JPS62293765A - Photoelectric conversion device - Google Patents

Abstract

PURPOSE:To perform high speed reading by a method wherein O/E converting partsin a planar type photosensor are divided into blocks and thin film transistors in the respective blocks, one in each block, are driven in parallel by timing signals simultaneously. CONSTITUTION:Thin film transistors 39 for switching operation in respective blocks, one in each block, are driven in parallel simultaneously by timing signals D1-Dn. At that time, photocurrents from respective driven O/E converting parts 37 are inputted to respective current-voltage converters 35 of the block units through common output lines 40 of the respectivr blocks and detected in parallel. In other words, the photocurrents of picture elements corresponding to the number of blocks can be detected simultaneously. With this constitution, even if the switching operation speed of a thin film transistor 39 itself is low, the reading operation can be performed with a high speed as a whole and, as the photosensor is of a planar type and signal detection is performed any time, there can be no problem even if such parallel reading operation is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to a photoelectric conversion device used for image reading such as a facsimile machine.

2. Description of the Related Art Conventionally, IC sensors such as COD image sensors and photodiode arrays have been used as reading elements in facsimiles and the like. However, a photoelectric conversion device using such an IC sensor requires a reduction optical system to form an image of a document onto a photosensor, which has the drawback of increasing the size of the entire device and increasing cost.

However, in recent years, in order to avoid such drawbacks, contact type image sensors that have a large 1=1 correspondence with the original have been developed.
has been proposed and implemented. FIG. 7 shows an equivalent circuit of a photoelectric conversion device using such a contact type image sensor.

This includes a plurality of photoelectric conversion units 1. ~1n are arranged at a predetermined pitch, switching elements 21 to 2n are individually connected to these photoelectric conversion units 1 and ~1n, and these switching elements 2 and ~2n are sequentially switched by driving pulses. Each photoelectric conversion unit 1. .about.1n is scanned, and the outputs (whether or not light is received) are sequentially taken out via the current-voltage conversion circuit 3.

Here, the structures of the light receiving element (photoelectric conversion section) include an accumulation type (sandwich type) and a planar type. First, as shown in FIG. 8, in the storage type photoelectric conversion section, a lower electrode 5 is formed on a substrate 4 made of glass or the like, and a photoconductive film 6 made of amorphous silicon A-3i or the like is formed on this lower electrode 5. , and has a sandwich structure on which a transparent electrode 7 is formed. The lower electrode 5 is the ninth
It is formed in a pattern shape as shown in the figure and functions as an individual electrode. Further, the circuit is shown as an equivalent circuit as shown in FIG. First, 8 is a sensor element part, which prevents injection of carriers from the electrode by forming a blocking layer at the junction surface of the transparent electrode 7/photoconductive film 6, for example, IT○/a-Si. . Further, the capacitor 9 represents an isometric capacitor formed in a circuit pattern or element. As a result, carriers (electrons) generated when light enters the sensor element section 8 are accumulated in this capacitor 9, and when the switching element 10 is turned on, the carriers flow and are input to the current-voltage conversion circuit 11. , a signal will be detected. Here, the time it takes for carriers generated by light incidence to become saturated is referred to as the accumulation time, and is the reading speed defined by (amount of incident light) x (accumulation time).

On the other hand, as shown in FIG. 11, the planar type photoelectric conversion unit is formed by forming a common electrode 13 and individual electrodes 14 on a substrate 12 so as to face each other in a plane, and a-3
A photoconductive film 15 made of L or the like is formed. As shown in FIG. 12, the electrodes 13 and 14 have a comb-like shape and are opposed to each other in a crossed state. The circuit is shown as an equivalent circuit as shown in FIG. That is, when light is incident, carriers are excited in the photoconductive film 15 to become a photocurrent, and when the switching element 16 is turned on, it is input to the current-voltage conversion circuit 17 and detected as an optical signal. Here, the reading speed is determined by the carrier excitation time after light incidence and the fall time when light is interrupted.

In conventional methods such as 2, if it is a planar type, it can be said to be a detection method that detects the signal current at any time, but if it is an accumulation type, the reading speed is detected by the photoelectric conversion section and accumulated, until it reaches the saturation level. It can be said that the reading speed is regulated by the accumulation time until reaching the limit. Then, by configuring a matrix wiring circuit as a method of sequentially scanning the photoelectric conversion parts one by one and detecting signals as in 2.

There is a method in which the number of elements in this signal detection circuit is reduced. Further, for each light-receiving element, a thin film transistor (TPT) is used as a driving element (switching element), and it can be formed using a-5i or the like in the same manner as a photoconductive film. FIG. 14 shows the isometric circuit configuration. First, an optical sensor 19 formed by a large number of photoelectric conversion units 18 arranged at a predetermined pitch is provided.

Here, these photoelectric conversion units 18 are denoted by reference numerals 18, 1 to 18.
+n+ 182+~18□. , 18. , ~18. n.

There are four blocks 201 to 20, each of which is n blocks, as shown by 1841 to 184n. It is divided into blocks. And each photoelectric conversion gHg,.

-184n, thin film transistors 21. to 184n are used as driving elements. 214n are connected in a 1:1 relationship. These thin film transistors 21.1 to 214° are connected to a matrix wiring circuit 22.

This matrix wiring circuit 22 connects the photoelectric conversion section 18 to four blocks 201 to 20. The first block 20. Photoelectric conversion units 186, -18. Thin film transistor 21.n corresponding to ,~21,. are commonly connected to the timing signal D1 line in the matrix wiring circuit 22.

The same goes for the others, and the timing signals of the matrix wiring circuit 22 are connected to the second blocks 202 . 3rd block 2o3. Thin film transistors 21□ to 212□ of the fourth block 204.

21.1-21. n, 21. , ~21. n are commonly connected. Further, this matrix wiring circuit 22 includes n thin film transistors 23 . ~23n are connected. Then, these thin film transistors 23. ~
For 23n, scanning signal c.

~Cn can be input, and a current-voltage conversion circuit 24 is connected to the output side.

In such a configuration, the read operation will be explained with reference to the timing chart of FIG. 15. D1~D4
is each block 20. ~20. is the timing signal of
For example, the first block 20. Photoelectric conversion unit 18. ~180
When detecting the signal of the thin film transistor 21. of the first block 20, the timing signal D1 is turned on. ~21n are all turned on at the same time, and scanning signals C1~Cn are applied to the thin film transistors 23 and ~23n.
By scanning the first block 201
Photoelectric conversion unit 18. ~18n signals are input one after another to the current-voltage conversion circuit 24 and detected. Other 2nd to 4th blocks 20. ~204 are also each provided with a timing signal D.
It operates similarly based on 2 to D4. According to such a matrix drive method, the number of thin film transistors 21 and 23 as drive elements can be reduced, and for example, the number of IC chips for driving the thin film transistors 23 can be reduced, thereby reducing costs. Further, the thin film transistor 21 has a role of selectively switching each block 201 to 204, and a blocking function of preventing a wrap-around current from other blocks during matrix drive.

Problems to be Solved by the Invention However, thin film transistors using a-Si 21.
When performing switching drive using 23, a-3i has the disadvantage that electron mobility is low and switching speed is slow. Therefore, for example, the thin film transistor 21.
The maximum driving frequency of 23 is 150 KHz, one light receiving element (photoelectric conversion unit 18) is one pixel, and the pixel density is 8.
Assuming pixels/mm, one line of an A4 size (210 mm) document has 1680 pixels, and it takes 6.7 μs to read and drive one pixel, so one line takes 11 m5, making it necessary to perform high-speed reading. This is something that cannot be done.

Therefore, the present invention has been made in view of the second point, and has an inexpensive structure that employs a matrix wiring circuit system, and uses a Brenna type optical sensor to detect signals at any time, and performs reading by thin film transistors. An object of the present invention is to obtain a photoelectric conversion device that can perform high-speed reading by improving the reduction in speed.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a planar optical sensor, a thin film transistor for switching drive of a photoelectric conversion section divided into blocks of this optical sensor, and a parallel drive of these thin film transistors. In the basic configuration of a matrix wiring circuit system using a matrix wiring circuit, the matrix wiring circuit simultaneously drives one thin film transistor in each block in parallel using a predetermined timing signal, and drives each photoelectric conversion unit in parallel. The output side of the is connected to a common connection line for each block, and a current-voltage conversion circuit connected to these common connection lines is provided in each block, and the photocurrent of the photoelectric conversion unit for each block is converted by each current-voltage conversion circuit. It amplifies and converts it into a voltage signal.

By applying the action timing signal, the thin film transistors for switching driving are simultaneously driven one by one in parallel across each block. At this time, the photocurrent from the driven photoelectric conversion section is inputted to each current-voltage conversion circuit in each block from the common output line of each block and detected in parallel.

In other words, detection for pixels corresponding to the number of blocks is performed simultaneously. Therefore, even if the switching operation of the thin film transistor itself is slow, the overall reading operation is performed at high speed. Even if such parallel reading operations are performed, there is no problem because the optical sensor is of a planar type and detects signals at any time.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 6. First, FIG. 2 shows a schematic external configuration of a photoelectric conversion device according to this embodiment, in which optical sensors 31 are formed in an array on an insulating substrate 30 made of glass or the like. or,
A thin film transistor group 32 corresponds to this optical sensor 31.
A matrix wiring circuit 33 is formed on the output side of this thin film transistor group 32. Two ICs for driving the thin film transistor group 32 and having the same configuration and selectively connected to the thin film transistor group 32 are provided at both longitudinal ends of the insulating substrate 3o.
Chips 34a and 34b are provided. Further, the output side of the matrix wiring circuit 33 is a current-voltage conversion circuit 35 having an OP amplifier configuration in blocks as described later.
It is connected to the. 36 is a terminal for external circuit connection.

The circuit is configured as an equivalent circuit as shown in FIG. First, the optical sensor 31 is formed of a large number of photoelectric conversion parts 37 arranged at a predetermined pitch. Here, these photoelectric conversion units 37 are 37++ to 37+n+ 3
7ml~37mn+ 31s+~37. , 37. ,~
374n, four blocks 38. ~
It is set to be divided into 384.

Then, each photoelectric conversion unit 373. ~374n for each thin film transistor 39.1 of the thin film transistor group 32
~394n are connected in a 1:1 relationship.

These thin film transistors 39,1 to 394n are connected to the photoelectric conversion section 373. -374n are provided as drive elements for individually switching and driving. Moreover, these thin film transistors 39.1 to 39. The gate side of n is connected to the matrix wiring circuit 33.

More specifically, each block 38. The thin film transistors 39 of the same timing signal D line, for example, the signal line D, are connected to the thin film transistors 39. ,．． 39□,,39. ,．． 394° is connected,
The signal D2 line has thin film transistors 39□, 39□,
, 39. ,．． 394. is connected to the signal Dn line, and the thin film transistor 39+n+391Q+3 is connected to the signal Dn line.
9, n+ 39 *n are connected. Further, the output side of this matrix wiring circuit 33 is connected to each of the photoelectric conversion sections 37□1 to 37. Common connection lines 40, -40. and these common connection lines 40. Current-voltage conversion circuits 35. to 404 provided in block units. .about.354 are connected to each other. In other words, this current-voltage conversion circuit 35 is also divided into a number corresponding to the blocks 38. The outputs from these current-voltage conversion circuits 35, -354 are input in parallel to a parallel-serial conversion circuit 41, and a serial signal is output. Note that this parallel-serial conversion circuit 41 is similar to the current-voltage conversion circuit 35. ~354
After converting the analog signal from the converter into a digital signal using a comparator, parallel-to-serial conversion is performed as described above.

Next, the structure of the thin film transistor 39 will be explained with reference to FIGS. 3 and 4. First, FIG. 3 shows the pattern shape of the gate electrode 43, source electrode 44, and drain electrode 45 of the thin film transistor 39. As shown in FIG. After forming the gate insulating film 46 to a thickness of 2,000 wafers, patterning is performed, and the gate insulating film 46 is formed with a thickness of 2,000 wafers from a-3i using a plasma CVD method. do.

A source electrode 44 and a drain electrode 45 are formed of NiCr on the semiconductor N47.

The photoelectric conversion section 37 described above is shown in FIGS. 11 and 12.
It is constructed as a planar type as shown in the figure. That is, as shown in FIG. 4, a common electrode 48 and individual electrodes 49 are formed on an insulating substrate 30 to face each other in a plane, and a photoconductive film 50 is formed on both electrodes 48° 49 by a-3i. It forms. Here, the common electrode 48 and the individual electrode 4
The shape of the tip on the side opposite to 9 is comb-shaped as in the case of FIG. 51 is a passivation film as a protective film.

Further, as shown in FIGS. 4 and 5, the matrix wiring circuit 33 is formed by laminating a lower lead pattern 52 and an upper lead pattern S3 via interlayer insulation [54], and a connection between both lead patterns 52 and 53. This is done through a through hole 55 formed in a necessary portion.

Here, the manufacturing process of the photoelectric conversion device as shown in FIG. 4 will be explained with reference to the process diagram in FIG. 6. First, a step of forming a first M film on the substrate 30 and patterning it is performed. This is done by forming a Cr layer using a sputtering method and patterning it using a photo-etching process, thereby forming a Cr layer of $1A48.49 for the photoelectric conversion section 37, the gate electrode 43 of the thin film transistor 39, and the matrix wiring circuit 3.
The lower lead pattern 52 of No. 3 is formed at the same time. Next, a photoconductive film 50 is formed on the electrodes 48 and 49 by plasma CVD using a-5i. and,
Gate insulating film 46 of thin film transistor (TPT) 39,
The semiconductor layer 47 is made of SiO, .
Continuously formed using a-Si. Then, by applying a photosensitive polyimide resin as an insulating layer and performing pattern formation, the passivation film 35 of the photoelectric conversion section 37 and the interlayer insulation Ji 54 of the matrix wiring circuit 33 are simultaneously formed. The thickness of this polyimide film is approximately 2 μm. As a result, 500 to 600
The transmittance of light with a wavelength of nm is as high as 95-98%.
Moreover, the moisture permeability is also low. Also, when considered as the interlayer insulating layer 54, the insulation resistance is high and
Through-holes 55 can also be easily formed using photosensitive polyimide. Subsequently, layers for the source electrode 44, drain electrode 45, and upper lead pattern 53 of the thin film transistor 39 are formed by vapor deposition of NiCr/Au.
The patterning is performed by a photo-etching process. According to such a manufacturing process, the photoelectric conversion section 3
Since the electrodes 48, 49 of 7, the gate electrode 43 of the thin film transistor 39, and the lower lead pattern 52 of the matrix wiring circuit 33 are formed at the same time, the process can be significantly shortened. This also applies to the formation of the passivation film 35 of the photoelectric conversion section 37 and the interlayer insulation N54 of the matrix wiring circuit 33, and simultaneous formation simplifies the process and reduces costs.

Next, a reading operation in this embodiment will be explained.

Basically, reading is performed using a parallel drive system instead of the serial drive system as shown in FIGS. 14 and 15. First, that is, in FIG. 1, the timing signal D1
is input and the thin film transistor 39. ,．． 39. ,．． 39
．． ,．． 39. , turn on at the same time and the corresponding photoelectric conversion unit 3
7. ,．． 377.・ 37,,, 374. are simultaneously switched and driven in parallel. At this time, these switching-driven photoelectric conversion units 37. ,．． 37. ,．． 37
．． ,．． 374. The photocurrents of each are connected to the common connection line 40. ,4
0. ,40. .

40, to the current-voltage conversion circuits 35, to 354, respectively. Thereby, the photocurrent is amplified and converted into a voltage signal, which is simultaneously input as a parallel signal to the parallel-serial conversion circuit 41, which is converted into a serial signal and output to a memory or the like. Next, the timing signal Da+D3
1...+Dn is input sequentially and similarly each block 3
The photoelectric conversion units 37 in 8 are simultaneously switched and scanned one by one in parallel. That is, signals from a number of blocks, in this case four, photoelectric conversion units 37 are simultaneously detected based on one timing signal. Therefore, the reading time is 1/4 compared to the serial drive method.

Considering more specifically, when reading A4 size (210 mm) with the pixel density of 8 pixels/mm as explained in the conventional example, there are 1680 pixels (photoelectric conversion part) in one line, and even if one pixel drive is 6 μm, for example, If it is divided into 6 blocks and driven in parallel, the reading time for one line is (1680/
6) The speed is increased to x6 m = 1.68 m5. Therefore, high-speed reading is possible without being affected by the poor switching characteristics of the core membrane transistor 39. Here, even if such a parallel drive method is adopted, it is effective because the structure of the photoelectric conversion section 37 is a planar type and the signal current is detected at any time. Incidentally, in the case of an accumulation type (sandwich type), the reading speed is regulated by the accumulation time until the photoelectric conversion unit detects and accumulates and reaches the saturation level, so such a parallel drive method is not suitable. Become.

By the way, in this embodiment, as shown in FIG. 2, two IC chips 34a and 34b are installed at both ends of the device as IC chips for driving the thin film transistor 39, that is, for driving the thin film transistor 39 by applying a scanning signal to the gate. , that is, M! ! One of the IC chips 34a is provided at the edge of the edge plate substrate 30.
Or 34b is selectively used.

Since the two IC chips 34a and 34b are provided in this way and can be used selectively, for example, even if one IC chip 34a or 34b has a defect, malfunction, poor bonding, etc., the other IC chip If the IC chip 34b or 34a is normal, the IC chip 34b or 34a can be used in a normal state, resulting in an improved yield. In this way, the two IC chips 34a, 3
Even if the IC chip 4b is formed, the cost of the IC chip is low, and since the patterns are the same and can be formed at the same time, no inconvenience will occur.

Effects of the Invention As described above, the present invention uses a planar type optical sensor, divides the photoelectric conversion parts of this optical sensor into blocks, and connects a matrix circuit to a group of thin film transistors that drive these photoelectric conversion parts, The thin film transistors in each block are simultaneously driven one by one in parallel using a timing signal, and the output side of each photoelectric conversion section is connected to the current-voltage conversion circuit in each block via a common connection line in each block. Even if the switching speed of thin film transistors is slow, reading of photoelectric conversion units for several blocks can be performed in parallel.
High-speed reading can be performed, and at this time, the optical sensor is of a planar type and detects signals at any time, so there is no problem due to parallel driving.

[Brief explanation of the drawing]

1 to 6 show an embodiment of the present invention,
Fig. 1 is a circuit diagram, Fig. 2 is an external perspective view, Fig. 3 is a plan view of the electrode shape of the thin film transistor, Fig. 4 is a sectional view showing the groove structure of the entire device, and Fig. 5 is a plan view of matrix wiring. ,
Fig. 6 is a process diagram, Fig. 7 is a circuit diagram showing a conventional example, Fig. 8 is a structural diagram of the storage type optical sensor, Fig. 9 is a plan view showing its electrode shape, Fig. 10 is a circuit diagram, and Fig. 10 is a circuit diagram. Fig. 11 is a structural diagram of a planar optical sensor, Fig. 12 is a plan view showing its electrode shape, Fig. 13 is a circuit diagram, Fig. 14 is a circuit diagram showing a matrix drive method, and Fig. 15 shows its vertical operation. FIG. 30... Insulating substrate, 31... Optical sensor, 32...
...Thin film transistor group, 33... Matrix wiring circuit, 35... Current voltage conversion circuit, 37... Photoelectric conversion section, 38... Block, 39... Thin film transistor, 40... Common connection line, 48... common electrode, 49
...Individual electrode, 50...Photoconductive film: $, 3 figure Jf35

Claims (1)

[Claims] A planar type in which a common electrode and individual electrodes are arranged facing each other in a plane on an insulating substrate, a photoconductive film is formed on these electrodes, and a photoelectric conversion unit for multiple pixels is formed with the electrodes. The photoelectric conversion section is divided into a plurality of blocks, and each photoelectric conversion section is provided with a thin film transistor group including a thin film transistor for switching and driving the photoelectric conversion section. A matrix wiring circuit is provided to simultaneously drive each of the thin film transistors in parallel, and the output side of each photoelectric conversion section is connected to a common connection line for each block, so that the photocurrent of the photoelectric conversion section is controlled for each block. A photoelectric conversion device characterized in that a current-voltage conversion circuit for amplifying and converting the current into a voltage signal is connected to the common connection line.