Patent Publication Number: US-2011062454-A1

Title: Light emitting device having remotely located light scattering material

Description:
FIELD OF THE INVENTION 
     The present invention relates to a light emitting device, and more particularly, to a light emitting device having remotely located light scattering material. 
     BACKGROUND OF THE INVENTION 
     Light emitting diodes (hereinafter referred to as “LEDs”) is currently one of the most innovative and fastest growing technologies in the semiconductor industry. While LEDs have been in use for decades as indicators and for signaling purposes, technology developments and improvements have allowed for a broader use of LEDs in illumination applications. 
     The use of LEDs in illumination applications is attractive for a number of reasons, including the ability to produce more light per watt, longer lifetime, smaller size, greater durability, environmental friendliness and flexibility in terms of coloring, beam control and dimming. In addition, many efforts have been made to produce white light sources, such as phosphor converted white light devices, using different kinds of phosphors, like yellow, green, blue or red phosphors. Another method of producing white light sources is by using red, blue and green LEDs. However, these and other methods face the challenge of providing an evenly distributed light and/or color mixing in a device having a relatively small area. Providing evenly distributed light and achieving sufficient color mixing can be difficult because different colors of light have a different light spectrum and they each exhibit different optical properties, like reflection and refraction. While currently known methods have attempted to generate a uniform light distribution and solve these and other problems, such methods have not been fully satisfactory. 
     Accordingly, there is a need for a light emitting device having remotely located light scattering material that addresses the above shortcoming. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a light emitting device having remotely located light scattering material is disclosed. The light emitting device includes a substrate defining a cavity; one or more light emitting elements bonded to the substrate, the one or more light emitting elements positioned in the cavity, the one or more light emitting elements configured to emit light; at least one first layer covering the one or more light emitting elements, at least part of the at least one first layer within the cavity, the at least one first layer having an upper surface, wherein the at least one first layer has a refractive index less than the refractive index of the one or more light emitting elements; and at least one second layer disposed on the at least one first layer, the at least one second layer including light scattering material, wherein the refractive index of the at least one second layer is less than the refractive index of the one or more light emitting elements, and the refractive index of the first layer is less than or equal to the refractive index of the second layer. 
     According to another embodiment of the present invention, a light emitting device having remotely located light scattering material is disclosed. The light emitting device includes a substrate; one or more light emitting elements bonded onto the substrate; at least one first layer covering the one or more light emitting elements on the substrate, the at least one first layer having an upper surface and side surfaces; and at least one second layer covering the at least one first layer, the at least one second layer including light scattering material, wherein the refractive index of the at least one second layer is less than the refractive index of the one or more light emitting elements, and the refractive index of the first layer is less than or equal to the refractive index of the second layer. 
     Still other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the invention are described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the spirit and the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a light emitting device, in accordance with a first embodiment of the present invention. 
         FIG. 2  is a cross sectional view of a light emitting device, in accordance with a second embodiment of the present invention. 
         FIG. 2A  is a partial top view of the light emitting device shown in  FIG. 2 , in accordance with a second embodiment of the present invention. 
         FIG. 2B  is a partial, side cross sectional view top view of the first layer shown in  FIG. 3 , in accordance with a second embodiment of the present invention. 
         FIG. 3  is a cross sectional view of a light emitting device, in accordance with a third embodiment of the present invention. 
         FIG. 4  is a cross sectional view of a light emitting device, in accordance with a fourth embodiment of the present invention. 
         FIG. 4A  is a partial top view of the light emitting device shown in  FIG. 3 , in accordance with a fourth embodiment of the present invention. 
         FIG. 4B  is a partial, side cross sectional view top view of the first layer shown in  FIG. 3 , in accordance with a fourth embodiment of the present invention. 
         FIG. 5  is a cross sectional view of a light emitting device, in accordance with a fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings where, by way of illustration, specific embodiments of the invention are shown. It is to be understood that other embodiments may be used as structural and other changes may be made without departing from the scope of the present invention. Also, the various embodiments and aspects from each of the various embodiments may be used in any suitable combinations. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature but not as restrictive. 
     Generally, embodiments of the present invention are directed to a light emitting device having remotely located light scattering material. 
       FIG. 1  is a cross sectional view of a light emitting device, in accordance with a first embodiment of the present invention. The light emitting device  100  includes a substrate  102  and a red LED  104 , a blue LED  106 , and a green LED  108  bonded onto a cavity  103  formed in the substrate  102 . A first layer  110  is filled into the optical cavity  103  and disposed on top of or surrounding the red LED  104 , the blue LED  106 , and the green LED  108  (collectively refer to as “the RBG LEDs”). A second layer  112  is disposed on top of or surrounding the first layer  11   0 . According to embodiments of the present invention, the second layer  112  includes light scattering material. According to one embodiment of the present invention, the light scattering material includes a plurality of particles configured to scatter light emitted by the RBG LEDs. Contact wires  114  may electrically connect each of the RBG LEDs to metal contacts  116 . First or secondary optics  118 , such as a lens or a reflector, may also be provided on top of the second layer  112  for directing or reflecting the light. According to one embodiment, the first and second layers are transparent and insulating. However, according to other embodiments, the first and second layers may be partially transparent or translucent. 
     According to the illustrated embodiment, the first layer  110  alters the light rays emitted from the RBG LEDs before it is transmitted to the second layer  112 . The first layer  11   0  may be configured to reflect, refract, and/or otherwise alter the light radiation pattern emitted from the RBG LEDs. Therefore, the light emitted from the RBG LEDs may be pre-mixed before it passes to the second layer  112 , which includes the light scattering material. As a result, the spatial color uniformity and mixing of red, blue, green and/or other lights can be improved by inclusion of the first layer  110 , especially when compared to light emitting device that omit the first layer  110  and only have the second layer  112 . 
     The first layer  110  and the second layer  112  may be any suitable translucent materials such as, for example, silicon, epoxy, or glass. The light scattering materials may be any organic or inorganic light scattering materials such as, for example, polymer powders or metal oxides. The light scattering materials may also be in any suitable shape such as spherical, pyramidal, or planar. In addition, they can be in any size. According to one embodiment, the particle size of them is less than or equal to 10 μm. However, any other suitable particle sizes may also be used. 
     According to one embodiment of the present invention, the first layer  110  and the second layer  112  do not have any wavelength conversion properties, configured to pass light through either the first layer  110  or the second layer  112 , or both layers, maintaining the original wavelength of the light. The refractive index of the first layer  110  is greater than 1. According to another embodiment, the refractive index of the first layer  110  is less than the refractive index of the RBG LEDs, or other light emitting elements that may be used, and less than or equal to the refractive index of the second layer  112 . The refractive index of the second layer  112  may also be less than the refractive index of the RBG LEDs, or other light emitting elements that may be used in the light emitting device  1   00 . 
       FIG. 2  is a cross sectional view of a light emitting device, in accordance with a second embodiment of the present invention. The light emitting device  200  includes a substrate  102 , a light emitting element  106  bonded onto an optical cavity  103  formed in the substrate  102 , a first layer  110  is filled into the optical cavity  103 , disposed on top of or surrounding the light emitting element  106 , and a second layer  112  including light scattering materials is formed over the first layer  110 . Contact wires  114  may electrically connect the light emitting element  106  to metal contacts  116 . A reflective coating  130  is coated onto the optical cavity  103  formed in the substrate  102 . According to one embodiment of the present invention, the reflective coating  130  is configured to enhance and/or increase the reflection of light emitted from the light emitting element  106  before the light is emitted out through the first layer  110  and the second layer  112 . For example, the reflective coating  130  can be silver (Ag) or aluminum (Al) coated, or coated with an alloy including silver, aluminum or other reflective material. The properties of the first layer  110  and the second layer  112  and the remaining components of the light emitting device for each of the embodiments shown and described with reference to  FIGS. 2 to 5  are generally similar to those as described with reference to  FIG. 1 , unless otherwise stated. 
       FIG. 2A  is a partial top view of the first layer of the light emitting device shown in  FIG. 2 , in accordance with a second embodiment of the present invention. The total surface area A 0  of the top surface of the first layer  110  is shown. A portion A 1  of total surface area A 0  is indicated by the surface line texturing. According to one embodiment, the light rays from any one of the light emitting elements passes through the portion A 1  of the total surface area of the first layer, and the portion A 1  is greater than or equal to approximately 80% of the total surface area A 0 . Accordingly, a large portion of the light is evenly distributed prior to passing through the second layer  112 . This condition should be effective in the condition either with or without reflective layer. According to one embodiment, more than half of the light is evenly distributed prior to passing through the second layer  112 . According to another embodiment, more than 75% of the light is evenly distributed prior to passing through the second layer  112 . 
       FIG. 2B  is a partial, side cross sectional side view of the first layer shown in  FIG. 2 , in accordance with a second embodiment of the present invention. A height t, a top surface diameter d, and a base diameter b of the first layer  110  are shown. The base diameter b is also the base diameter of the cavity. According to one embodiment, the height t and the top surface diameter d are chosen such that d/t (d divided by t) is greater than or equal to zero and less than or equal to 25.5, or approximately 26, such that most of the light emitted from any of the light emitting element  106  is evenly distributed prior to passing through the second layer  112 . According to another embodiment, d/b (d divided by b) is greater than or equal to  1  and less than or equal to 1.2 such that most of the light emitted from any one or more of the light emitting elements can be effectively reflected by the reflective coating  130  that is coated onto the optical cavity  103 . While  FIGS. 2A and 2B  refer to  FIG. 2 , the above features may similarly apply to the embodiments shown in  FIG. 1  and  FIG. 3 . Also, while the top view of the first layer  110  is shown as being circular, when the top surface of the first layer is not circular, b and d can be regarded as hydraulic diameters. 
       FIG. 3  is a cross sectional view of a light emitting device, in accordance with a third embodiment of the present invention. The light emitting device  300  is substantially similar to the light emitting device  200  as shown and described with reference to  FIG. 2 . However, the light emitting device  300  shown and illustrated with reference to  FIG. 3  includes multiple light emitting elements  106 . While the illustrated embodiment of the light emitting device  300  includes three light emitting elements  106 , any number of the light emitting elements may be incorporated into the light emitting device  300  depending on the requirements of the particular implementation. 
       FIG. 4  is a cross sectional view of a light emitting device, in accordance with a fourth embodiment of the present invention. The light emitting device  400  is substantially similar to the light emitting device  200  shown and illustrated with reference to  FIG. 2 . However, in the fourth embodiment of the light emitting device  400 , the substrate  102  does not have any optical cavity. Instead, the first layer  110  and the second layer  112  is formed on the substrate  102 . A reflective coating  130  may be formed on top of the substrate  102 , between the substrate  102  and the first and second layers  110 ,  112 . The first layer  110  covers and surrounds the light emitting element  106 , and the second layer  112 , which includes light scattering materials, covers and surrounds the first layer  110 . Contact wires  114  may electrically connect the light emitting element  106  to metal contacts  116 . While one light emitting element  106  is shown, two or more light emitting elements may be used with the illustrated embodiment. 
       FIG. 4A  is a partial top view of the first layer of the light emitting device shown in  FIG. 3 , in accordance with a fourth embodiment of the present invention. The total surface area A 0  of the top surface of the first layer  110  is shown, indicated by the circumference of the first layer  110 . A portion A 1  of total surface area A 0  is indicated by the surface line texturing. According to one embodiment, the light rays from any one of the light emitting elements passes through the portion A 1  of the total surface area of the first layer, and the portion A 1  is equal to the total surface area A 0 . Accordingly, A 1  completely covers A 0  and a large portion of the light is evenly distributed prior to passing through the second layer  112 . This condition should be effective in the condition either with or without reflective layer. 
       FIG. 4B  is a partial, side cross sectional side view of the first layer shown in  FIG. 4 , in accordance with a fourth embodiment of the present invention. A height t and a diameter d of the first layer  110  are shown. According to one embodiment, the height t and the top surface diameter d are chosen such that d/t (d divided by t) is greater than or equal to zero and less than or equal to 22.8, or approximately 23, such that most of the light emitted from any of the light emitting element  106  is evenly distributed prior to passing through the second layer  112 . While  FIGS. 4A and 4B  refer to  FIG. 4 , the above features may similarly apply to the embodiments shown in  FIG. 5 . Also, while the top view of the first layer  110  is shown as being circular, when the top surface of the first layer is not circular, d can be regarded as a hydraulic diameter. 
       FIG. 5  is a partial cross sectional view of a light emitting device, in accordance with a fifth embodiment of the present invention. The fifth embodiment of the light emitting device  500  is substantially similar to the light emitting device  400  as shown and described with reference to  FIG. 4 . However, in the fifth embodiment of the present invention, the light emitting device  500  includes at least one fluorescence layer  502  surrounding and covering at least part of the light emitting element  106 . The first layer  110  covers and surrounds the fluorescence layer  502 . The fluorescence layer  502  may include one or more fluorescence materials such as yellow, red, blue or green light emitting phosphors. While one light emitting element  106  is shown, two or more light emitting elements may be used with the illustrated embodiment. 
     In the embodiments of the present invention, since the light rays emitted by the light emitting elements are pre-mixed in the first layer  110  prior to reaching the second layer  112 , the amount of light scattering materials required in the second layer  112  can be reduced. In addition, the reduction in the amount of light scattering materials may thereby reduce the amount of optical loss and increase the intensity of the light emitted by the light emitting device. 
     While the invention has been particularly shown and described with reference to the illustrated embodiments, those skilled in the art will understand that changes in form and detail may be made without departing from the spirit and scope of the present invention. For example, while embodiments of the present invention are shown including the reflective coating  130 , embodiments of the present invention may optionally include or omit the reflective coating  130  depending on the requirements of the particular implementation. Also, any suitable combinations of the various embodiments may also be used. Therefore, embodiments of the present invention may include a single light emitting element or multiple light emitting elements. While an LED is one example light emitting element suitable for use with embodiments of the present invention, other light emitting elements may also be used. 
     Accordingly, the above description is intended to provide example embodiments of the present invention, and the scope of the present invention is not to be limited by the specific examples provided.