JPH02223942A - Picture reader - Google Patents

Abstract

PURPOSE:To improve resolution and S/N without impairing low costs and compactness by employing a thin electroluminescence element ETFEL of an end face light emission type as a light source. CONSTITUTION:A photoelectric conversion element 111 is composed of a lower electrode 102, a photoconductive layer 103, and an upper transparent electrode 104; plural photoelectric conversion elements 111 are arranged perpendicular to the surface of a paper; an illumination window 121 is formed with material with same as a lower electrode layer. The ETFEL 121 as the light source is bonded with an optical adhesive 122 of a refraction factor almost the same degree as that of an insulating transparent substrate, on the opposite side of the element surface of the insulating transparent substrate 101. Illumination light 123 emitted from the ETFEL 121 is made incident on the original surface 141 via the optical adhesive 122, the insulating transparent substrate 101, and the illumination window 131. Since the light from the EFFEL has sharp directivity, a higher illuminance is obtained on the original surface. Thus, resolution, sensitivity, S/N in reading can be improved without impairing low costs and compactness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the structure of an optical system in a part of a facsimile machine, digital copying machine, image scanner, etc. that performs image reading.

[Prior Art] A method of reading an image using a so-called contact type image sensor having a pixel row length that is the same as that of a document involves reading a same-magnification image formed using a self-focusing rod 1/lens array. There are two types: one in which a photoelectric conversion element is brought close to the original surface and the reflected light from the original surface is directly read without forming an image. Both have a much shorter optical path length than those that use a reduction type optical system, and the utilization rate of reflected light from the document surface is high.
It is possible to construct a compact and bright optical system, and is expected to be applied to facsimiles and various image input devices. In particular, the latter does not require an optical element for image formation, making it possible to lower costs compared to the former, and expanding the range of applications of image reading devices in that it is possible to configure the layer device compactly. It is expected as such.

FIG. 2 shows an example of an optical system that directly reads the reflected light from the surface of the document. In the figure, a photoelectric conversion element 211 includes a lower electrode 202, a photoconductive layer 203, and a transparent upper electrode 204.
, and a large number of them are arranged in the direction perpendicular to the plane of the paper. An illumination window 231 is provided in the photoelectric conversion element, and illumination light 223 from the light source 221 reaches the document surface 241 through the insulating transparent substrate and this illumination window. In this case, the lower electrode of the charge conversion element also serves as a light shielding layer, and prevents light from the light source from directly entering the conductive layer. By moving such an optical system in the horizontal direction of the paper surface, it is possible to read the image on the document surface.

There are two types of reflected light from the document surface: one is caused by specular reflection on the document surface, and the other is light that is emitted after once entering the document surface. The former is emitted according to the angle of incidence of the illumination light,
It contains almost no information about the shading of the original surface. The latter is almost independent of the incident angle of the illumination light, is emitted from the document surface in a form that is nearly completely scattered, and contains information on the shading of the document surface. Hereinafter, the former will be referred to as surface reflected light and the latter as original light. In order to read the image on the document surface, it is necessary to make only this document light enter the photoelectric conversion element.

In the example shown here, since the illumination light is incident approximately perpendicularly to the document surface, the surface reflected light is emitted approximately perpendicularly to the document surface and returns toward the light source through the illumination window. Therefore, surface reflected light does not enter the photoelectric conversion element. Although the original light is most intensely emitted in the direction perpendicular to the original surface, it also contains many angular components, so a portion of it is incident on the photoelectric conversion element.

In this manner, the image on the document surface can be read.

[Problems to be Solved by the Invention] As a light source for such an image reading system, a fluorescent tube or an LED array in which a large number of LEDs are arranged in one dimension can be used.

In the LED array, each LED is almost a point light source, and it is easy to control the angle at which the illumination light enters the illumination window, so the surface reflected light effectively enters the photoelectric conversion element in the manner shown above. can be prevented.

Therefore, it is possible to perform reading with a higher S/N than the former. Furthermore, since LED is a solid-state light source, it has a long lifespan and is advantageous in that it requires no maintenance. For this reason, LEDs are generally used as light sources.

However, since the light from the LED has small directivity and it is difficult to concentrate the light only on the illumination window, the efficiency of light utilization becomes extremely low. Therefore, in order to obtain sufficient brightness for image reading, it is necessary to make the illumination window of the charging conversion element considerably large. Although it is possible to use an optical system to collect light to compensate for this, the original advantages of low cost and compactness are lost.

Furthermore, since the illumination window cannot be made smaller, it is difficult to reduce the size of the photoelectric conversion element, which is a major obstacle in increasing the resolution of an imaging device.

Furthermore, since the LED array itself is a collection of point light sources and provides illumination without using any optical elements, variations in brightness in the longitudinal direction tend to become large. For this reason, significant sensitivity correction is required after reading, and there is a problem in that the S/N ratio of the image reading device decreases.

Therefore, the present invention is intended to solve such problems.
By using a light source with high directivity and high uniformity in the length direction, the aim is to increase resolution and improve S/N without sacrificing the low cost and compactness of this type of image reading device. [Means for Solving the Problems] The image reading device of the present invention is characterized in that an edge-emitting thin electroluminescent element is used as a light source.

[Example] First, an edge-emitting thin film electroluminescent device (hereinafter referred to as E T F
I'll call it EL. ) will be explained. E
TFEL is Proceeding of the S
ID, vol. 28.81 (1987), etc., the active layer of a thin film electroluminescent device is prepared under conditions such that it becomes a waveguide on the device surface. As shown in the figure.

In the figure, 301 is an insulating substrate, and 302 is a lower part 1! The pole layers 303 and 305 are dielectric layers, and 304 is an electroluminescent active layer. The lower electrode layer is a palladium film formed by sputtering with a thickness of 1000 mm, the dielectric layer is a yttrium oxide (Y 20 a ) film formed by electron beam evaporation with a thickness of 2500 mm, and the active layer is formed by sputtering. A manganese-added zinc sulfide film (ZnS: λ4 n ,) was formed using a method with a film thickness of 1
．． The upper electrode layer is an aluminum film formed by sputtering and has a thickness of 4,000 μm.

The basic structure is the same as a normal thin film electroluminescent element used for display and lighting, and light emission occurs within the active layer by applying an alternating current voltage of several hundred Hz = several hundred kHz between the upper and lower electrodes. Since the structure is simple, it is relatively easy to form an element over a large area, and it is possible to manufacture an element with a long light emitting surface.

In a typical thin-film electroluminescent device, one of the electrodes is a transparent electrode, and light is extracted in a direction perpendicular to the device surface and used for display or backlighting. In such applications, since it is desired to reduce the driving voltage, the active layer is also made as thin as possible, and a value of about 5,000 to 8,000 is usually used.

On the other hand, when it is intended to be used as an ETFEL, it is safe that light propagates in the active layer in a direction parallel to the element surface as shown at 310. Generally, the active layer has a higher refractive index than the dielectric layer, so a step-index waveguide can be constructed by utilizing this difference in refractive index.

In the case of devices used for normal displays and backlights, the active layer is thin, so sufficient propagation characteristics cannot be obtained as a waveguide. By increasing the thickness of this active layer, the propagation characteristics of this waveguide can be improved and it can be used as an E T F E L. The thicker the active layer, the more modes propagate within the waveguide and the better the propagation characteristics, but this also increases the driving voltage and reduces the directivity of light emitted from the ends.
It is inconvenient when used for such purposes. For this reason, the luminescent color is high, but the thickness of the active layer is 800 mm.
It is best to take a value of about 0 to 2μ■.

Although specific materials for constructing ETFEL have been described here, it is possible to use most of the +:t Fl that composes ordinary thin film electroluminescent elements as long as they can construct a waveguide. be.

For example, tantalum oxide (T a 2
It is also possible to use alumina (A1zO3), silicon oxide, silicon nitride, barium titanate (BaTiO3), silicon oxynitride'E (SiO,N,), etc. as the material of the active layer. In addition to zinc sulfide, it is also possible to use cadmium sulfide (CdS), strontium sulfide (SrS), and materials in which these materials are dispersed in organic materials. Further, as for the activator added to the active layer, copper, lead, terbinium, chlorine, fluorine, etc. can be used.

The present invention will be explained below with reference to Examples, and the ETFEL used as a light source here was manufactured by the method described above.

FIG. 1 is a sectional view showing an example of an image reading device according to the present invention.

In the figure, a charge conversion element 111 is composed of a lower electrode 102, a leading layer 103, and a transparent upper electrode 104, and is arranged in large numbers in a direction perpendicular to the plane of the paper.

The lower electrode is a chromium film formed by sputtering and has a thickness of 2000 mm, the photoconductive layer is an amorphous silicon film formed by plasma CVD and has a thickness of 8000 mm, and the transparent upper electrode layer is ITO formed by sputtering. The film thickness is 200
There are 0 people. In addition, the lighting window 1 is made of the same material as the lower electrode layer.
31 is formed.

A 1.3-layer passivation layer is provided on the photoelectric conversion element to improve reliability and protect the element from the surface of the original. Reference numerals 107 and 109 are passivation layers made of a non-polluting material such as silicon oxide, which are intended to improve moisture resistance and abrasion resistance. Reference numeral 108 is a passivation layer made of an organic material such as polyimide, which acts to flatten the surface of the element.

E T F E L 121 as a light source is bonded to the insulating transparent substrate on the side opposite to the element surface by an optical adhesive 121 having a refractive index comparable to that of the insulating transparent substrate. By doing so, it is possible to make illumination light enter the insulating transparent substrate very efficiently, which is also more advantageous than using an LED as a light source. Normal ETF
The end face from which the EL light is emitted is coated with glass or the like in order to alleviate the difference in refractive index and increase the efficiency of emission.

However, by doing this, the difference in refractive index at the exit surface can be reduced, and there is no need to provide a coating layer.

The ETFEL must be driven at a frequency such that fluctuations in light intensity do not affect the reading scan of the photoelectric conversion element. In the case of reading in the accumulation mode, which is normally used for this purpose, the scanning time is several ms. In this case, several kHz
.about.several tens of kHz is appropriate in terms of efficiency and the like. When reading in current mode, a higher frequency is required, although it depends on the method.

The illumination light 131 emitted from the ETFEL is the optical adhesive 1
21, the light enters the document surface 141 through the insulating transparent substrate 101 and the illumination window 131. Since the light from the ETFEL has sharp directivity, the spread of the light is not very large even when it passes through a substrate of about 1 mm.

Although it is inferior to LEDs in absolute light quantity, it is possible to obtain higher illuminance on the document surface.

This made it possible to make the illumination window smaller, thereby reducing the area of the pixel and improving resolution.

Further, since ETFEL is a linear light source, the brightness in the longitudinal direction is highly uniform, and there is no need to correct variations in the light source, making it possible to reduce costs.

Furthermore, if a scanning circuit or the like is formed using a thin layer transistor or the like on the same substrate as the photoelectric conversion element, it is advantageous for achieving higher reading resolution, lower cost, and miniaturization of the device.

The structure in which the illumination window is provided at the center of the pixel as in the embodiment shown in FIG. 1 has a problem in that it becomes difficult to manufacture when higher resolution is desired. When an illumination window is provided within a photoelectric conversion element, highly accurate positioning is required during pattern formation of each layer constituting the charge conversion element. This is because when the pattern is made finer in order to achieve higher resolution, the accuracy of this positioning also becomes more difficult.

FIG. 4 shows an embodiment that takes this point into consideration.

In the figure, an illumination window 431 is provided outside the photoelectric conversion element 411 using the lower electrode layer of the photoelectric conversion element.

Since only one layer constitutes the illumination window, the accuracy required for alignment between each layer is significantly reduced.

A passivation layer 406 made of an inorganic material such as silicon oxide is provided on the photoelectric conversion element in order to improve reliability.
A conductive layer 407 is formed thereon to prevent the influence of static electricity due to friction with the surface of the document. If a transparent material such as ITO is used as the material for this conductive layer, there is no need to perform pattern formation as in this example. A cover glass 409 for protecting the element from the document surface is adhered to the element surface using an optical adhesive layer 408. A commercially available cover glass with a thickness of about 50 μm can be used, and the reliability of the reading surface can be greatly improved. The reflected light at the interface between the optical adhesive layer and the cover glass is
Since there is a high possibility that stray light will cause a decrease in S/N in image reading, the optical adhesive layer is selected to have a refractive index that is equal to or slightly smaller than the refractive index of the cover glass. Further, such a reading surface structure can also be used in the embodiment shown in FIG.

Similar to the embodiment shown in FIG. 1, the ETFEL is bonded to the insulating transparent substrate on the side opposite to the element surface using an optical adhesive 422. This bonding method using optical adhesive can efficiently make the illumination light enter the insulating transparent substrate when trying to increase the angle of incidence of the illumination light on the document surface as in this example. There is a characteristic called. If this angle of incidence is too small, surface-reflected light from the surface of the document and the surface of the cover glass will enter the photoelectric conversion element, resulting in a decrease in S/N, unless the incident angle is almost vertical.

If it is too large, illumination light cannot be emitted from the surface of the cover glass, making it impossible to read the image. For this reason, the range that can be read is mostly vertical or 1
It is between 0 degrees and about 50 degrees.

30 degrees to 4 degrees depending on the distance between the lighting window and the photoelectric conversion element
Particularly good readings can be made in the 0 degree range.

Although the application to an image reading system in which reading is performed by placing a photoelectric conversion element close to the surface of an original has been described above as being particularly useful, it is also useful as a light source for image reading devices of other types.

[Effects of the Invention] As described above, by using the present invention, it is possible to perform reading without sacrificing low cost or compactness in an image reading device that performs reading by placing a charging conversion element close to the document surface. Higher resolution, higher sensitivity, S/N
We were able to improve this.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the image reading device of the present invention. FIG. 2 is a sectional view showing an example of a conventional image fm reading device. FIG. 3 is an example of a cross-sectional view of ETFEL used as a light source in the image reading device of the present invention, and FIG. 4 is a cross-sectional view showing another embodiment of the image reading device of the present invention. be. 101.201.401...Insulating transparent substrate 102.202.402...Lower electrode layer 103.203.403...Light Conductive layer 104.204.404...Transparent upper electrode layer 105.106.107.206.406...
...passivation layer 111.211.41
1...Photoelectric conversion element 121.141...
...... Edge-emitting type fi [GI electroluminescent element 122.422 ...... Optical adhesive 123.223.423 ...... Illumination light 131.231 .431......Lighting window 14
1.241.441......Manuscript surface 221.
········light source

Claims (1)

[Claims] An image reading device characterized in that an edge-emitting thin film electroluminescent light emitting element is used as a light source.