JPH0129012B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] This invention relates to a proximity image tube.

[Technical Background of the Invention] In general, a proximity image tube is constructed as shown in FIG.
are arranged facing each other and sealed at a predetermined interval by an annular insulator 5.

In this case, each face plate 3, 4 is made of a glass plate or a fiber optic plate, and the above-mentioned interval is usually 1 to 2.
mm. Further, the target surface 2 is usually a fluorescent screen that emits light by electron bombardment, but it may be any other structure (for example, a solid-state image pickup plate or an SEC target of an image pickup tube) as long as it can extract signals; here, a fluorescent screen is used. An image tube using an image tube will be explained.

Target surface lead 7 with respect to photocathode surface lead 6
It is operated by applying a high voltage (usually around 10kV) to the Then, the input light is irradiated from the direction of arrow 8, and when a light image is formed on the photocathode 1, photoelectrons are emitted, and these photoelectrons are accelerated in a direction perpendicular to the photocathode 1 by a strong electric field and hit the target surface 2. reaches a certain phosphor screen and causes the phosphor screen to emit light. Since the spread of photoelectrons in a direction parallel to the phosphor screen is restricted by the strong electric field, the incident light image is reproduced brighter on the phosphor screen.

[Problems in the Background Art] In the conventional proximity image tube described above, when light emitted from the phosphor screen leaks to the photocathode 1, photoelectrons are emitted due to this light, which impairs the sharpness of the reproduced image. To prevent this, a thin aluminum film of 1000 angstroms is provided over the entire surface of the phosphor screen. This is manufactured using the same method as a normal so-called metal bag.

However, since a part of the incident light passes through the photocathode 1, if the surface of the aluminum thin film has a high degree of light reflection, this reflected light will irradiate the photocathode 1 again, and for the same reason as above, the reconstructed image will be Sharpness is lost.

[Object of the Invention] An object of the present invention is to provide a stable proximity image tube in which the sharpness of reproduced images is not impaired.

[Summary of the Invention] The present invention provides a proximity image tube in which a photocathode plate having a photocathode on its inner surface and a target face plate having a target surface on its inner surface are disposed facing each other and sealed at predetermined intervals with an annular insulator. , a phosphor screen, a first dense aluminum layer, a porous aluminum layer on the target face plate toward the photocathode side, the first
This is a proximity type image tube characterized in that a second dense aluminum layer thinner than the dense aluminum layer is successively formed.

[Embodiments of the Invention] The proximity image tube of the present invention is shown in FIGS. 2 and 3.
It is constructed as shown in the figure, and FIG. 3 shows the main part of FIG. 2.

That is, the same parts as in the conventional example (FIG. 1) are given the same reference numerals. A photocathode plate 3 having a photocathode 1 on its inner surface and a target face plate 4 having a target surface 2 on its inner surface are disposed facing each other, and a ring-shaped insulator 10
They are sealed at predetermined intervals (for example, 1 to 2 mm). As shown in FIG. 3, the target surface 2 is made up of, for example, a fluorescent screen 11 and a first aluminum film (dense layer) 12a. A thin aluminum film (dense layer) 12b is formed.

The porous layer 13 is formed by first vapor depositing aluminum in an inert gas atmosphere (first step), then removing the gas, and then vapor depositing aluminum in a high vacuum (second step). By doing so, a thin aluminum film (dense layer) 12b is formed.

The amount of aluminum deposited in high vacuum is selected within a range that substantially maintains the blackness of the porous layer 13 and does not significantly impair electron transparency. Experience has shown that a range of around 200 angstroms in terms of a plane is appropriate, but even if this is not strictly regulated, the objective can be achieved to a certain extent.

Further, the annular insulator 10 has an annular projection 10a formed on its inner peripheral surface, and an annular projection 10b also formed on its outer peripheral surface.

In this case, since the protrusion 10a protruded into the tube, surface charges tended to accumulate, and the insulation properties sometimes deteriorated contrary to initial expectations. The problem was that it was necessary to dissipate the surface charge, but it turned out that an effective solution was to make the insulator itself out of a slightly conductive material.

The material selected is high-resistance, electronically conductive glass, or ceramic with slightly added conductivity by adding impurities.

Further, the volume resistivity is greater than the value determined from the allowable dark current of the tube, and is not uniformly and strictly determined.

To give an example, the applied voltage is 10kV, the dark current is
The vacuum sealing parts 14 and 15 have the same area of 2 cm ² and the thickness of the insulator 10 is 2 mm.
In this case, the desired volume specific resistance is 10Ω·cm.
Since the photocurrent when this tube is in use is about 1 nA at most, the above settings are sufficient to release the surface charge.

In addition, in this embodiment, the annular projections 10a and 10b are integrally provided on the inner and outer peripheral surfaces of the annular insulator 10, so the surface path becomes longer, and as a result, the surface insulation is significantly improved, and the tube itself is also more durable than before. Small (thin)
Can be done.

[Effects of the Invention] According to the present invention, there is a phosphor on the target face plate, a first dense aluminum layer having the function of an aluminum bag that reflects the luminescence of the phosphor and increases luminance, and a phosphor that is converted into electrons at the photocathode. Since it has a second dense aluminum layer that transmits light that is not transmitted, and a porous aluminum layer that absorbs this light, it has the advantage that the sharpness of the reproduced image is not impaired.

In addition, since the aluminum vapor deposition is carried out in a high vacuum, the soot-like aluminum is firmly bonded to the thin aluminum film of the substrate, and the bonding strength between the particles is increased, so that they are not easily peeled off.

In addition, the porous aluminum vapor deposited layer formed in an inert gas atmosphere normally occludes inert gas, which is gradually released into the vacuum during operation of the tube, causing deterioration of the characteristics of the tube. The formation of the dense aluminum layer in No. 2 suppresses gas release, producing favorable results.

The present invention is applicable not only to ordinary image tubes whose target surfaces are formed of fluorescent screens, but also to high-sensitivity image pickup tubes with close-up image tubes whose target surfaces are SEC targets, or to high-sensitivity image pickup tubes with close-up image tubes whose target surfaces are SEC targets. However, it can also be applied to special close-range image tubes made of solid-state image pickup plates such as CCDs.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional proximity image tube, FIG. 2 is a sectional view showing a proximity image tube according to an embodiment of the present invention, and FIG. 3 is an enlarged view of the main parts of FIG. 2. FIG. DESCRIPTION OF SYMBOLS 1...Photocathode, 2...Target surface, 3...Photocathode plate, 4...Target face plate, 6...Photocathode lead, 7
...Target surface lead, 10...Insulator, 10a...
Protrusion, 10b... Protrusion, 11... Fluorescent screen, 12a... First aluminum dense layer, 12b... Second aluminum dense layer, 13... Aluminum porous layer.

Claims (1)

[Claims] 1. In a proximity image tube, a photocathode plate having a photocathode on its inner surface and a target plate having a target surface on its inner surface are disposed facing each other and sealed at predetermined intervals with an annular insulator. A proximity type image tube, characterized in that a phosphor screen, a first dense aluminum layer, a porous aluminum layer, and a second dense aluminum layer thinner than the first dense aluminum layer are successively formed on a face plate.