JP2007250958A - Light-emitting element array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element array having improved resolution without deteriorating light-emitting efficiency. <P>SOLUTION: Two power feeding points (anode electrodes) 16, 18 are arranged on a light-emitting island 14 of each light-emitting section thyristor so that light-emitting barycenters can be aligned with an equal interval in a main scanning direction. The power-feeding point 16 on the left side of each light-emitting island is connected to a signal line 8a, and the power feeding point 18 on the right side is connected to a signal line 8b. With this configuration, resolution 2,400 dpi can be realized by providing the two power feeding points on the light-emitting region of 1,200 dpi pitch. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light-emitting element array, and more particularly to a light-emitting element array with an increased resolution, and further relates to an optical writing head using the light-emitting element array, an optical printer, a facsimile machine, and a copying machine using the optical writing head.

  In an LED array in which a plurality of light emitting diodes (LEDs) are used as a light source for an optical printer or the like, the light emitting regions of the LEDs are separated by mesa etching or pn junction. Each separated light emitting region is usually provided with one feeding point (electrode).

  Some high-power light emitting diodes are provided with a plurality of feeding points in one separated light emitting region for the purpose of improving current distribution. However, since a plurality of feeding points are connected by a transparent electrode or the like, they cannot be said to be electrically independent feeding points.

  Further, in the case of a self-scanning light emitting element array using a light emitting thyristor having a pnpn structure, there is a problem in that the resolution in the sub-scanning direction cannot be increased due to the limitation of the transfer speed of the transfer unit thyristor.

  The self-scanning light emitting element array is a light emitting element array according to the proposal of the present applicant (Japanese Patent No. 2744504, Japanese Patent No. 275887, etc.), and the on-state of the transfer unit thyristor is transferred and light emission corresponding thereto. The unit thyristors emit light sequentially.

  An example of the structure of the light emitting part of the light emitting thyristor array of the self-scanning light emitting element array is shown in FIG. FIG. 1A is an enlarged view of the vicinity of two adjacent light emitting points. FIG. 1B is a cross-sectional view taken along the line A-A ′ of FIG.

On the n-GaAs layer (cathode layer) 36 which is the uppermost layer of the pnpn structure (mesa etched) composed of the p-GaAs layer 30, the n-GaAs layer 32, the p-GaAs layer 34, and the n-GaAs layer 36. A cathode electrode (feeding point) 38 is provided. The entire surface of the structure is covered with a SiO ₂ protective film 40, and a power supply line (aluminum wiring) 42 is connected to the cathode electrode 38 through a contact hole. In FIG. 1A, reference numeral 44 denotes a light emitting region.

  Consider a problem when increasing the resolution in the main scanning direction of such a self-scanning light emitting element array. For example, when the resolution in the main scanning direction is doubled with the structure of FIG. 1, the result is as shown in FIG. FIG. 2B is a cross-sectional view taken along line B-B ′ of FIG. This structure is referred to as a type 1 structure.

  Even if the resolution in the main scanning direction is increased with such a structure, the electrode area of the feeding point, the wiring width of the feeding line, and the area necessary for mesa etching are almost the same, so the light emitting region 46 not covered with electrodes or wirings. Is considerably smaller than half the area of the light emitting region 44 having the structure shown in FIG.

  Further, since non-radiative recombination is likely to occur on the mesa-etched surface, it is desirable in terms of luminous efficiency that the mesa-etched surface is as far as possible from the feeding point electrode.

  FIG. 3 shows a structure in which two cathode islands 52 are provided on one gate island 50. FIG. 3B is a cross-sectional view taken along line C-C ′ of FIG. This structure is referred to as a type 2 structure.

  In this structure, since the area required for mesa etching is reduced, the area of the light emitting region can be made larger than that in FIG. 2, but the non-light emitting recombination increases when the gate layer 34 is exposed. Again, the luminous efficiency is lowered.

  FIG. 4 shows the result of comparing the light quantity distribution in the main scanning direction for each light emitting point in FIGS. 1, 2 and 3, assuming that the resolution in the structure of FIG. 1 is 1200 dpi and the area of the light emitting region is 18 μm × 18 μm. Shown in

  FIG. 4A is a light emission power density distribution of 1200 dpi light emission points in the structure of FIG.

  FIG. 4B is a light emission power density distribution of 2400 dpi light emission points in the structure of FIG. 2 (type 1).

  FIG. 4C is a light emission power density distribution of 2400 dpi light emission points in the structure of FIG. 3 (type 2).

  FIG. 5 shows a comparison of the integrated light amount per pixel (at 10 mA) at this time. For the reasons described above, in FIG. 5, the luminous efficiency drops to ¼ for type 1 and to less than half for type 2 in FIG.

  An object of the present invention is to provide a light emitting element array having an improved resolution without lowering the light emission efficiency.

Another object of the present invention is to provide an optical writing head having such a light emitting element array.
Still another object of the present invention is to provide an optical printer, a facsimile machine, or a copying machine having such an optical writing head.

  In the light emitting element array, when the current spread from the feeding point (electrode) is sufficiently wide, it is considered that the light emitting region emits light uniformly regardless of where the power is supplied in the light emitting region.

  When multiple feeding points are provided in the light emitting area and each feeding point is fed individually, if the current spread from each feeding point is small, only the vicinity of the feeding point shines strongly, and the plurality of feeding points are regarded as independent light emitting points. be able to.

  For example, when looking at the relationship between the current spread and the light emitting point when there are two feeding points in one light emitting region, if power is supplied to only one certain feeding point, If the light emission power density on the midpoint of the straight line connecting the two is less than half of the peak value, the light emission point viewed through the lens cannot be distinguished from the independent light emission point. That is, it can be regarded as an independent light emitting point. Here, two feeding points have been described. Even when there are three or more feeding points, the light emission power density on the midpoint of a straight line connecting two adjacent feeding points is also half of the peak value. The following is sufficient.

  Note that a straight line connecting two adjacent feeding points means a straight line connecting the centers of the feeding points.

  As described above, it is possible to increase the resolution by providing two or more feeding points in the light emitting region. By doing so, when N feeding points are arranged in the main scanning direction, the resolution can be increased N times without reducing the area of the light emitting region. Further, when N feeding points are arranged in the sub-scanning direction, the resolution in the sub-scanning direction can be increased N times without increasing the transfer speed.

  Here, the main scanning direction refers to the arrangement direction of the light emitting elements, and the sub-scanning direction refers to a direction orthogonal to the main scanning direction.

  In addition, by providing two feeding points with different IV characteristics in the same light emitting region and driving with the same feeding line, it is possible to shift the light emitting point gravity center by the current value (voltage value). This method can also increase the resolution in the sub-scanning direction.

  According to the present invention, it is possible to realize a light emitting element array with improved resolution by providing a plurality of feeding points in one light emitting region. Furthermore, an optical writing head including such a light emitting element array, and an optical printer, facsimile, and copying machine including such an optical writing head can be realized.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 6 shows a configuration example in which the present invention is applied to a self-scanning light emitting element array. 7A and 7B are an enlarged view and a cross-sectional view of the vicinity of the light emitting region in FIG. FIG. 7B is a cross-sectional view taken along line D-D ′ in FIG.

  In the present embodiment, two feeding points 16 and 18 are provided in the light emitting region 14, and each feeding point is fed from separate feeding lines 8a and 8b.

  In the figure, the feeding point is arranged at a position where the centers of gravity of the light emission power density when feeding from either feeding point are equally spaced (in this case, 2400 dpi).

  As shown in this embodiment, a structure having a plurality of feeding point electrodes capable of independently turning on / off current in one light emitting region is referred to as type 3.

FIG. 8 is an equivalent circuit diagram of the self-scanning light emitting element array. The self-scanning light emitting element array includes a shift unit 10 and a light emitting unit 12. The shift unit 10 includes light emitting thyristors T ₁ , T ₂ , T ₃ ,..., Diodes D ₁ , D ₂ , D ₃ ,... Connecting the gates of these thyristors, and a load resistance _RL. Composed. Transfer clock pulses φ1 and φ2 are alternately applied to the anode electrode of the thyristor. These clock pulses are supplied via clock pulse lines 2 and 4 (φ1 line 2 and φ2 line 4). V _GA is a power source, and is connected to the gate electrodes G ₁ , G ₂ , G ₃ ,... Of the thyristor from the power line 6 through the load resistors _RL .
On the other hand, the light emitting unit 12, the light-emitting thyristor _{L 1, L 2, L 3} , is composed of ..., to the anode electrode of the thyristor, via signal lines (phi ₁ line) 8a, to 8b, write signal phi ₁ is It has been added. The gates G ₁ , G ₂ , G ₃ ,... Of the light emitting unit thyristors are connected to the gates of the corresponding shift unit thyristors.

The self-scanning light-emitting element array having such a circuit configuration is fabricated on a semiconductor substrate having a pnpn structure. In FIG. 8, the same components as those in FIG. 6 are denoted by the same reference numerals. The shift unit thyristors L ₁ , L ₂ , L ₃ ,... Are arranged in the scanning direction at a pitch of 1200 dpi (dots / inch).

  In this embodiment, two feeding points (cathode electrodes) 16 and 18 are arranged on the cathode island 14 of each light emitting unit thyristor so that the light emission centers of gravity are arranged at equal intervals in the main scanning direction. The left feeding point 16 on each cathode island is connected to the signal line 8a, and the right feeding point 18 is connected to the signal line 8b.

  With the configuration as described above, the resolving power of 2400 dpi in the main scanning direction can be realized by providing two feeding points on the light emitting region with a 1200 dpi pitch.

FIG. 9 shows the measurement result of the light quantity distribution in the main scanning direction when a current is supplied from only the left feeding point 16 for the type 3 structure shown in FIGS. The measurement results shown in FIG. 7 (A), the light emitting power density _{P M} on the midpoint 62 of the straight line 60 connecting the centers of the feeding point 16 and the center of the feeding point 18 is about 1/3 of the peak value _{P P} And could be regarded as a sufficiently independent light emitting point.

  FIG. 10 shows a comparison of the integrated light quantity per pixel at this time with the result of FIG. From the comparison result, it can be seen that the luminous efficiency was improved to 2/3 of 1200 dpi. Moreover, the peak value became substantially equal to 1200 dpi.

  FIG. 11 shows another configuration example in which the present invention is applied to a self-scanning light emitting element array, as in the first embodiment. The same components as those in FIG. 6 are denoted by the same reference numerals. In this embodiment, two feeding points 20 and 22 are arranged on the cathode island 14 of each light emitting unit thyristor so as to be aligned in the sub-scanning direction.

  By doing so, the resolution in the sub-scanning direction can be doubled without increasing the transfer speed of the shift unit. For example, in order to realize 1200 dpi (main scanning direction) × 4800 dpi (sub-scanning direction), the light emission center of gravity of the feeding point is arranged so as to be shifted in the sub-scanning direction by approximately 5.29 μm (= 1/4800 inch). FIGS. 12A and 12B show an enlarged view and a cross-sectional structure diagram in the vicinity of the light emitting region. FIG. 12B is a cross-sectional view taken along line AA ′ or BB ′ in FIG.

  FIG. 13 shows another configuration example in which the present invention is applied to a self-scanning light emitting element array, similarly to the first and second embodiments. In this embodiment, only one signal line is used. One signal line is indicated by 8. In the figure, the same components as those in FIG. 6 are designated by the same reference numerals.

  In this embodiment, two feeding points (electrodes) 24 and 26 having different IV characteristics are arranged on the cathode island 14 of each light emitting unit thyristor so as to be arranged in the sub-scanning direction. Here, both the electrodes 24 and 26 have a structure of semiconductor / AuZn (1%) / Au, and the thickness of AuZn is common at 50 nm. The thickness of Au is 200 nm for the electrode 24 and 100 nm for the electrode 26. . By changing the Au film thickness, the rising voltage in the forward direction of the electrode 26 increased about 0.1 V compared to the rising voltage in the forward direction of the electrode 24 as shown in FIG. Here, the IV characteristics are adjusted by the Au thickness. However, the thickness and the Zn concentration of the AuZn layer, which is a p-type semiconductor electrode, may be changed, or an electrode material other than AuZn may be selected. good.

  FIG. 14 shows different IV characteristics. As the voltage is increased, first, a current starts to flow through the electrode 24 at the voltage v 1, but does not flow through the electrode 26. As the voltage is increased, the voltage 26 starts to flow to the electrode 26 as well. As the voltage is further increased, the current flowing through the electrodes 24 and 26 at the voltage v3 increases, and the ratio of the current flowing through the electrode 26 increases relatively from the initial zero.

  In accordance with the change in the ratio, the light emission center of gravity moves from the electrode 24 to the middle position between the electrode 24 and the electrode 26. This makes it possible to adjust the light emission center of gravity in the sub-scanning direction. In this case, if the light emission center of gravity is moved from the upper electrode 24 to the lower electrode 26, the amount of light emission also increases. Therefore, it is necessary to adjust that amount by the light emission time or the like. For example, the center of light emission can be adjusted by driving with a driver having a binary output impedance.

  In the above embodiments 1, 2, and 3, the self-scanning light emitting element array has been described. However, the present invention is not limited to this, and the present invention can also be applied to an LED array.

  The light emitting element array of the present invention can be used as a light source of an optical writing head used in an optical printer, a facsimile machine, a copying machine and the like.

  FIG. 15 shows an example of an optical writing head using the light emitting element array of the present invention. A plurality of light emitting element array chips 71 in which light emitting elements are arranged in a row are mounted on a chip mounting substrate 70 in the main scanning direction, and the light emitting elements of the light emitting element array chip 71 emit light on the optical path. An erecting equal-magnification rod lens array 72 that is long in the main scanning direction is fixed by a resin housing 73. A photosensitive drum 74 is provided on the rod lens array 72. Further, a heat sink 75 for releasing heat of the light emitting element array chip 71 is provided on the base of the chip mounting substrate 70, and the housing 73 and the heat sink 75 are fixed by a fastener 76 with the chip mounting substrate 70 interposed therebetween. ing.

  Next, an optical printer using such an optical writing head will be described. The basic structure of the optical printer is shown in FIG.

  An optical writing head 100 is installed in the optical printer. On the surface of the cylindrical photosensitive drum 102, a photoconductive material (photosensitive member) such as amorphous Si is made. The drum rotates at the printing speed. The surface of the photosensitive drum of the rotating drum is uniformly charged by the charger 104. Then, the optical writing head 100 irradiates the photosensitive member with the light of the dot image to be printed, neutralizes the charge where the light hits, and forms a latent image. Subsequently, the developing device 106 applies toner to the photoconductor according to the charged state on the photoconductor. The transfer device 108 transfers the toner onto the paper 112 sent from the cassette 110. The sheet is heated and fixed by the fixing device 114 and sent to the stacker 116. On the other hand, the drum that has been transferred is neutralized by the erasing lamp 118 over the entire surface, and the remaining toner is removed by the cleaner 120.

  Such an optical writing head can be used not only for printers but also for facsimile machines and copying machines. FIG. 17 shows the basic structure of a facsimile or copying machine. The same constituent elements as those in FIG. 16 are denoted by the same reference numerals.

  Light is emitted from the light source 124 to the read original 122 conveyed by the paper feed roller 130, and the reflected light is received by the image sensor 128 through the imaging lens 126. Based on the output of the image sensor 128, the light emitting element array 132 of the optical writing head 100 is turned on and irradiated to the photosensitive drum 102 through the rod lens array 134. Printing on the paper 112 is as described for the optical printer.

It is a figure which shows the structural example of the light emission part of the light emission thyristor array of a self-scanning light emitting element array. It is a figure which shows the structural example of the light emission part of the light emission thyristor array of a self-scanning light emitting element array at the time of doubling the resolution. It is a figure which shows the other structural example of the light emission part of the light emission thyristor array of the self-scanning type light emitting element array at the time of doubling the resolution. It is a figure which shows the result of having compared the light quantity distribution of the main scanning direction regarding each light emission point of FIG.1, FIG.2, FIG.3. FIG. 4 is a diagram showing an integrated light amount per pixel in the structures of FIGS. 1, 2, and 3. It is a figure which shows the structure which applied this invention to the self-scanning light emitting element array. FIG. 7 is an enlarged view and a cross-sectional view of the vicinity of the light emitting region in FIG. 6. FIG. 7 is an equivalent circuit diagram of the self-scanning light emitting element array of FIG. 6. FIG. 9 is a diagram illustrating a measurement result of a light quantity distribution in the main scanning direction when a current is supplied from only the left feeding point in the structure illustrated in FIGS. 7 and 8. FIG. 8 is a diagram showing a comparison of integrated light amounts per pixel in the structures of FIGS. 1, 2, 3, and 7. It is a figure which shows the other structural example which applied this invention to the self-scanning light emitting element array. FIG. 12 is an enlarged view and a cross-sectional view of the vicinity of the light emitting region of FIG. 11. It is a figure which shows the other structural example which applied invention to the self-scanning light emitting element array. It is a figure which shows a different IV characteristic. It is a figure which shows the structure of an optical writing head. It is a figure which shows the basic structure of an optical printer. It is a figure which shows the basic structure of a facsimile or a copying machine.

Explanation of symbols

2, 4 clock pulse line 6 power supply line 8, 8a, 8b signal line 10 shift unit 12 light emitting unit 14 cathode island 16, 18, 20, 22, 24, 26 feeding point 30, 32, 34, 36 GaAs layer 42 feeding point 44 Light Emitting Area 50 Gate Island 52 Cathode Island

Claims (14)

In a light emitting element array comprising a plurality of light emitting elements arranged in a first direction, and at least one power supply line for supplying current to the light emitting elements,
A light emitting element array, wherein a plurality of feeding points are provided in one light emitting region of each light emitting element.   The light emitting element array according to claim 1, wherein the plurality of feeding points are respectively connected to different feeding lines.   The light emitting element array according to claim 2, wherein the plurality of feeding points are arranged in the first direction.   The light emitting element array according to claim 3, wherein pitches of a plurality of light emission centroids formed by the plurality of feeding points are equally spaced in the first direction.   The light emitting element array according to claim 1, wherein the plurality of feeding points are arranged in a second direction orthogonal to the first direction. In a light emitting element array comprising a plurality of light emitting elements arranged in a first direction and at least one power supply line for supplying current to the light emitting elements,
A light emitting element array, wherein a plurality of feeding points having different IV characteristics are provided in one light emitting region of each light emitting element.   The light emitting element array according to claim 6, wherein the plurality of feeding points are connected to one feeding line.   When power is supplied to only one power supply point among the plurality of power supply points, the light emission power density on the midpoint of a straight line connecting two adjacent power supply points is less than half of the peak value. The light emitting element array according to any one of claims 1 to 7.   The light emitting element array according to claim 1, wherein the light emitting element is a light emitting thyristor.   The light emitting element array according to claim 9, wherein the light emitting element array is a self-scanning light emitting element array.   An optical writing head comprising the light emitting element array according to claim 1.   An optical printer comprising the optical writing head according to claim 11.   A facsimile comprising the optical writing head according to claim 11. A copying machine comprising the optical writing head according to claim 11.

Images