Method for inhibiting micro discharge of space traveling wave tube

Abstract

The invention provides a method for inhibiting micro discharge of a space traveling wave tube, which comprises the space traveling wave tube and comprises the following steps of: depositing an aluminum oxide film on the surface of a ceramic original sample by adopting an alternating action mode of a plurality of precursors; the ceramic original sample is that no film is deposited on the ceramic surface of the space traveling wave tube. The various precursors are trimethylaluminum and water; the deposition temperature is 250 DEG C to 350 DEG C. According to the method, the secondary electron emission coefficient of the surface of the ceramic original sample is reduced and the flashover voltage along the surface is improved by depositing the aluminum oxide thin film on the surface of the ceramic original sample, so that the probability of micro discharge of the space traveling wave tube is reduced, and the method has a relatively good application prospect in the aspect of solving the micro discharge of the space traveling wave tube; the method has important application value for improving the reliability of the space traveling wave tube in the spacecraft.

Description

Technical Field

[0001] The invention belongs to the field of electronic science and technology, relates to a space traveling wave tube, and specifically relates to a method for suppressing micro discharge of a space traveling wave tube. Background Art

[0002] As the final power amplifier of the spacecraft microwave system, the space traveling wave tube is a key component of the satellite payload. The traveling wave tube has the significant advantages of wide operating frequency band, large output power, high efficiency, large dynamic range and strong environmental adaptability. It is widely used in the fields of national economy and national defense equipment such as satellite communications, radar detection and electronic countermeasures. In recent years, the problem of micro discharge of space traveling wave tubes has frequently occurred in orbit and during the development process. Once a micro discharge problem occurs in the space traveling wave tube, it will cause the space traveling wave tube power supply to automatically restart or shut down, seriously affecting the continuity of communication. Summary of the invention

[0003] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for suppressing micro discharges of a space traveling wave tube, so as to solve the technical problem in the prior art that the probability of micro discharges of a space traveling wave tube needs to be further reduced.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0005] A method for suppressing micro discharge of a space traveling wave tube comprises a space traveling wave tube. The method adopts a plurality of precursors to alternately act to deposit an aluminum oxide film on the surface of a ceramic original sample.

[0006] The multiple precursors are trimethylaluminum and water.

[0007] The deposition temperature is 250°C to 350°C.

[0008] The present invention also has the following technical features:

[0009] Preferably, the thickness of the aluminum oxide film is 5 nm to 100 nm.

[0010] Specifically, the method comprises the following steps:

[0011] Step 1: clean the surface of the ceramic original sample to remove pollutants on the surface of the ceramic original sample to obtain a cleaned ceramic original sample.

[0012] Step 2: evacuate the reaction chamber and heat it to the deposition temperature, then put the cleaned ceramic obtained in step 1 into the reaction chamber for preheating, while controlling the temperature of the precursors, namely trimethylaluminum and water.

[0013] Step 3: After the ceramic original sample is preheated, the trimethylaluminum and water whose temperature is controlled in step 2 are used to interact with the surface of the ceramic original sample in an alternating manner, and then the surface of the ceramic original sample is purged with gas.

[0014] Step 4, repeating step 3, and performing a cycle to achieve a set reaction cycle, so that the aluminum oxide film grows layer by layer on the ceramic original sample.

[0015] Step 5: After the reaction is completed, turn off the precursor and the purge gas, and take out the product after the reaction chamber cools down to room temperature, thereby obtaining a ceramic sample after the aluminum oxide film is deposited.

[0016] Preferably, in step 1, the cleaning agent used to clean the surface of the original ceramic sample is a water-soluble organic solvent and deionized water.

[0017] Preferably, in step 2, the vacuum is drawn until the vacuum degree of the reaction chamber is less than 10 -1 Torr.

[0018] In step 2, the cleaned ceramic obtained in step 1 is placed in the center of the reaction chamber.

[0019] In step 2, the preheating time is 10 to 30 minutes.

[0020] In step 2, the temperature of the precursors, i.e., trimethylaluminum and water, is controlled to be 22°C with an accuracy of no more than ±2°C.

[0021] Preferably, in step three, the trimethylaluminum and water interact with the original ceramic surface in an alternating manner, wherein the trimethylaluminum interacts with the original ceramic surface for 0.1 s, and the water interacts with the original ceramic surface for 0.3 s.

[0022] In step three, the gas is nitrogen, argon or helium, the gas flow rate is 40sccm, and the accuracy does not exceed ±5sccm.

[0023] In step three, the thickness of the aluminum oxide film initially formed is calibrated and the cycle period is set so that the thickness of the aluminum oxide film on the ceramic sample after the aluminum oxide film is deposited is 5nm to 100nm.

[0024] Compared with the prior art, the present invention has the following technical effects:

[0025] (I) The present invention utilizes the method of depositing an aluminum oxide film on the surface of a ceramic original sample to achieve a reduction in the secondary electron emission coefficient of the ceramic original sample surface and an increase in the surface flashover voltage, thereby reducing the probability of occurrence of micro-discharges in space traveling wave tubes. The present invention has good application prospects in solving micro-discharges in space traveling wave tubes and has important application value for improving the reliability of space traveling wave tubes in spacecraft.

[0026] (II) The method of the present invention has the advantage that the deposited aluminum oxide film is not easy to fall off after long-term use, because the deposited aluminum oxide film is made of the same material as the original ceramic sample and has strong bonding force. Compared with films deposited from other materials, the film has the advantage of being difficult to fall off after long-term use. At the same time, the prepared film has high stability and is not easy to oxidize and corrode over time, and is suitable for long-term use of space traveling wave tubes. In addition, the method of the present invention only changes the surface state of the original ceramic sample after treatment, and does not change the dielectric constant and other insulation properties of the original ceramic sample surface itself, and does not affect other properties of the space traveling wave tube.

[0027] (III) Compared with other process methods, the method of the present invention does not add additional devices to the space traveling wave tube. At the same time, the aluminum oxide film formed by this method has good consistency, high uniformity, good density, good bonding strength and is not easy to fall off. The film thickness can be accurately controlled by controlling the number of reactions.

[0028] (IV) The method of the present invention can be used for surface treatment of ceramics with complex structures and has strong adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flow chart of a method for suppressing tiny discharges in a space traveling wave tube.

[0030] FIG. 2( a ) is a characteristic curve diagram of the secondary electron emission coefficient of the original ceramic sample.

[0031] FIG. 2( b ) is a characteristic curve diagram of the secondary electron emission coefficient of the ceramic sample after a 10 nm aluminum oxide film is deposited in Example 1. FIG.

[0032] Figure 3 This is a relationship diagram between the flashover voltage and the flashover number of the original ceramic sample, the ceramic sample after depositing a 10nm aluminum oxide film in Example 1, and the ceramic sample after depositing a 10nm TiN film in Comparative Example 1.

[0033] Figure 4 Graphs of the first and 20th surface flashover voltages of the original ceramic sample and samples after 5nm, 10nm, 15nm, 20nm and 30nm aluminum oxide films are deposited on the surface of the original ceramic sample using the method of the present invention in Examples 1 to 5, respectively.

[0034] FIG5( a ) is an XPS spectrum of the sample surface at the initial moment after a TiN film is deposited on the surface of the original ceramic sample in Comparative Example 2.

[0035] FIG5( b ) is an XPS spectrum of the sample surface after a TiN film is deposited on the surface of the original ceramic sample in Comparative Example 2 for 120 days.

[0036] The specific contents of the present invention are further explained in detail below in conjunction with embodiments. DETAILED DESCRIPTION

[0037] It should be noted that all raw materials and instruments in the present invention, unless otherwise specified, are all raw materials and instruments known in the prior art. For example, trimethylaluminum is commercially available trimethylaluminum.

[0038] In the present invention, the ceramic as is refers to the ceramic surface of the space traveling wave tube without any film deposited thereon.

[0039] The technical idea of ​​the present invention is: there are a large number of three-phase junctions of metal, ceramic and vacuum inside the space traveling wave tube, the electrode surface at the three-phase junction emits initial electrons, and the secondary electron emission process on the ceramic surface multiplies the electrons and forms charge migration, and finally forms a micro discharge on the medium. Therefore, by reducing the secondary electron emission coefficient on the ceramic surface, the electron multiplication process can be effectively suppressed, thereby reducing the probability of micro discharge in the space traveling wave tube.

[0040] The secondary electron emission on the surface of the material is closely related to the material itself, microscopic morphology, surface adsorption, oxidation or pollution. Space traveling wave tubes use ceramics as insulation and support materials. The ceramics are formed by sintering process, and the surface is relatively rough and porous. Based on the above reasons, the present invention deposits tens to hundreds of nanometers of aluminum oxide film on the surface of the ceramic through the interaction between trimethyl aluminum and water and ceramics, forming a more dense and smooth film, which can effectively suppress the secondary electron emission coefficient. At the same time, the aluminum oxide film and the ceramic are made of the same material but different processes, so the surface bonding force is strong and not easy to fall off, which is particularly suitable for the space traveling wave tube to be used in space for decades. In addition, compared with ion implantation and insulator doping methods, the method in the present invention will not reduce the insulation performance of ceramic materials; compared with magnetic field suppression methods, the method in the present invention does not add additional devices; compared with functional gradient materials, the method in the present invention will not cause local magnetic field distortion and external force cracking problems. Therefore, using trimethyl aluminum and water to interact with the ceramic surface to form a dense and smooth aluminum oxide film is a very potential method for suppressing micro discharges in space traveling wave tubes.

[0041] In the present invention, the ceramic sample after the aluminum oxide film is deposited refers to the ceramic surface of the space traveling wave tube on which the aluminum oxide film of a specified thickness is deposited.

[0042] In the present invention, room temperature refers to the natural environment temperature during the production process, and usually, the temperature is generally within the range of 20±10°C.

[0043] In the present invention, Torr is a unit of pressure, and 1 Torr is equal to 1.33322×10 2 Pa.

[0044] In the present invention, sccm is a gas flow unit, and sccm refers to standard cubic centimeters per minute.

[0045] In the present invention, SEY refers to the secondary electron emission coefficient.

[0046] In accordance with the above technical scheme, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical scheme of this application fall within the protection scope of the present invention.

[0047] Embodiment 1:

[0048] This embodiment provides a method for suppressing micro discharges in a space traveling wave tube. The method uses a plurality of precursors to alternately act to deposit an aluminum oxide film on the surface of a ceramic sample.

[0049] The various precursors are trimethylaluminum and water.

[0050] The deposition temperature was 300°C.

[0051] In this embodiment, the purity of trimethylaluminum is 99.9999%; the purity of water is 99.9999%, and the resistivity is greater than 18 MΩ.

[0052] The ceramic in the ceramic sample is made of more than 95% alumina by sintering process.

[0053] The thickness of the aluminum oxide film is 10 nm.

[0054] like Figure 1 As shown, the method specifically comprises the following steps:

[0055] Step 1: Use a water-soluble organic solvent and deionized water to clean the surface of the ceramic original sample to remove pollutants on the surface of the ceramic original sample to obtain a cleaned ceramic original sample.

[0056] In this embodiment, anhydrous ethanol and deionized water are used to ultrasonically clean the surface of the ceramic sample, and after cleaning, a nitrogen gas flow is used to blow dry the surface for later use.

[0057] Step 2: evacuate the reaction chamber until the vacuum degree of the reaction chamber is less than 10 -1 Torr and heat to 300°C; then, place the cleaned ceramic sample obtained in step 1 into the center of the reaction chamber and preheat for 30 minutes to fully preheat the sample; at the same time, control the temperature of the precursors, i.e., trimethylaluminum and water, to 22°C with an accuracy of no more than ±2°C.

[0058] In this embodiment, the cleaned spatial traveling wave tube obtained in step 1 is placed in the center of the reaction chamber to make the thickness of the aluminum oxide film deposition uniform.

[0059] In this embodiment, the temperature of the reaction chamber is increased to provide a temperature environment for the subsequent reaction, and the subsequent reaction process is a thermal reaction process.

[0060] Step 3: After the ceramic sample is preheated, trimethylaluminum and water whose temperature is controlled in step 2 are used to interact with the surface of the ceramic sample in an alternating manner.

[0061] Among them, first, trimethylaluminum reacts with the original surface of the ceramic sample for 0.1s; then, nitrogen is used to purge the reactants and by-products; then, water reacts with the original surface of the ceramic sample for 0.3s; finally, nitrogen is used to purge the surface of the ceramic sample after the aluminum oxide film is deposited, and the nitrogen flow rate is 40sccm. This process is a reaction cycle.

[0062] The thickness of the aluminum oxide film initially formed is calibrated and the cycle period is set. The reaction period is set so that the thickness of the aluminum oxide film on the ceramic sample after the aluminum oxide film is deposited is 10 nm.

[0063] In this embodiment, trimethylaluminum is used as the source of aluminum atoms in the aluminum oxide film, and water is used as the source of oxygen atoms in the aluminum oxide film. The time of the two reacting with the original surface of the ceramic ensures the formation of a single atomic layer of aluminum oxide film. Different reaction time ratios will affect the aluminum-oxygen ratio of the generated aluminum oxide film, and the length of the reaction time will affect the film thickness of the formed aluminum oxide film.

[0064] In this embodiment, the thickness of the aluminum oxide film was measured by an ellipsometer, and the film thickness of one reaction cycle was 0.1 nm.

[0065] Step 4, repeating step 3, and performing a cycle to achieve a set reaction cycle, so that the aluminum oxide film grows layer by layer on the surface of the original ceramic sample.

[0066] In this embodiment, when the thickness of the single-layer aluminum oxide film is known, the aluminum oxide film of the specified thickness can be obtained by performing the specified number of cycles in step 3. In this embodiment, the thickness of the aluminum oxide film is 10 nm, which corresponds to 100 reaction cycles.

[0067] In this embodiment, the aluminum oxide film with a thickness less than 10 nm is slightly insufficient in terms of the surface flashover voltage, and the aluminum oxide film that is too thick takes too long to process and has too low efficiency.

[0068] Step 5: After the reaction is completed, turn off the precursor and the purge gas, and take out the product after the reaction chamber cools down to room temperature, thereby obtaining a ceramic sample after the aluminum oxide film is deposited.

[0069] The secondary electron emission coefficient of the ceramic sample after the deposition of aluminum oxide film was measured using the secondary electron emission characteristic test platform. The system vacuum degree was 2.3×10 -8 Torr, the secondary electron emission coefficient of the original ceramic surface is shown in Figure 2(a), and the maximum value of the secondary electron emission coefficient can reach 7; the secondary electron emission coefficient of the ceramic sample after the aluminum oxide film is deposited is shown in Figure 2(b), and the secondary electron emission coefficient drops below 3.5. The results show that the method of the present invention can effectively suppress the secondary electron emission coefficient of the original ceramic surface.

[0070] The initial flash voltage of the unmodified space traveling wave tube tested using a surface flashover experimental device was 6.16 kV, and the initial flash voltage of the ceramic sample after deposition of 10 nm aluminum oxide film was 9.2 kV. The initial flash voltage was increased by 49%, which can effectively suppress the probability of micro-discharges at the triple point of the space traveling wave tube.

[0071] Comparative Example 1:

[0072] The method of the present invention is used to deposit 100 cycles of a 10 nm TiN film on the surface of the original ceramic sample. The steps in this comparative example are basically the same as those in Example 1, except that the deposited film is a TiN film.

[0073] The surface flashover voltage is Figure 3 As shown, the surface flashover voltage of the ceramic samples after deposition of TiN film is low, all below 9 kV, and with the increase of flashover times, the surface flashover voltage does not show a significant improvement as shown in the method of the present invention. The initial surface flashover voltage may be related to surface contamination and pollution. The surface flashover voltage after multiple flashovers can better represent the performance of the film layer itself.

[0074] However, with the increase of flashover times, the flashover voltage of the ceramic sample after depositing 10nm aluminum oxide film by the method of the present invention is generally on the rise, from 9kV to 19kV, which is significantly improved compared with the original ceramic sample. The corresponding results are as follows: Figure 3 shown.

[0075] Although the secondary electron emission coefficient on the surface of the ceramic sample after deposition of the TiN film is low, with the maximum secondary electron emission coefficient being only 1.7, which can reduce the surface secondary electron emission and the multiplication process, as the thickness of the surface coating increases, the surface conductivity increases, and it is easier to form a conductive channel on the surface, resulting in a lower flashover voltage. The aluminum oxide film deposited in the present invention can reduce the surface secondary electron emission without reducing the surface insulation performance, and is suitable for the application of space traveling wave tubes.

[0076] Embodiment 2:

[0077] This embodiment provides a method for suppressing micro discharges in a space traveling wave tube, which is basically the same as that in embodiment 1, except that the thickness of the aluminum oxide film is 5 nm. The reaction period in step 4 is 50.

[0078] The secondary electron emission coefficient of the ceramic sample after deposition of 5nm aluminum oxide film was measured using a secondary electron emission characteristic test platform. The maximum value of the secondary electron emission coefficient of the ceramic sample after deposition of 5nm aluminum oxide film was 3.3, and the energy was 400eV.

[0079] Embodiment 3:

[0080] This embodiment provides a method for suppressing micro discharges in a space traveling wave tube, which is basically the same as that in embodiment 1, except that the thickness of the aluminum oxide film is 15 nm. The reaction period in step 4 is 150.

[0081] The secondary electron emission coefficient of the ceramic sample after deposition of 15nm aluminum oxide film was measured using a secondary electron emission characteristic test platform. The maximum value of the secondary electron emission coefficient of the ceramic sample after deposition of 15nm aluminum oxide film was 3.3, and the energy was 400eV.

[0082] Embodiment 4:

[0083] This embodiment provides a method for suppressing micro discharges in a space traveling wave tube, which is basically the same as that in embodiment 1, except that the thickness of the aluminum oxide film is 20 nm. The reaction cycle in step 4 is 200.

[0084] The secondary electron emission coefficient of the ceramic sample after deposition of 20nm aluminum oxide film was measured using a secondary electron emission characteristic test platform. The maximum value of the secondary electron emission coefficient of the ceramic sample after deposition of 20nm aluminum oxide film was 3.2, and the energy was 350eV.

[0085] Embodiment 5:

[0086] This embodiment provides a method for suppressing micro discharges in a space traveling wave tube, which is basically the same as that in embodiment 1, except that the thickness of the aluminum oxide film is 30 nm. The reaction cycle in step 4 is 300.

[0087] The secondary electron emission coefficient of the ceramic sample after deposition of 30nm aluminum oxide film was measured using a secondary electron emission characteristic test platform. The maximum value of the secondary electron emission coefficient of the ceramic sample after deposition of 30nm aluminum oxide film was 3.32, and the energy was 400eV.

[0088] The flashover voltages of the different samples obtained in Examples 1 to 5 were tested using a surface flashover experimental device. Figure 4 As shown. The results show that the ceramic sample after depositing 10nm aluminum oxide film has the highest initial flash surface voltage, and the initial flashover is related to surface particles and dust. The ceramic sample after depositing more than 15nm aluminum oxide film has a higher surface flashover voltage after multiple flashovers than when the thickness of the deposited aluminum oxide film is smaller. This shows that for the suppression of micro discharges in space traveling wave tubes, it is necessary to pay attention not only to the secondary electron emission on the surface of the original ceramic sample, but also to the surface flashover voltage on the surface of the original ceramic sample, especially the threshold voltage after multiple flashovers. When the thickness of the aluminum oxide film deposited on the surface of the original ceramic sample is 10nm, both the film thickness and efficiency can be taken into account.

[0089] Comparative Example 2:

[0090] TiN film was deposited on the surface of the original ceramic sample by atomic layer deposition method, and its surface XPS spectrum is shown in Figure 5(a). As time goes by, the C / O element ratio increases, the Ti / N ratio decreases, and there is a serious oxidation problem. Its surface XPS spectrum is shown in Figure 5(b). After 120 days, the maximum secondary electron emission coefficient increased by 17%.

[0091] Under the conditions of the same preparation method and the same thickness of the deposited film, the only difference is the type of the deposited film. The ceramic sample after the aluminum oxide film was deposited by the method of the present invention has a maximum secondary electron emission coefficient of 3.8 on the surface just after the treatment. After 90 days of storage, the secondary electron emission coefficient remains basically unchanged, and the maximum secondary electron emission coefficient is still 3.8. This shows that the method of the present invention has obvious advantages in stability compared with other film layers.

Claims

1. A method for suppressing micro discharge of a space traveling wave tube, comprising a space traveling wave tube, characterized in that: The method uses a variety of precursors to alternately deposit aluminum oxide films on the surface of the original ceramic sample; The multiple precursors are trimethylaluminum and water; The deposition temperature is 250°C to 350°C.

2. The method for suppressing micro discharge of a space traveling wave tube according to claim 1, characterized in that: The thickness of the aluminum oxide film is 5nm-100nm.

3. The method for suppressing micro discharge of a space traveling wave tube according to claim 1, characterized in that: The method specifically comprises the following steps: Step 1, cleaning the surface of the ceramic original sample to remove pollutants on the surface of the ceramic original sample to obtain a cleaned ceramic original sample; Step 2, evacuating the reaction chamber and heating it to the deposition temperature, then placing the cleaned ceramic obtained in step 1 into the reaction chamber for preheating, while controlling the temperature of the precursors, namely trimethylaluminum and water; Step 3, after the ceramic original sample is preheated, trimethylaluminum and water whose temperature is controlled in step 2 are alternately allowed to interact with the surface of the ceramic original sample, and then the surface of the ceramic original sample is purged with gas; Step 4, repeating step 3, and performing a cycle to achieve a set reaction cycle, so that the aluminum oxide film grows layer by layer on the ceramic original sample; Step 5: After the reaction is completed, turn off the precursor and the purge gas, and take out the product after the reaction chamber cools down to room temperature, thereby obtaining a ceramic sample after the aluminum oxide film is deposited.

4. The method for suppressing micro discharge of a space traveling wave tube according to claim 3, characterized in that: In step 1, the cleaning agents used to clean the surface of the ceramic sample are water-soluble organic solvent and deionized water.

5. The method for suppressing micro discharge of a space traveling wave tube according to claim 3, characterized in that: In step 2, the vacuum is drawn until the vacuum degree of the reaction chamber is less than 10 -1 Torr; In step 2, the cleaned ceramic obtained in step 1 is placed in the center of the reaction chamber; In step 2, the preheating time is 10 to 30 minutes; In step 2, the temperature of the precursors, i.e., trimethylaluminum and water, is controlled to be 22°C with an accuracy of no more than ±2°C.

6. The method for suppressing micro discharge of a space traveling wave tube according to claim 3, characterized in that: In step 3, the trimethylaluminum and water interact with the original ceramic surface in an alternating manner, wherein the trimethylaluminum interacts with the original ceramic surface for 0.1 s, and the water interacts with the original ceramic surface for 0.3 s; In step 3, the gas is nitrogen, argon or helium, the gas flow rate is 40sccm, and the accuracy does not exceed ±5sccm; In step three, the thickness of the aluminum oxide film initially formed is calibrated and the cycle period is set so that the thickness of the aluminum oxide film on the ceramic sample after the aluminum oxide film is deposited is 5nm to 100nm.

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