Photoelectric conversion device

Abstract: A photoelectric converison device is provided with plural photoelectric conversion cells and signal lines for activating said photoelectric conversion cells. The signal line is composed of plural lines formed in plural layers. The plural lines are electrically connected to every unit composed of a desired number, at least equal to two, of photoelectric conversion cells.

Description: Photoelectric Conversion Device Field of the Invention The present invention relates to a photoelectric conversion device having signal lines for activating plural photoelectric conversion cells. Related Background Art Figs. 1(A) to 1(C) illustrate photoelectric conversion cells in a photoelectric conversion device described for comparison. The basic cell type comprising a bipolar transistor and an electrode capacitively coupled to the base region of said transistor is, e.g., described in EP-A-0 226 338. Fig. 1(A) is a schematic plan view of a photoelectric conversion cell in a comparison photoelectric conversion device; Fig. 1(B) is a cross-sectional view along a line I-I in Fig. 1(A); and Fig. 1(C) is a cross-sectional view along a line II-II in Fig. I(A). As shown in these drawings, the photoelectric conversion cells are arranged on an n⁻ layer 1 formed by epitaxial growth on a substrate, with an element separating area composed of an oxide film 2 formed by the LOCOS method. On the N⁻ layer there is formed a p-base area 3 of a bipolar transistor, in which formed is an n⁺ emitter area 4. On oxide films 2, 5 there is formed a horizontal signal input line 6 which forms, on the p-base area 3, a capacitor electrode for controlling the potential of the base across the oxide film 5. Said horizontal signal input line 6 is composed of polysilicon. In addition, across an insulating layer 7 there is formed a vertical signal output line 8, which is composed of aluminum and is connected to an n⁺- emitter area 4. In the insulating layer 7 there is formed a contact hole 9a through which an aluminum layer 9 is connected to the horizontal signal input line 6 composed of polysilicon. As the vertical signal output line 8 and the aluminum layer 9 are formed on the insulating layer 7, they will hereafter be called first aluminum layers. After the formation of an insulating layer 10, a hole 9b is formed on the aluminum layer 9, and an aluminum layer 11 formed parallel to the horizontal signal input line 6 is connected with the aluminum layer 9. The uppermost aluminum layer 11 is formed parallel to the horizontal signal input line 6 composed of polysilicon and is electrically connected therewith through the aluminum layer 9. The above-explained double-layered structure including the aluminum layer 11 of low resistance is adopted for preventing the delay in signal, resulting the higher resistance of the horizontal signal input line 6 composed of polysilicon. Said aluminum layer 11, being formed on said first aluminum layer across the insulating layer 10, will be called second aluminum layer. Fig. 2 is a schematic view of a comparison photoelectric conversion device consisting of a plurality of the above-explained photoelectric conversion cells. The above-explained photoelectric conversion cells C1, C2, ... are arranged as an array, and the horizontal signal input line 6 and the aluminum layer 11 are formed in parallel manner and are connected to the cells through the aluminum layer 9. Consequently the horizontal signal can be transmitted without delay even in the delay of a large number of cells, so that the signal read-out operation, refreshing operation etc. can be achieved at a high speed. However, the above-explained comparison photoelectric conversion device has been associated with a drawback that the aperture ratio cannot be increased, because the aluminum layer 9 constituting the connection portion in the above-explained double-layered structure occupies about 11 % of each cell area. Since the aluminum layer 9 serving as the connecting portion is opaque to light, the conparison structure having the aluminum layer 9 in each cell cannot increase the aperture ratio. Such drawback is not limited to the above-explained comparison structure but appears also in various photoelectric conversion devices such as a CCD, MOS or SIT structure, as long as the double-layered structure is employed. It is known from JP-A-58-199557 a dynamic memory device having a word line made up of a polysilicon layer which acts as a gate electrode for a signal transfer transistor, and an aluminium layer. The aluminium layer is connected to the polysilicon layer at the beginning, middle and end points of the word line, so as effectively to divide the resistive polysilicon layer into four parts in order to reduce a signal transmission delay in the word line. EP-A-0160392 proposes a semiconductor memory device having a double layer word line structure, in which a polycrystalline semiconductor layer and a metal layer are separated by an insulating layer. Connections between the two layers are closer together at the end of the word line remote from the point where a control voltage is placed on the word line than at the end of the word line which receives the control voltage. According to the present invention there is provided a photoelectric conversion device as set out in claim 1. The remaining claims set out optional features. An embodiment of the present invention provides a photoelectric conversion device having a signal line of a plurality of layers while reducing the loss of aperture ratio as compared with the arrangement of Fig. 2. By providing the connections between the first and second wirings at the cells which are more sensitive to light, the effect of the connections on the output signal is reduced. Fig 1(A) is a schematic plan view of a photoelectric conversion cell in a comparison photoelectric conversion device; Fig. (1(B) is a cross-sectional view along a line I-I in Fig. 1(A); Fig. 1(C) is a cross-sectional view along a line II-II in Fig. 1(A); Fig. 2 is a schematic view showing an example of the comparison photoelectric conversion device containing an array of plural photoelectric conversion cells explained above; Fig. 3 is a schematic view of a photoelectric conversion device constituting a first preferred embodiment of the present invention; Fig. 4 is a schematic plan view of a photoelectric conversion cell constituting a second preferred embodiment of the present invention; and Fig. 5 is a schematic view of a photoelectric conversion device having a two-dimensional array of a plurality of the photoelectric conversion cells mentioned above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified in detail by the embodiments thereof shown in the attached drawings, but it is not limited to these embodiments. Fig. 3 is a schematic view of a first preferred embodiment of the photoelectric conversion device of the present invention. In Fig. 3, the photoelectric conversion cells C₁₁, C₁₂, ..., C₂₁, C₂₂, ... have a basic structure same as that shown in Fig. 1 and are arranged two-dimensionally. Said cells are respectively provided with a white filter having a substantially uniform spectral transmission over the entire visible spectral range, a red color separation filter (R) or a blue color separation filter (B). In the present embodiment, the horizontal signal input line 6 composed of polysilicon and the aluminum layer 11 are connected only on the white (W) cell, and the red (R) and blue (B) cells do not have the opaque aluminum layer 9. Consequently the aperture ratio for each pixel, composed of white, red and blue cells, is increased in comparison with the arrangement of Fig. 2. Besides the cell with white filter can receive a larger amount of light in comparison with the cell with red or blue filter, so that the influence to the output signal can be made smaller, even in the presence of the aluminum layer 9 constituting the connecting portion, than in the red or blue cell. Consequently the sensitivity or S/N ratio of the device is not deteriorated. The connecting portion need not be formed for every two cells as in the above-explained embodiment, but can be formed for every three or four cells. However the interval of the connecting portions should be maintained at a value not causing the delay of the signal, since otherwise the horizontal signal input line 6 of polysilicon will show a high resistance. Fig. 4 is a schematic plan view of photoelectric conversion cells of a second preferred embodiment of the present invention. In the present embodiment, a horizontal signal input line 101 is formed as a first aluminum layer 101, which is connected through a contact hole to an underlying capacitor electrode 102 of polysilicon. A vertical signal output line 103 is composed of polysilicon and is connected with an n⁺ emitter area 4. Also an aluminum layer 104 is formed as a second aluminum layer parallel to the vertical signal output line 103 of polysilicon, and is connected on the emitter area 4. Fig. 5 is a schematic plan view of the second preferred embodiment of the present invention in which the above-explained photoelectric conversion cells are arranged two-dimensionally. The horizontal signal input lines 101 and the capacitor electrodes 102 are omitted. In the present embodiment, the vertical signal output lines 103 and the aluminum layers 104 are are mutually connected only on the cells having the white filter, whereby the loss in the aperture rate is prevented. In the present embodiment the vertical signal output line 103 is connected with the upper most aluminum layer 104, thereby reducing the resistance and the capacitance in the wiring, and improving the S/N ratio of the output signal. The color separation filters need not be composed of red and blue only but can be composed of red, green and blue. In such case said connection can be made only in the green cells showing higher sensitivity. Naturally the color separation filters are not limited to the above-mentioned combinations. As detailedly explained in the foregoing, the photoelectric conversion device of the present embodiments is capable of suppressing the loss in the aperture ratio, since plural lines formed in laminated plural layers are connected to every unit composed of two or more cells thus constituting a signal line. The term "aperture ratio" as used herein in relation to a photoelectric conversion device means the ratio of the effective photo-receiving area of the device to the whole area of the device.

Claims: A photoelectric conversion device comprising a plurality of photoelectric conversion cells (C11-C33) and filter means for the cells so that cells of a first set of cells (W) are more sensitive to light incident on the device than cells of a second set of cells (R,B), the device having a common signal line for a plurality of cells of the first set and a plurality of cells of the second set, the signal line comprising first and second parallel wirings (6,11; 103,104) separated by an insulating layer (7,10) and connected to each other at intervals, the connections (9) between the first and second wirings occurring at cells of the first set (W) but not at cells of the second set (R,B). A device according to claim 1 in which the filter means acts as a white filter for the cells of the first set and acts as a red filter or a blue filter for the cells of the second set. A device according to claim 1 in which the filter means acts as a green filter for the cells of the first set and acts as a red filter or a blue filter for the cells of the second set. A device according to any one of claims 1 to 3 in which the cells are disposed in a two-dimensional matrix. A device according to claim 4 in which the common signal line is a horizontal signal input line. A device according to claim 4 in which the common signal line is a vertical signal output line. A device according to claim 5 in which each cell is capacitively coupled to the first wiring of the common signal line. A device according to claim 7 in which the base region (3) of a bipolar transistor of each cell is capacitively coupled to the first wiring (6) of the common signal line. A device according to claim 6 in which the emitter region (4) of a bipolar transistor of each cell is connected to the first wiring (103) of the common signal line. A device according to any one of the preceding claims in which the first wiring (6;103) of the common signal line has a higher resistance than the second wiring (11;104) of the common signal line. A device according to any one of the preceding claims in which the first wiring (6;103) of the common signal line comprises a polycrystalline semiconductor and the second wiring (11;104) is aluminium. A device according to any one of the preceding claims in which there is a connection (9) between the first and second wirings at every cell of the first set on the common signal line. A device according to any one of claims 1 to 11 in which there is a connection (9) between the first and second wirings at some but not all of the cells of the first set on the common signal line. A device according to any one of claims 4 to 13 which has first and second said common signal lines, the filter means having a different spectral transmission characteristic for the cells of the second set (R) on the first common signal line from the spectral transmission characteristic for cells of the second set (B) on the second common signal line.

Inventors: HOSHI JUNICHI, HOSHI, JUNICHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H01L27
IPC codes: H04N9, H01L23, H04N5, H01L31, H01L27