JPH07161956A - Image sensor - Google Patents

Abstract

PURPOSE:To improve the ununiformity of the output and to improve an overall contrast by taking a capacity in a photoreceptor element and a driving circuit element into consideration. CONSTITUTION:A photoreceptor element 3 has capacitance 2, and a driving element 11 also has its internal capacitance 4. A wiring for connecting the photoreceptor element 3 with the driving element 11 has capacitance 5. A ratio is defined as fn=Cbn, n+1/(Cscrn+Cicn), where Cscrn is the capacitance of the n+h photoreceptor element, Cicn is the capacitance of the n+h driving element and Cbn, n+1 is the capacitance between n+h and (n+1)+h conductors. When the fn is 0.02-0.1, an overall contrast is good.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge storage type image sensor used in various reading devices such as a bill reading device, a form reading device and a facsimile, and more particularly,
The present invention relates to an improvement in the structure of a conductor wiring group that connects a light receiving element of an image sensor and a drive circuit element.

[0002]

2. Description of the Related Art In a conventional image sensor, in particular, a contact image sensor, the outputs taken from a plurality of light receiving elements are non-uniform, and the read image is uneven. It is known that the non-uniformity of the output of the contact image sensor is caused by the capacitance floating between the wirings connecting the drive circuit or the signal processing circuit and the light receiving element. Therefore, as a method of improving the non-uniformity of the output of the image sensor, it is considered to make the inter-wiring capacitance of the wiring pattern uniform.

For example, Japanese Examined Patent Publication No. 3-28871 discloses a technique in which an element having a capacitance sufficiently larger than the stray capacitance between wirings is formed in parallel with each conductor and reading is performed without being affected by the stray capacitance. ing. In Japanese Patent Publication No. 5-19859, the conductor wiring group is covered with an insulator having a high relative dielectric constant, the thickness or area of which is different depending on the wiring position of the conductor line, whereby the inter-line capacitance of the conductor wiring group is uniform. I am trying.

However, in these methods, attention is paid only to the capacitance between the wirings, and the only purpose is to make the capacitance between the wirings uniform. However, this is not enough and the image information could not be read correctly.
For example, the contrast decreases depending on the relationship between the capacity of the light receiving element and the capacity of the drive circuit. Therefore, it is effective when light is constantly radiated, but when reading a white and black mottled document, or when light is constantly radiated and bills or documents are illuminated. There is a case where it is not effective in the case of being used in a device for reading the outer shape or an image of transmitted light by blocking the light.

As another technique, for example, Japanese Patent Laid-Open No. 1-19
Japanese Patent No. 4654 discloses a technique of dividing a light receiving element into blocks, driving each block, and simultaneously taking out signals from the light receiving elements in the block. However, it requires multiple circuits to receive multiple signals at the same time,
Due to the non-uniformity of these circuits, the read signal is also non-uniform. Further, since the signal in the block is taken out through the adjacent wiring, the capacitance between the wirings also influences the signal from the reading target having a large contrast as described above.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and in addition to improving the nonuniformity of the output, considering the capacitance in the light receiving element and the driving element, the overall contrast is improved. It is an object of the present invention to provide an image sensor improved.

[0007]

According to the present invention, a large number of light receiving elements are arranged on a substrate, a driving element for driving the light receiving elements, and the light receiving element and the driving element are electrically connected. And an inter-wiring capacitance Cbn, n + 1 of the nth conductor wiring and the (n + 1) th conductor wiring of the conductor wiring group, and the light receiving element connected to the nth conductor wiring. Capacity of Cscr
When the ratio fn calculated from n and the capacitance Cicn of the drive element connected to the nth conductor wiring is fn = Cbn, n + 1 / (Cscrn + Cicn), the ratio fn is 0.02 to 0.1. It is characterized in that the conductor wiring group is wired so as to be within the range.

[0008]

According to the present invention, the inter-wiring capacitance Cbn, n + 1 of the nth conductor wiring and the (n + 1) th conductor wiring of the conductor wiring group.
And a ratio fn calculated from the capacitance Cscrn of the light receiving element connected to the n-th conductor wiring and the capacitance Cicn of the driving element connected to the n-th conductor wiring are fn = Cbn, n + 1 / (Cscrn + Cicn ). At this time, if the ratio fn is larger than 0.1, it is affected by the bits on both sides adjacent to each other, so there is no problem in reading a uniform original, but for example, a white and black spot pattern is read. In this case, the contrast becomes poor as a whole. Further, when the ratio fn is smaller than 0.02, the afterimage ratio increases and the resolution of image data becomes small. Therefore, by wiring the conductor wiring group so that the ratio fn is in the range of 0.02 to 0.1,
An image sensor with improved important characteristics of both output non-uniformity and overall contrast can be obtained.

[0009]

1 is an equivalent circuit diagram of an image sensor for explaining the principle of the present invention. In the figure, 1 is a light receiving element voltage, 2 is a light receiving element capacitance, 3 is a light receiving element, 4 is a drive element internal capacitance, 5 is a wiring capacitance, 6 is a sensor reset switch, 7 is a sensor output switch, and 8 is Sensor output signal lines, 9 is light, 10 is wiring, 11 is an amplifier, and 12 is a driving element.

A predetermined light receiving element voltage 1 is applied to the light receiving element 3.
Is being applied. When the light receiving element 3 is irradiated with the light 9,
The charges generated in the light receiving element 3 are accumulated in the light receiving element capacitor 2. The drive element 12 includes an amplifier 11, a sensor reset switch 6, a sensor output switch 7, a circuit (not shown) for driving the sensor output switch 7, and the like, and is connected to the light receiving element 3 by a wiring 10. By sequentially turning on the sensor output switch 7, the charges generated in the light receiving element 3 and accumulated in the light receiving element capacitor 2 are read out and output to the sensor output signal line 8. When the light receiving element 3 is driven, the electric charge accumulated in the light receiving element capacitor 2 moves to the driving element 12 through the wiring 10 and reading is performed. The drive element 12 also has the drive element internal capacitance 4. Sensor reset switch 6
Is for discharging the electric charge accumulated in the light receiving element capacitor 2 and resetting it by turning it on.

The respective light receiving elements 3 are arranged at intervals of the pixel density at the time of reading. A plurality of driving elements 12 are integrated and configured as one or several ICs. Therefore, the wirings 10 are arranged close to each other, and the inter-wiring capacitance 5 exists between the wirings 10 adjacent to each other.

Now, paying attention to the n-th wiring 10, the light-receiving element capacitance 2 of the light-receiving element 3 connected by this wiring is Cscrn, the driving element internal capacitance 4 is Cicn, and the wiring between the n + 1th wiring 10 The inter-capacity 5 is Cbn, n + 1. Further, the ratio fn is defined as fn = Cbn, n + 1 / (Cscrn + Cicn). To keep this ratio fn within an appropriate range,
Each capacity may be set.

FIG. 2 is a graph showing the relationship between the ratio fn and the afterimage ratio. In the figure, ● is a graph showing the afterimage ratio when the light receiving element is irradiated with light of 660 nm, and Δ is a graph showing the afterimage ratio when the light receiving element is irradiated with light of 570 nm. Each graph has an error of about ± 2%.

Whether the afterimage ratio is large or small affects the read image. When the afterimage ratio is less than 0%, the image data becomes smaller than the black reference value, and a special processing circuit is required. When this image sensor is used in a recognition device, it causes a recognition error. Further, when the afterimage ratio exceeds 20%, the resolution of the image data becomes small and the performance as a reading device deteriorates. For this reason, it is desirable to set the afterimage ratio to a value between 0% and 20%.

As a light source used for ordinary reading, a light source having a wavelength of about 570 to 660 nm is often used in consideration of sensitivity of a light receiving element. When receiving light in this wavelength range, the afterimage ratio may be set to an appropriate value. From the graph shown in FIG. 2, the ratio fn at which the upper limit of afterimage rate becomes 20%
Is 0.0 from the graph when light of 660 nm is used.
It turns out that it is 2. Further, the ratio fn at which the lower limit of afterimage rate is 0% is 0.1 from the graph when light of 570 nm is used. Thus, the ratio fn
Should be set in the range of 0.02 to 0.1. That is, from the above formula of the ratio fn, the light receiving element capacitance 2, the driving element internal capacitance 4, and the inter-wiring capacitance 5 may be determined so that the ratio fn falls within this range.

Based on a specific example, each capacitance will be calculated so that the ratio fn becomes the above-mentioned predetermined value. Consider a case where the light receiving element has a film thickness of 2.5 μm, ε ₀ = 11.7, and a size of 200 × 200 μm. At this time, the capacitance Cscr of the light receiving element is Cscr = 200 × 200 × 8.854 × 11.7 / (2.5 × 10 ⁶ ) = 1.7 (pF). If the drive element internal capacitance Cic = 2 pF, then from the above formula of the ratio fn, 0.02 ≦ Cbn, n + 1 / (1.7 + 2) ≦ 0.1, and the ratio fn is 0.02 to 0.1. The inter-wiring capacitance Cbn, n + 1 that is expressed as follows is 0.074 pF to 0.37 pF. For the wiring 10, the wiring length, wiring width, and wiring interval are designed according to the wiring position of the conductor wiring so that the inter-wiring capacitance is within this range, and the inter-wiring capacitance is made substantially uniform. At this time, the calculation of the inter-wiring capacitance is performed, for example, in Japanese Patent Publication 5-1.
It may be calculated using the technique disclosed in Japanese Patent No. 9859.

The inter-wiring capacitance Cbn, n + 1 is 0.0.
When it does not fall within the range of 74 pF to 0.37 pF, for example, the size of the light receiving element of 200 × 200 μm is made larger, the film thickness of 2.5 μm is made smaller, or ε ₀ = 1.
By increasing 1.7, the upper limit of inter-wiring capacitance can be changed. In addition, the size of the light receiving element, the film pressure,
By changing ε ₀ in reverse, the lower limit can be changed so that the inter-wiring capacitance is within the range obtained by recalculation.
Wiring can be designed. In addition, when the area for wiring cannot be sufficiently secured due to the restrictions of the outer size of the image sensor, a conductor can be formed on the wiring through an insulator to increase the light receiving element capacitance. Furthermore, if possible, for example, by replacing the drive element 12 and changing the drive element internal capacitance Cic,
It is also possible to change the upper and lower limits of the capacitance between the wirings and the capacitance of the light receiving element 3.

3 to 9 are plan views showing examples of wiring patterns of the wiring 10. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals. Reference numeral 13 is an inter-wiring capacitance correction pattern. As described above, when the range of the inter-wiring capacitance is obtained, the wiring pattern may be designed so that the inter-wiring capacitance is uniform within the range. The illustrated example shows some examples of wiring patterns that are wired such that the inter-wiring capacitance is uniform. In each illustrated example, the light receiving element 3 is set to 250
The driving elements 1 are arranged at a pitch of ~ 500 μm.
On the side of connection with No. 2, it is connected to an IC in which drive elements are integrated at a pitch of 110 μm using a wire bonding technique.

FIG. 3 shows an example of a wiring pattern which has been used more often than before. Even with such a wiring pattern, it is not impossible to equalize the inter-wiring capacitance, but in order to more easily equalize the inter-wiring capacitance, the refraction points of the wiring 10 are increased to make the inter-wiring capacitance uniform. I am trying to
FIG. 4 shows a wiring pattern having more refraction points than the wiring pattern shown in FIG. It was found that the more the number of refraction points, the smaller the variation in the capacitance between the wirings. Therefore, as shown in FIG. 5, the case where a part of the wiring 10 has a curved shape was also effective. Further, as shown in FIG. 6, it was also effective when it was curved and the wiring interval was changed. Further, as shown in FIGS. 5 and 6, the inter-wiring capacitance correction pattern 13 may be partially provided to make the inter-wiring capacitance uniform.

However, if a curved line is used for the wiring, it becomes difficult to correct the wiring open and short circuit in the manufacturing process. In such a case, a wiring pattern as shown in FIG. 7 can be used. However, in this case, there are cases where the correction cannot be sufficiently performed only by the width, length, and interval of the wiring, and by providing the inter-wiring capacitance correction pattern 13, it is possible to carry out wiring with no practical problems.

It is also possible to use some of the above-mentioned wiring patterns in combination. For example, by combining the wiring pattern shown in FIG. 3 and the wiring pattern shown in FIG.
The wiring pattern shown in FIG. 8 may be used, or the wiring wiring pattern shown in FIG. 5 or 6 may be combined with the wiring pattern shown in FIG. 7 to form the wiring pattern shown in FIG.

FIG. 10 is a cross-sectional view showing an example of a wiring portion when it is desired to increase the capacitance between wirings. In the figure, 10 is a wiring, 14 is an insulator, 15 is an insulating substrate, and 16 is a conductor. When it is desired to increase the inter-wiring capacitance, the conductor 16 is arranged on the insulator 14 covering the upper portion of the wiring 10 as shown in FIG. As a result, a capacitance close to that of a parallel plate capacitor can be obtained, so that it is possible to make the capacitance larger than the inter-wiring capacitance only by the wiring pattern. For example, when the insulator 14 is formed by thick film printing, the thickness is 2
Since it can be about 0 μm, if ε ₀ = 9 and the overlapping area is 4 mm × 0.05 mm, the increase in inter-wiring capacitance is (4000 × 50 × 8.854 × 9/20 × 10). ⁶ × 2) = 0.4 PF. Since the inter-wiring capacitance can be increased in this way, it can be used as one means for adjusting the inter-wiring capacitance when the ratio fn is set to a predetermined range, and the design selection range can be expanded. . For example, when the capacitance of the light receiving element and the internal capacitance of the driving element are large and a large inter-wiring capacitance is required to keep the ratio fn within a predetermined range, FIG.
The method as shown in 0 can be used.

[0023]

As is clear from the above description, according to the present invention, the inter-wiring capacitance, the light receiving element capacitance, and the driving element internal capacitance are taken into consideration in consideration of the inter-wiring capacitance as well as the capacitance in the light receiving element or the driving element. By designing the ratio of and to be within a predetermined range, it is possible to improve the non-uniformity of the output and improve the overall contrast.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of an image sensor for explaining the principle of the present invention.

FIG. 2 is a graph showing a relationship between a ratio fn and an afterimage rate.

FIG. 3 is a plan view showing an example of a wiring pattern of a wiring 10.

FIG. 4 is a plan view showing an example of a wiring pattern of a wiring 10.

5 is a plan view showing an example of a wiring pattern of the wiring 10. FIG.

6 is a plan view showing an example of a wiring pattern of the wiring 10. FIG.

7 is a plan view showing an example of a wiring pattern of the wiring 10. FIG.

8 is a plan view showing an example of a wiring pattern of the wiring 10. FIG.

FIG. 9 is a plan view showing an example of a wiring pattern of the wiring 10.

FIG. 10 is a cross-sectional view showing an example of a wiring portion when it is desired to increase the capacitance between wirings.

[Explanation of symbols]

1 voltage for light receiving element, 2 light receiving element capacity, 3 light receiving element, 4 driving element internal capacity, 5 wiring capacity, 6 sensor reset switch, 7 sensor output switch, 8
Sensor output signal line, 9 light, 10 wiring, 11 amplifier, 12 driving element, 13 inter-wiring capacitance correction pattern, 14 insulator, 15 insulating substrate, 16 conductor.

Claims (1)

[Claims] 1. A light-receiving element arranged in large numbers on a substrate, a driving element for driving the light-receiving element, and a conductor wiring group for electrically connecting the light-receiving element and the driving element. In the image sensor, the inter-wiring capacitances Cbn, n + 1 of the nth conductor wiring and the n + 1th conductor wiring of the conductor wiring group, the capacitance Cscrn of the light receiving element connected to the nth conductor wiring, and the nth conductor wiring. When the ratio fn calculated from the capacitance Cicn of the drive element connected to the conductor wiring is set to fn = Cbn, n + 1 / (Cscrn + Cicn), the ratio fn should be in the range of 0.02 to 0.1. An image sensor in which the conductor wiring group is wired.