Solid state device and light-emitting element Number:7,417,220 from the United States Patent and Trademark Office (PTO) owispatent

Title: Solid state device and light-emitting element

Abstract: A solid-state device having: a flip-chip mounted solid-state element; a power receiving/feeding portion having a mounting substrate to allow that a mounting surface of the solid-state element forms substantially the same plane as a surface of the mounting substrate; and an inorganic sealing portion made of an inorganic sealing material having a thermal expansion coefficient equal to that of the power receiving/feeding portion for sealing the solid-state element.

Patent Number: 7,417,220 Issued on 08/26/2008 to Suehiro,   et al.

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Inventors:	Suehiro; Yoshinobu (Aichi-ken, JP), Ichikawa; Masayoshi (Aichi-ken, JP), Wada; Satoshi (Aichi-ken, JP), Tasumi; Koji (Aichi-ken, JP)
Assignee:	Toyoda Gosei Co., Ltd. (Nishikasugai-gun, Aichi-ken, JP)
Appl. No.:	11/220,405
Filed:	September 7, 2005

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Foreign Application Priority Data

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Sep 09, 2004 [JP]			2004-263097
Oct 29, 2004 [JP]			2004-316007

Current U.S. Class:	250/239 ; 257/99; 362/545; 362/800; 438/108; 438/127; 438/26
Current International Class:	H01L 27/15 (20060101); H01L 33/00 (20060101)
Field of Search:	250/239

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References Cited [Referenced By]

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U.S. Patent Documents

2003/0011077	January 2003	Morishima et al.
2004/0041222	March 2004	Loh
2004/0046242	March 2004	Asakawa
2004/0237299	December 2004	Stelzl et al.
2005/0009244	January 2005	Shiobara et al.
2006/0012299	January 2006	Suehiro et al.
2006/0027934	February 2006	Edelstein et al.
2006/0091541	May 2006	Bojkov et al.
2006/0261364	November 2006	Suehiro et al.
2007/0096312	May 2007	Humpston et al.

Foreign Patent Documents

	8-102553		Apr., 1996		JP
	11-177129		Jul., 1999		JP
	2002-9427		Jan., 2002		JP

Primary Examiner: Lee; John R
Attorney, Agent or Firm: McGinn IP Law Group, PLLC

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Claims

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What is claimed is:

1. A solid-state device, comprising: a flip-chip mounted solid-state element; a power receiving/feeding portion comprising a mounting substrate to allow that a mounting surface of the solid-state element forms substantially the same plane as a surface of the mounting substrate; and an inorganic sealing portion comprising an inorganic sealing material having a thermal expansion coefficient equal to that of the power receiving/feeding portion for sealing the solid-state element.

2. The solid-state device according to claim 1, wherein the mounting substrate comprises: an inorganic substrate; and a conductive pattern formed thereon.

3. The solid-state device according to claim 1, wherein the mounting substrate comprises: an inorganic substrate; and a circuit pattern comprising: a first conductive pattern formed on the solid-state element mounting side; a second conductive pattern formed on the backside thereof; and a third conductive pattern for electrically connecting both the sides.

4. The solid-state device according to claim 3, wherein: the mounting substrate seals the solid-state element while being bonded to the inorganic sealing portion by chemical reaction.

5. The solid-state device according to claim 1, wherein: the inorganic sealing portion is formed by pressure-bonding a low melting point glass as the inorganic sealing material to the mounting substrate in a high-viscosity condition of 10.sup.4-10.sup.9 poises.

6. The solid-state device according to claim 1, wherein: the solid-state element comprises an electrode comprising a light reflectivity on the mounting surface side.

7. The solid-state device according to claim 1, wherein: the solid-state element is mounted on the power receiving/feeding portion through a conductive adhesive.

8. The solid-state device according to claim 1, wherein: the solid-state element is mounted on the power receiving/feeding portion through an eutectic material.

9. The solid-state device according to claim 1, wherein: the solid-state element is mounted on the mounting substrate by fusion-bonding an electrode with the mounting surface to a circuit pattern formed on the mounting substrate.

10. The solid-state device according to claim 1, wherein: the inorganic sealing portion comprises a thermal expansion coefficient equal to or up to 4 times that of the solid-state element.

11. The solid-state device according to claim 1, wherein the solid-state element comprises an optical element, and wherein the inorganic sealing material comprises a light-transmitting material.

12. The solid-state device according to claim 11, wherein: the optical element comprises a light-emitting element.

13. The solid-state device according to claim 12, wherein: the light-emitting element comprises an optical catalytic portion formed on a surface of the inorganic sealing portion.

14. The solid-state device according to claim 13, wherein the optical catalytic portion comprises a light-transmitting protective layer for protecting the surface of the inorganic sealing portion, and wherein the surface of the protective layer comprises an optical catalytic layer comprised of TiO.sub.2.

15. The solid-state device according to claim 12, wherein the light-emitting element comprises a GaN-based light-emitting element, wherein the GaN-based light-emitting element comprises: a sapphire substrate; and a GaN-based semiconductor layer formed on the sapphire substrate.

16. The solid-state device according to claim 11, wherein: the optical element comprises a light-receiving element.

17. The solid-state device according to claim 2, wherein: the solid-state element is mounted on the mounting substrate to prevent the penetration of the inorganic sealing material between the solid-state element and the conductive pattern.

18. The solid state device according to claim 2, wherein the conductive pattern comprises one of tungsten, nickel, and gold.

19. The solid state device according to claim 2, wherein joined surfaces of a p-electrode and an n-electrode of the solid-state element are electrically connected to the conductive pattern on substantially the same plane.

20. A method of manufacturing a solid state device, comprising: forming a circuit pattern layout on a surface of a mounting substrate having via holes; forming the circuit pattern layout on the mounting substrate; plating the circuit pattern layout to form a circuit pattern; forming a conductive adhesive on a surface of the circuit pattern; forming a solid-state element on the circuit pattern such that a mounting surface of a p-electrode and n-electrode of the solid state element are on substantially the same plane relative to the surface of the circuit pattern; and forming an inorganic sealing portion by pressure-bonding a low melting point glass to the mounting substrate in a high-viscosity condition of 10.sup.4-10.sup.9 poises.

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Description

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The present application is based on Japanese patent application Nos. 2004-263097 and 2004-316007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid state device, and particularly, to a solid state device which is sealed with a sealing material made of low melting point glass.

The present invention also relates to a light-emitting element made of a semiconductor material and a light-emitting device using the light-emitting element, and particularly, to a light-emitting element and a light-emitting device which are flip-chip mounted.

Herein, a solid state device includes various optical devices or elements such as a light-emitting device or element, a light-receiving device or element, and a solar cell. Also, herein, a light-emitting element includes an LED element, and a light-emitting device includes an LED.

2. Description of the Related Art

Conventionally, there are solid state devices with a solid state component such as a light-emitting diode (LED), or the like, sealed with a light-transmitting resin material such as epoxy resin, or the like. It is known that in such solid state devices, light-transmitting resin is degraded by light. Particularly, in the case of use of group III nitride-based compound semiconductor light-emitting elements which emit short-wavelength light, light-transmitting resin around the elements is caused to turn yellow by high-energy light emitted from the elements and heat produced by the elements themselves, which often unnegligibly degrades efficiency of deriving light.

To prevent degradation of such sealing materials, there have been proposed light-emitting devices using low melting point glass as sealing material (See Japanese patent application laid-open Nos. 8-102553, and 11-177129, for example).

The light-emitting device of Japanese patent application laid-open No. 8-102553 is constructed by covering an LED element, wire bonding portions, and upper ends of leads, with a transparent sealing material made of low melting point glass. In the low melting point glass, there is used glass whose melting point is 130-350.degree. C. by adding thereto selenium, thallium, arsenic, sulfur, etc., for example. In this case, there is used low melting point glass whose melting point is preferably 200.degree. C. or less, more preferably 150.degree. C. or less.

The light-emitting device of Japanese patent application laid-open No. 8-102553 uses a transparent sealing material made of low melting point glass, thereby obviating the problem with optical degradation with time of light-transmitting resin material due to ultraviolet rays.

On the other hand, the light-emitting device of Japanese patent application laid-open No. 11-177129 uses, as sealing material for covering its LED element, low melting point glass whose refractive index is on the order of 2 close to the refractive index of GaN-based LED elements, the order of 2.3.

The light-emitting device of Japanese patent application laid-open No. 11-177129 seals its LED element with low melting point glass whose refractive index is close to the refractive index of GaN-based LED elements, thereby lessening light totally reflected off the interface between the LED element and the low melting point glass, while increasing light radiated outwardly from the LED element and passed into the low melting point glass. As a result, the outward radiation efficiency becomes higher than that of conventional light-emitting devices with an LED element sealed with epoxy resin,

According to conventional solid state devices, however, because of high viscosity of conventional low melting point glass in a practical sealing temperature range, it is impossible to realize a solid state device having the sufficient sealing property when using a sealing material made of low melting point glass.

Conventionally, on the other hand, flip-chip mounting is known in which an LED element is electrically connected to a wiring pattern of a printed wiring board or the like through a stud bump of Au or the like.

In flip-chip mounting, a cathode and an anode on the LED element are connected to a wiring pattern via a stud bump, thus allowing mounting of the LED element without using pad electrodes and wires. In addition, light is radiated from the surface opposite the mounting surface, which thus allows excellent light-radiating performance without pad electrodes and wires blocking off light.

The above-mentioned flip-chip mounting requires arrangement of stud bumps according to the number of cathodes and anodes, and stable arrangement of the LED element requires 3 or more stud bumps. This requires time-consuming and costly bump formation. Particularly, in large-size LED elements, a plurality of stud bumps are arranged for multipoint joining, which can therefore be more significantly time-consuming and costly.

As a means for obviating time-consuming labor in such bump formation, there is a bump formation method in which a bump for mounting components is formed on the surface of a printed wiring board by plating (See Japanese patent application laid-open No. 2002-9427).

According to a bump formation method described in Japanese patent application laid-open No. 2002-9427, a resist film is formed by applying resist to the surface of a printed wiring board, using a spin coater or a printing method. The resist film formation is followed by light exposure using a mask having a mask window matching a desired position and shape of a bump. Next, an exposed portion is developed and dissolved by an immersion or spray method used in typical photoresist development to form an opening, followed by plating the opening and subsequently dissolving and removing the resist film, thereby forming a plurality of bumps for mounting components on the printed wiring board.

In the above-mentioned bump formation method, however, because the bumps for mounting components have to be formed by photolithography, the number of fabrication steps increases, which results in a high cost.

Further, it is required that the bumps for mounting components have high shape accuracy matching electrode shape of the light-emitting element, and that the light-emitting element be positioned accurately relative to the bumps for mounting components when mounting the light-emitting element.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a solid state device having the sufficient sealing property when using a sealing material made of low melting point glass.

It is a further object of the present invention to provide a solid state device which is excellent in solid state component packaging, sealing, electrical connection, and thermal dissipation.

It is a still further object of the present invention to provide an LED element and a light-emitting device, the packaging process of which can be simplified. (1) According to a first aspect of the invention, a solid-state device comprises:

a flip-chip mounted solid-state element;

a power receiving/feeding-portion comprising a mounting substrate to allow that a mounting surface of the solid-state element forms substantially the same plane as a surface of the mounting substrate; and

an inorganic sealing portion made of an inorganic sealing material having a thermal expansion coefficient equal to that of the power receiving/feeding portion for sealing the solid-state element. (2) According to a second aspect of the invention, a light-emitting element comprises:

p and n contact electrodes formed on a flip-chip mounting surface of the light-emitting element corresponding to one light-emitting layer of the light-emitting element; and

a fusion-bonding portion formed on the p and n contact electrodes corresponding to the p and n contact electrodes, for being fusion-bonded to an external mounting pattern. (3) According to a third aspect of the invention, a light-emitting device comprises:

a light-emitting element comprising on a flip-chip mounting surface a contact electrode which serves as a reflection mirror, and a fusion-bonding portion formed on the contact electrode;

a mounting substrate comprising an external mounting pattern fusion-bonded to the fusion-bonding portion; and

a light-transmitting sealing portion for sealing the light-emitting element fusion-bonded to the mounting substrate. (4) According to a fourth aspect of the invention, a light-emitting device comprises:

a light-emitting element comprising on a flip-chip mounting surface a contact electrode which serves as a reflection mirror;

a mounting substrate comprising a fusion-bonding portion fusion-bonded to the contact electrode; and

a light-transmitting sealing portion for sealing the light-emitting element fusion-bonded to the mounting substrate.

According to the present invention, it is possible to realize a solid state device having the sufficient sealing property when using a sealing material made of low melting point glass.

According to the present invention, it is possible to provide a solid state device which is excellent in solid state component packaging, sealing, electrical connection, and thermal dissipation.

According to the LED element and the light-emitting device of the present invention, since in the element fabrication process the fusion-bonded portion is electrically connected to the n-side and p-side of the LED element so as to be formed integrally with the LED element, the mounting process can be simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments according to the invention will be explained below referring to the drawings, wherein:

FIG. 1 is a cross-sectional view illustrating an LED as a solid state device according to a first embodiment of the invention;

FIG. 2 is a cross-sectional view illustrating an LED as a solid state device according to a second embodiment of the invention;

FIG. 3 is a cross-sectional view illustrating an LED as a solid state device according to a third embodiment of the invention;

FIG. 4 is a cross-sectional view illustrating an LED as a solid state device according to a fourth embodiment of the invention;

FIG. 5 is a cross-sectional view illustrating an LED as a solid state device according to a fifth embodiment of the invention;

FIG. 6 is a cross-sectional view illustrating an LED as a solid state device according to a sixth embodiment of the invention;

FIG. 7 is a cross-sectional view illustrating an LED according to a seventh embodiment of the invention;

FIG. 8 is a plain view where the LED element according to the seventh embodiment is viewed from electrode formation surface;

FIG. 9 is a cross-sectional view of the LED element cut along line A-A of FIG. 8;

FIG. 10 is an enlarged cross-sectional view illustrating an LED element according to an eighth embodiment of the invention;

FIG. 11A is a plain view illustrating a fusion-bonded portion of an LED element according to a ninth embodiment of the invention;

FIG. 11B is a cross-sectional view cut along line A-A of FIG. 11A;

FIGS. 12A and 12B are plain views illustrating a fusion-bonded portion of an LED element according to a tenth embodiment of the invention;

FIG. 13 is a plain view illustrating a fusion-bonded portion of an LED element according to an eleventh embodiment of the invention;

FIG. 14 is a plain view illustrating a fusion-bonded portion of an LED element according to a twelfth embodiment of the invention;

FIG. 15 is a plain view illustrating a fusion-bonded portion of an LED element according to a thirteenth embodiment of the invention;

FIG. 16 is a plain view illustrating a fusion-bonded portion of an LED element according to a fourteenth embodiment of the invention;

FIG. 17A is a plain view illustrating a fusion-bonded portion of an LED element according to a fifteenth embodiment of the invention;

FIG. 17B is a cross-sectional view cut along line A-A of FIG. 17A; and

FIG. 18 is a plain view illustrating a fusion-bonded portion of an LED element according to a sixteenth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

FIG. 1 is a cross-sectional view illustrating an LED as a solid state device according to a first embodiment of the invention.

This LED 1 comprises a flip-chip-type LED element 2 made of a GaN-based semiconductor material (thermal expansion coefficient .alpha.: 5-7 (.times.10.sup.-6/.degree. C.)), a glass-containing Al.sub.2O.sub.3 substrate 3 as an inorganic material substrate for mounting the LED element 2, a circuit pattern 4 consisting of tungsten (W)-nickel (Ni)-gold (Au) and formed in the glass-containing Al.sub.2O.sub.3 substrate 3, a conductive adhesive 5 made of Ag paste for electrically connecting the circuit pattern 4 to a p-electrode 24 and an n-electrode 25 of the LED element 2, and a glass sealing portion 6 made of transparent glass bonded to the glass-containing Al.sub.2O.sub.3 substrate 3 for sealing the LED element 2. In this embodiment, the glass-containing Al.sub.2O.sub.3 substrate 3 and the circuit pattern 4 form a power receiving/feeding portion, and the joined surfaces of the p-electrode 24 and the n-electrode 25 of the LED element 2 are electrically connected to the surface of the circuit pattern 4 on substantially the same plane.

The LED element 2 is formed by sequential crystal growth of an n-GaN layer 21, a light-emitting layer 22 and a p-GaN layer 23, via an AlN buffer layer not shown, on the surface of a sapphire (Al.sub.2O.sub.3) substrate 20, and has the p-electrode 24 provided on the surface of the p-GaN layer 23, and the n-electrode 25 formed on the n-GaN layer 21 exposed by etching and removing the region extending from the p-GaN layer 23 to a portion of the n-GaN layer 21, where an insulating layer 30 is provided on the mounting surface for forming the p-electrode 24 and the n-electrode 25, except for portions for electrical connection. This LED element 2 is epitaxially grown at 700.degree. C. or higher, and has a heat-resistant temperature of 600.degree. C. or higher, and is stable at temperatures at which sealing is performed using low melting point glass, as will be described later. The p-electrode 24 is formed of rhodium Rh for also serving as a lower reflection mirror for reflecting light emitted from the light-emitting layer 22 in the direction of the sapphire substrate 20, and is 0.34 mm.times.0.34 mm.times.thickness 0.09 mm in size.

The glass-containing Al.sub.2O.sub.3 substrate 3 has a thermal expansion coefficient of 12.3.times.10.sup.-6/.degree. C., and a plurality of via holes 3A. The metallized circuit pattern 4 on the front and back sides of the substrate is made electrically conductive through these via holes 3A. The circuit pattern 4 comprises a first conductive pattern formed on the LED element 2-mounting side, a second conductive pattern formed on its back side, and a third conductive pattern made of tungsten (W) for electrically interconnecting both the sides thereof.

The glass sealing portion 6 is formed of low melting point P.sub.2O.sub.5--ZnO--Li.sub.2O-based glass (thermal expansion coefficient: 11.4.times.10.sup.-6/.degree. C., yield point: 415.degree. C., refractive index n: 1.59, internal transmittance: 99% (470 nm)), which is bonded to the glass-containing Al.sub.2O.sub.3 substrate 3 by hot pressing with a mold, and thereafter is formed in a rectangular shape having a top surface 6A and side surfaces 6B formed by dicer cutting.

The low melting point glass is processed with viscosity on several orders of magnitude higher than a viscosity level which is generally said to be high in resin. Also, in the case of glass, its viscosity cannot decrease to a general resin sealing level even if the glass is at temperatures exceeding its yield point by a few ten .degree. C. Also, attempts at viscosity levels during general resin molding require temperatures exceeding the crystal growth temperature of the LED element, or cause adhesion to a mold, which results in difficulty in sealing and molding. For this reason, the viscosity during processing is preferably 10.sup.4-10.sup.9 poises.

The fabrication process for this LED 1 is explained below.

First, a glass-containing Al.sub.2O.sub.3 substrate 3 having via-holes 3A is prepared, and tungsten paste is screen-printed on the surface of the glass-containing Al.sub.2O.sub.3 substrate 3 according to a circuit pattern 4.

Next, the W-paste-printed glass-containing Al.sub.2O.sub.3 substrate 3 is heated at a little more than 1000.degree. C., thereby burning W into the glass-containing Al.sub.2O.sub.3 substrate 3, followed by Ni and Au plating over W, which results in the formation of a circuit pattern 4.

Next, high-viscous Ag paste is screen-printed on the surface of the circuit pattern 4 of the glass-containing Al.sub.2O.sub.3 substrate 3 (on the element-mounting side) as a conductive adhesive 5. An LED element 2 is positioned relative to this Ag-paste-printed circuit pattern 4, and heated at 150.degree. C., thereby hardening the Ag paste. The LED element 2 is mounted so that the mounting surfaces of its p-electrode 24 and n-electrode 25 are on substantially the same plane relative to the surface of the circuit pattern 4.

Next, a low melting point P.sub.2O.sub.5--ZnO--Li.sub.2O-based glass board is set parallel to the LED-element-mounted glass-containing Al.sub.2O.sub.3 substrate 3, followed by hot pressing at a temperature of 500.degree. C. in nitrogen atmosphere. The viscosity of the low melting point glass in this condition is 10.sup.8-10.sup.9 poises, and the low melting point glass is bonded to the glass-containing Al.sub.2O.sub.3 substrate 3 via the oxides contained therein.

Next, the glass-containing Al.sub.2O.sub.3 substrate 3 integral with the low melting point glass is set and diced in a dicer into the LED 1 separately.

There may be used the LED element 2 formed by scribing. In this case, because the LED element 2 formed by scribing tends to have uneven side surfaces with protrusions that are cut portions, it is desired to coat the side surfaces of the LED element 2 with an element-coating material. As this element-coating material, there may be used an SiO.sub.2-based coating material having light transmittance, for example. Use of an element-coating material allows preventing cracks and voids from occurring during resin overmolding, etc.

The effects of the first embodiment are as follows. (1) Since the low melting point P.sub.2O.sub.5--ZnO--Li.sub.2O-based glass is used and hot-pressed in a high viscous state, processing is possible at sufficiently low crystal growth temperatures, thus enhancing sealing. (2) Since the glass-containing Al.sub.2O.sub.3 substrate 3 and the glass sealing portion 6 are chemically bonded to each other via the oxide; firm sealing bonding strength can be obtained. For that reason, glass sealing is materialized even in the case of small-size packages with small joining area. (3) Since the sealing glass and the glass-containing Al.sub.2O.sub.3 substrate 3 have the same thermal expansion coefficient, after high temperature bonding, internal stress is small even at normal or low temperature, there is a less incidence of bonding failures of peeling, cracking, etc. In addition, glass tends to be caused to crack due to tensile stress, but has a less incidence of cracking due to compressive stress, so the thermal expansion coefficient of the sealing glass is made slightly small compared to the glass-containing Al.sub.2O.sub.3 substrate 3. The inventor has confirmed that no peeling and cracking occur even at 1000 cycles of -40.degree. C..revreaction.100.degree. C.liquid phase cold thermal shock tests. Also, as basic confirmation of bonding of a 5 mm square size glass piece to a ceramic substrate, experiments of combinations of various thermal expansivities of glass and ceramic substrate have verified that bonding is possible without cracking when the ratio of the low to high thermal expansion coefficient member is 0.85 or more. Although depending on the stiffness and size of the members, the same thermal expansion coefficient indicates this extent of range. (4) Since no wire is required by flip-chip mounting, no malfunction of electrodes occurs in high viscous processing. Since the viscosity of the low melting point glass during sealing is as hard as 10.sup.8-10.sup.9 poises which is significantly different in material properties compared to the order of 5 poises of liquid epoxy resin prior to thermal curing, no problems such as wire crushing and deformation occur when a face-up LED element is sealed in which electrodes on element surface and power-feeding members such as leads are electrically connected to each other by wires. Also, when a flip-chip LED element is sealed in which electrodes on element surface are flip-chip-joined to power-feeding members such as leads through a bump such as gold (Au), etc., it is possible to prevent bump crushing and a short-circuit between bumps due to pressure acting on the LED element in the direction of the power-feeding members according to the viscosity of glass. (5) Since the low melting point glass and the glass-containing Al.sub.2O.sub.3 substrate 3 are set parallel to each other and hot-pressed in a high viscous state, so as to move the low melting point glass parallel to the surface of the glass-containing Al.sub.2O.sub.3 substrate 3 and bring it into close contact therewith, no void occurs in sealing the GaN-based LED element 2. (6) Since the circuit pattern 4 of the glass-containing Al.sub.2O.sub.3 substrate 3 is drawn out to the backside at the via-holes 3A, there is no need of taking a particular action for preventing glass from penetrating into unwanted portions, from covering electrical terminals, and so on, thereby allowing the simplifying of the fabrication process. Also, since a plurality of devices are collectively sealed with the low melting point glass board, a plurality of LEDs 1 can easily be mass-produced by dicer cutting. Since the low melting point glass is processed in a high viscous state, without any need of taking a sufficient action as in resin, it is sufficiently possible to treat mass-production even without via-holes, provided that external terminals are drawn out to the backside (7) Since the GaN-based LED element 2 is flip-chip mounted, there are also the effects of being capable of overcoming the problems in materializing glass sealing, and of materializing 0.5 mm-square ultra-small-size LED 1. This is because no wire boding space is required, and no interface peeling occurs even in bonding in a small space by selecting the glass sealing portion 6 and the glass-containing Al.sub.2O.sub.3 substrate 3 with the same thermal expansion coefficient and by firm chemical bonding. (8) Since the LED element 2 is mounted so that the mounting surfaces of its p-electrode 24 and n-electrode 25 are on substantially the same plane relative to the surface of the circuit pattern 4, high-viscous glass cannot penetrate between the LED element 2 and the circuit pattern 4, thus allowing the prevention of a decrease in electrical connection characteristics and of cracking due to glass penetration, and thereby enhancing the mounting property. (9) Since the ratio of the mounting area to the element area of the LED element 2 is large, thermal dissipation can be enhanced and temperature irregularity can be prevented in the LED element 2. Also, since electrical connection characteristics are enhanced by enlarged conductive area, it is possible to sufficiently treat large light amount and high power of the LED 1. (10) Since portions other than the mounting surfaces of the LED element 2 are covered with the insulating layer 30, it is possible to prevent leak current from flowing through the portions other than the mounting surfaces of the LED element 2 even in the event of Ag paste adhesion thereto.

In the first embodiment, although Ag paste is used as the conductive adhesive 5, there may be used any conductive adhesive 5 other than Ag paste, which has material properties that do not lose the mounting property of the LED element 2 due to pressure exertion during glass sealing.

Also, if applicable to flip-chip mounting, any type of LED element may be used other than the GaN-based LED element 2. Also, as an optical element other than the LED element, there may be used a light-receiving element.

Embodiment 2

FIG. 2 is a cross-sectional view illustrating an LED as a solid state device according to a second embodiment of the invention. In the following embodiments, the same reference numbers as those of the first embodiment respectively denote the portions having the same structure and function as those in the first embodiment.

This LED 1 is different from that of the first embodiment in screen-printing high viscous Ag paste as the conductive adhesive 5 on a portion positioned on the n-electrode 25 of the LED element 2 explained in the first embodiment, and bringing the p-electrode 24 into close contact with the circuit pattern 4 directly without Ag paste therebetween.

The effects of the second embodiment are as follows. (1) Since no internal stress occurs in glass at high temperatures during glass processing, but glass contracts as cooled, which causes compression stress from the glass sealing portion 6 and the sapphire substrate 20 to the LED element 2, the element-mounting surface of the p-electrode 24 comes into close contact with the mounting surface of the circuit pattern 4 on substantially the same plane. This allows excellent-reliability electrical connection to be obtained without using Ag paste.

In flip-chip mounting using an Au-stud bump with epoxy resin and silicon resin, breaking can often be caused by tensile stress of the resin in solder reflow furnace treatment. This is because the resin with larger thermal expansion coefficient than that of the LED element 2 expands relatively more in higher-temperature atmosphere than resin-curing temperature. In contrast, in the solid state device of the invention, even in lead-free solder reflow furnace atmosphere on the order of 300.degree. C., which is lower than glass sealing temperature, compression stress therefore continues to act on the LED element 2, which results in no breaking.

Here, if no position shift of the LED element 2 occurs relative to the circuit pattern 4, glass sealing may be performed with low melting point glass by arranging the n-electrode 25 at a specified position on the circuit pattern 4 without fixing the n-electrode 25 with Ag paste. Also, even in the case of positioning by bonding, portions other than the mounting surfaces may be temporarily bonded with not conductive but thermal resistive adhesive

Embodiment 3

FIG. 3 is a cross-sectional view illustrating an LED as a solid state device according to a third embodiment of the invention.

This LED 1 is different from that of the first embodiment in that, to make possible electrical connection on the element side surfaces and surface mounting on the semiconductor layer side, an LED element 2 with a p-electrode 24 and an n-electrode 25 formed so as to be exposed to element edges from the element side surfaces to p-contact layer 240 surface are mounted on a circuit pattern 4 provided on an Al.sub.2O.sub.3 substrate 300 (thermal expansion coefficient: 7.times.10.sup.-6/.degree. C.), and sealed with a glass sealing portion 6 made of SiO.sub.2--Nb.sub.2O.sub.5-based low melting point glass. Here, the term "element edges" refers to edges of side surfaces of the LED element 2, and GaN-based semiconductor layer mounting surface formed in an insulating layer 31, as shown in FIG. 3.

The LED element 2 comprises an AlN buffer layer 200, an n-GaN layer 21, a light-emitting layer 22, a p-GaN layer 23, and a p-contact layer 240 for diffusing current into the p-GaN layer 23, which are sequentially stacked on a sapphire substrate 20, a light-transmitting insulating layer 30 on the side surfaces of the GaN-based semiconductor layer, an n-electrode 25 formed on the n-GaN layer 21 exposed by etching and removing the region extending from the p-GaN layer 23 to a portion of the n-GaN layer 21, a p-electrode 24 provided on the side surfaces of the GaN-based semiconductor layer extending from the AlN buffer layer 200 on the sapphire substrate 20 to the p-contact layer 240, and a light-transmitting insulating layer 31 for covering the element surface extending from the n-electrode 25 to the p-electrode 24.

The Al.sub.2O.sub.3 substrate 300 has a thin-film conductive plating layer 40 made of solder formed by electroplating the surface of the circuit pattern 4.

The fabrication process for this LED 1 is explained below.

First, the conductive plating layer 40 is formed by solder electroplating on the surface of the circuit pattern 4 that is provided on the Al.sub.2O.sub.3 substrate 300 for serving as an element mounting surface.

Next, the LED element 2 is positioned so that the formation surface of the insulating layer 31 comes into close contact with a specified position on the circuit pattern 4. Next, the Al.sub.2O.sub.3 substrate 300 with the LED element 2 positioned thereon is put and heated in a reflow furnace. This heating allows the conductive plating layer 40 to fuse so that the mounting surfaces of the p-electrode 24 and n-electrode 25 are soldered to the element-mounting surface of the circuit pattern 4 on substantially the same plane.

Next, an SiO.sub.2--Nb.sub.2O.sub.5-based low melting point glass board is set parallel to the LED-element 2-mounted Al.sub.2O.sub.3 substrate 300, followed by hot pressing at a temperature of 500.degree. C. in nitrogen atmosphere. The viscosity of the low melting point glass in this condition is 10.sup.8-10.sup.9 poises, and the low melting point glass is bonded to the Al.sub.2O.sub.3 substrate 300 via the oxides contained therein.

Next, the Al.sub.2O.sub.3 substrate 300 integral with the low melting point glass is set and diced in a dicer into the LED 1 separately.

The effects of the third embodiment are as follows. (1) Since the LED element 2 with the p-electrode 24 and n-electrode 25 exposed from the mounting surface to the side surfaces is mounted so as to come into contact with the circuit pattern 4, glass penetration to the mounting surface is blocked during glass sealing, thereby allowing obtaining effective joining area. This allows heat caused by light emission of the light emitting layer 22 to be promptly thermally conducted to the Al.sub.2O.sub.3 substrate 300, thus allowing enhancement in thermal dissipation. (2) Since the p-electrode 24 and n-electrode 25 are joined to the circuit pattern 4 via the conductive plating layer 40 made of solder, no solder adheres to portions other than the electrodes, thus allowing prevention of a decrease in electrical connection characteristics due to leak current. (3) Because of the surface mounting of the LED element 2 with the electrodes formed so as to be exposed to element edges, the occupation ratio of light emitting area to the entire element can be large, thus allowing ensuring high brightness. (4) Since the solder is made in a thin film shape by plating, the spacing between the p-electrode 24 and n-electrode 25 can be narrow, and there can be a less incidence of short-circuiting.

In the third embodiment, although the LED 1 has the LED element 2 with the electrodes exposed to element edges, the LED element 2 explained in the first embodiment may be joined to the circuit pattern 4 via the conductive plating layer 40. In this case, because of no solder penetration into portions other than mounting surface, no decrease is caused in electrical characteristics due to leak current.

Also, in the case of use of the LED element 2 explained in the first embodiment, the insulating layer 30 for preventing a short-circuit of the p-electrode 24 and n-electrode 25 may be omitted

Embodiment 4

FIG. 4 is a cross-sectional view illustrating an LED as a solid state device according to a fourth embodiment of the invention;

This LED 1 is different from that of the third embodiment in structure having an LED-element 2 on the order of light emission peak wavelength 380 nm, and a conductive plating layer 40 made of an Ni layer 41 and an Au layer 42 formed on a p-electrode 24 and n-electrode 25 of the LED-element 2.

The conductive plating layer 40 is constructed by forming a 20 .mu.m thick Ni-layer 41 on the surfaces of the p-electrode 24 and n-electrode 25, and forming thereon an Au layer 42 by flash plating. This conductive plating layer 40 allows the Au layer 42 to be fused by thermocompression bonding combined with ultrasound so that the mounting surfaces of the p-electrode 24 and n-electrode 25 are joined to the element-mounting surface of the circuit pattern 4 on substantially the same plane.

The effects of the fourth embodiment are as follows. (1) Since the conductive plating layer 40 consists of Ni and Au, the conductive plating layer 40 fused during mounting the LED-element 2 cannot again be fused by heat during glass sealing, and the LED-element 2 once fixed is thereby not shifted in position during glass sealing so that the fixed state is stable, thus allowing ensuring enhancement in sealing and reliability. (2) Since light of the order of 380 nm emitted from the LED element 2 is sealed by the glass sealing portion 6 with durability, there can easily be materialized a near-ultraviolet light LED 1 with light-emission characteristics which is stable over a long period of time. (3) If the temporal bonding is possible during mounting the LED-element 2, the subsequent glass sealing allows the joining of the LED-element 2 and the Al.sub.2O.sub.3 substrate 300 to be ensured by compressive stress. This is because of the shape effect of positioning the LED-element 2 in the middle of a solid-state device, in the case of the thermal expansion coefficient of the glass sealing portion 6 being equal to as well as larger than that of the LED-element 2. It should be noted that, in case of the thermal expansion coefficient of the glass sealing portion 6 being 4 times or more that of the LED-element 2, cracking is caused in the glass, depending on the size of the LED-element 2 and the material properties of the glass.

Embodiment 5

FIG. 5 is a cross-sectional view illustrating an LED as a solid state device according to a fifth embodiment of the invention.

This LED 1 is different from that of the fifth embodiment in structure having on the element-mounting surface of the circuit pattern 4 the conductive plating layer 40 explained in the fourth embodiment.

The effects of the fifth embodiment are as follows.

Since the mounting surfaces of the p-electrode 24 and n-electrode 25 are joined to the element-mounting surface of the circuit pattern 4 on substantially the same plane by thermocompression bonding combined with ultrasound without forming the conductive plating layer 40 on the LED-element 2, stable element fixation can be realized without plating the existing LED-element 2, allowing ensuring enhancement in sealing and reliability, in addition to the favorable effects of the fourth embodiment.

Embodiment 6

FIG. 6 is a cross-sectional view illustrating an LED as a solid state device according to a sixth embodiment of the invention.

This LED 1 is different from that of the fourth embodiment in structure having a coating layer 10 made of TiO.sub.2 having anatase structure on the surface of the glass sealing portion 6 of the LED 1 explained in the fourth embodiment, where organics in air are captured and decomposed by optical catalytic action of TiO.sub.2 excited by light of the order of 380 nm peak wavelength radiated from the LED element 2.

The effects of the sixth embodiment are as follows.

Since the coating layer 10 is formed over the glass sealing portion 6, and TiO.sub.2 constituting the coating layer 10 is therefore uniformly irradiated with light radiated from the LED element 2, thereby allowing enhancement in optical catalytic action. Also, in resin sealing, the sealing resin itself of the LED element 2 deteriorates due to optical catalytic action, but since the glass sealing portion 6 is formed of stable inorganic material, the function as an optical catalytic device can be performed without optical deterioration over a long period of time.

The glass sealing portion 6 is stable to light, but there is also material which is made turbid white by moisture caused by organic decomposition adhering to its surface for a long period of time. In this case, in order to prevent this, a light-transmitting MgF coating, for example, may be applied to the surface of the glass sealing portion 6, followed by forming thereover a further coating layer 10.

In the sixth embodiment, although the coating layer 10 is formed as an optical catalytic portion over the surface of the LED 1, an optical catalytic portion made of beads of TiO.sub.2 particles and having air permeability between beads may be disposed around the LED 1.

In the above embodiments, although the sealing material of the LED element 2 is glass, a portion of glass may be crystallized and turbid white according to uses, and material is not limited to a glass state, provided that good joining to a power receiving/feeding portion with chemically stable inorganic material is possible.

Also, although the LED using the LED element as the solid state device has been explained, the solid state device is not limited to the LED element, but may be another optical element such as a light-receiving element, solar cell, or the like.

Embodiment 7

FIG. 7 is a cross-sectional view illustrating an LED according to a seventh embodiment of the invention.

This LED 101 is formed by mounting a plurality of LED elements on a wafer substrate, sealing them from above, thereby forming a plurality of LEDs and cutting them with a dicer.

The LED 101 comprises a flip-chip-type LED element 102 made of a nitride-based compound semiconductor material (thermal expansion coefficient .alpha.: 7.times.10.sup.-6/.degree. C.), an Al.sub.2O.sub.3 substrate 103 as an inorganic material substrate for mounting the LED element 102, circuit patterns 104A and 104B and a via pattern 104C consisting of tungsten (W)-nickel (Ni)-gold (Au) and formed in the Al.sub.2O.sub.3 substrate 103 a fusion bonding portion 105 consisting of Ni thick film and Au on the surface of a p-electrode and an n-electrode of the LED element 102, and a glass sealing portion 106 as inorganic sealing material made of transparent glass thermocompression-bonded to the Al.sub.2O.sub.3 substrate 103 for sealing the LED element 102.

FIGS. 8 and 9 show the LED element used in the seventh embodiment. FIG.8 is a plain view where the LED element is viewed from electrode formation surface, and FIG. 9 is a cross-sectional view of the LED element cut along line A-A of FIG. 8.

This LED element 102 has the fusion bonding portion 105 formed according to the shape of the p-electrode and n-electrode as shown in FIG. 8, and, as shown in FIG. 9, has a GaN-based semiconductor layer formed by sequential crystal growth of an n-GaN layer 121, a light-emitting layer 122, and a p-GaN layer 123, via an AlN buffer layer not shown, on a sapphire (Al.sub.2O.sub.3) substrate 120

The GaN-based semiconductor layer further has a p-contact electrode 124 formed of rhodium Rh and on the surface of the p-GaN layer 123, and an n-contact electrode 125 formed of V/Al and on the n-GaN layer 121 exposed by dry-etching and removing the region extending from the p-GaN layer 123 to a portion of the n-GaN layer 121, where the fusion bonding portion 105 is integrally formed on the surface of the p-contact electrode 124 and the n-contact electrode 125 by electroless plating.

Here, the n-contact electrode 125 has a necessary and sufficient size capable of low contact voltage to conducting current, and most of the remaining space is the p-contact electrode 124. In other words, portion other than space around the element and spacing in which the p-contact electrode 124 and the n-contact electrode 125 do not short-circuit is occupied by the p-contact electrode 124.

The LED element 102 is 0.34 mm.times.0.34 mm.times.thickness 0.09 mm in size, and is epitaxially grown at 700.degree. C. or higher, and has a heat-resistant temperature of 600.degree. C. or higher, and is stable at temperatures at which sealing is performed using low melting point glass, as will be described later. The p-contact electrode 124 is formed of rhodium Rh having current diffusivity and light reflectivity for also serving as a lower reflection mirror for reflecting light emitted from the light-emitting layer 122 in the direction of the sapphire substrate 120.

The Al.sub.2O.sub.3 substrate 103 has a thermal expansion coefficient of 7.times.10.sup.-6/.degree. C., and has a plurality of via-holes 103A passing through from its front to back side. These via-holes 103A have the via pattern 104C for making the metalized circuit patterns 104A and 104B conductive on the front and back side of the Al.sub.2O.sub.3 substrate 103.

The fusion bonding portion 105 comprises an Ni layer 150 formed in a thick film shape by electroless plating on the surface of the p-contact electrode 124 and the n-contact electrode 125, and an Au layer 151 formed by flash plating on the surface of the Ni layer 150 in the fabrication process of the LED element 102, where during joining, the upper surface of the LED element 102 is formed so as to have the height parallel to the surface of the Al.sub.2O.sub.3 substrate 103. Also, the Au layer 151 is fused by thermocompression-bonding combined with ultrasound, and thereby joined to the circuit pattern 104B in area according to the shape of the p-contact electrode 124 and the n-contact electrode 125. The Ni layer 150 may have appropriate stiffness as the Au support layer against thermocompression-bonding combined with ultrasound, and may be formed of metal material such as Ag, Cu or the like.

The glass sealing portion 106 is formed of SiO.sub.2--NbO.sub.2-based low melting point glass (thermal expansion coefficient: 7.0.times.10.sup.-6/.degree. C.), and thermocompression-bonded to the Al.sub.2O.sub.3 substrate 103 by hot-pressing with a mold. A semi-spherical optically shaped surface 106A is formed on the light derivation side of the glass sealing portion 106 for radiating light radiated from the LED element 102 in a direction based on the optical shape. As the sealing material, it is possible to use resin sealing material such as epoxy resin, silicon resin, etc., in place of inorganic sealing glass.

The low melting point glass is processed with viscosity on several orders of magnitude higher than a viscosity level which is generally said to be high in resin. Also, in the case of glass, its viscosity cannot decrease to a general resin sealing level even if the glass is at temperatures exceeding its yield point by a few ten .degree. C. For this reason, in glass sealing by hot-pressing of the flip-chip mounted LED element 102, if there is a gap between the LED element 102 and the Al.sub.2O.sub.3 substrate 103, there is the possibility of pressurized glass penetrating there halfway, and causing partial peeling of electrodes, which results in an abnormal light-emitting pattern. The electrodes also serve as a reflection film, which radiates light arriving at electrode peeling portion and radiated outwardly from GaN into the air, in a direction different from its original direction.

The fabrication process for this LED 101 is explained below.

First, a glass-containing Al.sub.2O.sub.3 substrate 103 having via-holes 103A is prepared, and tungsten (W) paste is screen-printed on the frontside, backside and via-holes 103A of the glass-containing Al.sub.2O.sub.3 substrate 103 according to circuit patterns 104A and 104B and a via pattern 104C.

Next, the W-paste-printed Al.sub.2O.sub.3 substrate 103 is heated at a little more than 1000.degree. C., thereby burning W into the Al.sub.2O.sub.3 substrate 103, followed by Ni and Au plating over W, which results in the formation of circuit patterns 104A and 104B and a via pattern 104C.

Next, an Led element 102 is positioned relative to the circuit pattern 104B. The Au layer 151 of the fusion bonding portion 105 is fused by thermocompression-bonding combined with ultrasound, and thereby joined to the circuit pattern 104B. The LED element 102 is mounted by the fusion bonding portion 105 so that the mounting surface is on substantially the same plane relative to the surface of the circuit pattern 104B.

Next, a low melting point SiO.sub.2--NbO.sub.2-based glass board is set parallel to the LED-element 102-mounted Al.sub.2O.sub.3 substrate 103, followed by hot pressing at a temperature of 500.degree. C. in nitrogen atmosphere. The viscosity of the low melting point glass in this condition is 10.sup.8-10.sup.9 poises, and the low melting point glass is bonded to the Al.sub.2O.sub.3 substrate 103 via the oxides contained therein.

Next, the Al.sub.2O.sub.3 substrate 103 integral with the low melting point glass is set and diced in a dicer into the LED 101 separately.

There may be used the LED element 102 formed by scribing. In this case, it is preferred to form a V-groove for scribing in the Al.sub.2O.sub.3 substrate 103 beforehand, or a mark-off line.

In this LED 101, when connecting the circuit pattern 104A to a power supply not shown to apply voltage, current is caused to flow through the via pattern 104C, the circuit pattern 104B and the fusion bonding portion 105, to the p-contact electrode 124 and the n-contact electrode 125 of the LED element 102, followed by blue light emission of the light emission portion 122, whose light emission wavelength is 450 nm-480 nm. Of blue light emission, light radiated to the sapphire substrate 120 side is passed through the sapphire substrate 120 into the glass sealing portion 106, and radiated in a direction according to optical shape in the interface with outside of the optically shaped surface 106A. Also, of blue light emission, light radiated to the p-contact electrode 124 side is reflected in the direction of the sapphire substrate 120 by the p-contact electrode 124, and passed through the sapphire substrate 120 into the glass sealing portion 106, and radiated outwardly via the optically shaped surface 106A.

The effects of the seventh embodiment are as follows. (1) Since the fusion bonding portion 105 consisting of the thick film Ni layer 150 and Au layer 151 formed on its film in thin film shape is integrally formed in the fabrication process of the LED element 102, the conventional bump forming step can be omitted, thereby allowing enhancement in mass production and realizing low cost. Also, since an inclination of the LED element 102 that is a problem in flip-chip mounting with a stud bump is not caused even without forming 3-point bumps, the mass productivity is excellent. (2) Since most of space other than the n-contact electrode 125 having necessary and sufficient size is the p contact electrode 124 matching the light emission layer, the occupation ratio of light emission surface to size of the LED element 102 can be large. The GaN-based semiconductor layer (light emission layer) with large heat dissipation is positioned on the mounting side to the sapphire substrate 120. This allows making current density and temperature rise of the light emission layer low, and enhancing light emission efficiency and reliability. (3) Since the Ni layer 150 and Au layer 151 are formed in substantially the same shape of the p-contact electrode 124 and the n-contact electrode 125 and covering its surface, joining area relative to the circuit pattern 104B can be large, and bonding strength of the LED element 102 can be large, preventing peeling. Also, because of large joining area, heat dissipation from the LED element 102 can be enhanced, handling high power. (4) Since the LED element 102 is mounted so that mounting surface and the circuit pattern 104B are on substantially the same plane, hot pressing of low melting point glass allows preventing glass from penetrating between the mounting surface and the circuit pattern 4, thus allowing the prevention of a decrease in electrical connection characteristics and of peeling due to glass penetration to the mounting surface, which results in a high-reliability LED 101. Also, an abnormal light emission pattern due to partial electrode peeling can be prevented. (5) Because of chemical bonding of the Al.sub.2O.sub.3 substrate 103 and glass sealing portion 106 via an oxide, firm bonding strength can be obtained. This can materialize glass sealing even in the case of a small package with joining area. (6) Since the LED element 102, the Al.sub.2O.sub.3 substrate 103 and glass sealing portion 106 have the same thermal expansion coefficient, thermal stress due to a thermal expansion coefficient difference can be small during glass sealing, and there is a less incidence of package cracking, and productivity is excellent.

In the seventh embodiment, although the LED 101 uses the LED element 102 made of GaN-based semiconductor material, the LED element 102 is not limited thereto, but may be another LED element such as flip-chip mountable GaAs, GaP-based LED element 102. In particular, in material with high temperature dependency of optical power of an LED element such as AlInGaP, AlGaAs LED element 102, the effect of enhancing thermal dissipation is large.

Also, using a fluorescent material excited by blue light radiated from the LED element 102, there may be used an LED 101 radiating wavelength conversion light such as white light. As such a fluorescent material, there may be used a cerium-activated YAG (Yttrium Aluminum Garnet). The YAG is excited by blue light to produce yellow light, thereby allowing white light to be obtained by complementary color of blue and yellow light. The fluorescent material can uniformly provided by coating the surface of the LED element 102.

Also, a plurality of LED elements 102 having the seventh embodiment structure may be mounted on the substrate for glass sealing.

Also, the light emitting layer may be divided into two, to form LED elements 102 having one n-contact electrode and two p-contact electrode. In this case, for one light emitting layer, there are respectively provided one n-contact electrode and one p-contact electrode, but the n-contact electrode is the common electrode of two light emitting layers. Even if the light emitting layer is not divided, if the p-contact electrode is divided, because the light emitting portion is divided virtually, which is similar to division of the light emitting layer.

Also, in the seventh embodiment, although the fusion bonding portion 105 is formed on the LED element 102, the fusion bonding portion 105-applying target is not limited thereto, but may be a light receiving element, for example.

Embodiment 8

FIG. 10 is an enlarged cross-sectional view illustrating an LED element according to an eighth embodiment of the invention. In the following embodiments, the same reference numbers as those of the seventh embodiment respectively denote the portions having the same structure and function as those in the seventh embodiment.

This LED 101 is different from that of the first embodiment in structure having a fusion bonding portion 130 consisting of an Ni layer 131 and an Au layer 132 formed on the Al.sub.2O.sub.3 substrate 103 side according to a circuit pattern, and no Ni layer on the p-contact electrode 124 and the n-contact electrode 125 of the LED-element 2.

The effects of the eighth embodiment are as follows. (1) Even by forming on the Al.sub.2O.sub.3 substrate 103 side the fusion bonding porti