JPH067588B2 - Contact type image sensor - Google Patents

Description

The present invention relates to a contact type image sensor used as a photoelectric conversion device for facsimiles, optical character recognition and copying machines.

(Prior art and its problems) Compared with a MOS type IC image sensor, a CCD image sensor, etc., this contact type image sensor does not use a reduction optical system with a lens, so that a facsimile apparatus can be realized in a small size and is economical Are better. Amorphous silicon (hereinafter referred to as a-Si), which has high photosensitivity in the visible light region and is easy to form a large area, has recently been often used as a photoelectric conversion element material of the contact image sensor.

This a-Si has a high specific resistance and is suitable for the charge storage mode operation like the CCD image sensor and the MOS type IC image sensor. In this case, as the device structure, a structure in which a-Si is sandwiched between upper and lower electrodes is usually used. However, by adopting such a sandwich structure, the photoresponse speed of the device is as high as 0.1 msec or less. And an image sensor suitable for a high-speed reading device can be obtained.

FIG. 3 is a sectional view of an image sensor having a conventional sandwich element structure. For example, the a-Si photoelectric conversion film 12 is formed on the insulating substrate 10 made of glass or the like on the individual electrode 11 made of, for example, Cr or the like, for example, the plasma C.
It is formed by VD or the like. This a-Si photoelectric conversion film 1
A transparent electrode 13 made of, for example, Indium Tin Oxide (hereinafter referred to as ITO) is vapor-deposited on the second electrode by sputtering or the like, and further, a linear shape made of, for example, Cr or Ti that determines the dimension of the photoelectric conversion element opening in the sub-scanning direction. The light-shielding film 16 having an opening is formed in a band shape. This light-shielding film 16 is necessary also for lowering the resistance value of the ITO transparent electrode 13 as the common electrode and realizing high-speed reading.

A driving circuit capable of reading the optical signal charges generated by the a-Si photoelectric conversion element 12 at high speed and with high sensitivity is disclosed in Japanese Patent Application No. 59-143020 "contact type sensor and its driving method". There is a CCD drive circuit. This circuit is shown by FIG. Briefly explaining this figure, CC
The input terminal row 24 of the driving CCD 20 and at least the individual electrode terminal row 26 of the a-Si photoelectric conversion element 25, which are at least composed of the D shift register 21, the transfer gate row 22, and the floating gate amplifier 23, are bonded to each other by the bonding wire 47 in a one-to-one relationship. Is connected according to. a-Si
The optical signal charges generated in the photoelectric conversion element 25 are sent to the CCD shift register 21 through the transfer gate 22, then sequentially transferred in time series by the transfer clocks φ1 and φ2, and output through the floating gate amplifier 23.

However, when viewed from the transfer gate 22 in such a CCD drive system, the ground capacitance C _P on the a-Si photoelectric conversion element 25 side is larger than that of the IC image sensor,
As a result, the input signal potential obtained by dividing the optical signal charge amount Q _sig by the ground capacitance C _P Becomes smaller, so that an afterimage due to so-called incomplete transfer becomes remarkable. Particularly, in such a hybrid type sensor, since the wiring capacitance and the like are also included, this afterimage becomes extremely large as compared with a normal IC image sensor.

FIG. 5 shows a plan view of a conventional photoelectric conversion element portion having a sandwich structure. Here pairs mentioned above ground capacitance C _P is substantially determined by the sum of the wiring capacitance C _P2 between the device opening capacitance C _P1 and the individual electrode 11 and the light-shielding film 16 between the individual electrode 11 and the transparent electrode 13. Area of element opening is S ₁ , individual electrode 11 and light-shielding film 1
Let S _{2 be} the area of the overlapping portion of 6, the film thickness of a-Si 12 be d, the relative permittivity of a-Si 12 be ε _r , and the permittivity of vacuum be ε ₀ . Is represented.

In order to suppress this afterimage, that is, to reduce the capacity, a
-If the thickness of Si12 is increased, the photoresponse speed deteriorates, and
-Si12 vapor deposition time increases, which causes problems such as increased man-hours and cost, which is not effective.

As a constitution of the individual electrode 11 shown in FIG. 5, the alternate lead extraction is a very effective means for making patterning very easy, reducing man-hours and improving yield in a high resolution device of about 16 lines / mm or more. Yes, it is currently used in various devices. Therefore, the light-shielding film 16 is conventionally in the form of a strip having a linear opening as shown in FIG. To reduce the wiring portion area S ₂ is considered to narrow the width of the individual electrode 16, which also is limited, the yield, given the reproducibility of a normal photolithography 10μm~
It is up to about 15 μm. Another possible method is to narrow the stripe width of the light shielding film 16. However, if the stripe width of the light shielding film 16 serving as the common electrode is narrowed, the resistance increases and it becomes unsuitable for high speed operation. Although it is possible to increase the thickness of the light-shielding film 16 in order not to increase this resistance, if Cr, Ti, or the like as the material of the light-shielding film 16 is increased, cracks or the like easily occur, or problems such as peeling occur. , At most 1000Å ~ 2000Å. Normally, with Cr, Ti, etc., the sheet resistance is 10Ω to 50Ω at this thickness. For example, even if the stripe width of the light shielding film 16 is 5 mm, if the A4 size length is about 220 mm, it becomes 440Ω to 2.2 KΩ. Also becomes. At this time, the wiring capacitance C _P2 is about 5 pF or more, for example, when the film thickness of the a-Si 12 is about 1 μm and the width of the individual electrode 11 is 10 μm. At this time, at 16 elements / mm, the element opening capacitance C _P1 is smaller than the wiring capacitance by about 0.3 pF.

In the case of a conventional CCD image sensor, this capacitance to ground is
Since it is 0.01 pF or more, it can be seen that the wiring capacitance C _P2 is very large in comparison with this, which poses a serious problem in reading by CCD driving.

(Object of the Invention) An object of the present invention is to eliminate such drawbacks, provide a contact type image sensor which has a reduced wiring capacitance, can operate at high speed, and has a small afterimage.

(Structure of the invention) A structure of the present invention is such that a plurality of individual electrodes are provided on an insulating substrate.
A photoelectric conversion film provided so as to cover a part of each of the individual electrodes, and a transparent electrode provided in a band shape so as to partially cover the photoelectric conversion film and partially intersect with the individual electrodes, In a contact image sensor in which at least a strip-shaped opaque electrode that covers a part of a transparent electrode and has an opening at a portion where the individual electrode and the transparent electrode intersect is provided, each of the individual electrodes of the opaque electrode It is characterized in that a part of the facing portion is removed.

(Operation and principle of the invention) By adopting the configuration of the present invention, it is possible to adapt to high-speed operation,
An adhesive image sensor capable of reducing afterimages as much as possible can be obtained. That is, in the present invention, the wiring capacitance between the individual electrodes and the light-shielding film can be minimized without increasing the resistance of the light-shielding film that is the common electrode. Therefore, even when the drive circuit using the CCD shift register is used, The signal potential V _in can be set large, and afterimages due to incomplete transfer can be suppressed as much as possible. In addition, when used together with the afterimage suppression method of applying bias charges or the like, the conventional I
Higher performance of C image sensor or higher can be achieved.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a plan view of the first embodiment of the present invention. For example, at least a discrete electrode 11 made of, for example, Cr formed on the glass substrate 10, an a-Si photoelectric conversion film 12, an ITO transparent electrode 13, and a light-shielding film 14 made of, for example, Cr, Ti are formed on the individual electrode 11. Has been done. Here, the light-shielding film 14 is not a simple stripe as shown in the conventional example, but has a so-called comb-shaped structure in which the width of the portion corresponding to the upper part of the individual electrode 11 is narrow and the others are wide.
Therefore, as described above, the wiring capacitance C _P2 between the individual electrode 11 and the light shielding film 14 can be reduced, and the resistance of the light shielding film 14 can be suppressed as much as possible.

For example, consider the case of A4 size and 16 elements / mm. Here, when the thickness of the a-Si photoelectric conversion film 12 is 1 μm, the width of the individual electrode 11 is 10 μm, and the width of the light shielding film 14 is 0.5 mm and 50 mm, respectively, the wiring capacitance C _P2 is the same as that in the conventional example. It will be 1/10, which can be about 0.5 pF. At this time, the resistance of the light-shielding film 14 has a sheet resistance of 10Ω to 50Ω.
As a narrow partial resistance And the resistance of the wide part It is represented by the sum of. Therefore, the combined resistance is about 400Ω to 2K
Even if the capacitance to ground is 1/10, the resistance can be made approximately equal to that of the conventional wide pattern, and does not adversely affect the high speed operation. Further, the capacitance to ground becomes as small as 0.8 pF in total, and if it reaches this level, it can be reduced to 0. 0 in an A4 size, 16-element / mm contact image sensor due to the drive system using a CCD shift register and the afterimage suppression by bias charge injection. A high SN ratio equal to or higher than that of a conventional IC image sensor can be achieved by high-speed driving of 5 msec / line or less. In addition, the light shielding films 14 on both sides
May be common to both ends on the A4 size glass substrate 10.

FIG. 2 shows a plan view of another embodiment of the present invention. This embodiment has the same components as the first embodiment, and the light shielding film 1
The shape of No. 5 is an example in which the comb shape is changed to the lattice shape, and the effect is the same as that of the first embodiment.

Further, the patterning of the light-shielding film is not particularly different from that of the stripe pattern, and the same conventional process and man-hours are sufficient. Further, contrary to the configuration of this embodiment, a configuration in which the light-shielding film side and the individual electrode of the a-Si photoelectric conversion film are replaced may be used.

(Effects of the Invention) As described in detail above, according to the present invention, the capacitance to ground of the a-Si photoelectric conversion element portion can be reduced without increasing the resistance value of the light shielding film that is the common electrode, and the high speed operation can be achieved. It is possible to form a contact-type image sensor that can sufficiently cope with In particular, it is possible to reduce afterimage, which has been a big problem in constructing a high-speed, high-performance contact image sensor using a CCD shift register as a drive circuit. A high-performance contact-type image sensor is realized, and it is possible to apply not only to facsimiles, but also to optical character recognition and copying machines, and to halftone and color devices.

[Brief description of drawings]

1 and 2 are plan views of the first and second embodiments of the present invention, FIGS. 3 and 5 are sectional views and plan views of elements of a conventional contact image sensor, and FIG. 3 is a circuit diagram of an example of a circuit that drives the device of FIG. In the figure, 10 ... Glass substrate, 11 ... Individual electrode, 12 ... Amorphous silicon photoelectric conversion film, 13 ... Transparent electrode, 1
4, 15, 16 ... Shading film, 20 ... Driving CCD chip, 21 ... CCD shift register, 22 ... Transfer gate, 23 ... Floating gate amplifier, 2
4 ... Pad, 25 ... Amorphous silicon photoelectric conversion element, 26 ... Individual electrode terminal, 27 ... Bonding wire.

Claims (1)

[Claims] 1. A plurality of individual electrodes on an insulating substrate, a photoelectric conversion film provided so as to cover a part of each individual electrode, and each individual electrode covering a part of the photoelectric conversion film. The number of transparent electrodes provided in a strip shape so as to partially intersect with each other and the strip-shaped opaque electrode that covers a part of the transparent electrodes and has an opening at a portion where the individual electrodes intersect with the transparent electrodes are reduced. The contact type image sensor, wherein the part of the opaque electrode facing the individual electrodes is partially removed in the contact type image sensor.