JPH02192763A - Image sensor - Google Patents

Abstract

PURPOSE:To realize an image sensor of simple structure wherein crosstalk does not generate by forming a second insulating film and an upper surface ground electrode cn the upper surface of a matrix wiring part, and relatively reducing electrostatic capacitance between electrodes. CONSTITUTION:On a substrate 1, a lower electrode L is arranged; a first insulating film 5 is spread thereon; an upper electrode U is formed; a second insulating film 6 is arranged thereon; an upper surface ground electrode 7 is formed so as to cover the second insulating film 6. The upper electrode U and the lower electrode L have large areas facing the upper surface ground electrode 7, so that electrostatic capacitance C'' between these electrodes is comparatively large. As a result, electrostatic capacitance C' between the upper electrodes or between the lower electrodes becomes relatively small as compared with the above electrostatic capacitance C''.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an image sensor for reading images.

(Background of the Invention) Image sensors made of photodiode arrays are used in image reading devices such as facsimiles and image scanners.

Furthermore, amorphous silicon as a photoelectric conversion material has excellent properties and is used as a material for photodiodes.

Incidentally, as a method for driving an image sensor, matrix driving is often used, in which the number of driving ICs is small relative to the number of pixels. In this matrix drive, the photodiode array is divided into multiple blocks, and during reading, each block is sequentially switched and the signals corresponding to the optical signals that hit the photodiodes are sequentially read out for each block. It is.

(Problem to be Solved by the Invention) However, in matrix driving in which the image information as described above is read out as a current value, the inductance of the wiring connected to the photodiode and the stray capacitance between the wirings are large, which affects the signal level. However, there is a problem in that accurate image information cannot be obtained.

Therefore, a reading circuit as shown in FIG. 5 has been proposed.

In this figure, a part M surrounded by a broken line is a matrix wiring part, which has m photoelectric conversion elements (shown as an equivalent circuit).
n blocks having the following are connected. Bl (1
<l <n) is a common connection terminal of each block, and is connected to the bias voltage -■ (when a block is selected) or ground (when not selected) via a switch SBI (1<I <n). Each photoelectric conversion element includes a blocking diode BDlj (1<i<n, 1<j<m) and a photodiode PDIj (1<]<n, 1<j<m).
, a storage capacitor CP considered to be connected in parallel with the photodiode PDij, and a capacitor CB considered to be connected in parallel with the blocking diode BDIj. CRj(1<j<
m) is a reading capacitor connected to the photoelectric conversion element, and its capacitance value is selected to be sufficiently larger than that of the storage capacitor CP. Sj (1<j<m) is a reset switch for resetting the reading capacitor CRj;
Aj (1<j<m) is the reading capacitor CRj
A buffer amplifier, SRj (1<
J<m) is a switch that selects the output of the buffer amplifier Aj at the time of reading.

If such a reading circuit is used, the reading capacitor CR is charged with a current corresponding to the amount of light irradiated to the photodiode when a block is selected, so that optical signals can be sequentially extracted as a voltage across the reading capacitor CR.

FIG. 6 is an explanatory diagram showing a schematic configuration when the circuit shown in FIG. 5 described above is actually arranged on a board. In the figure, 1 is a substrate made of glass, ceramic, etc., and 2 is a diode section in which a photodiode PDIj and a blocking diode BDIj are arranged. Note that the details of the arrangement of this diode section 2 will be omitted. L, , -Lnm are lower r1 poles that lead the output of each photodiode PDIj of the diode section 2, respectively. U1 to U6 are lower electrodes Lu-L
This is the upper electrode that leads the output from r+m to the reading IC4. Although the upper electrodes up to U6 are shown here, the explanation will be made assuming that there are m electric currents tM (Ul to Um). Also,
The lower electrode and the upper electrode U are made of Al, Cr, and Ti.

It is made of metal such as MO. 3 is the lower electrode Lx-L
5i0 for insulation between nm and upper electrodes U1 to Um
2. This is an insulating film coated with SiN, polyimide, etc.

Note that the connection point between the lower electrode and the upper electrode is a contact hole.

FIG. 7 is an enlarged view showing the contact hole portion of FIG. 6 mentioned above. And, Fig. 8 is A-A of Fig. 7 mentioned above.
'It is a sectional view showing a cross section. Figure 9 is B of Figure 7 above.
It is a sectional view showing a -B' cross section. In this way, the upper electrode and the lower electrode are insulated by the insulating film 3, and necessary connection points are connected through contact holes.

However, since the matrix wiring part M has long signal lines and is wired in multiple layers, there is a non-negligible line capacitance between the signal lines (between the upper electrodes or between the lower electrodes), and capacitive coupling occurs between the signal lines. ing. This line capacitance causes crosstalk between adjacent elements and between blocks.

As an example, the reading length is 216mo+ (A4 size).

In the case of a line sensor with a pixel density of 8 doj 7 mg and a block number of 27.64 elements/block, the line capacitance between one line pair of upper electrodes is about 120 pF.

Therefore, when a voltage fluctuation occurs in a certain signal line due to the photoelectric conversion output, a voltage is also induced in the adjacent signal line via the line capacitance. For example, in FIG. 6, when a voltage fluctuation occurs in the upper mold WU2, a voltage is also induced in the adjacent upper electrodes U, , U. Crosstalk occurs in this way. Therefore, the MTF decreases, making it impractical.

The present invention has been made in view of these problems, and an object of the present invention is to provide an image sensor that has a simple configuration and does not cause crosstalk.

(Means for Solving the Problems) The present invention for solving the above-mentioned problems includes a photoelectric conversion means in which a plurality of photoelectric conversion elements are arranged in an array, and a device for reading out an output signal from the photoelectric conversion means to the outside. In the image sensor having a matrix wiring section, the matrix wiring section is a lower electrode.

The device is characterized in that a first insulating layer, an upper electrode, a second insulating layer, and a top electrode are laminated, and the top electrode is grounded.

(Function) In the image sensor of the present invention, the upper surface electrode formed to cover the wiring of the upper electrode reduces the influence of capacitance between the wirings.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a cross section of a wiring pattern on a substrate according to an embodiment of the present invention. This figure shows a cross section in a direction perpendicular to the lower electrode. In the figure, the same parts as in FIG. 8 are given the same numbers, and detailed explanations are omitted. In the figure, 5 is a first layer coated on the substrate 1 or the lower electrode layer.
It is an insulating film.

An upper electrode U is arranged on this first insulating film 5, and a second insulating film is further arranged above it. An upper ground electrode is formed to cover the second insulating film 6. This upper ground electrode 7 is connected to the ground (earth) of the circuit. Therefore, since the upper electrode U and the lower electrode have a large area facing the upper ground electrode 7, they have a relatively large capacitance C' between them.

Therefore, the capacitance (line capacitance ff1) C' between the upper electrodes and between the lower electrodes is relatively smaller than the capacitance C' described above. Therefore, the influence of crosstalk is almost eliminated.

FIG. 2 shows a cross section in a direction perpendicular to the upper electrode U. Here, the vicinity of upper electrodes UII+UI2 is shown. Generally, the capacitance C between parallel conductors is proportional to the opposing area of the conductors and inversely proportional to the distance between the conductors.

Therefore, it is clear that the capacitance between each electrode and the upper surface ground electrode 7, which has a large opposing area, becomes large.

FIG. 3 is a characteristic diagram showing the characteristics of an output signal when a repeating white/black pattern is read by an image sensor. Third
Figure (A) shows the characteristics that would be obtained with an ideal image sensor, Figure 3 (B) shows the characteristics that would be obtained with a conventional image sensor, and Figure 3 (C) shows the characteristics that would be obtained with the image sensor of the present invention. This shows the characteristics obtained with . Here, we will explain the pixel position and sensor output voltage when the m-th pixel in a, c, e, g, and l of the image sensor is illuminated and the other pixels are not illuminated. The characteristics were shown. In addition, in Fig. 3 (B) and (C), the reading length is 216 mm.
(A4 size) 1 pixel density 3 dat/mm.

Characteristics were shown when a line sensor with a block number of 27.64 elements/block was used to actually read a white/black repetitive line pattern of 4Ωp/llll11.

In the case of the ideal image sensor shown in FIG. 5(A), a,
Output voltages are obtained only from the c, e, g, i, k, and mth pixels.

On the other hand, in the case of conventional image sensors, as shown in Figure 3 (B), the voltage level of pixels receiving light decreases due to the influence of crosstalk, and the voltage level of pixels receiving light decreases (pixels receiving light do not receive light). A voltage is also generated in the pixels adjacent to the pixel. In this case, MTF (Modura f
an Transrer Function)
is about 16%, which is not very suitable for practical use.

In the case of the image sensor of the present invention shown in FIG. 3(C), the voltage level of the pixel receiving light is opposite, and the voltage level of the pixel not receiving light (the pixel adjacent to the pixel receiving light) is The output voltage also drops considerably. MTF at this time
is about 60%, which is a remarkable improvement in characteristics compared to the conventional one. This is because the line capacitance between the electrodes is relatively small due to the upper ground electrode 7, and crosstalk between the electrodes is reduced.

FIG. 4 is an explanatory diagram for explaining the manufacturing process of the matrix wiring section M. Note that a part of the matrix wiring section is shown here for explanation. First, lower electrodes L++ to L+3 of C' are formed by sputtering or vacuum evaporation on the substrate 1 on which the diode part 2 (not shown) is formed (FIG. 4(A)). A first insulating film 5 made of SiN, polyimide, etc. is formed, and then etched using a mask pattern. That is, the insulating film in the portion where the connection is made through the contact hole is removed (FIG. 4(B)).
. Then, form the 2L portion electrodes ①~U of Al1, and
Connections are made with the partial electrodes Lll to L, 3 (Fig. 6(C)).
. Thereafter, a second insulating film 6 is formed over the entire matrix wiring section M, and an upper ground electrode 7 is formed on this second insulating film 6. Then, this upper ground electrode 7 is connected to the ground of the circuit.

Incidentally, in the above embodiment, the upper surface ground 1i17 was formed so as to cover the entire surface of the second insulating film 6, but the present invention is not limited to this. For example, the upper ground electrode 7 may be formed in accordance with the pattern shape of the upper electrode U and the lower electrode.

(Effects of the Invention) As described above in detail, in the present invention, the second insulating film and the top ground electrode are formed on the top surface of the matrix wiring section. Therefore, the capacitance between the electrodes can be relatively reduced, and crosstalk can be reduced. Therefore, it is possible to realize an image sensor that does not cause crosstalk with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a cross section of a wiring pattern according to an embodiment of the present invention, FIG. 2 is a sectional view showing another cross section of the wiring pattern, and FIG. 3 is a characteristic diagram showing output voltage characteristics of an image sensor. FIG. 4 is an explanatory diagram explaining the manufacturing process of the image sensor of the present invention, FIG. 5 is a circuit diagram showing the circuit of the image sensor, FIG. 6 is a pattern diagram showing an example of the circuit pattern of a conventional image sensor, and FIG. 7 is a partial plan view of a part of the pattern shown in FIG. 6 on an enlarged scale, FIG. 8 is a sectional view taken along the line AA' in FIG. 7, and FIG. FIG. 1...Substrate 3...Insulating film 5...First insulating film 7...Top ground electrode U...Upper electrode 2...Diode part 4...Reading IC 6...No. 2 Insulating film L...lower electrode

Claims (1)

[Scope of Claims] An image sensor comprising a photoelectric conversion means in which a plurality of photoelectric conversion elements are arranged in an array, and a matrix wiring section for reading an output signal from the photoelectric conversion means to the outside, comprising: An image sensor characterized in that the wiring portion includes a lower electrode, a first insulating layer, an upper electrode, a second insulating layer, and an upper surface electrode, and the upper surface electrode is grounded.