JPH11220180A - LED array head - Google Patents

Abstract

(57) [Problem] To provide a structure that can suppress the adverse effect of side light from the side surface of an LED light-emitting unit having a protruding structure with a structure that is simple to manufacture. SOLUTION: A light absorbing material 3 is buried between LED light emitting portions 2 having a protruding structure. Thereby, the side surface 2 of the LED light emitting unit 2
Even if side light P1 is emitted from b in the array direction in the substrate surface, the light is absorbed and attenuated in the light absorbing material 3 embedded between the LED light emitting parts 2, and has almost no effect even when it goes outside. Becomes Here, the step of embedding the light absorbing material 3 does not require the use of the photolithography method and does not require the alignment of the photomask. As a result, the adverse effect of the side light P1 can be suppressed with a structure that can be easily manufactured. it can.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED array head used as a light source for an LED array printer.

[0002]

2. Description of the Related Art As a printer utilizing an electrophotographic process, an LED array printer using an LED array head as a light source has an advantage that it is more resistant to deformation of an optical system due to vibration and heat than a laser raster type laser printer.

FIG. 4 schematically shows the basic structure of such an LED array printer.
The light emitted from 0 is condensed on the surface of a drum-shaped photosensitive member 102 via a 1: 1 imaging optical system 101 to expose the photosensitive surface to form an electrostatic latent image.

As an LED array head 100 used in such an LED array printer, for example, FIG.
As shown in the figure, an inexpensive silicon substrate 1 is used as a head substrate.
An LED light emitting portion 111 protruding from the surface of the silicon substrate 110 is formed in an array by growing a compound semiconductor on the surface of the silicon substrate 110 (see, for example, JP-A-9-45555). . Such L
In the ED array head 100, the silicon substrate 110
Each LED light emitting unit 1 composed of a plurality of semiconductor layers electrically connected to the upper individual electrode 112 and the common electrode 113
Light emitted from the light source 11 is extracted in the front and back directions on the paper surface, and, for example, is transferred to the photosensitive member 102 via the above-described 1 × imaging optical system 101.
Imaged on top.

At this time, since the LED light emitting portion 111 protruding from the silicon substrate 110 is radiated from the side surface also as the side light in the in-plane direction of the substrate, the adjacent LED light emitting portion 111 and the individual electrode 112 are emitted. And common electrode 11
3, or reflected by a bonding wire (not shown) or the like to the individual electrode 112, and irradiates the photosensitive member 102 as a light emission pattern of an undesirable noise component as if each of those points is a light emission point. Will be done. A latent image is also formed on a portion exposed to the light emission pattern of such a noise component, and is transferred to a paper as a toner image after development, which causes image quality deterioration such as line width unevenness on an output image. Becomes

For this reason, as a structure for removing the influence of undesired side light radiated from the LED light-emitting portion having a protruding structure, a structure in which a light-shielding film is provided on the side surface of the LED light-emitting portion has been proposed. JP-A-6-252440
Has been proposed. An example of the structure will be briefly described with reference to FIG. FIG. 6 shows only one LED light emitting portion 111, which is formed in a protruding shape by growing and stacking four semiconductor layers 114a, 114b, 114c, 114d on a silicon substrate 110, and is formed on the upper surface side. When an electric current flows between the formed individual electrode 112 and the common electrode 113 formed on the lower surface side of the silicon substrate 110, the LED light emitting unit 111 emits light. Here, the originally desired emitted light is light extracted from the upper surface 111a of the LED light emitting unit 111,
1b also emits light, so that a reflective film (light-shielding film) 116 is formed via a protective film 115 to suppress side light.
It is a structure called.

[0007]

With respect to such a light-shielding structure, when the reflection film 116 has a structure that transmits a part of the light, even if the transmitted light is weak, the exposure pattern on the surface of the photoreceptor 102 is reduced. Therefore, it is necessary to use a material that is sufficiently light-shielded even if it is a thin film, specifically a metal material, instead of a transparent material such as an oxide.

Here, as a method of forming the metal reflection film, a method having anisotropy in a film forming direction, such as a vapor deposition method and a sputtering method, is generally used. Therefore, L to be formed
If the side surface 111b of the ED light emitting unit 111 is vertical or has an overhang in the shape of an inverted mesa (in the case of FIG.
The side surface shape of the light emitting portion 111 in the array direction is a U-shaped constriction shape or an inverted mesa shape), and a film forming process such as tilting and accumulating the substrate has to be adopted, and the LED array head is manufactured. There is a problem that the process becomes complicated. In addition, it is necessary to insulate the individual electrodes and the light-shielding film with an insulating film in order to avoid a short circuit between the electrodes due to a metal serving as a conductor, which may increase the number of steps.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an LED array head capable of suppressing an adverse effect due to side light from a side surface of an LED light emitting portion having a protruding structure with a structure that is simple to manufacture.

[0010]

According to the first aspect of the present invention,
In an LED array head in which a plurality of LED light emitting portions are formed in an array so as to protrude from a head substrate, each LE
A light absorbing material is embedded between the D light emitting units. Therefore, even if side light is emitted from the side surface of the LED light emitting portion of the protruding structure in the array direction in the substrate surface, the light is absorbed and attenuated in the light absorbing material embedded between the LED light emitting portions, so that it is externally emitted. Even if the light exits, the light has almost no effect, and the adverse effect of the side light can be suppressed with a structure that is easy to manufacture. Here, as the light-absorbing material, a resin containing a light-absorbing material, such as a resin material obtained by forming a metal oxide used as a light-shielding adhesive into a filler or a resin material in which carbon black is dispersed. Can be used.

According to a second aspect of the present invention, in an LED array head in which a plurality of LED light emitting portions are formed in an array so as to protrude from a head substrate, a high refractive index material is embedded between each LED light emitting portion. . Therefore, an LED having a protruding structure
Even if side light is emitted from the side surface of the light emitting unit in the array direction in the substrate surface, the light will be emitted into the high refractive index material embedded between the LED light emitting units, and external air and high refractive index will be emitted. Light incident within a total reflection angle determined by the refractive index with the material is totally reflected without being extracted from the surface to the outside, is returned to the substrate side, and is absorbed. In addition, if side light incident at an angle equal to or greater than the total reflection angle with respect to the interface between the high refractive index material and the external air layer is radiated to the outside from the interface, according to Snell's law,
Since the light is largely refracted at this interface, it is hardly emitted in the vertical direction. That is, since the side light is mainly emitted in the in-plane direction of the substrate, the angle of incidence on the interface between the high refractive index material and the external air layer is small, and it can be expected that most side light can be totally reflected. As a result, adverse effects due to side light can be suppressed with a structure that is simple to manufacture. Here, as the high refractive index material, a resin having a refractive index of about 1.7 is easily available if it is a resin, and an inorganic material having a refractive index of 2 or more is often used. You can choose. In addition, since light absorption is not essential, there are a wide range of materials available for embedding between the LED light emitting units. However, if the high refractive index material having the light absorbing property is used, the effect according to the first aspect of the present invention can be obtained, so that the light shielding effect against the side light is improved.

According to a third aspect of the present invention, in the LED array head in which a plurality of LED light emitting portions are formed in an array by projecting from the head substrate, the space between the LED light emitting portions is buried flat by an embedding material. A light-shielding film is formed on the embedding material between the LED light emitting units. Therefore, the projecting structure LE
D When side light is emitted from the side surface of the light-emitting portion in the array direction in the substrate surface, the light is incident on the embedding material and is emitted toward the outside air layer, but the light is blocked on the embedding layer. Since the film is formed, the light is shielded by this light-shielding film and is not emitted to the outside. Here, since the light-shielding film may be formed on the flattened surface together with the LED light-emitting portion by the embedding material,
The formation process is easier than in the case where the light-shielding film is formed while the D light-emitting portion is in a protruding state. Therefore, adverse effects due to side light can be suppressed with a structure that is simple to manufacture. Further, since the light-shielding film exerts a light-shielding function, the material of the embedding material may be a transparent material or the like, and may be appropriately selected.

[0013]

FIG. 1 shows a first embodiment of the present invention.
It will be described based on. In the LED array head of the present embodiment, a GaAs substrate 1 is used as a head substrate. A semiconductor layer is formed on the surface of such a GaAs substrate 1, and a plurality of LED light emitting portions 2 are formed in an array as a protruding structure by appropriately etching the pattern (the paper surface, the horizontal direction is the array direction). Is)
(See FIG. 1A). Aluminum oxide is dispersed over the entire surface of the GaAs substrate 1 having such an LED light emitting portion 2 and an epoxy resin exhibiting a light-shielding property with respect to visible light is applied as a light absorbing material 3 and flattened (FIG. b)). By etching back such a light absorbing material 3 by reactive ion etching, the light absorbing material 3 is removed so as to be flush with the upper surface 2a of the LED light emitting unit 2 (see FIG. 1C). Thus, a structure in which the space between the LED light emitting units 2 is embedded with the light absorbing material 3 is obtained. Thereafter, formation of individual electrodes on the upper surface 2a of each LED light emitting unit 2 and the GaAs substrate 1
The LED array head is completed through processes such as formation of a common electrode on the back surface.

According to such a configuration, when a certain LED light emitting section 2 emits light, the light is emitted from the upper surface 2a toward the photosensitive member surface. At this time, the side surface 2 of the LED light emitting unit 2
There is also side light P1 emitted from b, but such side light P1 enters the light absorbing material 3 embedded between the LED light emitting units 2 and is absorbed and attenuated. Therefore, such side light P1 is prevented from being emitted in the direction perpendicular to the substrate surface and directed toward the photoconductor surface, and adverse effects due to the side light P1 are suppressed. With the light absorbing material 3 performing such a function, L
In the step of embedding the space between the ED light-emitting portions 2, it is not necessary to use a photolithography method, and the application step is sufficient.

A second embodiment of the present invention will be described with reference to FIG. The same parts as those described in the above embodiment are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments). In the LED array head of the present embodiment, the light absorbing material 3
Instead, polyimide 4 is embedded as a high refractive index material. In this case, the basic manufacturing method is the same as that of FIG. 1, but after the polyimide 4 is applied, the flat shape as shown in FIG. 2 is obtained by etch back by dry etching.

According to such a configuration, when a certain LED light emitting section 2 emits light, it is radiated from the upper surface 2a toward the photosensitive member surface. At this time, the side surface 2 of the LED light emitting unit 2
b is also present and enters the polyimide 4 embedded between the LED light-emitting portions 2, but the side light entering the interface between the polyimide 4 and the external air layer at a shallower angle than the total reflection angle is P2 Is totally reflected at the interface as shown by
Eventually, it will be reflected to the GaAs substrate 1 side,
It does not exit to the outside. Also, even if there is side light incident on the interface between the polyimide 4 and the external air layer at an angle deeper than the total reflection angle, since the polyimide 4 has a higher refractive index than the air layer, P4 is emitted from the interface. Since the light is largely bent in the in-plane direction of the substrate as shown by (2), the light hardly reaches the surface of the photoreceptor, and the light has substantially no influence. In particular, since the side light from the LED light emitting unit 2 is mainly radiated in the in-plane direction of the substrate, the angle of incidence on the interface between the polyimide 4 and the external air layer is shallow, so that most of the side light can be totally reflected. Can be expected. In the step of embedding the space between the LED light emitting portions 2 with the polyimide 4 having such a function, it is not necessary to use a photolithography method and the application step is sufficient, so that alignment of a photomask is not required, and the objective is achieved with a structure that is easy to manufacture. it can.

A third embodiment of the present invention will be described with reference to FIG. In the LED array head of the present embodiment,
Ga in which the LED light emitting unit 2 is formed in an array with a protruding structure
An acrylic resist 5 which is an embedding material made of a transparent material is applied to the entire surface of the As substrate 1 and planarized (FIG. 3).
(A)), a chromium film 6 is formed as a light-shielding film on the surface of the acrylic resist 5, and each L is etched.
The chromium film 6 directly above the ED light emitting unit 2 is selectively removed (FIG. 3B). That is, the chromium film 6 is formed only on the acrylic resist 5 between the LED light emitting units 2.

According to such a configuration, when a certain LED light emitting section 2 emits light, the light is emitted from the upper surface 2a toward the photosensitive member surface as indicated by P5. At this time, since the acrylic resist 5 is transparent, there is no problem even if the acrylic resist 5 exists on the upper surface 2a. This is because the acrylic resist 5 is formed by dry etching in the manufacturing process.
Does not need to be etched back, and the heating of the GaAs substrate 1 accompanying dry etching can be generally avoided. In addition, a material having relatively low heat resistance can be selected as the embedding material. However, when using a non-transparent embedding material, it may be formed into a flat shape so as to be flush with the upper surface 2a of the LED light emitting section 2. Also, some L
The side light radiated from the side surface 2b of the ED light-emitting portion 2 along with the light emission of the ED light-emitting portion 2 enters the acrylic-based resist 5 as it is and tries to emit the light to the outside. Is shielded from light by the chrome film 6, and is reflected by the chrome film 6 as shown by P4, returned to the substrate side, and does not go outside. Therefore, with a structure that is simple to manufacture, it is possible to suppress the adverse effect of the side light on the photoconductor surface side.

[0019]

According to the first aspect of the invention, since the light absorbing material is embedded between the LED light emitting portions of the projecting structure, side light is emitted from the side surface of the LED light emitting portion in the array direction in the substrate surface. Even if it is radiated, it can be absorbed and attenuated in the light absorbing material embedded between the LED light emitting parts, so that it can be made light that has almost no effect even when it goes outside. It can be suppressed with a simple structure.

According to the second aspect of the present invention, since the high refractive index material is embedded between the LED light emitting portions of the projecting structure, side light is emitted from the side surface of the LED light emitting portion in the array direction in the substrate surface. Even if it is done, it will be radiated into the high refractive index material embedded between the LED light emitting parts, and the light incident within the total reflection angle determined by the refractive index of the external air and the high refractive index material It is totally reflected without being extracted from the surface to the outside, is returned to the substrate side and is absorbed, and the side light incident at an angle equal to or greater than the total reflection angle is radiated to the outside from the surface of the high refractive index material, but according to Snell's law, The light can be largely refracted at the surface, so that the side light does not substantially adversely affect the light. Thus, the adverse influence of the side light can be suppressed with a structure that is easy to manufacture.

According to the third aspect of the present invention, the space between the LED light emitting portions of the protruding structure is buried flat by the embedding material, and the light shielding film is formed on the embedding material between the LED light emitting portions. When side light is emitted from the side surface of the LED light emitting portion in the array direction in the substrate surface, the light is incident on the embedding material and is emitted toward the outside air layer, but the light is blocked on the embedding layer. The light can be prevented from being emitted to the outside by blocking the light with the film. In particular, since the light-blocking film may be formed on the flattened surface together with the LED light-emitting portions by the embedding material, each LED light-emitting portion remains in a protruding state. The formation process can be facilitated as compared with the case where the light shielding film is formed, so that the adverse effect due to side light can be suppressed with a structure that is simple to manufacture.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a first embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a schematic sectional view showing a second embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a third embodiment of the present invention in the order of manufacturing steps.

FIG. 4 is a schematic side view showing a basic configuration of a general LED array printer.

FIG. 5 is a plan view showing a configuration example of a conventional LED array head.

FIG. 6 is a cross-sectional view showing a conventional light-shielding film structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Head board 2 LED light emission part 2b Side surface 3 Light absorption material 4 High refractive index material 5 Embedding agent 6 Light shielding film

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B41J 2/455

Claims (3)

[Claims] A plurality of LEs projecting from a head substrate;
An LED array head in which D light emitting units are formed in an array, wherein a light absorbing material is embedded between the LED light emitting units. 2. A plurality of LEs protruding from a head substrate.
An LED array head in which D light emitting portions are formed in an array, wherein a high refractive index material is embedded between each LED light emitting portion. 3. A plurality of LEs protruding from the head substrate.
In the LED array head in which the D light emitting portions are formed in an array, it is required that the space between each LED light emitting portion is buried flat by an embedding material, and that the light shielding film is formed on the embedding material between each LED light emitting portion. Characteristic LED array head.