JPH0947429A - Electronic endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the fine irregularities, status change or the like of the surface of an object in sharp contract under the application of simple constitution by using an image pickup device having sensitivity to an ultraviolet ray as an image pickup device for converting the optical image of the object to an electric signal. SOLUTION: This endoscope has an ultraviolet source 101 to emit ultraviolet rays, and an image pickup element 102 having a photoconductor mainly composed of amorphous selenium. In this case, the image pickup element 102 uses a photoconductive film stacked type solid image pickup element with photoconductive thin films stacked on a scanning circuit. Also, each of the picture elements generates electrons with holes in a photoconductive film 204, due to a ultraviolet rays 202 transmitted through a transparent electrode 201, and the holes travel to a picture element electrode 206 through the photoconductive film, due to electric field applied across the transparent electrode 201 and the picture element electrode 206 for accumulation. Each picture element is provided with a MOS switch formed out of a source 207, a drain 208 and a gate 209, and the MOS switch is turned on and off, according to the prescribed timing, thereby sequentially sending accumulated signal charges to an output line 210.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic endoscope for irradiating a subject with ultraviolet light and detecting an image of the subject as an electric signal, and particularly to easily identify a fine structure or an altered portion of the subject. The present invention relates to a possible electronic endoscope.

[0002]

2. Description of the Related Art In an endoscope which is inserted into a human body, a machine or the like to observe the inside thereof, the light from an external light source is introduced by an optical fiber to illuminate the object, and the optics of the object imaged by a lens. It is well known to observe an image through a bundle of tens of thousands of optical fibers. In such an endoscope, usually one observer looks through the scope, and it is difficult for a large number of people to observe simultaneously.

On the other hand, a solid-state image pickup device such as CCD, which has been rapidly reduced in size and high definition in recent years, is provided at the tip of a scope to convert a subject image into a video signal and then externally output through a signal line. Many electronic endoscopes have been used for observing on TV monitors (eg Toshiba Review, No. 4).
Volume 3, Issue 7, pp 569-572). In such an electronic endoscope, white light emitted from a light source provided outside the subject is guided to the tip of the endoscope by a bundle of optical fibers to illuminate the subject, and a subject image formed through a lens is formed. It is general to photograph the image with a CCD type solid-state image pickup device using a photodiode of crystalline silicon for photoelectric conversion, and observe the obtained electric signal on a television monitor outside the subject through a signal line.

By the way, in the electronic endoscope as described above, it is general to mainly irradiate and detect light in the visible light range, but there is also one that irradiates the subject with ultraviolet light for observation. For example, JP-A-6-347707). In these devices, a subject is coated with a fluorescent substance, and the fluorescent substance is caused to emit light by irradiating with ultraviolet light, and the emission image is observed with an imaging device for visible light. Such an endoscope is used, for example, for observing a living tissue, an industrial inspection for observing a luminescent image of a fluorescent substance that has penetrated into a scratch or a crack of a subject.

[0005]

Among the electronic endoscopes described in the above-mentioned prior art, those that irradiate and detect light in the visible light region are often difficult to perform sufficient illumination. It was difficult to detect minute unevenness or changes in the surface state of the subject with high contrast.
In addition, in an electronic endoscope that irradiates ultraviolet light to observe a visible light image with a fluorescent substance, it is necessary to apply the fluorescent substance to the subject in advance, and a fluorescent agent, a coloring agent, and a cleaning agent are passed through a thin tube for introducing the endoscope. It is necessary to introduce and spray agents,
There is a problem that the device is complicated. Further, if the particle size or thickness of the phosphor is large, the resolution is deteriorated, and conversely if the particle size or thickness is small, the luminous efficiency is reduced, and it is difficult to observe the fine structure of the subject with high sensitivity. .

An object of the present invention is to solve the above problems and provide an electronic endoscope having a simple structure and capable of detecting minute unevenness of a subject and changes in the surface state with high contrast. is there.

[0007]

SUMMARY OF THE INVENTION The above-described object is to provide an electronic endoscope having at least a means for irradiating a subject with ultraviolet light and an image pickup device for converting an optical image of the subject into an electric signal. It is achieved by using an imaging device having sensitivity to.

Further, as an image pickup device having sensitivity to ultraviolet light, there is one having a photoconductive film mainly composed of amorphous selenium. Further, the avalanche multiplication of charges in the photoconductive film mainly composed of amorphous selenium can be utilized.

[0009]

[Function] As is clear from the fact that the technique of irradiating a subject with ultraviolet light and observing it with an image pickup device for ultraviolet light is used for ultraviolet microscopes, fingerprint detection, antiquity appraisal, etc. It is suitable for use in observing changes in tissue and tissue with high contrast. In the electronic endoscope according to the present invention,
Ultraviolet light is radiated to the subject from the tip of the scope, and it is observed directly with an imaging device that is sensitive to ultraviolet light, so there is no need to apply phosphor to the subject in advance, and for subjects where it is not possible to apply phosphor Can also be observed.

As the image pickup device used in the electronic endoscope of the present invention, a device having a photoconductive film mainly composed of amorphous selenium (a-Se) is suitable. Since a-Se is sensitive to visible light to ultraviolet light and has a high dark resistance and a uniform film can be formed relatively easily by a vapor deposition method, a high resolution can be obtained by using it as a photoconductive film. The most important feature of the electronic endoscope of the present invention is to directly observe an ultraviolet light image without passing through a phosphor, and to observe minute lesions and tissue changes in the body, or minute cracks inside the machine. In order to do so, it is important to be able to detect the ultraviolet light image with high resolution.

Further, in a-Se, when a strong electric field is applied in a structure in which charge injection from the outside is suppressed, a charge multiplication phenomenon due to impact ionization, that is, an avalanche phenomenon occurs. The avalanche phenomenon is found in various crystalline materials including crystalline silicon, and the avalanche phenomenon in a-Se is such that a large area uniform multiplication occurs, for example, the Television Society Technical Report, Vol. 15, No. .52, pp.
As described in 7-12, when applied to a storage-type image pickup device such as an image pickup tube, a noise reduction effect is obtained. Therefore, when applied to an electronic endoscope of the present invention that does not use a phosphor, a subject with high sensitivity can be obtained. The fine structure of can be observed.
In particular, ultraviolet light has a large absorption coefficient at a-Se, so a-
When incident on the Se film, it is absorbed in the vicinity of the interface on the incident side to generate electron-hole pairs. In a-Se, the collision ionization probability of holes is higher than that of electrons, so if the device is biased to operate in the direction in which the light incident side becomes positive, holes generated in the vicinity of the incident side are almost the same. Since it travels through the entire thickness, the multiplication effect is most efficiently obtained. Furthermore, in a-Se, the gemnate recombination phenomenon, in which electron-hole pairs generated by light of a relatively long wavelength from green to red are recombined by Coulomb's attractive force, is remarkable. Since the photon energy is large, this phenomenon hardly occurs, the generated electron-hole pairs are effectively separated, and high first-order quantum efficiency is obtained. That is, the use of a-Se or its avalanche phenomenon as an ultraviolet light imaging device is more advantageous than the use of ordinary visible light, and is suitable for the electronic endoscope of the present invention.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electronic endoscope according to the present invention will be described below with reference to the drawings. FIG. 1 is a basic configuration diagram of this embodiment. In FIG. 1, 101 is an ultraviolet light source that emits ultraviolet light, and 102 is an image sensor having a photoconductor mainly composed of amorphous selenium. Reference numeral 103 is a light guide, 104 is an image forming optical system, 105 is a signal line, 106 is a camera control unit (CCU), and 107 is a monitor.

As the ultraviolet light source 101, mercury xenon laser is used.
Pump and an ultraviolet filter were combined.
Alternatively, a lamp, a deuterium lamp, an ultraviolet laser, or the like may be used.
In addition, the light guide 102, the illumination optical system, and the imaging optical system
104 is quartz or LiF ₂, MgF₂UV transmittance of
Use a high-quality material. In FIG. 1, the subject is displayed on the monitor 107.
A system for directly observing images of CCU is shown.
Video signal output from 106 is converted to digital signal
Image processing such as pseudo-color display.
It can also be output to a linter or various storage devices.

Next, the structure of the image pickup device 102 used in this embodiment will be described with reference to FIG. In this embodiment, a photoconductive film laminated type solid-state imaging device in which a photoconductive thin film is laminated on a scanning circuit is used. FIG. 2 is a sectional view showing the basic structure of the one pixel portion. The ultraviolet light 202 transmitted through the transparent electrode 201 generates electron-hole pairs (not shown) in the photoconductive film 204, and the electric field applied between the transparent electrode 201 and the pixel electrode 206 causes holes to reach the pixel electrode. It travels in the photoconductive film and is accumulated. Each pixel has a source 207 and a drain 20.
8 and the gate 209 are provided with a MOS switch, and by turning on / off the switch at a predetermined timing, the accumulated signal charges are sequentially read out to the output line 210. In FIG. 2, 211 is a Si substrate, 2 is
12 and 213 are insulating layers. The photoconductive film 204 includes
1 μm thick amorphous Se formed by vacuum deposition method
(A-Se) was used. Further, between the transparent electrode 201 and the photoconductive film 204, the transparent electrode 201 and the photoconductive film 204 are provided.
10 nm thick CeO to prevent hole injection into the
_The hole injection element layer 203 composed of 2 is provided between the pixel electrode 206 and the photoconductive film 204 from the pixel electrode 206 to the photoconductive film 2.
To prevent the injection of electrons into 04.
_An electron injection blocking layer 205 made of ₂ Se ₃ was formed by vacuum vapor deposition.

In the image pickup device of this embodiment, the transparent electrode 201
Operates by applying a voltage to the pixel electrode 206 in a positive direction. At this time, when the applied voltage is about 90 V or higher, charge multiplication due to the avalanche phenomenon occurs in the a-Se film, and the sensitivity is increased about 10 times at the applied voltage of 140 V. The avalanche multiplication factor varies depending on the wavelength of incident light, but when used for ultraviolet light imaging, since the absorption coefficient in the a-Se film is large, all the holes are absorbed in the vicinity of the transparent electrode 201 side and the generated holes are generated. It runs toward 206 over the entire film thickness direction. Therefore, the multiplication effect can be effectively obtained with a-Se having a higher collision ionization probability of holes than that of electrons.
In addition, the excess noise generated by the avalanche phenomenon is also the smallest in the case where multiplication by almost only holes occurs in this way. Further, in a-Se, the charge generation efficiency (quantum efficiency) by light having a wavelength of about 400 nm or less is almost 1. For these reasons, the electronic endoscope of the present embodiment can photograph a fine structure of a subject with high contrast, high sensitivity, and high resolution.

As described above, the electronic endoscope having the structure in which the ultraviolet light from the outside is guided to the tip of the endoscope by the light guide and the ultraviolet light image of the subject is picked up by the a-Se film laminated type solid-state image pickup device is embodied. However, the ultraviolet light source does not necessarily have to be provided outside, and a small ultraviolet light source may be provided at the tip of the endoscope, for example. Also, as an imaging device for ultraviolet light,
It is not necessary to use the photoconductive film laminated type solid-state image pickup element, and for example, even if an image pickup tube using a-Se as a photoconductive film is provided outside and a subject image is guided to the outside by a light guide composed of a fiber bundle Good.

[0017]

As described above, according to the present invention, it is possible to obtain an electronic endoscope which has a simple structure and is capable of detecting minute unevenness of a subject and changes in the surface condition with high contrast.

[0018]

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an embodiment of an electronic endoscope according to the present invention.

FIG. 2 is a cross-sectional view showing the structure of one pixel portion of the image sensor used in one embodiment of the present invention.

[Explanation of Codes] 101 ... Ultraviolet light source, 102 ... Imaging device having sensitivity to ultraviolet light, 103 ... Light guide, 104 ... Imaging optical system, 105 ... Signal line, 106 ... Camera control unit ( CCU), 107 ... Monitor, 201 ... Transparent electrode, 202 ... UV light, 203 ... Hole injection blocking layer, 2
04 ... Photoconductive film, 205 ... Electron injection blocking layer, 206
...... Pixel electrode, 207 ...... Source, 208 ...... Drain, 209 ...... Gate, 210 ...... Output line, 211 ......
Si substrate, 212 ... Insulating layer, 213 ... Insulating layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Samejima 1-280, Higashi Koikeku, Kokubunji, Tokyo Metropolitan Research Laboratory, Hitachi, Ltd. (72) Inventor Tomoharu Kajiyama 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Center

Claims (3)

[Claims] 1. An electronic endoscope having at least a means for irradiating a subject with ultraviolet light and an imaging device for converting the subject optical image into an electric signal, wherein the imaging device is sensitive to ultraviolet light. An electronic endoscope characterized by being present. 2. The electronic endoscope according to claim 1, wherein the imaging device having sensitivity to ultraviolet light has a photoconductive film containing amorphous selenium as a main component. 3. The electronic endoscope according to claim 2, wherein the image pickup device having sensitivity to ultraviolet light utilizes avalanche multiplication of charges in the photoconductive film.