KR20070115404A - Klystron oscillator using cold cathode electron gun, and oscillation method - Google Patents

Abstract

A Klystron oscillator using a cold cathode electron gun and an oscillation method thereof are provided to extend a time required to stably operate a cold cathode vacuum electron device by lowering a current density of a cold cathode and raising a current density of a final electron beam. An electron source(11) has a cold cathode for emitting a primary electron. A first grid(20) focuses and accelerates an electron beam emitted from the electron source, and a second grid(30) focuses and accelerates the electron beam passing through the first grid, and has a resonator converting a part of mechanical energy of the electron beam into an electromagnetic wave energy. A secondary electron cold cathode(40) generates a secondary electron by colliding the electron beam passing through the second grid. The focusing and acceleration of the electron beam passing through the first grid and the second grid are implemented by a DC power supply.

Description

Klystron oscillator using cold cathode electron gun and its oscillation method {KLYSTRON OSCILLATOR USING COLD CATHODE ELECTRON GUN, AND OSCILLATION METHOD}

1 is a view illustrating a structure of a conventional cold cathode electron gun,

2 is a schematic diagram illustrating an internal structure of a klystron oscillator including a cold cathode and a vacuum electronic device having an electron amplification circuit according to the present invention;

3 is a diagram showing the field emission of the primary electrons and the propagation in each section of the electron beam and the internal structure of the oscillator;

4 is a view showing the electron beam emission by the field emission in the cold cathode for secondary electron emission absorbing the primary electrons and the progress in the intervals 2 and 3 of the electron beam and the structure inside the entire oscillator according to the present invention,

5 is a flowchart illustrating an electromagnetic wave oscillation method corresponding to the Klystron oscillator according to the present invention.

<Description of the symbols for the main parts of the drawings>

10 electrode substrate, 11 field emission structure (FEAs), 20 first grid, 30 second grid, 35 resonator 40 secondary electron cold cathode, 50 first voltage, 60 second voltage,

70: third voltage

The present invention relates to a Klystron oscillator, and more particularly, to a cold cathode Klystron oscillator and oscillation method using a cold cathode electron gun by using electron amplification by secondary electron emission.

Electron beams that focus electrons in space are widely used in various industrial and research equipments such as RF oscillation, amplifiers, displays, accelerators, electron microscopes, sensors, and various process equipment. There are many ways to make an electron beam, and the current widely used method is to accelerate and use hot electrons protruding from the metal surface when heating the metal.

As an opposite technology of such a hot cathode electron gun, there is a cold cathode electron gun which obtains electrons through field emission by applying a voltage without heating.

1 is a view illustrating the structure of a conventional cold cathode electron gun. Field Emitter Arrays (FEAs) 110 are stacked on the cathode 200, and a voltage V ₁ is applied to the grid 130 as an anode to emit and collect electron beams to focus and accelerate. .

Such a cold cathode electron gun has the advantage of low power consumption and simple structure without the process of heating the cathode like a hot cathode electron gun. In particular, the field emitter array (FEAs) cold cathode electron gun in FIG. 1 may utilize the protrusion 110 and the micrometer-scale electrode which are easy to emit a field in a micrometer or nanometer scale, and thus the size of various elements using the electron gun. It can be significantly reduced and a pre-modulated electron beam can be obtained even with a small voltage of several volts.

In addition, the company has successfully processed a micrometer-scale vacuum triode on a silicon wafer using a cold cathode electron gun using carbon nanotubes and a micro electro-mechanical system (MEMS). Research is underway to develop micro vacuum devices in the band.

However, despite the experimental success in some microwave bands, there are still many problems to be solved. In micrometer-scale vacuum electronic devices, the current density of electron beams for electromagnetic wave oscillation is much higher than the current density values that can be reliably obtained through current field emitter arrays (FEAs) cold cathode electron guns. This is one of the hardest problems that have not been solved yet, despite long research.

In addition, as it operates by cathode ray emission like conventional cathode ray tube (CRT), various technologies such as FED (Field Emission Display) and ultra-small X-ray generator, which have high luminous efficiency and wide viewing angle, and have a thin flat form Efforts are being made to replace the existing hot cathode electron guns in the field. However, as in most vacuum electron devices using cold cathodes, the physical characteristics of the electron beams obtained through cold cathodes are not sufficient to replace the existing hot cathodes.

Today's hot cathode electron guns can produce electron beams with hundreds of keV of energy and currents of hundreds of amperes. The current density of the electron beam emitted from the surface of the hot cathode reaches approximately 10 A / cm ² . Field Emitter Arrays (FEAs) cold cathode electron guns can emit electron beams with the same or higher physical quantities as hot cathodes under some limited conditions, but often have decisive problems in the performance conditions required for specific applications.

For example, in the case of a vacuum electronic device that converts the energy of an electron beam into electromagnetic energy, in order to make a high efficiency device in a microwave band, an electron gun capable of emitting an electron beam having a current density of approximately 1 A / cm ² or more is required and THz The band requires 1000 A / cm ² .

In addition, in the case of carbon nanotubes, which is a representative material used for FEA cold cathodes, 30nA can be obtained in a tube section having a diameter of several nanometers, which is a very large value compared to the current density obtained in a conventional hot cathode.

However, this is a value that can be obtained through one carbon nanotube. In general, a cold cathode using carbon nanotubes uses a cathode composed of a plurality of tubes to increase the total current. In such an environment, the current density decreases rapidly.

As can be seen from the Fowle-Nordheim relationship, which is the basic theory of field emission, to obtain a lot of current, the voltage between cold cathode and anode is increased. However, increasing the voltage causes problems such as discharge phenomena or the electron beam current changes severely with time, and in general, the life of the cold cathode is greatly reduced.

Therefore, the current or current density of electron beams that can be obtained through FEAs cold cathode electron guns that emit stable electron beams is generally very small compared to conventional hot cathode electron guns. Therefore, although many advantages, such as miniaturization, light weight, and efficiency, are expected, vacuum electronic devices using cold cathodes are still in the research stage.

In order to solve the above-mentioned problems, the present invention allows the FEAs cold cathode electron gun inside the oscillator to emit an electron beam under conditions that can operate stably for a long time, and uses the electron beam as a primary electron to emit a cold cathode. Amplify the total current by inducing an electron amplification phenomenon, including. In addition, the Klystron oscillator according to the present invention provides a structure that can simultaneously control the current amplification of the electron beam by the secondary electrons and the oscillation of the resonator.

A first feature of the cold cathode Klystron oscillator according to the present invention is an electron source by a cold cathode that emits primary electrons; A first grid for focusing and accelerating the electron beam emitted from the electron source; A second grid including a resonator for focusing and accelerating the electron beam passing through the first grid and converting a part of the dynamic energy of the electron beam into electromagnetic wave energy; And a secondary electron cold cathode that collides the electron beam passing through the second grid to generate secondary electrons, wherein the electron beam is focused and accelerated through a direct current power source.

In addition, the electron source is preferably formed of Field Emitter Arrays (FEAs), the DC power source is applied with a first voltage between the electron source and the first grid, the first It is also preferable that a second voltage is applied between the grid and the second grid, and a third voltage is applied between the second grid and the secondary electron cold cathode.

Preferably, the third voltage is opposite in polarity to the second voltage, and may have a magnitude smaller than that of the second voltage, and MgO, at a portion colliding with the primary electrons in the secondary electron cold cathode. A layer made of any one of GaP, GaAs, MgF ₂ , CaF ₂ , LiF, Al ₂ O ₃ , ZnO, CaO, SrO, SiO ₂ and La ₂ O ₃ may be formed, and an electromagnet may be used to focus the electron beam. Or it may be desirable to further include a permanent magnet.

In addition, as a second feature according to the present invention, the multiple cold cathode Klystron oscillator is characterized in that further connected at least one structure of the cold cathode Klystron oscillator of claim 1 in parallel.

On the other hand, as a third aspect according to the present invention, the electromagnetic wave oscillation method comprising the steps of: emitting primary electrons by a cold cathode electron source (electron source); Focusing and accelerating the emitted electron beam by a first grid and a second grid; Amplifying the electron beam by colliding the electron beam passing through the second grid with a secondary electron cold cathode having a field emission structure to generate secondary electrons; And converting a part of the dynamic energy of the amplified electron beam into electromagnetic wave energy to oscillate electromagnetic waves by a resonator included in the second grid.

And, as a fourth feature according to the present invention, the multiple electromagnetic wave oscillation method is a multiple electromagnetic wave oscillation method for connecting at least two or more structures in parallel using the electron beam amplification method of claim 9.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram illustrating an internal structure of a cold cathode electron gun according to the present invention. 5 is a flowchart illustrating an electromagnetic wave oscillation method corresponding to the Klystron oscillator according to the present invention. Hereinafter, both will be described in detail.

As shown in FIG. 2, the cold cathode electron gun according to the present invention includes an electron source 11 for generating electrons, a first grid 20 for focusing and accelerating an electron beam, a second grid 30 including a resonator, and two. It consists of a secondary electron cold cathode 40 which generates the secondary electrons and amplifies the electron beams. The primary and secondary electrons thus generated are accelerated and controlled by the DC voltage applied to the electron source, the first grid, the second grid, and the secondary electron cold cathode.

Here, the electron source is formed by stacking field emitter arrays 11 on the electrode substrate 10, and electrons are emitted by the first voltage with the first grid 20. In addition, the electron source is preferably formed of field emitter arrays (FEAs) 11.

The theoretical background of field emission is explained as follows. The tunneling of cold electrons into the vacuum at the surface of plate metals and semiconductors when a strong electric field is applied has already been foreseen by quantum mechanics, which is based on the electron's virtual potential and the potential energy of the applied electric field. It can be explained by the sum of.

In particular, when a strong electric field of 5 kV / μm or more is applied to the surface, the overall potential is changed to allow tunneling of electrons. However, when the FED is applied to a flat emitter, most of the metals in the electric field of 5 kV / μm or less tend to cause problems such as vacuum breakdown due to whisker formation. Research is being conducted on the sharp tip structure.

The current density due to the electric field applied to this type of emitter and the emitted electrons is generally described by the Fowler-Nordheim equation. In other words, it can be seen that the length of the electron terminating and the transmittance are closely related to the work function of the emitter and the applied electric field.

The relationship between the applied electric field and the emission current, described by the Fowler-Nordheim equation, is generally the smaller the radius of curvature of the emitter, the gate hole radius, the work function of the emitter material, and the higher the gate voltage, Is that the anode current increases.

This means that elements other than the work function, which is an inherent property of the material, can be improved through process development and modification of structural elements, resulting in the production of high efficiency emitter tips with the development of low work function materials and large area microlithography techniques. You can do it.

As such, as an electron source, it is possible to become a more efficient electron gun electron source through the development of the emitter tip, and the efficient control is possible through the structural change of the electron gun and the change of the DC power source.

The electron beam emitted from the electron source (S100) and passing through the first grid 20 is focused and accelerated by the second voltage 60 applied between the first grid 20 and the second grid 30 (S200). Pass through the second grid 30. The electron beam passing through impinges on the secondary electron cold cathode 40, and the secondary electron cold cathode 40 is laminated with a material having a high secondary electron emission yield on the surface of the secondary electron cold cathode 40 to act as one cold cathode. Will lead to release.

The electron beam amplification phenomenon in which the density of the electron beam is increased by the secondary electrons emitted in this manner and the primary electrons emitted from the electron source 11 occurs (S300). The second grid including the resonator is accelerated to, but blocked by the second voltage 60 opposite to the third voltage 70 applied in the section 3 and again amplified with the primary electrons. In part of the kinetic energy of the electron beam is converted into electromagnetic energy to oscillate electromagnetic waves.

As shown in FIG. 2, the cold cathode Klystron oscillator according to the present invention has a structure in which a resonator is added to a FEA cold cathode electron gun having an amplification structure through secondary electrons, and a region 2 (Region 2) and a region 3 (Region 3) are provided. It is a feature of the present invention. Each dimension of the structure of the present invention in Figure 2 serves to control the electromagnetic amplification phenomenon and to control the electromagnetic wave oscillation including a resonator.

The structure of the second grid 30 including the first grid 20 and the resonator 35 is an element that determines the electron beam passing rate. The electron beam passing rate of the second grid 30 is dependent on the electron amplification phenomenon caused by the secondary electrons. Influencing directly is an important factor in determining the amplification factor of the electron beam in the entire electron gun. Grid (lattice) structure can be a variety of structures and can achieve the object of the present invention through the principle all grid structure.

In addition, the second grid 30 Since it corresponds to a part of the resonator 35, the oscillation characteristics of the vacuum electronic device are affected. Also, the lattice structure of the second grid can achieve the object of the present invention through all the lattice structures utilized in principle in the vacuum electronic device.

As shown in Fig. 2, the second grid has a double lattice structure, and a resonator 35 including a resonator tube is connected to both sides of the lattice. Through this structure, in particular, it is composed of a Klystron oscillation type structure that absorbs a part of the kinetic energy of the electron beam amplified by the secondary electrons and passes through the second grid 30 to convert it into electromagnetic energy.

Here, the resonator has a rotational symmetry axis, but the shape of the resonator is not limited, such as cylindrical, polyhedral, and there is no limitation in the number of resonators. It is preferable that the first grid and the second grid are suitable patterns capable of all types of patterns through which an electron beam can pass, and can perform a role of an oscillator and a function of focusing and accelerating the electron beam.

In addition, the second grid 30 including the resonator 35 serves as an electrode. The resonator has an electrode structure protruding from the grating of the second grid, and this structure has two functions. In the periods 2 and 3, the electron beams are properly focused to control the electron amplification phenomenon by the secondary electron emission and the physical characteristics are controlled to have the conditions suitable for the oscillation conditions.

In FIG. 2, one side of the secondary electron cold cathode is a cold cathode that emits secondary electrons, and in general, the electron amplification phenomenon increases as the material having a maximum secondary electron emission coefficient (δ _max ) increases. The optimal secondary electron emission coefficient δ _op can be varied in consideration of the dimensions of the oscillator structure, the voltage, the screening effect, or the repulsive force due to space charge.

Here, the principle of the generation of secondary electrons is that the energy of the primary electron (primary electron) irradiated on the sample surface interacts with the electrons in the orbit of the atoms constituting the sample to transfer energy to the orbital electrons. Orbital electron refers to the principle of emitting to the outside. That is, it is caused by inelastic scattering between the incident electron beam and the sample. The amount of emitted secondary electrons varies depending on the degree of bending of the sample surface, and the information has two-dimensional shape on the surface.

Therefore, the cold cathode for secondary electron emission is any one of MgO, GaP, GaAs, MgF ₂ , CaF ₂ , LiF, Al ₂ O ₃ , ZnO, CaO, SrO, SiO ₂ and La ₂ O ₃ with high secondary electron emission coefficient. In addition, various materials can be laminated | stacked on various board | substrates, such as a metal or a silicon (Si) wafer in which the electrode was formed.

As shown in FIG. 2, the Klystron oscillator according to the present invention requires at least three voltage settings. The second voltage V ₂ 60 and the third voltage V ₃ 70 are voltages applied to the interval 2 and the interval 3, respectively, and the second voltage V ₂ 60 is the first voltage V _1. The electron beam accelerated by) 50 continues to be accelerated in the same direction, and the third voltage V ₃ 70 causes the electron beam to decelerate. The first voltage V ₁ (50) is a voltage that determines the final energy obtained by the electron in the region 1 (Region 1) when the electron enters the interval 2 has an energy of eV ₁ .

As described above, it is preferable to use a DC power source for controlling the electron beam. In the case of an AC power source, the circuit configuration is complicated and only a pulsed electron beam can be formed. It is simple and easy to control, and has the advantage of selectively forming both pulsed and continuous electron beams.

And when the electrons are absorbed in the secondary electronic material with eV _{δ max} , the gain of the secondary electrons by the primary electrons becomes maximum, so that the secondary electron emission is maximized in the cold cathode 45 for secondary electron emission. The relationship between V ₁ (50), V ₂ (60), and V ₃ (70) is V _{δ max} = V ₁ + V ₂ -V ₃ . And, it is also preferred that V ₂ 60 is always configured to be larger than V ₃ 70.

3 and 4 will be described the configuration and principle of the present invention through a conceptual diagram showing the generation of the primary and secondary electrons and the progress in the interval 1-3.

3 is a view showing the field emission of the primary electrons and the progress in each section of the electron beam and the internal structure of the oscillator. The primary electron beam generated from the FEAs cold cathode electron source of the oscillator is continuously accelerated in section 2 and then decelerated in section 3 so that some 90 collides with and is absorbed by the secondary electron emission material to emit secondary electrons. Here, the energy of electrons of the primary electron beam absorbed by the secondary electron emission material is e (V ₁ + V ₂ -V ₃ ) and this value is approximately eV _{δ max} .

The structure of each plate including the first grid 20 and the second grid 30 is set to be absorbed by the secondary electronic material while keeping the electron beam properly focused. In addition, it is preferable to further include an electromagnet or a permanent magnet to facilitate the concentration of the linear electron beam, it is located in the side or an appropriate position of the oscillator has the advantage that it can play a big role in uniform focusing and direction control (not shown). Not)

4 is a view showing the electron beam emission by the field emission in the cold cathode for secondary electron emission absorbing the primary electrons and the progress in the interval 2 and 3 of the electron beam and the structure of the entire oscillator according to the present invention.

The secondary electrons 95 generated at the position of the secondary electron cold cathode 40 are accelerated by the voltage V ₃ (70) in the section 3 and enter the section 2. In the section 2, the secondary electrons 95 are decelerated by the V ₂ (60) and the section 2 After stopping at, you change your direction and reenter section 3. (Always V ₂ Is larger than V _3.) In this case the structure of the plate containing each dimension value in particular the first grid 20 and second grid 30 of the internal structure of the electron gun is to be set up to suitably focus the electron beam, V _1, All mechanical structures, including V ₂ and V ₃ values and the current value of the electron beam, are affected.

In addition, the electron beam passes through the second grid 30 including the resonator 35 again before entering the section 3 in the section 2, and if the appropriate conditions are satisfied, the kinetic energy of the electron beam is converted into the electromagnetic wave 37 energy and the resonator Oscillate. This oscillation process is the same as the oscillation principle of the conventional reflective Klystron.

That is, a part of the mechanical energy of the electron beam reflected in the section 2 and passing through the resonator is converted into the electromagnetic wave 37 energy, and as shown in FIG. 4, the detailed structure of the portion connecting the resonator 35 to the external load is omitted. In this resonator, some electromagnetic waves 37 are generated to be connected to an external load (not shown).

In addition, the electron beam passing through the second grid 30 is decelerated again in the section 3 and loses almost all the kinetic energy near the secondary electron cold cathode 40. In detail, some electrons have zero or more kinetic energy when they reach the secondary electron cold cathode surface, and some do not have sufficient kinetic energy when entering the section 3 and thus do not reach the secondary electron cold cathode 40.

The variation of the energy distribution is much larger than the energy distribution of the initial secondary electrons generated in the secondary electron cold cathode 40, which is caused by the screening effect and the space charge force and each electrode ( It is determined by various factors such as focusing by 20, 30, 40, energy exchange with the resonator 35, and the like.

As such, the secondary electrons reabsorbed by some secondary electron emitting materials due to the increase of the energy distribution deviation may have energy enough to generate another secondary electron. As such, some secondary electrons may be primary electrons generating new secondary electrons. In principle, this chain reaction repeats indefinitely, increasing the number of electrons in sections 2 and 3, eventually converging to a constant value, depending on the conditions of the given circuit.

All electrons passing through the section 3 and the second grid 30 and entering the section 2 and entering the second grid 30 may contribute to the oscillation of the resonator. However, in the case of the reflective Klystron, an example of the vacuum electronic device proposed in the present invention, the electron beam supplied through the section 1 has little effect on the oscillation of the resonator.

These electrons only act as primary electrons in the secondary electron cold cathode 40. Between the interval 2, interval 3 and the second grid 30, the number of secondary electrons generated by suitable conditions is several to several tens of times larger than the number of primary electrons. The effect by secondary electrons is dominant.

Electromagnetic energy converted from the electron beam accumulates in the resonator, part of which is dissipated in the resonator, part of which is consumed by the speed modulation of the electron beam, and part of which can be transmitted to external load. Thus, the structure for connecting the resonator and the external load is the same as the structure of the resonator 35 shown in FIG. Such a structure can be utilized in all general methods used in the resonator of the vacuum electronic device.

In another embodiment of the present invention, when multiple electron guns having the basic structure of FIG. 2 are connected in parallel, an amplified multi-electron beam may be formed to form an amplified multi-electron beam, thereby making an electromagnetic wave oscillation device accordingly. have. This multiple klystron oscillator connected in parallel is the same as the example of the present invention shown in Figure 2, by forming a variety of beams by changing the dimensions and power supply of each structure, it is possible to oscillate electromagnetic waves of various frequencies accordingly. That is, by providing a multi-electron beam having a variety of characteristics to provide a high-efficiency multiple electromagnetic wave oscillation method capable of oscillating a variety of electromagnetic waves, by using the method can provide a cold cathode multiple Klystron oscillator.

While the invention has been shown and described in connection with specific embodiments thereof, it is well known in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

When providing the Klystron oscillator and the oscillation method according to the present invention, as a component of the oscillator, the cold cathode electron gun is added to the existing cold cathode electron gun by the electron amplification phenomenon by the secondary electrons dozens-hundreds of times higher than the conventional It is possible to stably emit a linear electron beam having a current density.

In addition, the electron amplification circuit provided in the present invention can increase the current density of the final electron beam while lowering the current density in the FEAs cold cathode that provides the primary electrons, thereby extending the time for stable operation of the cold cathode vacuum electronic device. It works.

In this way, the amplified secondary electrons are used for oscillation of the vacuum electronic device, so that the output or oscillation frequency band can be increased, and the resonator performs the role of the circuit of the electrode and the vacuum electronic device constituting the electron gun simultaneously. By minimizing the number of electrodes required for the configuration, minimizing the size of the device, and minimizing the path of the electron beam, it reduces the loss of the electron beam and increases the overall efficiency of the device.

Claims (9)

An electron source by a cold cathode that emits primary electrons; A first grid for focusing and accelerating the electron beam emitted from the electron source; A second grid including a resonator for focusing and accelerating the electron beam passing through the first grid and converting a part of the dynamic energy of the electron beam into electromagnetic wave energy; And And a secondary electron cold cathode that collides the electron beam passing through the second grid to generate secondary electrons. Wherein the electron beam is focused and accelerated through a direct current power source. The method of claim 1, The electron source (electron source) is cold cathode Klystron oscillator, characterized in that formed by field emitter arrays (FEAs). The method of claim 1, The DC power is applied with a first voltage between the electron source and the first grid, a second voltage is applied between the first grid and the second grid, the second grid and the secondary electron cold cathode Cold cathode Klystron oscillator, characterized in that the third voltage is applied between. The method of claim 3, And the third voltage is opposite in polarity to the second voltage and smaller in magnitude than the second voltage. The method of claim 1, One of MgO, GaP, GaAs, MgF ₂ , CaF ₂ , LiF, Al ₂ O ₃ , ZnO, CaO, SrO, SiO ₂ and La ₂ O ₃ in the portion colliding with the primary electrons in the secondary electron cold cathode A cold cathode klystron oscillator characterized in that a layer of material is formed. The method of claim 1, The cold cathode Klystron oscillator further comprises an electromagnet or a permanent magnet for focusing the electron beam. The multiple cold cathode klystron oscillator of claim 1, further comprising at least one structure of the cold cathode klystron oscillator further connected in parallel. In a method for oscillating electromagnetic waves through an electron beam, Emitting primary electrons by a cold cathode electron source; Focusing and accelerating the emitted electron beam by a first grid and a second grid; Amplifying the electron beam by colliding the electron beam passing through the second grid with a secondary electron cold cathode having a field emission structure to generate secondary electrons; And And oscillating electromagnetic waves by converting a part of the dynamic energy of the amplified electron beam into electromagnetic energy by a resonator included in the second grid. A multiple electromagnetic wave oscillation method for connecting at least two or more structures in parallel using the electron beam amplification method of claim 9.

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