JPH0473253B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to a backscattered electron removal electrode that is installed in an electron tube that handles electron beams, such as an image pickup tube, and absorbs and removes unwanted backscattered electrons. By doing so, it is possible to prevent the generation of false images due to return beams that are likely to occur in electrostatic deflection type image pickup tubes, thereby ensuring a clear image of the subject.

Prior Art In general, electrostatic deflection type image pickup tubes suitable for use in small television cameras, etc., include, for example, the IEEE
Transactions on Electron Devices magazine, Vo1.
ED-14, No. 3, pp163-170 (1967) “A Mixed
A typical image pickup tube is an image pickup tube equipped with an electrode called a deflectron, which is described in ``-field Type of Vidicon''. This is the common name for electrode 1.

Particularly in this type of electrostatic deflection type image pickup tube, as shown in FIG. The beam becomes a beam 6 and returns to the reflection position 8 of the electron gun section 2. A part of the returning beam 6 is reflected again at the reflection position 8 to become a secondary beam 7, which travels toward the target 5 again.

If the secondary beam 7 described above forms an image on the surface of the target 5 at the same position and with the same size as the original electron beam 3, the amount of the scanning beam has equivalently increased, so there will be no interference. It's not, and it's actually preferable. However, since both the return beam 6 and the secondary beam 7 are deflected in the same direction as the original electron beam 3 when passing through the electrostatic deflection electric field, each time these beams 6 and 7 are reflected, It will land at a position further away from the tube axis.

In addition, in an electromagnetic deflection type image pickup tube, an electron beam that reciprocates within a deflection magnetic field is deflected in the opposite direction on the return trip because the traveling direction of the beam current with respect to the deflection magnetic field is opposite on the outward and return trips. In reality, it should always follow the same route. However, in reality, the output image captured by the secondary beam 7 may be slightly blurred or Misalignment occurs. However, the interference caused by the secondary beam 7 in an electromagnetic deflection type image pickup tube is extremely small compared to that in an electrostatic deflection type image pickup tube.

However, as mentioned above, in the electrostatic deflection type image pickup tube, the secondary beam 7 and the original electron beam 3 land at different positions on the target 5. As described in , different parts of the subject image projected onto the target 5 are read out at the same time, and the interference image caused by the secondary beam 7 is mixed into the captured output image.

An example of the interference image produced by the secondary beam 7 made of such reflected electrons is shown in FIG. As mentioned above, the secondary beam 7 is deflected by the electrostatic deflection electric field.
Since the electron beam 3 lands on the target 5 at a position further away from the tube axis than the original electron beam 3, the output image taken by the original electron beam 3 appears to be reduced to the center. . As shown in the figure, the captured output image when no subject image is projected onto the target 5 shows slight damage such as raster burn on the surface of the target 5 caused by the original beam raster. Imaging output screen 1 as surface image 11
0 appears in a reduced size at the center, and around it, a circular image 12 appears due to the secondary beam 7 scanning a cylindrical or disk-shaped electrode section near the target 5. Such a disturbing image will be called a reflected image.

In order to prevent the occurrence of such a reflected image, conventionally, for example, Japanese Patent Application Laid-Open No. 56-38742 filed by the applicant has been proposed.
As described in the following publications, No. 56-38743 and No. 57-834, the following various means for removing reflected electrons were employed.

(1) As shown in FIG. 4, a normal electron gun section 2 is extended forward, and a reflector electrode 13 is provided at the front end of the electron gun section 2, so that the electron gun section 2 is placed in front of the object point 9 of the electron beam 3, that is, at a position closer to the target. By reflecting the return beam 6 at , the secondary beam 7 is blurred. However, although such backscattered electron removing means reduces the interference caused by the reflected image, it has the disadvantage that the tube length becomes long.

(2) As shown in Fig. 5, the front end of the electron gun section 2 is shaped into a conical shape that protrudes forward, and the return beam 6, which is approximately parallel to the tube axis, is reflected in a direction oblique to the tube axis. The secondary beam 7 obliquely intersecting the tube axis is repeatedly reflected by the deflectrons 22 arranged on the inner wall surface of the cylindrical outer tube 20 and has the shape shown in the first figure, thereby gradually blurring it. However, such a method has a disadvantage in that the effect of blurring the reflected image is small compared to the complexity of the electrode structure, and interference due to the reflected image cannot be sufficiently prevented.

(3) A thin film of a metal material such as gold or platinum, which has a low secondary electron emission ratio and has good absorption properties for incident electrons, is coated on the inner surface of the beam restriction hole 15 and the surface of the electrode provided with the beam restriction hole 15. There is also one that allows the return beam 6 to be absorbed.
Conventional vapor-deposited thin films were insufficient in absorbing the returned beam.

(4) As shown in FIG. 6, the maximum outer diameter 16 of the electron gun section 2 is made sufficiently smaller than the inner diameter 18 inside the tube, and an elongated cylindrical electrode 19 is added to the front end of the electron gun section 2. By shielding the original electron beam 3 from the deflection electric field caused by the deflection plate electrodes 22 arranged on the inner wall surface of the outer tube 20, the cylindrical electrode 1
A difference in deflection sensitivity is created between the return beam 6 which passes through the outside of the tube 9 and is affected by the deflection electric field and the original electron beam 3, so that the return beam 6 is relatively deviated from the tube axis and the inner wall surface of the outer tube 20 By directing the return beam 6 toward the electron gun section 2, the return beam 6 is prevented from colliding with the front end surface of the electron gun section 2 and being reflected, thereby preventing it from becoming a secondary beam heading toward the target. However, part of the return beam 6
Not only is there still a possibility that the electron beam enters the electron gun 9 and is reflected by the electron gun section 2 toward the target 5, but there is also the disadvantage that the electron gun section becomes long.

That is, the conventional reflected electron removal means (1) described above
Among (4), (1), (2), and (4) all have the drawback that the electron gun section is long, and a sufficient removal effect cannot be obtained. In order to increase the effect, the removal means (1), (2), and (4) are combined with the removal means (3), and the various reflector electrodes described above are coated with gold, which has good electron absorption. Even if a thin film of platinum or the like was deposited, a sufficient absorption effect could not be obtained as long as a normal vapor-deposited thin film was used.

In addition, when the electron gun section 2 of the electrostatic deflection type image pickup tube becomes long, it is necessary to increase the length of the outer tube 20 in order to secure the deflection electric field region 21 of the required length.

Summary of the Invention An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to improve the effect of removing reflected electrons without the need to particularly provide a long reflector electrode in the electron gun section of an electron tube such as an image pickup tube. An object of the present invention is to provide a backscattered electron removing electrode.

That is, the backscattered electron removal electrode of the present invention has a porous layer made of a substance having a small secondary electron emission ratio and having a thickness approximately equal to at least the height difference of the irregularities on the irregularly uneven rough surface of the base metal. It is characterized by being coated with.

EXAMPLES The present invention will be explained in detail below using examples with reference to the drawings.

First, the basic structure of the backscattered electron removing electrode of the present invention is shown in FIG. 7a. The basic configuration shown in the figure forms a prominently uneven rough surface 36 on the surface 34 of the base metal 33,
A thin layer 35 for absorbing incident electrons made of a porous film 32 is provided to cover the uneven rough surface 36.

To explain in detail the reflected electron removal electrode of the present invention having such a basic configuration, the material of the porous layer 32 deposited on the base metal 33 has excellent heat resistance and oxidation resistance, and has a secondary electron emission ratio. By using materials with small δ and good absorption properties for incident electrons, such as carbon C, gold Au, silicon Si, platinum Pt, etc., and depositing these materials in a low vacuum atmosphere, porous Forms a thin layer. In addition,
The heat resistance of the above-mentioned materials is necessary in order to withstand heat treatment during degassing, etc. when exhausting the electron tube, and the oxidation resistance is necessary to ensure that the above-mentioned materials oxidize and become insulators. This is necessary in order to prevent the absorption of incident electrons from deteriorating due to an increase in the secondary electron emission ratio δ. Moreover, if the above-mentioned types of materials are deposited in a low vacuum gas atmosphere of several Torr to several tens of Torr, a porous layer with a filling rate of 1% or less can be easily formed. The substantial thickness of the porous layer 32 formed in this way is preferably at least several μm for reasons described later.

Base metal 3 serving as the substrate of the porous layer 32 described above
For No. 3, a heat-resistant vacuum material that is a metal material that releases little gas even when heated in a vacuum, such as stainless steel, nichrome, tantalum, and molybdenum, is used. Before applying a porous layer to such a base metal,
Irregular irregularities with height differences of several micrometers or more, preferably ten-odd micrometers or more are formed on the surface 34 of the base metal by a chemical method such as etching or a mechanical method such as polishing or sandblasting. Note that the surface roughness of a normal rolled metal plate or a lathe-finished metal plate has a height difference of at most several micrometers or less, as shown in FIG. 7b. On the other hand, according to the present invention, as shown in FIG. 7a,
Since the rough surface 34 of the base metal plate 33 is covered with a sufficiently thick porous layer 32 with an extremely low filling rate, most of the reflected electrons 31 from the target direction are transferred to the surface 30 of the porous layer 32. It enters the layer without being reflected.

As shown in FIG. 8, the reflected electrons 31 that have entered the porous layer 32 are repeatedly reflected diffusely on the surface of the porous layer 32 and gradually lose their energy, and some of them While being absorbed into the material,
It passes through the layer and reaches the rough surface 34 of the base metal 33. Since the surface of the base metal 33 has irregular irregularities with large height differences, electrons reaching the rough surface 34 are diffusely reflected by the rough surface 34 and enter the porous layer 32 again. Diffuse reflection repeats again.
Therefore, in the backscattered electron removal electrode of the present invention, most of the backscattered electrons 31 are caused by diffuse reflection on the rough surface of the base metal 33 and the porous layer of a substance with a low secondary electron emission ratio deposited on the rough surface. Due to the synergistic effect with the repetition of diffuse reflection at 32, the light is almost completely absorbed and removed.

That is, assuming that 1% of the backscattered electrons 31 is absorbed by one collision with the porous material in the porous layer 32, as shown in FIG.
36.6% of the impact electrons are reflected by 100 collisions, and 0.04% of the impact electrons are reflected by 1000 collisions.
Only % will be reflected.

In addition, since the porous layer 32 is made porous by vapor-depositing a material with a small secondary electron emission ratio in a low vacuum atmosphere, almost no secondary electrons are emitted from the surface 30. Even if secondary electrons are emitted from the surface 30 of the porous layer, most of them enter the porous layer and are repeatedly absorbed and diffusely reflected. The amount of secondary electrons is extremely small, similar to the above-mentioned impact electrons 31.

In the configuration example of the backscattered electron removing electrode of the present invention described above, the thin layer 3 is deposited on the rough surface 34 of the base metal 33 to absorb and remove backscattered electrons.
5 is a porous layer 32, but the thin layer 35 for preventing electron reflection may be made of, for example, a vitreous material made of a material with an extremely low secondary electron emission ratio, as long as it has the effect of preventing reflection of incident electrons. It can also be formed into a layer or an amorphous layer, and has excellent adhesion to the rough surface 34, so it is effective in cases where thermal, mechanical, etc. strength and durability are required. However, thin layer 3
Compared to the case where No. 5 is made of a porous layer of the same material with a small secondary electron emission ratio, the effect of absorption and removal of reflected electrons is far inferior.

Effects As is clear from the above explanation, according to the present invention, reflected electrons that have conventionally caused serious trouble in electron tubes such as electrostatic deflection type image pickup tubes can be removed, and the occurrence of such trouble can be prevented. The following remarkable effects can be obtained.

That is, the backscattered electron removal electrode according to the present invention is
Electron gun section 2 in the electrostatic deflection type image pickup tube shown in the second diagram
A reflector electrode 17 provided at the front end of the reflector electrode 17, a reflector electrode 13 added by extending the electron gun section 2 forward in the conventional anti-reflection image pickup tube shown in FIG.
If applied to the conical reflector electrode 14 provided at the front end of the electron gun section 2 in the conventional electrostatic deflection type image pickup tube shown in FIG.
Therefore, it is possible to almost completely prevent the occurrence of a reflected image that conventionally occurs on the image pickup output screen as shown in FIG.

For example, if the reflector electrode 17 in the electrostatic deflection type image pickup tube shown in FIG. 2 is configured as shown in FIG. 7a, the following remarkable effects can be obtained.

Generally, the contrast of a reflected image due to reflected electrons as shown in FIG. 3 increases as the beam current of the original electron beam increases. now,
Assuming that the minimum amount of beam current necessary to extract a signal current of 0.2 μAmp is i _bj , in a conventional image pickup tube without countermeasures, even if the beam current i _b is reduced to the minimum value i _bj , the reflected image will not be reflected. It has a detectable contrast. When the beam current i _b was increased to twice or three times the minimum value i _bj , the contrast of the reflected image also increased almost proportionally.

On the other hand, when the present invention provides the effect of absorption and removal of reflected electrons, the beam current i _b
Until i bj is increased to at least five times the minimum value i _bj , such reflected images are reduced to such an extent that they are not detected at all. Moreover, the beam current i _b in this type of image pickup tube is usually set to about 2 to 3 times its minimum value i _bj , so if a particularly long reflector electrode is not provided as shown in Figure 2, Also, by applying the present invention, a necessary and sufficient effect can be obtained in preventing the generation of interference images due to reflected electrons. Further, as shown in FIGS. 4 to 6, if the present invention is applied to a case where a particularly long reflecting plate electrode is provided, a sufficient effect of preventing the generation of reflected images can be obtained.
Note that the present invention is not limited to the above-mentioned types of image pickup tubes, but can be applied to electrodes that require prevention of the generation of undesired secondary electrons and suppression of reflected electrons to obtain the same effects as described above. Of course, when the present invention is applied to an image pickup tube, it is possible to obtain a clear captured output image without reflected images while keeping the electron gun section compactly configured. It is a great contribution to the development of society.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the structure of the deflectron in an electrostatic deflection type image pickup tube, Figure 2 is a diagram showing how a reflected image is generated in an electrostatic deflection type image pickup tube, and Figure 3 is a diagram showing the manner in which a reflected image is generated in an electrostatic deflection type image pickup tube. FIGS. 4 to 6 are diagrams showing examples of conventional methods of preventing the generation of reflected images, and FIGS. FIG. 8 is a sectional view showing the principle of operation of the backscattered electron removal electrode of the present invention, and FIG. 9 is a characteristic curve diagram showing an example of the backscattered electron removal effect. 1... Deflectron, 2... Electron gun section, 3...
...Electron beam, 4...Mesh electrode, 5...Target, 6...Return beam, 7...Secondary beam,
8... Reflection position, 9... Object point, 10... Output screen of the image pickup tube, 11... Beam raster printed image on the target surface, 12... Annular image of the electrode near the target, 13, 14, 17... Reflector electrode, 15...
Beam restriction hole, 16...Maximum diameter of electron gun section, 18...
... Outer tube inner diameter, 19 ... Additional cylindrical electrode, 20 ... Outer tube, 21 ... Deflection region, 22 ... Deflectron electrode, 30 ... Porous surface, 31 ... Incident electron,
32... Porous layer, 33... Base metal, 34...
Base metal surface, 35... Thin layer for removing reflected electrons, 3
6...Uneven layer.

Claims (1)

[Scope of Claims] 1. A porous layer made of a substance having a small secondary electron emission ratio and having a thickness at least approximately equal to the height difference of the irregularities is deposited on the rough surface of the irregularly uneven surface of the base metal. A backscattered electron removal electrode characterized by: 2. The backscattered electron removing electrode according to claim 1, wherein the surface of the base metal has an uneven surface having a height difference of at least 10 μm. 3. The backscattered electron removal electrode according to claim 1 or 2, wherein the filling rate of the porous layer does not exceed 1%. 4. The backscattered electron removal electrode according to any of the preceding claims, wherein the material forming the porous layer is selected from the group of carbon, gold, silicon, and platinum. 5. The backscattered electron removal electrode according to any of the preceding claims, wherein the base metal is selected from the group of stainless steel, nichrome, tantalum, and molybdenum.