JPH0622100B2 - Camera tube - Google Patents

Description

The present invention relates to a photoconductive type image pickup tube.

[Prior art]

Most of this kind of image pickup tube has a mesh electrode on the cathode side facing the image pickup surface. On this mesh electrode, a part of the electron beam from the cathode to the image pickup surface or the electron beam reflected without landing on the image pickup surface is projected, and as a result,
X-rays are generated depending on the voltage applied to the electrodes. Especially, in order to obtain high resolution, the applied voltage to the mesh electrode is set to 1000
This phenomenon is remarkable when the voltage is increased to about 1600V.

Among these X-rays, especially those generated by electron beams reflected on the imaging surface do not have an intermediate absorption layer, so the imaging surface is damaged by radiation and dark current and photoconductive characteristics change. It often happens. In particular, this tendency is large on the blocking type imaging surface containing Si as a main component.

Therefore, a layer (beam landing layer), which is not directly related to photoconductive development and has a low electron reflectance and does not interfere with electron landing, is formed on the surface of the imaging surface on the electron beam incident side (beam landing layer). ing. For example, the most widely used one is Sb ₂ S ₃ which is slightly porous in a low vacuum atmosphere.

However, since the blocking rate of X-rays of Sb ₂ S ₃ is not sufficiently high, a considerable amount of X-rays reach the internal photoconductive portion without being blocked.

[Object of the Invention]

The present invention has been made in view of such a situation, and an object thereof is that X-rays generated at a mesh electrode enter a photoconductive portion forming an imaging surface to change photoelectric conversion and dark resistance characteristics. The object is to provide an image pickup tube capable of effectively preventing the above problem.

[Outline of Invention]

In order to achieve such an object, the present invention is particularly directed to Si.
Of a photoconductive surface having a photoconductive surface containing as a main component, 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 the manufacture of such a pickup tube. As a method, a porous Ba compound layer is formed on the photoconductive film by decomposing fractional vapor deposition in a gas atmosphere using BaAl ₄ as an evaporation source.

That is, the present invention is a super soft X generated at about 1500V.
Porous Ba as a beam-landing layer with low line transmittance
A feature is that a compound layer is provided. Other materials that achieve the same purpose include, for example, PbO and PbS, which are extremely unstable in air and are difficult to handle, resulting in low productivity. Similarly, metallic Ba has a large soft X-ray absorption effect, but it is unstable in air and it is practically difficult to use it as it is.

Generally, the beam landing layer as described above is required to satisfy various conditions. That is, it must first be porous. This is extremely important because a dense and flat surface has a high electron beam reflectance. In addition, it has conductivity itself so that electrons do not penetrate into the photoconductive portion, and naturally has a small secondary electron emissivity, and further has no photoconductivity itself. It is desired that it is sufficiently high for surface use. Oxides, sulfides and the like as the porous Ba compound satisfy these conditions and can form a desired beam landing layer. Further, in this case, the porous Ba compound layer may be formed to have a thickness of about 300 to 8000Å, more generally about 800 to 1500Å.

Example of Invention

The reasons for limiting various conditions when forming such a porous Ba compound layer on the photoconductive surface will be described below with reference to examples.

First, it is very common to use a vacuum deposition method as a method for forming such a thin film. In this case, BaO, BaS, Ba
The use of these compounds themselves as evaporation sources to form high resistance Ba compound films such as CO ₃ and mixtures thereof has a high melting point such as BaO and is difficult to vapor-deposit porous materials, sulfides and hydrochloric acid. It is difficult to form a film because salts and the like are decomposed by heating under vacuum and are easily exhausted. Further, metal Ba itself easily evaporates, but as described above, it is unstable in air and contacts oxygen during handling to be converted into BaO, which causes the same problem as described above. On the other hand, BaAl ₄ is usually used as a getter material and is extremely stable in air. Moreover, when using this as the evaporation source, first, Ba
Is decomposed and evaporated, and then Al is evaporated. Therefore, by utilizing this difference, only Ba can be decomposed and fractionally evaporated.

Therefore, a BaO film can be formed by performing this vapor deposition in an oxygen gas atmosphere. In this case, it is appropriate that the atmospheric pressure of the oxygen gas atmosphere is approximately 5 × 10 ⁻⁴ to 1 × 10 ⁻¹ torr.

On the other hand, the vapor deposition may be performed in an inert gas such as argon gas to form a Ba film and then oxidize it to form a BaO film. In this case, it is needless to say that after the Ba film is formed by vapor deposition, oxygen may be introduced into the vapor deposition apparatus to be oxidized, but it is only necessary to leave it in the air after the Ba film is formed.

Further, not limited to oxygen or air, H ₂ S, a gas or a mixture of such SO _2, CO _2, or BaS not limited to BaO by using the dilution thereof gases, BaSO _3, BaCO _3, or their double salt It is possible to form a porous film composed of a Ba compound. When forming a porous membrane composed of the above double salt, the component ratio can be changed by changing the concentration and speed of each gas.

Since the Ba compound film is made sufficiently porous by the reaction with such a gas body, it is not always necessary to use the porous vapor deposition method in a low vacuum where the film thickness control is difficult, and the Ba compound film can be easily porous. A membrane can be obtained.

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

Note that BaO has a slightly higher resistance than Sb ₂ S ₃ or the like which has been conventionally used for the beam landing layer. Therefore, it is useful to use these Sb ₂ S ₃ , Sb ₂ Se _{3 and} other substances together as a resistance reducing additive.

〔The invention's effect〕

As described above, according to the present invention, by using the highly conductive surface provided with the soft X-ray blocking layer made of the porous Ba compound layer on the electron beam incident side surface, X generated at the mesh electrode is used.
It is possible to effectively prevent the line from entering the photoconductive portion, and prevent photoelectric conversion and dark resistance characteristic change of the imaging surface. In addition, by performing decomposition fraction deposition in a gas atmosphere using BaAl ₄ as an evaporation source, such porous Ba
The compound layer can be easily formed.

Claims (1)

[Claims] 1. An image pickup tube comprising an image pickup surface composed of a photoconductive surface containing Si as a main component, and a mesh electrode arranged on the electron beam incident side facing the image pickup surface. An image pickup tube having a soft X-ray blocking layer made of a porous Ba compound on the incident side surface.