JPH02132860A - Close contact type image sensor - Google Patents

Abstract

PURPOSE:To make an image sensor large in capacitance without increasing a sensor region by a method wherein a sensor section formed of a semiconductor film of a photoelectric conversion film and a capacitance section formed of a transparent insulating film are provided onto a plane extended from a lower electrode. CONSTITUTION:A lower electrode 12 divided into bits is formed on a glass substrate 11 extending in a secondary scanning direction. A transparent insulating film 13 is formed thereon, and an opening 13a is provided to a sensor region. Moreover, a semiconductor thin film serving as a photoelectric conversion film 14 is formed covering the opening 13a, and an upper transparent electrode 15 is formed on the photoelectric conversion film 14. The photoelectric conversion film 14 is covered with a transparent insulating film 16 leaving an opening 16a uncovered, the part of the upper transparent electrode 15 of the sensor section is opened, and an upper electrode 17 is formed as being connected to the upper transparent electrode 15. As mentioned above, the transparent insulating films 13 and 16 are formed on the plane extended from the lower electrode 12 of the sensor section and the upper electrode 17 is formed thereon, whereby they can be formed into one piece, and the insulating films are made thin to constitute a capacitance component, so that an image sensor of this design can be made large in capacitance without increasing a sensor region.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a contact type image sensor for optically reading a document image in, for example, a facsimile transmitter.

[Prior art]

Generally, one-dimensional CCD image sensors are used in devices that optically read documents, such as facsimile machines. However, since this COD has a photoelectric conversion section of only about 25a+m, a reduction optical system is required to read the original. This made it difficult to miniaturize the device. In order to miniaturize the device, an image sensor that does not require a reduction optical system becomes necessary. Such an image sensor needs to have a length that is at least the same size as the original to be read. For example, to read an A4 size document, the image sensor must have a length of at least 216+am. It is impossible to make an image sensor with a length of 216 mm using crystalline Si, but it is possible to make an image sensor using low-quality thin film semiconductors (for example, amorphous Si).
Production is possible by using i). By using a semiconductor thin film as a photoelectric conversion layer, it has become possible to manufacture a large-area image sensor that is the same size as the original, and various contact-type image sensors using semiconductor thin films have been manufactured. This contact image sensor reads the original by coming into direct contact with it, eliminating the need for a reduction optical system and allowing the device to be made more compact. Such contact-type image sensor structures are broadly divided into sandwich type, in which a thin film semiconductor is sandwiched between lower and upper electrodes, and coplanar type, in which electrodes are drawn out from both sides in a plane. Of these, the sandwich type is more advantageous in terms of photoresponse characteristics because the thickness of the thin film semiconductor can be made thinner. Figure 3 shows a cross-sectional view of the sandwich type sensor. In FIG. 3, 1 is a transparent insulating substrate such as a glass substrate or ceramic, 2 is a lower metal electrode, 3 is a semiconductor film of a photoelectric conversion section,
4 indicates the upper transparent electrode. Conventionally, in such sensors, the light-receiving area is formed in the area sandwiched between the lower and upper electrodes, but photocurrent is detected even if the incident light enters outside the opposing area of the lower and upper electrodes. , the light-receiving area becomes wider than the area formed by the counter electrode, resulting in a decrease in resolution. In addition, since the capacitance of an accumulation-type contact sensor is formed in the opposing regions of the lower and upper electrodes, if it is divided into bits like a long sensor, the area will be small and the capacity will be limited. This has the disadvantage that it is easily affected by the connection wiring with the drive circuit. In order to improve the shortcomings of these accumulation-type contact sensors, a structure has been proposed in which the opposing areas of the lower and upper electrodes are enlarged and a light-shielding film is provided to limit the light-receiving area, as shown in Figure 4. (Unexamined Japanese Patent Publication No. 61-825)
Publication No. 70). In addition, in FIG. 4, 5 indicates an upper light-shielding film, and the other parts are the same as in FIG. 3. In such an image sensor, the region forming the capacitive component has the same layer structure as the photoelectric conversion section, so the dark current increases by the increase in the area of the sensor section, and the photocurrent is Because of the upper light-shielding layer, the photocurrent does not change and the photocurrent/dark current ratio, which indicates sensor performance, decreases. In addition, the part that forms the capacitor uses a semiconductor as a photoelectric conversion layer, but in the case of storage type reading, the capacitor's charge is stored once and the charge is released by the photocurrent caused by light incidence, so the voltage of the capacitor increases over time. Change. Therefore. Capacitors made of semiconductors have the problem that the capacitance value changes as the voltage changes.
Furthermore, there is a problem in that the capacitance value fluctuates due to electron holes generated internally due to light shielding by the upper light shielding layer. [Purpose] The present invention solves the problems of the conventional contact image sensor having a charge accumulation type with a sandwich structure as described above, and increases the capacitance even by the applied voltage applied to the capacitor without reducing the photocurrent/dark current ratio. The purpose of the present invention is to provide a contact image sensor in which the value does not change and the capacitance can be increased without increasing the sensor area by thinning the insulating film and forming a capacitive component. (Structure) The present invention is a contact type sensor that has a charge storage type sandwich structure in which a semiconductor thin film is sandwiched between a lower electrode and an upper transparent electrode on a transparent insulating substrate. A transparent insulating film is provided on the extended surface of the lower electrode, and an upper electrode connected to the upper transparent electrode is provided on the transparent insulating film.

The present invention will be explained in more detail below with reference to the drawings showing examples. Figure 1 shows a first embodiment of the contact type image sensor of the present invention. In FIG. 1, a lower electrode l2 is placed on a glass substrate 11.
is divided into bits and extended in the sub-scanning direction. A transparent insulating film l3 is formed thereon, and an opening l3a is provided in the sensor region. Furthermore, a semiconductor thin film forming the photoelectric conversion film 14 is formed to cover the opening. Further, an upper transparent electrode l5 is formed on the semiconductor film of the photoelectric conversion film 14. The semiconductor thin film of the photoelectric conversion film 14 is covered with a transparent insulating film 16, leaving an opening 16a, and the upper transparent electrode 15 of the sensor section is opened. Further, an upper electrode 17 is formed connected to the upper transparent electrode 15. As described above, in the image sensor according to the present invention, the transparent insulating film 13, ? 6 is formed, and an upper electrode 1 is further formed thereon.
7 is formed. Next, an example of manufacturing the image sensor of the first embodiment as described above will be explained. As the glass substrate 11, quartz or Pyrex (registered trademark) is used.
Approximately 1,500 layers of R are deposited by vacuum evaporation, and the lower electrode 12 is formed by photolithography. next. 500% SiO■ or Sin)xNy by plasma CVD method
The transparent insulation @13 is formed by about 0 people, and the opening 13a of the sensor part is formed by photolithography. Next, a hydrogenated amorphous silicon film with a thickness of 0.5 to 2.0 μm is formed as a semiconductor film of the photoelectric conversion film 14 by P-CVD using SiH4 gas, etc., and a transparent conductive film such as ITO is sputtered or vacuum evaporated. A total of 750 people deposited the semiconductor film using photolithography techniques, and the upper transparent electrode 15 and the semiconductor film 14 of the photoelectric conversion film 14 were formed using the photolithography technique. After that, the transparent insulating film 1
As 6, SiO■ or S is deposited by plasma CVD method.
iC) A film of about 3,000 xNy is deposited on the entire surface, and an opening 16a is formed in the upper transparent electrode 15 using photolithography. And finally Cr or A Q / Cr
A film of 0.15 to 0.5 μm is formed by vacuum evaporation, and the upper electrode 17 is connected to the upper transparent electrode 15 by photolithography. The contact-type image sensor obtained in this manner can obtain a high value without reducing the photocurrent/dark current ratio, and furthermore, the capacitance component of the transparent insulating film 13. 16 is sandwiched between the lower electrode 12 and the upper electrode 17, a very stable capacitance can be obtained. In addition, transparent insulating film 1
3. By changing the thickness of 16, the capacitance value can be changed without changing the pattern of the nootorizo, making it easy to optimize the capacitance. This makes it possible to reduce stray capacitance in wiring, etc., and as shown in the experimental results below, it becomes possible to obtain a large and stable output from the image sensor. FIG. 2 shows a second embodiment of the present invention. In FIG. 2, there is a light shielding 7! on the glass substrate 11. J21 is formed, and a transparent insulating layer 22 is formed thereon. Note that the light shielding layer 2l is provided with apertures 21a. An opening +2a for light incidence is formed on the lower electrode 12 at the same position as the light shielding layer 2l, and a protective layer 23 is formed on the top, and the rest is as shown in FIG. The structure is similar to that shown in . Although FIG. 2(a) shows a plurality of contact type image sensors arranged in the main scanning direction, it is needless to say that such an arrangement is not required.

According to the image sensor having the structure shown in Fig. 2, the original is read by bringing the original into direct contact with the protective layer 23 without using a 1-magnification imaging system, so it can be made smaller. becomes.

Here, when using the sensor of the second embodiment and using the capacitance (storage capacitance) as a parameter, the exposure amount-sensor output characteristic is shown in FIG. 5. In the measurement, first, the capacitance connected in parallel to the sensor (connected in parallel in terms of electric circuit) was changed by changing the length of the upper electrode 17 facing the lower electrode l2 shown in FIG. 6(a). A sensor was prepared, and the sensor output was measured at each exposure level (illuminance x reading time) by varying the sensor surface illuminance and plotted on a graph. The capacitance value was calculated by calculation. Figure 6(b) is an equivalent circuit of the image sensor shown in Figure 6(a). Cs in FIG. 6(b) represents the sensor capacitance. Ca indicates additional capacity. Capacity (storage capacity) C is C=Cs+Ca
It can be shown as In this experiment, as can be seen from Figure 5, it can be seen that the saturation voltage and saturation exposure amount increase in proportion to the capacitance. The saturation exposure amount Es is expressed as follows: Es=(C-■)/SC C: Storage capacity CF) V: Applied voltage (V) S: Sensor sensitivity (A/ρX).

For this reason, it is necessary to create a storage capacity that does not saturate even when reading a blank original. Therefore, in order to ensure sufficient storage capacity, a capacitor (additional capacitor) is built in parallel with the sensor as shown in Figure 6(b), so that Es=(Cs+Ca)・V/S Cs: Sensor capacitance Ca : It becomes possible to read the document up to the additional capacity and the exposure amount of Es. Therefore, in the present invention, the storage capacity is increased by using the above-mentioned configuration.

FIG. 7 shows a constant exposure amount (lQx-s) for the sensor of the second embodiment.
) is a diagram plotting the sensor output for each capacitance value when exposed to light. From FIG. 7, it can be seen that the sensor output is proportional to the capacitance and tends to saturate above 12 pF, and that a high output can be obtained by optimizing the capacitance. Figure 8 shows the sensor current of the sensor of the second embodiment (5V applied).
is measured in bright light (10 (lQx'': 550 nm) and in dark. From this figure, it can be seen that by creating a capacitance with a transparent insulating film, there is no increase in dark current and a high photocurrent/dark In these examples, a hydrogenated amorphous silicon film is used as the semiconductor thin film of the photoelectric conversion film 14, but the hydrogenated amorphous silicon film is a single layer or a p-
i-junction. It may be a pin junction. Furthermore, it contains oxygen as a peterojunction. If the structure has two or more layers of a hydrogenated amorphous silicon film and a hydrogenated amorphous silicon film, a high photocurrent/dark current ratio can be obtained, and better sensor characteristics can be obtained.

Moreover, in the present invention, 13, 16. The transparent insulating layer No. 22 is required to have high resistance and high voltage resistance as film quality, but the inventors used SiH 4 gas, CO as a film forming method.
Resistivity 101s~10"Q m, breakdown voltage 8~10Mv/
A high-quality SiOxNy film with a thickness of 1.5 cm was obtained. By using this, we were able to form a capacitor with high insulation properties. In the present invention, the semiconductor thin film of the photoelectric conversion film may be integral or may be divided into bits.

Furthermore, the lower and upper electrodes may be replaced, and the present invention is not limited to the above embodiment, and various changes and improvements may be made to other contact type image sensors without departing from the gist of the present invention. Of course, the following is possible.

〔effect〕

According to the present invention as described above, the sensor part can be integrated by forming the semiconductor thin film of the photoelectric conversion film and the capacitor part by forming the transparent insulator on the extended surface of the lower electrode. Therefore, by forming such a capacitance, a high signal output can be obtained in the storage reading method, and the influence of the line capacitance of the drive wiring can be reduced, the sharpness and reproducibility of the read image can be improved, and high fidelity can be obtained. This has the effect of providing a close-contact image sensor that can read images.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view showing a first embodiment of a contact type image sensor according to the present invention. FIG. 2 is an explanatory view showing a plane (a) and a cross section (b) of a second embodiment of a contact type image sensor according to the present invention, respectively. Figure 3 is a cross-sectional explanatory diagram showing an example of a conventional contact type image sensor. FIG. 4 is an explanatory cross-sectional view of a conventional contact type image sensor in which a capacitance is formed using the same material. FIG. 5 is an output exposure amount characteristic diagram in a second embodiment of the present invention. FIG. 6(a) is a plan view showing the main parts of the second embodiment, and FIG. 6(b) is an equivalent circuit diagram of the second embodiment. FIG. 7 is a diagram showing the relationship between capacity and output in the second embodiment of the present invention. FIG. 8 is a diagram showing the relationship between capacitance, photocurrent, and dark current in the second embodiment of the present invention. 1... Glass substrate 2... Lower electrode 3...
Semiconductor film 4 for photoelectric conversion... Upper transparent electrode 11... Glass substrate 12... Lower electrode 13,
16.22...Transparent insulating layer 13a, 16a, 21a - opening l4...
・Photoelectric conversion film 15... Upper transparent electrode l7...
Upper electrode 21... Light shielding layer 23... Protection layer

Claims (1)

[Claims] 1. In a contact image sensor that has a charge storage type sandwich structure in which a semiconductor thin film is sandwiched between a lower electrode and an upper transparent electrode on a transparent insulating substrate, a transparent insulating film is provided on the extended surface of the lower electrode, and the transparent insulating film is sandwiched between a lower electrode and an upper transparent electrode. A contact image sensor characterized by having an upper electrode connected to an upper transparent electrode provided on a film.