JPS5855614B2 - Chikusekisatsuzokanno Kodeninkiyokuno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a storage image tube having a photocathode, a storage target mesh and an electron gun, and more particularly to a method for manufacturing a photocathode.

A storage image pickup tube with a storage target mesh is the first in the past.
The structure shown in Figure a has been made.

This has a structure in which the distance between the photocathode 3 and the storage target mesh 4 is 20 to 50 mm apart, and the photoelectron image is formed on the storage target mesh 4 by an electrostatic lens or a magnetic field lens. It has an orthicon type.

Look at Figure 1. 1 is a glass envelope, 2 (Li
, face plate, 3(d) photocathode, 4 indicates a storage target mesh, 5 indicates an electron gun, 6 indicates a base metal evaporation source of the photocathode, and 7 indicates an alkali metal vapor generation source.

As shown in FIG. 1, the present invention utilizes a so-called proxy focus type image pickup tube structure in which the distance between the photocathode 3 and the storage target 4 is set close to 0.5 to 5 cm. The present invention relates to a method of forming a photocathode 3 in a storage image pickup tube.

In close focusing type image pickup tube storage, the photoelectrons emitted from the photocathode 3 collide with the accumulation target mesh 4 before they become diffused (blurred), thereby accumulating a charge pattern corresponding to the optical image on the accumulation target mesh 4. It is something that makes you

Such a close focusing type image pickup tube has a shorter tube length than the image orthicon type shown in FIG. 1A, and can omit a focusing coil or an electrostatic lens system in the image section.

Therefore, the number of electrodes in the storage image pickup tube can be reduced, and the image pickup apparatus has advantages such as being simpler and lighter in weight.

A commonly used photocathode 3 is prepared by vapor-depositing a base metal such as antimony SB, silver Ag, etc. in a vacuum, and then applying a vapor of an alkali metal such as cesium Cs, sodium Na, potassium Ka, etc. to the base metal.

In order to produce a photocathode 3 with high sensitivity, all of these processes must be performed in a high vacuum. are installed in advance.

For this reason, it is undesirable for there to be anything that impedes evaporation between the face plate 2 on which the photocathode 3 is formed and the base metal and the metal evaporation source 6, so usually an accumulation target is used as shown in No. 11a. A base metal evaporation source 6 is installed on the face plate 2 side of the mesh 4.

However, alkali metals have high vapor pressure at temperatures of 100 to 250°C, which is the normal steam generation condition, and fill the glass envelope 1 in a gaseous state and act on the base metal, so an alkali metal vapor generation source 7 is installed. The location where the base metal generation source 6 is used is not limited.

However, such a method cannot be used for close-focus storage image pickup tubes.

That is, in the close-focus storage image pickup tube, the distance between the storage target and the face plate is small, and it is not possible to arrange a base metal evaporation source or an alkali metal vapor generation source therebetween.

For this reason, as disclosed in Japanese Patent Publication No. 42-19009, the face plate part, the electron gun, and the storage target mesh part were installed separately in a vacuum belljar, and after forming a photocathode on the face plate part, the electron gun was installed. A method of indium-sealing the storage target mesh portion and the storage target mesh portion in the same vacuum bell jar has been considered.

However, this method requires extensive equipment.

Still another method is to deposit a base metal on the face plate in advance, incorporate it into a glass envelope, and then evacuate and apply alkali metal vapor.

However, in this method, since the base metal surface is exposed to air or other gas at least once, the surface undergoes oxidation or other changes, making it impossible to obtain sufficient photoelectric sensitivity.

In the method for producing a photocathode according to the present invention, unlike the conventional method, a base metal evaporation source 6 is installed on the opposite side of the accumulation target mesh 4 from the face plate 2 as shown in FIG. The method is characterized in that a base metal is vapor-deposited on the face plate 2 at a distance, and then alkali metal vapor is applied to the deposited base metal to form the photocathode 3.

In this case, the accumulation target mesh 4 becomes an obstacle to the base metal deposition, but by placing the base metal at a position that meets the conditions described below, it is possible to form a photocathode with sufficiently high sensitivity and a uniform sensitivity distribution. It is possible.

Although there are various targets for storage image pickup tubes, those used in the present invention have, for example, a mesh structure formed from a conductor and an insulator.

As shown in Figure 1, the conductor 4 faces the electron gun 5.
1 and an insulator 42 facing the face plate 2, respectively.

The conductor 41 usually has 1000 to 2000 mesh (
A copper mesh of approximately 1,000 to 2,000 pieces/inch) is used, and the insulator 42 is made of calcium fluoride (C).
aFt) or magnesium fluoride (MgF2), but they are not limited to these. Different materials, for example, nickel or stainless steel can be used as the conductor 41, and silicon oxide (StOz) or aluminum oxide (A1203) can be used as the insulator 42. ), heat-resistant insulating polymeric materials (for example, polyimide, polyamide, etc.), etc. can also be used.

Furthermore, the mesh itself does not necessarily have to be a conductor; the insulator 42 may be mesh-shaped, and the conductor 41 may be formed thereon by vacuum deposition or the like.

Particularly in this case, the conductor 41 may not be attached at the beginning, and a base metal layer, which is simultaneously deposited on the insulator mesh 42 during the formation of the photocathode, may be used as the conductor 41.

Furthermore, it goes without saying that the accumulation target mesh does not necessarily have to be a mesh, and may be in the form of a sash or the like.

A method for forming the photocathode 3 on the face plate 2 across the storage target mesh 4 in this way will be described below.

Of the base metal evaporated in vacuum, only the portion that passes through the opening of the target mesh 4 and adheres to the phase plate 2 can become the photocathode 3.

The base metal evaporation source 6 is usually located away from the longitudinal axis of the glass envelope 1 and close to the inner wall so as not to interfere with the electron beam scanning the target surface.

The apparent aperture ratio of the storage target mesh 4 seen from the base metal evaporation source 6 is maximum at the intersection of the perpendicular line drawn from the base metal evaporation source 6 to the storage target mesh 4 and the storage target mesh 4, The further away from this point, the smaller it becomes, and reaches the minimum at the end opposite to the central axis of the accumulation target mesh 4.

In other words, as shown in FIG. 2, the smaller the angle θ at which the accumulation target mesh 4 is viewed from the base metal evaporation source 6, the smaller the apparent aperture ratio.

This means that as θ becomes smaller, the amount of base metal deposited on the face plate 2 decreases, resulting in uneven sensitivity of the photocathode 3 that is finally formed.

Usually, two or four evaporation sources 6 are installed at symmetrical positions on a plane perpendicular to the axis of the glass envelope 1.

In the case of a normally used mesh with 1000 to 2000 meshes and a light transmittance of 40 to 60%, the effective end of the storage target mesh 4 on the opposite side to the central axis from these 601 evaporation sources is expected. Experiments have revealed that if the angle θ is greater than 45°, a photocathode 3 having a substantially uniform sensitivity distribution can be formed on the face plate 2 by combining two or more evaporation sources.

In other words, the base metal evaporation source 6 should be installed at a position that is twice (2rz) the distance r that it is away from the central axis of the glass envelope 1 or more away from the storage target mesh 4 on the electron gun 5 side. Bye.

Even if the deposition source 6 is placed closer to the storage target mesh 4 than this, it is of course possible to form the photocathode 3, but it becomes difficult to obtain a uniform sensitivity distribution.

On the other hand, the distance (t3) between the base metal evaporation source 6 and the target mesh should not be too large.

The reason for this is that when the face plate 2 is viewed from two base metal evaporation sources 6 located at symmetrical positions, if any one shaded part of the target mesh 4 overlaps with the other, the evaporated base metal This is because they become separated from each other like islands on the face plate, making it impossible to conduct electrically.

This state is schematically shown in FIG. 3a for each storage target mesh 4.

In FIG. 3a, the portion indicated by S is in the shadow of any of the base metal evaporation sources 6, 6', and no base metal is deposited.

On the other hand, if the base metal evaporation source 6°6' is installed at the position where S in FIG. 3a just disappears or at a position closer to the accumulation target mesh 4, as shown in FIG.
The deposited base metals are connected to each other to provide electrical continuity.

In the case of FIG. 3, the distance ts between the base metal evaporation sources 6, 6' and the accumulation target mesh 4 is the radius of one target mesh 4, and the distance between the target mesh 4 and the face plate 2. If t is t, then the following is obtained, and the base metal evaporation source 6 is located at a position closer to t3,
6' may be installed.

Target mesh 4 of 1000 to 2000 mesh, which is usually used, is 0.5 to 5
When installed at a distance of m, the above-mentioned t3 will be 500 mm or more. On the other hand, since the possible value of t3 with a normal image pickup tube is approximately 100 mm or less, this condition is almost always satisfied.

Photocathode surfaces produced by conventional methods are approximately flat.

On the other hand, the photocathode surface 3 manufactured by the method of the present invention has irregularities corresponding to the pitch of the storage target mesh 4, as shown in FIG.

Although the thickness of the photocathode surface 3 has a considerable effect on its sensitivity, the sensitivity of the photocathode 3 obtained by the method of the present invention was approximately the same as that obtained by the conventional method.

Although the reason for this is not clear, it is thought that the increase in the effective area of the photocathode surface 30 due to the unevenness compensates for the decrease in sensitivity due to the non-uniformity of the thickness.

When the photocathode 3 is produced by the method of the present invention, the photocathode is also formed on the electron gun side surface of the storage target mesh 4.

However, the light for imaging is mostly divided from the phase plate side and is blocked by the storage target mesh, so this light does not directly enter the photocathode formed on this mesh, so the photoelectron emission is extremely small. This does not cause any inconvenience to the operation of the storage image pickup tube.

The case where the base metal is evaporated from two or more points distant from the central axis of the glass envelope 1 has been described above.
The present invention can also be applied to the case of vapor deposition from one point on or near the axis.

In this case, the base metal evaporation source 6 needs to have a structure that allows it to be moved to a location where it does not interfere with electron beam scanning after the evaporation operation is completed.

As an example, one having a branch pipe will be explained with reference to FIG.

The base metal evaporation source 6 is attached to the tip of a loop 9 placed in a branch pipe 8, and is capable of high-frequency heating from the outside.

Further, the loop 9 can be moved up and down on the central axis of the branch pipe 8 by an external magnet 10 due to a magnetic body 91 attached to a part thereof.

When evaporating the base metal, the base metal evaporation source 6 and the loop 9 are moved by an external magnet 10 so that the base metal evaporation source 6 is on the central axis of the glass envelope 1 as shown in FIG. Deposited by evaporation.

After vapor deposition, the base metal evaporation source 6 and the loop 9 are moved again to the position shown in FIG.
It is separated at part A-N in Figure a.

When there is only one base metal evaporation source 6 as shown in FIG. For this purpose, the transparent conductive film 11 must be formed on the face plate 2 in advance.

Such a transparent conductive film 11 is made of tin oxide (SnOz
), indium oxide (Inz03), etc. can be used.

Note that the use of this transparent conductive film 11 can also be applied when two or more of the base metal evaporation sources 6 described above are installed and formed in an island shape as shown in FIG. 3a.

In the above explanation, we have explained the case where the base metal 3 is evaporated from one place using one evaporation source, but in this case too, the evaporation sources are provided at two or more places, but it is possible to change the position of one evaporation source. It is also possible to evaporate a plurality of times to substantially provide a plurality of evaporators.

Generally, a field mesh is sometimes installed on the electron gun side adjacent to the target in order to make the image pickup tube operate more effectively.

Copper mesh with a fineness of about 750 mesh is usually used as the field mesh, and it is suitable for target 4.
It is installed approximately 3rrrdl&shi.

It is also possible to make a storage image pickup tube having such a field mesh and having the structure of the present invention.

In that case, in one embodiment of the present invention shown in FIG.
A field mesh 12 is placed at a position rrIn away.

As a result, since the base metal 6 is deposited on the face plate 2 across the two meshes, the storage target mesh 4 and the field mesh 12, it passes through the mesh more than in the case where there is only one mesh as described above. As a result, the amount of base metal reaching the faceplate 2 is reduced.

However, if the amount of base metal to be deposited is increased by increasing the deposition time, etc., the amount of base metal to be deposited on the 7-Ace plate 2 can be made to the desired thickness.

A photocathode 3 can be formed on the face plate 2 in a similar manner to the method already described, and a storage image pickup tube having the structure of the invention having a field mesh 12 can be produced.

An embodiment according to the present invention will be described below for the case of an antimony cesium photocathode.

A 1500-mesh copper mesh for 1-inch videocon is used as the storage target mesh 4, and approximately 1□
Calcium fluoride (S a F2) to the thickness of Cron
The entire evaporation layer was used as an insulator layer.

This accumulation target mesh 4 is installed 4M apart from the face plate 2, and a base metal evaporation source 6 of 0.25 mm is located further 30 mm away from this and 10 m from the central axis.
Two antimony sb attached to a platinum-clad molybdenum wire of φ were installed at axially symmetrical positions.

The glass envelope 1 containing these was heated to 1O-7torr.
After evacuation to a higher vacuum, gas was vented at 400° C. for 3 hours.

Thereafter, the base metal evaporation source 6 was heated to evaporate antimony, and antimony was evaporated until the light transmittance of the face plate 2 reached 70%.

Next, while the entire glass envelope 1 is heated to 160°C, a nickel sleeve containing powder of cesium chromate (C82Cr04) and silicon, which is an alkali metal vapor generation source 7, is heated to generate cesium vapor, which acts on the antimony. I let it happen.

As a result, a photocathode 3 having a uniform sensitivity of 30 μA/Am was formed.

All of this process is within the range of conditions for producing a normal antimony cesium photocathode, and there is nothing particularly different about it.

As described above, the present invention is the same process as the conventional photocathode formation process except that the base metal and alkali metal vapor are deposited on the face plate 2 across the storage target mesh 4, but can be easily approached. It provides a useful means by which a focusing storage image tube can be created.

[Brief explanation of the drawing]

1a and 1b are partial cross-sectional side views of a storage image pickup tube and a close focusing type storage image pickup tube, and FIGS. 2a and 2b, 3a and 3b, and 4 are for detailed explanation of the present invention. FIGS. 5A and 5B are side views of the main parts of FIGS. 5A and 5B are partially sectional side views showing other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1...Glass envelope, 2...Face plate, 3...Photocathode, 4...Storage target mesh 5...Electron gun, 6...Substrate metal vapor deposition source, 7...
Alkali metal vapor source, 8... Branch pipe, 9... Loop, 10... Magnet, °11... Transparent electrode, 12...
・Field mesh 91...Magnetic material.

Claims (1)

Claims: 1. A storage target mesh having a conductor on one side and an insulator on the other side is placed within a glass envelope with the insulator side proximate to the faceplate side. A base metal evaporation source of a photocathode and an alkali metal evaporation source are arranged on the conductor side of the accumulation target mesh within the glass envelope, and the base metal evaporation source is located at a distance of at least twice the distance from the central axis of the glass envelope. Only the accumulated target mesh is deposited on the inner surface of the face plate via the accumulated target mesh from multiple positions distant from the accumulated target mesh,
1. A method for manufacturing a photocathode for a storage image pickup tube, the method comprising subsequently applying an alkali metal vapor to the photocathode.