JPH056749A - Image pickup device - Google Patents

Abstract

PURPOSE:To allow the miniaturization and low voltage operation of a device by arranging tunnel discharge type cold cathodes emitting electron beams on the reverse side of a photoconductive film. CONSTITUTION:A tunnel cathode is formed of a n-type Si base 4, an insulating film consisting of Al2O3 or the like formed thereon, and a band metal film 6 consisting of Al or the like laminated thereon nearly orthogonally to a transparent electrode 1. This cathode is laminated between a photoconductive film 2 and the film 6 through a layer-to-layer insulating film 9 to form an image pick up device. Scanning pulses are selectively generated by a horizontal scanning circuit connected to the electrode 1 and a vertical scanning circuit connected to the film 6, an electron beam is emitted from a tunnel cathode part 3 provided in their cross point, and the charge image accumulated in the film 2 can be taken out as an electric signal. Since no electron gun part is provided, the device can be miniaturized, and the electron beam can be released at low voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device for converting two-dimensional image information into a time-series electric signal, and in particular, uses a tunnel emission type cold cathode (hereinafter referred to as a tunnel cathode) for emission. The present invention relates to a new imaging device.

[0002]

2. Description of the Related Art Hitherto, an imaging tube or a solid-state imaging device has been used as an imaging device for converting a visible light image into an electric signal. Among them, the image pickup tube has been historically developed from an older age than the solid-state image pickup element, has undergone many improvements for a long time, and is now mainly used as a high image quality and highly reliable broadcast camera. ..

However, since such an image pickup tube is provided with an electron gun section for performing operations such as focusing and deflecting of an electron beam, it is structurally difficult to reduce the size and weight. Therefore, a solid-state image sensor has become the mainstream as an image pickup device used for applications requiring miniaturization and weight reduction.

On the other hand, a field emission type micro cold cathode is used as an emission source replacing the conventional electron gun section,
Research and development of a microchip type image pickup tube, which is comparable to a solid-state image pickup element in which each pixel is arranged, is underway. The minute cold cathode is formed as a conical protrusion (cathode) made of molybdenum or the like having a diameter of 1.0 μm or less on a substrate by, for example, a semiconductor manufacturing process, and on an insulating layer formed so as to surround the periphery of the protrusion. An electron beam is extracted from the tip of the protrusion by the gate electrode provided on the.

In the above-mentioned micro cold cathode, in order to emit an electron beam from the tip of the protrusion, it is necessary to apply a negative electric field of a certain value or more between the gate electrode and the protrusion. However, the applied voltage required to extract the electron beam is sensitive to the shape of the protrusion and the distance between the protrusion and the gate electrode. Therefore, when the current semiconductor manufacturing process is used, a very high voltage of several 100 V is required. Become. Also,
Adsorption of the residual gas on the electron emission portion (projection surface) changes the emission current and makes the electron beam unstable. Moreover,
Since the production of the above-mentioned micro cold cathode requires high process technology and high vacuum technology, it is not easy to produce, and there are problems in terms of cost and reliability.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and an object thereof is to provide a compact and highly reliable image pickup device capable of low voltage operation.

[0007]

In order to achieve the above object, an image pickup device according to the present invention is provided with a tunnel emission type cold cathode for irradiating the photoconductive film with an electron beam on the back side of the photoconductive film. It is characterized by being arranged.

[0008]

In the present invention, the tunnel cathode utilizing the tunnel phenomenon is used to take out the charge image converted by the photoconductive film as a time series electric signal. The principle of electron beam emission from the tunnel cathode will be briefly described below. As shown in FIG. 4, the tunnel cathode comprises a pair of metal films (semiconductors) 52 and 53 and a thin insulator film 51 having a thickness of 100 angstroms or less. It is a so-called three-layer structure sandwiched by 52 and 53. The one-dimensional band structure of this tunnel cathode is schematically shown in FIG. 5, and the insulator film 51 is expressed as a barrier against the electrons e in the metal films 52 and 53. When the barrier is thin, that is, the insulator film 51
Is thin, electrons e tunnel through the metal film 52 to the metal film 53 (or the metal film 53 to the metal film 52) with a certain finite tunnel probability. For example, as shown in FIG. 6, in the metal films 52 and 53 having work functions ψ ₁ and ψ ₂ , when a bias is applied between them, the metal film 5
Among the electrons e transmitted from 2 to the metal film 53, those having energy equal to or higher than the work function ψ ₂ of the metal film 53 are emitted into the vacuum. To briefly explain this, assuming that most of the transmitted electrons e are at the Fermi level of the metal film 52, electron emission into a vacuum can be obtained by applying a bias larger than the work function ψ ₂ of the metal film 53. .. This is the principle of electron emission of the tunnel cathode, and the applied voltage for emitting the electron e at this time is about several V because the work functions ψ ₁ , ψ _{2 of the} metal films 52, 53 are about several eV. A low voltage is enough.

In forming the above-mentioned tunnel cathode, an A is simply formed on a Si substrate by the MBE (Molecular Beam Epitaxy) method used in the semiconductor manufacturing process.
It is possible to deposit an insulator film made of l ₂ O ₃ and does not require advanced process technology or high vacuum technology as compared with the case of forming a conventional micro cold cathode. Since the tunnel cathode thus formed is a planar cathode, it has a high surface average emission electron density, and also has a small effect of adsorption and desorption of residual gas on the cathode operation, which can stabilize the electron beam. And so on.

Therefore, when electron beams are sequentially irradiated from the tunnel cathodes arranged on the back surface side of the photoconductive film, the charge image converted by the photoconductive film is taken out as a time series electric signal by the electron beam. At this time, the applied voltage required for emitting the electron beam is extremely low as compared with the voltage required for emitting the electron beam by the micro cold cathode, and low voltage operation is possible. Further, since the tunnel cathode has a simple structure and does not require a high-level manufacturing process technology, it is easy to manufacture and is advantageous in terms of cost.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The image pickup apparatus of this embodiment is shown in FIG.
As shown in FIG. 3, a photoelectric conversion part including the transparent electrode 1 and the photoconductive film 2, and a tunnel for irradiating with an electron beam for extracting the electric charge converted from an optical image into a charge image by the photoelectric conversion part as a time-series electric signal. And a field emission cathode part having a cathode part 3.

The photoelectric conversion section serves to convert an optical image into a charge image and temporarily store the charge image, and is mainly composed of a transparent electrode 1 and a photoconductive film 2. The transparent electrode 1 is made of a film called a Nesa film made of, for example, SnO _2, and has a plurality of strip-shaped electrodes on one main surface of a face plate (not shown) made of glass that serves as a substrate of the photoelectric conversion unit. Are arranged in parallel with each other, and form a matrix structure with one electrode 6 of a tunnel cathode described later, which is arranged substantially orthogonal thereto. Therefore, the intersection of this electrode 6 and the transparent electrode 1 becomes a pixel.

On the other hand, the photoconductive film 2 is for converting an optical image which is transmitted through the face plate and is incident thereon into a charge image, for example, Sb ₂ S ₃ , PbO, CdSe, S.
It is formed of a glass semiconductor film or the like containing e, As, and Te as main materials, and is formed on the transparent electrode 1. Any known material conventionally used as an image pickup tube can be applied to the transparent electrode 1 and the photoconductive film 2, and the material is not particularly limited. Further, similarly to the configuration of the photoelectric conversion unit, any conventionally known configuration can be applied.

The field emission cathode portion corresponds to an electron gun portion for taking out the charge image stored in the photoconductive film 2 as a time series electric signal, and is composed of a tunnel cathode utilizing a tunnel phenomenon. .. The tunnel cathode is provided on the back surface side of the photoconductive film 2 opposite to the surface on which the transparent electrode 1 is provided, and has a structure as shown in FIG. 2, for example. That is, the tunnel cathode is the n-type Si substrate 4
And a thin film of Al ₂ O formed on the Si substrate 4.
_It is composed of an insulator film 5 made of ₃ or the like, and a strip-shaped metal film 6 made of Al or the like, which is laminated on the insulator film 5 and provided substantially orthogonal to the transparent electrode 1.

A portion where the Si substrate 4, the insulator film 5 and the metal film 6 are laminated is a tunnel cathode portion 3 for emitting an electron beam, and several to several tens of these tunnel cathode portions 3 are used. It constitutes one pixel. And
The pixel composed of the plurality of tunnel cathode portions 3 is
A matrix is arranged corresponding to the intersections of the transparent electrode 1 and the metal film 6, respectively. Each of the tunnel cathode portions 3 is divided by an insulating film 7 made of thick SiO ₂ formed on the Si substrate 4, and its electron emitting portion is formed in a substantially circular shape.

Further, in this tunnel cathode, it is important how to transmit electrons with a high tunnel probability.
Insulator film 5 so that ideal tunnel transmission can be obtained
The film thickness of is determined. For example, the film thickness of the insulator film 5 is set to 100 angstroms or less. Besides this,
For the metal film 6, it is important to select and use a material with less scattering.

In the tunnel cathode thus constructed, AuSb formed on the lower surface of the Si substrate 4 is used.
The metal thin film 8 made of metal acts as one electrode, the metal film 6 sandwiched across the insulator film 5 functions as the other electrode, and a voltage higher than the work function of the metal film 6 is applied between these electrodes. As a result, the photoconductive film 2 is formed from the tunnel cathode part 3 above.
Electrons are emitted toward.

The field emission cathode portion formed of the tunnel cathode and the photoelectric conversion portion formed as described above are used as the photoconductive film 2.
The imaging device is configured by laminating the metal film 6 and the metal film 6 with the interlayer insulating film 9 interposed therebetween. And, the above-mentioned imaging device,
As shown in FIG. 3, a scanning cathode is selectively generated by a horizontal scanning circuit 10 connected to the transparent electrode 1 and a vertical scanning circuit 11 connected to the metal film 6, and a tunnel cathode arranged at the intersection thereof. An electron beam is emitted from the portion 3 to extract the charge image stored in the photoconductive film 2 as an electric signal. Therefore, if these are sequentially repeated for each pixel, the charge image stored in the photoconductive film 2 is taken out as a time series electric signal by the electron beam emitted from the tunnel cathode portion 3.

In the above-mentioned image pickup device, a MIS (metal-insulator-se) is used as a tunnel cathode.
Although a tunnel cathode having a microstructure is used, a MIM (metal-insulator-met) is used.
The same action and effect can be obtained even with a tunnel cathode having an al) structure.

[0020]

As is apparent from the above description, according to the present invention, a time series electric signal is generated by a tunnel cathode having a laminated structure of thin films formed by a semiconductor manufacturing process on a charge image stored in a photoconductive film. Therefore, it is possible to provide a small-sized image pickup device of microchip size without using an electron gun section provided with a converging coil and a deflection coil for scanning an electron beam as in the conventional image pickup tube. be able to. Further, in the present invention, since a low voltage of about several V is required to emit the electron beam, it is not necessary to apply a high voltage unlike the micro cold cathode,
It can be operated at low voltage. Further, in the present invention, since the fabrication of the tunnel cathode does not require any advanced process technology or high vacuum technology, it is very advantageous in terms of manufacturing and cost, and it is expected to provide an inexpensive imaging device.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an image pickup apparatus to which the present invention is applied.

FIG. 2 is an enlarged perspective view of an essential part showing an enlarged field emission cathode part.

FIG. 3 is a schematic configuration diagram of an image pickup apparatus to which the present invention has been applied.

FIG. 4 is a schematic diagram showing a structure of a tunnel cathode.

FIG. 5 is a schematic diagram showing a one-dimensional band structure of a tunnel cathode.

FIG. 6 is a schematic diagram for explaining the operation principle of the tunnel cathode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent electrode 2 ... Photoconductive film 3 ... Tunnel cathode part 4 ... Si substrate 5 ... Insulator film 6 ... Metal thin film

[Procedure amendment]

[Submission date] August 12, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

The Si substrate 4, the insulator film 5, the metal film 6
The layered portion is formed as a tunnel cathode portion 3 that emits an electron beam, and each tunnel cathode portion 3 constitutes one pixel. Each pixel is arranged in a matrix corresponding to each intersection of the transparent electrode 1 and the metal film 6. Each of the tunnel cathode portions 3 has a thick Si film formed on the Si substrate 4.
The electron emission portion is divided by the insulating film 7 made of O _{2 and} has a substantially circular shape.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Claims (1)

Claim: What is claimed is: 1. An imaging device comprising: a tunnel emission type cold cathode for irradiating an electron beam onto a back surface of a photoconductive film.