JPS62140461A - Image sensor - Google Patents

Abstract

PURPOSE:To obtain an image sensor having excellent output uniformity by fitting an auxiliary electrode in a clearance between discrete electrodes. CONSTITUTION:An image sensor is constituted of an insulating substrate 101, amorphous silicon 102, a transparent electrode 103, discrete electrode 104, IC chips 105 for drive, bonding wires 106 and an auxiliary electrode 107. the auxiliary electrode 107 is disposed to a section where a clearance between the discrete electrode 104 differs from other sections, a section between discrete electrode 104a and 104b. Capacitance in which each capacitance between the discrete electrode 104a and the auxiliary electrode 107 and between the discrete electrode 104b and the auxiliary electrode 107 is connected in series between the discrete electrode 104a and 104b by the auxiliary electrode 107. Accordingly, dispersion to respective discrete electrode is reduced, thus equalizing outputs.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an image sensor that performs photoelectric conversion in close contact with a document.

(Prior art) Figure 2 shows 1. For example, the Institute of Electronics and Communication Engineers technical research report CPM 8
8-42 (October 21, 1982) showing the operation of the image sensor. In the figure, (2
01) is a photodiode as a light sensor.

(202) is a voltage follower type buffer amplifier;
(2H), (204) are switch elements, (205) is a shift register, (208) is a start pulse input terminal, (207) is a clock input terminal, (209) is an output terminal, (210) is a sensor input terminal (206) indicates the drive IC block, and (212)! Source, (211) indicates the line capacitance.

@Figure 8 is a timing diagram showing the circuit operation of the image sensor in Figure 2. In the figure, (101) is the input signal to the clock input terminal (207), (802
) is the input signal to the start pulse input terminal (208),
(808) is the Q1 output of the shift register (205),
(804) is the Q2 output of the shift register (205),
(305) is the Qn output of the shift register (205), and (806) is the output from the output terminal (209), and their respective waveforms are shown.

Next, the operation will be explained. First, attention will be paid to the first photodiode (201). The switch element (203) connected to the cathode side of the photodiode (201) is Q2 of the shift register (205).
It is closed when the output (804) becomes H level, and a power supply (212) is connected to both ends of the photodiode (201).
A voltage Vs is applied. At this time, the capacitance component Cd (not shown) of the photodiode (201) has a charge q.

(=CdVs) is charged. Next, when the Q2 output (804) of the shift register (205) becomes L level, the cathode side of the photodiode (201) is opened. On the other hand, the photodiode (201) has
Light corresponding to the density of a read document (not shown) is input, and a photocurrent Ip flows in the direction shown by the arrow in FIG. The photocurrent 1p discharges the charges accumulated in the capacitance component Cd of the photodiode (201). In this state,
After the time Ts shown in FIG. 8 has elapsed, the voltage Vp between the terminals of the photodiode (201) is expressed by the following equation.

However, the influence of line capacitance (211) shown in FIG. 2 was ignored. After the above-mentioned time Ts has elapsed, when the Q1 output (808) of the shift register (205) becomes H level, the switch element (204) connected to the output of the first buffer amplifier (202) is closed, and the next The output voltage V shown by the formula. is output to the output terminal (209).

In the above equation (2), assuming that the photocurrent Ip does not depend on the terminal voltage vp of the photodiode (201), when the amount of light is constant, the above equation (2) becomes linear. , the output voltage Vo is proportional to the amount of light.

Therefore, as shown in Figure @8, the start pulse (30
2) is input at regular intervals, the output voltages V corresponding to the above equation (3) from the first to the nth.

are output to the output terminal (209) in time series.

Next, the configuration of an image sensor that implements the circuit configuration shown in FIG. 2 will be described. FIG. 4 shows a plan view and a sectional view showing the configuration of a conventional image sensor. In the figure,
(101) is an insulating substrate% (102) is amorphous silicon, (108) is a transparent electrode, (104) is an individual electrode, (
105) is a driving IC chip, and (106) is a bonding wire.

The above individual electrode (104), amorphous silicon (102)
and a transparent electrode [103], the photodiode (
201). The transparent electrode (108) is common to each photodiode and also serves as a common electrode, and the driving IC chip (105) includes the circuit elements shown in FIG. 2 (206). , are accumulated.

Next, the effect of the line capacitance Ci,j (211) will be described. - Example @2nd photodiode (201)
think about. When the Q8 output of the above shift register becomes H level, the second photodiode (201)
A switch element (208) connected to the cathode side of
turns on. At this time, if the effect of the line capacitance (211) is limited to both sides, the capacitance charged by the switch element is the capacity of the second photodiode (201), the line capacitance C12, and the first photodiode. This is a series capacitance of the diode capacitance cd, and a parallel capacitance of the series capacitance of the storage capacitor c23 and the third photodiode capacitance cd. Therefore, the charging charge Φ' becomes.

The amount of charge Δq lost from the charged charge q2 during the time Ts shown in both FIGS. 3 is as follows.

Therefore, when Q2 of the shift register (205) becomes H level, the voltage Vp between the terminals of the second photodiode (201) becomes as shown in the following equation.

However, "03" is the 8th photodiode (20
1) is the voltage between the terminals.

As can be seen from equation (6), the output voltage V0 (-Vp −
Vs) depends on the line capacitance. Therefore, considering an image sensor as shown in FIG. 5, the length of the individual electrodes is several mm, and in such a case, a line capacitance of about 0.1 to 19 F is usually generated. Furthermore, since the capacitance of the photodiode (201) made of amorphous silicon is about 0.5 to 5 pF, the line capacitance cannot be ignored.

Therefore, it can be seen that variations in the line capacitance (211) appear as non-uniformity in the output voltage.

Looking at the image sensor in Figure @5 from this perspective.

Individual electrodes (
104) are separated, and for this reason, the line capacitance between the individual electrodes (104J) on both sides is smaller than that of the other individual electrodes (104J).
104) is smaller than the interval.

[Problem that the invention seeks to solve]

Since the conventional image sensor is configured as described above, there is a problem in that even when a uniform amount of light is incident, large non-uniformity of output occurs.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain an image sensor having excellent output uniformity.

[Means for solving problems]

The image sensor according to the present invention is one in which an auxiliary electrode is newly provided in the gap between one individual electrode.

(Function) The auxiliary electrode according to the present invention has the function of eliminating variations in line capacitance, which were present in the conventional example, and can make the output of the image sensor uniform.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. @1
In the figure, (101) is an insulating substrate, (102)
is amorphous silicon, (108) is a transparent electrode, (104
) is an individual electrode, (105) is a driving IC chip, (10
6) is a bonding wire, and (107) is an auxiliary electrode.

Next, one important component in the present invention is the auxiliary electrode (
107) will be explained. As shown in FIG. 1, the auxiliary electrode is disposed between a portion of the individual electrode (104) with a different gap, that is, between (104a) and (104b).

This auxiliary electrode (107) is used between the individual electrodes (104a) and (104b), and between the individual electrode (104a) and the auxiliary electrode (107).

This means that a capacitor is inserted between the individual electrode (104b) and the auxiliary electrode (107), each of which is connected in series. Therefore, as can be seen from equation (6), the auxiliary electrode (107) reduces the variation in Cij (i, j are integers) for each individual electrode, and the output can be made uniform.

FIG. 4 shows another embodiment of the invention. In this embodiment, the auxiliary electrode is divided into two parts, one of which is connected to the individual electrode (104a) and the other to the individual electrode (104b).

In this case, the line capacitance (211) is the divided auxiliary electrode (1
07). The advantages and disadvantages are the same as in the above embodiment.

In the embodiment shown in FIG. 1, an example was shown in which the auxiliary electrode (107) was arranged in the gap between the individual electrodes (104).

The supplementary TiE! (10?) may be connected to the individual electrode (104a) or (104b), and the individual electrode may be further connected to a power source or the like and fixed at a constant potential. the above,
In either case, the same effects as in the above embodiments are achieved.

[Effects of the Invention] As described above, according to the present invention, the individual electrodes (104)
This is because the auxiliary electrode (107) is placed in the gap between the two.

The uniformity of the line-to-line volume 1 (211) is maintained, resulting in the effect of improving the output uniformity of the image sensor.

[Brief explanation of drawings]

1 is a plan view and a sectional view showing an image sensor according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the circuit configuration of the image sensor, FIG. 8 is a timing diagram showing the operation of FIG. 2, and FIG. 4 is a plan view and a sectional view of an image sensor according to another embodiment of the present invention, and FIG. 5 is a plan view and a sectional view of a conventional image sensor. In the figure, (101) is an insulating substrate, (102) is amorphous silicon, (108) is a transparent electrode (common electrode), (
104) is an individual electrode, and (107) is an auxiliary electrode. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (4)

[Claims] (1) An insulating substrate, an amorphous semiconductor film formed on the insulating substrate, a common electrode formed on one surface of the amorphous semiconductor film, and an individual electrode formed on the other surface. An image sensor comprising an image sensor comprising an auxiliary electrode disposed in a gap between the individual electrodes. (2) The image sensor according to claim 1, wherein the auxiliary electrode is arranged every other plurality of individual electrodes. (3) The image sensor according to claim 1 or 2, wherein the auxiliary electrode is electrically connected to one of the individual electrodes on both sides sandwiching the auxiliary electrode. (4) Claim 1, wherein the auxiliary electrode is electrically connected to a power source or a ground electrode.
The image sensor according to item 1 or 2.