Abstract:
A light source includes a light emitting diode (LED) module having a continuous substrate, a layer of n-type semiconductor material formed above the substrate, and a layer of p-type semiconductor material formed above the n-type semiconductor material. A p-n junction is formed between the p-type and n-type semiconductor materials. The p-type and n-type semiconductor materials are selected to emit light at the p-n junction when an electric current flows through the p-n junction. The LED module includes a plurality of electric contacts connected to the p-type semiconductor material, and at least one electric contact connected to the n-type semiconductor material. The electric contacts are configured to pass electric current through a plurality of regions in the p-n junction such that the plurality of regions have higher electric current densities and emit light brighter than areas outside of the plurality of regions.

Description:
BACKGROUND  
       [0001]    This invention relates to a failure tolerable light emitting diode (LED) light source using an LED matrix. 
         [0002]    A light emitting diode (LED), such as gallium nitride (GaN) based LED, includes one or more layers of n-type semiconductor material (e.g., n-GaN) and one or more layers of p-type semiconductor material (e.g., p-GaN) that are deposited on a substrate (e.g., a sapphire substrate) using metal-organic vapor deposition, molecular beam epitaxy, or another deposition technique. A p-n junction is formed between the n-type and p-type semiconductor materials. When a forward bias voltage is applied to the LED, electrons combine with holes at a region near the p-n junction, in which the electrons transition from a higher energy state to a lower energy state, releasing energy in the form of photons. The wavelength of the light emitted by the LED depends on the band gap energy of the n-type and p-type semiconductor materials. 
         [0003]    Commercially available LEDs are typically packaged LEDs, each including, e.g., an LED chip (which includes the substrate, the n-type semiconductor material layer(s) and p-type semiconductor material layer(s)), electrodes on the chip for electrical connection to the n-type and p-type layers and to provide pads for electrical connection to the electrodes of the package, electrodes for conducting an electric current from outside the packing to the LED chip, a heat sink for dissipating heat generated from the LED chip, a reflector or focusing lens for reflecting or focusing light emitted from the LED chip, and a transparent or semitransparent housing to protect the various components. In some examples, enhancement of the brightness of a packaged LED can be achieved by increasing the emission efficiency of the LED chip, increasing the area of the p-type and n-type semiconductor materials, and improving the heat dissipation and light reflection/focusing mechanisms. Multiple packaged LEDs can be connected in an array to increase brightness. Examples of packaged LED arrays can be found in flashlights and traffic lights. 
         [0004]    When a light source uses a single, large, high brightness LED chip, the light source has little or no failure tolerance. When the single LED chip fails, the light source fails. When a light source uses several packaged LEDs connected in series, the light source also has little or no failure tolerance. When any of the series-connected packaged LEDs fails, the failed LED becomes an open circuit and electric current to the other packaged LEDs is cut off, so the light source fails and cannot generate any light output. 
       SUMMARY  
       [0005]    In a general aspect, parallel arrangements or a series of parallel arrangements of light-emitting devices fabricated on a common substrate is tolerant on isolated device failures while maintaining substantially unchanged light output. The light-emitting devices are operated with the common substrate intact. The light emitting devices can be, e.g., light emitting diodes. 
         [0006]    In another general aspect, in order to provide high light output and also maintain a low probability of failure, a parallel arrangement or a series-parallel arrangement of light-emitting devices are fabricated and electrically interconnected on a single integrated circuit. The light emitting devices can be, e.g., light emitting diodes. 
         [0007]    In one aspect, in general, an apparatus includes a light emitting diode (LED) module or matrix having a continuous substrate, a layer of n-type semiconductor material formed above the substrate, and a layer of p-type semiconductor material formed above the n-type semiconductor material. A p-n junction is formed between the p-type and n-type semiconductor materials. The p-type and n-type semiconductor materials are selected to emit light at the p-n junction when an electric current flows through the p-n junction. The LED module includes a plurality of electric contacts connected to the p-type semiconductor material, and at least one electric contact connected to the n-type semiconductor material. The electric contacts are configured to pass electric current through a plurality of regions in the p-n junction such that the plurality of regions have higher electric current densities and emit light brighter than areas outside of the plurality of regions. 
         [0008]    Implementations of the apparatus may include one or more of the following features. The electric contacts connected to the p-type semiconductor material can be arranged in a plurality of columns and rows such that the LED module form an area light source. In some examples, the apparatus includes a circuit board having conducting lines, the LED module being flip-chip bonded to the circuit board in which the electric contacts are coupled to the conducting lines. In some examples, the apparatus includes a circuit board having conducting lines, the electric contacts of the LED module being coupled to the conducting lines on the circuit board through bonding wires. The apparatus can include a substantially transparent conducting layer that connects two or more of the electric contacts that are connected to the p-type semiconductor material. 
         [0009]    The layer of p-type material can include distinct regions, each distinct region of the p-type material and a portion of the n-type material in combination forming one of the LED chips. Each chip is not necessarily a separate component. For example, the n-type material of different chips may be connected. For example, use of the term ‘chip’ may connote a logical region of a fabricated integrated circuit that may not have a defined boundary on the circuit. The LED module can include LED chips that are connected in series. The layer of p-type material can include distinct regions, each distinct region of the p-type material and a distinct region of the n-type material in combination forming one of the LED chips. The LED module can include an insulation material to insulate an edge of the n-type material from an edge of the p-type material to reduce leakage current that flows from the p-type material to the n-type material through the edges of the materials. The LED chips can be connected in series using at least one of bonding wires and conducting layers. The LED module can include at least two LED chips that are connected in parallel. 
         [0010]    The p-type material between LED chips can be etched through, and the n-type material between the LED chips can be partially etched to expose the n-type material. The n-type material belonging to different LED chips can form a continuous layer. The LED module can include an insulation material to insulate the n-type material from the p-type material at the edges of the n-type and p-type materials exposed by the etching. The at least two LED chips can be connected in parallel using at least one of bonding wires and conducting layers. The n-type semiconductor material can be deposited on the substrate. 
         [0011]    In another aspect, in general, an apparatus includes a light emitting diode (LED) module that includes a continuous substrate, a layer of p-type semiconductor material formed above the substrate, and a layer of n-type semiconductor material formed above the p-type semiconductor material. A p-n junction is formed between the p-type and n-type semiconductor materials. The p-type and n-type semiconductor materials are selected to emit light at the p-n junction when an electric current flows through the p-n junction. The LED module includes a plurality of electric contacts connected to the n-type semiconductor material, and at least one electric contact connected to the p-type semiconductor material. The electric contacts are configured to pass electric current through a plurality of regions in the p-n junction such that the plurality of regions have higher electric current densities and emit light brighter than areas outside of the plurality of regions. 
         [0012]    In another aspect, in general, a light source includes a circuit board and a plurality of light emitting diode (LED) modules mounted on the circuit board. Each LED module includes a plurality of LED chips that are positioned adjacent to each other and fabricated on a common substrate that is a continuous piece of material. The light source includes a housing to enclose the circuit board and the LED modules. 
         [0013]    Implementations of the apparatus may include one or more of the following features. The light source can comply with MR-16 standard. 
         [0014]    In another aspect, in general, an apparatus includes a first array of LED chips fabricated on a common substrate, in which the common substrate is a continuous piece of material. Each LED chip forms a light source and can include a layer of p-type semiconductor material, a layer of n-type semiconductor material coupled to the p-type material to form a p-n junction, and an electric contact connected to the p-type material or an electric contact connected to the n-type material. The LED chips of the array can be connected in parallel such that the n-type material of the LED chips are electrically coupled together, and the p-type material of the LED chips are electrically coupled together. 
         [0015]    Implementations of the apparatus may include one or more of the following features. The apparatus can include a circuit board having conducting lines, the first array of LED chips being flip-chip bonded to the circuit board in which the conducting pads of the LED chips are electrically coupled to the conducting lines. The apparatus can include a second array of LED chips fabricated on a common substrate that is a continuous piece of material, the second array of LED chips being connected to the first array of LED chips in series. 
         [0016]    In another aspect, in general, an apparatus includes a first group of light emitting diode (LED) modules connected in parallel, in which each LED module includes a plurality of LED chips connected in series. The plurality of LED chips in each LED module are fabricated on a common substrate, the common substrate being intact without being divided to separate the LED chips. For each of the LED modules, the LED chips of the module emit light simultaneously when an electric current passes through the LED module. 
         [0017]    Implementations of the apparatus may include one or more of the following features. The plurality of LED chips can be connected in series by connecting an n-type semiconductor material of one of the LED chips to a p-type semiconductor material of another of the LED chips using at least one of bonding wires and conducting layers. The apparatus can include a second group of LED modules connected in parallel, each LED module in the second group including a plurality of LED chips connected in series, the second group being connected in series to the first group. The apparatus can include an elongated substrate, the plurality of LED chips in the first group being positioned along a lengthwise direction on the first elongated substrate to form a line light source. 
         [0018]    In another aspect, in general, an apparatus includes a first group of LED modules that are connected in parallel, each LED module including a plurality of LED chips connected in parallel. The plurality of LED chips of the LED module are fabricated on a common substrate, in which the common substrate is intact without being divided to separate the LED chips. The plurality of LED chips emit light simultaneously when an electric current passes through the LED module. 
         [0019]    Implementations of the apparatus may include one or more of the following features. The apparatus can include an elongated substrate, in which the plurality of LED chips in the first group of LED modules are positioned along a lengthwise direction on the elongated substrate to form a line light source. The apparatus can include a second group of LED modules that are connected in parallel, in which each LED module includes a plurality of LED chips connected in parallel, the second group being connected in series with the first group. 
         [0020]    In another aspect, in general, a lighting device includes a circuit board having signal lines, and a light emitting diode (LED) module mounted on the circuit board to receive electric power from the signal lines. The LED module includes a plurality of LED chips fabricated on a common substrate, in which the common substrate is intact without being cut to separate the LED chips. Each LED chip forms a light source, in which the LED chips are connected in series or parallel. The LED module also includes a controller to control the LED module. 
         [0021]    Implementations of the apparatus may include one or more of the following features. The LED chips of the LED modules can be arranged in a plurality of rows and columns to form an area light source. 
         [0022]    In another aspect, in general, a method includes fabricating a light emitting diode (LED) module having a plurality of LED chips on a continuous substrate. The LED chips are fabricated according to a process that includes fabricating a layer of n-type semiconductor material above the substrate, and fabricating a layer of p-type semiconductor material above the n-type semiconductor material. A p-n junction is formed between the p-type and n-type materials, the p-type and n-type materials selected to emit light at the p-n junction when an electric current flows through the p-n junction. The process includes fabricating a plurality of electric contact pads connected to the p-type material, and fabricating at least one electric contact pad connected to the n-type material. The electric contact pads connected to the p-type and n-type materials are configured to pass electric current through a plurality of regions in the p-n junction such that the plurality of regions have higher electric current densities and emit light brighter than areas outside of the plurality of regions. 
         [0023]    Implementations of the method may include one or more of the following features. In some examples, the method can include flip-chip bonding the LED module to a circuit board having conducting lines by coupling the electric contact pads to conducting lines on the circuit board. In some examples, the method can include coupling electric contact pads of the LED module to conducting lines on a circuit board through bonding wires. The LED module can include separating the p-type materials of different LED chips by etching portions of the p-type material to expose the underlying n-type material, the n-type material belonging to different LED chips of the LED module being a continuous layer. 
         [0024]    Fabricating the LED module can include connecting the LED chips in parallel. Fabricating the LED module can include fabricating an insulation material positioned between the exposed n-type material and an edge of the p-type material. The insulation material can be configured to prevent current from flowing from the p-type material to the n-type material through the edge of the p-type material. Fabricating the LED module can include separating the p-type and n-type materials of different LED chips by etching portions of the p-type and n-type materials to expose the underlying substrate. Fabricating the LED module can include connecting the LED chips in series. The method can include fabricating an insulation material positioned adjacent to the edges of the n-type and p-type materials that are exposed by the etching. Fabricating the layer of n-type semiconductor material above the substrate can include depositing the n-type semiconductor material on the substrate. 
         [0025]    In another aspect, in general, a method of operating a lighting device includes passing an electric current through a plurality of light emitting diode (LED) chips that are fabricated on a common substrate that is a continuous piece of material. Each LED chip forms a light source, in which the LED chips are connected in series or parallel, and the plurality of LED chips form a line light source or an area light source. The method includes regulating the electric current to control a brightness of light emitted by the LED chips. 
         [0026]    Implementations of the method may include one or more of the following features. Passing an electric current through a plurality of LED chips includes passing the electric current through separated regions of a layer of p-type semiconductor material and different portions of a continuous layer of n-type semiconductor material. 
         [0027]    In another aspect, in general, a method includes generating light from a plurality of light emitting diode (LED) chips that are positioned adjacent to each other and fabricated on a common substrate that is intact without being cut to separate the LED chips. 
         [0028]    Implementations of the apparatus may include one or more of the following features. The plurality of LED chips include a layer of p-type semiconductor material divided into separate regions and a continuous layer of n-type semiconductor material. 
         [0029]    In another aspect, in general, a light source includes a series of parallel arrangements of LED chips that are fabricated on a common substrate. Each LED chip includes a layer of p-type semiconductor material and a layer of n-type semiconductor material, in which a p-n junction is formed between the p-type and n-type materials. A first group of parallel connected LED chips are connected in series with a second group of parallel connected LED chips. The first and second group of LED chips are fabricated on a continuous substrate that is not cut when the LED chips are in operation. The p-type material and the n-type material can be etched to isolate the first group of LED chips from the second group of LED chips. 
         [0030]    Implementations of the light source may include one or more of the following features. The LED chips within the first group can be connected in parallel by wire bonding or conducting layers. The first group of parallel connected LED chips can be connected in series with the second group of parallel connected LED chips by using either wire bonding or conducting layers. The p-type material and the n-type material can be etched to isolate the LED chips within the first (and/or second) group of LED chips, so that when one of the LED chips fail, the failed LED chip is isolated from the rest of the LED chips and does not affect the operation of the remaining functional LED chips. Insulation material can be provided at the edges of the p-type or n-type material to prevent leakage current. 
         [0031]    Aspects can have one or more of the following advantages. The LED module or matrix can have a higher defect or failure tolerance, higher reliability, higher emitting efficiency, better thermal dissipation, and lower cost as compared to a single high brightness LED. By not cutting the substrate to separate individual LED chips, expensive cutting tools (e.g., diamond saw) can be avoided, and the cost of fabricating a large area light source having an array of LED chips can be reduced. In some examples, by etching the p-type and n-type layers to isolate the LED chips on the common substrate, failure of one LED chip will not affect the operation of other LED chips. By using insulation material at edges of the p-type and n-type materials to prevent or reduce leakage current, the LED module or matrix can have a more uniform brightness. 
         [0032]    Other features and advantages of the invention are apparent from the following description, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS  
         [0033]      FIG. 1  is a top view of an LED module. 
           [0034]      FIG. 2  is a cross sectional diagram of the LED module of  FIG. 1 . 
           [0035]      FIG. 3  is a schematic diagram of an equivalent circuit of the LED module of  FIG. 1 . 
           [0036]      FIG. 4  is a diagram of a large area light source. 
           [0037]      FIG. 5  is a diagram of LED modules fabricated on a common substrate 
           [0038]      FIG. 6  is a diagram of a large area LED light source. 
           [0039]      FIG. 7  is a schematic diagram of an equivalent circuit of the large area LED light source of  FIG. 6 . 
           [0040]      FIG. 8  is a cross sectional diagram of an LED module. 
           [0041]      FIG. 9  is a top view of the LED module of  FIG. 8 . 
           [0042]      FIG. 10A  is a diagram of an LED matrix. 
           [0043]      FIG. 10B  is a diagram of the LED chips of an LED module. 
           [0044]      FIG. 11A  is a diagram of an LED matrix. 
           [0045]      FIG. 11B  is a diagram of the LED chips of an LED module. 
           [0046]      FIG. 12  is a diagram of LED modules each having LED chips connected in series. 
           [0047]      FIG. 13  is a cross sectional diagram of an LED module. 
           [0048]      FIG. 14  is a diagram of an LED matrix. 
           [0049]      FIG. 15  is a diagram of an equivalent circuit of the LED matrix of  FIG. 14 . 
           [0050]      FIG. 16  is a top view of an LED module. 
           [0051]      FIGS. 17 and 18  are diagrams of LED modules. 
       
    
    
     DESCRIPTION  
       [0052]      FIG. 1  is a top view of an LED module  100  that includes twenty LED chips  102  that are fabricated on a common substrate  104 .  FIG. 2  is a cross sectional diagram of the LED module  100 . Referring to  FIGS. 1 and 2 , the LED module  100  includes four rows of LED chips  102 , each row including five LED chips  102 . Within the LED module  100 , the LED chips  102  are connected in parallel. An LED light source can include multiple LED modules  100  that are connected in parallel or in series. This allows the LED light source to be tolerable to failure of individual LED chips  102  (resulting in an open circuit at the failed LED chip). Even when some of the LED chips  102  fail, the total light output of the LED light source does not drop significantly. Because each LED chip  102  is small, and the LED chips  102  are densely packed together, one LED chip  102  that failed may not be noticeable to the user. Even if a few LED chips  102  fail, when the failed LED chips  102  are spaced apart, the user may still not notice the failed LED chips  102 . The probability of a number of adjacent LED chips  102  fail at the same time is small. By comparison, in a conventional LED light source that includes an array of packaged LEDs in which the LED chips are individually packaged, each packaged LED has a larger size, so even a single failed packaged LED would be noticeable to the user. 
         [0053]    In this description, each chip is not necessarily a separate component. For example, use of the term ‘chip’ may connote a logical region of a fabricated integrated circuit that may not have a defined boundary on the circuit. 
         [0054]    The twenty LED chips  102  are not cut and separated from one another. Rather, the p-type semiconductor material  108  of the twenty LED chips  102  form a continuous layer. Similarly, the n-type semiconductor material  106  of the twenty LED chips  102  form a continuous layer. By not cutting and separating the LED chips  102 , the manufacturing process for a light source that uses the LED module  100  can be made simpler and cheaper. Aligning the LED chips with other components of the light source, such as conducting lines, can be made simpler. Because the amount of light output per unit area is higher, the light intensity of the LED module  100  can be higher than a conventional LED light source that uses an array of packaged LEDs. 
         [0055]    Several LED modules  100  may be fabricated on a wafer (not shown). The wafer may be cut to separate the LED modules  100 , but each LED module  100  is not cut to separate the LED chips  102 . 
         [0056]    Referring to  FIGS. 1 and 2 , the LED chips  102  are fabricated by depositing a layer of n-type semiconductor material  106  (e.g., n-GaN) on the substrate  104  (e.g., made of sapphire (Al 2 O 3  crystal) or silicon carbide (SiC)), and depositing a layer of p-type semiconductor material  108  (e.g., p-GaN) on the n-type semiconductor material  106 . One or more layers of p-n junctions  110  are formed between the n-type and p-type semiconductor materials  106  and  108 . The p-n junction  110  emits light when current flows through. 
         [0057]    A metal contact pad, referred to as a P-pad  112 , is formed above the p-type semiconductor material  108  of each LED chip  102 . A transparent or semi-transparent conducting layer  114  is formed above the P-pad  112  and connects five P-pads  112  of a row. A metal contact pad, referred to as a P-pad  116 , is formed above each conducting layer  114 . 
         [0058]    In this description, when a layer or component X of a device is said to be above another layer or component Y, it is meant that X is above Y when the device is positioned in the orientation shown in the figure. The device may be used in different orientations, such as being flipped over, then X may become below Y. Similarly, terms such as “upward,” “downward,” “left,” and “right” are used for convenience of describing the positions or orientations of the layers and components of a device, and are not meant to limit the device to be used in a particular position or orientation. 
         [0059]    The p-type semiconductor material  108  is etched at the edges of the LED module  100  to expose portions  120  (see  FIG. 2 ) of the n-type semiconductor material  106 . Metal contact pads, referred to as N-pads  118 , are formed above the exposed portions  120  of the n-type semiconductor material  106 . The P-pad  116  and the N-pad  118  are used to connect to external components, such as power lines, other electronic devices (e.g., zener diode for electro-static discharge protection), or other LED modules  100 . 
         [0060]    When the LED module  100  is in operation, electric current flows from the P-pad  116  to the metal conducting layer  114  to the P-pads  112 . The current then flows from the P-pads  112  through the p-type semiconductor material, the p-n junction  110 , the n-type semiconductor material  106 , and to the N-pads  118 . The regions directly below the P-pads  112  have higher current densities than the regions between the P-pads  112 , so the regions directly below the P-pads  112  emit light having higher intensities. The LED module  100  is described as having twenty LED chips  102  because there are twenty regions that emit light with higher intensities. 
         [0061]    The arrangement of P-pads  112 , conducting layers  114 , P-pads  116 , and N-pads  118  provide better distribution of electric current in the LED module  100 , and better heat dissipation, as compared to a single large LED (having an area comparable to the LED module  100 ) having a single P-pad and a single N-pad. Because the twenty LED chips  102  are fabricated on the same substrate  104 , the LED chips  102  have similar light emittance characteristics, resulting in a light source having a more uniform brightness across the area of the LED module  100 , as compared to using twenty LED chips  102  that are fabricated on different substrates or on different regions of a substrate. 
         [0062]      FIG. 3  is a schematic diagram of an equivalent circuit of the LED module  100 . 
         [0063]      FIG. 4  is a diagram of an example of a large area light source  130  that includes a circuit board  120  and eight LED modules  100  that are flip-chip bonded to the circuit board  120 . The LED modules  100  are flipped and the P-pads  118  and N-pads  116  are bonded to conducting lines  122  on the circuit board  120 . In  FIG. 4 , the substrate  104  is on top while the P-pads  116  and N-pads  118  face downward and connect to the conducting lines  122 . 
         [0064]    The large area light source  130  includes two groups  126  of LED modules  100 . Within each group  126 , the LED modules  100  are connected in series, in which the P-pad  116  of one LED module  100  is connected to the N-pad  118  of another LED module  100 . The two groups  126  can be connected such that they emit light simultaneously. The two groups  126  can also be used as two light sources that can be individually controlled. For example, the light source  130  can be constructed into a light source having two brightness settings. In the lower brightness setting, only one group  126  emits light, and in the higher brightness setting, both groups  126  emit light. 
         [0065]    The large area light source  130  is fault tolerant because in each LED module  100 , each LED chip  102  is connected in parallel with one or more other LED chips  102 , and therefore an open circuit fault (due to failure of one LED chip) does not prevent other LED chips from functioning. The probability that all of the LED chips  102  within the same LED module  100  fail prematurely is low. When used with a constant current source, if one LED chip  102  within the LED module  100  fails (e.g., becomes open circuit), the amount of current flowing into the remaining LED chips  102  in the LED module  100  increases, so each of the remaining LED chips  102  becomes brighter, offsetting the loss of light from the failed LED chip  102 . Due to the non-linear current-voltage (I-V) characteristics of the LED chips  102 , the total brightness produced by the LED module  100  after one LED chip  102  fails may become slightly higher than the original brightness of the LED module  100 . 
         [0066]    For a given type of LED chips  102 , due to the non-linear I-V characteristics of the LED chips  102 , the voltage drop across each LED chip  102  under normal operating conditions is substantially constant even when the current flowing through the LED chip increases. For example, if the current flowing through each LED chip increases p %, the voltage across each LED chip increases less than 0.1*p %. The number of LED modules  100  that are connected in series can be determined by the voltage source to be applied to the large area light source  130 . For example, if the voltage drop across each LED chip  102  is about 3V, then eight LED chips  102  connected in series would result in a voltage drop of about 24V. Each group  126  of the large area light source  130  includes four LED modules  100  connected in series, so two groups  126  connected in series would result in a voltage drop of about 24V, suitable for connecting to a 24V light bulb socket. 
         [0067]      FIG. 5  shows four LED modules  140  that are fabricated on a common substrate  142 . Each LED module  140  includes five LED chips  102  that are connected in parallel, similar to a row of LED chips  102  shown in  FIG. 1 . A difference between an LED module  140  in  FIG. 5  and a row of LED chips  102  in  FIG. 1  is that, in  FIG. 5 , each LED module  140  is separated from the other LED modules  140  by etching away the n-type semiconductor material  106  between the LED modules  140 . Later, the LED modules  140  can be separated from each other by cutting and separating the substrate  142 . 
         [0068]    In each LED module  140 , the p-type semiconductor material  108  is etched on four edges of the LED module  140  to expose portions of the n-type semiconductor material  106 . Metal conducting pads, referred to as N-pads  144 , are formed above part of the exposed portions of the n-type semiconductor material  106 . In the example of  FIG. 5 , the N-pads  144  form a continuous loop that surrounds the LED module  140 . This provides better electric current distribution when the LED module  140  is in operation. 
         [0069]    Referring to  FIG. 6 , a large area LED light source  150  includes three LED modules  140  that are connected in series and spaced apart in an x-direction. Each LED module  140  includes five LED chips  102  that are positioned along a y-direction. The LED modules  140  are mounted on a circuit board  152  having conducting lines  154  that extend in the y-direction. 
         [0070]    For each LED module  140 , multiple bonding wires  156  extend in the x-direction to connect the conducting layer  114  to a conducting line  154  positioned to the right the LED module  140 . Multiple bonding wires  158  extend in the x-direction to connect the N-pad  144  to another conducting line  154  positioned to the left of the LED module  140 . The multiple bonding wires  156  and  158  allow electric current to spread more evenly on the conducting layer  114  and the N-pad  144  so that the current flowing to each LED chip  102  in the same module  140  will be substantially the same. Each LED module  140  forms a line light source that extends in the y-direction. 
         [0071]      FIG. 7  is a schematic diagram of an equivalent circuit of the large area LED light source  150 . 
         [0072]      FIG. 8  is a cross sectional diagram of an LED module  160  in which five LED chips  162   a  to  162   e  (collectively referred to as  162 ) are connected in series. The LED chips  162  are all fabricated on a common substrate  104 . Each LED chip  162  includes one or more layers of n-type semiconductor material  106  and one or more layers of p-type semiconductor material  108 . P-n junctions  110  are formed between the layers  106  and  108 . The p-n junctions  110  emit light when electric currents flow through. 
         [0073]    For each LED chip  162 , in order to form a contact to the n-type semiconductor material  106 , a portion of the p-type semiconductor material  108  is etched away to expose the n-type semiconductor material  106 . The exposed n-type semiconductor material  106  is partially etched away to provide an area for a metal contact pad, referred to as an N-pad  164 . Portions of the n-type material  106  between adjacent LED chips  162  are etched away to isolate the chips  162  so that electric currents do not leak from one chip  162  to another chip through the n-type material  106 . The N-pad  164  is formed on the n-type semiconductor material  106 . A metal contact pad, referred to as a P-pad  166 , is formed above the p-type semiconductor material  108 . An insulation material  168  isolates the N-pad  164  from the p-type semiconductor material  108 . 
         [0074]    A metal bonding wire  170  connects the N-pad  164  of an LED chip  162  to the P-pad  166  of an adjacent LED chip  162 . The wire  170  can be made of, e.g., gold. The P-pad  166  of the LED chip  162   a  and the N-pad  164  of the LED chip  162   e  are used to connect to external components, such as power lines or other LED modules. 
         [0075]      FIG. 9  is a top view of the LED module  160  of  FIG. 8 . In each LED chip  162 , an indium-tin-oxide (ITO) transparent conducting layer covers the portion of the p-type material  108  that has not be etched away. The ITO layer spreads the current more evenly through the p-type material  108 . 
         [0076]      FIG. 10A  is a diagram of an example of an LED matrix  190  that includes multiple groups  192  of LED modules  160  mounted on a circuit board  196 . Different groups  192  are connected in series, while each group  192  has LED modules  160  that are connected in parallel. Each LED module  160  has five LED chips  162  that are connected in series, similar to the configuration shown in  FIG. 8 . 
         [0077]    Each group  192  has twenty-five LED chips  162  (belonging to five LED modules  160 ) that are positioned lengthwise in the y-direction along an elongated packaging board  194 , forming a line light source. The LED matrix  190  includes five groups  192  that form five line light sources. In each LED module  160 , the LED chips  162   a  and  162   e  are connected to conducting lines  198  and  200  through bonding wires  202  and  204 , respectively. The conducting lines  198  and  200  extend in the y-direction parallel to the lengthwise direction of the elongated packaging board  194 . 
         [0078]      FIG. 10B  is a diagram of the LED chips  162   a  to  162   e  of an LED module  160  and the bonding wires (e.g.,  202  and  204 ) that connect to the LED chips  162   a  to  162   e.    
         [0079]      FIG. 11A  is a diagram of an example of an LED matrix  210  that includes groups  212  of LED modules  214  that are mounted on a circuit board  196 . Different groups  212  are connected in series, while different modules  214  within a group  212  are connected in parallel. In  FIG. 11A , each group  212  has twenty-five LED chips  162  that are positioned in the y-direction along an elongated packaging board  194 , forming a line light source. The LED matrix  210  includes five groups  212  that form five line light sources in parallel. 
         [0080]    The LED chips  162  in  FIG. 11A  are similar to those in  FIG. 10A , except there are no bonding wires connecting one LED chip  162  to another in series. In  FIG. 11A , the five LED chips  162  of an LED module  214  are connected in parallel. Each LED chip  162  is connected through bonding wires  216  and  218  to conducting lines  198  and  200 , respectively, positioned on two sides of the packaging board  194 . 
         [0081]      FIG. 11B  is a diagram of the LED chips  162  of an LED module  214  and the bonding wires  216  and  218  that connect to the LED chips  162 . 
         [0082]      FIG. 12  is a diagram of an example of LED modules  170  each having LED chips  162  connected in series, similar to those shown in  FIG. 8 . The difference between the LED modules  170  of  FIG. 12  and the LED modules  160  of  FIG. 8  is that, in the LED module  170 , a metal conducting layer  180  is formed above the N-pad  164  of one LED chip and the P-pad  166  of another LED chip to connect the two LED chips  162  together. 
         [0083]      FIG. 13  is a diagram of a cross sectional diagram of an LED module  170 . Portions of the n-type material  106  between LED chips  162  are etched away to form gaps  172  to prevent leakage current from flowing from one chip  162  to another through the n-type material  106 . Vertical insulation sidewalls  174  are formed to provide electrical isolation between the p-type material  108  and the n-type material  106  at the edges of the p-type and n-type materials. 
         [0084]      FIG. 14  is a diagram of an example of an LED matrix  220  that includes LED modules  170  that are flip-chip bonded to a circuit board  224 . In  FIG. 14 , the substrates  104  of the LED modules  170  are on top, while the conducting layers  180  are below the substrates  104  and connected to conducting lines  222  on the circuit board  224 .  FIG. 14  shows six conducting lines  222  in the LED matrix  220 . The four conducting lines  222  in the middle are optional. 
         [0085]      FIG. 15  is a diagram of an equivalent circuit of the LED matrix  220 . 
         [0086]      FIG. 16  is a top view of an LED module  240  that includes five LED chips  242  connected in parallel. Each LED chip  242  includes an N-pad  244  connected to the n-type semiconductor material and a P-pad  246  connected to the p-type semiconductor material of the LED chip  242 . The N-pads  244  are connected together by metal bonding wires  248 , and the P-pads  244  are connected together by metal bonding wires  250 . Bonding wires  252  are used to connect to external components, such as a power source or other LED modules. 
         [0087]    Referring to  FIG. 17 , the LED module  100  of  FIG. 3  (or the large area light sources  130  ( FIG. 4 ),  150  ( FIG. 6 ),  190  ( FIG. 10A ),  210  ( FIG. 11A ), and  220  ( FIG. 14 )) can be used in a lighting device  230  that includes an LED controller  232  for regulating the voltage and current provided to the LED module  100  (or the large area light sources). The lighting device  230  can be packaged according to industry standards (e.g., MR16) so that it can be easily coupled to a standard light bulb socket and connected to a standard voltage provided by a standard power source  234 . 
         [0088]    It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments are within the scope of the following claims. For example, in  FIG. 4 , rather than connecting the LED modules  100  in series, the LED modules  100  can also be connected in parallel, in which the P-pad  116  and N-pad  118  of an LED module  100  is connected to the P-pad  116  and N-pad  118 , respectively, of another LED module  100 . The number of LED chips that are connected in parallel or series can be different from those described above. The LED chips can be fabricated by forming the p-type material above the substrate, then forming the n-type material above the p-type material. The materials for the n-type semiconductor material, the p-type semiconductor material, the substrate, the conducting layers, the bonding wire, and so forth, can be different from those described above. The LED chips can be designed to emit different colors. 
         [0089]    In  FIG. 1 , the LED chips  102  are arranged in a square or rectangular array. The LED chips  102  can also be arranged in other shapes, such as a triangular, pentagonal, or hexagonal array. In  FIGS. 5 ,  6 ,  8 ,  9 ,  10 A,  11 A,  12 - 14 , and  16 , each LED module has an elongated shape and has LED chips arranged along a line to form a line light source. The LED modules can also have other shapes, in which the LED chips are arranged to form a modular light source having the shape of, e.g., a triangle, square, pentagon, or hexagon. 
         [0090]    In the LED module  100  of  FIGS. 1 and 2 , each of the p-type semiconductor material  108  and the n-type semiconductor material  106  is a continuous layer. Referring to  FIG. 18 , the p-type semiconductor material  108  can also be etched to form distinct regions, so that the p-type semiconductor material  108  in one LED chip  102  is separated from the p-type semiconductor material  108  of another LED chip  102 . An insulating material  260  is filled in the space between the p-type semiconductor materials  108  of adjacent LED chips  102  before the conducting layer  114  is formed. 
         [0091]    A light source can have a series of parallel arrangements of LED chips that are fabricated on a common substrate. For example, in  FIG. 5 , the LED modules  140  are separated from one another by etching away the n-type and p-type semiconductor material between the modules, in which the substrate  142  is not cut when operating the LED modules  140 . The four LED modules  140  on the common substrate  142  can be connected in series by, e.g., wire bonding or conducting layers. Similarly, several LED modules  160  ( FIG. 8 ) can be fabricated on a common substrate, in which the n-type and p-type semiconductor materials between the modules are etched away to isolate one LED module  160  from another LED module  160  without cutting the common substrate. A first LED module  160  can be connected in series with another LED module  160  by, e.g., wire bonding. The conducting layers can be patterned electrodes that connect the LED chips to form the series and parallel connections. Insulation layers can be used at the edges of the p-type and n-type layers to prevent leakage current. The light source can have an array of LED chips connected together on a common substrate, similar to an integrated circuit. The light source provides high light output and also maintain a low probability of failure.