USO005998925A
`5,998,925
`[1] Patent Number:
`[1
`United States Patent
`
` Shimizu etal. [45] Date of Patent: Dec. 7, 1999
`
`
`[54] LIGHT EMITTING DEVICE HAVING A
`NITRIDE COMPOUND SEMICONDUCTOR
`AND A PHOSPHOR CONTAINING A
`GARNET FLUORESCENT MATERIAL
`
`Japan .
`1/1980
`55-4898
`Japan .
`1/1987
`62-20237
`Japan.
`7/1989
`1-179471
`Japan.
`6/1993
`5-152609
`Japan .
`4/1995
`7-099345
`
`7-176794=7/1995 Japan .
`[75]
`Inventors: Yoshinori Shimizu, Naka-gun; Kensho
`8-007614
`1/1996
`Japan .
`Sakano, Anan; Yasunobu Noguchi,
`9-027642
`1/1997
`Japan .
`Naka-gun; Toshio Moriguchi, Anan, all
`of Japan
`
`OTHER PUBLICATIONS
`
`[73] Assignee: Nichia Kagaku Kogyo Kabushiki
`Kaisha, Tokushima, Japan
`[21] Appl. No.: 08/902,725
`[22]
`Filed:
`Jul. 29, 1997
`
`Foreign Application Priority Data
`[30]
`Ful. 29,1996
`[JP]
`Japan cecssessesusenemsereennn 8198585
`Sep. 17. 1996
`[JP]
`Japan .....
`_.. 8244339
`Sep. 18, 1996
`[JP]
`Japan.....
`a. 8245381
`Dec. 27, 1996
`[JP]
`Japan .....
`we 8359004
`Mar. 31, 1997
`[JP]
`Japan oo. F-O8LOLO
`
`
`
`[SL]
`Unt. C1 eee HO) 1/62; HOL 63/04
`[52] U.S. Ch. ccscsnsnsensenneee 313/503; 313/498; 313/501;
`
`313/502; 257/103
`Field Of S@AKCR ccinsnsonennsses 313/498; 503,
`[58]
`len,
`mney
`313/501, 502; 257/103
`Pe
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,600,478 10/1972 PINNOW' ELL rrmnennnnnne 832/751
`4,298,820
`11/1981 Bongers et al.
`.
`4.727.283
`2/1988 Van Kemenadeetal. .
`5,798,537
`B/L998 Nitta... eee eeeeeseseeeeeeeeeeeeeeeee 257/103
`FOREIGN PATENT DOCUMENTS
`
`“A New Phosphor for Frying—Spot Cathode—Ray Tubes for
`Color Television: Yellow-Emitting Y,al,;0,,-Ce**”, G.
`Glasse et al., Applied Physics Letters, vol. 11, No. 2, pp.
`a2OP UeD: ae
`Improvedcolor rendition in high pressure mercury vapor
`lamps”, Mary V. Hoffman, Journal of IES, pp. 89-91(1977).
`S. Nakamura, SPIE, 3002:26-35 (1997).
`
`Primary Examiner—Vip Patel
`Assistant kxaminer—Michael J. Smith
`Attorney, Agent, or Firm—Birch, Stewart, Kolasch & Birch,
`LLP
`
`[57]
`
`ABSTRACT
`ook
`:
`cg
`.
`o |
`The white light emitting diode comprising a light emitting
`component using a semiconductor as a light emitting layer
`20 a phosphor which absorbs a part oflight emitted by the
`light emitting component and emits light of wavelength
`;
`;
`:
`different from that of the absorbedlight, wherein the light
`emitting layer of the light emitting componentis a nitride
`compound semiconductor and the phosphor contains garnet
`fluorescent material activated with cerium which containsat
` Wast_one element selectedfrom the group consisting of Y,
`Lu, Se, La, Gd and Sm, and at least one element selected
`from the group consisting of Al, Ga and In and, andis
`subject to less deterioration of emission characteristic even
`when used with high luminance for a long period of time.
`
`50-43913
`
`4/1975
`
`Japan .
`
`23 Claims, 19 Drawing Sheets
`
`102
`
`TCL 1037, Page 1
`LOWES 1037, Page 1
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`LOWES 1037, Page 1
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`

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`U.S. Patent
`
`Dec.7, 1999
`
`Sheet 1 of 19
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`5,998,925
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`Fig.1
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`TCL 1037, Page 2
`LOWES 1037, Page 2
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`LOWES 1037, Page 2
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`

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`U.S. Patent
`
`Dec.7, 1999
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`Sheet 2 of 19
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`5,998,925
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`TCL 1037, Page 3
`LOWES 1037, Page 3
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`LOWES 1037, Page 3
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`

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`U.S. Patent
`
`Dec. 7, 1999
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`Sheet 3 of 19
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`LOWES 1037, Page 4
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`LOWES 1037, Page 4
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`

`

`U.S. Patent
`
`Dec.7, 1999
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`Sheet 4 of19
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`5,998,925
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`TCL 1037, Page 5
`LOWES 1037, Page 5
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`LOWES 1037, Page 5
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`

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`U.S. Patent
`
`Dec. 7, 1999
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`Sheet 5 of 19
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`TCL 1037, Page 6
`LOWES 1037, Page 6
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`LOWES 1037, Page 6
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`

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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 6 of 19
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`5,998,925
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`TCL 1037, Page 7
`LOWES 1037, Page 7
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`LOWES 1037, Page 7
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 7 of 19
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`5,998,925
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`Fig.10
`
`601
` LED display unit
`
`
`Gradation control unit
`Image data memory
`(RAM)
`(CPU)
`
`
`
`TCL 1037, Page 8
`LOWES 1037, Page 8
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`LOWES 1037, Page 8
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`

`

`U.S. Patent
`
`Dec. 7, 1999
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`Sheet 8 of 19
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`5,998,925
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`Fig.11
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`TCL 1037, Page 9
`LOWES 1037, Page 9
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`LOWES 1037, Page 9
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`

`

`U.S. Patent
`
`Dec. 7, 1999
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`Sheet 9 of 19
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`5,998,925
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`Fig. 13A
`
`Life test
`
`If=20mMA Ta=25'C
`
`Relative
`power
`(%)
`
` 120
`
`100
`
`80
`60
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`
`Relative
`power
`(%)
`
`120
`
`100
`
`80
`60
`
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`
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`
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`
`Lighting time (H)
`
`TCL 1037, Page 10
`LOWES 1037, Page 10
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`LOWES 1037, Page 10
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`

`

`U.S. Patent
`
`Dec. 7, 1999
`
`Sheet 10 of 19
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`5,998,925
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`Fig.14A
`
`Weathering test
`
`Brightness
`holding rate
`(%)
`
`20
`
`60
`
`40
`
`200
`
`400
`
`600
`
`Time (hr)
`
`Fig.14B
`
`0.38
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`
`0.36
`
`TCL 1037, Page 11
`LOWES 1037, Page 11
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`LOWES 1037, Page 11
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`

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`U.S. Patent
`
`Dec.7, 1999
`
`Sheet 11 of 19
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`5,998,925
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`Fig.15A
`
`Reliability test
`
`120
`
`100
`
`Brightness
`holding rate
`
`(%)
`
`500
`
`Time (hr)
`
`1000
`
`Fig.15B
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`1000hr
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`
`0.36
`
`TCL 1037, Page 12
`LOWES 1037, Page 12
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`LOWES 1037, Page 12
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 12 of 19
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`5,998,925
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`gLbly
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`
`TCL 1037, Page 13
`LOWES 1037, Page 13
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`LOWES 1037, Page 13
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 13 of 19
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`5,998,925
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`Jaudsoud
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`TCL 1037, Page 14
`LOWES 1037, Page 14
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`LOWES 1037, Page 14
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 14 of 19
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`5,998,925
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`
`
`380
`
`430
`
`480
`
`530
`
`580
`
`630
`
`680
`
`730
`
`Fig. 78B
`
`Wavelength (nm)
`
` 0
` 0
`
`
` (%)Aylsuajuleaiejoy
`
`
`
`
`
`
`
`380
`
`430
`
`480
`
`530
`
`580
`
`630
`
`680
`
`730
`
`Wavelength (nm)
`
`TCL 1037, Page 15
`LOWES 1037, Page 15
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`LOWES 1037, Page 15
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 15 of 19
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`5,998,925
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`Fig.19A
`oh|__|ZN]
`
`380
`
`430
`
`480
`
`530
`
`580
`
`#630
`
`680
`
`730
`
`Fig. 79B
`
`Wavelength (nm)
`
`
`
`
`
`
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`a
` (%)Ajsuejulsaeey
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` 0
`sAeley 0
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`380
`
`430
`
`480
`
`530
`
`580
`
`630
`
`680
`
`730
`
`Fig. 19C
`
`Wavelength (nm)
`
`380
`
`430
`
`480
`
`530
`
`580
`
`630
`
`680
`
`730
`
`Wavelength (nm)
`
`TCL 1037, Page 16
`LOWES 1037, Page 16
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`LOWES 1037, Page 16
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`

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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 16 of 19
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`5,998,925
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`
`
`
`
`
`
`
`
`sAeyoYy 0
`
`
`
` (9%)Ajlsuajur
`
`
`
`380 430
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`580
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`#4630
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`680
`
`730
`
`Wavelength (nm)
`
`TCL 1037, Page 17
`LOWES 1037, Page 17
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`LOWES 1037, Page 17
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 17 of 19
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`5,998,925
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`
`
`
`
`380
`
`430
`
`480
`
`530
`
`580
`
`630
`
`680
`
`730
`
`F,ig.21B
`
`Wavelength (nm)
`
` 0
` 0
` 0
`
`380
`
`430
`
`480
`
`530
`
`580
`
`630
`
`680
`
`730
`
`Fig.2 1 C
`
`Wavelength (nm)
`
`
`
`
`
`380
`
`430
`
`480
`
`530
`
`580
`
`#630
`
`680
`
`730
`
`Wavelength (nm)
`
`TCL 1037, Page 18
`LOWES 1037, Page 18
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`LOWES 1037, Page 18
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 18 of 19
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`5,998,925
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`Fig.22A
`mor TCOCdC(‘CYd
`
`
`
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`
`380
`
`430
`
`480
`
`530
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`580
`
`630
`
`680
`
`730
`
`Fig.22B
`
`Wavelength (nm)
`
`
`
`
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`
`
`
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`
`
`
` 0
`
`
`380=.480 480 530 580 630 680 730
`
`
`
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`
`Fig.2ODo
`
`Wavelength (nm)
`
`80
`
`430
`
`480
`
`530
`
`580
`
`#630
`
`680
`
`730
`
`Wavelength (nm)
`
`TCL 1037, Page 19
`LOWES 1037, Page 19
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`LOWES 1037, Page 19
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`U.S. Patent
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`Dec. 7, 1999
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`Sheet 19 of 19
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`5,998,925
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`600650700750
`400450500
`
`550
`
`350
`
`0
`
`
`
`Wavelength(nm)
`
`TCL 1037, Page 20
`LOWES 1037, Page 20
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`Fig.23
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`
`LOWES 1037, Page 20
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`

`

`5,998,925
`
`1
`LIGHT EMITTING DEVICE HAVING A
`NITRIDE COMPOUND SEMICONDUCTOR
`AND A PHOSPHOR CONTAINING A
`GARNET FLUORESCENT MATERIAL
`
`BACKGROUNDOF THE INVENTION
`
`it
`
`20
`
`2
`in a cup
`large energy band gap of light emitting layer,
`providedat the tip of a lead frame, and having a fluorescent
`material
`that absorbs light emitted by the light emitting
`component and emits light of a wavelength different from
`that of the absorbed light (wavelength conversion), con-
`tained in a resin mold which covers the light emitting
`component.
`The light emitting diode disclosed as described above
`capable of emitting white light by mixing the light of a
`plurality of sources can be made by using a light emitting
`component capable of emitting blue light and molding the
`light emitting component with a resin including a fluorescent
`material that absorbs the light emitted by the blue light
`emitting diode and emits yellowish light.
`However, conventional light emitting diodes have such
`problems as deterioration ofthe fluorescent material leading
`to color tone deviation and darkening of the fluorescent
`material resulting in loweredefficiency of extracting light.
`Darkening here refers to, in the case of using an inorganic
`fluorescent material such as (Cd, Zn)S fluorescent material,
`for example, part of metal elements constituting the fluo-
`rescent material precipitate or change their properties lead-
`ing to coloration, or,
`in the case of using an organic
`fluorescent material, coloration due to breakage of double
`bond in the molecule. Especially when a light emitting
`component made of a semiconductor having a high energy
`bandgap is used to improve the conversion efficiency ofthe
`fluorescent material (that is, energy of light emitted by the
`semiconductor is increased and number of photons having
`energies above a threshold which can be absorbed by the
`fluorescent material increases, resulting in more light being
`absorbed), or the quantity of fluorescent material consump-
`tion is decreased (that is, the fluorescent material is irradi-
`ated with relatively higher energy), light energy absorbed by
`the fluorescent material
`inevitably increases resulting in
`more significant degradation ofthe fluorescent material. Use
`of the light emitting component with higher intensity oflight
`emission for an extendedperiodoftime causes further more
`significant degradation of the fluorescent material.
`Also the fluorescent material provided in the vicinity of
`the light emitting component may be exposed to a high
`temperature such as rising temperature of the light emitting
`component and heat transmitted from the external environ-
`ment (for example, sunlight
`in case the device is used
`outdoors).
`Further, some fluorescent materials are subject to accel-
`erated deterioration due to combination of moisture entered
`
`introduced during the production
`from the outside or
`process, the light and heat transmitted from the light emit-
`ting component.
`When it comesto an organic dye of ionic property, direct
`current electric field in the vicinity of the chip may cause
`electrophoresis, resulting in a change in the color tone.
`SUMMARYOF THE INVENTION
`
`1. (Field of the Invention)
`The present
`invention relates to a light emitting diode
`used in LED display, back light source, traffic signal, trail-
`way signal,
`illuminating switch,
`indicator, ete. More
`particularly,
`it relates to a light emitting device (LED)
`comprising a phosphor, which converts the wavelength of
`light emitted by a light emitting component and emits light,
`and a display device using the light emitting device.
`2. (Description of Related Art)
`A light emitting diode is compact and emits light of clear
`color with high efficiency. It is also free from such a trouble
`as burn-out and has goodinitial drive characteristic, high
`vibration resistance and durability to endure repetitive
`ON/OFFoperations, because it is a semiconductor element.
`Thus it has been used widely in such applications as various
`indicators and various light sources. Recently light emitting
`diodes for RGB (red, green and blue) colors having ultra-
`high luminance and high efficiency have been developed,
`and large screen LED displays using these light emitting
`diodes have been put
`into use. The LED display can be
`operated with less power and has such good characteristics
`as light weight and longlife, and is therefore expected to be
`more widely usedin the future.
`Recently, various attempts have been made to make white
`light sources by using light emitting diodes. Because the
`light emitting diode has a favorable emission spectrum to
`generate monochromatic light, making a light source for
`white light requires it to arrange three light emitting com-
`ponents of R, G andB closely to each other while diffusing
`and mixing the light emitted by them. When generating
`white light with such an arrangement, there has been such a
`problem that white light of the desired tone cannot be
`generated due to variations in the tone, luminance and other
`factors of the light emitting component. Also when the light
`emitting components are made ofdifferent materials, elec-
`tric power required for driving differs from one light emit-
`ting diode to another, making it necessary to apply different
`voltages different light emitting components, which leads to
`complex drive circuit. Moreover, because the light emitting
`components are semiconductor light emitting components,
`color tone is subject to variation due to the difference in
`temperature characteristics, chronological changes and oper-
`aling environment, or unevenness in color may be caused s;
`due to failure in uniformly mixing the light emitted by the
`light emitting components. Thus light emitting diodes are
`effective as light emitting devices for generating individual
`colors, although a satisfactory light source capable of emit-
`ting white light by using light emitting components has not
`been obtained sofar.
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`In order to solve these problems, the present applicant
`previously developed light emitting diodes which convert
`the color of light, which is emitted by light emitting
`components, by meansof a fluorescent material disclosed in
`Japanese Patent Kokai Nos. 5-152609, 7-99345, 7-176794
`and 8-8614. The light emitting diodes disclosed in these
`publications are such that, by using light emitting compo-
`nents of one kind, are capable of generating light of white
`and other colors, and are constituted as follows.
`The light emitting diode disclosed in the above gazettes
`are made by mounting a light emitting component, having a
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`Thus, an object of the present invention is to solve the
`problems described above and provide a
`light emitting
`device which experiences only extremely low degrees of
`deterioration in emission light intensity, light emission effi-
`ciency and color shift over a long time of use with high
`luminance.
`
`The present applicant completed the present invention
`through researches based on the assumption that a light
`emitting device having a light emitting component and a
`fluorescent material must meet the following requirements
`to achieve the above-mentioned object.
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`(1) The light emitting component must be capable of
`emitting light of high luminance with light emitting char-
`acteristic which is stable over a long time of use.
`(2) The fluorescent material being providedin the vicinity
`of the high-luminancelight emitting component, must show
`excellent resistance against light and heat so that the prop-
`erties thereof do not change even when used over an
`extended period of time while being exposedto light of high
`intensity emitted by the light emitting component
`(particularly the fluorescent material provided in the vicinity
`of the light emitting component is exposed to light of a
`radiation intensity as high as about 30 to 40 times that of
`sunlight according to our estimate, and is required to have
`more durability against light as light emitting component of
`higher luminance is used).
`(3) With regard to the relationship with the light emitting
`component,
`the fluorescent material must be capable of
`absorbing with high efficiency the light of high monochro-
`maticity emitted by the light emitting component and emit-
`ting light of a wavelength different from that of the light
`emitted by the light emitting component.
`Thus the present
`invention provides a light emitting
`device, comprising a light emitting component and a phos-
`phor capable of absorbing a part oflight emitted by the light
`emitting component and emitting light of wavelength dif-
`ferent from that of the absorbed light; wherein said light
`emitting component comprises a nitride compound semi-
`conductor represented by the formula: In,Ga;Al,N where
`051, OS), OSk and i+j+k=1) and said phosphor contains a
`garnet fluorescent material comprising 1) at
`least one ele-
`ment selected from the groupconsisting of Y, Lu, Sc, La, Gd
`and Sm, and 2) at least one element selected from the group
`consisting of Al, Ga andIn, and being activated with cerium.
`The nitride compound semiconductor (generally repre-
`sented by chemical formula In,Ga,Al,N where 03i, 03},
`OSk and i1+j+k=1) mentioned above contains various mate-
`rials including InGaN and GaN doped with various impu-
`rities.
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`In the light emitting device of the present invention, the
`phosphor may be a fluorescent material represented by a
`general
`formula (Re,_,5m,)3(Al,_,Ga,);0,,.:Ce, where
`OSr<1 and OSs=1 and Reisat least one selected from Y
`and Gd, in which case good characteristics can be obtained
`similarly to the case where the yttrium-aluminum-garnet
`fluorescent material is used.
`
`Alsoin the light emitting device of the present invention,
`it is preferable, for the purpose of reducing the temperature
`dependence of light emission characteristics (wavelength of
`emitted light,
`intensity of light emission, etc.),
`to use a
`fluorescent material
`represented by a general
`formula
`(Yj -p-g-rGd,,Ce,Sm,),(Al,_,Ga,);0,. as the phosphor,
`where O£p£08 0.0032q150.2, 0,0003=r=0.08 and
`OSs21.
`
`Also in the light emitting device of the present invention,
`the phosphor may contain two or more yttrium-aluminum-
`garnet fluorescent materials, activated with cerium, of dif-
`ferent compositions including Y and Al. With this
`configuration,
`light of desired color can be emitted by
`controlling the emission spectrum of the phosphor according
`to the property (wavelength of emitted light) of the light
`emitting component.
`Further
`in the light emitting device of the present
`invention, in order to have light of a specified wavelength
`emitted by the light emitting device, it is preferable that the
`phosphor contains two or more fluorescent materials of
`different compositions represented by general
`formula
`(Re,_,Sm,)5(Al,_.Ga,);0,.:Ce, where OSr<1 and OSs31
`and Reis at least one selected from Y and Gd.
`
`Also in the light emitting device of the present invention,
`in order to control
`the wavelength of emitted light,
`the
`phosphor may contain a first
`fluorescent material repre-
`sented by general formula Y,(Al,_,Ga,).O,.:Ce and a sec-
`ond fluorescent material represented by general formula
`Re,Al,0,,:Ce, where 0£s=1 andReis at least one selected
`from Y, Ga and La.
`Alsoin the light emitting device of the present invention,
`in order to control
`the wavelength of emitted light,
`the
`phosphor may be an yttrium-aluminum-garnet fluorescent
`material containing a first fluorescent material and a second
`fluorescent material, with different parts of each yttrium
`being substituted with gadolinium.
`Further
`in the light emitting device of the present
`invention, it is preferable that main emission peak of the
`light emitting component is set within the range from 400
`nm to 530 nm and main emission wavelength of the phos-
`phor is set to be longer than the main emission peak ofthe
`light emitting component. This makes it possible to effi-
`ciently emit white light.
`Further
`in the light emitting device of the present
`invention, it is preferable that the light emitting layer of the
`light emitting component contains gallium nitride semicon-
`ductor which contains In, and the phosphor is yttrium-
`aluminum-garnet fluorescent material wherein part of Al is
`substituted by Ga so that the proportion of Ga:Al is within
`the range from 1:1 to 4:6 and part of Y is substituted by Gd
`so that the proportion of Y:Gd is within the range from 4:1
`to 2:3. Absorption spectrum of the phosphor which is
`controlled as described above shows good agreement with
`that of light emitted by the light emitting component which
`contains gallium nitride semiconductor including In as the
`light emitting layer, and is capable of improving the con-
`version efficiency (light emission efficiency). Also the light,
`generated by mixing blue light emitted by the light emitting
`component andfluorescentlight of the fluorescent material,
`is a white light of good color rendering and, in this regard,
`an excellent light emitting device can be provided.
`
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`
`The phosphor mentioned above contains various materi-
`als defined as described above, including Y,Al,0,5:Ce and
`Gd,In,O,4:Ce.
`Because the light emitting device of the present invention
`uses the light emitting component made ofa nitride com-
`pound semiconductor capable of emitting light with high
`luminance, the light emitting device is capable of emitting
`light with high luminance. Also the phosphor usedin the
`light emitting device has excellent resistance against light so
`that the fluorescent properties thereof experience less change
`even whenused over an extendedperiod of time while being 5
`exposed to light of high intensity. This makesit possible to
`reduce the degradation ofcharacteristics during long period
`of use and reduce deterioration duetolight of high intensity
`emitted by the light emitting component as well as extra-
`neous light (sunlight including ultraviolet light, ete.) during 5
`outdooruse, thereby to provide a light emitting device which
`experiences extremely less color shift and less luminance
`decrease. The light emitting device of the present invention
`can also be used in such applications that require response
`speeds as high as 120 nsec.,
`for example, because the
`phosphor used therein allows alter glow only for a short
`period of time.
`The phosphor used in the light emitting diode of the
`present invention preferably contains an yttrium-aluminum-
`garnet fluorescent material that contains Y and Al, which
`enables it
`to increase the luminance of the light emitting
`device.
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`The light emitting device according to one embodiment of
`the present invention comprises a substantially rectangular
`optical guide plate provided with the light emitting compo-
`nent mounted on one side face thereofvia the phosphor and
`surfaces of which except
`for one principal surface are
`substantially covered with a reflective material, wherein
`light emitted by the light emitting component is turnedto
`planarlight bythe optical guide plate and the phosphor, and
`is output from the principal surface of the optical guide
`plate.
`The light emitting device according to another embodi-
`ment of the present invention has a substantially rectangular
`optical guide plate, which is provided with the light emitting
`component mounted on oneside face thereof and the phos-
`phorinstalled on one principal surface with surfaces thereof,
`except for the principal surface being substantially covered
`with a reflective material, wherein light emitted by the light
`emitting component is turned to planar light by the optical
`guide plate and the phosphor, andis output from the prin-
`cipal surface ofthe optical guide plate.
`The LED display device according to the present inven-
`tion has an LED display device comprisingthe light emitting
`devices of the present invention arrangedin a matrix and a
`drive circuit which drives the LED display device according
`to display data which is input thereto, This configuration
`makes it possible to provide a relatively low-priced LED
`display device which is capable of high-definition display
`with less color unevenness due to the viewing angle.
`The light emitting diode according to one embodiment of
`the present invention comprises:
`a mount lead having a cup anda lead;
`an LED chip mountedin the cup of the mount lead with
`one of electrodes being electrically connected to the mount
`lead;
`a transparent coating material filling the cup to cover the
`LED chip; and
`a light emitting diode having a molding material which
`covers the LED chip covered with the coating material
`including the cup of the mount lead,
`the inner lead and
`another electrode of the LED chip, wherein
`the LED chip is a nitride compound semiconductor and
`the coating material contains at least one element selected
`from the group consisting of Y, Lu, Sc, La, Gd and Sm,at
`least one element selected from the group consisting ofAl,
`Ga and In and a phosphor made of garnet
`fluorescent
`material activated with cerium.
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`The phosphor used in the light emitting diode of the
`present
`invention preferably contains yttrium-aluminum-
`garnet fluorescent material that contains Y and Al.
`In the light emitting diode of the present invention, the
`phosphor may be a fluorescent material represented by a
`general
`formula (Re,_,Sm,),(Al,_,Ga,).0,,:Ce, where
`OSr<l and OSs=1 and Reisat least one selected from Y
`and Gd.
`
`Alsoin the light emitting diode of the present invention,
`a fluorescent material represented by a general
`formula
`(Yy_p-q-rGd,,Ce,Sm,),(Al,_,Ga,);0,. may be used as the
`phosphor, where 0O£=p=0.8, 0.003 =q=0.2, 0.0003 =r=0.08
`and OSs21.
`
`In the light emitting diode of the present invention, the
`phosphor preferably contain two or more yltrium-
`aluminum-garnet
`fluorescent materials, activated with
`cerium, of different compositions including Y and Al,
`in
`order to control the emitted light to a desired wavelength.
`In the light emitting diode of the present
`invention,
`similarly,
`two or more fluorescent materials of different
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`compositions represented by a general formula (Re,_,Sm,)5
`(Al,_, Ga,),0,,:Ce, where O2r<1 and OSs=1 andReisat
`least one selected from Y and Gd may be used as the
`phosphor in order to control the emitted light to a desired
`wavelength.
`invention,
`In the light emitting diode of the present
`similarly, a first fluorescent material represented by a general
`formula Y,(Al,_.Ga,);0,.:Ce and a second fluorescent
`material represented by a general formula Re,Al,O,,:Ce,
`may be used as the phosphor where O£s21 and Reis alleast
`one selected from Y, Ga and La,
`in order to control
`the
`emitted light to a desired wavelength.
`invention,
`In the light emitting diode of the present
`similarly, yttrium-aluminum-garnet fluorescent material a
`first fluorescent material and a second fluorescent material
`
`may be used wherein part of yttrium being substituted with
`gadolinium to different degrees of substitution as the
`phosphor, in order to control the emitted light to a desired
`wavelength.
`Generally, a fluorescent material which absorbslight of a
`short wavelength and emits light of a long wavelength has
`higher efficiency than a fluorescent material which absorbs
`light of a long wavelength and emits light of a short
`wavelength. It is preferable to use a light emitting compo-
`nent which emits visible light than a light emitting compo-
`nent which emits ultraviolet
`light
`that degrades resin
`(molding material, coating material, etc.). Thus for the light
`emitting diode of the present invention, for the purpose of
`improving the light emitting efficiency and ensure longlife,
`it is preferable that main emission peakof the light emitting
`component be set within a relatively short wavelength range
`of 400 nm to 530 nm in the visible light region, and main
`emission wavelength ofthe phosphorbe set to be longer than
`the main emission peak of the light emitting component.
`With this arrangement, because light converted by the
`fluorescent material has longer wavelength than that of light
`emitted by the light emitting component,
`it will not be
`absorbed by the light emitting component even when the
`light emitting component is irradiated with light which has
`been reflected and converted by the fluorescent material
`(since the energy ofthe converted light is less than the band
`gap energy). Thus the light which has beenreflected by the
`fluorescent material or the like is reflected by the cup
`wherein the light emitting component is mounted, making
`higher efficiency of emission possible.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic sectional view of a lead type light
`emitting diode according to the embodiment of the present
`invention.
`
`FIG, 2 is a schematic sectional view ofa tip type light
`emitting diode according to the embodiment of the present
`invention.
`
`FIG. 3A is a graph showing the excitation spectrum ofthe
`garnet fluorescent material activated by cerium used in the
`first embodiment ofthe present invention.
`FIG. 3B is a graph showing the emission spectrum of the
`garnet fluorescent material activated by cerium usedin the
`first embodiment ofthe present invention.
`FIG. 4 ts a graph showing the emission spectrum ofthe
`light emitting diode ofthe first embodiment of the present
`invention.
`
`FIG. 5A is a graph showing the excitation spectrum ofthe
`yttrium-aluminum-garnet fluorescent material activated by
`cerium used in the second embodiment of the present
`invention.
`
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`FIG. 5B is a graph showing the emission spectrum ofthe
`yttrium-aluminum-garnet fluorescent material activated by
`cerium used in the second embodiment of the present
`invention.
`
`FIG. 6 shows the chromaticity diagram oflight emitted by
`the light emitting diode of the second embodiment, while
`points A and B indicate the colors of light emitted by the
`light emitting component and points C and D indicate the
`colors of light emitted by two kinds of phosphors.
`FIG, 7 is a schematic sectional view ofthe planar light
`source according to another embodiment of the present
`invention.
`
`FIG. 8 is a schematic sectional view of another planar
`light source different from that of FIG, 7.
`FIG, 9 is a schematic sectional view of another planar
`light source different from those of FIG. 7 and FIG. 8.
`FIG, 10 is a block diagram 10 of a display device which
`is an application of the present invention.
`FIG. 11 is a plan view ofthe LED display device ofthe
`display device of FIG. 10.
`FIG, 12 is a plan view ofthe LED display device wherein
`one pixel
`is constituted from four light emitting diodes
`including the light emitting diode of the present invention
`and those emitting RGB colors.
`FIG. 13A showsthe results of durable life test of the light
`emitting diodes of Example | and Comparative Example 1,
`showingthe results at 25° C. and FIG, 13B showsthe results
`of durable life test of the light emitting diodes of Example
`1 and Comparative Example 1, showing the results at 60° C.
`and 90% RH.
`
`FIG. 144 shows the results of weatherability test of
`Example 9 and Comparative Example 2 showing the change
`of luminance retaining ratio with time and FIG. 14B shows
`the results of weatherability test of Example 9 and Com-
`parative Example 2 showing the color tone before and after
`the test.
`
`FIG. 15A showsthe results of reliability test of Example
`9 and Comparative Example 2 showing the relationship
`between the luminance retaining ratio and me, and FIG.
`15B is a graph showingthe relationship between color tone
`and time.
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`FIG, 16 is a chromaticity diagram showing the range of
`color tone which can be obtained with a light emitting diode
`which combines the fluorescent materials shown in Table |
`and blue LED having peak wavelength at 465 nm.
`FIG. 17 is a chromaticity diagram showing the change in
`color tone when the concentration of fluorescent material is
`changed in the light emitting diode which combines the 5
`fluorescent materials shown in Table | and blu