DISPLAY DEVICE AND ELECTRONIC DEVICE INCLUDING DISPLAY DEVICE

• US 20110090207A1
• Filed: 10/18/2010
• Published: 04/21/2011
• Est. Priority Date: 10/21/2009
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: MIYAKE, Hiroyuki, YAMAZAKI, Shunpei, KOYAMA, Jun
• Granted Patent: US 8,890,781 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H01L 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO
• CPC Class Codes: H01L 29/78609 for preventing leakage current H01L29/78618 takes precedence
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
• CPC Class Codes: H01L 29/78693 the semiconducting oxide being amorphous
• CPC Class Codes: H01L 29/78696 characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel H01L29/78612 takes precedence; transistors having a drain offset region or a lightly doped drain [LDD] H01L29/78621
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs
• CPC Class Codes: H10K 59/131 Interconnections, e.g. wiring lines or terminals

Abstract

Objects are to provide a display device the power consumption of which is reduced, to provide a self-luminous display device the power consumption of which is reduced and which is capable of long-term use in a dark place. A circuit is formed using a thin film transistor in which a highly-purified oxide semiconductor is used and a pixel can keep a certain state (a state in which a video signal has been written). As a result, even in the case of displaying a still image, stable operation is easily performed. In addition, an operation interval of a driver circuit can be extended, which results in a reduction in power consumption of a display device. Moreover, a light-storing material is used in a pixel portion of a self-luminous display device to store light, whereby the display device can be used in a dark place for a long time.

Claims

1. A display device comprising:

a power supply line;

a light-emitting element configured to receive power from the power supply line;

a first thin film transistor for electrically connecting the power supply line and the light-emitting element;

a signal line for supplying a video signal;

a second thin film transistor for electrically connecting the signal line and a gate of the first thin film transistor;

wherein a channel formation region in the second thin film transistor comprises an oxide semiconductor layer having a band gap of greater than or equal to 2 eV and a hydrogen concentration of less than or equal to 5×

10¹⁹/cm³, and

wherein the second thin film transistor in which off-state current per a channel width of 1 μ

m is suppressed to less than or equal to 1×

10<sup>−

16</sup> A/μ

m is configured to hold the first thin film transistor in an on state and connect the power supply line to the light-emitting element to display a still image.

2. The display device according to claim 1, wherein the power supply line is configured to supply a pulsed DC power.

3. The display device according to claim 1, wherein a carrier concentration of the oxide semiconductor layer is less than 1×

10¹⁴/cm³.

4. The display device according to claim 1, wherein a period in which the still image is displayed includes a period in which output of a scan line signal is stopped.

5. The display device according to claim 1,

wherein the light-emitting element comprising:

a pair of electrodes; and

a layer containing a light-emitting organic substance between the pair of electrodes.

6. The display device according to claim 1, wherein a light-storing layer is included.

7. An electronic device comprising the display device according to claim 1.

8. The display device according to claim 1, wherein the display device is lighting device.

9. A display device comprising;

a signal line;

a scan line;

a power supply line to which pulsed DC power is supplied; and

a pixel portion, the pixel portion comprising;

a first thin film transistor;

a second thin film transistor; and

a light-emitting element,

wherein a gate of the second thin film transistor is electrically connected to the scan line, a first electrode of the second thin film transistor is electrically connected to the signal line, and a second electrode of the second thin film transistor is electrically connected to a gate of the first thin film transistor,

wherein a first electrode of the first thin film transistor is electrically connected to the power supply line, and the second electrode of the first thin film transistor is electrically connected to a first electrode of the light-emitting element,

wherein a channel formation region in the second thin film transistor comprises an oxide semiconductor layer having a band gap of greater than or equal to 2 eV and a hydrogen concentration of less than or equal to 5×

10¹⁹/cm³, and

wherein the second thin film transistor in which off-state current per a channel width of 1 μ

m is suppressed to less than or equal to 1×

10<sup>−

16</sup> A/μ

m is configured to hold the first thin film transistor in an on state and connects the power supply line to the light-emitting element to display a still image.

10. The display device according to claim 9, wherein a carrier concentration of the oxide semiconductor layer is less than 1×

10¹⁴/cm³.

11. The display device according to claim 9, wherein a period in which the still image is displayed includes a period in which output of a scan line signal is stopped.

12. The display device according to claim 9,

wherein the light-emitting element comprising:

a pair of electrodes; and

a layer containing a light-emitting organic substance between the pair of electrodes.

13. The display device according to claim 9, wherein a light-storing layer is included.

14. An electronic device comprising the display device according to claim 9.

15. The display device according to claim 9, wherein the display device is an electronic paper.