JP4912448B2 - Light emitting device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a light emitting device capable of reducing uneven brightness and a method for manufacturing the same.

  Conventionally, a surface light source device has been proposed in which light incident from a light emitting diode is refracted by a light flux controlling member to reduce uneven brightness due to emitted light (see Patent Document 1 (Japanese Patent Laid-Open No. 2006-32172)). Further, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2003-195792), a plurality of light emitting diodes are divided into a plurality of groups, and the light emitting diodes of each of the plurality of groups are pulsed with the same phase and each group of pulsed lightings. There has been proposed a surface light source device capable of avoiding power shortage when all the light emitting diodes are turned on simultaneously by shifting the timing, and reducing unevenness of brightness even with low power.

  By the way, in order to reduce unevenness of brightness, the former surface light source device requires a light flux controlling member, and the latter surface light source device requires a pulse generation circuit and a timing generation circuit. Therefore, the conventional surface light source device requires a component for reducing unevenness in brightness, leading to a problem of increasing costs.

JP 2006-32172 A JP 2003-195792 A

  Accordingly, an object of the present invention is to provide a light emitting device that can obtain uniform brightness at a low cost without using parts for reducing unevenness of brightness, and a method for manufacturing the same.

In order to solve the above problems, a light-emitting device of the present invention includes a substrate having a first electrode and a second electrode,
The maximum dimension connected between the first electrode and the second electrode is 100 μm or less, and the number per 1 cm ² of the area is substantially uniform in a region of 10 cm ² or more on the substrate. A plurality of light emitting diode elements,
The arrangement density of the light emitting diode elements in a region of 10 cm ² or more on the substrate is 100 / cm ² or more.

According to the light emitting device of the present invention, the brightness unevenness can be reduced to 10% or less as described below. Here, the unevenness of brightness refers to variation in brightness of each light emitting region when the substrate is divided into light emitting regions having an area of 1 cm ^{2 on} the substrate.

First, a region where a plurality of light emitting elements are arranged on a substrate is a light emitting region. Generally, when a backlight or a lighting device is viewed, it is about 30 cm away from the backlight or the lighting device. When the distance from the light source is about 30 cm, since the area of the light emitting region is 10 cm ² or more, a human recognizes this region as a surface light source instead of a point light source, and uneven brightness in the light emitting region. Become sensitive to.

When viewing a surface light source 30 cm away, the human eye sensitively detects uneven brightness when the brightness changes on a scale of 1 cm or more in the light emitting region. Therefore, it is appropriate to take a 1 cm × 1 cm scale in the light emitting region, that is, a brightness of an area of 1 cm ² in the light emitting region as a reference. As an example, a backlight or a lighting device can be considered as an application target of the present invention. Generally, when viewing the backlight or the lighting device, the backlight or the lighting device is approximately 30 cm away from the backlight or the lighting device.

The brightness variation dI of one light emitting element, when ± 50%, if the light-emitting device having an intermediate value I0 brightness of an area 1 cm ² of the light emitting region arranged one area 1 cm ² per the emission region Is calculated by the following equation (1).
I = I0 ± 0.5 × I0 (1)

Also, an area 1 cm ² of the light emitting region, the light-emitting element having a brightness of 1 / n of the intermediate value I0 brightness (n is a natural number) when n pieces arranged, the brightness of the area of 1 cm ² per light emitting area The length I is calculated by the following equation (2).
I = n × (1 / n) × I0 ± n ^1/2 × (1 / n) × 0.5 × I0
= I0 ± 1 / n ^1/2 × 0.5 × I0 (2)

Therefore, in the above equation (2), if n = 100,
I = I0 ± 0.1 × 0.5 × I0
= I0 ± 0.05 × I0 (3)

From the above equation (3), by arranging 100 light emitting elements having a brightness of 1/100 of the intermediate value I0 of brightness in the area of the light emitting region of 1 cm ² , the brightness unevenness can be reduced to ± 5% or less. . Here, since the human eye sensitively detects unevenness in brightness exceeding 10% (± 5%), it becomes a defective product if the unevenness in brightness exceeds 10%. On the other hand, according to the light emitting device of the present invention, the uneven brightness can be reduced to 10% or less without using a component for reducing the uneven brightness, and uniform brightness can be achieved at low cost. Obtainable.

In addition, the upper limit of the arrangement density of the light-emitting elements is 10000000 / cm ² as a practical limit in the current manufacturing. Further, the upper limit value of the area of the region on the substrate is 10 m × 10 m as a practical limit at present.

In one embodiment, the arrangement density of the light emitting elements in a region of 10 cm ² or more on the substrate is 120 / cm ² or more.

  According to the light emitting device of this embodiment, as will be described below, even when one of the plurality of light emitting elements fails, the uneven brightness can be reduced to 10% or less, and the yield can be improved.

First, consider a case where n light emitting elements are arranged in a certain area of 1 cm ² in one of the light emitting regions of the substrate. Here, it is assumed that the brightness variation Id of each light-emitting element is 50%, and m light-emitting elements out of the n light-emitting elements have failed (do not emit light). Then, in the region having a certain area of 1 cm ² , when there is no faulty light emitting element and m = 0 and n light emitting elements are dispersed so as to be brightest, the certain area of 1 cm ^{2 is obtained.} The brightness Imax in the region is calculated as the following equation (4) based on the above equation (2).
Imax = I0 + 1 / n ^1/2 × 0.5 × I0 (4)

On the other hand, in the other area of 1 cm ² in area, m (m> 0) of the arranged n light emitting elements fail, and the n light emitting elements are the most. When it varies so as to be dark, the brightness Imin in the other area of 1 cm ² is calculated as the following expression (5) based on the above expression (2).
Imin = I0−1 / n ^1/2 × 0.5 × I0−m × I0 / n (5)

The brightness unevenness Id is a value obtained by subtracting Imin calculated by the above equation (5) from Imax calculated by the above equation (4) and dividing by I0, and is calculated by the following equation (6). The
Id = (Imax−Imin) / I0
= {(I0 + 1 / n ^1/2 × 0.5 × I0)
− (I0−1 / n ^1/2 × 0.5 × I0−m × I0 / n)} / I0
= 1 / n ^1/2 + m / n (6)

The relationship between the light emitting element density N (pieces / cm ⁻² ) and the allowable failure number M, which makes the brightness unevenness Id calculated by the above formula (6) 0.1 or less (10% or less), As shown in FIG. Referring to FIG. 3, when the light emitting element density element density N is 120 (pieces / cm ² ) or more, it is determined that the defective light emitting element is a non-defective product when there is a darkest variation. If it is less than cm ² , it can be seen that if there is a failed light emitting element in the darkest variation, it becomes a defective product.

Moreover, in the light-emitting device of one Embodiment, the arrangement density of the said light emitting element in the area | region 10 cm < ² > or more on the said board | substrate is 1111 piece / cm < ² > or more.

  According to the light emitting device of this embodiment, the interval between the plurality of light emitting elements arranged on the substrate can be set to 300 μm or less. When the distance between the light emitting elements is 300 μm or less, even if there is one light emitting element that does not emit light among the many light emitting elements that emit light, the human eye will see the portion of the light emitting element that does not emit light (darkness). Do not recognize point). Therefore, even if there is a light emitting element that does not emit light due to a failure of the light emitting element, the dark spot becomes inconspicuous due to other light emitting elements emitting light near the failed light emitting element.

In one embodiment, the area of the region on the substrate on which the plurality of light emitting elements are arranged is 28 cm ² or more.

  According to the light emitting device of this embodiment, as will be described below, heat dissipation is improved, and an expensive heat sink is not required.

  First, the characteristic diagram of FIG. 5 shows the characteristics where the horizontal axis represents the reciprocal of the temperature (absolute temperature) Tj of the light emitting part of the light emitting diode and the vertical axis represents the lifetime of the light emitting diode. According to this characteristic, it is understood that the junction temperature of the light emitting diode needs to be 150 ° C. or lower in order to obtain a lifetime of 40000 hours.

Next, the experimental results showing the relationship between the power consumption (W / cm ² ) of the seat heater without the heat sink and the substrate temperature rise (° C.) are shown in the characteristic diagram of FIG. On the other hand, the temperature (° C.) of the light emitting part of the light emitting diode is calculated from the room temperature (° C.) and the substrate temperature rise (° C.) by the following equation (7).
(Light emitting part temperature) = (Room temperature) + (Substrate temperature rise) +30 (° C.) (7)

From the above equation (7), it can be seen that the substrate temperature rise needs to be 90 ° C. or lower in order to make the temperature of the light emitting part 150 ° C. or lower. Since heat is generated in the light emitting part, the temperature of the light emitting part is usually 30 ° C. higher than the substrate temperature. From the experimental results shown in FIG. 3, it can be seen that the power consumed by heat must be 0.2 (W / cm ² ) or less in order to reduce the substrate temperature rise to 90 ° C. or less. Here, the power consumption of the bulb-type LED is approximately 8 (W), and 70% is converted into heat, so the power consumed by the heat is 5.6 (W). Therefore, in order to obtain the same luminous intensity as that of the bulb-type LED and to reduce the power consumed by heat to 0.2 (W / cm ² ) or less, (5.6 W ÷ 0.2 W / cm ² ) = 28 cm ² The above substrate area is required.

In one embodiment of the method for manufacturing a light emitting device, a step of preparing a substrate having a first electrode and a second electrode;
Applying a solution containing a plurality of light emitting elements having a maximum dimension of 100 μm or less to the substrate;
A voltage is applied to the first electrode and the second electrode to place the light emitting element in a region defined by the first and second electrodes in a region of 10 cm ² or more on the substrate. And a step of arranging the light emitting elements so as to have a substantially uniform arrangement density of 100 / cm ² or more in a region of 10 cm ² or more on the substrate.

  According to the method for manufacturing a light emitting device of this embodiment, so-called dielectrophoresis can be used to arrange a fine light emitting element having a maximum dimension of 100 μm or less at a position defined by the first and second electrodes. The light emitting elements can be arranged substantially uniformly.

  According to the light emitting device of the present invention, the brightness unevenness can be reduced to 10% or less without using parts for reducing the brightness unevenness, and uniform brightness can be obtained at low cost. .

It is a top view which shows embodiment of the light-emitting device of this invention. It is a figure which shows an example of the light emitting element with which the said embodiment is provided. It is a figure which shows another example of the light emitting element with which the said embodiment is provided. It is a figure which shows the relationship between the light emitting element density N (piece / cm ^<-2 >) which makes the brightness nonuniformity Id in a light-emitting device 0.1 or less (10% or less), and the allowable number M of faults. It is a characteristic view which shows the experimental result showing the relationship between the power consumption (W / cm < ² >) of a seat heater without a heat sink, and a board | substrate temperature rise (degreeC). FIG. 6 is a characteristic diagram showing characteristics in which the horizontal axis represents the reciprocal of the temperature (absolute temperature) Tj of the light emitting part of the light emitting diode and the vertical axis represents the lifetime of the light emitting diode. It is process drawing of the manufacturing method of the light emitting diode of a rod-shaped structure. It is process drawing of the manufacturing method of the rod-shaped structure light emitting element following FIG. 6A. It is process drawing of the manufacturing method of the rod-shaped structure light emitting element following FIG. 6B. It is process drawing of the manufacturing method of the rod-shaped structure light emitting element following FIG. 6C. It is process drawing of the manufacturing method of the rod-shaped structure light emitting element following FIG. 6D.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 is a plan view showing an embodiment of a light emitting device according to the present invention. The light emitting device of this embodiment includes a substrate 1 and a plurality of light emitting diodes 2 arranged on the substrate 1 so that the number per unit area is substantially uniform. In this embodiment, as shown in FIG. 2A, the light-emitting diode 2 includes an N-type portion 21 made of an N-type semiconductor and a P-type portion 22 made of a P-type semiconductor at a substantially PN junction. A rod-like light emitting diode joined at the surface S1 was formed.

The plurality of light emitting diodes 2 are arranged in a matrix. In this embodiment, as an example, the length L of each light emitting diode 2 is 10 μm and the width W is 3 μm. Further, the distance d1 between two light emitting diodes 2 adjacent in the row direction was set to 11 μm. The distance d2 between two light emitting diodes 2 adjacent in the column direction was set to 9 μm. In this embodiment, as an example, the dimension of the substrate 1 in the row direction is 8 cm, and the dimension of the substrate 1 in the column direction is 5 cm. In this embodiment, as an example, the number of light emitting diodes 2 in the row direction is 3800, and the number of light emitting diodes 2 in the column direction is 4100. Therefore, in this case, 3800 × 4100 = 1558 million light-emitting diodes 2 are arranged in a matrix on the substrate 1. Therefore, in this case, the arrangement density of the light-emitting diodes 2 is (15.58 million / 40 cm ² ) = 389,500 / cm ² .

  The substrate 1 is formed with a first electrode 3 and a second electrode 5 extending in the column direction. As shown in FIG. 1, the first electrode 3 and the second electrode 5 are alternately arranged in the row direction at a predetermined interval. One end portion 2A of the first row of light emitting diodes 2 arranged in the column direction is connected to the other end of the first first electrode 3 arranged at one end in the row direction. The other end 2 </ b> B of the diode 2 is connected to one end of the first second electrode 5. Also, one end 2A of the second row of light emitting diodes 2A is connected to the other end of the first second electrode 5, and the other end 2B of the second row of light emitting diodes 2 is connected to the first row 2A. The second electrode 5 is connected to one end side of the second first electrode 3 adjacent to the other end side of the second electrode 5. Further, one end 2A of the light emitting diode 2 in the third row is connected to the other end of the second first electrode 3, and the other end 2B of the light emitting diode 2 in the third row is connected to the second end. It is connected to one end side of the second electrode 5. Similarly, the end portions 2A and 2B of the light emitting diodes 2 in the fourth and subsequent rows are connected between the first electrode 3 and the second electrode 5. On the substrate 1, a light emitting diode 2 whose one end 2A is an anode and whose other end 2B is a cathode, and a light emitting diode 2 whose one end 2A is a cathode and whose other end 2B is an anode, and Are mixed and arranged in a matrix.

  In this embodiment, an AC voltage from an AC power source 6 is applied between the first electrode 3 and the second electrode 5, and each light emitting diode 2 is driven with an AC. In addition, it is preferable that the frequency of this alternating current is 60 Hz or more and 1 MHz or less. By setting the AC frequency of the AC power supply 6 to 60 Hz or more, flickering due to blinking of the light emitting diode 2 that occurs in AC driving can be suppressed. Further, since the AC frequency of the AC power supply 6 is set to 1 MHz or less, loss in the wiring due to the high frequency can be suppressed.

According to the light emitting device of this embodiment, the unevenness of brightness can be reduced to about ± 0.08% or less. Here, the uneven brightness refers to the variation in brightness of each light emitting area when the substrate 1 is divided into light emitting areas each having an area of 1 cm ² . This will be described below.

First, a region where a plurality of light emitting diodes 2 are arranged on the substrate 1 is a light emitting region. In general, when viewing a backlight or a lighting device, the distance from the backlight or the lighting device is approximately 30 cm. When the distance from the light source is about 30 cm, since the area of the light emitting region is 10 cm ² or more, a human recognizes this region as a surface light source instead of a point light source, and uneven brightness in the light emitting region. Become sensitive to.

When viewing a surface light source 30 cm away, the human eye sensitively detects uneven brightness when the brightness changes on a scale of 1 cm or more in the light emitting region. Therefore, it is appropriate to take a 1 cm × 1 cm scale in the light emitting region, that is, a brightness of an area of 1 cm ² in the light emitting region as a reference. As an example, a backlight or a lighting device can be considered as an application target of the present embodiment. Generally, when viewing the backlight or the lighting device, the backlight or the lighting device is approximately 30 cm away from the backlight or the lighting device.

Here, assuming that the brightness variation dI of one light emitting diode is ± 50%, when one light emitting element having an intermediate brightness value I0 is arranged in the area 1 cm ² of the light emitting region, the area of the light emitting region is as follows. The brightness I per cm ² is calculated by the following formula (1).
I = I0 ± 0.5 × I0 (1)

Next, when n light emitting diodes having a brightness of 1 / n (n is a natural number) of an intermediate brightness value I0 are arranged in an area 1 cm ² of the light emitting area of the substrate 1, The brightness I per 1 cm ^{2 of} area is calculated by the following equation (2).
I = n × (1 / n) × I0 ± n ^1/2 × (1 / n) × 0.5 × I0
= I0 ± 1 / n ^1/2 × 0.5 × I0 (2)

In this embodiment, since n = 389,500 light emitting diodes 2 are arranged per 1 cm ² , the second term (± 1 / n ^1/2 × 0.5 × I0) on the right side of the above formula (2). ), The brightness variation Id is calculated as in the following equation (3).
Id = ± 1 / (389500) ^1/2 × 0.5≈8.012 × 10 ⁻⁴ (3)

Therefore, the uneven brightness can be reduced to about ± 0.08%. When 100 light emitting diodes having a brightness of 1/100 of the intermediate brightness value I0 are arranged per 1 cm ² of the area of the light emitting region, n = 2 in the second term on the right side of the above formula (2). By substituting 100, the brightness unevenness Id can be ± 5%. Here, since the human eye sensitively detects unevenness in brightness exceeding 10% (± 5%), it becomes a defective product if the unevenness in brightness exceeds 10%.

According to the light emitting device of the present embodiment, the brightness unevenness can be reduced to about 0.16% without using components for reducing the brightness unevenness, and uniform brightness can be obtained at low cost. be able to. In addition, the unevenness in brightness can be reduced to 10% or less by setting the arrangement density of the light emitting diodes 2 in the region of 10 cm ² or more on the substrate 1 to 100 pieces / cm ² or more.

In addition, according to this embodiment, m = 10 light emitting diodes of n = 389,500 light emitting diodes 2 arranged in a certain area of 1 cm ² of the light emitting regions of the substrate 1. Even when 2 breaks down, the brightness unevenness can be reduced to 0.16%, which is 10% or less, and the yield can be improved. This will be described below.

First, consider a case where n light emitting diodes are arranged in a certain area of 1 cm ² of the light emitting region of the substrate 1. Here, it is assumed that the brightness variation Id of each light-emitting diode is 50%, and m light-emitting elements out of the n light-emitting diodes fail (do not emit light). In the area of one certain area of 1 cm ² , when there is no failed light emitting diode, m = 0, and n light emitting diodes vary so as to be brightest, the certain area of 1 cm ^{2 is obtained.} The brightness Imax in the region is calculated as the following equation (4) based on the above equation (2).
Imax = I0 + 1 / n ^1/2 × 0.5 × I0 (4)

On the other hand, in another area of 1 cm ² in area of the light emitting area, m (m> 0) light emitting diodes out of the arranged n light emitting diodes fail, and the n light emitting diodes are the most. When it varies so as to be dark, the brightness Imin in the other area of 1 cm ² is calculated as the following expression (5) based on the above expression (2).
Imin = I0−1 / n ^1/2 × 0.5 × I0−m × I0 / n (5)

The brightness unevenness Id is a value obtained by subtracting Imin calculated by the above equation (5) from Imax calculated by the above equation (4) and dividing by I0, and is calculated by the following equation (6). The
Id = (Imax−Imin) / I0
= {(I0 + 1 / n ^1/2 × 0.5 × I0)
− (I0−1 / n ^1/2 × 0.5 × I0−m × I0 / n)} / I0
= 1 / n ^1/2 + m / n (6)

In this embodiment, the brightness unevenness Id when m light-emitting elements out of n = 389500 light-emitting diodes 2 arranged in a certain area of 1 cm ² fail is expressed by the above-described equation (6). By
Id (m) = 1 / (389500) ^1/2 + m / (389500)
= 1.6023 × 10 ⁻³ + m × 2.567 × 10 ⁻⁶
The uneven brightness Id (10) when the number of failures m = 10 is
Id (10) = 1.60323 × 10 ⁻³ + 10 × 2.574 × 10 ⁻⁶
≒ 1.628 × 10 ^-3

Therefore, even if the number of failures m is 10, the unevenness of brightness becomes 0.16%. Note that the relationship between the light emitting diode density N (pieces / cm ⁻² ) and the allowable number M of faults that make the brightness unevenness Id calculated by the above formula (6) 0.1 or less (10% or less). Is shown in FIG. Referring to FIG. 3, when the light emitting element density N is 120 (pieces / cm ² ) or more, it is determined that the light emitting diode is defective even if the light emitting diode is darkest. If it is less than cm ² , it can be seen that if there is a failed light emitting element in the darkest variation, it becomes a defective product. Therefore, by setting the arrangement density of the light emitting diodes 2 in the region of 10 cm ² or more on the substrate 1 to be 120 pieces / cm ² or more, even when one of the plurality of light emitting diodes 2 fails, the brightness is increased. The unevenness of the thickness can be reduced to 10% or less, and the yield can be improved.

  In this embodiment, the distance d1 between two light emitting diodes 2 adjacent in the row direction is 11 μm, and the distance d2 between two light emitting diodes 2 adjacent in the column direction is 9 μm. Accordingly, since the interval between the light emitting diodes 2 arranged on the substrate 1 is 300 μm or less, even if there is one light emitting diode 2 that does not emit light among the many light emitting diodes 2 that emit light, The eye does not recognize the light emitting diode portion (dark spot) that does not emit light. Therefore, even if there is a light emitting diode 2 that does not emit light due to the failure of the light emitting diode 2, the dark spot becomes inconspicuous due to the other light emitting diodes 2 that emit light near the failed light emitting diode 2.

Further, in this embodiment, the area of the region where the plurality of light emitting diodes 2 on the substrate 1, the plurality of light emitting diodes 2 are arranged is disposed, a 8 cm × 5 cm = 40 cm ^2, with 28cm ² or more is there. Therefore, according to the light-emitting device of this embodiment, heat dissipation is improved and an expensive heat sink is not required. This will be described below.

  First, the characteristic diagram of FIG. 5 shows the characteristics where the horizontal axis represents the reciprocal of the temperature (absolute temperature) Tj of the light emitting part of the light emitting diode and the vertical axis represents the lifetime of the light emitting diode. According to this characteristic, it is understood that the junction temperature of the light emitting diode needs to be 150 ° C. or lower in order to obtain a lifetime of 40000 hours.

Next, the experimental results showing the relationship between the power consumption (W / cm ² ) of the seat heater without the heat sink and the substrate temperature rise (° C.) are shown in the characteristic diagram of FIG. On the other hand, the temperature (° C.) of the light emitting part of the light emitting diode is calculated from the room temperature (° C.) and the substrate temperature rise (° C.) by the following equation (7).
(Light emitting part temperature) = (Room temperature) + (Substrate temperature rise) +30 (° C.) (7)

From the above equation (7), it can be seen that the substrate temperature rise needs to be 90 ° C. or less in order to make the temperature of the light emitting portion of the light emitting diode 150 ° C. or less. Since heat is generated in the light emitting part, the temperature of the light emitting part is usually 30 ° C. higher than the substrate temperature. From the experimental results shown in FIG. 4, it can be seen that the power consumed by the heat must be 0.2 (W / cm ² ) or less in order to reduce the substrate temperature rise to 90 ° C. or less. Here, the power consumption of the bulb-type LED is approximately 8 (W), and 70% is converted into heat, so the power consumed by the heat is 5.6 (W). Therefore, in order to obtain the same luminous intensity as that of the bulb-type LED and to reduce the power consumed by heat to 0.2 (W / cm ² ) or less, (5.6 W ÷ 0.2 W / cm ² ) = 28 cm ² The above substrate area is required.

In the above embodiment, the arrangement density of the light emitting diodes is 389500 (pieces / cm ² ) and the size of the area in which the light emitting diodes are arranged on the substrate 1 is 8 cm × 5 cm. Of course, the size of the substrate in the region where the light emitting diode is disposed is not limited to this. In short, the arrangement density of the light emitting diodes may be 100 / cm ² or more, and the area of the region where the light emitting diodes are arranged on the substrate may be 10 cm ² or more. The arrangement density of the light emitting diodes in a region of 10 cm ² or more on the substrate is preferably 120 / cm ² or more. The arrangement density of the light emitting diodes in a region of 10 cm ² or more on the substrate is preferably 1111 pieces / cm ² or more. Moreover, it is preferable that the area of the area | region where the said several light emitting diode on the said board | substrate is arrange | positioned is 28 cm < ² > or more. In the above embodiment, as shown in FIG. 2A, the light-emitting diode 2 includes an N-type portion 21 made of an N-type semiconductor and a P-type portion 22 made of a P-type semiconductor at a substantially central position. Although it is a rod-like light emitting diode joined at the PN junction surface S1, as shown in FIG. 2B, a cylindrical core portion 31 made of an N-type semiconductor and an outer peripheral surface of the cylindrical core portion 31 Alternatively, the cylindrical shell portion 33 made of a P-type semiconductor covering 32 may be used. A part 32 </ b> A of the outer peripheral surface 32 of the cylindrical core portion 31 is exposed from the shell portion 33. The joint surface 35 between the cylindrical core portion 31 and the shell portion 33 is formed concentrically around the cylindrical core portion 31. A portion 31A of the core portion 31 exposed from the shell portion 33 forms the cathode K, and an end portion 33A of the shell portion 33 forms the anode A. The cathode K and the anode A are directly connected to one of the first and second electrodes 3 and 5. In the light emitting diode having the configuration shown in FIG. 2B, the joint surface 35 between the N-type columnar core portion 31 and the P-type shell portion 33 can be formed in a cylindrical shape along the outer peripheral surface 32 of the core portion 31. The surface can be increased. Further, since the part 32A of the outer peripheral surface 32 of the core part 31 is exposed from the P-type shell part 33, the electrodes 3 and 5 can be easily connected to the part 32A of the outer peripheral surface 32 of the core part 31. become. The end surface 31C of the one end 31B of the core portion 31 may be exposed from the end portion 33A of the shell portion 33, but the end portion 33A of the shell portion 33 covers the end surface 31C of the one end 31B of the core portion 31. It is good also as a structure. The semiconductor forming the shell 33 may be N-type, and the semiconductor forming the core 31 may be P-type. In the configuration shown in FIG. 2B, the core portion 31 is formed in a columnar shape and the shell portion 33 is formed in a cylindrical shape. However, a polygonal columnar core portion and a polygonal cylindrical shell portion may be used. For example, a hexagonal columnar core portion and a hexagonal cylindrical shell portion, a quadrangular columnar core portion and a rectangular cylindrical shell portion, or a triangular columnar core portion and a triangular cylindrical shell portion may be used. Moreover, it is good also as an elliptic cylindrical core part and an elliptical cylindrical shell part.

  An example of a method for manufacturing a bar-shaped light emitting diode composed of such a core part and a shell part will be described with reference to FIGS. 6A to 6E.

  First, as shown in FIG. 6A, a mask 72 having a growth hole 72a is formed on a substrate 71 made of n-type GaN. Next, as shown in FIG. 6B, in the semiconductor core formation process, an MOCVD (Metal Organic Chemical Vapor Deposition) apparatus is used to form n on the substrate 71 exposed by the growth hole 72a of the mask 72. A rod-shaped semiconductor core 73 is formed by crystal growth of type GaN. Here, the n-type GaN has a hexagonal crystal growth, and a hexagonal columnar semiconductor core can be obtained by growing the n-type GaN in the c-axis direction perpendicular to the surface of the substrate 71.

  Next, as shown in FIG. 6C, in the semiconductor layer forming step, a semiconductor layer 74 made of p-type GaN is formed on the entire surface of the substrate 71 so as to cover the rod-shaped semiconductor core 73. Next, as shown in FIG. 6D, in the exposure step, the region excluding the portion of the semiconductor layer 74a covering the semiconductor core 73 and the mask 72 are removed by lift-off, and the substrate side of the rod-shaped semiconductor core 73 is moved to the substrate 71 side. The outer peripheral surface is exposed to form an exposed portion 73a. In this state, the end surface of the semiconductor core 73 opposite to the substrate 71 is covered with the semiconductor layer 74a. In this exposure step, lift-off is used, but a part of the semiconductor core may be exposed by etching.

  Next, in the separation step, the base 71 close to the substrate 71 side of the semiconductor core 73 standing on the substrate 71 is bent by vibrating the substrate 71 along the substrate plane using ultrasonic waves (for example, several tens of kHz). Furthermore, stress acts on the semiconductor core 73 covered with the semiconductor layer 74a, and the semiconductor core 73 covered with the semiconductor layer 74a is separated from the substrate 71 as shown in FIG. 6E. In this way, the fine rod-shaped structure light emitting element 70 separated from the substrate 71 can be manufactured. In this method for manufacturing a light emitting diode having a rod-like structure, the diameter of the rod-like light emitting element 70 is 1 μm and the length is 10 μm.

  In the light emitting diode manufacturing method, a semiconductor using GaN as a base material is used for the substrate 71, the semiconductor core 73, and the semiconductor layer 74a. A semiconductor material may be used. Further, although the substrate and the semiconductor core are n-type and the semiconductor layer is p-type, a rod-shaped structure light emitting diode having a reverse conductivity type may be used. In addition, the method for manufacturing a rod-shaped structure light emitting diode having a semiconductor core with a hexagonal column in the cross section has been described. However, the present invention is not limited to this, and the cross section may be a circular or elliptical rod shape, or the cross section may be another polygon such as a triangle. A bar-shaped light emitting diode having a bar-shaped semiconductor core can also be manufactured by the same manufacturing method as described above. Further, in the above-described light emitting diode manufacturing method, the rod-shaped light emitting diode has a micro-order size of 1 μm in diameter and 10 μm in length. However, as a nano-order size element having at least a diameter of less than 1 μm in diameter or length. Good. The diameter of the semiconductor core of the rod-shaped structure light emitting diode is preferably 20 nm or more and 100 μm or less, and variation in the diameter of the semiconductor core can be suppressed as compared with a rod-shaped structure light emitting diode of several nm, thereby reducing variation in light emitting area, that is, light emission characteristics. This can improve the yield. The diameter of the semiconductor core of the rod-shaped light emitting diode is more preferably 500 nm or more and 10 μm or less, and variation in light emission characteristics can be reduced.

  In the light emitting diode manufacturing method, the semiconductor core 73 is crystal-grown using the MOCVD apparatus. However, the semiconductor core may be formed using another crystal growth apparatus such as an MBE (molecular beam epitaxial) apparatus. . Further, although the semiconductor core is crystal-grown on the substrate using a mask having a growth hole, the semiconductor core may be crystal-grown from the metal seed by arranging a metal species on the substrate. In the above-described light emitting diode manufacturing method, the semiconductor core 73 covered with the semiconductor layer 74a is separated from the substrate 71 using ultrasonic waves. However, the present invention is not limited thereto, and the semiconductor core is mechanically removed from the substrate using a cutting tool. May be separated. In this case, a plurality of fine rod-shaped light emitting elements provided on the substrate can be separated in a short time by a simple method.

  Next, a method for manufacturing the light emitting device of the above-described embodiment will be described. In this method for manufacturing a light emitting device, first, a substrate 1 on which a first electrode 3 and a second electrode 5 are formed on a surface 1A is prepared. The substrate 1 is an insulating substrate, and the first and second electrodes 3 and 5 are metal electrodes. As an example, the metal electrodes 3 and 5 having a desired electrode shape can be formed on the surface 1A of the insulating substrate 1 using a printing technique. Also, a metal film and a photoreceptor film are uniformly laminated on the surface 1A of the insulating substrate 1, and this photoreceptor film is exposed and developed into a desired electrode pattern, and the metal film is etched using the patterned photoreceptor film as a mask. Thus, the first electrode 3 and the second electrode 5 can be formed.

  In addition, gold, silver, copper, iron, tungsten, tungsten nitride, aluminum, tantalum, alloys thereof, or the like can be used as a metal material for forming the metal electrodes 3 and 5. The insulating substrate 1 is an insulating material such as glass, ceramic, alumina, resin, or a substrate in which a silicon oxide film is formed on a semiconductor surface such as silicon and the surface is insulative. When a glass substrate is used, it is desirable to form a base insulating film such as a silicon oxide film or a silicon nitride film on the surface.

  The distance between the first electrode 3 and the second electrode 5 is preferably slightly shorter than the length L of the light emitting diode 2. As an example, the distance is desirably 4 to 9 μm when the length L of the light emitting diode 2 is 10 μm. That is, the distance is desirably about 40 to 90% of the length L of the light emitting diode 2, more preferably 60 to 80% of the length.

  Next, a procedure for arranging a plurality of light emitting diodes 2 on the insulating substrate 1 will be described. First, isopropyl alcohol (IPA) as a solution containing a plurality of light emitting diodes 2 is thinly applied on the insulating substrate 1. In addition to IPA, the solution may be ethylene glycol, propylene glycol, methanol, ethanol, acetone, or a mixture thereof, and liquids such as other organic substances, water, and the like can be used. However, if a large current flows between the metal electrodes 3 and 23 through the liquid, a desired voltage difference cannot be applied between the metal electrodes 3 and 5. In such a case, the entire surface of the insulating substrate 1 may be coated with an insulating film of about 5 nm to 50 nm so as to cover the metal electrodes 3 and 5.

The thickness of applying the IPA including the plurality of light emitting diodes 2 is a thickness that allows the light emitting diodes 2 to move in the liquid so that the light emitting diodes 2 can be arranged in the next step of arranging the light emitting diodes 2. Therefore, it is more than the thickness of the light emitting diode 2, for example, several micrometers-several mm. If the applied thickness is too thin, the light emitting diode 2 becomes difficult to move, and if it is too thick, the time for drying the liquid becomes long. Preferably, it is 100 micrometers-2 mm. Further, the number of the light emitting diodes 2 is preferably 1 × 10 ⁴ / cm ³ to 1 × 10 ⁷ / cm ³ with respect to the amount of IPA.

  In order to apply the IPA including the plurality of light emitting diodes 2 to the insulating substrate 1, a frame (not shown) is formed around the metal electrodes 3 and 5 on which the plurality of light emitting diodes 2 are arranged. The IPA including the plurality of light emitting diodes 2 may be filled to a desired thickness. However, when the IPA including the plurality of light emitting diodes 2 is viscous, it can be applied to a desired thickness without the need for a frame. The IPA, ethylene glycol, propylene glycol, methanol, ethanol, acetone, a mixture thereof, a liquid made of other organic substances, or a liquid such as water has low viscosity for the arrangement process of the light emitting diodes 2. Desirably, it is desirable that it is easily evaporated by heating.

  Next, a potential difference is applied between the metal electrodes 3 and 5. This potential difference is, for example, a potential difference of 0.5V or 1V. Note that the potential difference between the metal electrode 3 and the metal electrode 5 can be 0.1 to 10 V, but the arrangement posture of the light emitting diodes 2 starts to be disturbed at 0.1 V or less, and the insulation between the metal electrodes at 10 V or more. Begins to become a problem. Therefore, the potential difference is preferably 0.5 V to 5 V, and more preferably about 0.5 V. When a potential VL is applied to the metal electrode 3 and a potential VH (VL <VH) higher than the potential VL is applied to the metal electrode 5, a negative charge is induced in the metal electrode 3, and a positive charge is induced in the metal electrode 5. Is done. When the light emitting diode 2 approaches the metal electrodes 3 and 5, a positive charge is induced on the side of the light emitting diode 2 close to the metal electrode 3, and a negative charge is induced on the side close to the metal electrode 5. The charge is induced in the light emitting diode 2 by electrostatic induction. Therefore, the light emitting diode 2 has a posture along the electric lines of force generated between the metal electrodes 3 and 5 and the charges induced in the light emitting diodes 2 are substantially equal. Are regularly arranged in a certain direction. At this time, if the surface of the metal electrodes 3 and 5 is coated with an insulating film and the potential difference applied between the metal electrodes 3 and 5 is constant (DC), the insulating film coated on the metal electrodes 3 and 5 Ions having the opposite polarity to the potential of the metal electrodes 3 and 5 are induced on the surface, and the electric field in the solution becomes very weak. In such a case, it is preferable to apply an AC voltage between the metal electrodes 3 and 5. Thereby, it is possible to prevent the ions having the opposite polarity to the potentials of the metal electrodes 3 and 5 from being induced, and to arrange the light emitting diodes 2 normally. The frequency of the alternating voltage applied between the metal electrodes 3 and 5 is preferably 10 Hz to 1 MHz. However, when the frequency of the alternating voltage is less than 10 Hz, the light emitting diode 2 vibrates vigorously and the arrangement is disturbed. There is a possibility. On the other hand, when the frequency of the alternating voltage applied between the metal electrodes 3 and 5 exceeds 1 MHz, the force that the light-emitting diode 2 is adsorbed to the metal electrodes 3 and 5 becomes weak, and the arrangement is disturbed by external disturbance. There is. For this reason, in order to stabilize the arrangement of the light emitting diodes 2, it is more preferable that the frequency of the AC voltage is 50 Hz to 1 kHz. Furthermore, the waveform of the AC voltage is not limited to a sine wave, but may be any waveform that varies periodically, such as a rectangular wave, a triangular wave, and a sawtooth wave. For example, the amplitude of the AC voltage is preferably about 0.5V.

  As described above, in this embodiment, the external electric field generated between the metal electrodes 3 and 5 generates charges in each light-emitting diode 2, and the light-emitting diodes 2 are adsorbed on the metal electrodes 3 and 5 by the attractive force of the charges. The size of the light emitting diode 2 needs to be a size that can move in the liquid. Therefore, the allowable value of the size (maximum dimension) of each light emitting diode 2 varies depending on the application amount (application thickness) of the liquid. When the amount of liquid applied is small, the size (maximum dimension) of each light emitting diode 2 must be nanoscale. When the amount of liquid applied is large, the size of each light emitting diode 2 is on the order of microns. It does not matter.

  When the light emitting diode 2 starts to be arranged for a while, the light emitting diode 2 is arranged between the first electrode 3 and the second electrode 5 as schematically shown in FIG. The light emitting diodes 2 are aligned in a posture perpendicular to the direction in which the first and second electrodes 3 and 5 extend, and are arranged at substantially equal intervals in the extending direction. A repulsive force acts between the light emitting diodes 2 due to the charges induced in the light emitting diodes 2 in a row, and the light emitting diodes 2 are arranged at almost equal intervals.

  Thus, after arranging the light emitting diodes 2 between the first electrode 3 and the second electrode 5, the substrate 1 is heated or left for a certain period of time to evaporate and dry the liquid of the solution. The light emitting diodes 2 are fixedly arranged at equal intervals along the lines of electric force between the first electrode 3 and the second electrode 5.

As described above, according to the method for manufacturing the light emitting device of this embodiment, the light emitting diodes 2 can be arranged between the first electrode 3 and the second electrode 5 with high controllability and high accuracy. Become. Further, in the method of the present embodiment, it is difficult to determine the direction (polarity) of each light emitting diode 2 to one side, and the direction (polarity) of each light emitting diode 2 is not necessarily aligned to one side. As described above, since the light emitting device of the above embodiment is AC driven as described above, the directions (polarities) of the respective light emitting diodes 2 may be mixed at random. Therefore, the manufacturing method of this embodiment is suitable for manufacturing the light emitting device as in the above embodiment in which the directions (polarities) of the light emitting diodes are mixed. Further, in the manufacturing method of the present embodiment, a large number of fine light emitting diodes can be arranged and connected between the electrodes at one time, and as an example, as in the light emitting device of the above embodiment, the length is 389,500 pieces. This is suitable when light emitting diodes 2 having a length L of 10 μm are arranged. In the method for manufacturing the light emitting device according to the present embodiment, the case where the size of the light emitting diode 2 is 10 μm and the number of the light emitting diodes 2 is 389,500 has been described as an example, but the method for manufacturing the light emitting device of the present invention is as follows. It is suitable when light emitting diodes having a maximum dimension of 100 μm or less are arranged so that the number per unit area is substantially uniform in a region of 10 cm ² or more on the substrate with an arrangement density of 100 pieces / cm ² or more.

  Note that when the light-emitting device used in the backlight for the display, the illumination device, and the LED display is the light-emitting device described in the above embodiment, uneven brightness can be suppressed at low cost. Moreover, as a semiconductor which manufactures each light emitting diode demonstrated in the said embodiment, semiconductors, such as GaN, GaAs, GaP, AlGaAs, GaAsP, InGaN, AlGaN, ZnSe, AlGaInP, are employable, for example. The light emitting diodes may have a quantum well structure to improve the light emission efficiency.

DESCRIPTION OF SYMBOLS 1 Board | substrate 1A Surface 2 Light emitting diode 2A One end part 2B Other end part 3 1st electrode 5 2nd electrode 6 AC power supply 21 N-type part 22 P-type part S1 PN junction surface 31 Core part 32 Outer peripheral surface 33 Shell part 33A end Part 35 joint surface

Claims (5)

A substrate having a first electrode and a second electrode;
The maximum dimension connected between the first electrode and the second electrode is 100 μm or less, and the number per 1 cm ² of the area is substantially uniform in a region of 10 cm ² or more on the substrate. A plurality of light emitting diode elements,
The light-emitting device, wherein an arrangement density of the light-emitting diode elements in a region of 10 cm ² or more on the substrate is 100 / cm ² or more. The light-emitting device according to claim 1.
The light emitting device according to claim 1, wherein an arrangement density of the light emitting diode elements in a region of 10 cm ² or more on the substrate is 120 pieces / cm ² or more. The light-emitting device according to claim 1.
The light emitting device according to claim 1, wherein an arrangement density of the light emitting diode elements in a region of 10 cm ² or more on the substrate is 1111 pieces / cm ² or more. The light emitting device according to any one of claims 1 to 3,
The area of the area | region where the said several light emitting diode element on the said board | substrate is arrange | positioned is 28 cm < ² > or more. A method for producing the light emitting device according to claim 1,
Providing a substrate having a first electrode and a second electrode;
Applying a solution containing a plurality of light emitting diode elements having a maximum dimension of 100 μm or less to the substrate;
By applying a voltage to the first electrode and the second electrode, the number of light emitting diode elements per unit area in a region of 10 cm ² or more on the substrate at a position defined by the first and second electrodes. And a step of arranging so that the arrangement density of the light emitting diode elements in the region of 10 cm ² or more on the substrate is 100 pieces / cm ² or more. Method.

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