silicon.
11. The semiconductor device according to claim 10 , further comprising a fourth transistor, a fifth transistor, a sixth transistor, and a seventh transistor,
wherein one of a source and a drain of the fourth transistor is electrically connected to the first gate signal line,
wherein the other of the source and the drain of the fourth transistor is electrically connected to a second wiring,
wherein one of a source and a drain of the fifth transistor is electrically connected to the gate of the first transistor,
wherein the other of the source and the drain of the fifth transistor is electrically connected to the second wiring,
wherein one of a source and a drain of the sixth transistor is electrically connected to a gate of the fourth transistor,
wherein the other of the source and the drain of the sixth transistor is electrically connected to the second wiring,
wherein one of a source and a drain of the seventh transistor is electrically connected to the gate of the fourth transistor,
wherein the other of the source and the drain of the seventh transistor is electrically connected to a gate of the seventh transistor, and
wherein the other of the source and the drain of the seventh transistor is electrically connected to a third wiring.
12. The semiconductor device according to claim 11 ,
wherein a voltage is supplied to the second wiring.
13. The semiconductor device according to claim 10 ,
wherein a clock signal is input to the first wiring.