A HIGH RESOLUTION IMAGE SENSOR ARRAY USING AMORPHOUS PHOTO-DIODES

Abstract: An image sensor array comprises an insulating sub­ strate, a plurality of individual electrodes formed on the substrate, a plurality of blocking diodes formed on the re­ spective individual electrodes, a plurality of photo diodes formed on the blocking diodes to form a plurality of series connections of a blocking diode and a photo diode, a plural number of common electrodes of a transparent conductor material, each of the common electrodes covering one of the photo diodes on the same individual electrodes, and a filter covering portions of the common electrodes above the photo diodes. A photo-shielding layer of metal, amorphous silicon, amorphous germanium or amorphous silicon ger­ manium may be interposed between the blocking diode and the photo diode.

Description: BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to an image sensor array using amorphous silicon photo-diodes, and more particularly to a structure for improving resolution of color image. Description of the Prior Art: A contact type image sensor have been recently developed for use in a facsimile equipment. Since the contact type image sensor can be formed in the same size as the document to be read, an optical lens system can be removed from the facsimile equipment to make the equipment compact. As the semiconductor material of photo-diodes, amorphous silicon (hereinafter, referred to as α-Si) have been widely used in the contact type image sensors. The α-Si was deposited on individual electrodes formed on an insulating substrate. Transparent electrode were formed on the α-Si as a common electrodes. The photo-diodes were formed at the interfaces between the α-Si and the common electrodes by using a transparent metal which forms a Schottky junction with the α-Si, as the common electrode. Alternatively, the photo-diodes were formed in the α-Si as P-N diode or PIN diode by introducing appropriate impurities into the α-Si. Color filters of red, green and blue are formed on parts of the common electrode positioned upon the individual electrodes. The red, green and blue filters are serially arranged in a line. The photo carriers accumulated in the photo-diodes were sequentially read out from the individual electrodes. Such reading was performed by scanning switches which are respectively connected between a power source and the individual electrodes. An example of the switches was a MOS field effect transistor. One picture element of a color image was reproduced by using three outputs from photo-diodes positioned under the red, green and blue filters. Here, these three filters were arranged in a line. Therefore, the resolution of the reproduced picture was low, compared with a reproduced monochrome picture. Such low resolution may be improved by increasing the density of the photo-diodes. However, the increment of the density results in a minimization of each photo-diode. This causes a deterioration of S/N ration in output signals. Such low resolution may alternately be improved by arranging the photo-diodes and color filters in three parallel lines so as to form a red line, a blue line and a green line. However, in such structure, all three sets of the photo-diode and the color filter are formed on a one individual electrode. Such structure cannot read out the photo carriers from a selected one of the photo-diodes. That is, the photo carriers accumulated in the other two photo-diodes which are formed on the same individual electrode cannot be prevented from being read out together. Thus, a reproducibility of color image may be poor. H. Yamamoto et al proposed a use of blocking diode connected in series with a photo diode in "Extended Abstracts of the 15th Conference on Solid State Devices and Materials" 1983, pages 205 to 208. The blocking diode and the photo diode are formed side by side on an insulating substrate and connected in series by wiring layers. All the blocking diodes and the photo diodes are arranged in lines. Therefore, the resolution in the reproduced picture was held poor. Many complicated wirings and wide area were required on the insulating substrate. This means the color image sensor could not be formed in compact. In "Patent Abstracts of Japan, Vol. 7, No. 236 (E-205) (1381), and JP-A-58 127 373 an image sensor is disclosed having a plurality of blocks of photodiodes and blocking diodes on a single individual electrode. However, all the diode blocks are placed in a single line by dividing the tip of an individual electrode. According to this structure, at least three diode blocks disposed side by side are required to reproduce one colour picture element, resulting in a large occupation of the diode blocks for one picture element and causing no improvement of colour picture resolution. Similar structures are shown in EP-A-0 075 858 and "Extended Abstracts of the 15th Conference on Solid State Devices and Materials", Sep. 1983, Tokyo, pages 205-208, H. Yamamoto et al.: "High speed contact type linear sensor array using α-Si pin diodes". In these structures three or more photodiodes are disposed side by side on a single individual electrode or a common electrode so that all the photodiodes form a single line. It is the object of the present invention to provide an image sensor array by which an image of high resolution and high S/N ratio can be reproduced. Another object of the present invention is to provide a colour image sensor array by which an image of high colour fidelity can be reproduced. This objects are achieved by a colour image sensor array as defined in claim 1; the dependent claims are related to further developments of the invention. According to the colour image sensor array of the present invention as described in claim 1, a plural number of sets of the blocking diode, the photo-diode and the filter are formed on one individual electrode, and the individual electrodes are formed in parallel with each other. Therefore, the high resolution in a reproduced picture or color picture is obtained. Here, the minimization of each photo diode is not required. Thus, the S/N ratio in output signals is held at high level. The blocking diodes are respectively formed under the photo-diodes. Therefore, the flow of photo carriers in the photo-diodes is blocked by appropriate potential applied to the common electrode. In case of a color image sensor, if two of the common electrodes are held at the appropriate potential which backward biases the blocking diode, the photo carriers in the photo diodes under the remaining common electrode are exclusively read out in response to scanning of the individual electrodes. This results in a high color fidelity of reproduced picture. According to the improved color image sensor array of the present invention, a conductive photo-shield layer is interposed between the blocking diode and the photo-diode. If there is no photo-shield layer, a part of light radiated on non-selected photo-diodes reaches the the blocking diodes thereunder, allowing the read out of photo carriers generated in the blocking diode and resulted in a poor color fidelity in a reproduced color picture. However, such light is prevented from reaching the blocking diodes by the conductive photo-shield layer. Thus, the color fidelity in the reproduced picture is further improved. BRIEF DESCRIPTION OF THE DRAWINGS The above and further objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein: Fig. 1(a) is a sectional view of photo sensor element in the prior art and Fig. 1(b) is a plan view of a contact type color image sensor array in the prior art which uses the photo sensor shown in Fig. 1(a); Fig. 2 is a circuit diagram of the contact type color image sensor in the prior art which includes a driving circuit; Fig. 3(a) is a sectional view of photo sensor elements of a first preferred embodiment of the present invention and Fig. 3(b) is a plan view of a contact type color image sensor array according to the first preferred embodiment; Fig. 4 is a circuit diagram of the color image sensor according to the first preferred embodiment which includes a driving circuit; Fig. 5 is a sectional view of the blocking diode and the photo diode for explaining first and second examples of them; Fig. 6 is a sectional view of the blocking diode and the photo diode for explaining a third example of them; Fig. 7 is a sectional view of the blocking diode and the photo diode for explaining a fourth example of them; Fig. 8 is a sectional view of the blocking diode and the photo diode for explaining a fifth example of them; Fig. 9 is a sectional view of a second preferred embodiment of the present invention; Fig. 10 is a sectional view of a third preferred embodiment of the present invention; Fig. 11 is a sectional view of a fourth preferred embodiment of the present invention; The conventional contact type color image sensor array was formed by fabricating a plurality of photo sensor elements 11 on an insulating substrate 21 such as glass, as shown in Figs. 1(a) and 1(b). A plurality of individual electrodes 22 of chromium were formed on the substrate 21 in parallel with each other. A layer of α-Si 23 were deposited to cover one ends of the individual electrodes 22. A layer of common electrode 24 of transparent conductor material was formed on the α-Si 23 to cover the one ends of the individual electrodes 22. The photo-diodes were formed in the α-Si 23 or the interface of the α-Si 23 and the common electrode. The photo-diodes in the α-Si 23 were formed by introducing P- and N-type impurities into the α-Si 23 to form PN-junctions or PIN junctions. Alternately, photo-diodes at the interface were fabricated by using an undoped material as the α-Si 23 and indium tin oxide as the common electrode to form schottky junctions. Another type of photo-diodes were MOS type which was formed by forming a transparent insulator between the α-Si 23 and the common electrode 24. A photo-shield 25 of chromium were deposited on the common electrode 24 to improve the resolution of reproduced picture, but might be removed. Filters 26 were formed on the common electrode 24 and the photo-shield 25. The filters 26 includes red filters R, blue filters B and green filters G each covering the photo-diode on the respective individual electrodes 22. The red, green and blue filters R, G, B were arranged repeatedly in a line in this order. The contact type color image sensor array were driven by scanning FET's 13 each connected between the respective individual electrodes 22 and an output line 17, as shown in Fig. 2. Such scanning was controlled by scanning circuits 14 using a shift register, for example. The FET's 13 and the scanning circuits 14 were formed on integrated circuit devices 12. One picture element of color image was reproduced from outputs of three photo sensor elements having a red filter R, a blue filter B and a green filter G. The resolution of the reproduced picture were less than one third of the reproduced picture of monochrome picture. This resolution may be improved by increasing the density of photo sensor elements in their line. This measurement results in a decrement of surface area of each photo sensor element, and therefore, in a deterioration of S/N ratio in output signal due to a decrement of accumulated photo carriers. The resolution may also be improved, if the photo sensor elements are formed in three line, each line being formed by photo sensors having same color filters. In facsimile or copying equipments, the photo sensor array is moved on document in a direction perpendicular to the line of photo sensor elements. The resolution in the direction perpendicular to the line can be improved by increasing the scanning speed. The resolution in the direction parallel with the line may be improved by the above-mentioned three line photo sensor structure. However, this three line structure faces another problem off deteriorated color fidelity. More specifically, although each line of photo sensor elements may be independently driven by controlling potentials at the respective common electrodes in the three lines of photo sensor elements, the photo carriers accumulated in one photo sensor elements on one individual electrode flows to the individual electrode together with the photo carriers accumulated in other two photo sensor elements on the same individual electrode in response to a drive of the individual electrode. This deteriorates the color fidelity of reproduced picture. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first preferred embodiment has three lines of photo sensor elements on an insulating substrate 31 such as glass. A plurality of individual electrodes 32 are formed by depositing chromium with a thickness of 70 nm (700 Å) and etching it to form stripes having a width of 100 µm. A line density of eight elements / mm is obtained by the 100 µm width. Blocking diodes 37, α-Si layer 38 and photo diodes 39 are consecutively formed on the ends of the respective individual electrodes 32. These may be formed by a consequtive deposition of α-Si. The α-Si is generally deposited by the method of decomposition of SiH₄ or Si₂H₆ gas in a glow discharge. The α-Si is subjected to a selective etching to form a plurality of square islands of 100 µm x 140 µm, and followed by a deposition of SiO₂ of 1 µm as a passivation layer 33. Three common electrodes 34, 34' and 34'' are formed on the photo-diodes 39 in perpendicular to the lines of individual electrodes 32. Each of the blocking diode 37, the α-Si layer 38 and the photo diode 39 are piled at each crossing between the individual electrodes 32 and the common electrodes 34, 34' and 34''. The blocking diodes 37 may be formed as PN junction diodes or PIN junction diodes by introducing P and N type impurities, as Schottky junction diodes by using an undoped α-Si as the α-Si and chromium as the individual electrodes 32 or as MIS type diodes by interposing an insulating layer between the α-Si and the individual electrodes 32. Here, the Schottky junction diodes are employed. Similarly, the photo diodes 39 may be formed as PN or PIN junction diodes, Schottky junction diodes or MIS type diodes. This embodiment employes the Schottky junction diodes by using an undoped α-Si as the α-Si and indium tin oxide as the common electrodes 34, 34' and 34''. The thickness of α-Si layer 38 is 100nm (1,000 Å), for example. The thickness of α-Si's for the photo diodes 39 and the blocking diodes 37 are respectively 1 µm. After the passivation layer 33 on the photo diodes 39 is etched away, three common electrodes 34, 34' and 34'' are then formed by evaporating transparent conductor material such as indium tin oxide with a thickness of 0.06 µm, photo-shields 35 is formed by evaporating chromium with a thickness of 150 nm (1,500 Å) to expose the common electrodes 34, 34' and 34'' at the centers of respective photo-diodes 39. This photo-shield 35 is formed to improve the resolution, but may be omitted. Finally, color filters 36 cover the exposed common electrodes 34, 34' and 34'' and the photo-shields 35. Three types of color filters 36 are used, red filters R, green filters G and blue filters B. The same color filters are formed on the same common electrode so as to form lines of red filters R, green filters G and blue filters B in parallel. The preparation of the color filters 36 will be explained. After polymer resin is coated, three types of dyes are permeated. The examples of dyes are Eastmanpolyesterblue 4RL (a trade name) for blue, Eastmanpolyesterred 901 (a trade name) for red and a mixture of Eastmanyellow R-GFD and Eastmanblue BGN (both are trade names) for green. The shape of each color filter is square of 180 µm x 220 mm. Other sets of color filters are also applicable in place of red, blue and green filters. The examples of other sets are white, yellow and cyan, white, green and cyan, white, green and yellow and green, cyan and yellow. The circuit for driving the color image sensor array is shown in Fig. 4. Respective common electrodes 34, 34' and 34'' are connected on the insulating substrate 31 with terminals 45, 46 and 47. The individual electrodes 32 are respectively connected with an output terminal 48 through MOS type FET's 43. The output terminal is typically grounded through an external resistor to produce output potentials. The MOS type FET's 43 are scanned by scanning circuits 44. An example of the scanning circuits 44 is a shift register shifting an input pulse applied at a terminal 49. As shifting of the input pulse, FET's 43 are sequentially driven into conductive state. The terminals 45, 46 and 47 are also scanned to rise sequentially their potentials to a value necessary to forward bias the photo diodes 39 from a grounding potential. The potential to bias the photo diodes 39 forward is six volts, for example. As apparent from the drawings of Figs. 3(a) and 3(b), three photo sensor elements for detecting three primary colors are formed on one individual electrodes. One picture element of color image is formed by outputs from those three photo sensor elements. Therefore, the resolution in a direction perpendicular to the individual electrodes 32 is held at high level. To obtain such high resolution, the area of each photo sensor element is not made small. Sufficient photo carriers can be accumulated in each photo sensor element. This fact keeps the S/N ratio in an output signal at high. Further, one photo diode 39 in one photo sensor element is forward biased to allow the accumulated photo carriers therein flow to the output terminal 48, in response to the scannings of the FET's 43 and the terminals 45, 46 and 47. At this time, the selected individual electrode 32 is connected to other two photo sensor elements. However, the flows of photo carriers from photo diodes in the non-selected two photo sensor elements are blocked by the blocking diodes 37. Thus, photo carriers in non-selected photo sensor elements do not mix in an output from the selected photo sensor element, resulted in a high color fidelity of reproduced picture. Furthermore, one blocking diode 37 and one photo diode 39 are piled through α-Si layer 38. This structure saves area on the insulating substrate 31 and gives a possibility to widen each photo sensor element in a direction parallel with the individual electrodes 32. The wide photo sensor elements further improves the S/N ratio in output signals. In the above-mentioned first embodiment, the α-Si layer 38 is preferably N type material. But any other conductive materials which from ohmic contact with α-Si's in the blocking diode 37 and the photo diode 39 may be replaced therefor. In Figs. 5 to 8, other examples of the blocking diode 37 and the photo diode 39 are shown in sectional views First example uses NIP diodes. On a stripe of individual electrode 32, an N type α-Si 51 is deposited with a thickness of 50 nm (500 Å) and followed by depositions of undoped high resistive α-Si 52 having a thickness of 500 nm (5,000 Å) and a P type α-Si 53 having a thickness of 600 nm (600 Å) to form a blocking diode 37 of NIP junction type. A conductive α-Si layer 54 of N type α-Si is deposited on the P type α-Si 53 with a thickness of 200 nm (2,000 Å). This may be replaced with other appropriate conductive material forming an ohmic contact with the P type α-Si 53, or otherwise omitted by using a thick P type α-Si as the α-Si 53. On the conductive α-Si layer 54, a P type α-Si 53' of 50 nm (500 Å), a nondoped high resistive α-Si 52' of 500 nm (5,000 Å) and an N type α-Si 51' of 20 nm (200 Å) are consecutively deposited to form a photo diode 38 of NIP junction type. As explained with reference to Fig. 3(a), the common electrode 34, the photo shield 35 and the color filter 36 are formed on the photo diode. Here, it is apparent for the skilled in the art that the conductivity types of the α-Si's 51 and 51' and the α-Si's 53 and 53' may be changed from N type to P type and P type to N type, respectively, to form PIN junction diodes. Here, boron may be slightly doped in the high resistive α-Si's 52 and 52'. The second example uses an NIP junction diode and a diode using a hetero junction as the blocking diode 37 and the photo diode 38. Since the sectional view is same as Fig. 5, this second example will be explained with reference to the same sectional view of Fig. 5. A P-type amorphous silicon carbide is used for the P-type α-Si 53' only. The silicon carbide may be deposited by decomposing a mixture of a gas of SiH₄ or Si₂H₆ and a gas of CH₄ or C₂H₆ in a glow discharge atomosphere. This decomposition may be performed in the same apparatus as used for the decomposition of α-Si, the undoped high resistive α-Si, the N type α-Si and the P type α-Si are used for the α-Si's 52 and 52' and the α-Si's 51 and 51' and the α-Si 53, similarly to the first example. The conductive α-Si layer 54 is also same. The heterojunction type photo diode using the amorphous silicon carbide has a good sensitivity to the visible radiation of wavelength between 400 nm and 500 nm. The third example shown in Fig. 6 uses a Schottky junction diode as the photo diode 38 and an NIP junction diode as the blocking diode 37. In this example, the N type α-Si 51' is removed from the first example to allow a direct contact between the undoped high resistive α-Si 52' and the common electrode 34. Such direct contact forms a Schottky junction, if the appropriate transparent conductor material such as indium tin oxide is employed as the common electrode 34. The fourth example shown in Fig. 7 uses an MIS type diode as the photo diode 38 and an NIP junction diode as the blocking diode 37. The blocking diode is formed by an N type α-Si 51 of 100 nm (1,000 Å), an undoped high resistive α-Si 52 of 700 nm (7,000 Å) and a P type α-Si 53 of 100 nm (1,000 Å), similar to the above-explained first to third examples. The photo diode 38 is formed by a P type α-Si 53 of 100 nm (1,000 Å), an undoped high resistive α-Si 52' of 700 nm (7,000 Å), an insulator layer 55 of 20 (200) to 30 nm (300 Å) such as silicon nitride or silicon oxide, and the common electrode 34. The silicon nitride may be formed by decomposing a gas mixture of a gas of SiH₄ or Si₂H₆ and a gas of NH₃ or N₂ in a glow discharge atomosphere. Similarly, the silicon oxide may be formed by decomposing a gas mixture of a gas of SiH₄ or Si₂H₆ and a gas of N₂O, CO₂ or O₂ in a glow discharge atomosphere. These decompositions may be performed in the same apparatus as the decomposition of α-Si to allow the continuous depositions of α-Si and the insulator material. The undoped high resistive α-Si's 52 and 52' may be slightly doped with boron. The fifth example shown in Fig. 8 uses a Schottky junction diode as the photo diode 38 a combination diode of a Schottky junction and a heterojunction as the blocking diode 37. A high resistive α-Si 52 is directly deposited on the individual electrode 32 of chromium to form a Schottky junction. A P type silicon carbide 56 is deposited on the high rssistive α-Si 52 to form a heterojunction. The blocking diode 37 is formed by a combination of the Schottky junction and the heterojunction. A P type α-Si 53' is deposited on the blocking diode via a conductive α-Si 54. Another high resistive α-Si 52' is then deposited. A common electrode 34 of indium tin oxide is formed on the high resistive α-Si 52 to form a Schottky junction. The photo diode 38 uses the Schottky junction. Here, the high resistive α-Si's 52 and 52' may be undoped α-Si or α-Si doped slightly with boron. A second preferred embodiment has a similar structure as the first preferred embodiment, as shown in Fig. 9. The plan view is same as Fig. 3(b) and then same reference numerals are used in Fig. 6 except for the structure of the photo diodes 38 and the blocking diodes 37. The blocking diodes 37 are formed on the individual electrode 32 by depositing an N type α-Si 61, an undoped high resistive α-Si 62 and a P type α-Si 63 to form NIP junction diodes. Molybdenum is then deposited with a thickness of 100 nm (1,000 Å) to form a photo-shield layer 64. The photo diodes 38 are, thereafter, formed on the photo-shield layer 64 by depositing a P type α-Si 63', an undoped high resistive α-Si 62' and an N type α-Si 61' to form NIP type diodes. The photo-shield layer 64 prevents the radiated light from permeating to the blocking diodes 37. If the light permeates to the blocking diodes 37 through the photo diodes 38, photo carriers are generated in the blocking diode and flow to the individual electrodes 32. Such additional photo carriers generated in unselected photo sensor elements on the selected individual electrode 32 flow to the selected individual electrode 32 together with the photo carriers generated in the selected photo sensor element, resulted in a deterioration of color fidelity of the reproduced picture. The photo-shield layer 64 of molybdenum prevents such deterioration of color fidelity by blocking the penetration of light. Therefore, the material of the photo-shield layer is not limited to molybdenum but may be other conductive material such as aluminum, nickel, chromium, platinum and conductive carbon, which performs an ohmic contact with both the P type α-Si's 63 and 63' and has a thickness sufficient to block the light. The photo diodes 38 and the blocking diodes 37 may be formed as PIN junction diodes, heterojunction diodes or Schottky junction diodes, as explained in the first to fifth examples of the first preferred embodiment. The intermediate layer of conductive α-Si 54 is replaced with the photo-shield layer 64 of conductive metal or the like. A third preferred embodiment also has the same plan view as Fig. 3(b). Only the sectional view is shown in Fig. 10. The passivation layer 33 of silicon oxide, the polymer resin 69 and the color filters 60 are expressed in more detail than Figs. 3(a) and 9. The passivation layer 33 oil SiO₂ is deposited with 0.8 µm to prevent leak current from flowing through side surface of photo sensor elements. The passivation layer 33 is removed at center portions of the upper surfaces of the photo sensor elements to expose the center portions. A transparent common electrodes 34 of indium tin oxide of 0.06 µm cover the exposed center portions and adjacent surfaces of the passivation layer 33. Photo shield layers 35 of chromium having a thickness of 0.1 µm are deposited on the common electrodes 34 except for portions on the exposed center portions. The polymer resin 69 is then coated to cover the passivation layer 33, the common electrodes 34 and the photo shield layer 25. Thereafter, by thermally diffusing dyes into the polymer resin 69 at the portions above the photo sensor elements to form color filters 60 of red, blue and green. The photo sensor elements respectively consist of a photo diode 38, a blocking diode and a photo absorber 57 interposed therebetween. The photo diodes 38 and the blocking diodes 37 are NIP junction diodes formed by an N type α-Si's 51 and 51', a high resistive α-Si's 52 and 52' and a P type α-Si's 53 and 53'. The high resistive α-Si's 52 and '52 may be undoped α-Si or α-Si doped slightly with boron. The photo absorber 57 operates as the photo shield layer 64 of the second preferred embodiment by absorbing light which permeates the photo diodes. The example of the material for the photo absorber 57 is amorphous germanium having a thickness of 0.2 µm which is deposited by a decomposition of germane (GeH₄) in a glow discharge atomosphere. The material for the absorber 57 may be amorphous silicon germanium which is deposited by a decomposition of a gas mixture of germane (GeH₄) and silane (SiH₄) in a glow discharge atomosphere, as described in "Journal of Electrochemical Society" December 1982, pages 2850 to 2855. These absorber 57 can be formed in the same apparatus as that for depositing α-Si. Therefore, the blocking diodes 37, the absorbers 57 and the photo diodes 38 can be continuously formed in the same apparatus. The amorphous germanium has a low resistivity without doping impurities, but the amorphous silicon germanium must be lowered its resistivity by doping impurities. The light having a wavelength of about 650 nm passes the α-Si photo diode, but is absorbed by the amorphous germanium or the amorphous silicon germanium. Thus, a high color fidelity in the reproduced picture is obtained, as explained in the second preferred embodiment. It is needless to say that the structure of first to five examples may be applicable to the blocking diodes 37 and the photo diodes 38 of the third preferred embodiment with a replacement of the intermediate layer of the conductive α-Si 54 with the amorphous germanium or the amorphous silicon germanium. A fourth preferred embodiment shown in Fig. 11 has the same structure as the third preferred embodiment except for the photo sensor elements. The photo sensor elements consist of a blocking didoe 37, a photo diode 38 and a light absorber 57 interposed therebetween, similarly to the third preferred embodiment. The blocking diodes 37 are NIP junction diodes and formed of an N type α-Si 51 of 0.2 µm, a high resistive α-Si 52 of 0.6 µm and a P type α-Si 53 of 0.2 µm. The light absorber 57 is undoped amorphous germanium of 0.2 µm or impurity doped amorphous silicon germanium of 0.4 µm. The photo diodes 38 are NIP junction diodes but formed of a P type amorphous silicon germanium 73 of 0.2 µm, a high resistive amorphous silicon germanium 72 of 0.6 µm and an N type amorphous silicon 71. Since the α-Si, the amorphous germanium and the amorphous silicon germanium are formed in the same apparatus by decomposing silane and/or germane, all the blocking diodes 37, the light absorbers 57 and the photo diodes 38 can be continuously formed in the same apparatus. Furthermore, since the photo diodes 38 uses amorphous silicon germanium, the red light having a wavelength of about 650 mm is absorbed in the photo diodes 38 to prevent more effectively from arriving at the blocking diodes 37. Generally, the increment of the germanium ratio in the amorphous silicon germanium enhances the red light absorbing effect but deteriorates the leakage current of photo diodes. Therefore, the germanium is contained in the material forming the photo diode with such value that the leakage current may not be increased. More specifically, uppermost N type layer 71 does not contain amorphous germanium, the high resistive layer 72 and the lowest P type layer 73 contain amorphous germanium of 30%. As a result, an excellent color fidelity is obtained in the reproduced picture.

Claims: A colour image sensor array comprising a substrate (31) having an insulating surface; a plurality of individual electrodes (32) formed on said insulating surface, said individual electrodes being arranged parallel to each other; a plurality of diode blocks (37, 39) being formed in equal groups of at least three in line on each of said individual electrodes, each diode block consisting of a vertical stack (51-54, 51'-53') of a photo-diode (39) and an underlying blocking diode (37) which diodes are serially connected so that said blocking diode may control a current flow from said photo-diode, and said diode blocks being disposed in form of a matrix, whereby each row of said matrix comprises said group of at least three diode blocks formed on each respective individual electrode, and each column of said matrix consists of corresponding diode blocks on each of said individual electrodes; common electrodes (34) of a transparent conductive material, said common electrodes being formed on said diode blocks to connect each column of diode blocks to one of said common electrodes; and a plurality of colour filters covering said matrix of diode blocks in a predetermined way. The color image sensor array as claimed in claim 1, characterized in that said group of at least three diode blocks in said row of said matrix consists of three diode blocks, and that said color filter is comprised of three kinds of filter elements sensing different colors. The color image sensor array as claimed in claim 1 or 2, characterized in that each of said diode blocks involves a conductive photo-shield layer (54) inserted between said photo diode and said blocking diode in said stack.

Inventors: KANEKO, SETSUO, OKUBO, TOSHIO, UCHIDA, HIROYUKI
Applicants: NEC CORPORATION
Application year: 1985
Main classification: H01L27
IPC codes: H01L27