JPS60246545A - Pickup tube - Google Patents

Abstract

PURPOSE:To reduce dark current and prevent the dark current from being varied even if the scanning electron beam amount is varied by screening a transparent conductive film and an electrode section from which signals are extracted so that scanning electrons or secondary electrons are not incident directly. CONSTITUTION:Signals from a transparent conductive film 1 is extracted from a target ring 14 through an indium ring 9 for vacuum seal that makes contact to the transparent conductive film 1. Besides, an insulating screening ring 15 made of ceramics is provided between a mesh electrode 12 and a photoconductive target and electrons are prevented from being incident directly on the photoconductive film 1 and the indium ring 9. The photoconductive target forms the transparent conductive film 1 made of tin oxide and an electron injection checking layer 16 made of SiO2 on a transparent glass substrate 5 and a photoconductive film is formed by accumulating an a-Si:H film 6 on this substrate. Then, a secondary electron emission layer 17 is obtained by accumulating a layer made of MgO on the a-Si:H film 6. As a result, dark current can greatly be reduced and the dark current can be prevented from being increased even if the scanning electron beam amount is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a high-speed electron beam scanning type light guide imaging tube.

[Background of the invention]

Conventionally, image pickup tubes use a scanning method using a low-speed electron beam (hereinafter referred to as the LP method), so the 8-sensitivity afterimage caused by the scanning electron beam resistance is large, and the peripheral resolution is
Unfortunately, the beam benzo ink also had the disadvantage of easily distorting images. As a method to improve the above-mentioned problems, a scanning method using a high-speed electron beam (hereinafter referred to as the HN method) has been proposed (for example, Japanese Patent Laid-Open No. 54
-44487). FIG. 4 is an explanatory diagram of the operating principle of the HN method, in which a positive voltage higher than that of the cathode electrode 2 is applied to the transparent conductive film 1, and the secondary electron emission ratio δ of the photoconductive target is
Use it so that it is 1 or more.

When a high-speed electron beam is scanned in this state, the surface of the photoconductive target emits secondary electrons 3 and is balanced with the potential of the collector electrode 4, allowing light to pass through the transparent insulating substrate 5 and the transparent conductive film l. is absorbed by the photoconductive film 6 and generates electron-hole pairs, but the electrons flow to the scanning side and land the scanning side potential in a negative direction, and this drop is taken out as a signal. In FIG. 4, 7 is a load resistance, and 8 is a target voltage.

Compared to the conventional LI) type image pickup tube, the iN type image pickup tube has the following advantages: (1) less capacitive afterimage, (2) better peripheral resolution, and (3) less image distortion. .

Generally, in a light-guide type imaging tube, when a current other than the signal current caused by light is detected as a signal, it becomes a so-called dark current.
This causes deterioration of the S/N ratio, afterimage characteristics, color reproducibility, etc.

It is desirable to keep the dark current as low as possible in the HN type image pickup tube as well. Therefore, regarding the HN type image pickup tube, a layer to prevent injection of electrons is provided on the transparent conductive film side of the photoconductive film, and a layer to prevent injection of holes is provided on the beam scanning side of the photoconductive film. However, even if the dark current is reduced by this method, it is still not sufficient, and there is a problem that when the amount of the scanning electron beam increases, the dark current increases as the amount of the scanning electron beam increases.

[Purpose of the invention]

It is an object of the present invention to provide an image pickup tube of the HN type, which has a smaller dark current than the conventional one and which does not increase even if the amount of scanning electron beam changes.

[Summary of the invention]

Regarding the dark current of the HN image pickup tube, the inventors found that in addition to the dark current caused by electrons or holes injected into the photoconductive film, there are A scanning electron beam or secondary electrons are directly incident on an electrode portion for extracting a signal current from a transparent conductive film, and there is a dark current component due to further secondary electrons being emitted from there. We discovered that the dark current component is the main cause of the increase in dark current due to changes in the amount of scanning electron beam. Figure 5 is a diagram showing the mechanism of dark current generation discovered by the inventors.
1 shows the main parts of an HN type image pickup tube when used as an electrode for extracting a signal current from a transparent conductive film 1. Secondary electrons 11 and mesh electrodes 12 emitted from the photoconductive target by being bombarded with a scanning electron beam 10
Secondary electrons emitted from the image pickup tube, secondary electrons emitted from other parts of the image pickup tube, or scanning electrons that have deviated from the scanning orbit may cause photoconductivity of the indium ring 9 or the transparent conductive film 1 outside the scanning area. The secondary electrons 13 are incident on the part not covered by the film 6 and are emitted from there, and the mesh electrode 12
Therefore, current flows through the load resistor 7 and becomes a dark current. FIG. 6 shows the relationship between the signal current and the scanning beam amount in an image pickup tube having the structure shown in FIG. 5, except that the transparent conductive film 1 is removed. In this figure, the horizontal axis represents the scanning beam current, and the vertical axis represents the signal current at a target voltage of 20V. Since this is the case where there is no transparent conductive film 1,
No current flowing through the photoconductive targeter 1- is detected;
It is clear that all the signal currents shown in FIG. 6 are generated when electrons are incident on the indium ring 9 and secondary electrons are emitted, and the currents flow based on the above mechanism. The current based on such a mechanism is detected in exactly the same way even when the transparent conductive film 1 is present, and becomes a dark current unrelated to the incident light. In addition, when a transparent conductive film is present, a similar dark current may be generated not only by the indium ring but also by electrons entering the part of the transparent conductive film that is not covered by the photoconductive film. is clear.

The above describes the case where the signal current is extracted from the transparent conductive film using an indium ring, but even if other methods are used, the transparent conductive film and the electrode part for extracting the signal from it can be used. , if electrons can be directly incident on a conductor that is in electrical contact with them, then
Needless to say, dark current is generated based on the above mechanism.

The image pickup tube according to the present invention has a photoconductive target that is provided with at least a transparent conductive film and a photoconductive film on a predetermined transparent insulating substrate, and the transparent conductive film is disposed on the light incident side. In a high-speed electron beam scanning negative charging type image pickup tube,
By shielding the transparent conductive film and the electrode portion for extracting signals from it to prevent direct incidence of scanning electrons or secondary electrons, dark current can be significantly reduced.
Furthermore, the dark current does not change even if the amount of scanning electron beam is changed.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing a photoconductive target and its surrounding area in a first embodiment of an image pickup tube according to the present invention.

In the first embodiment, the signal from the transparent conductive film 1 can be taken out from the target ring 14 via the vacuum sealing indium ring 9 that is in contact with the transparent conductive film 1. .

By providing an insulating shielding ring 15 made of ceramic between the mesh electrode 12 and the photoconductive target, electrons are prevented from directly entering the transparent conductive film 1 and the indium ring 9.

In the photoconductive target in this example, a transparent conductive film 1 made of tin oxide and an electron injection blocking layer 16 made of 5102 are formed on a transparent glass substrate 5, and then the target is made of high-purity Si in a high frequency sputtering device. and place the above board opposite it. Inside the sputtering equipment
After evacuating to a high vacuum of less than X 10-”rorr,
A mixed gas of argon and hydrogen is introduced to bring the pressure in the apparatus to 5xlo-' to 5xIQ-3 Torr. The concentration of hydrogen in the mixed gas is 30 to 65%. 1. After setting the substrate temperature to 150 to 300°C, reactive sputtering is performed to form the transparent conductive film 1 and the electron injection blocking layer 16.
A of 0.5-4t in film thickness was formed on the -1-originated plate.
-8j: Deposit H film 6 to form a photoconductive film. Next, using another high-frequency sputtering device, high-purity Mg○ is used as a target, and an L-shaped plate on which an a-8i nide ■ film 6 is deposited is placed opposite to it. Inside the sputtering equipment I
' Create a high vacuum below Torr and introduce argon to 5X
Sputtering is performed at a pressure of 10-4 to 5 x 1O-3 Torr and a substrate temperature of 50 to 150°C. In this way, a layer made of MgO is deposited on the a-8i:I-1 film 6 to a thickness of about 5 to 30 nm, and this is used as the secondary electron emitting layer 17.

The photoconductive target produced as described above was combined with an electron gun equipped with the shielding ring 15, and the tube was evacuated and sealed to obtain an I-N type optical guide chamber type imaging tube.

FIG. 2 compares the electron beam amount dependence of the dark current 18 of the image pickup tube obtained in the first embodiment and the dark current 19 of the image pickup tube without the shielding ring 15.

The horizontal axis of the figure is the amount of scanning electron beam (1), and the vertical axis is the logarithmic representation of the dark current.A comparison between curve 18 and curve i9 shows that the image pickup tube according to the present invention significantly reduces the dark current, and the scanning type It is clear that even if the amount of T beam is increased, the dark current does not increase.

FIG. 3 is a sectional view showing a second embodiment of a photoconductive target in an image pickup tube according to the present invention. In the second embodiment shown in FIG. 3, a signal is extracted from the transparent conductive film 1 by a metal pin electrode 20 penetrating the glass substrate 5, and the pin electrode 20 and the transparent conductive film 1 are connected to a dielectric. By covering with the body 21, the structure is such that electrons are not directly incident on the pin electrode 20 and the transparent conductive film 1. In other words, a transparent conductive film 1 mainly composed of Sn○ is formed on a glass plate 5, and a circular Cr
A layer 22 and an Au layer 23 are formed one after the other by vacuum evaporation, and a hole is made through the glass substrate 5 approximately in the center of these Cr and Au layers 22 and 23. Next, electrons are injected into the second disk - LCr, except for the Au layer 22 and 23.
Sealing layer 16, a-8i: H photoconductive film 6 and secondary set f.
The emissive layer 17 is deposited in a manner similar to that of the first embodiment described above. a-5i:)i The photoconductive film 6 is formed by using a plate of polycrystalline S'' in Ar+○, dregs, by reaction 1'1 sputtering method, or S-i)■, tallow discharge CV in gas. I
−,) can also be formed by the photoelectric conversion cloud′
is a good material. After that, pin wire + box 2 for signal extraction
Insert CrJfi22 and Au layer z into the above hole;
3, and a dielectric layer 21 such as 5 in 2 is deposited on top of the pin electrode 20 to completely cover the top of the pin electrode 20 and the conductive portion around it. When the image pickup tube obtained as described above was subjected to HN operation in the method described in Fig. 4, it was found that a conventional image pickup tube in which part of the transparent conductive film and the electrode part for signal extraction are not shielded. The dark current was significantly reduced compared to the conventional method, and a remarkable effect was observed in that the dark current did not increase even when the scanning beam amount was increased.

In both the first and second embodiments, the mesh electrode 12 is shown, but it has been experimentally confirmed that the same effect can be obtained even when there is no mesh electrode. Further, in the above embodiments, the case where the material of the photoconductive target is an a-3i:H film has been described, but it goes without saying that the present invention can also be applied to an HN type image pickup tube using a material other than the above-mentioned material. Furthermore, in the second embodiment, a method was described in which the transparent conductive film 1 and the pin electrode 20 were covered with another dielectric material WI (SiO2). A similar effect can be obtained by covering it with

[Effects of the Invention] As described above, the image pickup tube according to the present invention includes at least a light-transmitting conductive film and a photoconductive film on a predetermined light-transmitting insulating substrate, and the light-transmitting conductive film is exposed to light. In a high-speed electron beam scanning type negatively charged image pickup tube having a photoconductive target disposed on the side, the above-mentioned transparent conductive film and an electrode portion for extracting signals from the transparent conductive film are used to prevent direct incidence of scanning electrons or secondary electrons. By shielding the secondary electrons emitted from the photoconductive target and mesh electrode by the scanning electron beam, the secondary electrons emitted from other parts of the imaging tube are
Secondary electrons or scanning electrons that have deviated from the scanning orbit will not enter the indium ring outside the scanning area or the part of the transparent conductive film that is not covered with the photoconductive film and will not emit secondary electrons. It is possible to obtain an effect that the dark current does not increase even if the current is significantly reduced and the amount of scanning electron beam is increased. Therefore, an image pickup tube with a good S/N ratio and good color reproducibility can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a photoconductive target and its surrounding area in a first embodiment of an image pickup tube according to the present invention, and FIG. 2 is a sectional view showing the photoconductive target and its surrounding area in the first embodiment of the image pickup tube according to the present invention, which has no dark current and no shielding ring. Figure 3 is a cross-sectional view showing a second embodiment of the photoconductive target in the image pickup tube according to the present invention, and Figure 4 is a diagram comparing the dependence of the dark current on the electron beam amount in the image pickup tube. An explanatory diagram of the operating principle, Figure 5 is a diagram showing the mechanism of dark current generation, and Figure 6 is a diagram showing the scanning electron beam amount and signal current density of the image pickup tube with the structure shown in Figure 5 except for the transparent conductive film. FIG. 1... Transparent conductive film 5 Transparent insulating substrate 6 - Photoconductive film 12 - Mesh electrode 15 - Shielding ring 20 Pin electrode, 21 - Dielectric layer Attorney Junnosuke Nakamura 1 Diagram 1 Beam amount Rest A) Transmit the 5-figure scanning bee to the computer A) Continued from page 1 0 Inventor Tadaaki Hirai Kokubunji City Higashibono Research Institute

Claims (4)

[Claims] (1) A high-speed electron beam having a photoconductive target on a predetermined translucent insulating substrate, comprising at least a translucent conductive film and a photoconductive film, with the translucent conductive film disposed on the light incident side. An image pickup tube of a scanning type negatively charging type, characterized in that the transparent conductive film and an electrode portion for extracting (lj) from it are shielded so that scanning electrons or secondary electrons do not directly enter the image pickup tube. (2) The imaging tube according to claim 1, wherein the shielding of the electrode portion is an insulating shielding ring provided between the photoconductive target and the mesh electrode. (3) The imaging tube according to claim 1, wherein the electrode portion is shielded by covering the exposed conductive portion in contact with the pin electrode and the bottle electrode with a dielectric layer. (4) The image pickup tube according to any one of claims 1 to 3, wherein the photoconductive film is made of amorphous silicon containing hydrogen.