JPH06166213A - Led array - Google Patents

Abstract

PURPOSE:To avoid the effect to illuminants on a side face luminous LED array at the time of cutting a substrate, control the scatter of light beam because of the recesses and projections of a cut face and enhance the pickup efficiency of beam. CONSTITUTION:Illuminants are arranged at intervals from the side face onto the main face of an LED array 2 to avoid the effect at the time of cutting. The side face of a GaAs substrate 4 is coated with a resin layer 14 to avoid the scatter of beam all over the recesses and projections on the end face of the substrate 4, and the light shutting-up effect generated by the difference between the refraction index of air and that of the GaAs substrate 4 is controlled to enhance the pickup efficiency of beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in LED arrays used in LED print heads and the like.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 4-216684 proposes an edge-emitting LED array. In this LED array, a light emitter is formed along the end surface of a semiconductor substrate such as GaAs, and light is extracted from the end surface of the array.

However, the end surface of the substrate is a cut surface when the LED array is cut out from the wafer, and if a light emitting body is provided here, it is easily affected by the cutting. As a result, the output variation of the light emitter and the defect rate increase. Since the end surface of the LED array is not smooth and the cut surface is not smooth, there are irregularities. Here, when light is extracted from the end face, the light is diffused due to the unevenness of the end face, and the directional angle is widened. Since the degree of unevenness varies, the output distribution of the light emitting body is further widened.
Further, when the light is extracted from the end surface, the efficiency of extracting light to the outside is lower than in the case where the light is extracted from the main surface.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the influence of cutting a substrate from a wafer in a side-emission type LED array and to cause a defect in the light-emitting body due to impact or stress at the time of cutting. This is to prevent the output from fluctuating. Another problem in the invention of claim 1 is that
This is to suppress light diffusion due to the unevenness of the end surface of the substrate. Another object of the invention of claim 1 is to improve the extraction efficiency of light from the light emitting body. Still another object of the invention of claim 1 is to make it possible to reduce the head width when the array is used for an LED head, and to facilitate miniaturization of the optical printer.

In addition to these, the object of the invention of claim 2 is to facilitate the improvement of the resolution of the LED array. The problems in the inventions of claims 3 and 4 are:
In addition to the above problem, it is to further improve the extraction efficiency of light from the LED array.

[0006]

According to the LED array of the present invention, a large number of light emitting bodies are arranged on one main surface of a semiconductor substrate at a position spaced from one side surface, and the upper portion of each light emitting body is covered with an electrode. An LED array in which light emitted from a light emitter is emitted from one side surface of the semiconductor substrate, wherein one side surface of the semiconductor substrate from which light is emitted is covered with a resin layer having a refractive index higher than that of a surrounding medium. It is characterized by Preferably, on one main surface of the semiconductor substrate, the light-emitting bodies are arranged in a plurality of rows at a position spaced from the one side surface,
Further, the emission intensity of the light-emitting body in the row having a larger distance from the one side surface is made higher than the emission intensity of the light-emitting body in the row having a smaller distance from the one side surface. Further, preferably, a reflective layer is provided on the surface of the resin layer having a high refractive index. The reflective layer is preferably provided on both surfaces of the resin layer, but may be provided on only one surface, in which case it is preferably provided on the one main surface side of the semiconductor substrate, that is, on the side covered with the electrodes.
More preferably, a resin layer covering one side surface of the semiconductor substrate covers at least a part of one main surface of the semiconductor substrate, and a reflection layer is provided on the surface of the resin layer covering one main surface of the semiconductor substrate. It

[0007]

According to the present invention, on the main surface of the semiconductor substrate,
The light emitters are arranged at intervals from the side surface. Since the light-emitting body has a distance from the side surface (end surface) of the substrate, it is possible to reduce the influence of cutting the substrate onto the light-emitting body, and to reduce the yield and the variation in output. Next, the side surface of the semiconductor substrate is covered with a layer of resin having a higher refractive index than the surrounding medium. Generally, the refractive index of a semiconductor substrate is higher than the refractive index of a medium such as ambient air, and if the side surface of the substrate has irregularities, light is scattered under the influence of the irregularities. Here, if the side surface is covered with a resin having a higher refractive index than air or the like, the difference in refractive index between the inside and outside of the substrate is reduced, and light scattering due to unevenness is reduced. For example, if the refractive index of the resin is equal to the refractive index of the semiconductor substrate, the light cannot recognize the difference in the refractive index at the interface between the substrate and the resin, and the light goes straight without being scattered. It is difficult to find a resin with the same refractive index as the semiconductor substrate because the refractive index of the substrate is high, but if the refractive index of the resin approaches the refractive index of the substrate, the light scattering at the interface between the substrate and the resin will be reduced. can do.

The coated resin layer has the function of improving the efficiency of extracting light from the LED array, in addition to preventing the scattering of light. The refractive index of the semiconductor substrate is much higher than that of the surrounding air. Therefore, a part of the light generated by the light emitter is trapped inside the LED array. For example, even if the angle of incidence on the interface of the substrate is 0 degrees (incident perpendicularly to the interface), if there is a difference in refractive index, the transmittance is not 100%, and part of the light returns to the inside of the substrate. Here, when the side surface of the semiconductor substrate is covered with a resin having a higher refractive index than the surrounding medium such as air, the difference in the refractive index at the interface is reduced and the LED
The efficiency of light extraction from the array is improved. Further, the electrode covers the upper part of the light-emitting body, and the light emitted to the upper part is reflected by the electrode and taken out from the side surface to enhance the intensity of light emission to the side surface.

In an ordinary LED head, the width of the head is determined by the width of the substrate on which the LED array is mounted. This is because the width of the substrate such as glass on which the array is mounted becomes the minimum width of the head in order to extract light from the main surface of the array.
The actual width of the head is the width of the substrate such as glass plus the width of the housing. Therefore, there is a limit to reducing the width of the head. On the other hand, if the light is extracted from the side surface of the LED array, the lens array is arranged in parallel with the substrate, and the width of the head is not restricted by the width of the substrate such as glass. The lower limit of the width of the head in this case is the sum of the thickness of the substrate and the thickness of the LED array. As a result, the width of the print head can be reduced, the diameter of the photosensitive drum can be reduced, and the size of the printer can be reduced. That is, if the width of the head is made smaller, a smaller photosensitive drum can be used and the printer can be made smaller.

The following effects can be obtained as the width of the LED head is reduced. In a conventional LED head, a board on which an LED array or the like is mounted and a board on which a driving IC for the LED array is mounted are separate two boards, and these boards are connected to each other. This is because the width of the head increases when one substrate is used. On the other hand, if the width of the head is determined by the sum of the thickness of the substrate and the thickness of the LED array, all the circuits can be integrated on one substrate.

The use of the side-emitting LED array facilitates the improvement of the resolution of the LED array. For example, in the case of an LED array that emits light from the main surface, when the light emitters are arranged in two rows, the image forming position is displaced unless the lens array is also arranged in two rows. On the other hand, side emission type LE
In the D array, even if the distance from the side surface to the light emitter is changed,
The imaging position does not change. Therefore, the luminous bodies can be arranged in two rows or three rows, and the resolution can be easily improved. Here, in order to compensate for the difference in the degree of spread of light depending on the distance from the side surface of the semiconductor substrate, the light emitting body farther from the side surface has a larger light emitting area to compensate for the decrease in light output.

According to the third aspect of the invention, the reflective layer is provided on at least one surface of the resin layer. Therefore, the light traveling through the resin layer is reflected by the reflective layer, and the resin layer serves as a kind of light guide,
The light extraction efficiency is further improved. When one main surface of the semiconductor substrate is covered with a resin layer and the surface thereof is covered with a reflective layer, the light entering the resin layer is reflected by the substrate and the reflective layer and proceeds. , The light can be efficiently extracted from the side surface.

[0013]

EXAMPLE A first example is shown in FIGS. In FIG. 1, reference numeral 02 denotes a glass substrate for mounting the LED array 2, which is different from the LED array 2. Reference numeral 04 is a lens array for forming an image of light on a photosensitive drum or the like (not shown). Explaining the LED array 2, reference numeral 4 is a matrix GaAs substrate, on which epitaxial growth portions 6 having different impurity concentrations are epitaxially grown, and impurities are injected into the impurity injection portion 10 through a diffusion mask layer 8 such as SiO2 or silicon nitride. And then pn
The characteristics are inverted to form the junction. The interface (junction interface) between the epitaxial growth portion 6 and the impurity injection portion 10 serves as a light emitting surface. Reference numeral 12 is an electrode of Al, Au, or the like. A resin layer 14 such as a transparent silicon resin, an epoxy resin, or an acrylic resin covers the end surface of the LED array 2 on the light extraction side. The right end surface of the resin layer 14 in the drawing is a smooth end surface. The LED array 2 of the present invention includes the resin layer 14.

FIG. 2 shows one main surface of the LED array 2.
The impurity injection part 10 is parallel to the side surface of the GaAs substrate 4,
For example, one row is arranged on the main surface with a space from the side surface. As a result, it is possible to prevent damage and output fluctuation when cutting out from the wafer. Since light is extracted from the side surface of the LED array 2, the impurity injection portion 10 can be entirely covered with the electrode 12. Therefore, the connection of the electrode 12 to the impurity injection portion 10 becomes easy.

The operation of the embodiment will be described. Part of the light generated at the interface between the impurity-implanted portion 10 and the epitaxial growth portion 6 goes out from the side surface of the array 2. This light is usually L
It is called leakage light of the ED array, and its intensity is about 30% of the light from the main surface (light on the side where the electrode 12 is provided). In the embodiment, this light is extracted from the side surface and is extracted to the outside using the resin layer 14. Here, first, the impurity-implanted portion 10 is entirely covered with the electrode 12, and the light is reflected by the electrode 12 to improve the light extraction efficiency to the side surface.

The end face of the GaAs substrate 4 is formed by cutting with a cutter when taking out the array 2 from the wafer.
Therefore, the end surface of the substrate 4 is not smooth, and the surface has many irregularities. Due to these irregularities, the light emitted to the side surface of the substrate 4 is scattered and spread. When the resin layer 14 is provided here, the influence of the unevenness of the end surface of the substrate 4 is reduced. For example, if the refractive index of the resin layer 14 is the same as the refractive index of the substrate 4,
The unevenness of the end face is eliminated by the light, and the light goes straight. Ga
The refractive index of As is as high as about 3.5, and it is not easy to find a resin having a refractive index equal to this. However, even if the refractive index is about 1.5, which is smaller than that of the GaAs substrate 4 like silicon resin, but the refractive index is larger than that of air, the substrate 4
The difference in the refractive index between the inside and the outside of the glass is reduced, and the light scattering at the end face is reduced. As a result, it is possible to reduce light scattering due to the unevenness of the end surface of the GaAs substrate 4.

Providing the resin layer 14 improves the efficiency of extracting light from the LED array 2 in addition to reducing the influence of unevenness on the end face. The refractive index of GaAs is n1,
Assuming that the refractive index of air is n2, the transmittance of light from the LED array 2 side to the air is given by equation (1).
However, when the incident angle is 0 degree and the light enters the interface perpendicularly,
The resin layer 14 is not provided. T = [1- (n1-n2) ² / (n1 + n2) ² ] (1) The refractive index n1 of GaAs is about 3.5, the refractive index n2 of air is 1.0, and the transmission by the formula (1) is The rate T is 69%. On the other hand, if a resin layer 14 having a refractive index of n3 is provided in the middle,
The transmittance T of light from the ED array 2 to the air is determined by the equation (2). T = [1- (n1-n3) ² / (n1 + n3) ² ]-[1- (n3-n2) ² / (n3 + n2) ² ] (2) Here, the resin layer 14 is made of silicone resin and its refraction When the rate n3 is 1.5, the transmittance T is about 81%. This means that the light confined in the GaAs substrate 4 can be extracted by interposing the resin layer 14 to reduce the difference in the refractive index at the interface due to the large difference in the refractive index. Here, the transmittance T was improved by about 20%, but this is the case of light that is incident perpendicularly to the interface, and when the incident angle other than 0 degrees is taken into consideration, the transmittance T is improved by about 30% as a whole. To do.

[0018]

Second Embodiment FIG. 3 shows a second embodiment. In the figure, 32 is a new LED array, 34 is a reflective layer provided on the substrate side of the resin layer 14, and 36 is a reflective layer provided on the air side. For the substrate-side reflective layer 34, for example, an electrode having a high reflectance such as Al or Au provided on the substrate 02 is used. For the air-side reflection layer 36, for example, silver paste is used, and the resin layer 14
After forming, the silver paste is applied to form the air side reflection layer 36. With this configuration, the light entering the resin layer 14 travels while being reflected by the two reflective layers 34 and 36, and the resin layer 14 serves as a kind of light guide. As a result, the light extraction efficiency is further improved. In the embodiment of FIG. 3, the resin layer 14 is coated so as to cover the light emitting body, and the air side reflection layer 36 is also provided on the upper portion of the light emitting body so that the light leaked to the main surface side of the light emitting body is exposed to the air side. The light is guided to the lens array 04 while being reflected by the reflective layer 36. As a result, the resin layer 14 and the air-side reflective layer 36 have Ga
It also acts as a light guide for the light leaked to the main surface side of the As substrate 4. The air-side reflective layer 36 is arranged so as not to short-circuit with the electrode 12. Further, the substrate side reflection layer 34 may not be provided.

[0019]

Third Embodiment FIG. 4 shows a third embodiment. In the figure, 42 is a new LED array, 44 is a new diffusion mask layer, 46 is a new electrode, 48 is a light guide, SiO2
And a film of silicon nitride or the like, and the electrode 46 is connected through a hole provided in the light guide 48. The difference from the embodiment of FIG. 3 lies in the light guide 48, in which the light guide 48 covers most of the surface of the impurity implantation part 10 and the electrode 46 is connected to the impurity implantation part 10 through a window provided in a part thereof. Of the light generated by the light emitter, the light that has traveled to the main surface side is confined in the light guide 48 and the diffusion mask layer 44. This is because the surface of the light guide 48 is the electrode 46.
It is because it is covered with and the light is reflected by the electrode 46. In addition, the light guide 48, the diffusion mask layer 44, and the impurity implantation portion
0 and the epitaxial growth portion 6 have a large difference in refractive index, and the light entering the light guide 48 and the diffusion mask layer 44 is confined there. For example, it is assumed that the light guide 48 and the diffusion mask layer 44 have the same refractive index.
In the above formula (1), the transmittance T is symmetrical with respect to n1 and n2. Therefore, light can be confined also on the side of the diffusion mask layer 44 and the light guide 48, which have a smaller refractive index than GaAs. First, there is an electrode 46 between the surrounding air and the light is reflected by the electrode 46 and confined. Ga
Since there is a large difference in the refractive index between the As side and the As side, GaA
The transmittance to the s side is small, and light can be confined on the side of the diffusion mask layer 44 or the light guide 48 having a small refractive index. Here, the light guide 48 is provided in the impurity injection part 1.
This is because the light emitted from the surface of 0 is confined in the light guide 48 and is extracted to the side surface. That is, the light emitted to the surface of the impurity-implanted portion 10 is the strongest, and the light is not returned to the substrate 4.
And the diffusion mask layer 44 leads.

It should be noted that the connection form of the electrodes to the impurity injection portion 10 itself is arbitrary, and for example, the LED array 52 of the modified example of FIG. 5 is used.
You may do like this. In FIG. 5, 54 is a new diffusion mask layer, and 58 is a new light guide. In this modification, the light emitted to the main surface is confined in the right side portion of the diffusion mask layer 54 and the light guide 58, and is guided and extracted while being reflected by the air side reflection layer 36.

[0021]

Fourth Embodiment FIGS. 6 and 7 show a fourth embodiment. In the figure, 62 is a new LED array, 64 is a new diffusion mask layer such as SiO2 or silicon nitride, 66 and 67 are electrodes, and 68 and 70 are impurity implantation portions arranged in two rows.
In this embodiment, the light emitters are arranged in two rows on the main surface of the GaAs substrate 4 while changing the distance from one side surface thereof. Since the light is extracted from the side surface of the LED array 62, even if the light emitters are arranged in two rows, the image forming position of the light on the photoconductor drum or the like not shown does not change. As a result, by arranging the light emitters in two rows, it is possible to easily obtain a high resolution LED array 62 having a resolution of 600 dots / inch, for example. Moreover, in this case, the accuracy of the pattern is the same as that of the LED array of 300 dots / inch. Next, GaA
As the distance from the end surface of the substrate 4 increases, the light from the light emitting body diffuses and enters the resin layer 14, and the intensity of the light decreases. Therefore, the light-emitting area farther from the side surface has a larger light-emitting area, and the area of the impurity injection portion 70 is larger than that of the impurity injection portion 68.

[0022]

Fifth Embodiment FIGS. 8 and 9 show a fifth embodiment. In the figure, 82 is a new LED array, 84 is a new diffusion mask layer, 86 and 87 are electrodes, 88 and 90 are impurity implantation portions arranged in, for example, two rows, and 91 is a new light guide. For the light guide 91, a SiO2 film or a silicon nitride film is used. The difference between the embodiment shown in FIGS. 8 and 9 and the embodiment shown in FIGS. 6 and 7 lies in the connection of the electrode to the impurity implantation portion and the light guide 91. In the embodiment shown in FIGS. The electrodes 86 and 87 are connected to the impurity implantation portions 88 and 90 through the provided small circular holes, and the light to the surfaces of the impurity implantation portions 88 and 90 is confined by the diffusion mask layer 84 and the light guide 91 and extracted from the side surface.

[0023]

Sixth Embodiment FIG. 10 shows a sixth embodiment. In the figure, reference numeral 92 denotes a new LED array, which is the same as the embodiment of FIGS. 6 and 7 except for the arrangement of the resin layer 14 and the air side reflection layer 36. Further, in this embodiment, the resin layer 14 and the air side reflection layer 36 cover the impurity injection portions 68 and 70,
The light emitted to the main surface side of the D array 92 is reflected by the reflective layer 36 to be guided through the resin layer 14 and taken out from the end surface on the right side of the drawing.

[0024]

According to the first aspect of the invention, the side emission type LE is used.
In the D array, the influence when the substrate is cut from the wafer is reduced, and it is possible to prevent the light emitting body from being defective or the output from being varied due to the impact and stress at the time of cutting. Further, according to the invention of claim 1, the diffusion of light due to the unevenness of the end face of the substrate is suppressed. Further, in the invention of claim 1, the difference in the refractive index at the interface is reduced, and the light extraction efficiency from the LED array is improved. Further, in the invention of claim 1, the head width can be shortened when the array is used for the LED head, and the miniaturization of the optical printer is facilitated.

In the invention of claim 2, in addition to these, L
Improve the resolution of the ED array. According to the inventions of claim 3 and claim 4, in addition to the effect of the invention of claim 1,
Further improve the extraction efficiency of light from the array.

[Brief description of drawings]

FIG. 1 is a sectional view of an LED array according to an embodiment.

FIG. 2 is a plan view of an LED array according to an embodiment.

FIG. 3 is a sectional view of an LED array according to a second embodiment.

FIG. 4 is a sectional view of an LED array according to a third embodiment.

FIG. 5 is a cross-sectional view of a modified LED array.

FIG. 6 is a sectional view of an LED array according to a fourth embodiment.

FIG. 7 is a plan view of an LED array according to a fourth embodiment.

FIG. 8 is a sectional view of an LED array of a fifth embodiment.

FIG. 9 is a plan view of an LED array according to a fifth embodiment with a partially cutout portion.

FIG. 10 is a sectional view of an LED array of a sixth embodiment.

[Explanation of symbols]

2, 32, 42, 52, 62, 82 LED array 02 Glass substrate 04 Lens array 4 GaAs substrate 6 Epitaxial growth part 10, 68, 70, 89, 90 Impurity injection part 8, 44, 64, 84 Diffusion mask layer 12, 46 , 66, 67, 86, 87 Electrode 14 Resin layer 34 Substrate side reflection layer 36 Air side reflection layer 48, 58, 91 Light guide

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01L 23/29 23/31 27/15 8934-4M 33/00 N 7376-4M H04N 1/036 A 8721-5C

Claims (4)

[Claims] 1. A large number of light-emitting bodies are arranged on one main surface of a semiconductor substrate at a position spaced from one side surface, and an upper portion of each light-emitting body is covered with an electrode so that light emitted by each light-emitting body is An LED array in which light is emitted from one side of a semiconductor substrate, wherein one side of the semiconductor substrate from which light is emitted is covered with a resin layer having a refractive index higher than that of a surrounding medium. array. 2. A light emitting body arranged at a position spaced from the one side surface in a plurality of rows on one main surface of the semiconductor substrate, and a row having a larger distance from the one side surface. The luminous intensity of the luminous body is set to be larger than the luminous intensity of the luminous body of the row whose distance from one side is smaller,
The LED array according to claim 1. 3. The LED array according to claim 1, wherein a reflective layer is provided on the surface of the resin layer having a high refractive index. 4. A resin layer covering one side surface of the semiconductor substrate covers at least a part of one main surface of the semiconductor substrate, and a reflection layer is provided on a surface of the resin layer covering one main surface of the semiconductor substrate. The L according to claim 1, wherein the L is provided.
ED array.