Photoelectric conversion device

Abstract: A photoelectric conversion device comprises plural photoelectric conversion elements arranged in a linear array, plural common lines (305,308) each connecting at least two of individual output electrodes (301,304) of the plural photoelectric conversion elements, conductor layers of a constant potential provided in the vicinity of crossing portions of the individual output electrodes (301,304) and said common lines, and wirings mutually connecting the conductor layers.

Description: BACKGROUND OF THE INVENTION The present invention relates to a photo-electric conversion device, and more particularly a photoelectric conversion device adapted for use in an image reading apparatus such as facsimile apparatus, image reader, digital copying machine, electronic black-board or the like. In recent years there have been developed long line sensors with a same-size optical system, as the image conversion device for facsimile apparatus, image reader or the like. This is mainly due to the compactization and high density structure of the photoelectric conversion device enabled by the progress in the technology of printed wiring boards. In a long image sensor with a same-size optical system, a linear array of photoelectric converting elements is capable of reading an original image in contact therewith, so that the apparatus can be compactized and achieve a high image reading speed in comparison with the conventional method of reading the original image point by point with a photoelectric converting element and an optical system utilizing lenses. Document US-A 3 838 276 discloses a phototransistor array in which a plurality of photoelectric conversion elements are arranged in a linear array. This array comprises common lines connecting output electrodes of the plurality of photoelectric conversion elements and further interconnected collector regions which can be connected to metallized leads. Since the individual phototransistors are spaced very closely to each other, there occurs a certain amount of crosstalk between adjacent phototransistors caused by incident radiation. Metallized leads connecting adjacent phototransistors block out this incident light, thereby eliminating this "light-crosstalk". In such a conventional long line sensor with same-size optical system, the photoelectric converting elements constituting an array are respectively connected to signal processing IC's composed for i example of switch devices. However, for example in the G3 facsimile format, there are required 1728 photoelectric converting elements for the A4 size, so that there are required many signal processing IC's. For this reason there are required a large number of device mounting steps, and there has not been obtained an apparatus satisfactory in terms of production cost and reliability. For the purpose of reducing the number of signal processing IC's and the number of steps of board mounting, there has been employed a structure utilizing matrix wirings. Fig. 1 shows a photoelectric conversion device utilizing such matrix wirings, wherein there are shown a photoelectric conversion device 1 consisting of a linear array of plural photoelectric conversion elements; a scanning unit 2; a signal processing unit 3; and matrix wirings 4. Among the wirings connecting the scanning unit 2 and the signal processing unit 3, vertical wirings constitute individual output electrodes while horizontal one constitute common lines. In such matrix wiring, the individual output electrodes and common lines are inevitably close in order to compactize the matrix wiring. Consequently floating capacitances are present between the wirings, thus generating crosstalks among the output signals, and deteriorating the obtained image signals. This drawback can be most simply resolved by increasing the distances of the wirings. However such solution increases the dimension of the matrix wiring, and is not desirable for a device requiring a large number of photoelectric conversion elements as explained before. A not prepublished in-house state of the art document proposes a photoelectric conversion device in which a conductor layer and a wiring capable of maintaining a constant potential at each crossing point of the individual output electrode and the common line, thereby controlling the floating capacity between the individual output electrodes and the common lines and preventing the crosstalk of the output signals released through such floating capacitances. Fig. 2A is a plan view of matrix wiring in which a conductor layer of a constant potential is formed at the insulated crossing point of the individual output electrode and the common line, while Fig. 2B is a cross-sectional view along a line B-B′ of the matrix wiring shown in Fig. 2A. In Figs. 2A and 2B there are shown individual output electrodes 301 - 304; common lines 305 - 308; intermediate lines 309 - 313 positioned in the spaces of the common lines 305 - 308; a conductor layer 314 positioned between the individual output electrodes 301 - 304 and the common lines 305 - 308 in the insulated crossing points thereof and is connected to an unrepresented power source capable of maintaining a constant potential; and contact holes 315 for ohmic contact of the individual output electrodes 301 - 304 and the common lines 305 - 308. However the photoelectric conversion device with such matrix wiring having a conductor layer of a constant potential in the insulated crossing points of the individual output electrodes and the common lines have been associated with the following drawbacks. In such matrix wiring, there is provided a conductor layer of a constant potential in the insulated crossing points of the individual output electrodes and the common lines for reducing the capacitances therebetween. Though such structure can reduce the floating capacitances between the individual output electrodes and the common lines, new floating capacitances are formed between the conductor layer of constant potential and the individual output electrodes, and between the conductor layer and the common lines. Said floating capacitances are generated between the conductor layer of constant potential and all the individual output electrodes, and between said conductor layer and all the common lines because said conductor layer is extended over the entire area of the matrix wiring, and are practically not negligible. Fig. 3 is an equivalent circuit of an accumulating photoelectric conversion device employing said conductor layer of constant potential. In this drawing, 501 denotes a photoelectric conversion unit. 503 denotes a storage capacitor. 502 denotes a switch unit. 505 denotes a load capacitor. 506 denotes a signal output terminal unit. If the above-explained matrix wiring is employed in the output side of the accumulating photoelectric conversion circuit shown in Fig. 3, a floating capacitance 504 not negligible in comparison with the load capacitor 505 may deteriorate the efficiency of charge transfer. SUMMARY OF THE INVENTION In consideration of the foregoing, the object of the present invention is to provide a photoelectric conversion device equipped with matrix wiring capable of suppressing the crosstalks among the output signals and also suppressing the floating capacitances resulting from a structure for suppressing said cross-talks. According to a first aspect of the invention, this object is accomplished by a photoelectric conversion device, comprising: Plural photoelectric conversion elements arranged in a linear array, an individual output electrode being electrically connected to the photoelectric conversion element; plural common lines, each connected with at least one of the individual output electrodes of the plural photoelectric conversion elements; a conductor layer provided at least at an unconnected cross-overpoint between the individual output electrodes and the common lines, wherein the conductor layer is maintained at a constant potential; and wirings connecting the conductor layer to other conductor layers. According to a further aspect of the present invention this object is achieved by a reading apparatus, comprising: A photoelectric conversion device with a plurality of photoelectric conversion elements, and a matrix wiring section, including plural common lines for deriving electric signals from the photoelectric conversion elements, and having respective individual output electrodes provided for each of the photoelectric conversion elements, wherein an insulating layer is disposed between the plural common lines and the individual output electrodes, and wherein the common lines are each electrically connected to a respective set of the individual output electrodes, each set inciuding at least one of the individual output electrode, and at least one conductive layer provided only in a vicinity of a portion where one of the individual output electrodes crosses one of the common lines, wherein the conductive layer is electrically insulated from the individual output electrodes and the common lines wherein the conductor layer is maintained at constant potential; a wiring for providing the conductive layer with a desired potential; a circuit for driving the photoelectrice conversion device; and a source for providing the desired potential. The principal feature of the present invention is the presence of a conductor layer of a constant potential in the vicinity of the crossing point of the individual output electrode and the common line. Said conductor layer is maintained at a constant potential for example by connection to a constant voltage source. The present invention is capable of suppressing the floating capacitance formed at the insulated crossing point of the individual output electrode and the common line, and also suppressing the floating capacitances between said conductor layer of constant potential and the individual electrode and between said conductor layer and the common line. As said conductor layer provided at the insulated crossing point of the individual output electrode and the common line is maintained at a constant potential, the potential difference between the individual output electrode and the conductor layer is made independent from the potential difference between the common line and the conductor layer. Consequently the change in potential or current in the individual output electrodes does not influence the common line since the conductor layer positioned between is maintained at a constant potential despite of such change. Similarly the change in the potential or current in the common line does not affect the individual output electrode. In this manner the influence of the floating capacitance between the individual output electrode and the common line can be suppressed. Outside said crossing area of the individual output electrode and the common line, said conductor layer is eliminated except the wirings therefor to reduce the crossing area between the conductor layers of constant potential and the individual output electrodes and between said conductor layers and the common lines, thereby reducing the newly generated capacitances and preventing the deterioration of the transfer efficiency. DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a photoelectric conversion device with matrix wiring; Fig. 2A is a plan view of conventional matrix wiring; Fig. 2B is a cross-sectional view along a line B-B′ in Fig. 2A; Fig. 3 is an equivalent circuit diagram of an accumulating photoelectric conversion device with conventional matrix wiring; Fig. 4 shows illustratively a photoelectric conversion device according to the present invention, Fig. 4A shows a plan view thereof, Fig. 4B shows a sectional view along line X-X′ in Fig. 4A, and Fig. 4C show a sectional view along line Y-Y′ in Fig. 4A; Fig. 5A is a plan view of matrix wiring embodying the present invention; Fig. 5B is a cross-sectional view along a line A-A′ in Fig. 5A; Fig. 6A is a plan view of matrix wiring constituting another embodiment of the present invention; and Fig. 6B is a cross-sectional view along a line A-A′ in Fig. 6A. With reference to the accompanying drawings, the embodiments of the present invention are explained as follows. Fig. 4 illustratively shows a portion corresponding to 1-bit of the photoelectric conversion device according to an embodiment not forming part of the claimed invention. Fig. 4A shows plan view. Fig. 4B shows a sectional view along line X-X′ in Fig. 4A. Fig. 4C shows a sectional view along line Y-Y′ in Fig. 4A. Fig. 4A shows only upper and lower wiring pattern and contact hole unit, for the purpose of prevention of complex illustration. In Fig. 4A, 13 denotes a signal line matrix unit. 14 denotes a photoelectric conversion unit. 15 denotes a contact hole for connection between gate and source. 16 denotes a storage capacitor. 17 denotes a transfer TFT. 18 denotes TFT for reset. 19 denotes a wiring unit of gate driving line. In the embodiment, so called lens less structure directly contacting an original to read it is used. Accordingly, a window 20 for illuminating the original is provided. Further, a lower gate electrode of the sensor unit is made of opaque material for use as a light shielding film. Referring to Figs. 4B and 4C, 1 denotes a substrate such as glass. 21 denotes a lower electrode, which is a gate electrode of the sensor in Fig. 4B and which is a gate electrode of TFT in Fig. 4C. 3 denotes an insulating layer made of SiNxH, SiO₂ or the like. 4 denotes a photoconducting semiconductor layer made of a-Si:H or the like. 5 denotes n⁺ layer for ohmic contact to the upper electrode. 22 and 23 denotes upper electrodes which is a source electrode of the sensor unit in Fig. 4B and which is the source and drain electrode of the TFT in Fig. 4C. 6 denotes an insulating layer. The photoelectric conversion device of the present invention is produced by using, as a photoconductive semiconductor material, a-Si:H film formed by a glow discharge process to provide on a common substrate TFT type photoelectric conversion portion, the storage capacitor, the transfer and reset TFT, and the matrix wiring portion, as a stacked layer structure comprising a lower electrode, SiNH insulating layer, a-Si:H layer, n⁺ layer and upper electrode, in a single process simultaneously. Figs. 5A and 6A are schematic plan views of matrix wiring embodying the present invention, and Figs. 5B and 6B are cross-sectional views respectively along lines A-A′ in Figs. 5A and 6A. In Figs. 5A, 5B, 6A and 6B there are shown individual output electrodes 101 - 106, 201 - 206 at the lowermost position; common lines 107 - 110, 207 - 210 at the uppermost position; intermediate lines 111 - 115, 211 - 215 positioned between the common lines at the uppermost position; and conductor layers and wirings connecting said conductor layers 116, 216 positioned between the individual output electrodes 101-106,201-206 at the lowermost position and the common lines 107-110,207-210 at the uppermost position and connected to a power source (not shown) capable of maintaining a constant potential. In Fig. 6A there are shown conductor layers 217 of constant potential, and wirings 218 connecting said conductor layers 217. In the structure shown in Fig. 5A, the conductor layers 116 and the wirings therefor are integrally constructed. In the embodiments shown in Figs. 5A, 5B, 6A and 6B, the conductor layers of constant potential exist only in the vicinity 120, 220 of the crossing points of the individual output electrodes 101-106, 201-206 at the lowermost position and the common lines 107-110,207-210 in the uppermost position, as shown in the cross-sectional views in Figs. 5B and 6B. In this manner it is rendered possible to suppress the floating capacitances between said individual output electrodes 101-106,201-206 and said common lines 107-110,207-210, thereby preventing the crosstalks among the output signals. Also as shown in the plan views in Figs. 5A and 6A, the crossing areas between the wirings for connecting the conductor layers 116,216-218 of constant potential and said individual output electrodes 101-106,201-206 or said common lines 107-110,207-210 are reduced to suppress the floating capacitances in comparison with the conventional matrix wiring, thereby preventing the deterioration of the transfer efficiency. The photoelectric conversion device of the present invention may be prepared by any known process.

Claims: A photoelectric conversion device comprising: plural photoelectric conversion elements (14) arranged in a linear array, an individual output electrode (101-106; 201-206) being electrically connected to said photoelectric conversion element (14); plural common lines (107-110; 207-210) each connected with at least one of said individual output electrodes (101-106; 201-206) of said plural photoelectric conversion elements (14); a conductor layer (116; 217) provided at least at an unconnected cross-over point between said individual output electrodes (101-106; 201-206) and said common lines (107-110; 207-210); wherein said conductor layer (116; 217) is maintained at a constant potential, and wirings (218) connecting said conductor layer (217) to other conductor layers. A photoelectric conversion device according to claim 1, wherein said plural common lines (107-110; 207-210) derive an electric signal from said photoelectric conversion elements (14), wherein an insulating layer (6) is disposed between said plural common lines (107-110; 207-210) and said individual output electrodes (101-106; 201-206), wherein said common lines (107-110; 207-210) are each electrically connected to an individual one of the said set of output electrodes (101-106; 201-206), each said set including at least one of said individual output electrodes (101-106; 201-206), and wherein at least a conductor layer (116; 216) is provided in the vicinity (120; 220) of a region where one of said individual output electrodes (101-106; 201-206) crosses one of said common lines (107-110; 207-210), said conductor layer (116; 216) being electrically insulated from both said individual output electrodes (101-106; 201-206) and said common lines (107-110; 207-210). A device according to claim 1, further comprising intervening wiring (111-115; 211, 215) between at least two of said common lines (107-110; 207-210). A device according to claim 3, wherein said in wirings (111-115; 211-215) are insulated from said individual output electrodes (101-106; 201-206), said common lines (107-110; 207-210), said conductor layer (116-210), and said wiring (218) for providing a predetermined potential. A device according to claim 1, wherein said individual output electrodes (103; 203) are formed in an elongated arrangement over portions where said individual output electrodes (103; 203) are electrically connected with said common lines (109; 209). A device according to claim 1, wherein said conductor layer (116; 216) is provided between said individual output electrodes (101-106; 201-206) and said common lines (107-110; 207-210). A reading apparatus comprising: a photoelectric conversion device (1) with a plurality of photoelectric conversion elements (14), and a matrix wiring section (4), including plural common lines (107-110; 207-210), for deriving electric signals from said photoelectric conversion elements (14), and having respective individual output electrodes (101-106; 201-206) provided for each of said photoelectric conversion elements (14), wherein an insulating layer (6) is disposed between said plural common lines (107-110; 207-210) and said individual output electrodes (101-106; 201-206), and wherein said common lines (107-110; 207-210) are each electrically connected to a respective one of the said output electrode set (101-106; 201-206), each said set including at least one of said individual output electrodes, and at least one conductive layer (116; 216) provided only in a vicinity (120; 220) of a portion where one of said individual output electrodes (101-106; 210-206) crosses one of said common lines (107-110; 207-210), wherein said conductive layer (116; 216) is electrically insulated from said individual output electrodes (101-106; 201-216) and said common lines (107-110; 207-210) wherein said conductor layer (116,217) is maintained at a constant potential; a wiring for providing said conductive layer (116; 216) with a desired potential; a circuit for driving said photoelectric conversion device; and a source for providing said desired potential. An apparatus according to claim 7, wherein said wiring (218) electrically connects said conductive layers (217) to each other. An apparatus according to claim 7, further comprising an intervening wiring (111-115; 211-215) between at least two of said common lines (107-110; 207-210). An apparatus according to claim 7, further comprising intervening wiring (111-115; 211-215) provided between said common lines (107-110; 207-210), wherein said intervening wiring (111-115; 211-215) is insulated from said individual output electrodes (101-106; 201-206), said common lines (107-110; 207-210), said conductive layer (116; 216), and said wiring for providing said desired potential. An apparatus according to claim 7, wherein said individual output electrodes (103; 203) are formed in an elongated arrangement over portions where said individual output electrodes (103; 203) are electrically connected with said common lines (109; 209). An apparatus according to claim 7, wherein said conductive layer (116; 216) is provided between said individual output electrodes (101-106; 201-216) and said common lines (107-110; 207-210). An apparatus according to claim 7, wherein said desired potential is constant.

Inventors: HATANAKA KATSUNORI, ISHII TAKAYUKI, SAIKA TOSHIHIRO, YAMADA KATSUHIKO, HATANAKA, KATSUNORI, ISHII, TAKAYUKI, SAIKA, TOSHIHIRO, YAMADA, KATSUHIKO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H01L27
IPC codes: H01L27, H04N5