Patent Publication Number: US-9853189-B2

Title: Backlight module with MJT LED and backlight unit including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and the benefit of Korean Patent Application No. 10-2014-0026574, filed on Mar. 6, 2014, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND 
     Field 
     The present disclosure relates to a backlight module using a multi junction technology (MJT) light emitting diode (LED) and a backlight unit including the same. More particularly, the present disclosure relates to a backlight module which employs an MJT LED configured to increase an effective light emitting area of each of light emitting cells to allow operation at low current, and a backlight unit including the same. 
     Description of the Background 
     A liquid crystal display creates an image by controlling transmittance of a backlight light source. Although a cold cathode fluorescent lamp (CCFL) has generally been used as a backlight light source in the related art, light emitting diodes (hereinafter, LEDs) are being recently used due to various advantages such as low power consumption, long lifespan, eco-friendliness, and the like. 
     Backlight units can be classified into edge type backlight units and direct type backlight units according to the locations of LEDs for backlighting a liquid crystal display. In an edge type backlight unit, with LEDs arranged as light sources on a side surface of a light guide plate, light entering the light guide plate from the light sources is used for backlighting of a liquid crystal panel. Thus, the edge type backlight unit can reduce the number of LEDs and does not require strict control of quality deviation among the LEDs, thereby enabling manufacture of low power consumption products, which is advantageous in terms of cost. However, in the edge type backlight unit it is difficult to overcome contrast between a corner area and a central area of the liquid crystal display and it is difficult to create high quality images. 
     Alternatively, a direct type backlight unit is placed under a liquid crystal panel and allows light emitted from a surface light source, which has substantially the same area as that of the liquid crystal panel, to directly illuminate a front side of the liquid crystal panel. The direct type backlight unit can overcome contrast difference between a corner area and a central area of the liquid crystal display and can achieve high quality images. 
     However, in the direct type backlight unit, if each of the LEDs does not illuminate a relatively wide area for backlighting, a number of LEDs must be densely arranged, thereby causing increase in power consumption. Moreover, deviation in quality between the LEDs can make it difficult to secure a uniform screen illumination due to uneven backlighting of a liquid crystal panel. 
     Particularly, with the increasing size of liquid crystal panels, the size of the direct type backlight unit is also increased, thereby causing deterioration in stability or reliability of the direct type backlight unit. Specifically, since the LED backlight unit controls the operating current supplied to a plurality of LED groups, that is, LED arrays, through a plurality of LED drive circuits, the number of LED drive circuits and the number of LED corresponding arrays are significantly increased as the size of the LED backlight unit increases. As a result, a disconnection can occur between the plurality of LEDs or LED arrays arranged adjacent each other, whereby the drive circuits are damaged due to overcurrent, overvoltage, or overheating, thereby deteriorating the stability and reliability of the backlight unit. 
       FIG. 1  is a configuration block diagram of a typical backlight unit using LEDs in the related art. With reference to  FIG. 1 , problems of the related art will be described in more detail. As shown in  FIG. 1 , a typical backlight unit  1  includes a backlight control module  2  and a backlight module  5 . 
     The backlight control module  2  includes an operating power generator  3 , which generates/outputs DC power based on input voltage Vin input from an external power source, and an operation controller  4  controlling operation of each of a plurality of LED arrays  6   a ˜ 6   n  constituting the backlight module  5 . The operating power generator  3  generally generates DC voltages such as 12V, 24V, 48V, and the like as operating power. 
     The backlight module  5  includes a plurality of LED arrays  6   a ˜ 6   n  each formed by connecting a plurality of LEDs in series, and an optical unit (not shown) for enhancing efficacy of light emitted from the plurality of LED arrays  6   a ˜ 6   n . In  FIG. 1 , the backlight unit  5  includes n LED arrays  6   a ˜ 6   n  connected to each other in parallel and each including five LEDs connected to each other in series. Here, since each of the LEDs used in the backlight unit generally has a forward voltage level in the range from 3V to 6.5V and is difficult to individually control/operate when connected to the operating power generator  3 , plural LEDs are connected to each other in series to constitute LED arrays such that each of the LED arrays can be operated/controlled. In such a typical backlight unit  1  in the related art, the operation controller  4  is configured to control brightness of all of the LED arrays  6   a ˜ 6   n  constituting the backlight module  5  through pulse width modulation (PWM) control with respect to the operating power supplied to the backlight module  5  in response to an external dimming signal (Dim). Otherwise, in such a typical backlight unit  1 , the operation controller  4  adjusts the operating current flowing through a specific LED array among the n LED arrays  6   a ˜ 6   n  in response to an external dimming signal (Dim) to control brightness of the specific LED array. 
     LEDs used in such a typical backlight unit  1  are generally single-cell LEDs capable of being operated at low voltage and high current. For example, such a single-cell LED has an operating voltage of 3.6V and can be operated at an operating current of 250˜500 mA. Thus, in order to control operation of the backlight module  5  constituted by such single-cell LEDs, peripheral circuits including the operation controller  4  in the related art must be constituted by large capacity electronic devices capable of handling large current, thereby causing increase in manufacturing costs of the backlight unit  1 . In addition, the peripheral circuits including the operation controller  4  are damaged due to the high current operation characteristics of the aforementioned typical single-cell LEDs, thereby causing deterioration in stability or reliability of the backlight unit  1 . In addition, the high current operation characteristics of the single-cell LEDs cause an increase in power consumption and a droop phenomenon. 
     SUMMARY 
     The present disclosure is aimed at providing a backlight module which can be operated at low current using an MJT LED including a plurality of light emitting cells and a backlight unit including the same. 
     In addition, the present disclosure is aimed at providing an MJT LED chip, which can increase an effective light emitting area of a light emitting cell, and a method of manufacturing the same. 
     Further, the present invention is aimed at providing a backlight unit, which allows a backlight module to be operated at low current using the aforementioned MJT LED, thereby improving stability and reliability of drive circuits for controlling operation of the backlight module, and enabling reduction in manufacturing costs. 
     Further, the present disclosure is aimed at providing a backlight unit, which allows a backlight module to be operated at low current using the aforementioned MJT LED, thereby improving power efficiency and luminous efficacy while preventing a droop phenomenon due to operation at high current. 
     Further, the present disclosure is aimed at providing a backlight unit, in which a backlight module is constituted by MJT LEDs, thereby minimizing the number of LEDs while enabling individual control of the MJT LEDs. 
     The above and other objects and advantageous effects of the present disclosure can be obtained by the following features of the present disclosure. 
     In accordance with one aspect of the present disclosure, a backlight module includes a printed circuit board; a plurality of MJT LEDs disposed on the printed circuit board; and a plurality of optical members disposed on the MJT LEDs or the printed circuit board so as to correspond to the MJT LEDs and each including a light incident face through which light emitted from the corresponding MJT LED enters the optical member and a light exit face through which light exits the optical member at a wider beam angle than that of the corresponding MJT LED, wherein each of the MJT LEDs includes a first light emitting cell and a second light emitting cell separated from each other on a growth substrate; a first transparent electrode layer placed on the first light emitting cell and electrically connected to the first light emitting cell; a current blocking layer placed between the first light emitting cell and the first transparent electrode layer and separating a portion of the first transparent electrode layer from the first light emitting cell; an interconnection line electrically connecting the first light emitting cell to the second light emitting cell; and an insulation layer separating the interconnection line from a side surface of the first light emitting cell. Here, the second light emitting cell has a slanted side surface; and the interconnection line includes a first connection section for electrical connection to the first light emitting cell and a second connection section for electrical connection to the second light emitting cell. The first connection section contacts the first transparent electrode layer within an upper area of the current blocking layer, and the second connection section contacts the slanted side surface of the second light emitting cell. 
     In one aspect, each of the MJT LEDs includes first to N-th light emitting cells (N being a natural number of 2 or more), and the N-th light emitting cell may be electrically connected to a (N−1)th light emitting cell using the same structure as a connection structure between the first light emitting cell and a second light emitting cell. 
     In one aspect, the first to N-th light emitting cells are connected to each other in series and each operated by an operating voltage of 2.5V to 4 V. Here, each of the MJT LEDs may be operated at an operating voltage of at least 10 V or more. 
     In one aspect, each of the MJT LEDs includes three light emitting cells each being operated at an operating voltage of 3V to 3.6V, and is operated at an operating voltage of 12V to 14V. 
     In one aspect, the light exit face includes a concave section formed near a central axis of the optical member and a convex section extending from the concave section and separated from the central axis of the optical member. 
     In one aspect, the light exit face includes a total internal reflection surface so as to form an apex under the central axis of the optical member. 
     In one aspect, the light incident face includes an opening formed near the central axis of the optical member, and the height of the opening is 1.5 times or more a width thereof. 
     In one aspect, each of the optical members has a light scattering pattern formed on at least a portion of a bottom surface facing the printed circuit board. 
     In one aspect, each of the optical members includes a lower surface having a concave section, through which light emitted from the MJT LED enters the optical member; and an upper surface through which light entering the optical member through the concave section exits the optical member. Here, the upper surface includes a concave surface placed at the central axis of the optical member, and the concave section of the lower surface includes at least one of a perpendicular surface relative to the central axis and a downwardly convex surface, and the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface may be placed within a narrower area than an area for an entrance of the concave section. 
     In one aspect, the upper surface and the concave section of the optical member form a mirror symmetry structure relative to a plane passing through the central axis of the optical member. 
     In one aspect, the upper surface and the concave section of the optical member form a rotational body shape relative to the central axis of the optical member. 
     In one aspect, each of the optical members has a light scattering pattern formed on the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface within the concave section of the lower surface and on a surface closer to the central axis than the at least one surface. 
     In one aspect, each of the optical members has a light scattering pattern formed on the concave surface of the upper surface. 
     In one aspect, each of the optical members further includes a material layer having a different index of refraction than the optical member on the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface within the concave section of the lower surface and on a surface closer to the central axis than the at least one surface. 
     In one aspect, each of the optical members further includes a material layer having a different index of refraction than the optical member on the concave surface of the upper surface. 
     In one aspect, the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface is defined within a narrower area than an area surrounded by an inflection curve at which the concave surface of the upper surface meets the convex surface thereof. 
     In one aspect, the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface is defined within a narrower area than an area of a light exit face of the light emitting diode. 
     In one aspect, each of the optical members further includes a flange connecting the upper surface and the lower surface and the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface within the concave section is placed above the flange. 
     In one aspect, each of the optical members has an optical axis L, a light incident section, and a light exit face, and is formed of a material, the index of refraction of which is higher than that of a material adjoining the light incident section and that of a material adjoining the light exit face. 
     In one aspect, the light incident section is formed such that the shortest distance from a point (p) on the optical axis L to an apex of the light incident section is greater than the shortest distance (a) from the point (p) to a side surface of the light incident section within an angle of 50° or less from the optical axis L. 
     In one aspect, an upper center of the light exit face is formed of a flat surface or a convex curve. 
     In one aspect, the light incident section includes a lower entrance placed adjacent the light emitting diode and having a circular shape, and has a shape gradually converging to the apex while maintaining a circular shape. 
     In one aspect, the light incident section has a height which is 1.5 times greater than a radius of the lower entrance. 
     In one aspect, the material adjoining the light incident section is air. 
     In one aspect, the material adjoining the light exit face is air. 
     In one aspect, the optical members are formed of a resin or glass. 
     In accordance with another aspect of the present disclosure, a backlight unit includes the aforementioned backlight module; and a backlight control module supplying DC operating voltage to the plurality of MJT LEDs within the backlight module and independently controlling operation of each of the plurality of MJT LEDs. 
     In one aspect, the backlight control module supplies the DC operating voltage to each of the plurality of MJT LEDs within the backlight module, and performs pulse width modulation control with respect to the DC operating voltage supplied to at least one MJT LED among the plurality of MJT LEDs in response to a dimming signal to perform dimming control of the at least one MJT LED. 
     In one aspect, the backlight control module allows independent detection and control of operating current of each of the plurality of MJT LEDs within the backlight module, and controls operating current of at least one MJT LED among the plurality of MJT LEDs in response to a dimming signal to perform dimming control of the at least one MJT LED. 
     According to embodiments of the present disclosure, the backlight module is fabricated using MJT LEDs having low current operation characteristics, thereby enabling low current operation of the backlight module and the backlight unit including the same. 
     In addition, according to the embodiments of the present disclosure, one connection section of the interconnection line electrically contacts a slanted side surface of light emitting cell, thereby increasing an effective light emitting area of each of light emitting cells in an MJT LED chip. 
     Further, according to the embodiments of the present disclosure, it is possible to enhance stability and reliability of drive circuits for controlling operation of the backlight module while reducing manufacturing costs. 
     Further, according to the embodiments of the present disclosure, the backlight unit has improved power efficiency and luminous efficacy, and can prevent a droop phenomenon due to operation at high current. 
     Further, according to the embodiments of the present disclosure, it is possible to minimize the number of LEDs constituting the backlight module and to allow individual operation of the MJT LEDs constituting the backlight module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a configuration block diagram of a typical backlight unit including LEDs in the related art; 
         FIG. 2  is a schematic block diagram of a backlight unit employing MJT LEDs according to one exemplary embodiment of the present disclosure; 
         FIG. 3  is a schematic sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure; 
         FIG. 4  is a schematic perspective view of the MJT LED according to the one exemplary embodiment of the present disclosure; 
         FIG. 5  is a schematic plan view of an MJT LED chip according to one exemplary embodiment of the present disclosure; 
         FIG. 6  is a schematic sectional view of the MJT LED chip taken along line B-B of  FIG. 5 ; 
         FIG. 7  to  FIG. 13  are schematic sectional views illustrating a method of fabricating an MJT LED chip according to one exemplary embodiment of the present disclosure; 
         FIG. 14  is a schematic sectional view of an MJT LED chip according to another exemplary embodiment of the present disclosure; 
         FIG. 15  to  FIG. 18  are schematic sectional views illustrating a method of fabricating an MJT LED chip according to another exemplary embodiment of the present disclosure; 
         FIG. 19  shows sectional views of various modifications of an optical member according to the present disclosure; 
         FIG. 20  shows sectional views of an optical member, illustrating an MJT LED module according to a further exemplary embodiment of the present disclosure; 
         FIG. 21  is a sectional view illustrating dimensions of an MJT LED module used for simulation; 
         FIG. 22  shows graphs depicting a shape of an optical member of  FIG. 21 ; 
         FIG. 23  shows traveling directions of light beams entering the optical member of  FIG. 21 ; 
         FIG. 24  shows graphs depicting illuminance distribution, in which (a) is a graph depicting illuminance distribution of an MJT LED, and (b) is a graph showing illuminance distribution of an MJT LED module using an optical member; 
         FIG. 25  shows graphs depicting light beam distributions, in which (a) is a graph depicting a light beam distribution of an MJT LED and (b) is a graph depicting a light beam distribution of an MJT LED module using an optical member; 
         FIG. 26  is a sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure; 
         FIGS. 27 ( a ), ( b ) and ( c )  are sectional views of the MJT LED module taken along lines a-a, b-b and c-c of  FIG. 26 ; 
         FIG. 28  is a detailed view of an optical member of the MJT LED module shown in  FIG. 26 ; 
         FIG. 29  shows a light beam angle distribution of the MJT LED module using the optical member of  FIG. 28 ; 
         FIG. 30  is a sectional view of an optical member according to another exemplary embodiment of the present disclosure; 
         FIG. 31  shows a beam angle distribution curve of an MJT LED module using the optical member of  FIG. 30 ; 
         FIG. 32A  and  FIG. 32B  show an optical member according to Comparative Example 1 and a beam angle distribution curve thereof; 
         FIG. 33A  and  FIG. 33B  show an optical member according to Comparative Example 2 and a light beam angle distribution thereof; and 
         FIG. 34  is a sectional view of an optical member according to another exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are illustrated. These embodiments will be described such that the disclosure can be easily understood by a person having ordinary knowledge in the art. Here, although various embodiments are disclosed herein, it should be understood that these embodiments are not intended to be exclusive. For example, individual structures, elements or features of a particular embodiment are not limited to that particular embodiment and can be applied to other embodiments without departing from the spirit and scope of the disclosure. In addition, it should be understood that locations or arrangement of individual components in each of the embodiments may be changed without departing from the spirit and scope of the present disclosure. Therefore, the following embodiments are not to be construed as limiting the disclosure, and the present disclosure should be limited only by the claims and equivalents thereof. Like components will be denoted by like reference numerals, and lengths, areas, thicknesses and shapes of the components are not drawn to scale throughout the accompanying drawings. 
     Now, exemplary embodiments of the disclosure will be described in detail with reference to the accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. 
     As used herein, the term “MJT LED chip” means a single LED chip, in which a plurality of light emitting cells is connected to each other via interconnection lines. The MJT LED chip may include N light emitting cells (N is an integer of 2 or more), in which N may be set in various ways as needed. Further, each of the light emitting cells may have a forward voltage in the range from 3V to 3.6V, but is not limited thereto. Accordingly, a forward voltage of a certain MJT LED chip (or MJT LED) is proportional to the number of light emitting cells included in the corresponding MJT LED chip. Since the number of light emitting cells included in the MJT LED chip may be set in various ways as needed, the MJT LED chip according to the present disclosure may be configured to have an operating voltage of 6V to 36V depending upon a specification of an operating power generator (for example, a DC converter) used in a backlight unit, but is not limited thereto. Further, operating current of the MJT LED chip is much smaller than a typical single-cell LED, and may range, for example, from 20 mA to 40 mA, without being limited thereto. 
     In addition, the term “MJT LED” refers to a light emitting device or an LED package, on which the MJT LED chip according to the present disclosure is mounted. 
     Further, the term “MJT LED module” refers to a component in which a single MJT LED and a single optical member corresponding to the MJT LED are coupled to each other. The corresponding optical member may be directly placed on the MJT LED, or may be placed on a printed circuit board on which the MJT LED is mounted. Regardless of displacement of the optical member, the case wherein a single MJT LED and a single optical member corresponding thereto are coupled to each other will be referred to as the MJT LED module. 
     Further, the term “backlight module” means a lighting module, in which a plurality of MJT LEDs is disposed on a printed circuit board and optical members are provided corresponding to the respective MJT LEDs. Thus, the term “backlight module” may mean a lighting module in which plural MJT LED modules are mounted on a printed circuit board in a predetermined manner. In one aspect, a backlight module according to one exemplary embodiment of the disclosure may be a direct type backlight module. However, it should be understood that the present disclosure is not limited thereto. In other embodiments, the backlight module according to the present disclosure may be used as a light source for surface lighting. Accordingly, it will be apparent to those skilled in the art that any component including the subject matter of the backlight module according to the present disclosure falls within the scope of the present disclosure, despite the name of the component. 
     Overview of Backlight Unit Using MJT LEDs 
     Before detailed descriptions of the backlight unit according to the present disclosure are given, several technical features of the present disclosure will be described. The present disclosure is based on characteristics of an MJT LED in order to solve the aforementioned problems in the related art. That is, in order to solve the problems due to low voltage and high current operation characteristics of a typical single-cell LED in the related art, the present disclosure has been created based on high voltage and low current operation characteristics of the MJT LED (for example, an operating voltage of 6 V to 36 V and an operating current of 20 mA to 40 mA), and provides a backlight module using such an MJT LED. As described above, unlike a typical single-cell LED, the MJT LED may include any number of light emitting cells and may have various forward voltages depending upon the number of light emitting cells included therein. In addition, since the MJT LED includes a plurality of light emitting cells, it is possible to illuminate a wider area than the typical single-cell LED, and since the MJT LED is constituted by a single MJT LED chip, design and application of an optical member therefor can be easily achieved. Thus, when using such an MJT LED, one divided area among a plurality of divided areas in a liquid crystal panel can be covered by one MJT LED module (that is, one MJT LED and one optical member). As a result, the number of LEDs required for the backlight module is reduced as compared with the typical single-cell LED. Consequently, according to the present disclosure, a plurality of MJT LED modules is used to constitute a backlight module and a backlight unit is configured to allow independent control of each of the MJT LEDs constituting the backlight module, thereby achieving the above and other objects of the present disclosure. 
     Now, referring to  FIG. 2  to  FIG. 4 , a backlight unit  1000  according to one exemplary embodiment of the disclosure will be described in more detail. 
     First,  FIG. 2  is a schematic block diagram of a backlight unit employing MJT LEDs according to one exemplary embodiment of the present disclosure. Referring to  FIG. 2 , the backlight unit  1000  according to this embodiment includes a backlight control module  400  and a backlight module  300 . 
     More specifically, the backlight control module  400  according to this disclosure includes an operating power generator  410 , which generates/outputs DC power based on input voltage Vin input from an external power source, and an operation controller  420  controlling operation of each of a plurality of MJT LEDs  100  constituting the backlight module  300  (on/off control and dimming control). The operating power generator  410  generally generates stable DC voltage such as 12V, 24V, 48V, and the like, as operating power and supplies the DC voltage to the plurality of MJT LEDs  100  constituting the backlight module  300 . Here, the input voltage Vin supplied to the operating power generator  410  may be a commercially available alternating voltage of 220V or 110V. The operating power generator  410  may have substantially the same configuration as the typical operating power generator  410  as shown in  FIG. 1 . 
     The backlight module  300  according to this disclosure may include a plurality of MJT LEDs  100  and optical members (not shown in  FIG. 2 ) corresponding to the respective MJT LEDs  100  and disposed in a regular arrangement (for example, in a matrix arrangement) on a printed circuit board (not shown in  FIG. 2 ). In the embodiment shown in  FIG. 2 , it is assumed that M MJT LEDs  100  are disposed in a longitudinal direction and N MJT LEDs  100  are disposed in a transverse direction to form an M×N matrix arrangement within the backlight module  300 . In addition, an MJT LED placed at a left side uppermost portion of the backlight module will be referred to as a 1-1st MJT LED ( 100 _ 11 ) and an MJT LED placed at a right side lowermost portion thereof will be referred to as an M-Nth MJT LED ( 100 _MN). 
     Here, it should be noted that, unlike the related art shown in  FIG. 1 , the MJT LEDs  100  within the backlight module  300  according to the embodiment of  FIG. 2  are independently connected to the operating power generator  410  and the operation controller  420  instead of being connected to each other in series, in parallel, or in series/parallel. That is, in the embodiment shown in  FIG. 2 , an anode terminal of each MJT LED  100  is independently connected to the operating power generator  410  and a cathode terminal of each MJT LED  100  is independently connected to the operation controller  420 . 
     With this configuration, the operation controller  420  according to this disclosure may independently control operation of each of the plurality of MJT LEDs  100  constituting the backlight module  300 . More specifically, the operation controller  420  according to this disclosure may control a dimming level of a specific MJT LED among the plurality of MJT LEDs  100  in response to a dimming signal (Dim). 
     In one embodiment, the operation controller  420  according to the present disclosure includes a PWM (Pulse Width Modulation) controller (not shown) and may perform dimming control through pulse width modulation control with respect to operating power supplied to a specific MJT LED, which is a dimming control target, among the MJT LEDs  100 . Particularly, unlike the typical backlight unit in the related art as shown in  FIG. 1 , the backlight unit  1000  according to the present disclosure as shown in  FIG. 2  includes the plurality of MJT LEDs  100 , each of which is connected to the operating power generator  410  to independently receive operating power, thereby enabling dimming control in such a pulse width modulation manner. For example, when there is a need for dimming control of the 1-1st MJT LED ( 100 _ 11 ), the operation controller  420  performs pulse width modulation of the generated operating power at a predetermined duty ratio (for example, 60%) in response to a dimming signal (Dim), and supplies the modified operating power to the 1-1st MJT LED ( 100 _ 11 ) to perform dimming control of the 1-1st MJT LED ( 100 _ 11 ). At this time, operating power, which is not subjected to pulse width modulation and has a duty ratio of 100%, will be supplied to other MJT LEDs except for the 1-1st MJT LED ( 100 _ 11 ). Alternatively, operating power, which is subjected to pulse width modulation at a normal duty ratio (a duty ratio of, for example, 80% when no separate dimming control is provided), is provided to the other MJT LEDs except for the 1-1st MJT LED ( 100 _ 11 ). Consequently, the backlight unit  1000  according to the present disclosure allows local dimming with respect to only the 1-1st MJT LED ( 100 _ 11 ). Of course, it will be apparent to those skilled in the art that it is possible to perform simultaneous dimming control with respect to the plurality of MJT LEDs at the same dimming level and/or at different dimming levels for the respective MJT LEDs through PWM control. The PWM controller for PWM control of the operating power is well known in the art, and thus, a detailed description thereof will be omitted. 
     In another embodiment, the operation controller  420  according to the present disclosure includes an operating current detector (not shown) and an operating current controller (not shown), and may perform dimming control by controlling the operating current supplied to a specific MJT LED, which is a dimming control target, among the MJT LEDs  100 . Particularly, unlike the typical backlight unit shown in  FIG. 1 , in the backlight unit  1000  according to the present disclosure shown in  FIG. 2 , each of the plural MJT LEDs  100  is independently connected to the operation controller  420 , thereby enabling dimming control by control of the operating current of each of the MJT LEDs. Here, the operating current detector and the operating current controller included in the operation controller  420  correspond one to one to each of the MJT LEDs  100 . Accordingly, when the backlight module  300  is composed of M×N MJT LEDs  100  as described above, the operation controller  420  includes M×N operating current detectors and M×N operating current controllers. For example, when there is a need for dimming control with respect to an M-Nth MJT LED ( 100 _MN), the operation controller  420  detects operating current flowing through the M-Nth MJT LED ( 100 _MN) using the operating current detector, and changes the operating current flowing through the M-Nth MJT LED ( 100 _MN) (for example, to 100% of a maximum operating current) in response to a dimming signal (Dim), thereby performing dimming control with respect to the M-Nth MJT LED ( 100 _MN). Here, since normal operating current (a preset standard operating current, for example, 80% of the maximum operating current, when there is no separate dimming control) flows through other MJT LEDs except for the M-Nth MJT LED ( 100 _MN), local dimming can be performed with respect only to the M-Nth MJT LED ( 100 _MN). It will be apparent to those skilled in the art that dimming control of the plurality of MJT LEDs can be performed to the same dimming level through simultaneous control of the operating current with respect to the plurality of MJT LEDs and/or to different dimming levels for the respective MJT LEDs. In such an embodiment, since there is no need for independent supply of operating power to the MJT LEDs  100 , the anode terminal of each of the MJT LEDs  100  may be connected in parallel to one operating power line connected to the operating power generator  410 , unlike the embodiment shown in  FIG. 2 . The operating current detector and the operating current controller are well known in the art and detailed descriptions thereof will thus be omitted. 
     Overview of MJT LED and MJT LED Module 
       FIG. 3  is a schematic sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure, and  FIG. 4  is a schematic perspective view of the MJT LED according to the one exemplary embodiment of the present disclosure. Now, detailed configurations of an MJT LED  100  and an MJT LED module according to embodiments of the present disclosure will be described with reference to  FIG. 3  and  FIG. 4 . 
     Referring to  FIG. 3 , the MJT LED module includes an MJT LED  100  and an optical member  130 . When the MJT LED  100  is mounted on a printed circuit board  110 , the corresponding optical member  130  is mounted on the printed circuit board  110  at a place corresponding to the position of the MJT LED  100 . As described above, in other embodiments, the optical member  130  may be directly connected to the MJT LED  100 . Although the printed circuit board  110  is partially shown in  FIG. 3 , a plurality of MJT LEDs  100  and the optical members  130  corresponding thereto are disposed on a single printed circuit board  110  in various arrangements such as a matrix arrangement or a honeycomb arrangement to form the backlight module  300  as described above. 
     The printed circuit board  110  is formed on an upper surface thereof with conductive land patterns to which terminals of the MJT LED  100  are bonded. Further, the printed circuit board  110  may include a reflective layer on the upper surface thereof. The printed circuit board  110  may be a MCPCB (Metal-Core PCB) based on a metal having good thermal conductivity. Alternatively, the printed circuit board  110  may be formed of an insulating substrate material such as FR4. Although not shown, the printed circuit board  110  may be provided at a lower side thereof with a heat sink to dissipate heat from the MJT LED  100 . 
     As clearly shown in  FIG. 4 , the MJT LED  100  may include a housing  121 , an MJT LED chip  123  mounted on the housing  121 , and a wavelength conversion layer  125  covering the MJT LED chip  123 . The MJT LED  100  further includes lead terminals (not shown) supported by the housing  121 . 
     The housing  121  forms a package body and may be formed by injection molding of a plastic resin such as PA, PPA, and the like. In this case, the housing  121  may be formed in a state of supporting the lead terminals by an injection molding process, and may have a cavity  121   a  for mounting the MJT LED chip  123  therein. The cavity  121   a  defines a light exit area of the MJT LED  100 . 
     The lead terminals are separated from each other within the housing  121  and extend outside of the housing  121  to be bonded to the land patterns on the printed circuit board  110 . 
     The MJT LED chip  123  is mounted on the bottom of the cavity  121   a  and electrically connected to the lead terminals. The MJT LED chip  123  may be a gallium nitride-based MJT LED which emits UV light or blue light. A detailed configuration of the MJT LED chip  123  according to the present disclosure and a method of manufacturing the same will be described below with reference to  FIG. 5  to  FIG. 18 . 
     The wavelength conversion layer  125  covers the MJT LED chip  123 . In one embodiment, the wavelength conversion layer  125  may be formed by filling the cavity  121   a  with a molding resin containing phosphors after mounting the MJT LED chip  123  in the cavity  121   a . At this time, the wavelength conversion layer  125  may fill the cavity  121   a  of the housing  121  and have a substantially flat or convex upper surface. Further, a molding resin having a shape of the optical member may be formed on the wavelength conversion layer  125 . 
     In another embodiment, the MJT LED chip  123 , which has a coating layer of the phosphors formed by conformal coating, may be mounted on the housing  121 . Specifically, the coating layer of the phosphors may be formed on the MJT LED chip  123  by conformal coating and the MJT LED chip  123  having the conformal coating layer may be mounted on the housing  121 . The MJT LED chip  123  having the conformal coating layer may be molded with a transparent resin. In addition, the molding resin may have the shape of the optical member and thus may act as a primary optical member. 
     The wavelength conversion layer  125  converts—wavelengths of light emitted from the MJT LED chip  123  to provide light of mixed colors, for example, white light. 
     The MJT LED  100  is designed to have a light beam distribution of a mirror symmetry structure, particularly, a light beam distribution of a rotational symmetry structure. At this time, an axis of the MJT LED directed towards the center of the light beam distribution is defined as an optical axis L. That is, the MJT LED  100  is designed to have a light beam distribution which is bilaterally symmetrical with respect to the optical axis L. Generally, the cavity  121   a  of the housing  121  may have a mirror symmetry structure, and the optical axis L may be defined as a straight line passing through the center of the cavity  121   a.    
     The optical member  130  includes a light incident face through which light emitted from the MJT LED  100  enters the optical member and a light exit face through which the light exits the optical member at a wider light beam distribution than that of the MJT LED  100 , thereby enabling uniform distribution of the light emitted from MJT LED  100 . The optical member  130  according to the present disclosure will be described below with reference to  FIG. 19  to  FIG. 33 . 
     Configuration of MJT LED Chip and Method of Manufacturing the Same 
     Next, the configuration of the MJT LED chip  123  mounted on the MJT LED according to the present disclosure and a method of manufacturing the same will be described in more detail with reference to  FIG. 5  to  FIG. 18 . 
       FIG. 5  is a schematic plan view of an MJT LED chip according to one exemplary embodiment of the present disclosure, and  FIG. 6  is a schematic sectional view of the MJT LED chip taken along line B-B of  FIG. 5 . 
     Referring to  FIG. 5  and  FIG. 6 , the MJT LED chip  123  includes a growth substrate  51 , light emitting cells S 1 , S 2 , a transparent electrode layer  61 , a current blocking layer  60   a , an insulation layer  60   b , an insulation protective layer  63 , and an interconnection line  65 . Further, the MJT LED chip  123  may include a buffer layer  53 . 
     The growth substrate  51  may be an insulation or conductive substrate, and may include, for example, a sapphire substrate, a gallium nitride substrate, a silicon carbide (SiC) substrate, or a silicon substrate. In addition, the growth substrate  51  may have a convex-concave pattern (not shown) on an upper surface thereof as in a patterned sapphire substrate. 
     A first light emitting cell S 1  and a second light emitting cell S 2  are separated from each other on a single growth substrate  51 . Each of the first and second light emitting cells S 1 , S 2  has a stack structure  56 , which includes a lower semiconductor layer  55 , an upper semiconductor layer  59  placed on a region of the lower semiconductor layer, and an active layer  57  interposed between the lower semiconductor layer and the upper semiconductor layer. Here, the upper and lower semiconductor layers may be an n-type semiconductor layer and a p-type semiconductor layer, respectively, or vice versa. 
     Each of the lower semiconductor layer  55 , the active layer  57  and the upper semiconductor layer  59  may be formed of a gallium nitride-based semiconductor material, that is, (Al, In, Ga)N. The compositional elements and ratio of the active layer  57  are determined depending upon desired wavelengths of light, for example, UV light or blue light, and the lower semiconductor layer  55  and the upper semiconductor layer  59  are formed of a material having a greater band gap than the active layer  57 . 
     The lower semiconductor layer  55  and/or the upper semiconductor layer  59  may have a single layer structure, as shown in  FIG. 5 . Alternatively, these semiconductor layers may have a multilayer structure. Further, the active layer  57  may have a single quantum-well structure or a multi-quantum well structure. 
     Each of the first and second light emitting cells S 1 , S 2  may have a slanted side surface, an inclination of which may range, for example, from 15° to 80° relative to an upper surface of the growth substrate  51 . 
     The active layer  57  and the upper semiconductor layer  59  are placed on the lower semiconductor layer  55 . An upper surface of the lower semiconductor layer  55  may be completely covered by the active layer  57  such that only a side surface thereof is exposed. 
     Although portions of the first light emitting cell S 1  and the second light emitting cell S 2  are shown in  FIG. 6 , the first and second light emitting cells S 1 , S 2  may have a similar or the same structure as that shown in  FIG. 5 . That is, the first light emitting cell S 1  and the second light emitting cell S 2  may have the same gallium nitride-based semiconductor stack structure, and may have slanted side surfaces of the same structure. 
     The buffer layer  53  may be interposed between the light emitting cells S 1 , S 2  and the growth substrate  51 . The buffer layer  53  relieves lattice mismatch between the growth substrate  51  and the lower semiconductor layer  55  formed thereon. 
     The transparent electrode layer  61  is placed on each of the light emitting cells S 1 , S 2 . That is, a first transparent electrode layer  61  is placed on the first light emitting cell S 1  and a second transparent electrode layer  61  is placed on the second light emitting cell S 2 . The transparent electrode layer  61  may be placed on the upper semiconductor layer  59  to be connected to the upper semiconductor layer  59 , and may have a narrower area than the upper semiconductor layer  59 . That is, the transparent electrode layer  61  may be recessed from an edge of the upper semiconductor layer  59 . With this structure, it is possible to prevent current crowding at the edge of the transparent electrode layer  61  through the side surfaces of the light emitting cells S 1 , S 2 . 
     In another aspect, the current blocking layer  60   a  may be placed on each of the light emitting cells S 1 , S 2 . That is, the current blocking layer  60   a  is placed between the transparent electrode layer  61  and each of the light emitting cells S 1 , S 2 . Part of the transparent electrode layer  61  is placed on the current blocking layer  60   a . The current blocking layer  60   a  may be placed near an edge of each of the light emitting cells S 1 , S 2 , but is not limited thereto. Alternatively, the current blocking layer  60   a  may be placed in a central region of each of the light emitting cells S 1 , S 2 . The current blocking layer  60   a  is formed of an insulation material and, particularly, may include a distributed Bragg reflector in which layers having different indices of refraction are alternately stacked one above another. 
     The insulation layer  60   b  covers a portion of the side surface of the first light emitting cell S 1 . As shown in  FIG. 5  and  FIG. 6 , the insulation layer  60   b  may extend to a region between the first light emitting cell S 1  and the second light emitting cell S 2 , and may cover a portion of a side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . The insulation layer  60   b  may have the same structure and the same material as those of the current blocking layer  60   a , and may include a distributed Bragg reflector, without being limited thereto. The insulation layer  60   b  may be formed of a different material than that of the current blocking layer  60   a  by a different process. Here, when the insulation layer  60   b  is a distributed Bragg reflector formed by stacking multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in the insulation layer  60   b . The insulation layer  60   b  may be connected to the current blocking layer  60   a  to form continuous layers, but is not limited thereto. In other embodiments, the insulation layer  60   b  may be separated from the current blocking layer  60   a.    
     The interconnection line  65  electrically connects the first light emitting cell S 1  to the second light emitting cell S 2 . The interconnection line  65  includes a first connection section  65   p  and a second connection section  65   n . The first connection section  65   p  is electrically connected to the transparent electrode layer  61  on the first light emitting cell S 1 , and the second connection section  65   n  is electrically connected to the lower semiconductor layer  55  of the second light emitting cell S 2 . The first connection section  65   p  may be placed near one edge of the first light emitting cell S 1 , but is not limited thereto. In other embodiments, the first connection section  65   p  may be placed in the central region of the first light emitting cell S 1 . 
     The second connection section  65   n  may contact the slanted side surface of the second light emitting cell S 2 , particularly, the slanted side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . Further, as shown in  FIG. 5 , the second connection section  65   n  may electrically contact the slanted side surface of the lower semiconductor layer  55  while extending to both sides along the circumference of the second light emitting cell S 2 . The first light emitting cell S 1  is connected to the second light emitting cell S 2  in series by the first and second connection sections  65   p ,  65   n  of the interconnection line  65 . 
     The interconnection line  65  may contact the transparent electrode layer  61  over an overlapping region with the transparent electrode layer  61 . In the related art, a portion of the insulation layer is placed between the transparent electrode layer and the interconnection line. On the contrary, according to the present disclosure, the interconnection line  65  may directly contact the transparent electrode layer  61  without any insulation material interposed therebetween. 
     Further, the current blocking layer  60   a  may be placed over the overlapping region between the interconnection line  65  and the transparent electrode layer  61 , and the current blocking layer  60   a  and the insulation layer  60   b  may be placed over an overlapping region between the interconnection line  65  and the first light emitting cell S 1 . Further, the insulation layer  60   b  may be placed between the second light emitting cell S 2  and the interconnection line  65  in other regions excluding a connection region between the interconnection line  65  and the second light emitting cell S 2 . 
     In  FIG. 5 , the first connection section  65   p  and the second connection section  65   n  of the interconnection line  65  are connected to each other through two paths. However, it should be understood that the first and second connection sections may be connected to each other via a single path. 
     When the current blocking layer  60   a  and the insulation layer  60   b  have reflective characteristics like the distributed Bragg reflector, the current blocking layer  60   a  and the insulation layer  60   b  are preferably placed substantially in the same region as the region for the interconnection line  65  within a region having an area of two times or less the area of the interconnection line  65 . The current blocking layer  60   a  and the insulation layer  60   b  block light emitted from the active layer  57  from being absorbed into the interconnection line  65 . However, when occupying an excessively large area, the current blocking layer  60   a  and the insulation layer  60   b  can block emission of light to the outside. Thus, there is a need for restriction of the area thereof. 
     The insulation protective layer  63  may be placed outside the region of the interconnection line  65 . The insulation protective layer  63  covers the first and second light emitting cells S 1 , S 2  outside the region of the interconnection line  65 . The insulation protective layer  63  may be formed of silicon oxide (SiO 2 ) or silicon nitride. The insulation protective layer  63  has an opening through which the transparent electrode layer  61  on the first light emitting cell S 1  and the lower semiconductor layer of the second light emitting cell S 2  are exposed, and the interconnection line  65  may be placed within the opening. 
     A side surface of the insulation protective layer  63  and a side surface of the interconnection line  65  may face each other, and may contact each other. Alternatively, the side surface of the insulation protective layer  63  and the side surface of the interconnection line  65  may be separated from each other while facing each other. 
     According to the present embodiment, since the second connection section  65   n  of the interconnection line  65  electrically contacts the slanted side surface of the second light emitting cell S 2 , there is no need to expose the upper surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . Accordingly, there is no need for partial removal of the second semiconductor layer  59  and the active layer  57 , thereby increasing an effective light emitting area of the MJT LED chip  123 . 
     In addition, the current blocking layer  60   a  and the insulation layer  60   b  may be formed of the same material and have the same structure, and thus may be formed at the same time by the same process. Further, since the interconnection line  65  is placed within the opening of the insulation protective layer  63 , the insulation protective layer  63  and the interconnection line  65  may be formed using the same mask pattern. 
     Although two light emitting cells including the first light emitting cell S 1  and the second light emitting cell S 2  are illustrated in this embodiment, it should be understood that the present disclosure is not limited thereto. That is, a greater number of light emitting cells may be electrically connected to each other via the interconnection lines  65 . For example, the interconnection lines  65  may electrically connect the lower semiconductor layers  55  and the transparent electrode layers  61  of adjacent light emitting cells to each other to form a series array of light emitting cells. A plurality of such arrays may be formed and connected in inverse-parallel to each other to be operated by an AC power source connected thereto. In addition, a bridge rectifier (not shown) may be connected to the series array of light emitting cells to allow the light emitting cells to be operated by the AC power source. The bridge rectifier may be formed by bridging the light emitting cells having the same structure as that of the light emitting cells S 1 , S 2  using the interconnection lines  65 . 
       FIG. 7  to  FIG. 13  are schematic sectional views illustrating a method of fabricating an MJT LED chip according to one exemplary embodiment of the present disclosure. 
     Referring to  FIG. 7 , a semiconductor stack structure  56  including a lower semiconductor layer  55 , an active layer  57  and an upper semiconductor layer  59  is formed on a growth substrate  51 . In addition, a buffer layer  53  may be formed on the growth substrate  51  before formation of the lower semiconductor layer  55 . 
     The growth substrate  51  may be formed of a material selected from among sapphire (Al 2 O 3 ), silicon carbide (SiC), zinc oxide (ZnO), silicon (Si), gallium arsenic (GaAs), gallium phosphide (GaP), lithium alumina (LiAl 2 O 3 ), boron nitride (BN), aluminum nitride (AlN), and gallium nitride (GaN), without being limited thereto. That is, the material for the growth substrate  51  may be selected in various ways depending upon materials of semiconductor layers to be formed on the growth substrate  51 . Further, the growth substrate  51  may have a convex-concave pattern on an upper surface thereof as in a patterned sapphire substrate. 
     The buffer layer  53  is formed to relieve lattice mismatch between the growth substrate  51  and the semiconductor layer  55  formed thereon, and may be formed of, for example, gallium nitride (GaN) or aluminum nitride (AlN). When the growth substrate  51  is a conductive substrate, the buffer layer  53  is preferably formed of an insulation layer or a semi-insulating layer. For example, the buffer layer  53  may be formed of AlN or semi-insulating GaN. 
     Each of the lower semiconductor layer  55 , the active layer  57  and the upper semiconductor layer  59  may be formed of a gallium nitride-based semiconductor material, for example, (Al, In, Ga)N. The lower and upper semiconductor layers  55 ,  59  and the active layer  57  may be intermittently or continuously formed by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy, hydride vapor phase epitaxy (HVPE), and the like. 
     Here, the lower and upper semiconductor layers may be n-type and p-type semiconductor layers, or vice versa. Among the gallium nitride-based compound semiconductor layers, an n-type semiconductor layer may be formed by doping an n-type impurity, for example, silicon (Si), and a p-type semiconductor layer may be formed by doping a p-type impurity, for example, magnesium (Mg). 
     Referring to  FIG. 8 , a plurality of light emitting cells S 1 , S 2  separated from each other is formed by a photolithography and etching process. Each of the light emitting cells S 1 , S 2  is formed to have a slanted side surface. In a typical method of manufacturing an MJT LED chip, an additional photolithography and etching process is performed to partially expose an upper surface of the lower semiconductor layer  55  of each of the light emitting cells S 1 , S 2 . However, in this embodiment, the photolithography and etching process performed to partially expose the upper surface of the lower semiconductor layer  55  is omitted. 
     Referring to  FIG. 9 , a current blocking layer  60   a  covering some region on the first light emitting cell S 1  and an insulation layer  60   b  partially covering the side surface of the first light emitting cell S 1  are formed. The insulation layer  60   b  may extend to cover a region between the first light emitting cell S 1  and the second light emitting cell S 2  while partially covering a side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . 
     The current blocking layer  60   a  and the insulation layer  60   b  may be formed by depositing an insulation material layer, followed by patterning through photolithography and etching. Alternatively, the current blocking layer  60   a  and the insulation layer  60   b  may be formed of an insulation material layer by a lift-off technique. Particularly, each of the current blocking layer  60   a  and the insulation layer  60   b  may be a distributed Bragg reflector formed by alternately stacking layers having different indices of refraction, for example, SiO 2  and TiO 2  layers. When the insulation layer  60   b  is a distributed Bragg reflector formed by stacking multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in the insulation layer  60   b , whereby the insulation layer  60   b  can be formed to a smaller thickness than in the related art. 
     As shown in  FIG. 9 , the current blocking layer  60   a  and the insulation layer  60   b  may be connected to each other. However, it should be understood that the present disclosure is not limited thereto. 
     Then, a transparent electrode layer  61  is formed on the first and second light emitting cells S 1 , S 2 . The transparent electrode layer  61  may be formed of an indium tin oxide (ITO) layer, a conductive oxide layer such as a zinc oxide layer, or a metal layer such as Ni/Au. The transparent electrode layer  61  is connected to the upper semiconductor layer  59  and is partially placed on the current blocking layer  60   a . The transparent electrode layer  61  may be formed by a lift-off process, without being limited thereto. Alternatively, the transparent electrode layer  61  may be formed by a photolithography and etching process. 
     Referring to  FIG. 10 , an insulation protective layer  63  is formed to cover the first and second light emitting cells S 1 , S 2 . The insulation protective layer  63  covers the transparent electrode layer  61  and the insulation layer  60   b . In addition, the insulation protective layer  63  may cover an overall area of the first and second light emitting cells S 1 , S 2 . The insulation protective layer  63  may be formed of an insulation material layer, such as a silicon oxide or silicon nitride layer, by chemical vapor deposition. 
     Referring to  FIG. 11 , a mask pattern  70  having an opening is formed on the insulation protective layer  63 . The opening of the mask pattern  70  corresponds to a region for an interconnection line. Then, some region of the insulation protective layer  63  is removed by etching through the mask pattern  70 . As a result, an opening is formed on the insulation protective layer  63  to expose some of the transparent electrode layer  61  and the insulation layer  60   b  while exposing the slanted side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . 
     Referring to  FIG. 12 , with the mask pattern  70  remaining on the insulation protective layer  63 , a conductive material is deposited to form the interconnection line  65  within the opening of the mask pattern  70 . Here, some of the conductive material  65   a  may be deposited on the mask pattern  70 . The conductive material may be deposited by plating, e-beam evaporation, sputtering, and the like. 
     Referring to  FIG. 11 , the mask pattern  70 , together with some of the conductive material  65   a , is removed from the mask pattern  70 . As a result, the interconnection line  65  electrically connecting the first and second light emitting cells S 1 , S 2  to each other is completed. 
     Here, a first connection section  65   p  of the interconnection line  65  is connected to the transparent electrode layer  61  of the first light emitting cell S 1 , and a second connection section  65   n  thereof is connected to the slanted side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . The first connection section  65   p  of the interconnection line  65  may be connected to the transparent electrode layer  60   a  within an upper region of the current blocking layer  60   a . The interconnection line  65  is separated from the side surface of the first light emitting cell S 1  by the insulation layer  60   b.    
     In this embodiment, the current blocking layer  60   a  and the insulation layer  60   b  are formed by the same process. As a result, the insulation protective layer  63  and the interconnection line  65  may be formed using the same mask pattern  70 , whereby the MJT LED chip can be manufactured by the same number of exposure processes while adding the current blocking layer  60   a.    
       FIG. 14  is a schematic sectional view of an MJT LED chip according to another exemplary embodiment of the present disclosure. 
     Referring to  FIG. 14 , the MJT LED chip according to this embodiment is generally similar to the MJT LED chip described with reference to  FIGS. 5 and 6 , and further includes a transparent conductive layer  62 . 
     The growth substrate  51 , the light emitting cells S 1 , S 2 , the buffer layer  53 , the transparent electrode layer  61 , the current blocking layer  60   a , the insulation layer  60   b , the insulation protective layer  63  and the interconnection line  65  are similar to those of the light emitting diode described with reference to  FIGS. 5 and 6 , and thus detailed descriptions thereof will be omitted. 
     The transparent conductive layer  62  is placed between the insulation layer  60   b  and the interconnection line  65 . The transparent conductive layer  62  has a narrower width than the insulation layer  60   b , thereby preventing a short circuit of the upper semiconductor layer  59  and the lower semiconductor layer  55  due to the transparent conductive layer  62 . 
     On the other hand, the transparent conductive layer  62  is connected to a first transparent electrode layer  61 , and may electrically connect the first transparent electrode layer  61  to the second light emitting cell S 2 . For example, the transparent conductive layer  62  may be connected at one end thereof to the lower semiconductor layer  55  of the second light emitting cell. In addition, when two or more light emitting cells are connected thereto, a second transparent conductive layer  62  may extend from a second transparent electrode layer  61  on the second light emitting cell S 2 . 
     In this embodiment, since the transparent conductive layer  62  is placed between the interconnection line  65  and the insulation layer  60   b , current can flow through the transparent conductive layer  62  even in the case where the interconnection line  65  is disconnected, thereby improving electric stability of the MJT LED chip. 
       FIG. 15  to  FIG. 18  are schematic sectional views illustrating a method of fabricating an MJT LED chip according to another exemplary embodiment of the present disclosure. 
     Referring to  FIG. 15 , first, as described with reference to  FIGS. 7 and 8 , a semiconductor stack structure  56  is formed on a growth substrate  51 , and a plurality of light emitting cells S 1 , S 2  separated from each other is formed by a photolithography and etching process. Then, as described with reference to  FIG. 9 , a current blocking layer  60   a  covering a region on the first light emitting cell S 1  and an insulation layer  60   b  partially covering a side surface of the first light emitting cell S 1  are formed. 
     As described with reference to  FIG. 9 , each of the current blocking layer  60   a  and the insulation layer  60   b  may include a distributed Bragg reflector formed by alternately stacking layers having different indices of refraction, for example, SiO 2  and TiO 2  layers. When the insulation layer  60   b  include the distributed Bragg reflector formed by stacking multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in the insulation layer  60   b , whereby the insulation layer  60   b  can be formed to a smaller thickness than in the related art. 
     Then, a transparent electrode layer  61  is formed on the first and second light emitting cells S 1 , S 2 . As described with reference to  FIG. 9 , the transparent electrode layer  61  may be formed of an indium tin oxide (ITO) layer, a conductive oxide layer such as a zinc oxide layer, or a metal layer such as Ni/Au. The transparent electrode layer  61  is connected to the upper semiconductor layer  59  and is partially placed on the current blocking layer  60   a . The transparent electrode layer  61  may be formed by a lift-off process, without being limited thereto. Alternatively, the transparent electrode layer  61  may be formed by a photolithography and etching process. 
     During formation of the transparent electrode layer  61 , a transparent conductive layer  62  is formed. The transparent conductive layer  62  may be formed together with the transparent electrode layer  61  using the same material and the same process. The transparent conductive layer  62  is formed on the insulation layer  60   b  and may be connected to the transparent electrode layer  61 . Further, the transparent conductive layer  62  may be electrically connected at one end thereof to the slanted side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . 
     Referring to  FIG. 16 , an insulation protective layer  63  is formed to cover the first and second light emitting cells S 1 , S 2 . The insulation protective layer  63  covers the transparent electrode layer  61 , the transparent conductive layer  62 , and the insulation layer  60   b . In addition, the insulation protective layer  63  may cover an overall area of the first and second light emitting cells S 1 , S 2 . The insulation protective layer  63  may be formed of an insulation material layer, such as silicon oxide or silicon nitride, by chemical vapor deposition. 
     Referring to  FIG. 17 , as described with reference to  FIG. 11 , a mask pattern  70  having an opening is formed on the insulation protective layer  63 . The opening of the mask pattern  70  corresponds to a region for an interconnection line. Then, a portion of the insulation protective layer  63  is removed by etching through the mask pattern  70 . As a result, an opening is formed on the insulation protective layer  63  to expose some of the transparent electrode layer  61  and the transparent conductive layer  62 , while exposing the slanted side surface of the lower semiconductor layer  55  of the second light emitting cell S 2 . Further, the insulation layer  60   b  is partially exposed through the opening. 
     Referring to  FIG. 18 , as described with reference to  FIG. 12 , with the mask pattern  70  remaining on the insulation protective layer  63 , a conductive material is deposited to form an interconnection line  65  within the opening of the mask pattern  70 . 
     Then, referring to  FIG. 13 , the mask pattern  70 , together with some of the conductive material  65   a , is removed from the mask pattern  70 . As a result, the interconnection line  65  electrically connecting the first and second light emitting cells S 1 , S 2  to each other is completed. 
     In the embodiments described with reference to  FIG. 7  to  FIG. 13 , the insulation layer  60   b  can be damaged during etching of the insulation protective layer  63 . For example, when the insulation protective layer  63  is subjected to etching using an etchant, which contains, for example, hydrofluoric acid, the insulation layer  60   b  including an oxide layer can be damaged by the etchant. In this case, the insulation layer  60   b  can fail to insulate the interconnection line  65  from the first light emitting cell S 1 , thereby causing a short circuit. 
     However, in the present embodiment, since the transparent conductive layer  62  is placed on the insulation layer  60   b , the insulation layer  60   b  under the transparent conductive layer  62  can be protected from etching damage. As a result, it is possible to prevent a short circuit due to the interconnection line  65 . 
     In this embodiment, the transparent electrode layer  61  and the transparent conductive layer  62  may be formed by the same process. Accordingly, the MJT LED chip can be manufactured by the same number of exposing processes while adding the transparent conductive layer  62 . 
     Structure of optical member according to first embodiment and MJT LED module including the same 
     Next, referring to  FIG. 3 ,  FIG. 4 , and  FIG. 19  to  FIG. 25 , detailed structures and functions of an optical member according to a first embodiment and an MJT LED module including the same will be described. 
     Referring to  FIG. 3  again, the optical member  130  according to the first embodiment may include a lower surface  131  and an upper surface  135 , and may further include a flange  137  and legs  139 . The lower surface  131  includes a concave section  131   a , and the upper surface  135  includes a concave surface  135   a  and a convex surface  135   b.    
     The lower surface  131  is composed of a substantially circular disc-shaped plane, and has the concave section  131   a  placed at a central portion thereof. The lower surface  131  is not required to be a flat surface, and may have various convex-concave patterns. 
     Further, an inner surface of the concave section  131   a  has a surface  133  including side surface  133   a  and an upper end surface  133   b . Here, the upper end surface  133   b  is perpendicular to a central axis C and the side surface  133   a  extends from the upper end surface  133   b  to an entrance of the concave section  131   a . Herein, when aligned to coincide with the optical axis L of the MJT LED  100 , the central axis C is defined as a central axis of the optical member  130 , which becomes a center of a beam distribution of light exiting the optical member  130 . 
     The concave section  131   a  may have a shape, a width of which gradually decreases from the entrance thereof to an upper side thereof. Specifically, the side surface  133   a  gradually approaches the central axis C from the entrance of the concave section  131   a  to the upper end surface  133   b  thereof. With this structure, a region for the upper end surface  133   b  may be formed narrower than the entrance of the concave section  131   a . The side surface  133   a  may have a relatively gentle slope near the upper end surface  133   b.    
     The region for the upper end surface  133   b  is defined within a narrower region than a region for the entrance of the concave section  131   a . In addition, the region for the upper end surface  133   b  may be defined within a narrower region than a region surrounded by an inflection curve at which the concave surface  135   a  of the upper surface  135  meets the convex surface  135   b  thereof. Further, the region for the upper end surface  133   b  may be placed within a narrower region than a region for the cavity  121   a  ( FIG. 4 ) of the MJT LED, that is, a light exit region. 
     The region for the upper end surface  133   b  reduces variation of the beam distribution of light exiting the optical member  130  through the upper surface  135  thereof even in the case of misalignment between the optical axis L of the MJT LED and the central axis C of the optical member  130 . Thus, the region for the upper end surface  133   b  may be minimized in consideration of misalignment between the MJT LED  100  and the optical member  130 . 
     Further, the upper surface  135  of the optical member  130  includes the concave surface  135   a  and the convex surface  135   b  continuously extending from the concave surface  135   a  with reference to the central axis C. A line at which the concave surface  135   a  meets the convex surface  135   b  becomes the inflection curve. The concave surface  135   a  disperses light exiting near the central axis C of the optical member  130  through refraction of the light at a relatively large angle. Further, the convex surface  135   b  increases the quantity of light exiting towards an outer direction of the central axis C. 
     The upper surface  135  and the concave section  131   a  have a symmetrical structure relative to the central axis C. For example, the upper surface  135  and the concave section  131   a  have a mirror symmetry structure relative to a plane passing through the central axis C and may have a rotational body shape relative to the central axis C. In addition, the concave section  131   a  and the upper surface  135  may have various shapes according to a desired light beam distribution. 
     In another aspect, the flange  137  connects the upper surface  135  to the lower surface  131  and defines an outer size of the optical member. A side surface of the flange  137  and the lower surface  131  may be formed with convex-concave patterns. The legs  139  of the optical member  130  are coupled to the printed circuit board  110  to support the lower surface  131  while separating the lower surface  131  from the printed circuit board  110 . Coupling of the legs  139  to the printed circuit board  110  may be performed by bonding a distal end of each of the legs  139  to the printed circuit board  110  using an adhesive or by fitting each of the legs  139  into a corresponding hole formed in the printed circuit board  110 . 
     The optical member  130  is separated from the MJT LED  100 , so that an air gap is formed in the concave section  131   a . The housing  121  of the MJT LED  100  is placed below the lower surface  131 , and the wavelength conversion layer  125  of the MJT LED  100  is separated from the concave section  131   a  to be placed under the lower surface  131 . With this structure, light traveling in the concave section  131   a  is prevented from being lost due to absorption by the housing  121  or the wavelength conversion layer  125 . 
     According to this embodiment, when a perpendicular plane relative to the central axis C is formed within the concave section  131   a , it is possible to reduce variation of the beam distribution of light exiting the optical member  130  even upon misalignment between the MJT LED  100  and the optical member  130 . Furthermore, since the concave section  131   a  does not have a relatively sharp apex, the optical member can be easily manufactured. 
       FIG. 19  shows sectional views of various modifications of the optical member. Herein, various modifications of the concave section  131   a  shown in  FIG. 3  will be described. 
     In  FIG. 19( a ) , the upper end surface  133   b  perpendicular to the central axis C described in  FIG. 3  has a downwardly protruding surface formed at a portion thereof near the central axis C. With this downwardly protruding surface, the optical member can achieve primary control of light entering the portion of the optical member near the central axis C thereof. 
     The upper end surface of  FIG. 19( b )  is similar to that of  FIG. 19( a )  except that the upper end surface of  FIG. 19( b )  has upwardly protruding surfaces formed at portions thereof perpendicular to the central axis C of the optical member. Since the upper end surface is combined with the upwardly protruding surfaces and the downwardly protruding surface, the optical member can reduce variation in light beam distribution due to misalignment between the MJT LED and the optical member. 
     The upper end surface of  FIG. 19( c )  is different from that of  FIG. 3  in that the upper end surface  133   b  is formed with an upwardly protruding surface at a portion thereof near the central axis C of the optical member. With this upwardly protruding surface, the optical member can achieve further dispersion of light entering the portion of the optical member near the central axis C thereof. 
     The upper end surface of  FIG. 19( d )  is similar to that of  FIG. 19( c )  except that the upper end surface has downwardly protruding surfaces at portions thereof perpendicular to the central axis C of the optical member. Since the upper end surface is combined with the upwardly protruding surfaces and the downwardly protruding surface, the optical member can reduce variation in light beam distribution due to misalignment between the MJT LED and the optical member. 
       FIG. 20  shows sectional views of an optical member, illustrating an MJT LED module according to a further exemplary embodiment of the present disclosure. 
     Referring to  FIG. 20( a ) , the upper end surface  133   b  may be formed with a light scattering pattern  133   c . The light scattering pattern  133   c  may be a convex-concave pattern. In addition, the concave surface  135   a  may also be formed with a light scattering pattern  135   c . The light scattering pattern  135   c  may also be a convex-concave pattern. 
     Generally, a relatively large luminous flux is concentrated near the central axis C of the optical member. Furthermore, according to embodiments of the present disclosure, since the upper end surface  133   b  is perpendicular to the central axis C, more luminous flux can be concentrated near the central axis C. Accordingly, with the structure of the upper end surface  133   b  and/or the concave surface  135   a  having the light scattering patterns  133   c ,  135   c , it is possible to disperse luminous flux near the central axis C of the optical member. 
     Referring to  FIG. 20( b ) , a material layer  139   a  having a different index of refraction than that of the optical member  130  may be placed on the upper end surface  133   b . The index of refraction of the material layer  139   a  may be higher than that of the optical member, thereby allowing change of an optical path of light incident on the upper end surface  133   b.    
     Further, a material layer  139   b  having a different index of refraction than that of the optical member  130  may also be placed on the concave surface  135   a . The index of refraction of the material layer  139   b  may be higher than that of the optical member, thereby allowing change of an optical path of light exiting through the concave surface  135   a.    
     The light scattering patterns  133   c ,  135   c  of  FIG. 20( a )  and the material layers  139   a ,  139   b  of  FIG. 20( b )  may also be applied to the various optical members of  FIG. 19 . 
       FIG. 21  is a sectional view illustrating dimensions of an MJT LED module used for simulation. Here, the same reference numerals as those of  FIGS. 3 and 4  are used (please also refer to  FIGS. 3 and 4  for a depiction of some elements). 
     In the MJT LED  100 , the cavity  121   a  has a diameter of 2.1 mm and a height of 0.6 mm. The wavelength conversion layer  125  fills the cavity  121   a  and has a flat surface. A distance (d) between the MJT LED  100  and the lower surface  131  of the optical member  130  is 0.18 mm and the MJT LED  100  and the optical member  130  are arranged such that the optical axis L of the MJT LED  100  is aligned with the central axis C of the optical member. 
     The optical member  130  has a height (H) of 4.7 mm and an upper surface of the optical member has a width (W 1 ) of 15 mm. The concave surface  135   a  has a width (W 2 ) of 4.3 mm. Further, the entrance of the concave section  131   a  placed on the lower surface  131  has a width (w 1 ) of 2.3 mm, and the upper end surface  133   b  has a width (w 2 ) of 0.5 mm. The concave section  131   a  has a height (h) of 1.8 mm. 
       FIG. 22  shows graphs depicting a shape of the optical member of  FIG. 21 . Here, (a) is a sectional view of the optical member illustrating reference point P, distance R, angle of incidence θ 1 , and exit angle θ 5 ; (b) shows variation of distance R according to angle of incidence θ 1 ; and (c) shows variation of θ 5 /θ 1  according to angle of incidence θ 1 .  FIG. 23  shows traveling directions of light beams entering the optical member  130  from reference point P at intervals of 3°. 
     Referring to  FIG. 22( a ) , reference point P indicates a light exit point of the MJT LED  100  placed on the optical axis L. Properly, reference point P is set to be placed on an outer surface of the wavelength conversion layer  125  in order to exclude external factors, such as light scattering by the phosphors in the MJT LED  100  and the like. 
     θ 1  indicates an angle of incidence of light entering the optical member  130  from the reference point P, and θ 5  indicates an exit angle of light exiting the optical member  130  through the upper surface  135  thereof. R indicates a distance from reference point P to the inner surface of the concave section  131   a.    
     Referring to  FIG. 22( b ) , since the upper end surface  133   b  of the concave section  131   a  is perpendicular to the central axis C, R slightly increases with increasing θ 1 . An enlarged graph in  FIG. 22( b )  shows an increasing curve of R. On the side surface  133   a  of the concave section  131   a , R decreases with increasing θ 1  and slightly increases near the entrance of the concave section  131   a.    
     Referring to  FIG. 22( c ) , as θ 1  increases, θ 5 /θ 1  rapidly increases near the concave surface  135   a  and relatively gently decreases near the convex surface  135   b . In this embodiment, as shown in  FIG. 23 , luminous flux exiting the optical member through the concave surface  135   a  thereof may overlap luminous flux exiting the optical member through the convex surface  135   b  thereof. That is, among light beams entering the optical member from reference point P, light exiting the optical member through the concave surface  135   a  near the inflection curve may have a higher refraction angle than light exiting the optical member through the convex surface  135   b . Thus, it is possible to reduce concentration of luminous flux near the central axis C by forming the upper end surface  133   b  of the concave section  131   a  to have a planar shape and adjusting the shapes of the concave surface  135   a  and the convex surface  135   b.    
       FIG. 24  shows graphs depicting illuminance distribution, in which (a) is a graph depicting illuminance distribution of an MJT LED, and (b) is a graph showing illuminance distribution of the MJT LED module using an optical member. Illuminance distribution is represented as a magnitude of luminous flux density of light entering a screen separated a distance of 25 mm from a reference point. 
     As shown in  FIG. 24( a ) , the MJT LED  100  provides a bilaterally symmetric illumination distribution with reference to the optical axis (C), and has a luminous flux density which is very high at the center thereof and rapidly decreases towards the periphery thereof. When the optical member  130  is applied to the MJT LED  100 , the MJT LED  100  can provide a substantially uniform luminous flux density within a radius of 40 mm, as shown in  FIG. 24( b ) . 
       FIG. 25  shows graphs depicting light beam distributions, in which (a) is a graph depicting a light beam distribution of an MJT LED, and (b) is a graph depicting a light beam distribution of the MJT LED module using an optical member. The light beam distribution shows light intensity at a place separated a distance of 5 m from reference point P according to a beam angle, and beam distributions in orthogonal directions are shown to overlap each other in one graph. 
     As shown in  FIG. 25( a ) , the intensity of light emitted from the MJT LED  100  is high at a beam angle of 0°, that is, at the center thereof, and gradually decreases with increasing beam angle. When the optical member is applied to the MJT LED  100 , the intensity of light emitted from the MJT LED  100  is relatively low at a beam angle of 0° and is relatively high near a beam angle of 70°, as shown in  FIG. 25( b ) . 
     Accordingly, when the optical member  130  is applied to the MJT LED  100 , it is possible to achieve uniform backlighting of a relatively wide area through change of the light beam distribution of the MJT LED, which has high light intensity at the center thereof. 
     Structure of optical member according to second embodiment and MJT LED module including the same 
     Next, referring to  FIG. 26  to  FIG. 33 , detailed structures and functions of an optical member according to a second embodiment and an MJT LED module including the same will be described. 
       FIG. 26  is a sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure, and  FIGS. 27 ( a ), ( b ) and ( c )  are sectional views of the MJT LED module taken along lines a-a, b-b and c-c of  FIG. 26 . Here, line a-a corresponds to a line on a lower surface of the optical member, line c-c corresponds to a line on an upper surface of the optical member, and line b-b corresponds to a cutting line at the middle of the height of a diffusion lens between line a-a and line c-c. Further,  FIG. 28  is a detailed view of an optical member of the MJT LED module shown in  FIG. 26 , and  FIG. 29  shows a light beam angle distribution of the MJT LED module using the optical member of  FIG. 28 . 
     Referring to  FIG. 26 , the MJT LED module includes an MJT LED  100  and an optical member  230  disposed on the MJT LED  100  and formed of a resin or glass material. Although the printed circuit board  110  is partially shown to show a single MJT LED module in this embodiment, a plurality of MJT LED modules is regularly arranged on a single printed circuit board  110  to form the backlight module  300  as described above. 
     First, the MJT LED  100  and the printed circuit board  110  are the same as those of the first embodiment described above with reference to  FIG. 3  and  FIG. 4 , and detailed descriptions thereof will be omitted. Thus, the optical member  230  according to the second embodiment will be mainly described hereinafter. 
     Referring to  FIG. 26 , the optical member  230  includes a lower surface  231  and a light exit face  235  at the opposite side thereof, and may further include legs  239 . The lower surface  231  includes a concave light incident section  231   a . The light exit face  235  is generally composed of an upwardly protruding round surface, and includes a flat surface  235   a  formed at an upper center thereof. The flat surface  235   a  is placed corresponding to a concave section of an optical member such as aspects of the optical member shown in the first embodiment, and the optical member  230  according to the present embodiment can disperse light near the optical axis by the structure of a light incident section  231   a  described in detail hereinafter even without the concave section at the upper center of the light exit face. The light incident section  231   a  has a substantially bell-shaped cross-section. That is, the light incident section  231   a  has a shape which gradually converges from a lower entrance thereof adjacent the MJT LED  100  towards an upper apex thereof. 
     Referring to  FIG. 27( a ) , the lower surface  231  of the optical member  230  has a circular shape. In addition, the light incident section  231   a  has a lower portion placed at a center of the lower surface  231 , and the lower portion of the light incident section  231   a  has a circular shape. The light incident section  231   a  maintains a circular shape from the lower entrance immediately before the upper apex thereof, and has a gradually decreasing diameter in an upward direction. Referring to  FIG. 27( c ) , the upper flat surface  235   a  of the optical member  230  also has a circular shape. 
     Referring to  FIGS. 27 ( a ), ( b ) and ( c )  in order, the optical member  230  includes the lower surface  231  having a circular shape, and has a gradually decreasing diameter in the upward direction. The optical member  230  may have a greater variation in diameter of a circular outer circumference at an upper portion of a side surface thereof than that of the circular outer circumference at a lower portion of the side surface thereof. The circular shape of the light incident section  231   a  has a gradually decreasing diameter. 
     Referring to  FIG. 28 , an optical axis L corresponding to the central axis of the optical member  230  is shown. To obtain a uniform light distribution using the optical member  230 , it is necessary to have a light intensity peak at an angle of 60° or more from the optical axis L. To obtain such optical characteristics, it is important to achieve effective dispersion of light at an angle of 50° or less from the optical axis L.  FIG. 28  shows reference line (r) at an angle of 50° or less relative to the optical axis L. 
     To achieve effective dispersion of light at an angle of 50° or less from the optical axis L, within the range between the optical axis L and the reference line (r), that is, at an angle of 50° or less from the optical axis L, the shortest distance ‘b’ from a certain point (p) on the optical axis L to the apex of the light incident section  231   a  is greater than the shortest distance ‘a’ from the point (p) to the side surface of the light incident section  231   a . As above, when b&gt;a, the light incident section  231   a  can contribute to wide dispersion of light traveling within an angle of 50° or less from the optical axis L to an angle of 60° or more from the optical axis L. In contrast, when b&lt;a, the light incident section  231   a  fails to contribution to wide dispersion of light traveling within an angle of 50° or less from the optical axis L. As such, it is necessary to form a separate concave section for wide dispersion of light at the upper center of the light exit face in the related art. In other words, the optical member  230  according to the present disclosure employs the curved structure of the light incident section  231   a  satisfying the condition of b&gt;a within an angle of 50° or less from the optical axis L and thus the concave section at the upper center of the light exit face can be omitted. 
     Here, the light incident section  231   a  preferably has a height greater than a radius R of the lower entrance of the light incident section  231   a . More preferably, the height H of the light incident section  231   a  is 1.5 times or more the radius R thereof. In addition, a lower portion of the light incident section  231   a  adjoins air which has a lower index of refraction than the resin or glass material, and an upper portion of the light exit face also adjoins air which has a lower index of refraction than the resin or glass material. 
       FIG. 29  shows a light beam angle distribution of the MJT LED module using the optical member of  FIG. 28 . Referring to  FIG. 29 , it can be seen that a light intensity peak is formed at about 72° from the optical axis L and light is widely distributed. From the result of  FIG. 29 , it can be seen that the optical member  230  according to the present disclosure can uniformly disperse light at an angle of 60° or less from the optical axis L through the curved structure of the light incident section  231   a  satisfying the condition of b&gt;a at an angle of 50° or less from the optical axis L even without the concave section at the upper center of the light exit face, thereby achieving uniform distribution of light. 
       FIG. 30  is a sectional view of an optical member according to another exemplary embodiment of the present disclosure. As clearly shown in  FIG. 30 , the optical member  230  according to this embodiment has the same curved structure of the light incident section  231   a  as that of the optical member shown in  FIG. 28 . Thus, the light incident section  231   a  of the optical member according to this embodiment satisfies the condition of b&gt;a at an angle of 50° or less from the optical axis L. Here, unlike the optical member according to the above embodiment, which has the flat surface formed at the upper center of the light exit face, the optical member  230  according to this embodiment has a convexly round surface  235   b  at the upper center of the light exit face. 
       FIG. 31  clearly shows a beam angle distribution curve of an MJT LED module using the optical member of  FIG. 30 . Referring to  FIG. 31 , it can be seen that a light intensity peak is formed at about 72° from the optical axis L and light is widely distributed. In addition, there is no significant difference between the light beam angle distribution of  FIG. 31  and the light beam angle distribution of  FIG. 29 . Thus, it can be seen that, when the light incident section  231   a  satisfies the condition of b&gt;a at an angle of 50° or less from the optical axis L, there is no significant difference in light beam angle distribution, regardless of whether the light exit face has the flat surface or the convex surface at the upper center thereof. 
       FIGS. 32A and 32B  show an optical member according to Comparative Example 1 and a beam angle distribution curve thereof. 
     In the optical member of  FIG. 32A , at an angle of 50° or less from the optical axis L, the shortest distance ‘b’ from a certain point on the optical axis to an apex of a light incident section is greater than the shortest distance ‘a’ from the same point to a side surface of the light incident section, and the light exit face has a concave section formed at an upper center thereof. In  FIG. 32B  showing a beam angle distribution curve under these conditions, it can be seen that there is no substantial difference in light beam angle distribution between the above embodiments and this comparative example. This result means that, under the condition of b&gt;a, the concave section formed at the upper center of the light exit face provides substantially no function in change of the light beam angle distribution. 
       FIGS. 33A  and B show an optical member according to Comparative Example 2 and a light beam angle distribution thereof. 
     In the optical member of  FIG. 33A , at an angle of 50° or less from the optical axis L, the shortest distance ‘b’ from a certain point on the optical axis to an apex of a light incident section is smaller than the shortest distance ‘a’ from the same point to a side surface of the light incident section, and the light exit face has a concave section formed at an upper center thereof. In  FIG. 33B  showing a beam angle distribution curve under these conditions, it can be seen that there is no substantial difference between the light beam angle distribution of Comparative Example 1 and that of the above embodiments. This result means that, under the condition of b&lt;a, the concave section formed at the upper center of the light exit face contributes to wide dispersion of light at an angle of 50° or less from the optical axis L. 
       FIG. 34  is a sectional view of an optical member according to another exemplary embodiment of the present disclosure. As shown in  FIG. 34 , the light exit face  135  includes a total reflection surface  135   c  so as to form an apex  135   d  under the central axis C of the optical member. Light can be dispersed laterally based on the light axis C, by total refection of light in the total reflection surface  135   c . 
     Although the present disclosure has been illustrated with reference to some exemplary embodiments in conjunction with the drawings, it should be understood that some features of a certain embodiment may also be applied to other embodiments without departing from the spirit and scope of the disclosure. Further, it should be understood that these embodiments are provided by way of illustration only, and that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.