JPH0837288A - Image reading device - Google Patents

Abstract

PURPOSE:To enhance a image reading device in utilization efficiency of diffused light, wherein the picture image reading device has such a structure that a two-dimensional image sensor is formed on a light-transmitting board, diffused light transmitted through the light-transmitting board is made to impinge on a manuscript through a lighting window formed on a two-dimensional sensor side. CONSTITUTION:A image reading device has such a structure that a glass board 1 of a two-dimensional image sensor is used as a light guiding board, a light source 4 is provided to the end face of the glass board 1, and light radiated from the light source 4 is guided to irradiate a manuscript through a lighting window 5, wherein a metal film is inserted in a certain region which is located on the side of the glass board 1 and where it has no electrical effect on the reading device to serve as a light reflecting plate 30 so as to prevent light scattered by a light diffusion-reflection plate 3 from being absorbed by an insulating film (gate insulating film 12) of a photodetective device of thin film structure or the like. By this setup, light is effectively used as much as possible as reflected by the above-mentioned light reflecting plate 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device used for an image scanner, an optical character reading device, etc., in which a light receiving element is formed of a thin film laminated structure and an image is read in close contact with an original. The present invention relates to a structure of an image reading device that improves the light utilization efficiency of a light source for illuminating a document.

[0002]

2. Description of the Related Art For example, as shown in an equivalent circuit diagram of FIG. 5, some image reading apparatuses are constituted by a two-dimensional image sensor and a light source. Two-dimensional image sensor 1
00 is formed by forming a pixel unit with a pair of light receiving elements and switching elements Tr, and arranging m pixels in the row direction and n pixels in the column direction. A light receiving element composed of a side switch structure is equivalent to a photodiode.
And a parasitic capacitance Cs formed in the light receiving element itself are connected in parallel. In addition, the switching element T
r is composed of a thin film transistor (TFT) having a thin film laminated structure, and a drain electrode of a switching element Tr (hereinafter referred to as TFT) is connected to an anode side of a photodiode PD. Further, the gate electrodes of the TFTs arranged in the row direction are connected to the scanning lines Sc1 to Scm respectively in the row direction, and the scanning lines are connected to the output section of the shift register 102 of the scanning line driving circuit 101. 103
It is connected to the. Further, a constant bias voltage VB is applied to the cathode side of the photodiode PD by a bias line. In addition, each TFT arranged in the column direction
Source electrodes of the data lines Da1 to D for each column direction.
This data line is connected to an and is connected to the data reading circuit 104.
It is connected to the. Further, each data line Da is connected to one electrode of the load capacitor CL, and the other electrode of the load capacitor CL is connected to a reset potential line (ground potential) (for example, Japanese Patent Laid-Open Publication No. Sho. 57-1158
80, JP-A-64-62980).

The image reading apparatus represented by the above equivalent circuit has a plurality of light receiving elements and switching elements on one surface side of the glass substrate 1 as shown in the plan explanatory view of FIG. 6 and the sectional explanatory view of FIG. The sensor unit 2 made of the glass substrate 1 is formed, the light diffusing and reflecting plate 3 is provided on the other surface side of the glass substrate 1, and the light emitted from the pair of linear light sources 4 arranged on the opposite end surface sides of the glass substrate 1 is glass. The light is guided into the substrate 1, and the light scattered and reflected by the light diffusing and reflecting plate 3 irradiates the document 200 arranged on the element through the illumination window 5 formed on the element side. As the light diffusing / reflecting plate 3, a white or specular sheet is used, which is attached to the glass substrate 1 with an adhesive or a presser.

The detailed structure of the pixel portion in the two-dimensional image sensor of the image reading apparatus is as shown in FIGS. That is, the gate electrode 1 is formed on the glass substrate 1.
1, a gate insulating layer 12, a semiconductor active layer 13, an upper insulating layer 14, an ohmic contact layer 15, a source electrode 16 and a drain electrode 17 are stacked to form a switching element (TF).
T) is formed, the lower electrode 18 is formed at the same time when the source electrode 16 and the drain electrode 17 are formed, and the photoconductive layer 19 and the transparent electrode 20 are laminated to form a light receiving element. An illumination window 5 for guiding light to the original 200 side is formed at an intermediate position between the TFT and the light receiving element.

The operation of the image reading apparatus having the above structure will be described. In the cross-sectional explanatory views shown in FIGS. 7 and 9, the light from the linear light source 4 arranged on the end surface of the glass substrate 1 of the two-dimensional image sensor is diffused by the diffuse reflection plate 3 arranged on the back surface of the substrate.
When the original 200 is scattered through the window 5 for illuminating the pixels and the light reflected from the original surface is applied to the light receiving element, the parasitic capacitance Cs of the light receiving element is photoelectrically converted according to the irradiation light. The charges are accumulated, and the accumulated charges are depleted by the switching operation of the switching element Tr.
Data is sequentially transferred to the load capacitor CL via the data line Da in units of scanning lines Sc, the voltage value obtained there is amplified in the data reading circuit 104, and the analog multiplexer 105 outputs the sequential signal as VCOM to the output line. It is designed to be read (Fig. 5). In this way, it is possible to configure a device that electrically reads out optical signals for pixels arranged two-dimensionally by line-sequential scanning.

[0006]

However, according to the image reading apparatus having the above structure, scattered light from the light diffusing reflection plate 3 arranged on the back surface of the glass substrate 1 is generated on the lower surface of the light receiving element formed on the glass substrate 1. The light is absorbed by the gate insulating film 12, the semiconductor active layer 13, the ohmic contact layer 15, etc., and as a result, the amount of light reaching the illumination window 5 of the two-dimensional image sensor is reduced, and the original 200 is irradiated. There is a problem in that the amount of light emitted decreases and the light utilization efficiency of the light source decreases. That is, the reflection optical path in the glass substrate 1 will be described with reference to FIG. 10. The light from the light source arranged on the end surface of the glass substrate is the light diffusion reflection plate arranged on the back surface of the substrate as shown by the optical paths a and b. Scattered at. First, TFT
In the section, the component indicated by the reflected optical path a1 is the gate electrode 1
1, and the reflected light path a2 component is reflected again by the light diffusing reflector 3
Is reflected to become a reflected light path a3 component and is guided to the illumination window 5 to be used as document illumination light. However, the light on the optical path which is not reflected by the gate electrode 11, for example, the component indicated by the reflected optical path b1 which is reflected by the light receiving element portion is the gate insulating film 1
2, the semiconductor active layer 13, the ohmic contact layer 15 and the like are absorbed, and the light on the reflection optical path b2 reflected at this portion becomes very weak light. The reflected light path b3 component that is reflected and guided to the illumination window 5 is not sufficiently utilized for illuminating the original, and there is a problem that the utilization efficiency of the light source is low.

The present invention has been made in view of the above situation, in which a two-dimensional image sensor is formed on a transparent substrate, and diffused light guided in the transparent substrate is provided on the two-dimensional image sensor side. An object of the present invention is to obtain a structure for improving the light utilization efficiency of diffused light in an image reading apparatus having a structure in which light is emitted to the document side through an illumination window formed in the.

[0008]

In order to solve the above-mentioned problems of the conventional example, the present invention provides a plurality of light-receiving elements on one side of a light-transmissive substrate and a plurality of switching elements respectively connected to the light-receiving elements. It is formed with a thin film laminated structure, a light diffusing reflector is provided on the other surface side of the transparent substrate, and the light emitted from the light source arranged on the end surface side of the transparent substrate is guided into the transparent substrate. In the image reading device, the light scattered and reflected by the light diffusing and reflecting plate irradiates a document arranged on the element through an illumination window formed in the thin film laminated portion, and the reflected light is detected by the light receiving element. It is characterized in that a reflecting plate formed of a metal film is provided in a region on the element formation surface side of the translucent substrate that does not electrically affect.

[0009]

According to the present invention, the light-transmissive substrate of the two-dimensional image sensor is used as the light guide plate, and the irradiation light from the light source arranged on the end face of the light-transmissive substrate is guided to the original from the illumination window. In the structure that enables irradiation, the light diffused by the light diffusing and reflecting plate is used to prevent the light scattered by the light diffusing / reflecting plate from being absorbed by the insulating film in the light receiving element formed in a thin film structure on the transparent substrate. By inserting a reflection plate on the substrate side, the light is reflected at this portion and the amount of light is utilized as effectively as possible. That is, on the element formation surface side of the translucent substrate, a metal film is inserted in a region that has no electrical influence to form a reflection plate, and the reflection plate reflects scattered light to again diffuse the light. By returning to, the absorption of light by the insulating film and the like is avoided, and the light utilization efficiency of the light source is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image reading apparatus according to the present invention will be described with reference to the drawings. The equivalent circuit of the image reading apparatus is the same as that of FIG. 5 described above, and a pixel composed of a light receiving element and a switching element Tr is set as one unit, and two-dimensional in a row direction (m bits) and a column direction (n bits). Two-dimensional image sensor 100 arranged in the vertical direction, and a scanning line driving circuit 101 and a data line reading circuit 104 as its peripheral circuits.
It has and. FIG. 1 shows a cross-sectional view of a pixel portion of a two-dimensional image sensor, and FIG. 2 shows a plan view of a plurality of pixels.

The switching element Tr is formed of a thin film transistor (TFT) having a thin film laminated structure. TFT
Is a gate electrode 11 made of a chromium (Cr) layer, a gate insulating layer 12 made of a silicon nitride film (SiNx), a semiconductor active layer 13 made of a hydrogenated amorphous silicon (a-Si: H) layer, and silicon. Upper insulating layer 14 made of nitride film (SiNx), n ⁺ hydrogenated amorphous silicon (n ⁺
Ohmic contact layer 1 composed of a-Si: H) layer
5, source electrode 16 and drain electrode 17 made of chromium (Cr) layer, and interlayer insulating film layer 21 made of polyimide layer
Are sequentially stacked on the glass substrate 1 to form a reverse staggered transistor. Contact holes 22 and 23 are formed in the interlayer insulating layer 21 located on the source electrode 16 and the drain electrode 17, and the data wiring 25 formed of an aluminum (Al) film is provided through the contact holes 22 and 23.
And the connection wiring 26 are connected to each other. Further, on the interlayer insulating film layer 21 on the upper insulating layer 14, a light shielding layer 27 made of the same aluminum (Al) film as the data wiring 25 and the connection wiring 26 is formed.

In the light receiving element, a chromium (Cr) layer deposited as the source electrode 16 and the drain electrode 17 of the TFT (switching element Tr) is used as a lower electrode 18, and the light receiving element is divided and formed for each of the light receiving elements. A photoconductive layer 19 made of hydrogenated amorphous silicon (a-Si: H) is formed, and a transparent electrode 20 made of indium oxide (ITO) or the like, which is separately formed for each light receiving element, is laminated on the photoconductive layer 19. It is formed of a sandwich type photodiode. The interlayer insulating layer 21 is also formed on the transparent electrode 20, and the contact hole 2 is formed in the interlayer insulating layer 21.
The transparent electrode 20 of the light receiving element and the drain electrode 17 of the TFT are connected by the connection wiring 26 via 8.

On the lower side of the lower electrode 18 of the photodiode, n is formed as the ohmic contact layer 15, the semiconductor active layer 13 and the gate insulating film 12 of the TFT.
⁺ a-Si: H film, a-Si: H film, and SiNx film remain. The TFT and the photodiode are covered with a passivation film 29, and a passivation film 29, an interlayer insulating layer (n ⁺ a-Si: H film) 21, an ohmic contact layer (a-Si :) are provided between the switching element and the photodiode. H film 15 and gate insulating film (SiN
The illumination window 5 is formed by opening the (x film) 12.

Next, the reflector 3 which is a characteristic constitution of the present invention
0 will be described. The reflector 30 is a metal film made of the same chromium (Cr) layer as the gate electrode 11 of the TFT and is formed directly on the glass substrate 1. The reflector 30 is a TFT
And an area that does not electrically affect the photodiode, that is, as shown in FIG. 2, provided in a shaded area excluding the TFT and the illumination window 5 from one pixel portion including the TFT and the photodiode. ing. This area is 2
It is only necessary that the region does not have an electrical influence on the operation of the dimensional image sensor due to additional capacitance, withstand voltage, etc., and it is not necessary to be continuously connected to any of the electrodes. The reflector 30 is formed at the same time when the gate electrode 11 of the TFT is formed, and a metal film made of a chromium (Cr) layer is deposited on the glass substrate 1 and patterned to form the gate electrode 11 and The reflection plate 30 has a desired shape.

A light diffusing reflector 3 is provided on the surface (rear surface of the glass substrate) opposite to the element forming surface of the glass substrate 1 on which the two-dimensional image sensor is formed.
And, as shown in FIG. 7, the linear light sources 4 are arranged along both side surfaces of the glass substrate. Therefore, the linear light source 4
The light is emitted from the end surface of the glass substrate 1 and is repeatedly reflected by the light diffusing and reflecting plate 3 to be guided inside the glass substrate 1.

Next, the reflection optical path due to the provision of the reflection plate 30 will be described with reference to FIG. Light from the linear light source 4 arranged on the end surface of the glass substrate 1 is guided through the glass substrate 1 as indicated by the optical paths a and c as in the conventional example described in FIG. The light is diffused by the light diffusing and reflecting plate 3 arranged at. The light reflected by the light diffusive reflector 3 on the lower side of the TFT portion is reflected by the gate electrode 11 in the component indicated by the reflected light path a1 as in the conventional example, and the reflected light path a2
The component is again reflected by the light diffusing and reflecting plate 3 to become a reflected light path a3 component, which is used as document illumination light from the illumination window 5 to the document 200.
Guided to the face side. On the other hand, the light reflected by the light diffusing and reflecting plate 3 below the photodiode section is reflected by the reflecting plate 30 formed of the same metal film as the gate electrode 11, so that the component indicated by the reflected light path c1 is the same as in the TFT section. The light is reflected by the reflection plate 30 without being affected by absorption by the gate insulating film 12 and the like, and the reflected optical path c2
The component is again reflected by the light diffusing and reflecting plate 3 to become a reflected light path c3 component, and is emitted from the illumination window 5 as the document illumination light to the document 200.
Guided to the face side.

That is, the reflection plate 30 which is a characteristic configuration of the present invention avoids absorption and attenuation of the reflected light from the light diffusion reflection 3 due to the gate insulating film 12 and the like, and the light diffusion reflection plate 3 again.
By returning to the above, the light from the linear light source 4 is effectively used to irradiate the original 200 from the illumination window 5, so that the light utilization efficiency of the linear light source 4 can be significantly improved.

A pair of the above-mentioned TFT and photodiode constitutes one pixel unit, and the gate electrode 1 of each TFT is formed.
1 is connected to the scanning line 31 that is common to each row (FIG. 2),
Each scanning line 31 is connected to the scanning line driving circuit 101 (FIG. 5). The source electrode 16 of each TFT is connected to the data line 25 which is common to each column (FIG. 2), and each data line 25 is connected to the data reading circuit 104 (FIG. 5). A ground vertical wiring 33 is provided along the data line 32 outside the data line 25 at the end of the two-dimensional image sensor, and a load capacitor CL (FIG. 5) is provided between the data line 25 and the ground vertical wiring 33. Is forming. Further, the ground vertical wiring 33 is connected to the light shielding layer 27 via a ground horizontal wiring 34 provided in parallel with the scanning line 31 and contact holes 35 and 36 formed in the interlayer insulating layer 21. Further, the lower electrodes 18 of the respective photodiodes are patterned so as to be connected to each other by a connecting portion 18 '(FIG. 2), and a bias voltage VB is applied to their ends.

A reading operation in the image reading apparatus having the above-mentioned structure will be described with reference to the driving timing chart of FIG. When the reflected light from the document surface 200 is incident on the photodiode, the charge generated by photoelectric conversion according to the optical signal is parasitic capacitance Cs.
Are integrated and accumulated in the accumulation period Ts. The TFTs are sequentially scanned for each row by the scanning line drive signal Sc, and within each scanning period, in the data line reading circuit 104,
The charges accumulated in the pixel are collectively transferred to the load capacitor CL in units of scanning lines in steps of each period of t1 to t4 for each bit. In those steps, first, in the period t1, resetting is performed by discharging the electric charge of the load capacitor CL to the reset potential by the reset signal, and in the embodiment, discharging to the ground. In the period t2, the offset voltage is taken in and in the period t3. The TFT (Tr) is turned on by the scanning line drive signal Sc to transfer the charge accumulated in the light receiving element to the load capacitor CL. In period t4, T
In the feedthrough due to the capacitance between the gate electrode 11 and the source electrode 16 of the FT (Tr), the transfer peak voltage VOP in the period t3 drops to the transfer data voltage VDA. The voltage VDA is held by the sampling signal SPL. The voltage value of the transfer data voltage VDA on each data line 32 in each bit is amplified in the data reading circuit 104 and sequentially read out as a time series signal by the analog multiplexer 105.

[0020]

According to the image reading apparatus of the present invention, a reflection film is formed by inserting a metal film in a region on the element forming surface side of a light-transmissive substrate, which has no electrical influence, and forming the reflection plate. The scattered light is reflected by the plate and returned to the light diffuse reflection plate to avoid the absorption of light by the insulating film, improving the light utilization efficiency of the light source and reducing the diffused light radiated to the document side through the illumination window. It is possible to increase the illuminance and improve the quality of the read image.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing one pixel of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory plan view showing a plurality of pixels of the image reading apparatus according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a reflected optical path in an example.

FIG. 4 is a drive timing chart for explaining the operation of the image reading apparatus.

FIG. 5 is an equivalent circuit diagram showing a circuit configuration of the image reading apparatus.

FIG. 6 is a plan view of the image reading apparatus.

FIG. 7 is a cross-sectional explanatory diagram of the image reading apparatus.

FIG. 8 is an explanatory plan view showing a plurality of pixels of a conventional image reading device.

FIG. 9 is a cross-sectional explanatory view showing one pixel of a conventional image reading device.

FIG. 10 is an explanatory diagram of a reflected light path in a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 3 ... Light diffusion reflection plate, 4 ... Linear light source, 5 ... Illumination window, 11 ... Gate electrode, 12 ... Gate insulating film, 13 ... Semiconductor active layer, 14 ... Upper insulating layer, 15 Ohmic contact Layer, 16 ... Source electrode, 17 ... Drain electrode, 18 ... Lower electrode, 19
... Photoconductive layer, 20 ... Transparent electrode, 25 ... Data line,
30 ... Reflector, 31 ... Scanning line, 100 ... Two-dimensional image sensor, 101 ... Scanning line drive circuit, 104 ... Data reading circuit

Claims (1)

[Claims] 1. A plurality of light receiving elements and a plurality of switching elements respectively connected to the light receiving elements are formed in a thin film laminated structure on one surface side of the transparent substrate, and light diffusion is performed on the other surface side of the transparent substrate. A reflector is provided, and the light emitted from the light source arranged on the end face side of the transparent substrate is guided into the transparent substrate, and the light diffusely reflected by the light diffusing reflector is formed in the thin film laminated structure portion. In an image reading device that irradiates a document placed on the element through the illuminated window and detects the reflected light by the light receiving element, there is no electrical influence on the element forming surface side of the transparent substrate. An image reading device, characterized in that a reflection plate formed of a metal film is provided in the area.