JPH045866A - Optoelectric transducer - Google Patents

Abstract

PURPOSE:To increase the sensibility of a light output while improving accuracy by forming ohmic connections between both a first conductor electrode formed onto a substrate and a thin-film composed of a semiconductor material and both a second conductor electrode and said thin-film respectively. CONSTITUTION:A conductor electrode 12 is formed onto a glass substrate 11 by using a metal having a small work function such as Ti in an optoelectric transducer 10, and an a-Si:H thin-film 13 is shaped onto the electrode 12 in thickness L of 1mum. A conductor electrode 14 is formed onto the film 13 by employing a metal equal to the electrode 12, and the electrodes 12 and 14 form ohmic connections with the film 13, thus changing the intensity of incident light into the alteration of the resistance value of the element 10. That is, photoconductive currents I are made to flow from the electrode 14 to the electrode 12 in the thickness direction in the film 13, which irradiated with light 15 and a resistance value of which is reduced. Since the space of the electrodes 12, 14 is brought to 1mum as the thickness of the film L, field strength between the electrodes is made larger than conventional devices by approximately tencuple, thus flowing large currents I. Accordingly, the sensibility of a light output is increased, and accuracy can be improved.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a photoelectric conversion device that converts light into an electrical signal.

(Prior Art) In facsimiles, which have become rapidly popular in recent years, a contact image sensor is used in which photoelectric conversion elements are arranged with the same width as the document and at a desired resolution in order to convert the image of the document into an electrical signal. It is used.

In order to transmit high-quality images, it is preferable that the light output sensitivities of the photoelectric conversion elements arranged as many as the resolution are the same.

In such contact type image sensors, photoconductive photoelectric conversion elements that utilize the photoconductive effect of semiconductors are widely used.

FIG. 4 is a diagram showing the structure of a conventional photoconductive type photoelectric conversion element.

As shown in the figure, the photoelectric conversion element 1 includes a thin film of a semiconductor material, for example, an a-3i:H thin film 3 formed on a substrate 2, and conductor electrodes 4. 5
It is formed by forming.

The conductor electrode 4.5 is formed by removing unnecessary portions of a metal such as Ti or AI deposited on the surface of the a-8i:H thin film 3 by photo-etching so as to form a desired pattern.

The light 6 irradiated on this photoelectric conversion element causes a photoconductive effect in the thin film 3 made of a semiconductor material, and as shown in FIG. 5, a photoconductive current I flows due to the voltage applied to the conductive electrode 4.5.

Incidentally, the light output sensitivity of a photoconductive type photoelectric conversion element is proportional to the amount of photoconductive current I flowing between the conductive electrodes 4.5.

Furthermore, since the semiconductor material used for the thin film 3 can be considered to be a resistor whose resistance value changes depending on light, the amount of photoconductive current I flowing between the conductive electrodes 4.5 is
It is proportional to the cross-sectional area through which the photoconductive current (1) flows between the conductor electrodes 4.5, and is inversely proportional to the spacing between the conductor electrodes 4.5.

Therefore, conventionally, in order to increase the optical output sensitivity, the conductor electrodes were formed in a comb-teeth shape as shown in FIG. 6 to increase the cross-sectional area of the photoconductive current flowing between the conductor electrodes 4.5. It was done.

On the other hand, efforts have been made to make the spacing between the conductor electrodes 4.5 as narrow as possible.

However, when trying to narrow the spacing between the conductor electrodes 4.5, the photo-etching method poses difficulties in the step of forming the battens, so the spacing can only be kept at around 10 μm at most, and the accuracy of the spacing is limited. The problem is that the light output sensitivity varies from element to element.

(Problems to be Solved by the Invention) As described above, in the photoconductive photoelectric conversion element of the conventional structure, two
Since the gap between the two conductor electrodes is formed using a photoetching method, it is not possible to increase the light output sensitivity due to the limitations of the accuracy of this method. There was a problem that the yield of the product was poor due to variations in the product quality.

The present invention has been made to solve these conventional problems, and provides a photoelectric conversion device with high light output sensitivity and high precision.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized in that a thin film made of a semiconductor material is formed covering a first conductive electrode provided on a substrate, and on the surface of this thin film,
a second conductor electrode is provided so as to sandwich the thin film between the first conductor electrode, and the first conductor electrode and the thin film;
The second conductive electrode and the thin film each form an ohmic connection.

(Function) In the present invention, since two conductor electrodes are provided to sandwich a thin film made of a semiconductor material, the thickness of the thin film becomes the interval between the conductor electrodes. The thickness of the thin film made of this semiconductor material is
For example, since it can be set to around 1 μm, the light output sensitivity can be increased and the accuracy is also good.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the structure of a photoelectric conversion element according to an embodiment of the present invention.

As shown in the figure, in this photoelectric conversion element 10, a metal with a small work function such as Ti is used on a glass substrate 11.
A conductor electrode 12 is formed by vapor deposition and photoetching. On this conductive electrode 12, a plasma vCVD method (Chemical Vapor Deposition) is applied.
The a-3i:H thin film 13 is formed to have a thickness of about 1 μm using a vapor phase growth method.

Furthermore, a conductor electrode 14 is formed on the a-3i:H thin film 13 using the same metal as the conductor electrode 12. Since the conductive electrode 14 itself does not transmit the light 15 irradiated to the photoelectric conversion element]0, the light 15 is not transmitted to the a-8i:H thin film 3.
A notch is provided in the conductor electrode 14 so that the light can be irradiated.

The conductor electrode 12.14 made of metal such as Ti is a-8
In order to form an ohmic connection with the i:H thin film]3, the photoelectric conversion element]0 forms a photoconductive type photoelectric conversion element.

That is, the intensity of the incident light is converted into a change in the resistance value of the photoelectric conversion element]0.

In the a-8i:H thin film 13 whose resistance value has decreased by being irradiated with the light 15, a photoconductive current I flows from the conductive electrode 14 to the conductive electrode 12 in the thickness direction, as shown in the cross-sectional view of FIG.

In this photoelectric conversion element 10, the distance between the conductive electrodes 12 and 14 could be set to 1 μm, which is the thickness of the thin film.
The electric field strength between the electrodes is approximately 10 times that of the conventional example, allowing a large photoconducting current I to flow and increasing the photosensitivity output.

In addition, in the above-mentioned embodiment, an example was explained in which the same kind of metal was used for the conductive electrodes 2 and 14, but the present invention is not limited to this, and the ohmic connection with the semiconductor material used for the thin film 13 was explained. Any conductive material that is possible may be used.

Furthermore, if a conductive material having light transparency is used for the conductive electrode 14 on the incident light side, it is not necessary to provide a notch in the conductive electrode 14 as shown in FIG.
The utilization efficiency of the light 15 irradiated to the area is also high.

Furthermore, the semiconductor material used in this example is aSi:H
Any other semiconductor may be used as long as it has a photoconductive effect, and the thin film structure may be formed not only in a single layer structure but also in a multilayer structure.

[Effects of the Invention] In the present invention, since the thickness of the thin film made of semiconductor material corresponds to the spacing between the conductor electrodes, it is possible to narrow the spacing between the conductor electrodes with high accuracy. good.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of an embodiment of the photoelectric conversion element of the present invention, FIG. 2 is a diagram showing the flow of photoconducting current in this photoelectric conversion element, and FIG. 3 shows the conductive electrodes made of a light-transmitting material. FIG. 4 is a perspective view showing the structure of a conventional photoelectric conversion element, FIG. 5 is a diagram showing the flow of photoconductive current in this photoelectric conversion element, and FIG. FIG. 2 is a diagram showing a configuration of a conductive electrode of a photoelectric conversion element in which the cross-sectional area through which a photoconductive current flows is increased. 10... Photoelectric conversion element, 11... Glass substrate, 12
．． 14...Conductor electrode, 13...a-5i:H thin film. Applicant Toshiba Corporation Patent Attorney Sasa Suyama - Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A thin film made of a semiconductor material is formed to cover a first conductive electrode provided on a substrate, and a second conductive electrode is formed on the surface of this thin film so as to sandwich the thin film with the first conductive electrode. A photoelectric conversion device characterized in that the first conductor electrode and the thin film, and the second conductor electrode and the thin film each form an ohmic connection.