JP2807910B2 - Light emitting element array - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light-emitting element array including a plurality of light-emitting elements.

[Conventional technology]

Conventionally known optical printers, particularly optical printers using LED arrays (hereinafter referred to as LED printers)
This will be described with reference to FIGS.

As shown in FIG. 5, a photoconductive photoreceptor 58 is formed on the surface of a cylindrical photosensitive drum 51 by amorphous silicon or the like. The drum 51 rotates at a rotation speed corresponding to the printing speed.

First, the photoreceptor surface 58 of the drum 51 is uniformly charged by the charger 57. Next, the light output from the LED (light emitting element) array 62 in which the LED corresponding to the image information is turned on is imaged on the photosensitive member surface 58 of the drum 51 by the rod lens array 63. Then, the charge due to the charge is neutralized in the image forming portion of the light, and the charge state of the photosensitive member surface 58 changes according to the image information. Thus, a pattern corresponding to the image information is formed on the photoreceptor surface 58.

Next, the developing device 60 causes the toner to adhere to the photoreceptor surface 58 in accordance with the charged state of the pattern. Then, the toner is transferred to the sheet fed from the cassette 61 by the transfer unit 52. Next, the sheet on which the toner is transferred is heated by a fixing device 53 to fix the toner, and then sent to the stacker 54.

On the other hand, the residual toner is removed by the cleaning device 56 from the photosensitive drum 51 after the transfer, and the charging of the photosensitive member surface 58 is completely neutralized by the erase lamp 55 to prepare for the next operation. As described above, the image information can be transferred to the paper by the LED printer.

FIG. 6 shows a positional relationship of the LED (light emitting element) array 62 with respect to the rod lens array 63 and the photosensitive drum 51. The horizontally elongated rod lens array 63 is disposed substantially at right angles to the tangent plane of the photosensitive drum 51 and substantially parallel to the photosensitive member surface 58. The LED array 62 in which a plurality of minute light emitting elements are arranged in a line is arranged so that light from the LED array 62 is incident on the rod lens array 63 via the rod lens array 63.

The LED array 62 includes a driving IC provided outside the
This drive IC generates a light emission signal to each light emitting element. FIG. 7 shows an equivalent circuit including such an LED array and a driving IC.

Usually, 64 or 128 light emitting elements 103, which are diodes having an anode and a cathode, are arranged side by side and integrated to form a light emitting element array chip 102. Then, the light emitting element array is configured by arranging the light emitting element array chips 102 by a size necessary for printing on the photosensitive drum.

The driving IC 101 includes a shift register 101a and a latch 101b.
The latch 101b and the anode of the light emitting element 103 are connected so that a current as a light emitting signal from the latch 101b flows through each light emitting element 103. Further, the cathode of the other pole of each light emitting element 103 is grounded and configured as a common electrode.

FIG. 8 shows the actual arrangement of the light emitting element array chip 102 and the driving IC 101. In the light-emitting element array chip 102, the light-emitting areas 103a of the respective light-emitting elements are formed in a substantially square plane, and these light-emitting areas 103a are arranged in a row in the vicinity of the center. Driving ICs 101 having electrodes 101c are arranged on both sides of the column at positions away from the column.

Also, for the actual connection between each anode of the light emitting element 103 and the electrode 101c of the driving IC 101, a light emitting element array chip
The necessary number of electrodes 104 provided on 102 are arranged on both sides of the light emitting element for each light emitting element. These electrodes 104
Are connected to the electrodes 101c by bonding wires 105, respectively.

Since these electrodes 104 are provided on both sides with respect to each light emitting region 103a, the electrodes 104 correspond to the arrangement pitch of the light emitting regions 103a.
The arrangement pitch of 104 is doubled. Therefore, the arrangement pitch of the electrodes 104 can be reduced, and the width of the electrodes 104 with respect to the light emitting region 103a can be increased.

As a mounting technology for connecting between the electrode 104 and the electrode 101c, a wire bonding method is generally used. According to the arrangement of the electrodes 104 shown in FIG. 8, the light emitting elements can be arranged up to half the limit pitch at which wire bonding can be actually performed.

Accordingly, since the density of the arrangement of the light emitting elements can be approximately doubled, the resolution of the light emitting element array can be increased, and the resolution of the LED printer using such a light emitting element array can be increased.

[Problems to be solved by the invention]

However, according to the arrangement example shown in FIG.
500DPI (dot / inch) is the limit at the arrangement pitch of 3a. This pitch is determined by the limit pitch of the wire bonding method.
A pitch of 104 corresponds to about 100 μm.

Since it is substantially impossible to set such an arrangement pitch to 500 DPI or more due to the above-described restrictions on mounting technology, it is not possible to arrange light emitting elements in a light emitting element array at a higher density. Therefore, the resolution of the light emitting element array could not be increased more than before.

An object of the present invention is to achieve high resolution, low cost, and high reliability of a light emitting element array by reducing the number of electrodes required to be provided in the light emitting element array and arranging light emitting elements at high density. It is in.

[Means for solving the problem]

In order to achieve the above object, a light emitting element of the present invention has a third electrode as a common electrode, and when a control signal is supplied between the first electrode and the second electrode, A plurality of light-emitting element blocks each including at least two light-emitting elements capable of emitting light by flowing a main current between one electrode and the third electrode are provided, and light-emitting portions of the light-emitting elements are arranged in a row. Each light emitting element of the light emitting element block has a first electrode in common and supplies a first signal to one of the common first electrodes, and the light emitting element block corresponds to the number of light emitting elements of the block. A plurality of the light emitting element blocks, the second electrodes of each of the light emitting element blocks are connected to each other over the plurality of light emitting element blocks, and any one of the second electrode wirings is provided. To supply the second signal to It is preferable that the light emitting element has a structure in which a p-type semiconductor and an n-type semiconductor are alternately stacked, for example, a light emitting element having a thyristor structure having an anode electrode and a gate electrode. Can be.

[Action]

In the light emitting device array according to the present invention, the second
Is supplied in a time-division manner for each of the plurality of second electrodes, even if the first electrode is provided only for each light-emitting element block, all the light-emitting elements are specified. It can emit light.

Therefore, the number of electrodes can be reduced as compared with the case where electrodes for supplying signals for light emission are provided for all of the light emitting elements. For this reason, the arrangement pitch of the light emitting elements can be reduced, and the connection between the electrodes and other electrical components is small.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 shows an equivalent circuit of the light emitting element array of the present embodiment. N light-emitting element arrays (n: even number)
, T (1), T (2), T (3), T (4),
(5), T (6),..., T (n) are light emitting thyristors having a pnpn structure.

The light-emitting element T (1) the anode electrode a _1, and a gate electrode g ₁ and the cathode electrode k _1. T (2) through T anode electrode also similarly each light emitting element of the _(n) a ₂ ~a n, the gate electrode g ₂
To g _n and cathode electrodes k _{2 to} k _n , respectively.

The n light emitting elements T (1) to T (n) are divided into n / n by making T (1) and T (2) one light emitting element block.
Divide into two light emitting element blocks.

Block B the light-emitting element T (1) at ₁ and T (2) an anode electrode a ₁ and a ₂ Metropolitan from become of anode a ₁ of
First electrode A ₁ common to and a ₂ is configured with. Similarly, the anode electrode a ₃ and a ₄ Metropolitan first electrode A ₂ consisting of T (3) and T (4) at block _{B 2, ......, T (n} -1) at block B _{n / 2} and the first electrode a _{n / 2} composed of an anode electrode a _n-1 and a _n of T (n) are respectively configured.

According to these first electrodes A ₁ ~A n / _2, can supply a light emission signal is a first signal to the anode electrode a ₁ ~a _n of each light emitting element.

The gate electrode g ₁ of T (1) in the block B _1,
The gate electrode g ₃ of T (3) in the block B _2, ......, consists gate electrode g _n-1 of T (n-1) in the block B _{n / 2,} across the blocks B ₁ ~B n / ₂ these gate electrodes Te _{g 1, g 3, g 5} , ......, g n-1 to the common second electrode G ₁
Is configured. Similarly, the gate electrodes g ₂ , g ₄ , g ₆ ,.
..., the second electrode G ₂ is formed common to g _n.

According to these second electrodes G _1, G _2, can supply a control signal which is a second signal to the gate electrode g ₁ to g _n of each light emitting element.

Incidentally, the cathode electrode _{k 1, k 2, ......,} k n are configured to all be grounded common electrode k (see FIG. 3).

The operation of the light emitting element array as described above will be described with reference to FIG. Two curves in FIG. 2 is a diagram showing respectively an anode voltage V _A · anode current I _A characteristic when the voltage V _G of the gate electrode and the 0V and 5V.

If a control signal gate voltage V _G is 5V, the anode voltage V _A is the anode current I _A does not flow is the emission signal does not exceed about 6V, the light-emitting thyristor emits no light. On the other hand, when the gate voltage V _G is 0V, the light-emitting thyristor anode voltage V _A is the anode current I _A flows at about 1V or emits light. The emission intensity of the light emitting element is substantially proportional to the anode current I _A.

From above characteristics, it can be seen that controlling the emission and non-emission of the light-emitting thyristor, the potential of the gate electrode g ₁ to g _n of the light-emitting thyristor having a pnpn structure.

In the light emitting element array shown in FIG. 1, the second electrode G ₁
The 0V, the G ₂ to 5V. The flow of the anode current I _A as a light emitting signal depending on the desired emission intensity through the first electrode A ₁ to A n / ₂ in the anode a ₁ ~a _n. Then, the gate electrodes g ₂ , g ₄ ,... Connected to the second electrode G ₂ .
The light emitting elements T (2), T (4), T (6) having g _n
..., T anode a _2, a _4, a ₆ in (n), ......, a is the anode current I _A is not flow through the _n, the gate electrode is connected to the second electrode G ₁ g _{1 , g 3, g 5, ......} , the light-emitting element having a _{g n-1 T (1)} , T (3), T (5), ......, T (n-
1) flows anode current I _A to.

Next, the second electrode G ₁ 5V, when the G ₂ to to 0V, and at all happen to be opposite to the case described above.

As described above, the light emitting element array of the present embodiment has the first electrode
By providing A _{1 to An / 2} and the second electrodes G ₁ , G ₂ , even-numbered light emitting elements T (2), T (4), T
(6),..., T (n) and odd-numbered light emitting elements T
(1), T (3), T (5),..., T (n−1) can be emitted in time division.

Further, since the light emission can be controlled by the first electrode, it is possible to eventually specify all the light emitting elements T (1) to T (n) to emit light.

In this embodiment, assuming that the total number of electrodes required to be provided in a light-emitting element array composed of n light-emitting elements is Y, Y = n / 2 + 2 + 1 (1). Here, “n / 2” is the number of first electrodes, “2” is the number of second electrodes, and “1” is the number of cathode electrodes common to all light emitting elements.

In general, when the number of second electrodes is m, the total number Y of electrodes required to be provided in the light emitting element array is Y = n / m + m + 1 (2). From equation (2), it can be seen that m = n ^1/2 (3) is sufficient to minimize the total number Y of the electrodes. From the equations (2) and (3), the total number Y of electrodes in this case is Y = 2n ^1/2 +1 (4).

In the prior art, for example, the total number Y _C of required electrodes be provided in the light-emitting element array shown in FIGS. 7 and 8, including a common grounded electrode in all the light emitting _{elements, Y C = n + 1 (} 5 ).

Comparing the above formulas (4) and (5), the number of both electrodes is the same when n = 4, but usually n is larger than 4, and as n increases, the number of both electrodes decreases. It can be seen that the difference increases.

Therefore, the number of electrodes required to be provided in the light emitting element array in the present invention is considerably reduced as the number of light emitting elements increases, as compared with the case of the conventional light emitting element array shown in FIG. 7 and FIG. I understand.

Next, a specific structure example of the light emitting element array having the above-described configuration will be described. FIG. 3 is a cross-sectional view showing a structure when a light emitting element array is actually formed on a semiconductor substrate.

This light emitting element array can be prepared by the following procedure. First, an n-type semiconductor layer 2 is formed on an n-type semiconductor substrate 1.
4, p-type semiconductor layer 23, n-type semiconductor layer 22, and p-type semiconductor layer 2
1 are sequentially formed. Next, individual light emitting elements are formed by applying a photoetching method to the base 1 on which the above-described semiconductor layers 21 to 24 are formed.

In this way, light emitting elements T (1), T (2), T (3)... Composed of semiconductor layers 21 to 24 can be formed.

In each of the above light-emitting elements, the p-type semiconductor layer 21 is used as an anode electrode a ₁ , a ₂ , a ₃ ... And the n-type semiconductor layer 22 is used as a gate electrode.
g ₁ , g ₂ , g ₃ ... And, depending on the metal wiring material,
The first electrodes A ₁ , A ₂ ... Are respectively formed from the above-mentioned anode electrodes, and the second electrodes G ₁ and G ₂ are respectively formed from the above-mentioned gate electrodes.

Note that a cathode electrode k common to all light emitting elements can be formed from the n-type semiconductor substrate 1 as the cathode electrode.

The semiconductor material of the semiconductor substrate 1 is generally GaAs, but is not limited to this and may be any material. Semiconductor layers 21 to 24 formed on semiconductor substrate 1
Is freely selected according to a desired emission wavelength. For example, when GaAs is used for each of the semiconductor layers 21 to 24, the emission wavelength is about 900 nm. When AlGaAs is used, the emission wavelength can be freely changed up to the order of 600 nm by changing the Al composition.

Next, an example in which the light emitting element array as described above is configured as a light emitting element array chip will be described with reference to FIG.

In FIG. 4, the same portions as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. The light emitting element array chip can be used to constitute the LED array of the LED printer described above with reference to FIGS.

As shown in FIG. 4, the light emitting element array chip 100 has a light emitting region 100a having the same shape as that shown in FIG.
They are arranged at the same pitch as in the figure. Further, second electrodes G ₁ and G ₂ are arranged at the end of the light emitting element array chip 100,
First electrodes A ₁ , A ₂ , A ₃ ... Are arranged on both sides of each light emitting region 100a.

Each anode electrode of two light emitting elements adjacent to each other constitutes _first electrodes A ₁ , A ₂ , A _3, ... Respectively. The odd-numbered drive electrodes A ₁ , A ₃ , A _5, ... Are arranged on the upper side of FIG. 4, and the even-numbered drive electrodes A ₂ , A ₄ , A ₆ ,. . The first electrodes A ₁ , A ₂ , A ₃ ... And the second electrodes G ₁ , G ₂
Are respectively connected to the electrodes 101c of the drive IC 101 by a wire bonding method.

According to the light emitting element array chip 100 configured as described above, as can be seen from the comparison with the array chip 103 shown in FIG. 8, the arrangement pitch of the electrodes is roughly twice as large as that in FIG. Can be. Also, the second electrode
G ₁ and G ₂ can be arranged without any trouble.

Therefore, wire bonding is easier to perform than in the conventional example shown in FIGS. 7 and 8, and the number of steps can be reduced. According to such a light emitting element array chip 100, the light emitting element array can be made highly reliable and low. Price can be realized.

Also, if the same electrode arrangement pitch as that of the conventional example shown in FIG. 8 is used, approximately twice as many light emitting elements can be arranged on the light emitting element array chip and the light emitting elements can be arranged at a high density. According to such a light emitting element array chip, high resolution of the light emitting element array can be realized. Therefore, also LED
It can also contribute to higher resolution printers.

As described above, in this embodiment, a light-emitting thyristor having the simplest structure was used as a light-emitting element. However, in order to increase luminous efficiency, a more complex structure such as a double hetero structure, for example, a layer structure of six or more layers was used. Even if used, the same function can be achieved and the same effect can be obtained. Further, an electrostatic induction (SI) thyristor, an electric field control thyristor (FCT), or the like can be used as a light-emitting element.

Further, the light-emitting element that can be used is not limited to the light-emitting thyristor as described above, and any light-emitting element having an electrode that can control light emission of the light-emitting element and light emission non-emission and an electrode that applies a light-emitting signal is provided. Anything can be used.

A similar effect can be obtained with a light-emitting element array in which a large number of light-emitting elements are arranged two-dimensionally or three-dimensionally.

〔The invention's effect〕

In the light emitting element array according to the present invention, the arrangement pitch of the light emitting elements can be reduced, so that high resolution can be achieved.

In addition, since there is little connection between the electrodes and other electrical components, cost reduction and high reliability can be achieved.

[Brief description of the drawings]

1 to 4 show an embodiment of the present invention.
1 is an equivalent circuit of a light emitting element array using a light emitting thyristor as a light emitting element, FIG. 2 is an anode voltage / anode electrode characteristic curve of the light emitting thyristor shown in FIG. 1, and FIG. 3 is a light emitting element shown in FIG. FIG. 4 is a cross-sectional view showing a specific example of the structure of the array, and FIG. 4 is a plan view showing a specific arrangement of the driving IC and the light emitting element array shown in FIG. 5 to 8 show a conventional example, and FIG. 5 is a schematic sectional view of a conventional optical printer which can use the light emitting element array shown in FIGS. 1 and 7. 6 is a perspective view showing the positional relationship of the light emitting element array with respect to the rod lens array and the photosensitive drum shown in FIG. 5, FIG. 7 is an equivalent circuit of the conventional light emitting element array, and FIG. FIG. 3 is a plan view showing a specific arrangement state with the light emitting element array shown in the figure. In the reference numerals used in the drawings, T (1) to T (n)... N light emitting elements B _{1 to} B _{n / 2} ... Light emitting element blocks A _{1 to An / 2} . Electrodes G ₁ , G ₂ ... Are second electrodes.

Claims (2)

(57) [Claims] 1. Each of the first and third electrodes has a third electrode as a common electrode, and when a control signal is supplied between the first and second electrodes. A plurality of light-emitting element blocks each including at least two light-emitting elements capable of emitting light when a main current flows therebetween are provided, and light-emitting portions of the light-emitting elements are arranged in a line. A first electrode is used in common, a first signal is supplied to one of the common first electrodes, and the light-emitting element block has a number of the second electrodes corresponding to the number of light-emitting elements in the block. And the second electrode of each of the light emitting element blocks is wired and connected over the plurality of light emitting element blocks, and supplies a second signal to any of the second electrode wirings. A light-emitting element array, characterized in that: 2. The light emitting device array according to claim 1, wherein said light emitting device has a structure in which p-type semiconductors and n-type semiconductors are alternately stacked.