Patent Publication Number: US-6713877-B2

Title: Light-emitting diode

Description:
This is a divisional application of U.S. appln. Ser. No. 09/493,183, which was filed on Jan. 28, 2000 U.S. Pat. No. 6,445,011 and whose contents are incorporated in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light-emitting diode using a flip-chip-type light-emitting element having a widened light-emitting surface. 
     2. Description of the Related Art 
     A conventional light-emitting diode  5  which uses a flip-chip-type semiconductor light-emitting element will be described with reference to FIGS. 12 and 13. FIG. 13 is a vertical cross section schematically showing the appearance and structure of the conventional light-emitting diode  5 , which comprises a flip-chip-type semiconductor light-emitting element  100  (hereinafter referred to as the “flip chip  100 ”). FIG. 12 depicts a light-emitting element member  570  that is formed of a sub-mount  520  serving as a substrate and the flip chip  100  mounted thereon. 
     A lead frame  50  is composed of a metal post  51  and a metal stem  53 , which are used for application of voltage to the light-emitting element member  570 . The metal stem  53  has a reflection portion  55  and a flat portion  54  on which the light-emitting element member  570  is placed. A resin mold  40  encloses the light-emitting element member  570 . The bottom surface  527  of the light-emitting element member  570  is bonded to the metal stem  53  by use of silver paste or any other suitable material, to thereby be electrically connected thereto. An electrode  521  is formed on the sub-mount  520  to be located in an exposed portion  528  thereof. The electrode  521  is connected to the metal post  51  through wire bonding using gold wire  57 . 
     Light emitted by the flip chip  100  reflects off a positive electrode disposed on a first main face, passes through a sapphire substrate disposed on a second main face, and then radiates to the outside. Therefore, the flip chip  100  is mounted on the sub-mount  520  in a face-down orientation such that the first main face faces downward. 
     Next, the sub-mount  520  serving as a substrate will be described. FIG. 12A is a plan view of the sub-mount  520  before attachment of the flip chip  100 ; FIG. 12B is a plan view of the sub-mount  520  after attachment of the flip chip  100 ; and FIG. 12C is a cross sectional view of the sub-mount  520  after attachment of the flip chip  100 . 
     The sub-mount  520  is formed of, for example, an electrically conductive semiconductor substrate. The upper surface of the sub-mount  520  is covered with an insulation film  524  made of SiO 2  except for a portion  523 , to which an Au micro-bump  533  is soldered for establishing connection with the positive electrode of the flip chip  100 . A negative electrode  521  is formed on the insulation film  524  by means of aluminum vapor deposition. On the negative electrode  521  are defined a pad region in which the negative electrode  521  is wire-bonded to the metal post  51  and a region in which an Au micro-bump  531  is soldered to the negative electrode  521  in order to establish connection with the negative electrode of the flip chip  100 . 
     Conventionally, in order to perform wire bonding, there must be formed a circular bonding pad region having a diameter of at least 100 μm, or a square bonding pad region, each side of which has a length of at least 100 μm. In order to allow formation of the electrode  521  providing such a bonding pad region on the exposed portion  528  of the sub-mount  520 , as shown in FIG. 12B, the flip chip  100  having a square shape must be disposed on the sub-mount  520  at a position offset toward one side. That is, since the exposed portion  528  must be formed to have a predetermined area or greater, the flip chip  100  cannot be disposed on the sub-mount  520  such that the center P 2  of the flip chip  100  coincides with the center P 501  of the sub-mount  520  and the center axis (indicated by broken line B—B in FIG. 12B) of the flip chip  100  coincides with the center axis (indicated by broken line A—A in FIGS. 12A and 12A) of the sub-mount  520 . Further, when the light-emitting element member  570  is placed on the flat portion  54  having substantially the same area as the light-emitting element member  570 , the center axis A—A of the sub-mount  520  inevitably coincides with the center axis (indicated by broken line D—D in FIG. 13) of the reflection portion  55  having a parabolic shape. 
     As described above, the sub-mount  520  must have the exposed portion  528  in order to enable formation of the electrode  521  serving as a bonding pad which is used for wiring between the flip chip  100  and the metal post  51 . Therefore, the sub-mount  520  has a rectangular shape. In addition, the flip chip  100  is disposed on the sub-mount  520  in an offset manner, so that the center axis of the flip chip  100  deviates from the center axis of the reflection portion  55  of the lead frame  50 . Therefore, the conventional light-emitting diode  5  has a drawback in that luminous intensity changes with position of view; i.e., luminous intensity differs according to whether the diode  5  is viewed from the right side or left side, or from the upper side or lower side. Further, since the area of the flat portion  54  of the lead frame  50  is small, the area of the sub-mount  520  inevitably becomes small. Therefore, if there is employed a design in which the flip chip  100  is disposed on the sub-mount  520  such that the center axis of the flip chip  100  coincides with that of the rectangular sub-mount  520 , and the exposed portion for formation of an attachment electrode is secured, the size of the flip chip  100  decreases, so that a required luminance cannot be obtained. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present invention is to provide a light-emitting diode which provides constant luminous intensity regardless of position of view. 
     Another object of the present invention is to provide a light-emitting diode in which the area of a flip chip is maximized in order to secure high luminance, while a region for an electrode for electrical connection is secured on a sub-mount. 
     Still another object of the present invention is to provide a light-emitting diode which has a reduced overall size and improved durability and which can be fabricated through a simplified fabrication process. 
     In order to achieve the above-described objects, according to a first aspect of the present invention, there is provided a light-emitting diode using a flip chip which is a flip-chip-type semiconductor light-emitting element, comprising: a rectangular flip chip; and a rectangular sub-mount on which the flip chip is placed. The sub-mount has a shorter side longer than a diagonal of the flip chip. The flip chip is placed on the sub-mount such that a side of the flip chip intersects a corresponding side of the sub-mount. 
     According to a second aspect of the present invention, there is provided a light-emitting diode using a flip chip which is a flip-chip-type semiconductor light-emitting element, comprising a substantially square flip chip; and a substantially square sub-mount on which the flip chip is placed. The flip chip is placed on the sub-mount at a position and posture which are obtained through superposition of a center point and center axis of the flip-chip on a center point and center axis of the sub-mount and subsequent rotation of the flip chip about the center points by a predetermined angle. Here the term of a substantially square means the figure including a parallelogram, a trapezoid, or a quadrangle which is slightly shifted from a right square. 
     According to a third aspect of the present invention, the predetermined angle is about 45 degrees. 
     According to a fourth aspect of the present invention, the sub-mount is formed of a semiconductor substrate, and a diode for over-voltage protection is formed within the semiconductor substrate. 
     According to a fifth aspect of the present invention, the diode for over-voltage protection is formed to be located below an upper exposed region of the sub-mount. 
     According to a sixth aspect of the present invention, the sub-mount is formed of a semiconductor substrate having an insulation film formed on an upper surface of the substrate; and at least one of two lead electrodes for the flip chip is formed on the insulation film to be located in an upper exposed region remaining after placement of the flip chip. 
     According to a seventh aspect of the present invention, a bottom surface of the semiconductor substrate serves as one of two lead electrodes for the flip chip; and the semiconductor substrate is directly connected to a lead frame adapted for receiving the semiconductor substrate and application of voltage to the flip chip. 
     According to an eighth aspect of the present invention, the semiconductor substrate is insulative; and two lead electrodes for the flip chip are formed on the sub-mount to be located in an upper exposed region remaining after placement of the flip chip. 
     According to a ninth aspect of the present invention, the sub-mount is insulative; and two lead electrodes for the flip chip are formed on the sub-mount to be located in an upper exposed region remaining after placement of the flip chip. 
     According to a tenth aspect of the present invention, a mark for detecting position or posture of the sub-mount is formed on the upper exposed region of the sub-mount. 
     According to an eleventh aspect of the present invention, a reflection film for reflecting light emitted from the flip chip is formed on the sub-mount. 
     According to a twelfth aspect of the present invention, a lead electrode which is provided for the flip chip and serves as a refection film for reflecting light emitted from the flip chip is formed on the sub-mount. 
     According to a thirteenth aspect of the present invention, the two lead electrodes are formed to cover an area below the flip chip and serve as refection films for reflecting light emitted from the flip chip. 
     According to a fourteenth aspect of the present invention, the two lead electrodes are formed to cover substantially the entirety of an upper surface of the sub-mount and serve as reflection films for reflecting light emitted from the flip chip. 
     In the light-emitting diode according to the first aspect, since the flip chip is disposed on the sub-mount while being rotated with respect thereto, exposed regions not covered by the flip chip are present at four corners of the sub-mount. Electrodes for wiring can be formed in the exposed regions. Accordingly, the optical axis of the flip chip can be placed at an approximate center of the sub-mount, while the area of the flip chip is maximized. As a result, when the sub-mount is placed on a lead frame, the optical axis of the flip chip coincides with an approximate center of the lens frame. In other words, the optical axis of the flip chip coincides with the center axis of a lamp, so that uniform luminous intensity distribution is obtained without sacrifice of luminance. 
     In the light-emitting diode according to the second aspect, the substantially square flip chip is placed on the substantially square sub-mount at a position and posture which are obtained through superposition of a center point and center axis of the flip-chip on a center point and center axis of the sub-mount and subsequent rotation of the flip chip about the center points by a predetermined angle. Therefore, even when the substantially square flip chip is placed on the substantially square sub-mount such that their centers coincide with each other, triangular exposed regions are formed on the sub-mount, in which lead electrodes can be formed. As a result, without necessity of decreasing the size of the flip chip, the flip chip can be placed on the sub-mount such that their centers coincide with each other, and upper exposed regions used for formation of lead electrodes can be secured on the sub-mount. 
     Further, since the sub-mount is formed in a substantially square shape, the sub-mount carrying the flip chip can be placed on a lead frame such that the center and center axis of the sub-mount coincide with the center and center axis of a parabola of the lead frame. As a result, constant luminous intensity can be provided regardless of position of view. Since the ratio of the area of the sub-mount to that of the parabola can be maximized, the size of the flip chip itself can be increased. Therefore, without an increase in the size of the light-emitting diode itself, the luminance can be increased. 
     In the light-emitting diode according to the third aspect, since the angle of rotation is set to about 45 degrees, the ratio of the area of the flip chip to that of the sub-mount can be maximized, and the light-emitting diode can provide further increased luminance. 
     In the light-emitting diode according to the fourth aspect, the sub-mount is formed of a semiconductor substrate, and a diode for over-voltage protection is formed within the semiconductor substrate. Therefore, the diode for over-voltage protection such as a Zener diode is connected in parallel to the light-emitting diode, and breakage of the light-emitting diode due to excessive voltage is prevented, so that the durability of the light-emitting diode is expectedly improved. 
     In the light-emitting diode according to the fifth aspect, since the diode for over-voltage protection is formed within the semiconductor substrate to be located below an upper exposed region of the sub-mount, heat is easily radiated from the protection diode, so that thermal breakage of the protection diode is prevented. Since the protection diode is formed outside a region where bumps are formed to establish connection between the flip chip and the sub-mount, the protection diode is not affected by heat generation of bumps, and thermal breakage of the protection diode is effectively prevented. 
     In the light-emitting diode according to the sixth aspect, electrodes can be formed on the insulation film, and a semiconductor element, such as a diode, for over-voltage protection can be formed within the semiconductor substrate. 
     In the light-emitting diode according to the seventh aspect, a bottom surface of the semiconductor substrate constituting the sub-mount serves as one of two lead electrodes for the flip chip; and the semiconductor substrate is directly connected to a lead frame adapted for receiving the semiconductor substrate and application of voltage to the flip chip. This structure eliminates necessity of formation of one lead electrode for the flip chip on the sub-mount. 
     In the light-emitting diode according to the eighth aspect, the semiconductor substrate constituting the sub-mount is insulative; and two lead electrodes for the flip chip are formed on the sub-mount to be located in an upper exposed region of the sub-mount remaining after placement of the flip chip. Since the semiconductor substrate used for the sub-mount may be insulative, the range of selection of constituent materials is widened. 
     In the light-emitting diode according to the ninth aspect, the sub-mount is insulative; and two lead electrodes for the flip chip are formed on the sub-mount to be located in an upper exposed region remaining after placement of the flip chip. Therefore, the lead electrodes can be wire-bonded to the lead frame used for application of voltage to the flip chip. 
     In the light-emitting diode according to the tenth aspect, a mark for detecting position or posture of the sub-mount is formed on the upper exposed region of the sub-mount. Therefore, alignment between the flip chip and the sub-mount, and control of position and orientation of the sub-mount during operation for connecting the sub-mount and the lead frame by wire bonding are facilitated. 
     In the light-emitting diode according to the eleventh aspect, the reflection film reflects light emitted from the flip chip, so that the light can be effectively radiated to the outside. 
     In the light-emitting diodes according to the twelfth, thirteenth, and fourteenth aspects, since the lead electrodes for the flip chip are used to reflect light emitted from the flip chip, the structure can be simplified, and the light can be effectively radiated to the outside. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A-1D and FIGS. 2A-2C are explanatory views showing the structure of a light-emitting diode according to a first embodiment of the present invention; 
     FIGS. 3A and 3B are explanatory views showing the structure of a flip-chip-type light-emitting element used in the present invention; 
     FIGS. 4A-4D and FIG. 5 are explanatory views showing the structure of a light-emitting diode according to a second embodiment of the present invention; 
     FIGS. 6A-6D and FIG. 7 are explanatory views showing the structure of a light-emitting diode according to a third embodiment of the present invention; 
     FIG. 8 is a circuit diagram of the first embodiment; 
     FIG. 9 is a circuit diagram of the second through fourth embodiments; 
     FIGS. 10A-10C and FIGS. 11A and 11B are explanatory views showing the structure of a light-emitting diode according to a fourth embodiment of the present invention; and 
     FIGS. 12A-12C and FIG. 13 are explanatory views showing the structure of a conventional light-emitting diode. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described by way of specific embodiments. However, the present invention is not limited to the embodiments. 
     First, the structure of a flip chip  100  formed of a gallium nitride compound semiconductor will be described. FIGS. 3A and 3B respectively show cross-sectional and plan views of the flip chip  100 . Reference numeral  101  denotes a sapphire substrate;  102  denotes a buffer layer formed of aluminum nitride (AlN);  103  denotes an n-type gallium nitride compound semiconductor layer formed of silicon (Si)-doped gallium nitride (GaN) having a high carrier density;  104  denotes an active layer formed of In x Ga 1-x N (0&lt;x&lt;1);  107  denotes a p-type gallium nitride compound semiconductor layer comprising a p cladding layer  105  formed of p-type Al y Ga 1-y N (0&lt;y&lt;1) and a p contact layer  106  formed of p-type gallium nitride (GaN);  110  denotes a positive electrode formed of nickel (Ni);  120  denotes an insulating protective film formed of SiO 2 ; and  130  denotes a negative electrode comprising a metal layer  131  formed of silver (Ag) and a metal layer  132  formed of nickel (Ni). 
     In the flip chip  100 , the insulating protective film  120  is formed to cover a side wall surface  10  of the n-type gallium nitride compound semiconductor layer  103  formed through etching, as well as side wall surfaces  10  of the respective layers formed on the n-type gallium nitride compound semiconductor layer  103 . The insulating protective film  120  is extended to reach the upper exposed surface of the positive electrode  110  formed on the p-type gallium nitride compound semiconductor layer  107 . The negative electrode  130  is formed on the insulating protective film  120  such that the negative electrode  130  extends upward from an upper exposed surface of the n-type gallium nitride compound semiconductor layer  103  along the insulating protective film  120 . 
     FIG. 1A is a plan view of a sub-mount  20 . FIG. 1B is a vertical cross-sectional view of the sub-mount  20  taken along broken line A—A in FIG.  1 A. The broken line A—A also represents a center axis passing through a center P 1  of the sub-mount  20 . FIG. 1C is a plan view of the flip chip  100  as viewed from the bottom surface side or electrode side. FIG. 1D is a plan view corresponding to FIG. 1C but in a state in which the flip chip  100  has been rotated about a center P 2  by an angle R. In the present embodiment, the angle R is about 45 degrees. FIG. 2A is a plan view of a light-emitting element member  70  in which the flip chip  100  is mounted on the sub-mount  20  in such a manner that the flip chip  100  is rotated about 45 degrees about the center P 2  after being placed such that the center axis A—A of the sub-mount  20  coincides with the center axis B—B of the flip chip  100 . FIG. 2B is a vertical cross-sectional view of the light-emitting element member  70  taken along broken line C—C in FIG.  2 A. FIG. 2C is a vertical cross-sectional view schematically showing the appearance and structure of the light-emitting diode  1  according to the first embodiment, in which the light-emitting element member  70  is mounted on a lead frame  50 . 
     The sub-mount  20  serving as a substrate is formed of an insulating material such as a ceramic or resin. A positive electrode  21  and a negative electrode  23  each having a strip shape are formed on the surface of the sub-mount  20  through vapor deposition of aluminum. Specifically, the positive electrode  21  and the negative electrode  23  are formed in upper exposed regions  28  having the shapes of right-angled isosceles triangles  28  (hatched regions in FIG. 2A) formed as result of placement of the flip chip  100  with rotation of about 45 degrees. The positive electrode  21  extends from one of diagonally opposite corners to a region where the positive electrode  110  of the flip chip  100  is placed, and the negative electrode  23  extends from the other corner to a region where the negative electrode  130  of the flip chip  100  is placed. 
     The light-emitting element member  70  is assembled in the following manner. First, the flip chip  100  is placed on the sub-mount  20  at a position and posture as shown in FIG. 2, which are obtained through 45-degree rotation of the flip chip  100  about the center P 1  from a position at which the center P 1  of the sub-mount  20  coincides with the center P 2  of the flip chip  100  and the center axis A—A of the sub-mount  20  coincides with the center axis B—B of the flip chip  100 . At this position, the positive electrode  110  of the flip chip  100  is electrically connected and soldered to the positive electrode  21  of the sub-mount  20  via a micro-bump  31  of Au, and the negative electrode  130  of the flip chip  100  is electrically connected and soldered to the negative electrode  23  of the sub-mount  20  via a micro-bump  33  of Au. Thus, the flip chip  100  is fixedly mounted on the sub-mount  20 . 
     A gold wire  57  extending from a metal post  51  is bonded to a bonding pad portion  25  of the positive electrode  21  formed on the sub-mount  20 , and a gold wire  58  extending from a metal stem  53  is bonded to a bonding pad portion  27  of the positive electrode  23  formed on the sub-mount  20 . The light-emitting element member  70  is placed on a parabolic reflection portion  55  of the lead frame  50  such that the center of the light-emitting element member  70  coincides with the center axis of the parabolic reflection portion  55  (as indicated by broken line D—D in FIG.  2 C). Subsequently, the lead frame  50  and the light-emitting element member  70  are enclosed by use of a resin mold  40 . 
     The above-described structure enables fabrication of the light-emitting diode  1  in which all the center axes of the flip chip  100 , the sub-mount  20 , the parabolic reflection portion  55 , and the resin mold  40  coincide with one another. Therefore, the light-emitting diode  1  can provide constant luminous intensity regardless of position of view; i.e. the light-emitting diode  1  can provide uniform or constant luminance on a plane perpendicular to the center axis of the light-emitting diode  1 . Further, without an increase in the size of the light-emitting diode  1  itself, the size of the flip chip  100  can be increased in order to increase luminance. 
     Next, a light-emitting diode  2  according to a second embodiment will be described with reference to FIGS. 4A-4D and FIG.  5 . 
     FIG. 4A is a plan view of a sub-mount  220 . FIG. 4B is a vertical cross-sectional view of the sub-mount  220  taken along broken line A—A in FIG.  4 A. FIG. 4C is a plan view of a light-emitting element member  270  in which the flip chip  100  is mounted on the sub-mount  220  in such a manner that the flip chip  100  is rotated about 45 degrees about the center P 2  after being placed such that the center axis A—A passing through the center P 201  of the sub-mount  220  coincides with the center axis B—B passing through the center P 2  of the flip chip  100 . FIG. 4D is a vertical cross-sectional view of the light-emitting element member  270  taken along broken line C—C in FIG.  4 C. FIG. 5 is a vertical cross-sectional view schematically showing the appearance and structure of the light-emitting diode  2  according to the second embodiment, in which the light-emitting element member  270  is mounted on the lead frame  50 . The structure of the flip chip  100  of the second embodiment is the same as that of the first embodiment shown in FIGS. 1C,  1 D,  3 A, and  3 B. 
     The sub-mount  220  serving as a substrate is formed of an insulative semiconductor substrate such as a silicon (Si) substrate  240 . A p-layer  243  serving as a lower layer is formed in the silicon substrate  240  through doping of a group III element. Subsequently, through doping of a group V element, an n-layer  241  is formed at a portion to which the positive electrode  110  of the flip chip  100  is bonded via a micro-bump  231 . The thus-formed p-layer  243  and the n-layer  241  constitute a pn-junction diode, which functions as a Zener diode when the positive electrode  110  of the flip chip  100  is connected to the n-layer  241  and the negative electrode  130  of the flip chip  100  is connected to the p-layer  243 . The forward operation voltage of the Zener diode is preferably lower than the reverse-direction breakdown voltage of the flip chip  100 , and the reverse-direction breakdown voltage of the Zener diode is preferably higher than the operation voltage of the flip chip  100  but lower than the forward-direction breakdown voltage of the flip chip  100 . 
     Subsequently, the entire upper surface of the sub-mount  220  is covered with an insulation film  224  formed of SiO 2 . A positive electrode  221  and a negative electrode  223  each having a strip shape are formed on the surface of the sub-mount  220  through vapor deposition of aluminum. Specifically, the positive electrode  221  and the negative electrode  223  are formed in triangular upper exposed regions remaining after placement of the flip chip  100  with rotation of about 45 degrees. The positive electrode  221  extends from one of diagonally opposite corners to a region where the positive electrode  110  of the flip chip  100  is placed, and the negative electrode  223  extends from the other corner to a region where the negative electrode  130  of the flip chip  100  is placed. Further, a window reaching the n-layer  241  is formed by etching in the insulation film  224  at a portion of the positive electrode  221  where the micro-bump  231  is formed. Similarly, a window reaching the p-layer  243  is formed by etching in the insulation film  224  at a portion of the negative electrode  223  where the micro-bump  233  is formed. 
     The light-emitting element member  270  is assembled in the following manner. First, the flip chip  100  is placed on the sub-mount  220  at a position and posture which are obtained through 45-degree rotation of the flip chip  100  about the center P 2  from a position at which the center axis A—A passing through the center P 201  of the sub-mount  220  coincides with the center axis B—B passing through the center P 2  of the flip chip  100 . At this position, the positive electrode  110  of the flip chip  100  is electrically connected and soldered to the positive electrode  221  of the sub-mount  220  and the n-layer  241  of the sub-mount  220  via the micro-bump  231  of Au. Similarly, the negative electrode  130  of the flip chip  100  is electrically connected and soldered to the negative electrode  223  of the sub-mount  220  and the p-layer  243  of the sub-mount  220  via the micro-bump  233  of Au. Thus, the flip chip  100  is fixedly mounted on the sub-mount  220 . 
     The gold wire  57  extending from the metal post  51  is bonded to a bonding pad portion  225  of the positive electrode  221  formed on the sub-mount  220 , and the gold wire  58  extending from the metal stem  53  is bonded to a bonding pad portion  227  of the positive electrode  223  formed on the sub-mount  220 . The light-emitting element member  270  is placed on the parabolic reflection portion  55  of the lead frame  50  such that the center of the light-emitting element member  270  coincides with the center axis of the parabolic reflection portion  55  (as indicated by broken line D—D in FIG.  5 ). Subsequently, the lead frame  50  and the light-emitting element member  270  are encased by use of the resin mold  40 . 
     As in the case of the first embodiment, the above-described structure enables fabrication of the light-emitting diode  2  which can provide constant luminous intensity regardless of position of view. Further, without an increase in the size of the light-emitting diode  2  itself, the flip chip  100  can be increased in size in order to increase luminance. Moreover, since a Zener diode is included in the sub-mount  220 , without disposition of a Zener diode as an additional part, breakage of the light-emitting diode  2  due to excessive voltage is prevented, so that the durability of the light-emitting diode  2  is improved. 
     Next, a light-emitting diode  3  according to a third embodiment will be described with reference to FIGS. 6A-6D and FIG.  7 . 
     FIG. 6A is a plan view of a sub-mount  320 . FIG. 6B is a vertical cross-sectional view of the sub-mount  320  taken along broken line A—A in FIG.  6 A. FIG. 6C is a plan view of a light-emitting element member  370  in which the flip chip  100  is mounted on the sub-mount  320  in such a manner that the flip chip  100  is rotated about 45 degrees about the center P 2  after being placed such that the center axis A—A passing through the center P 301  of the sub-mount  320  coincides with the center axis B—B passing through the center P 2  of the flip chip  100 . FIG. 6D is a vertical cross-sectional view of the light-emitting element member  370  taken along broken line C—C in FIG.  6 C. FIG. 7 is a vertical cross-sectional view schematically showing the appearance and structure of the light-emitting diode  3  according to the third embodiment, in which the light-emitting element member  370  is mounted on the lead frame  50 . The structure of the flip chip  100  of the second embodiment is the same as that of the first embodiment shown in FIGS. 1C,  1 D,  3 A, and  3 B. 
     The sub-mount  320  serving as a substrate is formed of a silicon (Si) substrate  343  into which a group III element is doped and which therefore serves as a p-type lower layer. Subsequently, through doping of a group V element, an n-layer  341  is formed at a portion to which the positive electrode  110  of the flip chip  100  is bonded via a micro-bump  331 . The thus-formed p-layer and the n-layer constitute a pn-junction diode, which functions as a Zener diode. Since the action of the Zener diode has been described in the second embodiment, description thereof will be omitted. 
     Subsequently, the entire upper surface of the sub-mount  320  is covered with an insulation film  324  formed of SiO 2 . A positive electrode  321  having a strip shape is formed on the insulation film  324  to be located in a triangular exposed region remaining after placement of the flip chip  100  with rotation of about 45 degrees. The positive electrode  321  extends from a corresponding corner to a region where the positive electrode  110  of the flip chip  100  is placed. Further, a window reaching the n-layer  341  is formed by etching in the insulation film  324  at a portion of the positive electrode  321  where the micro-bump  331  is formed. Similarly, a window reaching the p-layer  343  is formed by etching in the insulation film  324  at a portion where the micro-bump  333  is formed. 
     The light-emitting element member  370  is assembled in the following manner. First, the flip chip  100  is placed on the sub-mount  320  at a position and posture which are obtained through 45-degree rotation of the flip chip  100  about the center P 2  from a position at which the center axis A—A passing through the center P 301  of the sub-mount  320  coincides with the center axis B—B passing through the center P 2  of the flip chip  100 . At this position, the positive electrode  110  of the flip chip  100  is electrically connected and soldered to the positive electrode  321  of the sub-mount  320  and the n-layer  341  of the sub-mount  320  via the micro-bump  331  of Au. Similarly, the negative electrode  130  of the flip chip  100  is electrically connected and soldered to the negative electrode  323  of the sub-mount  320  and the p-layer  343  of the sub-mount  320  via a micro-bump  333  of Au. Thus, the flip chip  100  is fixedly mounted on the sub-mount  320 . 
     The gold wire  57  extending from the metal post  51  is bonded to a bonding pad portion  325  of the positive electrode  321  formed on the sub-mount  320 . Further, since the sub-mount  320  serving as a negative electrode is formed of a conductive semiconductor substrate, the bottom surface  327  of the sub-mount  320  is bonded to the flat portion  54  of the metal stem  53  by use of silver paste or any other suitable conductive bonding material to thereby be electrically connected thereto. The light-emitting element member  370  is placed on the parabolic reflection portion  55  of the lead frame  50  such that the center of the light-emitting element member  370  coincides with the center axis of the parabolic reflection portion  55  (as indicated by broken line D—D in FIG.  7 ). Subsequently, the lead frame  50  and the light-emitting element member  370  are encased by use of the resin mold  40 . The light-emitting diode  3  is completed. 
     As in the case of the first embodiment, the above-described structure enables fabrication of the light-emitting diode  3  which can provide constant luminous intensity regardless of position of view. Further, without an increase in the size of the light-emitting diode  3  itself, the flip chip  100  can be increased in size in order to increase luminance. Moreover, since a Zener diode is included in the sub-mount  320  as in the case of the second embodiment, without disposition of a Zener diode as an additional part, breakage of the light-emitting diode  3  due to excessive voltage is prevented, so that the durability of the light-emitting diode  3  is improved. Moreover, since the sub-mount  320  is formed of a conductive semiconductor substrate, the bottom surface  327  of the sub-mount  320  can be used as an electrode used for connection with the metal stem  53 . Therefore, electrode formation and wiring through wire-bonding are required to perform for only one electrode, so that the fabrication process of the light-emitting diode  3  can be simplified. If necessary, gold is vapor-deposited on the bottom surface  327  of the sub-mount  320 . 
     Next, a fourth embodiment will be described with reference to FIGS. 10A-10C and FIGS. 11A and 11B. 
     FIG. 10A is a plan view of a flip chip  100 . FIG. 10B is a plan view of a sub-mount  420 . FIG. 10C is a cross-sectional view showing a layered structure of the flip chip  100 . FIG. 11A is a plan view of a light-emitting element member  470  in which the flip chip  100  is mounted on the sub-mount  420  in such a manner that the flip chip  100  is rotated approximately 45 degrees about the center P 2  after being placed such that the center axis A—A passing through the center P 401  of the sub-mount  420  coincides with the center axis B—B passing through the center P 2  of the flip chip  100 . FIG. 11B is a cross-sectional view of the light-emitting element member  470  taken along broken line C—C in FIG.  11 A. 
     As shown in FIG. 10A, a positive electrode  110  and a negative electrode  130  are formed on the flip chip  100 . Each electrode has a two-layer structure of rhodium (Rh) and gold (Au). Other layers are the same as those shown in FIGS. 3A and 3B, and layers in FIG. 10A having the same functions as respective layers shown in FIG. 3 are denoted by the same reference numbers. In the present embodiment, the insulation film  120  is not used. The electrodes  110  and  130  may be formed of an alloy of rhodium and gold. 
     The sub-mount  420  serving as a substrate is formed of a silicon (Si) substrate  443  into which an impurity such as a group V element is doped and which therefore serves as an n-type lower layer. Subsequently, through doping of a group III element, a p-layer  441  is formed at a portion in which the flip chip  100  is not existed and under the negative electrode  421  to which the negative electrode  130  of the flip chip  100  is bonded via a micro-bump  433 . The thus-formed p-layer and the n-layer constitute a pn-junction diode, which functions as a Zener diode. Although the conductive type is the reverse of that of the Zener diodes described in the second and third embodiments, the structure and action are the same. Therefore, description thereof is omitted. 
     Subsequently, the entire upper surface of the sub-mount  420  is covered with an insulation film  424  formed of SiO 2 . Through aluminum vapor deposition, a negative electrode  421 , which also serves as a reflection film, is formed on the insulation film  424  to cover two of four upper exposed regions formed as result of placement of the flip chip  100  with rotation of about 45 degrees. That is, the negative electrode  421  is formed over substantially the entirety of a lower half of the upper surface of the sub-mount  420  (in FIG.  11 A). The micro-bump  433  is formed on the negative electrode  421  in order to establish connection between the negative electrode  421  and the negative electrode  130  of the flip chip  100 . Further, through aluminum vapor deposition, a positive electrode  422 , which also serves as a reflection film, is formed on the insulation film  424  in order to cover substantially the entirety of an upper half of the upper surface of the sub-mount  420  (in FIG.  11 A). Windows are formed in the insulation film  424 , so that the positive electrode  422  is electrically connected to the n-layer (semiconductor substrate)  443  via the windows. Micro-bumps  431   a,    431   b,  and  431   c  for establishing connection with the positive electrode  110  of the flip chip  100  are formed on the positive electrode  422  at positions corresponding to the windows. Through the micro-bumps  431   a,    431   b,  and  431   c,  the positive electrode  110  of the flip chip  100  is electrically connected to the n-layer  443 . The p-layer  441  is connected to the negative electrode  421  via another window formed in the insulation film  424 . 
     Further, a right-angled mark  425  is formed on the negative electrode  421 . The mark  425  is formed through prevention of vapor deposition of aluminum at a portion corresponding to the mark, etching deposited aluminum film at a portion corresponding to the mark, or additional vapor deposition of a material having a different color at a portion corresponding to the mark. The mark  425  can be used for attaining alignment between the flip chip and the sub-mount and for control of position and orientation of the sub-mount during wire-bonding operation. Thus, fabrication of the light-emitting diode can be simplified. 
     As described above, in the present embodiment, since the negative electrode  421  and the positive electrode  422 , both formed of aluminum, together are formed over the entirety of the insulation film on the semiconductor substrate serving as the sub-mount, the negative electrode  421  and the positive electrode  422  constitute a reflection surface. Therefore, light emitted from the flip chip  100  is efficiently reflected off the reflection surface, so that light can be efficiently emitted through the entire surface of the sapphire substrate. 
     The light-emitting element member  470  is assembled through bonding of the flip chip  100  to the sub-mount  420  at a position and posture which are obtained through 45-degree rotation of the flip chip  100  about the center P 2  from a position at which the center axis A—A passing through the center P 401  of the sub-mount  420  coincides with the center axis B—B passing through the center P 2  of the flip chip  100 . The bonding is performed by use of the micro-bumps  431   a,    431   b,    431   c,  and  433 , which are made of Au. 
     As in the case shown in FIG. 7, the gold wire  57  extending from the metal post  51  is bonded to a bonding pad portion  425  of the negative electrode  421  formed on the sub-mount  420 . Further, since the sub-mount  420  is formed of a conductive semiconductor substrate, a gold deposition layer formed on the bottom surface  427  of the sub-mount  420  is bonded to the flat portion  54  of the metal stem  53  by use of silver paste or any other suitable conductive bonding material to thereby be electrically connected thereto. The light-emitting element member  470  is placed on the parabolic reflection portion  55  of the lead frame  50  such that the center of the light-emitting element member  470  coincides with the center axis of the parabolic reflection portion  55  (as indicated by broken line D-D in FIG.  7 ). Subsequently, the lead frame  50  and the light-emitting element member  470  are encased by use of the resin mold  40 . Thus, the light-emitting diode  3  is completed. 
     As in the case of the first through third embodiments, the above-described structure enables fabrication of the light-emitting diode  3  which can provide constant luminous intensity regardless of position of view. Further, without an increase in the size of the light-emitting diode  3  itself, the flip chip  100  can be increased in size in order to increase luminance. Moreover, since a Zener diode is included in the sub-mount  420  as in the case of the second embodiment, without disposition of a Zener diode as an additional part, breakage of the light-emitting diode  3  due to excessive voltage is prevented by means of the circuit configuration shown in FIG. 9, so that the durability of the light-emitting diode  3  is improved. Moreover, since the sub-mount  420  is formed of a conductive semiconductor substrate, the bottom surface  427  of the sub-mount  420  can be used as an electrode used for connection with the metal stem  53 . Therefore, electrode formation and wiring through wire-bonding are required to be performed for only one electrode, so that the fabrication process of the light-emitting diode  3  can be simplified. 
     In the present embodiment, the Zener diode is formed at a portion which is not covered with the flip chip and at which no bump is formed. Therefore, the Zener diode is prevented from being broken due to heat generated by the light-emitting diode, especially heat generated at bumps. Further, since the Zener diode is formed at a portion which does not undergo wire bonding, the Zener diode is prevented from being broken due to heat or from being mechanically deformed during wiring bonding. 
     Since a reflection film of aluminum is formed on the sub-mount, light can be radiated effectively through an intended light-emitting surface. In order to obtain a satisfactory result, the reflection film is preferably formed on the sub-mount such that the reflection film extends under the flip chip. When the reflection film is formed on the sub-mount to cover portions other than the portion under the flip chip, the brightness of the entire background surface can be increased. 
     Although the positive electrode  422  and the negative electrode  421  together constitute the reflection film, a reflection film may be formed separately from the positive electrode  422  and the negative electrode  421 . 
     In the present invention, the flip chip is disposed on the sub-mount while being rotated relative thereto, and wiring electrodes for wire bonding are formed in triangular exposed portions of the sub-mount. Therefore, without necessity of decreasing the area of the flip chip, the optical axis of the flip chip can be placed at the center of the sub-mount, so that uniform luminous intensity distribution is obtained. 
     In the second through fourth embodiments, when the sub-mount is formed of an insulative semiconductor substrate, wiring electrodes can be formed on the surface of the substrate without formation of insulation film on the surface of the substrate. Further, it becomes possible to form a Zener diode within the substrate. 
     In the present embodiment, the positive electrode  110  of the flip chip  100  is formed of nickel (Ni) or a rhodium (Rh)/gold (Au) layer or alloy, and the negative electrode  130  of the flip chip  100  is formed of nickel (Ni)/silver (Ag) or a rhodium (Rh)/gold (Au) layer or alloy. However, the positive electrode  110  may be a single layer electrode containing at least one metal selected from the group consisting of platinum (Pt), cobalt (Co), gold (Au), palladium (Pd), nickel (Ni), magnesium (Mg), silver (Ag), aluminum (Al), vanadium (V), manganese (Mn), bismuth (Bi), rhenium (Re), copper (Cu), tin (Sn), and rhodium (Rh); or a multi-layer electrode containing two or more metals selected from the above-described group. 
     Further, the negative electrode  130  may be a single-layer electrode containing at least one metal selected from the group consisting of platinum (Pt), cobalt (Co), gold (Au), palladium (Pd), nickel (Ni), magnesium (Mg), silver (Ag), aluminum (Al), vanadium (V), copper (Cu), tin (Sn), rhodium (Rh), titanium (Ti), chromium (Cr), niobium (Nb), zinc (Zn), tantalum (Ta), molybdenum (Mo), tungsten (W), and hafnium (Hf); or a multi-layer electrode containing two or more metals selected from the above-described group. 
     Although in the above-described embodiments the angle of rotation of the flip chip  100  is about 45 degrees, the angle of rotation is arbitrary, insofar as exposed regions for electrode wiring can be secured. Further, in the above-described embodiments, exposed regions remaining after placement of the flip chip  100  have the shape of a right-angled isosceles triangle. However, the shape of the triangle is arbitrary. 
     The insulation films  224  and  324  are not limited to SiO 2 , and may be formed of any other insulative material such as silicon nitride or titanium oxide. The materials of the micro-bumps and wire are not limited to Au and may be any other conductive material. In the above-described embodiments, the reflection film and the positive and negative electrodes serving as reflection films are formed through vapor deposition of aluminum. However, the reflection film and the positive and negative electrode may be formed of any other conductive material having a high reflectance. Although the sub-mount  220  used in the second embodiment is formed of an insulative silicon substrate, the sub-mount  220  may be formed of any other insulative semiconductor substrate. Although the sub-mount  320  used in the third embodiment is formed of a conductive silicon substrate, the sub-mount  320  may be formed of any other material which can constitute a p-layer. 
     Further, in the first to third embodiments, the metal stem  53  serves as a negative terminal, and the metal post  51  serves as a positive terminal, and in the fourth embodiment, the metal stem  53  serves as a positive terminal and the metal post  53  serves as a negative terminal, which is a typical configuration. However, the polarities of the metal stem  53  and the metal post  51  may be reversed. In this case, the positions of the p- and n-layers are reversed. 
     The diode used for over-voltage protection is not limited to the Zener diode; other suitable diodes such as an avalanche diode may be used. 
     The operation voltage (Zener voltage) of the diode for over-voltage protection is preferably set to as low a voltage as possible, provided that the operation voltage does not become lower than a drive voltage Vf of a light-emitting element under conditions of use; for example, the lower limit of the Zener voltage=drive voltage Vf of a light-emitting element+variation in drive voltage Vf among mass-produced light-emitting elements+variation in drive voltage Vf due to temperature characteristics of the light-emitting elements+variation in Zener voltage among mass-produced Zener diodes+variation in Zener voltage due to temperature characteristics of the Zener diodes. Through use of such design parameters, the Zener voltage was able to be set to 6.2 V, and the light-emitting diode was able to have an electrostatic breakdown voltage of 3000 V or greater. 
     The layered structure of the light-emitting diode is not limited to that shown in FIGS. 3A and 3B. The light-emitting layer may employ a single quantum well structure or a multiple quantum well structure. 
     The light-emitting diode may be a laser. That is, the light-emitting diode may be a surface-emitting laser diode. The substrate of the light-emitting diode is not limited to the sapphire substrate, and may be formed of other materials such as spinel, silicon, silicon carbide, zinc oxide, gallium phosphide, gallium arsenide, magnesium oxide, or manganese oxide. 
     When the sub-mount is formed of a semiconductor, silicon, gallium arsenide, silicon carbide, and other semiconductor materials may be used.