JP2008147421A - Photoelectric conversion device, and image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion device and an image reading apparatus which can secure sufficient storage capacitance. <P>SOLUTION: In a second interlayer insulating film 41 covering a TFT 21 provided on a substrate, a capacitance forming portion 43 which sags in a thickness direction is formed in a concave shape. Storage capacitance 22 is provided along the side surface 43a of the capacitance forming portion 43. Thus, the storage capacitance 22 is formed not in a planar shape but in a solid shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a photoelectric conversion device that outputs an electrical signal corresponding to the amount of incident light, and an image reading device using the photoelectric conversion device.

Conventionally, as an image reading apparatus for reading various image data, an active matrix type in which pixels having a photoelectric conversion element such as a photodiode or a phototransistor, a switching element such as a TFT (thin film transistor), and a storage capacitor are arranged in a two-dimensional form. Are known (for example, see Patent Document 1). In such an image reading apparatus, image information photoelectrically converted by each photoelectric conversion element is temporarily stored as a charge in a storage capacitor, and an electric signal corresponding to the accumulated charge amount is sequentially output from each photoelectric conversion apparatus. Image data is read.
JP 2004-96079 A

On the other hand, recent image reading apparatuses are required to increase the number of pixels formed on a chip of the same size, that is, to increase the density of pixels. However, in the photoelectric conversion device as described above, since the photoelectric conversion element and the storage capacitor are formed on the substrate, the electrode area of the storage capacitor is reduced by increasing the density, and a sufficient capacity cannot be secured. There was a problem.

SUMMARY An advantage of some aspects of the invention is that it provides a photoelectric conversion device and an image reading device capable of securing a sufficient capacity.

In order to solve the above problems, in the photoelectric conversion device of the present invention, a switching element provided on a substrate, a storage capacitor electrically connected to the switching element, and a storage capacitor electrically connected to the switching capacitor A photoelectric conversion device comprising: a photoelectric conversion element, storing an electric signal generated according to the amount of light received by the photoelectric conversion element in the storage capacitor, and outputting the electric signal via the switching element, The storage capacitor is provided on at least a side surface of the capacitor forming portion that is recessed in the thickness direction of the interlayer insulating film provided on the switching element.

According to the present invention, in the interlayer insulating film covering the switching element provided on the substrate, the capacitor forming portion that is depressed in the thickness direction is recessed, and the storage capacitor is provided on the side surface of the capacitor forming portion. It is done. That is, since the storage capacitor is provided three-dimensionally rather than planarly, the electrode area can be increased compared to the case where a planar storage capacitor is formed. Therefore, by appropriately adjusting the thickness of the interlayer insulating film, a sufficient storage capacity can be ensured even when the density of the photoelectric conversion device is increased.

In the photoelectric conversion device according to the present invention, the photoelectric conversion element is connected to the switching element through a contact hole formed through the interlayer insulating film, and the capacitance forming portion is the interlayer insulation in which the contact hole is formed. You may form in a film | membrane.

According to the present invention, since the capacitor forming portion is formed in the interlayer insulating film in which the contact hole is formed, it becomes possible to form the contact hole and the capacitor forming portion at the same time, thereby simplifying the manufacturing process of the photoelectric conversion device. Can contribute.

In the photoelectric conversion device according to the present invention, the interlayer insulating film includes a first interlayer insulating film and a second interlayer insulating film using an acrylic resin laminated on the first interlayer insulating film, and the storage capacitor May be formed in the second interlayer insulating film.

According to the present invention, since the acrylic resin is used for the second interlayer insulating film, the second interlayer insulating film can be formed by the coating process and the curing process. Accordingly, the film forming process can be performed in a short time, and an interlayer insulating film having a large thickness can be easily formed. And
By increasing the thickness of the second interlayer insulating film and forming the capacitor forming portion in the second interlayer insulating film, a storage capacitor having a wider electrode area can be formed.

In the photoelectric conversion device of the present invention, one electrode of the storage capacitor may also serve as an electrode connected to the photoelectric conversion element.
According to this invention, one electrode of the storage capacitor also serves as an electrode connected to the photoelectric conversion element. Thereby, since it is not necessary to provide the electrode for connecting with a photoelectric conversion element as another member, the number of parts of a photoelectric conversion apparatus can be reduced.

The photoelectric conversion device of the present invention may include a second storage capacitor connected to the storage capacitor in series or in parallel and formed on the substrate.
According to the present invention, since the second storage capacitor is formed on the substrate in addition to the storage capacitor provided on the side surface of the recess of the interlayer insulating film, a sufficient capacity can be ensured more reliably. .

In the photoelectric conversion device according to the present invention, the interlayer insulating film includes a first interlayer insulating film and a second interlayer insulating film stacked on the first interlayer insulating film, and the storage capacitor is the second interlayer insulating film. It may be formed in an interlayer insulating film, and the photoelectric conversion element may be provided on the second interlayer insulating film so as to cover the switching element.

According to the present invention, since the second interlayer insulating film in which the storage capacitor is formed and the photoelectric conversion element are stacked above the switching element, the light receiving area of the photoelectric conversion element can be reliably ensured, and the photoelectric conversion element can be secured. It is possible to increase the density of the conversion device. Further, since the photoelectric conversion element covers the switching element, noise generated when the switching element receives light can be improved.

In the present invention, the photoelectric conversion device is used in the image reading device.
According to the present invention, it is possible to provide an image reading apparatus having sufficient sensor output while increasing the density.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 2, the image reading apparatus 1 according to the present embodiment is used for an image scanner, for example, and includes a plurality of photoelectric conversion sensors 11 as photoelectric conversion devices arranged in a two-dimensional manner. Yes. The photoelectric conversion sensors 11 in each column are connected to the gate drive circuit 12 through the gate wiring 12a, and the photoelectric conversion sensors 11 in each row are connected to the reading circuit 13 through the source wiring 13a. Each photoelectric conversion sensor 11 includes a thin film transistor (hereinafter referred to as TFT) 21 as a switching element, and the gate of the TFT 21 is connected to a gate wiring 12a.
The source of the TFT 21 is connected to the source line 13a, and the drain of the TFT 21 is the storage capacitor 2
2 is connected to the first terminal, and the second terminal of the storage capacitor 22 is connected to the ground. Also,
The drain of the TFT 21 is connected to the cathode of a photodiode 23 as a photoelectric conversion element, and the anode of the photodiode 23 is connected to the ground.

As shown in FIG. 1, the photoelectric conversion sensor 11 includes a substrate 2 made of glass or the like, and the substrate 2
The TFT 21 is formed on the element formation surface 2a.
The TFT 21 has a semiconductor layer 31 formed on the element formation surface 2a by patterning a semiconductor film made of polysilicon or the like. The semiconductor layer 31 includes a channel region 31c containing an intrinsic semiconductor or p-type impurity formed at the center thereof, and n on both sides thereof.
It has a source region 31s and a drain region 31d which are type impurity regions. In addition, a gate insulating film 32 made of a silicon oxide film or the like is formed on the upper side of the semiconductor layer 31, and on the upper side of the gate insulating film 32 and above the channel region 31c, the gate wiring 1 is formed.
A gate electrode 33 extending from 2a is formed. Gate electrode 33 (gate wiring 12
a) is formed by patterning a conductive film made of an aluminum film or the like formed on substantially the entire element formation surface 2a. A first interlayer insulating film 34 made of a silicon nitride film or a silicon oxide film that electrically insulates the gate electrodes 33 is formed on the gate electrode 33.

Through holes 35 penetrating the gate insulating film 32 and the first interlayer insulating film 34 are formed on the source region 31 s and the drain region 31 d of the semiconductor layer 31, and the source regions 31 s are respectively formed in the through holes 35. A source electrode 36 and a drain electrode 37 corresponding to the drain region 31d are formed. The source line 13 a extends above the source electrode 36, and the source line 13 a is electrically connected to the source region 31 s through the source electrode 36. On the other hand, a relay electrode 38 is formed above the drain electrode 37,
The relay electrode 38 is electrically connected to the drain region 31 d through the drain electrode 37. The relay electrode 38 is provided so that a part of the relay electrode 38 is exposed from the first interlayer insulating film 34.

A second interlayer insulating film 41 made of acrylic resin is formed on the first interlayer insulating film 34 so as to cover the relay electrode 38 of each photoelectric conversion sensor 11. The second interlayer insulating film 41 is
It is formed on the first interlayer insulating film 34 by being applied and then cured. A contact hole 42 penetrating in the thickness direction of the second interlayer insulating film 41 is formed at a position corresponding to the relay electrode 38 in the second interlayer insulating film 41. Capacitance forming portions 43 penetrating in the thickness direction of the second interlayer insulating film 41 are formed in the vicinity of the contact holes 42 in the second interlayer insulating film 41. Further, the contact hole 42 and the capacitor forming portion 43 have a circular appearance (not shown) in the thickness direction of the second interlayer insulating film 41, and the side surfaces 42a and 43a become narrower toward the lower end. Tapered. Further, the lower end of the capacitance forming portion 43 is closed by the upper surface of the first interlayer insulating film 34, and the first interlayer insulating film 34 is closed.
Is the bottom surface 43 b of the capacitance forming portion 43. That is, the capacitor forming portion 43 has a concave shape that is depressed in the thickness direction by the first interlayer insulating film 34 and the second interlayer insulating film 41. The capacitor forming portion 43 and the contact hole 42 are simultaneously formed by etching the second interlayer insulating film 41, and the first interlayer insulating film 34 made of a silicon nitride film is formed when the etching is performed. Acts as an etching stop film. Therefore, the first interlayer insulating film 3
4 suppresses the influence on the photoelectric conversion sensor 11 due to the etching of the second interlayer insulating film 41.

On the capacitor forming portion 43, the holding capacitor 22 including the first electrode 22 a, the second electrode 22 b, and the insulating film 44 as a dielectric interposed between both electrodes 22 a, 22 b is a concave shape of the capacitor forming portion 43. It is formed along. That is, on the side surface 43a and the bottom surface 43b of the capacitance forming portion 43, the storage capacitor 22 is provided in which the first electrode 22a, the insulating film 44, and the second electrode 22b are sequentially formed from the lower side. Specifically, the first electrode 22a is formed so as to cover the side surface 43a and the bottom surface 43b of the capacitance forming portion 43 and is connected to a ground line (not shown). The insulating film 44 covers substantially the entirety of the first electrode 22a and the contact hole 42, and penetrates in the thickness direction at a position corresponding to the relay electrode 38 in the insulating film 44, but a through hole 44a is formed. Is formed. The second electrode 22b is formed on the contact hole 42 and the insulating film 44 in the capacitance forming portion 43, and is in contact with the relay electrode 38 through the through hole 44a. The second electrode 22 b is electrically connected to the drain region 31 d through the relay electrode 38 and the drain electrode 37. In the present embodiment, the first electrode 22a and the second electrode 22b of the storage capacitor 22 are made of an aluminum film.

The photodiodes 23 are provided on the upper side of the second electrode 22b of the storage capacitor 22 so as to be in close contact with the upper surface of the second electrode 22b and to cover the TFT 21, respectively. The photodiode 23 has a PI in which an n layer 23n, an i layer 23i, and a p layer 23p are stacked in order from the bottom.
It has an N-type structure and converts light incident from the p-layer 23p side into an electrical signal corresponding to the amount of light. Further, the lowermost n layer 23 n in the photodiode 23 is electrically connected by being in close contact with the second electrode 22 b of the storage capacitor 22. That is, the photodiode 23 is connected to the drain electrode 37 of the TFT 21 through the contact hole 42 and the relay electrode 38. The uppermost p layer 23p is electrically connected to a grounded electrode (not shown). On the upper side of the photodiode 23, a protective sheet 46 made of glass bonded to the upper surface of the p layer 23p with an adhesive 45 is provided. The upper surface of the protective sheet 46 is an image detection surface 46a, and the image reading object and the image detection surface 46a are arranged so as to face each other to read an image.

In the image reading operation in the image reading apparatus 1 having the above configuration, first, each photoelectric conversion sensor 1 is operated.
With the one TFT 21 turned on, the storage capacitor 22 is precharged using the source wiring 13a. Next, each TFT 21 is turned off, and each photodiode 23 receives light from the object, and charges corresponding to the amount of light received are generated. As a result, the charge of the storage capacitor 22 that has been precharged according to the amount of charge generated in the photodiode 23 is discharged. Next, the TFTs 21 are sequentially turned on using the gate drive circuit 12 and the reading circuit 13, and the charges remaining in the storage capacitor 22 are sequentially detected, whereby the two-dimensional information of the object is read.

Next, characteristic actions and effects of the present embodiment will be described.
(1) In the second interlayer insulating film 41 covering the TFT 21 provided on the substrate, a capacitor forming portion 43 that is recessed in the thickness direction is recessed, and the storage capacitor 22 is provided on the side surface of the capacitor forming portion 43. 4
3a is provided. That is, since the storage capacitor 22 is provided in a three-dimensional manner rather than a plane,
Compared with the case where the planar storage capacitor 22 is formed, the electrode area can be increased. Therefore, by appropriately adjusting the film thickness of the second interlayer insulating film 41, a sufficient storage capacity 22 can be ensured even when the photoelectric conversion sensor 11 is densified.

(2) Since the capacitor forming portion 43 is formed in the second interlayer insulating film 41 in which the contact hole 42 is formed, the contact hole 42 and the capacitor forming portion 43 can be formed at the same time, and the photoelectric conversion sensor 11 can contribute to the simplification of the manufacturing process.

(3) Since acrylic resin is used for the second interlayer insulating film 41, the second interlayer insulating film 41 can be formed by the coating process and the curing process. In addition, the film forming process can be performed in a short time, and the second interlayer insulating film 41 having a large thickness can be easily formed. And
The thickness of the second interlayer insulating film 41 is increased, and the capacitance forming portion 4 is added to the second interlayer insulating film 41.
By forming 3, it is possible to form the storage capacitor 22 having a larger electrode area.

(4) The second electrode of the storage capacitor 22 is electrically connected to the n layer 23 n of the photodiode 23. That is, the second electrode 22 b also serves as the electrode of the photodiode 23. Thereby, since it is not necessary to provide the electrode for connecting with n layer 23n of the photodiode 23 as a separate member, the number of parts of the photoelectric conversion sensor 11 can be reduced.

(5) Since the second interlayer insulating film 41 in which the storage capacitor 22 is formed and the photodiode 23 as a photoelectric conversion element are stacked above the TFT 21, a light receiving area of the photodiode 23 must be ensured. Thus, the density of the photoelectric conversion sensor 11 can be increased. In addition, since the photodiode 21 covers the TFT 21, noise generated when the TFT 21 receives light can be improved.

(6) In the second interlayer insulating film 41 covering the TFT 21 provided on the substrate, a capacitor forming portion 43 that is depressed in the thickness direction is recessed, and the storage capacitor 22 is provided on the side surface of the capacitor forming portion 43. 4
3a is provided. Therefore, by controlling the film thickness of the second interlayer insulating film 41, the capacitance value of the storage capacitor 22 can be easily changed.

(7) Since the storage capacitor 22 is formed with the capacitor forming portion 43, selection of materials that can be used for the first electrode 22a and the second electrode 22b of the storage capacitor 22 compared to the case where the storage capacitor is formed on the substrate. The width of. For this reason, if the electrodes 22a and 22b of the storage capacitor 22 are made of the same material as the other wiring electrodes, the electrodes 22a and 22b of the storage capacitor 22 can be formed simultaneously with the wiring electrodes.

The embodiment of the present invention may be modified as follows.
In the above embodiment, the acrylic resin is used for the second interlayer insulating film 41, but other resins may be used.

In the above embodiment, the interlayer insulating film covering the TFT 21 as the switching element is the first
Although the interlayer insulating film 34 and the second interlayer insulating film 41 are configured, the present invention is not limited to this, and a single layer or three or more layers may be used.

In the above-described embodiment, the PIN type photodiode 23 is used as the photoelectric conversion element, but other types such as a PN type photodiode, a phototransistor, or the like may be used.

In the above embodiment, in the storage capacitor 22 provided on the capacitor forming portion 43, the grounded first electrode 22a is disposed on the lower side, and the second electrode 22b in contact with the relay electrode 38 is disposed on the upper side. On the contrary, the first electrode 22a may be disposed on the upper side and the second electrode 22b may be disposed on the lower side. In this case, an insulating film is provided between the first electrode 22a and the n layer 23n of the photodiode 23,
The first electrode 22a and the photodiode 23 are electrically insulated.

In the above embodiment, the second electrode 22b also serves as the electrode of the n layer 23n of the photodiode 23. However, a separate lower electrode connected to the n layer 23n is provided, and the lower electrode and the storage capacitor 22 The second electrode 22b may be electrically connected.

In the above embodiment, the capacitance forming portion 43 penetrates the second interlayer insulating film 41, but may be a recess that does not penetrate.
In the above embodiment, only one storage capacitor 22 is provided. However, a plurality of capacitor formation portions 43 are formed in the second interlayer insulating film 41, and a plurality of capacitor formation portions 43 are provided with a plurality of storage capacitors 22. Also good. Further, as shown in FIG. 3, a second storage capacitor 50 connected in parallel with the first electrode 22a of the storage capacitor 22 may be formed on the substrate. In the second storage capacitor 50, the lower electrode 5
0a is electrically connected to the first electrode 22a of the storage capacitor 22 through the connection electrode 51, the upper electrode 50b is grounded, and the gate insulating film 32 interposed between the lower electrode 50a and the upper electrode 50b. Is a dielectric. Note that the second storage capacitor 50 may be connected in series with the storage capacitor 22, and the lower electrode 50 a and the upper electrode 50 b may be configured oppositely. According to the said structure, sufficient capacity | capacitance in the photoelectric conversion sensor 11 can be ensured more reliably.

In the above embodiment, the color image reading is not particularly mentioned, but the color image may be read.
In addition to the image scanner, the image reading apparatus of the above embodiment may be used for a digital camera, a touch sensor, or the like. Alternatively, the light-emitting device may be provided over the substrate to serve as the image display device.

1 is a cross-sectional view showing an image reading apparatus in the present embodiment. It is a circuit diagram which shows a part of image reading apparatus. It is sectional drawing which shows the image reading apparatus in another example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image reading apparatus, 2 ... Board | substrate, 11 ... Photoelectric conversion sensor as a photoelectric conversion apparatus, 21 ... TFT as a switching element, 22 ... Retention capacity, 22a ... 1st electrode of retention capacity, 22b
2nd electrode of storage capacitor, 23 ... Photodiode as photoelectric conversion element, 34 ... 1st interlayer insulation film, 41 ... 2nd interlayer insulation film, 42 ... Contact hole, 43 ... Capacitance formation part, 43a ...
Side surface of the capacity forming portion, 50... Second holding capacity.

Claims (7)

A switching element provided on a substrate, a storage capacitor electrically connected to the switching element, and a photoelectric conversion element electrically connected to the storage capacitor,
A photoelectric conversion device that accumulates an electrical signal generated according to the amount of light received by the photoelectric conversion element in the storage capacitor and outputs the electrical signal via the switching element,
The photoelectric conversion device according to claim 1, wherein the storage capacitor is provided on at least a side surface of a capacitor forming portion that is recessed in a thickness direction of an interlayer insulating film provided on the switching element. The photoelectric conversion device according to claim 1,
The photoelectric conversion element is connected to the switching element through a contact hole formed in the interlayer insulating film,
The photoelectric conversion device, wherein the capacitance forming portion is formed in the interlayer insulating film in which the contact hole is formed. In the photoelectric conversion device according to claim 1 or 2,
The interlayer insulating film includes a first interlayer insulating film and a second interlayer insulating film using an acrylic resin laminated on the first interlayer insulating film,
The photoelectric conversion device, wherein the storage capacitor is formed in the second interlayer insulating film. In the photoelectric conversion device according to any one of claims 1 to 3,
One electrode of the storage capacitor also serves as an electrode connected to the photoelectric conversion element. In the photoelectric conversion device according to any one of claims 1 to 4,
A photoelectric conversion device comprising a second storage capacitor connected to the storage capacitor in series or in parallel and formed on the substrate. In the photoelectric conversion device according to any one of claims 1 to 5,
The interlayer insulating film includes a first interlayer insulating film and a second interlayer insulating film stacked on the first interlayer insulating film,
The storage capacitor is formed in the second interlayer insulating film,
The photoelectric conversion device is provided on the second interlayer insulating film so as to cover the switching element. An image reading apparatus using the photoelectric conversion device according to claim 1.

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