JPS5968152A - Image tube - Google Patents

Abstract

PURPOSE:To effectively inhibit X-rays which are generated at a mesh electrode from penetrating an photoelectrically-conductive part, and prevent the photoelectric conversion of an image surface and the change of a ballast resistance characteristic, by installing the photoelectrically-conductive face provided with a soft X-ray inhibiting layer made of porous Ba compound layer on the surface of electron beam incidence side. CONSTITUTION:To a camera tube, a porous Ba compound is provided as a low beam landing layer which has low-transmissivity for ultra-soft X-rays generated at about 1,500V. The beam-landing layer is desired to satisfy those conditions that it is porous, said layer itself has electrical conductivity so that electrons do not penetrate up to a photoelectrically-conductive part, said layer has small secondary electron emissivity, further said layer itself does not have photoelectrical conductivity and has high electrical resistance to serve as an image-pickup screen or the like. Ba oxides, Ba sulfides, or the like used for this porous Ba compound satisfy these conditions. In this case, the thickness of this porous Ba compound is preferred to be formed in about 300-8,000Angstrom , more in general, in about 800-1,500Angstrom . BaO film can be formed by performing this vapor-deposition of the Ba compound in the atmosphere of carbon dioxide gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a photoconductive type image pickup tube and a method for manufacturing the same.

[Prior art]

Many of this type of imaging tubes are equipped with a mesh electrode on the cathode side facing the imaging surface. A part of the electron beam heading from the cathode toward the imaging surface and electron beams reflected without landing on the imaging surface impinge on this mesh electrode, and as a result,
Although it depends on the voltage applied to the electrode, X@ is generated. In particular, in order to obtain high resolution, the voltage applied to the mesh electrode was increased to 1000
This phenomenon becomes remarkable when the voltage is increased to about 1600V.

Of these X-rays, especially those generated by electron beams reflected on the imaging surface, the imaging surface may be damaged by radiation because there is no absorption layer between the two. This often results in changes in dark current and photoconductive properties. This tendency is particularly strong in blocking type imaging surfaces containing St as a main component.

Therefore, a layer (beam landing layer) consisting of a structure of a material with low electron reflectance that is not directly related to photoconductive development and does not hinder electron landing is formed on the electron beam incident side surface of the imaging surface. ing. For example, the most widely used materials include sb and s3, which are formed in a low vacuum atmosphere or porous.

However, since this 5bts3 does not have a sufficiently high X-ray blocking rate, a considerable amount of X-rays reach the internal photoconductive part without being blocked.

[Purpose of the invention]

The present invention was made in view of these circumstances, and its purpose is to change the photoelectric conversion and dark resistance characteristics by allowing X-rays generated by the mesh electrode to enter the photoconductive part forming the imaging surface. It is an object of the present invention to provide an image pickup tube that can effectively prevent such problems, and to provide a method of manufacturing an image pickup tube that can easily manufacture such an image pickup tube.

[Summary of the invention]

In order to achieve such an object, the present invention provides an image pickup tube using a photoconductive surface provided with a soft X-ray blocking layer made of a porous Ba compound layer on the electron beam incident side surface, and an image pickup tube using such a photoconductive surface. As a method for manufacturing an image pickup tube, a porous Ba compound layer is formed on a photoconductive film by decomposition-fractional vapor deposition in a gas atmosphere using BaA74 as an evaporation source.

In other words, the present invention provides super soft X generated at about 1500V.
Porous B as a beam landing layer with low transmittance
It is characterized by providing a compound layer. There are other materials that achieve the same purpose, such as pbo and pbs, but these are extremely unstable in air, making them difficult to handle and having low productivity. Similarly, metal Ba is also soft
Although the line absorption effect is strong, it is unstable in the air and is practically B.
It is difficult to use it as is.

Generally, the beam landing layer as described above is required to satisfy various conditions. That is, first of all, it must be porous. This is extremely important because dense and flat surfaces have a high electron beam reflectance. In addition, it must have conductivity itself to prevent electrons from penetrating into the photoconductive part, and of course have a low secondary electron emissivity, and must not have photoconductivity itself. It is desirable that it be sufficiently high for surface use. Oxides, sulfides, and the like as porous Ba compounds satisfy these conditions and are capable of forming a desirable Beam Lande 477 layer. In addition, in this case, the porous Ba compound layer has a power of about 300 to 8000 A, and generally 8
It may be formed to have a thickness of about 00 to 1500A.

[Embodiments of the invention]

The reasons for limiting various conditions when forming such a porous Ba compound layer on a photoconductive surface will be explained below using Examples.

First, it is very common to use vacuum evaporation as a method for forming such thin films, but in this case BaO, H
High resistance B such as as, BaCO3 and mixtures thereof
Using these compounds themselves as evaporation sources to form a compound film is difficult because they have a high melting point, such as BaO, and are difficult to evaporate, and sulfides, carbonates, etc. are decomposed by vacuum heating. This makes film formation difficult. Further, metal B& easily evaporates by itself, but as mentioned earlier, it is unstable in air and turns into BaO when exposed to oxygen during handling, resulting in the same problem as mentioned above. On the other hand, BaAl4 is commonly used as a getter material and is extremely stable in air. Moreover, when this is used as an evaporation source, Ba is decomposed and evaporated first, and then Al is evaporated, so this difference can be used to decompose and fractionally evaporate only Ba.

Therefore, by performing this vapor deposition in an oxygen gas atmosphere, a BaO film can be formed. In this case, the appropriate pressure of the oxygen gas atmosphere is about 5×1O to I×10 torr.

On the other hand, the above vapor deposition is performed in an inert gas such as argon gas, and after forming a Ba film, it is oxidized and BaO
A method of forming a film may also be used. In this case, it is of course possible to oxidize the Ba film by introducing oxygen into the deposition apparatus after forming the Ba film by vapor deposition. After forming one film, it may be simply left in the air.

In addition to oxygen or air, IItS, SO! .

By using a gas such as CO, or a mixture thereof, or a diluent gas thereof, I) Not only BaO but also BaS.

A porous membrane can be formed from a B& compound such as B a S OB , B a COB or a double salt thereof. When forming a porous membrane made of the above-mentioned double salt, the component ratio can be changed by changing the concentration and speed of each gas.

Since the Ba compound film becomes sufficiently porous through the reaction with such a gas, it is possible to easily form a porous Ba compound film without using a porous vapor deposition method in a low vacuum, which is difficult to control the film thickness. Obtainable.

Incidentally, sputtering is also widely used as a method for forming BaO thin films, but in this case, the BaO film formed is dense and has a high electron reflectance, so it is not suitable.

Note that B2O has a slightly higher resistance than sb, s5, etc., which are conventionally used for beam landing layers.

Therefore, it is advantageous to use these 5b2S, 1, 5b18+4 and other substances as resistance reducing additives.

〔Effect of the invention〕

As explained above, according to the present invention, by using a photoconductive surface having a soft X-ray blocking layer made of a porous Ba compound layer on the surface on the electron beam incident side, Entry into the photoconductive section can be effectively prevented, and changes in photoelectric conversion and dark resistance characteristics of the imaging surface can be prevented.

However, such a porous Ba compound layer can be easily formed by decomposition-fractional vapor deposition in a gas atmosphere using BaAl4 as an evaporation source.

Claims (1)

[Scope of Claims] 1. In an image pickup tube equipped with an imaging surface made of a photoconductive surface and a mesh electrode disposed on the electron beam incidence side opposite to the imaging surface, the electron beam incidence side is provided as the photoconductive surface. Porous surface B
1. An image pickup tube characterized in that a photoconductive surface is provided with a soft X-ray blocking layer made of a compound. 2. A method for manufacturing an image pickup tube, which includes the step of forming a porous layer by treating BaA4 as an evaporation source in an inert gas atmosphere in an atmosphere containing H, O, So, or a mixture thereof.