Abstract:
A high brightness light emitting diode includes a carrier substrate and an epitaxial multi-layer formed thereon. The carrier substrate includes a metal material and a medium, and a coefficient of thermal expansion (CTE) of the medium is less than a CTE of the metal material.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure generally relates to light emitting diodes, and particularly to a high brightness light emitting diode with a metal substrate. 
         [0003]    2. Description of the Related Art 
         [0004]    Light emitting diodes (LEDs) have many advantages, such as high luminosity, low operational voltage, low power consumption, compatibility with integrated circuits, easy driving, long-term reliability, and environmental friendliness, which have promoted the LEDs as a widely used light source. 
         [0005]    Referring to  FIGS. 1 to 6 ,  FIG. 1  and  FIG. 2  are schematic views showing a commonly used light emitting diode, and  FIG. 3  to  FIG. 6  are schematic views of a vertical cross section of the light emitting diode. As shown in  FIG. 1 , a frequently used manufacturing method of a light emitting diode (LED)  100  provides a sapphire substrate  102 , on which a buffer layer (not shown), an n-type semiconductor layer  104 , an active layer  106 , and a p-type semiconductor layer  108  are sequentially epitaxially formed. 
         [0006]    Referring to  FIG. 2 , since the sapphire provides only limited thermal and electrical conductivity, in preparation of the LED  100  with a sapphire substrate  102 , a partial active layer  106  and p-type semiconductor layer  108  must be removed to expose partial n-type semiconductor layer  104 . The electrodes  112  and  114  are on the same side and separately formed on the p-type semiconductor layer  108  and the exposed partial n-type semiconductor layer  104 . 
         [0007]    For improving heat dissipation and uniformity of electrical distribution, an electric conductive substrate replacing the sapphire substrate  102  is used. Referring to  FIG. 3 , after forming the n-type semiconductor layer  104 , the active layer  106 , and the p-type semiconductor layer  108  on the sapphire substrate  102 ,  FIG. 4  shows a thicker copper layer as metal substrate  110  is formed on the top surface of the p-type semiconductor layer  108 . The sapphire substrate  102  is removed using laser, with enhanced thermal and electric conduction metal substrate  110  replacing the sapphire substrate  102  (as shown in  FIG. 5 ). Referring to  FIG. 6 , an electrode (not shown) of the p-type semiconductor layer  108  is formed on the metal substrate  110 , and another electrode  114  is formed on the n-type semiconductor layer  104 . The dies are cut to obtain an isolated LED  150 . 
         [0008]    The difference of coefficient of thermal expansion (CTE) of metal and semiconductor will cause stress and damage to the LED  150 . Moreover, when the metal substrate  110  is used, thickness thereof must exceed 100 μm to support the LED  150 . The thickness renders cutting more difficult. 
         [0009]    What is needed, therefore, is a light emitting diode which can prevent damage caused by stress of different CTE, and ameliorate the described limitations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Many aspects of the disclosure can be better understood with reference to the drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the high brightness light emitting diode. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the views. 
           [0011]      FIGS. 1  and  FIG. 2  are schematic views of a vertical cross section of a commonly used light emitting diode and its semi-finished product. 
           [0012]      FIG. 3  to  FIG. 6  are schematic views of a vertical cross section of another commonly used light emitting diode and its semi-finished products. 
           [0013]      FIG. 7  to  FIG. 11  are schematic views of a vertical cross section of a light emitting diode in accordance with a first embodiment of the present disclosure and its semi-finished products, wherein  FIG. 7  to  FIG. 10  sequentially represent the semi-finished products at different manufacturing steps and  FIG. 11  represents the finished product. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Embodiments of a light emitting diode and manufacturing process thereof as disclosed are described in detail here with reference to the drawings. 
         [0015]      FIGS. 7-10  are schematic views of a vertical cross section of a light emitting diode in accordance with a first embodiment and its semi-finished products at different manufacturing processes. As shown in  FIG. 7 , a temporary substrate  202  is provided, of material matching the lattice of epitaxial layer, such as sapphire, silicon carbide, or gallium arsenide. In this embodiment, the temporary substrate  202  is sapphire. A buffer layer  212 , an n-type semiconductor layer  214 , an active layer  216 , and a p-type semiconductor layer  218  are sequentially formed on the temporary substrate  202 . The n-type semiconductor layer  214 , the active layer  216 , and the p-type semiconductor layer  218  define an epitaxial multi-layer  210 . 
         [0016]    Referring to  FIG. 8 , a contact layer  220  is formed on the epitaxial multi-layer  210 . The contact layer  220  includes transparent conductive material such as nickel, gold, aluminum, silver, platinum, palladium, chromium, indium tin oxide, indium zinc oxide, or an alloy thereof. A carrier substrate  230  is formed on the contact layer  220  by vapor deposition, sputtering, electrolytic deposition, or electrodeless plating. The carrier substrate  230  mainly contains copper, nickel, cobalt, or an alloy thereof. 
         [0017]    The CTE is 16.5 ppm/k of copper, 13.3 ppm/k of nickel, 13.36 ppm/k of cobalt, and are all relatively very large. The carrier substrate  230  is metal and doped with a medium having less CTE, such as diamond particle, diamond-like carbon particle, silicon oxide particle, silicon nitride particle, strontium titanate particle, yttrium aluminum garnet particle, zirconium oxide particle, or silicon carbide particle. A ratio of the metal material to the medium in volume is between 0.1:1 and 1:1. 
         [0018]    For example, if the diamond particle has CTE of 1.1 ppm/k and thermal conductivity  4  fold as the copper, in this embodiment, the ratio of the metal material (copper) and the medium (diamond particle) is 4:6 for the carrier substrate  230  to improve the thermal conduction and modulate the CTE. The diamond particle can also improve the hardness for support and the thickness of the carrier substrate  230  can be reduced from 100 μm to 70 μm. The cost of process of the carrier substrate  230  is also reduced significantly. 
         [0019]    Referring to  FIG. 9 , the temporary substrate  202  and the buffer layer  212  are turned over and removed by polishing, chemical etching, or Laser lift-off to expose the n-type semiconductor layer  214  of the epitaxial multi-layer  210 . 
         [0020]    As shown in  FIG. 10 , an electrode  240  is formed on the n-type semiconductor layer  214 . The electrode  240  is the same as the contact layer  220  comprising a transparent conductive layer of nickel, gold, aluminum, silver, platinum, palladium, chromium, indium tin oxide, indium zinc oxide, or an alloy thereof. The thickness of the carrier substrate  230  is less than 70 μm in this embodiment and is more easily cut. As shown in  FIG. 11 , a light emitting diode  300  in accordance with a first embodiment comprises a carrier substrate  230  including a metal material  232  and a medium  234 , a contact layer  220 , a p-type semiconductor layer  218 , an active layer  216 , an n-type semiconductor layer  214 , and an electrode  240 . In this embodiment, the contact layer  220  and the electrode  240  are the contacting electrodes of the light emitting diode  300 . 
         [0021]    It is to be understood, however, that even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structures and functions of the embodiment(s), the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.