Electroluminescent Display Devices

• US 20070241998A1
• Filed: 03/02/2005
• Published: 10/18/2007
• Est. Priority Date: 03/17/2004
• Status: Active Grant

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Oepts, Wouter, Fish, David, Lifka, Herbert, Young, Nigel, Giraldo, Andrea
• Granted Patent: US 8,310,413 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H01L 23/552 Protection against radiation, e.g. light or electromagnetic waves
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H10K 2102/3026 Top emission
• CPC Class Codes: H10K 50/824 combined with auxiliary electrodes
• CPC Class Codes: H10K 50/856 comprising reflective means
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs
• CPC Class Codes: H10K 59/13 comprising photosensors that control luminance
• CPC Class Codes: H10K 59/878 comprising reflective means

Abstract

An active matrix display device comprises an array of display pixels, with each pixel comprising an EL display element, a light-dependent device for detecting the brightness of the display element and a drive transistor circuit for driving a current through the display element. The drive transistor is controlled in response to the light-dependent device output so that ageing compensation can be implemented. The light-dependent device is located laterally of the area of light emitting material of the EL display element. In this way, the light-dependent device does not cause step coverage problems and can be integrated into the pixel layout without affecting the pixel aperture. Furthermore, the light dependent device can extend alongside the full length of the area of light emitting material so that it receives light input from a large part of the display element area.

Claims

1. An active matrix display device comprising an array of display pixels, each pixel comprising:

a current-driven light emitting display element (2) comprising an area of light emitting material (76) sandwiched between electrodes (74,80);

a light-dependent device (27,52,90) for detecting the brightness of the display element (2); and

a drive transistor circuit (16,22,24,29;

16,22,24,34,36,40) for driving a current through the display element, wherein the drive transistor (22) is controlled in response to the light-dependent device output, wherein the light-dependent device (52,90) is located laterally of the area of light emitting material.

2. A device as claimed in claim 1, wherein the light-dependent device (27,52,90) comprises a photodiode.

3. A device as claimed in claim 2, wherein the photodiode comprises a PIN or NIP diode stack or a Schottky diode and top (93) and bottom (94) contact terminals.

4. A device as claimed in claim 3, wherein the top (93) contact terminal extends over the top of the stack and down one side of the stack and acts as a light shield to pixels on the one side of the photodiode.

5. A device as claimed in claim 1, wherein the electrodes comprise a top substantially transparent electrode (80a) and a bottom substantially non-transparent, reflective electrode (74a).

6. A device as claimed claim 5, wherein the bottom electrode (74a) is for reflecting light from the display element to the light dependent device.

7. A device as claimed in claim 6, wherein the bottom electrode (74a) is for reflecting light emitted at an angle to the normal greater than a first angle to the light dependent device.

8. A device as claimed in claim 6, further comprising a reflecting layer (102) above the light dependent device and for reflecting light from the bottom electrode (74a) to the light dependent device.

9. A device as claimed in claim 8, wherein the device further comprises a plurality of printing dams (78) and the light emitting material (76) comprises a printable material.

10. A device as claimed in claim 9, wherein the reflecting layer (102) is formed at the base of the printing dams (78).

11. A device as claimed in claim 9, wherein the printing dams comprise an insulating body and a conducting metal layer (79) over the insulating body.

12. A device as claimed in claim 11, wherein the conducting metal layer (79) provides a lower resistance shunt connecting the top substantially transparent electrodes.

13. A device as claimed in claim 11, wherein the conducting metal layer (79) defines the reflecting layer.

14. A device as claimed in claim 9, wherein the light sensitive devices (90) are formed beneath the printing dams.

15. A device as claimed in claim 1, wherein the electrodes comprise a top substantially transparent electrode and a bottom substantially transparent electrode (74).

16. A device as claimed in claim 15, wherein the device further comprises an additional reflective layer (70;

62) beneath the bottom electrode (74).

17. A device as claimed in claim 16, further comprising a reflecting layer (102;

110) above the light dependent device (90) and for reflecting light from the reflecting layer (102;

110) to the light dependent device.

18. A device as claimed in claim 17, wherein the reflecting layer (110) is formed at the level of the bottom electrode (74) of the light emitting display element.

19. A device as claimed in claim 17, wherein the device further comprises a plurality of printing dams (78) and the light emitting material (76) comprises a printable material.

20. A device as claimed in claim 19, wherein the reflecting layer (102) is formed at the base of the printing dams (78).

21. A device as claimed in claim 1, wherein the light-dependent device extends alongside the area of light emitting material and extends along substantially the full length of one side of the area of light emitting material.

22. A device as claimed in claim 21, wherein the light-dependent device extends around an upper and lower portion of the area of light emitting material.

23. A device as claimed in claim 1, wherein the light emitting display element comprises an electroluminescent display element.