Method for driving semiconductor device
To provide a method for driving a semiconductor device, by which influence of variation in threshold voltage and mobility of transistors can be reduced. The semiconductor device includes an n-channel transistor, a switch for controlling electrical connection between a gate and a first terminal of the transistor, a capacitor electrically connected between the gate and a second terminal of the transistor, and a display element. The method has a first period for holding the sum of a voltage corresponding to the threshold voltage of the transistor and an image signal voltage in the capacitor; a second period for turning on the switch so that electric charge held in the capacitor in accordance with the sum of the image signal voltage and the threshold voltage is discharged through the transistor; and a third period for supplying a current to the display element through the transistor after the second period.
1. A method for driving a display device, wherein the display device comprises a pixel comprising a transistor, a capacitor and a light-emitting element, wherein one of a source and a drain of the transistor is electrically connected to a first electrode of the capacitor, wherein a gate of transistor is electrically connected to a second electrode of the capacitor, and wherein the one of the source and the drain of the transistor is electrically connected to the light-emitting element,
the method comprising the steps of:
inputting an image signal to the pixel,
discharging electric charges from the capacitor through the transistor after inputting the image signal to the pixel; and
supplying a current to the light-emitting element after discharging the electric charges,
wherein a channel formation region of the transistor comprises an oxide semiconductor layer, and
wherein the oxide semiconductor layer comprises a plurality of nanocrystals.
2. The method for driving the display device, according to claim 1 ,
wherein the transistor comprises a first region and a second region,
wherein the first region is between the channel formation region and the second region, and
wherein an impurity concentration of the first region is lower than an impurity concentration of the second region.
3. The method for driving the display device, according to claim 1 , wherein the transistor has n-type conductivity.
4. The method for driving the display device, according to claim 1 , wherein only the capacitor is used for retaining the electrical charges.
5. The method for driving the display device, according to claim 1 , wherein the oxide semiconductor layer comprises In, Ga, and Zn.
6. The method for driving the display device, according to claim 1 , wherein the oxide semiconductor layer is a non-single crystal film.
7. A method for driving a display device, wherein the display device comprises a pixel comprising a transistor, a capacitor and a light-emitting element, wherein one of a source and a drain of the transistor is electrically connected to a first electrode of the capacitor, wherein a gate of transistor is electrically connected to a second electrode of the capacitor, and wherein the one of the source and the drain of the transistor is electrically connected to the light-emitting element,
the method comprising the steps of:
charging the capacitor so that a first voltage is applied to the capacitor;
discharging the capacitor so that a second voltage is applied to the capacitor after charging the capacitor;
inputting an image signal to the pixel after discharging the capacitor,
discharging the capacitor after inputting the image signal to the pixel so that a third voltage is applied to the capacitor; and
supplying a current to the light-emitting element while holding the third voltage in the capacitor,
wherein a channel formation region of the transistor comprises an oxide semiconductor layer, and
wherein the oxide semiconductor layer comprises a plurality of nanocrystals.
8. The method for driving the display device, according to claim 7 ,
wherein when the first voltage is applied between the gate and the source of the transistor, the transistor is in an on-state.
9. The method for driving the display device, according to claim 7 ,
wherein the second voltage is a threshold voltage of the transistor.
10. The method for driving the display device, according to claim 7 ,
wherein the third voltage depends on electric charges which are discharged from the capacitor through the transistor after the image signal is input to the pixel.
11. The method for driving the display device, according to claim 7 ,
wherein the transistor comprises a first region and a second region,
wherein the first region is between the channel formation region and the second region, and
wherein an impurity concentration of the first region is lower than an impurity concentration of the second region.
12. The method for driving the display device, according to claim 7 , wherein the transistor has n-type conductivity.
13. The method for driving the display device, according to claim 7 , wherein only the capacitor is used for retaining the electrical charges.
14. The method for driving the display device, according to claim 7 , wherein the oxide semiconductor layer comprises In, Ga, and Zn.
15. The method for driving the display device, according to claim 7 , wherein the oxide semiconductor layer is a non-single crystal film.
16. A method for driving a display device, wherein the display device comprises a pixel comprising a transistor and a light-emitting element, and wherein one of a source and a drain of the transistor is electrically connected to the light-emitting element,
the method comprising the steps of:
establishing an electrical continuity between a gate and the other of the source and the drain of the transistor and an electrical continuity between a wiring and the other of the source and the drain of the transistor during a first period while supplying a potential from the wiring to the other of the source and the drain of the transistor;
establishing an electrical continuity between the gate and a source signal line and an electrical continuity between the light-emitting element and the one of the source and the drain of the transistor during a second period while disestablishing the electrical continuity between the gate and the other of the source and the drain of the transistor;
establishing the electrical continuity between the gate and the other of the source and the drain of the transistor during a third period while disestablishing the electrical continuity between the gate and the source signal line; and
establishing the electrical continuity between the light-emitting element and the one of the source and the drain of the transistor and the electrical continuity between the wiring and the other of the source and the drain of the transistor during a fourth period while disestablishing the electrical continuity between the gate and the source signal line and the electrical continuity between the gate and the other of the source and the drain of the transistor.
17. The method for driving the display device, according to claim 16 ,
wherein during the third period, the electrical continuity between the light-emitting element and the one of the source and the drain of the transistor is disestablished.
18. The method for driving the display device, according to claim 16 ,
wherein during the third period, the electrical continuity between the wiring and the other of the source and the drain of the transistor is disestablished.