Light-emitting elements

• US 5,554,911 A
• Filed: 03/18/1994
• Issued: 09/10/1996
• Est. Priority Date: 03/18/1993
• Status: Expired due to Term

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi, Ltd.
• Inventors: Nakayama, Takahiro, Kakuta, Atsushi, Iwayanagi, Takao
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): RICHARDSON, LAW
• Application Number:
  US08/214,767
• Time in Patent Office: 907 Days
• Field of Search: 313/504, 313/503, 313/505, 313/506, 313/507, 313/508, 313/509, 372/7, 372/99, 372/42, 428/690, 428/917, 359/838, 385/47, 385/131
• US Class Current: 313/504
• CPC Class Codes: H05B 33/12 Light sources with substantially two-dimensional radiating surfaces
• CPC Class Codes: H05B 33/22 characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers
• CPC Class Codes: H05B 33/28 of translucent electrodes
• CPC Class Codes: H10K 50/125 specially adapted for multicolour light emission, e.g. for emitting white light
• CPC Class Codes: H10K 50/852 comprising a resonant cavity structure, e.g. Bragg reflector pair

Abstract

A multi-color light-emitting element has at least two optical micro-cavity structures having respectively different optical lengths determining their emission wavelengths. Each micro-cavity structure contains a film of or organic material as a light-emitting region, which may be a single film of uniform thickness in the element.

Claims

1. A multi-color light-emitting element comprising a first optical micro-cavity structure having a first film of organic material providing a light-emitting region thereof and an optical length determining its emission wavelength, and a second optical micro-cavity structure having a second film of organic material providing a light-emitting region thereof and an optical length, different from said optical length of said first micro-cavity structure, determining its emission wavelength, whereby said emission wavelengths of said first and second optical micro-cavity structures are different from one another to provide multi-color light emission.

2. A multi-color light-emitting element according to claim 1, wherein said first film of organic material is made of the same material as said second film of organic material.

3. A multi-color light-emitting element according to claim 2, wherein said first and second films of organic material are respective portions of a layer of said organic material.

4. A multi-color light-emitting element according to claim 1, wherein each said optical micro-cavity structure includes at least one further film providing a part of the optical length of the optical micro-cavity structure.

5. A multi-color light-emitting element having at least two optical micro-cavity structures, each said optical micro-cavity structure comprising at least a thin film of organic light-emitting material, at least two reflecting surfaces on opposite sides of said thin film and a path for light emission from said optical cavity structure, each said optical micro-cavity structure having an optical length determined by the spacing of said two reflecting surfaces thereof, wherein said optical lengths of said at least two optical micro-cavity structures are different from one another so that said optical micro-cavity structures emit light at different wavelengths provides multi-color light emission.

6. A multi-color light-emitting element according to claim 5, wherein each said optical micro-cavity structure comprises, between said two reflecting surfaces thereof, at least one further film selected from a transparent electrode, a hole-injection film, an electron-injection film and a transparent spacer film.

7. A multi-color light-emitting element according to claim 6, wherein the thickness of said further film in a first one of said optical micro-cavity structures is different from the thickness of said further film in a second one of said optical micro-cavity structures, thereby to provide said different optical lengths.

8. A multi-color light-emitting element according to claim 5, wherein in each said optical micro-cavity structure, said film of light-emitting material has the same thickness.

9. A multi-color light-emitting element according to claim 5, wherein each said micro-cavity structure comprises a pair of electrodes for passing electrical current through said film of organic material.

10. A multi-color light-emitting element according to claim 5, wherein said optical micro-cavity structures are mounted on a common substrate.

11. A multi-color light-emitting element according to claim 5, wherein said path for light emission from each said optical micro-cavity structure is provided by a half-mirror which also provides one of said reflecting surfaces.

12. A multi-color light-emitting element according to claim 7, wherein the thickness of the further film in the first one of said optical micro-cavity structures is 190 nm and the thickness of the further film in the second one of said optical micro-cavities is 160 nm so that the first micro-cavity generates red light and the second micro-cavity generates green light.

13. A multi-color light-emitting element according to claim 7, wherein the thickness of the further film in the first one of said optical micro-cavities is 160 nm and the thickness of the further film in the second one of said optical micro-cavities is 140 nm so that the first micro-cavity generates green light and the second micro-cavity generates blue light.

18. A multi-color light-emitting element according to claim 11, wherein said half mirror has a reflectance in the range of 50% to 99.9%.

14. A multi-color light-emitting element having a substrate and, formed on said substrate, a plurality of pixels of each of at least two types respectively emitting light of different wavelength from one another to provide multi-color emission, each said pixel having an optical micro-cavity structure including, as a light-emitting region, a thin film of organic material for emitting light of the wavelength of the pixel, said optical micro-cavity structure having an optical length determining the peak wavelength of the light emitted by it under resonant condition.

15. A multi-color light-emitting element according to claim 14, wherein each of said pixels includes, in said micro-cavity structure, a pair of electrodes for passing current through said thin film of organic material to cause light emission therein, said electrodes of said pixels being interconnected as an array.

16. A substrate for use in the manufacture of a multi-color light emitting element having a plurality of micro-cavities having optical lengths different from one another to provide multi-color light emission, comprising a transparent substrate, a half mirror structure formed on said substrate and comprised of a plurality of dielectric films and a transparent conductive layer formed on said half mirror structure.

17. A substrate according to claim 16, wherein said half mirror structure has a reflectance in the range of 50% to 99.9%.

19. A multi-color light-emitting element comprising:

a semitransparent reflective layer;

a plurality of transparent conductive first electrodes formed as strips extending parallel to each other in a first direction;

an organic light-emitting layer of substantially constant thickness formed over said plurality of transparent conductive first electrodes; and

a plurality of second electrodes formed as strips extending over the organic light-emitting layer in a second direction, substantially perpendicular to said first direction, such that portions where the first electrodes intersect the second electrodes form pixels for emission of light from optical micro-cavities formed between the second electrodes and the semitransparent conductive first electrodes have different thicknesses from one another to provide different optical lengths of the optical micro-cavities corresponding thereto to thereby emit light at different wavelengths from one another to provide multi-color emission.

21. A multi-color light-emitting element according to claim 19, wherein said semitransparent reflective layer is a multi-layer structure comprised of alternating layers of TiO₂ and SiO₂.

23. A multi-color light-emitting element according to claim 19, wherein said semitransparent reflective layer has a reflectance in a range between 50% and 99.9%.

25. A multi-color light-emitting element according to claim 19, wherein three of said transparent conductive first electrodes in three of said optical micro-cavities have respective thicknesses of 190 nm, 160 nm and 145 nm to provide different optical lengths so that the three micro-cavities respectively generate red, green and blue light.

20. A multi-color light-emitting element comprising:

a semitransparent reflecting layer;

a plurality of transparent conductive first electrodes formed as strips extending parallel to each other in a first direction;

an organic light-emitting layer of substantially constant thickness formed over said plurality of transparent conductive first electrodes; and

a plurality of spacers formed between said semitransparent reflective layer and said first electrodes, wherein said spacers have different thicknesses from one another to provide different optical lengths of the optical micro-cavities corresponding thereto to thereby emit light at different wavelengths from one another to provide multi-color emission.

22. A multi-color light-emitting element according to claim 20, wherein said semitransparent reflective layer is a multi-layer structure comprised of alternating layers of TiO₂ and SiO₂.

24. A multi-color light-emitting element according to claim 20, wherein said semitransparent reflective layer has a reflectance in a range between 50% and 99.9%.

26. A multi-color light-emitting element comprising:

a semitransparent reflective layer;

a plurality of transparent conductive first electrodes formed as strips extending parallel to each other in a first direction; and

an organic light-emitting layer of substantially constant thickness formed over said plurality of transparent conductive first electrodes;

wherein a first one of said transparent conductive first electrodes is formed directly on said semitransparent reflective layer to provide a first optical cavity having a first optical length such that said first optical micro-cavity emits light of a first wavelength, wherein a second one of said transparent conductive first electrodes is formed on a first spacer having a first predetermined thickness to provide a second optical micro-cavity having a second optical length so that said second optical micro-cavity emits light of a second wavelength, and wherein a third one of said transparent conductive first electrodes is formed on a second spacer having a second predetermined thickness to provide a third optical micro-cavity having a third optical length so that said third optical micro-cavity emits light of a third wavelength.

27. A multi-color light emitting element according to claim 26, wherein said first predetermined thickness of said first spacer is 18 nm, wherein the second predetermined thickness of the second spacer is 54 nm, and wherein the first wavelength of the first micro-cavity is 470 nm to provide blue light, the second wavelength of the second micro-cavity is 520 nm to provide green light, and the third wavelength of the third micro-cavity is 620 nm to provide red light.