Photo sensor circuit, photo sensor pixel, and display device having the photo sensor pixel

1. A photo sensor pixel, comprising:

a pixel circuit including a driving transistor, wherein the pixel circuit drives a light emitting element therein based on a data voltage provided thereto through a data line;

a switching transistor having a double gate structure, wherein the switching transistor comprises a top gate electrode and a bottom gate electrode, which are connected to different gate lines, respectively; and

a photo sensing transistor connected in series with the switching transistor, wherein the photo sensing transistor senses incident light.

2. The photo sensor pixel of claim 1 , wherein

the top gate electrode of the switching transistor is connected to a first gate line, and

the bottom gate electrode of the switching transistor is connected to a second gate line.

3. The photo sensor pixel of claim 2 , wherein the switching transistor further comprises:

a first electrode connected to the data line; and

a second electrode connected to the photo sensing transistor.

4. The photo sensor pixel of claim 3 , wherein the switching transistor turns on in a period in which a gate signal applied to the first gate line is activated and in a period in which a gate signal applied to the second gate line is activated.

5. The photo sensor pixel of claim 3 , wherein the photo sensing transistor comprises:

a first electrode connected to the second electrode of the switching transistor;

a second electrode connected to a photo sensing line through which a sensing current generated by the photo sensing transistor is output; and

a gate electrode connected to a third gate line.

6. The photo sensor pixel of claim 5 , wherein the first to third gate lines transmit gate signals having activation levels in different periods, respectively.

7. The photo sensor pixel of claim 1 , wherein a channel length of an active layer of the photo sensing transistor is longer than a channel length of an active layer of the switching transistor.

8. The photo sensor pixel of claim 1 , wherein the switching transistor comprises:

a substrate;

the bottom gate electrode on the substrate;

a buffer layer on the substrate and the bottom gate electrode to cover the bottom gate electrode;

an active layer on the buffer layer to overlap the bottom gate electrode;

a first gate insulation layer on the buffer layer and the active layer;

the top gate electrode on the first gate insulation layer to overlap the active layer;

a second gate insulation layer on the first gate insulation layer and the top gate electrode to cover the top gate electrode;

an insulating interlayer on the second gate insulation layer;

a first electrode on the insulating interlayer and connected to the active layer via a first contact hole defined through the first gate insulation layer, the second gate insulation layer and the insulating interlayer; and

a second electrode on the insulating interlayer and connected to the active layer via a second contact hole defined through the first gate insulation layer, the second gate insulation layer and the insulating interlayer.

9. The photo sensor pixel of claim 8 , wherein the photo sensing transistor comprises:

the gate electrode at the same layer as the bottom gate electrode of the switching transistor;

an active layer at the same layer as the active layer of the switching transistor to overlap the gate electrode of the photo sensing transistor;

a first electrode on the insulating interlayer and connected to the active layer of the photo sensing transistor via a third contact hole defined through the first gate insulation layer, the second gate insulation layer and the insulating interlayer; and

a second electrode on the insulating interlayer and connected to the active layer of the photo sensing transistor via a fourth contact hole defined through the first gate insulation layer, the second gate insulation layer and the insulating interlayer.

10. The photo sensor pixel of claim 9 , wherein a channel length of an active layer of the photo sensing transistor is longer than a channel length of an active layer of the switching transistor.

11. The photo sensor pixel of claim 1 , wherein each of the switching transistor and the photo sensing transistor is one of an oxide thin film transistor, a low temperature poly-silicon thin film transistor and a low temperature polycrystalline oxide thin film transistor.

12. A photo sensor circuit connected to a pixel circuit, the photo sensor circuit comprising:

a first switching transistor having a double gate structure, wherein the first switching transistor comprises a top gate electrode connected to a first gate line and a bottom gate electrode connected to a second gate line; and

a photo sensing transistor connected in series with the switching transistor, wherein the photo sensing transistor senses incident light.

13. The photo sensor circuit of claim 12 , further comprises:

a second switching transistor having the double gate structure, wherein the second switching transistor comprises a top gate electrode connected to a third gate line and a bottom gate electrode connected to a fourth gate line,

wherein the second switching transistor is connected in parallel with the first switching transistor.

14. The photo sensor circuit of claim 13 , wherein each of the first and second switching transistors further includes:

a first electrode connected to a data line; and

a second electrode connected to a first node.

15. The photo sensor circuit of claim 13 , wherein the photo sensing transistor includes:

a first electrode connected to the first node;

a second electrode connected to a photo sensing line, through which a sensing current generated by the photo sensing transistor is output; and

a gate electrode connected to a fifth gate line.

16. The photo sensor circuit of claim 15 , wherein the first to fifth gate lines transmit gate signals having activation levels in different periods, respectively.

17. The photo sensor circuit of claim 12 , wherein a channel length of an active layer of the photo sensing transistor is greater than channel lengths of active layers of the first and second switching transistor.

18. The photo sensor circuit of claim 12 , wherein each of the first switching transistor and the photo sensing transistor is one of an oxide thin film transistor, a low temperature poly-silicon thin film transistor, and a low temperature polycrystalline oxide thin film transistor.

19. A display device comprising:

a photo sensing display panel including a plurality of photo sensor pixel rows in which a plurality of photo sensor pixels is arranged;

a gate driver which provides a gate signal to the display panel;

a data driver which provides a data voltage to the display panel; and

a timing controller which controls the gate driver and the data driver,

wherein each of the photo sensor pixels comprises:

a pixel circuit including a driving transistor, wherein the pixel circuit drives a light emitting element therein based on the data voltage provided thereto;

a switching transistor having a double gate structure, wherein the switching transistor comprises a top gate electrode and a bottom gate electrode, which are connected to different gate lines, respectively; and

a photo sensing transistor connected in series with the switching transistor to sense incident light.

20. The display device of claim 19 , wherein the photo sensing display panel further comprises:

a plurality of normal pixel rows in which a plurality of normal pixels is arranged,

wherein each of the normal pixels comprises the pixel circuit, and

wherein the photo sensor pixel rows is arranged between the normal pixel rows with predetermined spacing.