JPH08255558A - Cold cathode and electron gun and microwave tube using the cold cathode - Google Patents

Abstract

PURPOSE: To provide an electron gun having a long service life as well as a microwave tube having a high performance by forming a cold cathode having a spherical electron emission surface, and further forming an electron beam of high current density and small ripple. CONSTITUTION: An electron emission zone formed out of a material having a low work function, or an electron emission zone having a micro cold cathode processed and formed via a focusing ion beam(FIB) passing the center of the radius of curvature of a spherical surface 2 or the neighborhood thereof, is formed on a spherical substrate 1, thereby forming a cold cathode 6. Then, an electron gun is formed out of the cathode 6 and a beam formation electrode 21 at cathode potential or a beam formation electrode at positive or negative potential on the basis of the cathode potential as reference, and an anode 22. Furthermore, a microwave tube is also formed by use of the electron gun.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold cathode which emits electrons by a tunnel effect, in particular, a cold cathode having an electron emission region on a spherical surface, an electron gun which forms an electron beam using the cold cathode, and this electron. It relates to a microwave tube using a gun.

[0002]

2. Description of the Related Art Conventionally, in order to form a high current density electron beam used in a traveling wave tube (TWT) or a klystron, a Pierce electron gun (JR Pie) is used.
rce, “Theory and design of
electron beam ", 2nd ed. Va
n Nostrand, New York, 1954).
Focusing type electron guns called as are used. FIG.
Shows a sectional view of this piercing electron gun. This electron gun has an electron emission surface 101 of a hot cathode processed on a spherical surface, a Wehnelt electrode 102 surrounding the electron emission surface 101 and having a cathode potential or a negative potential, and a positive voltage is applied to the cathode to generate a current from the cathode. It is composed of the anode 103 to be taken out,
Since a relatively large focusing ratio (cathode diameter / electron beam type) and a stable electron beam 104 can be obtained, it is widely used.

Generally, the current (cathode current density) that can be taken out from the cathode unit surface area is limited by the cathode material and the cathode temperature, and the life for raising the cathode temperature in order to take out a current exceeding the cathode capacity is greatly shortened. It However, by adopting such a focused electron gun,
An electron beam having a high current density can be formed without affecting the life, and high output and high frequency of a traveling wave tube can be achieved.

A conventional technique using an FEA (electrolytic radiation cold cathode array) for a traveling wave tube is disclosed in Japanese Patent Laid-Open No. 5-266809. FIG. 9 is a sectional view of the traveling wave tube disclosed in the publication, and FIG. 10 is an enlarged sectional view of only the electron gun portion. In FIG. 9, the electron beam 104 is extracted from the cold cathode 105 having a planar electron emission region 110, and is subjected to the focusing action by the Wehnelt electrode 102,
It flows into the helix 105 that also serves as the anode.

Electrolytic radiation in which an array of micro-cold cathodes composed of a minute conical emitter and a gate electrode formed immediately near the emitter and having a function of drawing out a current from the emitter and a current control function are arranged. The cold cathode array (FEA) is a C.I. A. Spint, etc. (Jo
internal of Applied Physics,
Vol. 39, no. 7, pp. 3504, 1968)
And H .; F. Proposed by Gray. This FEA is obtained from a higher current density than a hot cathode, and has advantages such as small velocity dispersion of emission current. Further, the current noise is smaller than that of a single electrolytic emission cathode, and it operates at a low voltage of several 10 to 200 V, and operates even in an environment with a relatively poor vacuum degree.

This FEA is usually formed on a flat surface by using a semiconductor manufacturing technique, and a technique for forming it on a curved substrate is disclosed in Japanese Patent Laid-Open No. 6-290702. FIG. 11 shows a method of manufacturing the curved FEA disclosed in the publication. In FIG. 11, the substrate 111 has a spherical or cylindrical three-dimensional curved surface shape with a radius of curvature R, and the insulating layer 112 and the gate electrode layer 1 are formed by a normal technique.
13 are stacked, and a cavity 114 is formed in the insulating layer 112 and the gate electrode layer 113. The evaporation source of the emitter material is placed at the center of curvature O of the radius of curvature R, and the emitter material is deposited on the substrate 111 to form the emitter 115.

In the manufacturing method shown in FIG. 11, since the emitter material is always deposited vertically on the substrate, the emitter 115 is formed vertically on the substrate 111 on the entire surface of the substrate 111.
FEA having uniform properties over the entire surface can be manufactured.

Further, Japanese Patent Laid-Open No. 4-249841 proposes a structure using a spherical FEA for a flat display, as shown in FIG. In FIG. 12, the FEA substrate 111 is formed into a spherical surface along the entire glass 116 of the flat display, and the emitter and gate electrodes are formed on the convex surface thereof.

As a result, the distance between the FEA, which is an electron source, and the front glass 116 coated with the phosphor is kept constant, and the vacuum envelope is spherical while maintaining a uniform focus characteristic over the entire display screen. As a result, it has the strength to withstand the pressure difference between the vacuum and the atmosphere, enabling the size of the display to be increased.

[0010]

In a microwave tube such as a traveling wave tube, a slow wave circuit such as a helix is a portion for interacting an electron beam and an electromagnetic wave. It is constant regardless of and decreases as the frequency increases. On the other hand, the output power is about 10 to 30% of the electron beam power (beam current x beam voltage) converted, so that high shipment of the microwave tube,
In order to increase the frequency and reduce the voltage to stop, it is necessary to increase the electron beam current density.

However, the current density at the cathode (cathode current density) is governed by the type of cathode, cathode material, cathode temperature, etc., and if an attempt is made to obtain a current density higher than the capability, then a hot cathode,
Example Both the cathode and the service life are shortened rapidly.

In order to solve this, a focusing type pierce electron gun has been proposed in which the electron beam diameter is smaller than the cathode diameter for the hot cathode (FIG. 8). This electron gun uses a spherical electron emission surface and forms an equipotential surface on a concentric spherical surface to create an electron beam having an electron orbit similar to a laminar (laminar flow) shape or a laminar flow shape. It is widely used in waveband electron tubes and applications that require high-current electron beams. The laminar flow type electron beam is an electron beam in which the orbit emitted from any position in the radial direction of the cathode and the cathode curvature does not intersect with the orbit of electrons emitted from other radial positions. The result is a stable electron beam with little ripple. However, since the conventional pierce electron gun is a hot cathode, it requires heater power, and it takes several seconds to several tens of seconds until stable thermoelectrons are emitted after the heater power is turned on. 1
A structure that can withstand high heat of 000 ° C or higher for a long time is required.
Further, since the emitted thermoelectrons have a thermal velocity that is the initial velocity in the random direction of the above temperature, when the diameter is smaller than the cathode diameter and the length is longer than the diameter, the beam is focused.
Beam diameter spread and ripple occur. Further, since the electron emitting material of the cathode evaporates at a high temperature of about 700 to 1000 ° C. or more, the cathode current decreases with the lapse of time.

In order to solve these problems, FIG. 9 and FIG.
As shown in 0, a traveling wave tube using an electrolytic radiation cold cathode as a cathode has been proposed. However, the electron gun used here does not completely satisfy the design condition of the pierce electron gun because the electron emission region of the cathode is flat. For this reason, ripples are generated in the electron beam, and some electrons collide with the low-speed wave circuit on the way to heat them, and there is a problem that an electron gun with a large focusing ratio cannot be realized.

In the method of manufacturing a three-dimensional curved FEA shown in FIG. 11, the main purpose is not to form a curved cathode, but to form a uniform emitter. In a general vacuum vapor deposition apparatus, the distance between the evaporation source O and the substrate 111 is usually selected to be about several tens of cm in order to maintain the uniformity of the vapor deposition thickness as well as the direction of the vapor deposition material. However, in the case of the cathode of the microwave tube, the radius of curvature of the cathode is several mm
Since it is necessary to set the thickness to about several tens of mm, it is necessary to evaporate from a distance very close to the substrate, but it is extremely difficult to adopt such a method in consideration of the uniformity of the thickness of the vapor-deposited emitter material. is there. In addition, molybdenum,
When evaporating a material such as tungsten, an electron beam is applied to the sample to heat and evaporate, and electron beam evaporation technology is used. However, when the distance between the evaporation source and the sample is short, the evaporation source is used. It cannot be irradiated with an electron beam. Further, the substrate may be heated by the heat radiation of the evaporation source.

Further, in the case of the microwave tube, since the radius of curvature is small, the unevenness formed on the surface of the substrate 111 causes
It is difficult to form an opening having a diameter of 1 μm or less with good uniformity in the gate electrode 113 by a normal exposure technique.

Further, the cathode structure shown in FIG.
Although it is shown as an idea in Japanese Patent No. 249841,
As can be seen from the publication, the conventional technique is “very difficult to realize in terms of manufacturing process”.

[0017]

A cold cathode is formed by forming an electron emission region in which a material having a small work function is laminated on a spherical curved surface formed on a substrate. With this cold cathode,
One or two along the curved surface of the cold cathode on the front surface of the cold cathode
An electron gun is composed of a single grid electrode, a beam forming electrode having a cathode potential, a Wehnelt electrode which is a beam forming electrode having a positive or negative potential with reference to the cathode potential, and an anode.

Alternatively, a cold cathode is formed by forming an electron emission region having a minute cold cathode processed / formed by a focused ion beam (FIB) passing through or near the center of curvature of a spherical curved surface formed on a substrate. Configure. An electron gun is constituted by the cold cathode, a beam forming electrode having a cathode potential, a Wehnelt electrode which is a beam forming electrode having a positive or negative potential with reference to the cathode potential, and an anode.

A microwave tube is constructed using these cold cathodes.

[0020]

As a result, a focused electron gun having a cold cathode as an electron source can be realized, and the following advantages are brought about.

By adopting a cold cathode in the electron gun,
The heater power is not required, the power consumption can be reduced, the thermal structure design near the cathode can be simplified, and an electron gun with no time delay from power-on to reaching a stable operation state can be realized.

Further, since the focused electron gun satisfying the design condition of the pierce electron gun can be realized, it has the above advantages, and at the same time, a stable electron beam having a high current density, a small ripple and a small current ripple can be formed. Furthermore, an electron gun with a long life can be realized.

[0023]

Embodiments of the present invention will be described in detail with reference to the drawings. Example 1 FIG. 1 is a principle configuration diagram showing a method for manufacturing an electrolytic radiation cold cathode which is a first example of the present invention, and shows a processing method by a focused ion beam (FIB). In FIG. 1, the whole is housed in a vacuum chamber, and the inside is kept at an appropriate degree of vacuum. A spherical surface 2 having a radius of curvature designed by the electron gun is formed on the substrate 1 by a mechanical method, and a spherical surface 2 is formed on the spherical surface 2.
The insulating layer 3 is laminated on the entire surface including the above, and the pattern of the bonding pad 5 is formed on the portion excluding the upper portion of the spherical surface 2. The substrate 1, the electron emission region on the spherical surface 2, the insulating layer 3, the electrode layer 4, and the bonding pad 5 constitute a cold cathode 6, which is prepared in advance by a usual processing method. The cold cathode 6 is fixed on a movable mechanism 7 of the FIB processing apparatus, and the focused ion beam 8 is irradiated from the ion beam generator 9 to the spherical surface 2 portion serving as an electron emission region.

The movable mechanism 7 controls the position and direction of the substrate 1 so that the angle of the ion beam 8 incident on a specific point on the spherical surface 2 to be processed is always perpendicular to the curved surface at that point. That is, the position and direction of the substrate 1 are controlled so that the ion beam 8 always passes through the curvature center O of the curved surface 2 or in the vicinity thereof while processing an arbitrary curved surface point.

Further, the ion beam generator 9 is used to change the ion beam 8 by a very small amount to form the structure shown in FIG. Example 2 FIG. 2 is a structural diagram showing the structure of an electrolytic radiation cold cathode according to a second example of the present invention, which is an example cathode 6 processed by irradiation with FIB.
It is an enlarged view of the portion of the spherical surface 2. In the processing setting state shown in FIG. 1, by controlling the circular processing of the ion beam 8 so as to draw a circle having a diameter of 1 μm or less, the electrode layer 4, the insulating layer 3 and a part of the substrate 1 in this portion are removed, An opening 11, a cavity 12 and a conical emitter 13 as shown in FIG. 2 are simultaneously formed. The opening 11, the cavity 12, and the emitter 13 form a micro cold cathode 14, which is the minimum unit of the electron emission structure.

Ishikawa et al. Reported a method of forming a micro cold cathode on a flat substrate by FIB (IVMC 94 Techn. Digest pp.
37-40, 1994). Third Embodiment FIG. 3 shows a principle sectional structure view of an electron gun which is a third embodiment of the present invention. In FIG. 3, the Wehnelt electrode 21 is placed immediately in front of the cold cathode 6, and the anode 22 is further placed in front of the Wehnelt electrode 21. Cold cathode 6 spherical surface 2
A large number of micro-cold cathodes 14 are formed on the substrate, and a voltage of several tens of volts that makes the electrode layer 4 positive is applied between the substrate 1 and the electrode layer 4, which are electron emission regions, and electrons are emitted from the tip of the emitter 13. Is emitted. The Wehnelt electrode 21 is applied with the same potential or a negative potential as the substrate 1 or the electrode layer 4, and the anode 22 is applied with a voltage of 1 kV to several kV with respect to the substrate 1. When the conditions of the Pierce electron gun are satisfied by the shapes of the substrate 1, in particular, the spherical surface 2 serving as the electron emission region, the Wehnelt electrode 21, the anode 22 and the voltages of the Wehnelt electrode 21 and the anode 22, the electrons emitted from the electron emission region are laminar. The flow is converged on the flow and passed through the opening formed in the anode 22.

As described above, since the focused electron gun satisfying the design condition of the pierce electron gun can be realized, the current density is high,
A small electron ripple and a stable electron beam can be formed. Furthermore, in order to achieve an electron beam with the same current density, the focusing ratio of the electron gun (the ratio between the cathode type and the electron beam diameter) can be increased without increasing the current density of the cathode, so that the cathode, especially the emitter tip, can be heated. It is possible to realize an electron gun with a long life without causing the above problems. Embodiment 4 FIG. 4 shows a structural diagram of an electrolytic radiation cold cathode which is a fourth embodiment of the present invention. In FIG. 4, a substrate 31 has a spherical surface 32 formed by a mechanical method with a polar radius of an electron gun design, and an electron emission layer 33 is laminated on the spherical surface 32 to form a cathode 34.

The substrate 31 is made of, for example, silicon, a metal, or single crystal diamond or c.
BN is used. The electron emission layer 33 is a material containing a material having a low work function, and is preferably a material containing one or at least two of single crystal diamond, polycrystalline diamond, and amorphous diamond. Here, the material contains one or at least two of amorphous diamond. Here, the amorphous diamond is a thin film formed by a carbon laser ablation technique or the like, and is in an amorphous state, an extremely minute diamond crystal state, or a state in which these are mixed. Polycrystalline diamond is plasma C
It is made by vapor phase growth such as VD method or hot filament CVD method.

An electron-emitting electron element using only a diamond thin film is disclosed in JP-A-6-36680, and a flat display device using only a diamond thin film is also disclosed in JP-A-6-20883.
It is disclosed in Japanese Patent Publication No. 5 but it goes without saying that it does not suggest the present embodiment. Embodiment 5 FIG. 5 shows a principle cross-sectional structural diagram of an electron gun which is a fifth embodiment of the present invention. 5, the substrate 31 has a spherical curved surface as shown in FIG. 4, and the electron emission layer 33 is formed on the curved surface.
Is made. Number of entire surface of the base 31 10 μm to about 200
to cover the entire surface of the electron emission layer 33 at μm,
A cathode grid 35 having a curved surface along the curved surface of the substrate 31 is placed. The Wehnelt electrode 21 is arranged immediately in front of the cathode grid 35, and the anode 22 is further placed ahead of the Wehnelt electrode 21. The substrate 31, the cathode grid 35, the Wehnelt electrode 21, and the cathode 22 are insulated from each other so that an independent voltage can be applied.

Between the substrate 31 and the cathode grid, a voltage of DC furniture 10 V having a positive cathode grid 35 is applied, and electrons are emitted from the electron emission layer 33. The same potential or a negative potential as the substrate 31 or the cathode grid 35 is applied to the Wehnelt electrode 21, and the anode 22 is applied with a voltage of 1 kV to several kV with respect to the substrate 31. The shapes of the substrate 31, particularly the spherical surface 32 serving as an electron emission region, the Wehnelt electrode 21, the anode 22, and the Wehnelt electrode 21, the anode 22.
When the conditions of the Pierce electron gun are satisfied by the voltage of, the electrons emitted from the electron emission region are focused in a laminar flow state and pass through the opening formed in the anode 22. Embodiment 6 FIG. 6 shows a principle cross-sectional structure diagram of an electron gun which is a sixth embodiment of the present invention. In FIG. 6, the cathode grid 35 and the substrate 31
A second cathode grid 36, which is aligned with the cathode grid 35, is arranged between the two, and a slightly negative voltage is applied to the substrate 31.

In Example 5 shown in FIG. 5, some of the electrons emitted from the electron emission layer 33 collide with the cathode lattice 35 to which a positive voltage is applied to the substrate 33, and become a cathode lattice current. . However, in the sixth embodiment shown in FIG. 6, due to the negative voltage applied to the second cathode grid 36, electrons are emitted from the electron emission layer 33 into the cathode grid 35 and the second cathode grid 3.
It does not enter 6. Example 7 Microwave tube (traveling wave tube) according to Example 7 of the present invention
FIG. 7 shows a principle cross-sectional view of the above. The electrons emitted from the electron emission surface 101 of the cold cathode 105 are the Wehnelt electrode 10
2. It is focused by the electrolysis formed by the anode 103 and the example cathode 105, shrinks in shape as it moves away from the cold cathode 105, and passes through the anode 103. Electron beam 10
4 reaches the collector 108 while passing through the inside of the helix 106 while being converged to a constant beam diameter under the influence of the magnetic force lines generated by the magnet 107.

While passing through the helix 106, the input electromagnetic wave traveling along the flix 106 interacts with the electron beam, converting the direct current energy in the electron beam 104 into the electromagnetic wave energy and amplifying it.

[0033]

As described above, according to the present invention, a focusing type electron gun using a cold cathode as an electron source can be realized, so that the following advantages occur.

By adopting a cold cathode for the electron gun,
The heater power is not required, the power consumption can be reduced, the thermal structure design near the cathode can be simplified, and the electron gun without the time delay from the power-on to the operation state can be tested.

Further, since the focused electron gun can realize the design condition of the pierce electron gun, it has the above advantages and at the same time,
An electron gun having a high current density, a small ripple, a stable electron beam and a long life can be realized.

As a result, if the electron gun of the present invention is applied to a microwave tube such as a traveling wave tube or a klystron, it is possible to increase the output, increase the frequency, stop the voltage, and extend the life of the tube. Further, when it is applied to an electron gun of a device using a large current electron beam such as an electric beam processing device and an electron beam accelerating device, the life and performance of these devices can be extended.

[Brief description of drawings]

FIG. 1 is a principle configuration perspective view showing a method for manufacturing an electrolytic radiation cold cathode according to a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional perspective view showing the structure of an electrolytic radiation cold cathode according to a second embodiment of the present invention.

FIG. 3 is a sectional view of an electron gun that is a third embodiment of the present invention.

FIG. 4 is a partial sectional perspective view of a field emission cold cathode according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of an electron gun that is a fifth embodiment of the present invention.

FIG. 6 is a sectional view of an electron gun that is a sixth embodiment of the present invention.

FIG. 7 is a sectional view of a microwave tube according to a seventh embodiment of the present invention.

FIG. 8 is a cross-sectional view of a conventional pierce electron gun.

FIG. 9 is a conceptual diagram of a traveling wave tube of a conventional technique disclosed in Japanese Patent Laid-Open No. 5-266809.

FIG. 10 is a cross-sectional view of an electron gun portion of a traveling-wave tube according to the related art disclosed in Japanese Patent Laid-Open No. 5-266809.

FIG. 11 is a method for manufacturing a three-dimensional contour shape FEA disclosed in JP-A-6-290702.

FIG. 12 is a sectional view of a spherical FEA disclosed in Japanese Patent Laid-Open No. 4-249841.

[Explanation of symbols]

 1 Substrate 2 Spherical Surface 3 Insulating Layer 4 Electrode Layer 5 Bonding Pad 6 Cold Cathode 7 Moving Mechanism 8 Ion Beam 9 Ion Beam Generator 11 Opening 12 Cavity 13 Emitter 14 Micro Cold Cathode 21 Wehnelt Electrode 22 Anode 23 Electron Beam 31 Substrate 32 Spherical 33 Electron emission layer 34 Cold cathode 35 Anode lattice 36 Second cathode lattice 101 Electron emission surface 102 Wehnelt electrode 103 Anode 104 Electron beam 105 Cold cathode 106 Helix 107 Magnet 108 Collector 110 Electron emission region 111 Substrate 112 Insulation layer 113 Gate electrode 114 Cavity 115 Emitter 116 Front glass

Claims (7)

[Claims] 1. A cooling device comprising: a substrate (31) having a spherical curved surface (32) on its surface; and a thin-film electron emission layer (33) laminated on the curved surface (32). cathode. 2. The electron emission layer (33) comprises any one or at least any one of single crystal diamond, polycrystalline diamond and amorphous diamond as a constituent material. Cold cathode. 3. A cold cathode (34) having a substrate (31) having a spherical curved surface (32) on its surface and a thin-film electron emission layer (33) laminated on said curved surface (32), The electron emission layer (3) is located in front of the cold cathode (34).
3) A grid-shaped electrode (35) having a curved surface along the curved surface (32), and a beam forming electrode (2) positioned in front of the electrode (35) and surrounding the electron emission layer (33).
1) A cold cathode electron gun, which is configured to have an anode 22. 4. The cold cathode (34) and the electrode (35)
Between the cold cathode (34) and the electrode (35)
And a second electrode (36) which is insulated and has a lattice aligned with the lattice of the electrode (35) and in which a curved surface is formed along the electrode (35). The cold cathode electron gun according to claim 3. 5. A substrate (1) partially formed with a spherical curved surface (2), and a plurality of minute electron emission structures (14) formed on the curved surface (2), Focused ion beam (8) in which the minute electron emission structure (14) passes through or near the center of curvature of the curved surface (2).
A cold cathode formed by. 6. The cold cathode (6) according to claim 5, a beam forming electrode (21) positioned in front of the cold cathode (6) and surrounding the curved surface (2), and an anode (22). And a cold cathode electron gun. 7. A microwave tube using the cold cathode electron gun according to claim 3, 4, or 5 as an electron beam source.