Patent Publication Number: US-2011068695-A1

Title: Method and Apparatus for Providing LED Package with Controlled Color Temperature

Description:
PRIORITY 
     This patent application is a divisional patent application of U.S. patent application Ser. No. 12/323,924, filed Nov. 26, 2008, entitled “Method and Apparatus for Providing LED Package with Controlled Color Temperature” by Rene Peter Helbing and Alexander Shaikevitch, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD 
     The exemplary aspect(s) of the present invention relates to lighting devices. More specifically, the aspect(s) of the present invention relates to manufacturing light-emitting devices based on semiconductor diodes using a transparent substrate. 
     BACKGROUND 
     A light emitting diode (“LED”) is a lighting semiconductor device capable of converting electrical energy to light. With recent improvements in luminous output from an LED, conventional lighting apparatus such as incandescent light bulbs and/or fluorescent lamps are likely to be replaced with LEDs in the foreseeable future. Various commercial applications of LEDs, such as traffic lights, automobile lightings, and electronic billboards, have already been placed in service. 
     A conventional semiconductor package for an LED is typically fabricated with one or more phosphor layers and/or materials. The phosphor materials or layers are typically used to convert bluish radiation emitted from a semiconductor chip to brighter yellowish light with, for instance, yellowish wavelength. For example, a combination of blue light and yellow light may create warm and/or white natural light. The light color is typically measured by a standard measurement of color temperature. A resulting color temperature of an optoelectronic device is typically determined by the materials used as well as properties of phosphor materials. Properties of phosphor materials include specifics of phosphor formulation, concentration, as well as thickness of the phosphor layer. 
     A problem associated with a conventional LED fabrication technique for dispensing phosphor layers is that the fabrication process can create variations in physical dimension of each phosphor layer dispensed. Variations in physical dimension of phosphor layers result in variations in color temperature of the fabricated packages. Variations in color temperature of fabricated LED packages complicate a binning system, which adds additional steps in an inventory system for sorting LED packages according to different color temperatures. 
     A conventional approach to maintain color consistency across multiple LED devices or packages is to carefully pre-manufacture the conversion layer with controlled properties and subsequently join the conversion layer in an LED chip. A drawback for this conventional approach, however, is complexity and additional processing steps. 
     SUMMARY 
     An optical device capable of illuminating visual light with adjusting light color after fabrication is disclosed. The optical device includes a solid state light emitter and a phosphor layer, which is formed over the solid state light emitter. The solid state light emitter, which can be a light emitter diode (“LED”) chip, converts electrical energy to light. The phosphor layer converts a first light having a first wavelength to a second light having a second wavelength. In one example, the first light is a blue light while the second light is a white light. A portion of the phosphor layer can be adjusted by a trimmer after the phosphor layer is formed for adjusting color of the white light in accordance with color quality of the light detected by a light detector. 
     Additional features and benefits of the exemplary aspect(s) of the present invention will become apparent from the detailed description, figures and claims set forth below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary aspect(s) of the present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various aspects of the invention, which, however, should not be taken to limit the invention to the specific aspects, but are for explanation and understanding only. 
         FIGS. 1(   a - c ) are cross-section views illustrating an optical device including a phosphor layer with controlled color temperature in accordance with an aspect of the present invention; 
         FIG. 2  illustrates a color temperature chart  200  showing a desirable correlated color temperature in accordance with an aspect of the present invention; 
         FIGS. 3(   a - c ) are cross-section views illustrating an optical device  300  capable of controlling color temperature in accordance with an aspect of the present invention; 
         FIGS. 4(   a - c ) are cross-section views illustrating an optical device including a phosphor layer with two colors in accordance with an aspect of the present invention; 
         FIG. 5  is a cross-section diagram illustrating an optical device having an adjustable warm phosphor layer in accordance with an aspect of the present invention; 
         FIG. 6  is a cross-section diagram illustrating a trimming device capable of trimming phosphor layer to adjust light color in accordance with an aspect of the present invention; 
         FIG. 7  illustrates an exemplary lighting device  700  having multiple solid state light emitters with controlled color temperature in accordance with an aspect of the present invention; and 
         FIG. 8  is a flowchart illustrating a process of adjusting light color of an optical device in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Aspect(s) of the present invention is described herein in the context of a method, device, and apparatus of improving light color generated by an optical device with controlled color temperature. 
     Those of ordinary skills in the art will realize that the following detailed description of the exemplary aspect(s) is illustrative only and is not intended to be in any way limiting. Other aspects will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the exemplary aspect(s) as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. 
     In the interest of clarity, not all routine features of the implementations described herein are shown and described. It will, of course, be understood that in the development of any such actual implementation, numerous implementation-specific decisions may be made in order to achieve the developer&#39;s specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be understood that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skills in the art having the benefit of this disclosure. 
     It is understood that an aspect of the present invention may contain integrated circuits that are readily manufacturable using conventional semiconductor technologies, such as, CMOS (complementary metal-oxide semiconductor) technology, MEMS (Micro-electromechanical systems) technology, or other semiconductor manufacturing processes. In addition, the aspect of the present invention may be implemented with other manufacturing processes for making optical as well as electrical devices. 
     An optical device capable of illuminating visual light with adjusting light color after fabrication is disclosed. The optical device includes a solid state light emitter and a phosphor layer, which is formed over the solid state light emitter. The solid state light emitter, which can be a light emitter diode (“LED”) chip, converts electrical energy to light, which may be a blue light. The solid state light emitter, in one aspect, provides light which can be visible light or invisible light. The phosphor layer subsequently converts a first light with a first wavelength to a second light with a second wavelength. In one example, the first light is blue light while the second light is white light. A portion of the phosphor layer is adjusted after the phosphor layer is formed for adjusting color of the white light in accordance with color quality of the light detected by a light detector. 
       FIGS. 1(   a - c ) are cross-section views illustrating an optical device  100  including a phosphor layer with controlled color temperature in accordance with an aspect of the present invention. Device  100   a , illustrated in  FIG. 1(   a ), includes a substrate  106 , a solid state light emitter  104 , a phosphor layer  102 , and dividers  114 . In one aspect, device  100   a  includes a clear silicon layer  112  dispensed between solid state emitter  104  and phosphor layer  102  for light extracting. It should be noted that the underlying concept of the exemplary aspect(s) of the present invention would not change if one or more blocks (or layers) were added to or removed from device  100   a.    
     Solid state light emitter  104 , in an aspect, is a light emitter diode (“LED”) chip, wherein LED chip can further include gallium nitride layer(s), active layer, and indium tin oxide (“ITO”) layer for generating light. LED chip  104  is capable of producing light  110  when electrons and holes in the semiconductor materials are combined in accordance with quantum mechanics of biased p-n junction(s). Light  110 , for instance, has a range of wavelengths between 400 and 475 nanometer (“nm”). When light  110  reaches phosphor layer  102 , light  110  transforms from bluish light into white or yellowish light  108  when it passes through phosphor layer  102 . The color of light  108  depends on composition of the phosphor layer, the thickness of phosphor layer, as well as the property of LED chip. Light  108 , for instance, has a range of wavelengths between 440 and 650 nm. It should be noted that substance  112  can be either air or clear silicon for light extraction. 
       FIG. 1(   b ) illustrates a device  100   b , a trimmer  116 , and a light detector  118 , wherein light detector  118  is capable of sensing or reading color of light  108 . Trimmer  116  can be an adjustment instrument using various different technologies, such as a laser gun, metal scraper, micro-scalpel, chemical remover, photo etcher, or so forth. Trimmer  116 , in one example, can be a laser instrument, which includes a laser beam  117 . It should be noted that although  FIG. 1(   b ) may include other component(s) or layers, other component(s) or layers not are necessary to understand the present aspect(s) of the invention. 
     During an operation, upon detecting white light  108 , light detector  118  reports reading result to trimmer  116  indicating the detected color temperature or color quality. After comparing the reading result with predefined color temperature, trimmer  116  removes a portion of phosphor layer  102  in response to the result of the comparison. Trimmer  116  continues to trim phosphor layer  102  until a reading result matches with a predefined color temperature. It should be noted that color quality of cool light, visible light, blue light, red light, white light or the like can be measured by color temperature. 
     Color temperature is a chart characterizing a range of visible light such as lightings from light sources. The color temperature of a light source, for example, uses chromaticity to measure the light. Chromaticity identifies the quality of a color via its colorfulness and hue. It should be noted that other types of light color measurements such as color rendering index (“CRI”) may be used in place of color temperature for identifying the color quality. 
       FIG. 1(   c ) illustrates a device  100   c  after trimming in accordance with controlled color temperature. Multiple microscopic openings  120  have been created on phosphor layer  122  to adjust light color from yellowish to bluish. For example, blue light  124  emitted by LED chip  104  can pass through openings  120  without going through phosphor layer  122  whereby the combination of blue light  124  and yellowish light  108  changes the combined light from more yellowish to more bluish light. To achieve controlled color temperature, phosphor layer  122 , in one aspect, is dispensed purposefully larger than minimal which is a necessary dimensional requirement for achieving a predefined color specification. In an alternative aspect, controlled color temperature can be achieved by adding substances such as phosphor materials on phosphor layer  102  or  122 . 
     During fabrication of an LED device, a phosphor layer is produced with a thickness that is purposely larger than a minimum dimension for achieving a desirable color temperature. After fabrication, the phosphor layer is subsequently trimmed to create an LED package with specific and desirable color requirements. Laser trimming, which is similar to fabricating thick film passive components, may be used to trim phosphor layer(s). The laser is used to cut or drill microscopic holes into phosphor layer  122 , thereby allowing more blue light to exit the package without passing through the phosphor layer  122 . A mixture of additional blue light into the white light causes a shift of color from a warmer color to a colder color. As such, if a phosphor layer is fabricated or manufactured with a color temperature that is beyond the specification in the yellow color region, the color can be adjusted to a more desirable color region. The created microscopic holes are generally too small for human eyes to notice. The yellowish and bluish areas of the device can be blended to obtain desirable color(s). The trimming or adjusting process is monitored by a detector  118  and the process is terminated when the desirable color temperature is reached 
       FIG. 2  illustrates a color temperature chart  200  showing a desirable correlated color temperature in accordance with an aspect of the present invention. Chart  200  illustrates a relationship between light color and its associated temperature. For example, match flame is approximately 1700 kelvin temperature (“° K”) while cool white light is approximately 3500° K. Chart  200  includes a blue region  202 , a green region  204 , a red region  206 , and a temperature scale  208 . Temperature scale  208  illustrates various lines showing correlated color temperature (“CCT”). An x-axis and a y-axis are used to show the chromaticity space associated with chart  200 . For example, a white point, which may be a neutral reference characterized by a chromaticity, is approximately [0.3, 0.3] on the x-axis and y-axis of chromaticity space. 
     Chart  200  illustrates a desired CCT  210  and a fabricated CCT  212 . In an aspect, after the device is fabricated, the light color of the device can be trimmed from fabricated CCT  212  to a desired CCT  210 . It should be noted that the device or package is fabricated with a phosphor layer larger than a desire phosphor layer for the purpose of scaling back the phosphor layer after the fabrication of the phosphor layer. In an alternative aspect, if the fabricated device has lower CCT  216 , the device can be adjusted to desired CCT  210  via adding phosphor substances on the phosphor layer. 
       FIGS. 3(   a - c ) are cross-section views illustrating an optical device  300  capable of controlling color temperature in accordance with an aspect of the present invention.  FIG. 3(   a ) shows a device  300   a , which is similar to device  100   a  illustrated in  FIG. 1(   a ), wherein device  300   a  includes a substrate  106 , a solid state light emitter  104 , a phosphor layer  102 , and dividers  114 . In one aspect, device  100  includes a clear silicon layer  112  dispensed between solid state emitter  104  and phosphor layer  102  for light extracting. It should be noted that the underlying concept of the exemplary aspect(s) of the present invention would not change if one or more blocks (or layers) were added to or removed from device  300 . 
       FIG. 3(   b ) shows a device  300   b , which is similar to device  100   b  illustrated in  FIG. 1(   b ), and a trimmer  116 , and a light detector  118 . Light detector  118  is capable of sensing or reading color of light  106 . Trimmer  116 , in one example, can be a laser instrument including a laser beam  117 . 
       FIG. 3(   c ) illustrates a device  300   c  after performance of trimming in accordance with controlled color temperature. In addition to microscopic openings  120  on phosphor layer  122 , it also includes cavity  320  or multiple cavities used for adjusting light color  308  from yellowish to bluish. For example, upon obtaining a desirable color requirement, portions of phosphor layer  122  can be removed to comply with the desirable color requirement. A laser instrument  116  is used to create one or more cavities until the desirable color requirement or color temperature is reached. To achieve controlled color temperature, phosphor layer  122 , in one aspect, is dispensed purposefully larger than minimal dimensional requirements for achieving the predefined color specifications. In an alternative aspect, controlled color temperature can be achieved by adding substances such as phosphor materials over a phosphor layer. 
       FIGS. 4(   a - c ) are cross-section views illustrating an optical device  400  including a phosphor layer having two colors in accordance with an aspect of the present invention. Device  400   a , illustrated in  FIG. 4(   a ), includes a substrate  106 , a solid state light emitter  104 , a phosphor layer  402 , and dividers  114 . In one aspect, device  400   a  includes a clear silicon layer  112  dispensed between solid state emitter  104  and phosphor layer  402  for light extracting. It should be noted that the underlying concept of the exemplary aspect(s) of the present invention would not change if one or more blocks (or layers) were added to or removed from device  400   a.    
     Solid state light emitter  104 , in an aspect, is a light emitter diode (“LED”) chip, wherein LED chip can further include gallium nitride layer(s), active layer, and indium tin oxide (“ITO”) layer for generating light. LED chip  104  is capable of producing light  110  when electrons and holes in the semiconductor materials are combined. When light  110  reaches phosphor layer  102 , a portion of light  110  is transformed from bluish light into greenish light  410  while another portion of light  110  is transformed from bluish light to reddish light  408 . 
     Phosphor layer  402 , in an aspect, includes green sections  404  and red sections  406  wherein green sections  404  converts blue light  110  to yellowish green light  410  while red sections  406  converts blue light  110  to warm reddish light  408 . When yellowish green light  410  merges with warm reddish light  408 , the combination of lights  408  and  410 , for example, generates natural white light. It should be noted that the color of light  408  or light  410  depends on the composition of the phosphor layer, the thickness of phosphor layer, as well as the property of the LED chip. It should be noted that substance  112  can be either air or clear silicon for light extracting. 
       FIG. 4(   b ) illustrates a device  400   b , a trimmer  116 , and a light detector  118 , wherein light detector  118  is capable of sensing or reading color temperature of light  408 . Trimmer  116  is an adjustment instrument using various different technologies, such as a laser, metal scraper, chemical remover, optical etcher, or the like. During an operation, upon detecting yellowish green light  410  and warm reddish light  408 , light detector  118  reports the reading result to trimmer  116  indicating the detected color temperature of light  408 . After comparing the reading result with predefined color temperatures, trimmer  116  removes a portion of phosphor layer  404  in response to the result of the comparison. Trimmer  116  continues to trim phosphor layer  402  until the reading result matches with the predefined color temperatures. It should be noted that the predefined color temperatures may indicate a range of colors. 
       FIG. 4(   c ) illustrates a device  400   c  after the performance of trimming in accordance with controlled color temperature. Multiple microscopic openings  424  and  425  have been created on phosphor layer  402  to adjust light color from yellowish to bluish light. For example, some blue light  428  emitted by LED chip  104  can pass through openings  425  without going through phosphor layer  406  whereby the combination of blue light  428  with yellowish green light  422  and warm reddish light  426  changes the combined light color from yellowish to bluish light. To achieve controlled color temperature, phosphor layer  402 , in one aspect, is dispensed purposefully larger than minimal requirements for achieving the color specifications. In an alternative aspect, controlled color temperature can be achieved by adding substances such as phosphor materials on phosphor sections  404  and/or  406 . 
       FIG. 5  is a cross-section diagram  500  illustrating an optical device having an adjustable warm phosphor layer in accordance with an aspect of the present invention. Diagram  500  includes an optical device  501 , a trimming instrument  116 , and a light detector  118 . As illustrated in  FIG. 1(   b ), instrument  116 , which may be a laser trimmer, is capable of removing a portion of phosphor layer in response to color temperature detected by detector  118 . It should be noted that the underlying concept of the exemplary aspect(s) of the present invention would not change if one or more blocks (or layers) were added to or removed from device  500 . 
     Optical device  501  includes a substrate  106 , a solid state light emitter  104 , a first phosphor layer  504 , a second phosphor layer  502 , and dividers  114 . In one aspect, device  501  includes an additional clear silicon layer dispensed between solid state emitter  104  and first phosphor layer  504 . In an aspect, first phosphor layer  504  is a yellow phosphor layer while second phosphor layer  502  is a red phosphor layer. The yellow phosphor layer is used to convert the blue light emitted by solid state light emitter  104  to cool light, and red phosphor layer is used to convert the cool light to warm light. Depending on the properties of the red phosphor layer, the color temperature of device  501  can be different. In an alternative aspect, first phosphor layer  504  is a green phosphor layer while second phosphor layer  502  is an orange phosphor layer. 
     During fabrication of device  501 , yellow phosphor layer  504  and red phosphor layer  502  are dispensed with thicknesses that are purposely larger than minimal dimensions of yellow and red phosphor layers for achieving a desirable range of color temperatures. After fabrication, the phosphor layers are subsequently trimmed to create a specific and desirable color light. Laser trimmer  116  is configured to remove a portion of phosphor layer via its laser beam  508 . Laser beam  508  is capable of cut or drill microscopic holes  506  in the phosphor layer  502  thereby more cool light exits the package, which results a shift of reddish to yellowish light. As such, if a phosphor layer is fabricated or manufactured with a color temperature that is beyond the specification in the reddish color region, the color can be adjusted to a more desirable yellow color region. The trimming or adjusting process is monitored by detector  118 , wherein the trimming process is stopped when a desirable color temperature is reached. 
     It should be noted that the trimming process of a referenced device or final device can be applied to one or multi-color patterns. It should be further noted that the trimming technique, which is combined with the process of screen printed dots with different phosphor materials (red and yellow) capable of adjusting color separately, can achieve even larger control over the final color temperature of the device. 
       FIG. 6  is a cross-section diagram  600  illustrating a trimming device capable of trimming phosphor layer for adjusting light color in accordance with an aspect of the present invention. Diagram  600  includes an optical device  601 , a trimming instrument  616 , and a light detector  618 . Device  601  is configured to perform similar functions as device  501  illustrated in  FIG. 5 , wherein device  601  includes a substrate  106 , a solid state light emitter  104 , a first phosphor layer  604 , a second phosphor layer  602 , and dividers  114 . Similar to device  501 , first phosphor layer  604  is a yellow or yellowish green phosphor layer while second phosphor layer  602  is a red or reddish orange phosphor layer. The yellow phosphor layer is used to convert the blue light emitted by solid state light emitter  104  to cool light, and red phosphor layer is used to convert the cool light to warm light. 
     Instrument  616 , in one aspect, includes a body  618 , a lens  608 , and a lens holder  610 . Lens  608 , for example, is a biconvex lens, which is capable of converging a collimated beam to a converging beam  612 . After traveling a focal distance, beam  612  converges to a point, which is also known as a focal point  620 . The focal length is a distance between focal point  620  and the lens. Upon reaching focal point  620 , light beam  612  diverges as it continues traveling. In an aspect, light beam  612  is capable of trimming phosphor layer up to focal point  620 , and it loses its trimming capability once it travels beyond focal point  620 . As such, the depth of trimming to a phosphor layer can be accurately controlled. For example, instrument  616  can be carefully calibrated to only trim the first layer while the second layer is intact. For example, to obtain cooler light, instrument  616  is calibrated to create openings  606  in first phosphor layer  602  while second phosphor layer  604  is intact. 
       FIG. 7  illustrates an exemplary lighting device  700  having multiple solid state light emitters with controlled color temperature in accordance with an aspect of the present invention. Device  700  includes a substrate  702 , four LEDs  704 ,  706 ,  708 , or  710 , a phosphor layer  707 , a lens  716 , and walls  720 . Walls  720  are used to separate optical device  700  from other components such as neighboring optical devices. Walls  720  can also be a part of housing or cup configuration. Substrate  702 , for example, is further coupled to a circuit board, not shown in  FIG. 7 , via coupling elements  714 . It should be noted that the underlying concept of the exemplary aspect(s) of the present invention would not change if one or more blocks (or layers) were added to or removed from device  700 . 
     In an aspect, device  700  includes multiple LEDs  704 - 710  wherein LEDs can be placed on substrate  702  via various connecting mechanisms such as wire bonds  712 , solder balls, or conductive adhesions, not shown in  FIG. 7 . Phosphor layer  707  includes various microscopic openings or holes allowing blue light  730  to pass through phosphor layer  707  without conversion. An advantage of installing more than one LED in device  700  is to increase total luminous output. Lens  716  can be a glass, plastic, or silicon lens used for protecting phosphor layer  707  and device  700 . In addition to providing device protection, lens  716  can provide a function of congregating light to form one or more light beams. It should be noted that additional layers or gas may be added between lens  716  and phosphor layer  707 . 
     The exemplary aspect of the present invention includes various processing steps, which will be described below. The steps of the aspect may be embodied in machine or computer executable instructions. The instructions can be used to cause a general purpose or special purpose system, which is programmed with the instructions, to perform the steps of the exemplary aspect of the present invention. In another aspect, the steps of the exemplary aspect of the present invention may be performed by specific hardware components that contain hard-wired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
       FIG. 8  is a flowchart illustrating a process of adjusting light color of an optical device in accordance with an aspect of the present invention. At block  802 , a process places a light emitter diode (“LED”) on a substrate. In an aspect, the process is capable of facilitating the LED to convert electrical energy to blue light. In another aspect, the process dispenses a silicone layer over the LED for extracting light from the LED. 
     At block  804 , the process identifies a dimension of a phosphor layer, wherein the dimension is purposely larger than minimal dimension required for a phosphor layer to generate white light in accordance with a predefined color temperature. In an aspect, the process is capable of determining adequate length, width, and thickness of a phosphor layer in response the predefined color temperature. 
     At block  806 , the process dispenses a phosphor layer in accordance with the dimension over the LED for generating white light. For one example, the process is capable of dispensing a dome shaped light extracting layer over the LED for extracting the blue light and dispensing the phosphor layer over the dome shaped light extracting layer. 
     At block  808 , the process detects color temperature of the white light emitted from the phosphor layer. In an aspect, the process is further capable of comparing the color temperature detected from the white light with the predefined color temperatures. 
     At block  810 , the process trims the phosphor layer in response to the color temperature detected and the predefined color temperatures. In an aspect, the process removes a portion of the phosphor layer in response to a result of comparison between the color temperature detected from the white light and the predefined color temperatures. For example, the process is also capable of creating at least one cavity on the phosphor layer to adjust light color in accordance with the predefined color temperatures. The process, for instance, sets a cavity diameter ranging from 50 micrometers to 1 millimeter. In an alternative aspect, the process is capable of trimming a red phosphor layer to adjust warm light in response to the predefined color temperatures. 
     While particular aspects of the present invention have been shown and described, it will be obvious to those ordinary skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this exemplary aspect(s) of the present invention and its broader aspects. Therefore, the appended claims are intended to encompass within their scope all such changes and modifications as are within the true spirit and scope of this exemplary aspect(s) of the present invention.