JP2001024231A - Light emitting element array device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make even the quantities of light rays outputted from a rod lens array by making uniform the light reflectivity distributions on the surfaces of chips on which light emitting arrays are formed. SOLUTION: In a light emitting element array device which is composed of a plurality of chips on which light emitting elements are one-dimensionally arranged, metallic wiring is formed, and the light rays from the light emitting elements are led out through a rod lens array; a low-reflectance film is provided on a high-reflectance area when the reflectance is not uniformly distributed on the surfaces of the chips. The low-reflectance film can be constituted of a light absorbing film 44.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device array device, and more particularly to a light emitting device array device used for an optical printer head.

[0002]

2. Description of the Related Art FIG. 1 shows the principle of an optical printer having an optical printer head. On the surface of the cylindrical photosensitive drum 2,
Photoconductive materials (photoconductors) such as amorphous Si are manufactured. This drum rotates at the speed of the print. The surface of the photosensitive member of the rotating drum is uniformly charged by the charger 4. Then, light of the dot image to be printed is irradiated on the photoreceptor by the optical printer head 6 to neutralize the charging at the place where the light is applied. Subsequently, toner is applied to the photoconductor by the developing device 8 according to the charged state on the photoconductor. Then, the transfer device 10 transfers the toner onto the paper 14 sent from the cassette 12. The paper is fixed by applying heat or the like in a fixing device 16 and sent to a stacker 18. On the other hand, the drum on which the transfer has been completed is the erase lamp 2
At 0, the charge is neutralized over the entire surface, and the remaining toner is removed by the cleaner 22.

FIG. 2 shows the structure of the optical printer head 6.
The optical printer head includes a light emitting element array 24 and a rod lens array 26, and the lens focuses on the photosensitive drum 2.

[0004]

When the light-emitting element array is composed of light-emitting elements arranged in a line, if the light-emitting amount of each light-emitting element is the same, an image in the light-emitting element arrangement direction obtained by an optical printer is obtained. No unevenness should occur in the density distribution. However, unevenness may occur depending on the structure of the light emitting element array.

[0005] The inventors of the present application have investigated the cause and found the following. That is, when light from the light emitting element array 24 is to be extracted through the rod lens array 26, part of the light from the light emitting element is reflected by the lens surface of the rod lens because the transmittance of the rod lens is not high, The surface of the chip on which the light emitting element array is formed is irradiated. Since the metal wiring on the chip surface has a high light reflectance, the light is reflected by the metal wiring. It has been found that the reflected light again enters the rod lens, which causes unevenness in the amount of light on the photosensitive drum 2, that is, unevenness in image density.

As described above, the light extracted from the rod lens is not only the light output from the light emitting point of the light emitting element, but also the light reflected by the lens surface of the rod lens and further reflected by the metal wiring on the chip surface. Are superimposed.

[0007] Such image density unevenness occurs when the repetition cycle of the metal wiring coincides with the repetition cycle of the light emitting point.
It was found that it was not noticeable, but when it was different from the repetition period of the light emitting point, unevenness was noticeable.

As an example of the case where the repetition period of the metal wiring coincides with the repetition period of the light emitting point, for example, one light emitting point has one bonding pad for connection to an external drive circuit for driving it. There is a light emitting element array provided as such.

As an example of the case where the repetition period of the metal wiring is different from the repetition period of the light emitting point, there is a self-scanning light emitting element array device already proposed by the present applicant (Japanese Patent Laid-Open No. Hei 2-263668). reference). This self-scanning light-emitting element array device is a self-scanning light-emitting element array device having a structure in which a switch element array is used as a shift register and is separated from the light-emitting element array.

FIG. 3 shows an equivalent circuit diagram of the self-scanning light-emitting element array device. This self-scanning light emitting element array device includes switch element arrays T (-1) to T (2) constituting a shift register, and a light emitting element array L for writing.
(-1) to L (2). The gate electrodes of adjacent switch elements are connected using a diode. Each anode electrode of the switch element is alternately connected to transfer clock lines φ ₁ and φ ₂ . The gate electrodes G _{−1 to} G ₁ of the switch element are also connected to the gate of the light emitting element for writing. The write signal S _in is applied to the anode electrode of the light emitting element for writing. The gate electrode of the first-stage switching element, a start pulse phi _s is applied to the switching element is turned on.

Assuming now that the switching element T (0) is in the ON state, the voltage of the gate electrode G ₀ is equal to the power supply voltage V _GK
(Here, 5 volts), and becomes almost zero volts. Therefore, the voltage of the write signal S _in becomes PN
If the junction diffusion potential (about 1 volt) or higher, the light emitting element L (0) can be in a light emitting state.

[0012] In contrast, the gate electrode G _-1 is about 5 volts, the gate electrode G ₁ is about 1 volt (diode D0
In the forward rise voltage). Therefore, the light emitting element L
The write voltage of (-1) is about 6 volts, and the light emitting element L
The write voltage of (1) is about 2 volts. from now on,
Voltage of the write signal S _in which can write only in the light emitting element L (0) is a range of 1-2 volts. Light emitting element L (0)
Is turned on, that is, enters the light emitting state, the write signal S _in
Since the line voltage is fixed at about 1 volt, an error that another light emitting element is selected can be prevented.

The light emission intensity is determined by the amount of current flowing _{in the} write signal _Sin, and an image can be written at an arbitrary intensity. Further, in order to transfer the light emitting state to the next light emitting element, it is necessary to once lower the voltage of the write signal S _in line to zero volt and to temporarily turn off the light emitting element which emits light.

When such a light emitting device array device is applied to an optical printer or the like, the light emitting device array device is formed in the form of one light emitting chip in which a certain number of switch elements and light emitting devices are integrated, and this light emitting chip is used. For example, they are arranged in a line to form a linear light source of a predetermined size.

FIG. 4 shows an overall image of one light emitting chip.
In one chip, 128 switch element arrays T
(1) to T (128) and 128 light emitting element arrays L
(1) to L (128) are arranged, and the switch element array
During b, φ_s, Φ₁, Φ_Two, V _GK, S_inBondin for
Pad is arranged.

FIG. 5 is a layout diagram of a specific wiring pattern of the light emitting chip of FIG. In the figure, 28 indicates a bonding pad. Since the metal wiring including such a bonding pad is different from the repetition period of the light emitting unit 30, unevenness in image density is conspicuous.

FIG. 6 shows an image density distribution by an optical printer head using the light emitting element array device constituted by the light emitting chips shown in FIG. In FIG. 6, the horizontal axis represents the position (mm) of the light emitting element array in the arrangement direction, and the vertical axis represents the image density. The unevenness of the image density shown in FIG.
It can be seen that it is repeated at a period of m. This cycle is
It matches the arrangement cycle of the bonding pads. That is, it was found that unevenness in image density occurred due to light reflected by the bonding pad.

An object of the present invention is to provide a light emitting element in which the distribution of light reflectance on the surface of a chip on which a light emitting element array is formed is uniform, so that the amount of light output from a rod lens array is not uneven. An object of the present invention is to provide an array device.

[0019]

With respect to an optical printer head for a color printer, the visual chromaticity spatial frequency characteristic has a resolution of 1/5 or less of the light and dark frequency characteristic (Television and Image Engineering Handbook, p. 50). Fig. 1.76 /
Edited by the Institute of Television Engineers of Japan (S. 55)). For this reason, it is considered that the conspicuous unevenness in the amount of light due to the reflected light is determined by the reflected light in a region surrounded by a square whose one side is five times the light emitting element array light emitting point pitch Λ.

In FIG. 5, A and B indicate square areas each having a side of five times the light emitting point pitch Λ. A indicates a region in the metal wiring portion of the switch element array, and B indicates a square region in the metal wiring portion including the bonding pad 28.

Since the region B has many portions without metal wiring,
The reflectance is lower than that of the area A. Therefore, in the present invention, the reflectance of the area A is substantially equal to the reflectance of the area B.
The region A is hidden by a light absorbing film or an anti-reflection film.

According to the present invention, there is provided a light-emitting element array device comprising a plurality of chips in which light-emitting elements are arranged one-dimensionally or two-dimensionally and on which metal wiring is formed, and in which light from the light-emitting elements is extracted through a rod lens array. A light-emitting element array device characterized in that, when the reflectance on the chip surface is not uniformly distributed, a low-reflection film is provided on a high-reflectance region to make it uniform.

The low reflection film is preferably a light absorption film or an antireflection film.

[0024]

Embodiments of the present invention will be described below.

[0025]

First Embodiment FIG. 7 is a plan view of a light emitting element array device 32 according to a first embodiment, and FIG. 8 is a sectional view taken along line XY of FIG. This light-emitting element array device 32 has a light-absorbing film provided on the surface of the self-scanning light-emitting element array device shown in FIG.

The light emitting element array device 32 is made of GaAs.
A light emitting element array main body having a metal wiring 40 formed on a substrate 34 via an epitaxial film (pnpn structure) 36 and an interlayer insulating film 38 is provided. On the light emitting element array main body, the bonding pad 28 and the light emitting section 3
The light absorbing film 44 is formed on the entire surface except for the area above zero. Light incident from the surface of the light absorbing film 44 is
Reflects at 0 and emerges again from the surface. Therefore, the light passes through an optical path having a thickness twice that of the light absorbing film 44. The absorptance during this time lowers the overall reflectivity of the area A to be equal to the reflectivity of the area B. For example, assuming that the reflectance of the area B where the light absorbing film is not provided is 0.8 and the reflectance of the area A is 0.6, the light is absorbed so that about 25% is absorbed by the reciprocating movement of the light absorbing film. Good.

As an example, a polyimide film having a thickness of 1 μm was formed as a light absorbing film. The polyimide used was RN-8
12 (Nissan Chemical), 30 sec at 3430 rpm
And baked at 180 ° C. for 30 minutes. A photoresist 1400-27 (shipley) was applied thereto, exposed to light, and resist development and polyimide etching were simultaneously performed using an MF319 (shipley) developer. The transmittance of the resulting film at an emission wavelength of 780 nm was 0.86. As described above, light has a thickness of 2
Since the light passes through the double optical path, the absorption is 0.86 ² = 0.75, and the substantial reflectance of the region A provided with the light absorbing film is 0.8 × (0.86) ² = 0.59. Becomes almost 0.6
Is equal to

As the material of the light absorbing film, in addition to the above, a photo-processable resin in which carbon particles are dispersed (Color Mosaic System (trade name) manufactured by Fuji Photo), Cr-SiO or Au-
A cermet such as SiO or a high-resistance amorphous silicon thin film may be used.

[0029]

Second Embodiment FIG. 9 is a plan view of a light emitting element array device 46 according to a second embodiment, and FIG. 10 is a sectional view taken along line XY of FIG. FIG. 10 also includes an enlarged view of the light emitting unit. This light emitting element array device 42 is obtained by providing an antireflection film on the surface of the self-scanning light emitting element array device shown in FIG.

In the light emitting element array device 46, as in the first embodiment, an epitaxial film (pnpn structure) 36 and an interlayer insulating film 38 are formed on a GaAs substrate 34.
The light-emitting element array main body on which the metal wiring 40 is formed is provided. An anti-reflection film 48 is formed on the entire surface of the light-emitting element array body except on the bonding pads 28.

When the thickness of the interlayer insulating film 38 is t ₁ , the thickness of the anti-reflection film 48 is t ₂ , and the interlayer insulating film and the anti-reflection film are formed of the same SiO ₂ , light emitted from the light emitting section 30 is obtained. Is t ₁ + t ₂ , and the light thickness reflected by the chip is t ₂ . That is, t ₁ + t
₂ can be independently set to the maximum transmittance, and t ₂ can be independently set to the minimum reflectance. The condition of the transmittance maximum is

[0032]

(Equation 1)

The condition for the minimum reflectance is approximately

[0034]

(Equation 2)

Is as follows. Where n _S is the refractive index of SiO ₂ ,
λ is the emission wavelength.

Now, assuming that the refractive index n _{S of} SiO ₂ is 1.46 and the emission wavelength λ is 780 nm, when N = 3,
t ₁ + t ₂ = 670 nm, and when M = 1, t ₂ = 134 nm. According to the simulation, the reflectivity of the antireflection film 48 at this thickness is about 91% when no antireflection film is provided.

The reflectivity of the area A in FIG.
Is about 0.8, the substantial reflectance of the area A where the antireflection film 48 is provided is 0.8 × 0.91 =
It was 0.73, which was close to 0.6.

It is preferable that the thickness of the antireflection film be selected within ± 20% of the thickness at which the reflectivity is minimized.

As another material of the antireflection film, SiO 2_Two
Besides, SiN, Ta_TwoO_Five, Al _TwoO_Three, TiO_TwoTo
Can be used. Anti-reflective coatings are better than these materials
Single-layer film, or multiple layers combining these materials
It can be a membrane.

In each of the embodiments described above, the self-scanning light-emitting element array device has been described. However, the present invention is not limited to the self-scanning light-emitting element array device. It is apparent that the arranged light emitting element array can be applied to a light emitting element array device in which reflected light from metal wiring causes unevenness in the amount of light emitted from a rod lens.

[0041]

According to the present invention, since the film for lowering the reflection of the metal wiring is provided on the metal wiring, the surface reflection distribution of the chip can be effectively reduced, and the adverse effect on the image due to the chip surface reflection can be reduced. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of an optical printer including an optical printer head.

FIG. 2 is a diagram illustrating a structure of an optical printer head.

FIG. 3 is a diagram showing an equivalent circuit of a self-scanning light-emitting element array device.

FIG. 4 is a diagram showing an overall image of a light emitting chip.

FIG. 5 is a diagram showing a specific layout of a light emitting chip.

6 is a diagram showing an image density distribution by an optical printer head using a light emitting element array device constituted by the light emitting chips shown in FIG.

FIG. 7 is a plan view of the light emitting element array device according to the first embodiment.

FIG. 8 is a sectional view taken along line XY of FIG. 7;

FIG. 9 is a plan view of a light emitting element array device according to a second embodiment.

FIG. 10 is a sectional view taken along line XY of FIG. 9;

[Explanation of symbols]

 28 Bonding pad 30 Light emitting section 32, 46 Light emitting element array device 34 GaAs substrate 36 Epitaxial film 38 Interlayer insulating film 40 Metal wiring 44 Light absorbing film 48 Antireflection film

Claims (6)

[Claims] 1. A light-emitting element array device comprising a plurality of chips in which light-emitting elements are arranged one-dimensionally or two-dimensionally and on which metal wiring is formed, wherein light from the light-emitting elements is extracted via a rod lens array. A light-emitting element array device characterized in that, when the reflectance on the chip surface is not uniformly distributed, a low-reflection film is provided on a high-reflectance region to make it uniform. 2. The light-emitting element array device according to claim 1, wherein said low-reflection film is a light-absorbing film. 3. The light-emitting element array device according to claim 2, wherein said light-absorbing film is made of a photo-processable resin in which carbon particles are dispersed, polyimide, cermet, or amorphous silicon. 4. The light-emitting element array device according to claim 1, wherein said low-reflection film is an anti-reflection film. 5. The antireflection film is made of SiO ₂ , SiN, Ta.
_5. The light emitting element array device according to claim 4, comprising a single layer film of ₂ O ₅ , Al ₂ O ₃ , TiO ₂ or a multilayer film of these. 6. The light emitting element array device according to claim 1, wherein a plurality of switch elements each having a control electrode of a threshold voltage or a threshold current for a switching operation are arranged, and the control electrode of each switch element is located near the switch elements. Connecting to a control electrode of at least one switch element via a connection resistor or an electrically unidirectional electric element, connecting a power supply line to a control electrode of each switch element via a load resistor, and A switch element array formed by connecting a clock pulse line to each switch element; and a light emitting element array in which a plurality of light emitting elements having a control electrode for a threshold voltage or a threshold current for a light emitting operation are arranged. Each control electrode of the light emitting element array is connected to the control electrode of the switch element by electrical means, and a current for light emission is supplied to each light emitting element. Light-emitting element array according to claim 1, characterized in that it is a self-scanning light-emitting device provided with a line for.