Thermal evaporation device with controllable evaporation rate for evaporation of bismuth telluride film

Abstract

The invention belongs to the technical field of vacuum evaporation, and relates to an evaporation-rate-controllable thermal evaporation device used for evaporation of a bismuth telluride film, the evaporation-rate-controllable thermal evaporation device comprises an evaporation main body prepared from a conductive material, an evaporation source and electrodes located at the two ends of the evaporation main body, a cavity is formed in the evaporation main body, the evaporation source is fixed at one end or two ends of the cavity, and the electrodes are located at the two ends of the evaporation main body. A plurality of round holes are formed in the end, away from an evaporation source, of the evaporation main body or the middle of the evaporation main body, the evaporation main body is made of a seamless tube made of a nichrome material, and the electrodes are integrally formed by necking and flattening the two ends of the seamless tube. The thermal evaporation device is controllable in evaporation rate, the integrally-formed electrode structure, the flexible round hole layout, the specific evaporation source preparation process and the optimized evaporation main body structure of the thermal evaporation device are particularly suitable for preparing the high-precision and high-quality bismuth telluride film, the equipment technical index reaches the international leading level, and the thermal evaporation device is suitable for large-scale popularization and application. And a subversive technical platform is provided for industrialization of next-generation high-performance thermoelectric devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum evaporation, and relates to a thermal evaporation device with controllable evaporation rate for evaporating bismuth telluride film. The thermal evaporation device can realize the preparation of high-quality Bi2Te3 thermoelectric thin film devices, effectively control the evaporation rate of the evaporation source, and effectively improve the performance of the thermoelectric thin film devices. Background Art

[0002] Thermoelectric materials are solid materials that can realize the mutual conversion of heat energy and electrical energy. Bismuth telluride (Bi2Te3) materials are widely used in thermoelectric materials, electronic components and other fields due to their excellent thermoelectric properties. They are also thermoelectric materials that have been studied earlier and have relatively mature technology. Most thermoelectric cooling components currently use this type of material. In order to achieve the above applications, it is usually necessary to deposit it on a substrate through a coating technology to form a thin film. The existing bismuth telluride film preparation is mostly carried out by magnetron sputtering. From a thermodynamic point of view, the growth mode of the film prepared by magnetron sputtering is a three-dimensional island growth mode. This growth mode is prone to form internal stress during the film formation process, resulting in large internal stress in the product film. Even with the subsequent annealing process, it is difficult to completely eliminate it. The existence of this internal stress will always affect the thermoelectric properties of the film, thereby affecting the use of thermoelectric devices in thin film applications. Thermal evaporation, as an important branch of physical vapor deposition (PVD), has been widely used in optical coating, semiconductor devices, solar cells and other fields. Its principle is to evaporate or sublimate the film-forming material in a vacuum environment through resistance heating, electron beam bombardment and other methods, and then condense or deposit on the surface of the low-temperature workpiece or substrate after a period of transportation to form a coating. According to the type of heating source, it can be divided into: resistance heating evaporation using high-temperature resistant metals such as tungsten and molybdenum as heating bodies for direct or indirect heating and evaporation, electron beam evaporation using high-energy electron beam focusing to heat the material, and laser evaporation using laser pulses to instantly heat the material to achieve local evaporation. Thermal evaporation technology can prepare high-purity thin films and effectively avoid impurity doping; at the same time, it can accurately control the composition and thickness, and the deposition rate can be precisely controlled by simply adjusting the evaporation source temperature (or current intensity) and evaporation time. However, thermal evaporation also has certain defects, such as short life of evaporation source: traditional resistance heating evaporation source (such as tungsten wire, molybdenum boat) is easy to react with evaporation material at high temperature. At high temperature, part of the evaporation material atoms will diffuse into the lattice of the heated tungsten wire to form brittle compounds, resulting in evaporation source fracture failure. For example, when a quartz crucible is used to hold the material, quartz reacts with bismuth telluride at high temperature when heated by external resistance, resulting in film contamination; low material utilization rate, point source characteristics of thermal evaporation cause the evaporation direction of the material to be hemispherical, only about 10-15% of the material is deposited on the substrate, and the remaining 85-90% is wasted on the vacuum chamber wall and baffle, significantly increasing production costs. The dual-source evaporation method that uses Bi and Te elements to evaporate separately and controls the ratio on the substrate surface to synthesize bismuth telluride requires precise synchronization of the evaporation rates of the two materials, and the equipment is complex and costly. In addition, ion beam assisted deposition that improves the density of the film by ion beam bombardment increases the risk of substrate damage, and the equipment is relatively complex and expensive.

[0003] In the traditional evaporation process, point source heating, line source heating or a combination of the two is often used for heating. However, as the size of the evaporation substrate increases further, the traditional heating method cannot meet the requirements of large-area uniformity, and the evaporation rate is difficult to accurately control. The commonly used device for thermal evaporation is an evaporation crucible or an evaporation boat, in which the vaporization and evaporation rate of the evaporation material is proportional to the heating temperature inside the evaporation crucible. The higher the heating temperature inside the evaporation crucible, the faster the heat transfer speed, and the higher the vaporization and evaporation rate of the evaporation material. After the evaporation material inside the evaporation crucible begins to vaporize and evaporate, the evaporation material in the solid state gradually decreases, so that the internal space of the evaporation crucible increases. The vapor pressure inside the evaporation crucible will decrease as the diffusion space inside the evaporation crucible increases, thereby reducing the rate of vaporization and evaporation of the evaporation material. In order to keep the vaporization and evaporation of the evaporation material at a fixed rate, it is necessary to continuously increase the heating temperature inside the evaporation crucible as the evaporation time of the evaporation material. For this purpose, some people use a tungsten wire winding method to wrap the tellurium bismuth alloy on the surface of the tungsten wire and heat it with electricity for evaporation. However, due to the difference in thermal expansion coefficients between the evaporation material and the tungsten wire, the evaporation material is easy to fall off at high temperatures; the tungsten wire is easy to burn out due to local overheating, and the tellurium-bismuth alloy is easy to splash or the liquid tellurium-bismuth alloy may drip from the surface of the evaporation source at high temperatures, affecting the uniformity and thickness control of the coating, resulting in a decrease in film quality. Some people also use nickel-based alloy strips to stamp and form evaporation boats to load materials for evaporation, but there are disadvantages such as cracking at the edge of the boat body leading to vapor escape (cracking rate >30% when the thickness is ≤0.1mm); the evaporation rate fluctuates in a large range and the directionality of the vapor cannot be controlled. At the same time, as the required heating temperature increases, on the one hand, it will lead to increased energy loss and increased costs, and on the other hand, it may cause the evaporation source temperature to be too high, the raw materials to decompose, and the thermal evaporation material cannot be obtained. The film quality is directly related to the temperature and rate of evaporation. To obtain a uniform film layer, the evaporation material needs to be heated evenly. For this purpose, there have been many studies on heat sources or evaporation devices, hoping to improve the heating uniformity of the evaporation heating system. For example, CN222139240U discloses an evaporation heating and cooling system and evaporation equipment, including: a cooling device, a heating device, an evaporation material container and a temperature control device. The heating device is arranged in the cooling device, and the heating device includes a heating component and a heat-conducting medium container. The evaporation material container is arranged in the heat-conducting medium container, and the heat-conducting medium container is used to transfer heat to the evaporation material container. Since the evaporation material container is placed in the heat-conducting medium container, the heat-conducting medium container can transfer heat from the bottom and the side to the evaporation material container, and the temperature control device can control the heat distribution in the heat-conducting medium container to be uniform, so that the evaporation material container can be ensured to be heated more evenly, which is conducive to quickly and accurately controlling the heating rate of the evaporation material, thereby improving the coating quality and coating efficiency.CN118773551A discloses an evaporation source and an evaporation device, wherein the evaporation source comprises a crucible, an electromagnetic coil, a supporting structure and an inductor; the crucible is used to load evaporation materials; the electromagnetic coil is arranged around the crucible, and the electromagnetic coil is used to generate an electromagnetic field under the control of an alternating current; the supporting structure is located in the crucible and fixedly connected to the crucible; the inductor is located on the supporting structure, and the inductor is used to generate an induced current under the action of the electromagnetic field to heat the evaporation materials in the crucible, thereby directly heating the evaporation materials from the inside of the crucible, and the thermal interaction is simple and efficient, thereby improving the heating efficiency and the hysteresis of the temperature control, and can significantly improve the process stability of the evaporation, and improve the product performance and production yield. CN110777334B discloses an evaporation source and a vacuum evaporation system, the evaporation source comprising: a cavity, a crucible and a driving assembly arranged in the cavity, and a heating assembly; wherein the crucible is a retractable structure for placing the evaporation material; an air outlet is arranged on one side of the cavity, the driving assembly is located on the side of the crucible away from the air outlet, and the driving assembly is used to drive the crucible to shrink toward the side close to the air outlet; the heating assembly is used to heat the evaporation material. Since the crucible in the present application is a retractable structure, the driving assembly can drive the crucible to shrink toward the side close to the air outlet. Therefore, in the process of gradually reducing the evaporation material in the crucible, the distance between the evaporation material and the air outlet can always be maintained in a small range, and the deposition rate of the evaporation material can be ensured to remain stable without increasing the heating temperature, thereby avoiding the influence of excessive temperature on the quality of the film layer formed on the substrate. CN110629168B discloses an evaporation device of a vacuum coating machine, comprising: an evaporation boat, a heating system, and an air distribution system. The evaporation boat comprises an evaporation boat inner layer, an evaporation boat outer layer and a movable cover plate. The evaporation boat inner layer is located between the evaporation boat outer layer and the movable cover plate. The movable cover plate is provided with a plurality of evaporation holes. The evaporation boat inner layer is provided with evaporation grooves corresponding to the evaporation holes. The heating system comprises a plurality of relatively independent evaporation sources. The evaporation source is provided with an inner crucible, which is nested in the evaporation groove. The evaporation source can heat an object placed in the inner crucible. A multi-stage binary structure air distribution pipeline is provided to realize the control of the uniformity of the air intake, so that the evaporated gas and the externally introduced gas can be fully mixed to form a uniform composite film. CN105603364B discloses a heat-conducting device and an evaporation crucible, wherein the heat-conducting device comprises a heat-conducting tube and a plurality of heat-conducting sheets mounted on the heat-conducting tube in a radial shape, or comprises a radial heat-conducting tube in a radial shape. By placing the heat-conducting device in the evaporation crucible, the heat on the crucible wall can be evenly transferred to the inside and center of the crucible through the heat transfer path of the heat-conducting device, which is beneficial to improving the uniformity of heating of the material inside the crucible, so that the evaporation state of the material remains stable and the evaporation effect is improved; and the heat-conducting device is easy to process, low in cost and good in thermal conductivity.CN106987807B discloses an evaporation source, an evaporation device and an evaporation method, comprising: an evaporation crucible; a movable platform, arranged in the evaporation crucible, the movable platform at least comprising a bottom plate, for placing the evaporation material, the movable platform and the side and upper surface of the evaporation crucible surround to form an evaporation cavity; a moving mechanism, driving the movable platform to move in the evaporation crucible along a direction perpendicular to the bottom plate. It can solve the problem of the existing evaporation crucible that the internal diffusion space increases due to the vaporization and evaporation of the evaporation material, thereby causing the evaporation rate to decrease and affecting the evaporation effect. CN220012776U discloses an evaporation boat and an evaporation device, the evaporation boat comprises a boat body and an electrode connection structure located at two opposite ends of the boat body along a first direction, the boat body extends along the first direction, and at least one row of evaporation grooves is arranged on the first surface of the boat body, the evaporation grooves are used to place evaporation materials, so that after adding evaporation materials into each evaporation groove, the materials at each evaporation groove of the boat body are uniform, the temperatures at each evaporation groove of the boat body are uniform, and the evaporation rates at each evaporation groove of the boat body are similar, so as to achieve the purpose of improving the uniformity of vacuum coating and improving the quality of vacuum coating. CN107400859A discloses an evaporation source, comprising an evaporation source body made of a conductive material; the evaporation source body comprises: a main body, wherein a material chamber is provided inside the main body; wherein a first electrode connection end and a second electrode connection end having a polarity opposite to that of the first electrode connection end are provided at any position outside the main body, and after the first electrode connection end and the second electrode connection end are energized, the main body itself conducts electricity to generate heat to heat the material in the material chamber; compared with the existing evaporation source, the evaporation source provided by the present invention is made of a conductive material, and self-heating of the evaporation source can be achieved by providing positive and negative electrodes at corresponding positions of the evaporation source, thereby obtaining a uniform heating effect, and obtaining a high-quality film layer by evaporation deposition.

[0004] However, most of the current thermal evaporation devices still need to be carried out in a vacuum or negative pressure environment. The devices are complex, have poor versatility, and cannot effectively control the evaporation rate of the target material, resulting in poor uniformity of the bismuth telluride film and the inability to effectively improve the performance of the prepared thin film material, which seriously affects the quality and production efficiency of the tellurium bismuth alloy film. Based on this, it is necessary to provide a thermal evaporation device with controllable evaporation rate to overcome the above challenges and prepare high-performance bismuth telluride thin film materials. Summary of the invention

[0005] In order to solve the defects in the prior art, one object of the present invention is to provide a thermal evaporation device with controllable evaporation rate for evaporating bismuth telluride film, the evaporation device comprising an evaporation body made of conductive material, an evaporation source and electrodes located at both ends of the evaporation body, a chamber is opened inside the evaporation body, the evaporation body and the electrode are integrally formed, the evaporation source is 1 or 2, when the evaporation source is 1, the evaporation source is fixed at one end of the chamber, and a plurality of circular holes are provided on the surface of the end of the evaporation body away from the evaporation source; when the evaporation source is 2, a plurality of circular holes are provided on the middle surface of the evaporation body, and the evaporation sources are symmetrically fixed at the ends of the circular holes away from the chamber. The integrated formation of the evaporation body and the electrode reduces assembly steps, reduces operation difficulty and maintenance costs, improves the overall stability and reliability of the equipment, reduces the problem of increased resistance or unstable current caused by poor connection, and cooperates with the evaporation body of conductive material to effectively conduct current, ensure that heat is evenly distributed on the entire evaporation source, avoid local overheating, make the surface temperature of the entire evaporation source more uniform, reduce the risk of material sputtering and dripping, achieve a more stable heating effect, and improve current efficiency; according to the setting of the evaporation source, it corresponds to the end of the evaporation body away from the evaporation source or the middle area of ​​the evaporation body away from the evaporation source A number of circular holes are provided to precisely control the evaporation rate, that is, the evaporation rate can be adjusted by adjusting the aperture size, number and opening and closing state of these circular holes, so as to obtain a film of desired thickness and uniformity; the overall design of the thermal evaporation device helps to maintain an isolated internal environment. When the device is heated for use, the internal air is quickly expelled, and as the evaporation source evaporates, the internal air is further discharged, making the evaporation process more efficient and less affected by external interference, ensuring uniform volatilization of bismuth telluride material during the evaporation process, thereby forming a film of uniform thickness and uniform composition, and realizing the preparation of bismuth telluride thermoelectric film by thermal evaporation without vacuum conditions.

[0006] Furthermore, the evaporation body is made of a seamless tube made of nickel-chromium alloy, and the electrode is made by shrinking and flattening the two ends of the seamless tube into one piece. Nickel-chromium alloy has excellent high temperature resistance and mechanical strength, and can work stably for a long time in a high temperature environment, avoiding the burning problem that is easy to occur in traditional materials.

[0007] Furthermore, the distance between two adjacent circular holes on the evaporation body is equal. When there is one evaporation source, there are 2 to 10 circular holes, which are evenly arranged at one end of the evaporation body. When there are 2 or 3 or 5 or 7 circular holes, the circular holes are arranged along the length of the seamless tube or the circumferential surface; when there are 4 or 10 circular holes, the circular holes are arranged in two rows along the length of the seamless tube; when there are 6 circular holes, the circular holes are arranged in two or three rows along the length of the seamless tube; when there are 8 circular holes, the circular holes are arranged in two or four rows along the length of the seamless tube; when there are 9 circular holes, the circular holes are arranged in three rows along the length of the seamless tube. When there are 2 evaporation sources, there are 2 to 10 circular holes, which are evenly arranged in the middle of the evaporation body along the length of the seamless tube or the circumferential surface. When the number of the circular holes is 2, 3, 5 or 7, the circular holes are arranged along the circumferential surface of the seamless tube; when the number of the circular holes is 4 or 10, the circular holes are arranged in two rows along the circumferential direction of the seamless tube; when the number of the circular holes is 6, the circular holes are arranged in two or three rows along the circumferential direction of the seamless tube; when the number of the circular holes is 8, the circular holes are arranged in two or four rows along the circumferential direction of the seamless tube; when the number of the circular holes is 9, the circular holes are arranged in three rows along the circumferential direction of the seamless tube.

[0008] Furthermore, the diameter of the circular holes is 0.02-0.5 mm, the distance between adjacent circular holes is 0.5-2 mm, and more preferably the distance between adjacent circular holes is 1 mm. The evenly distributed circular holes can effectively control the evaporation rate and the amount of steam, which helps to achieve uniform heating of the evaporation source, ensure the uniformity of thin film deposition, and reduce sputtering.

[0009] Further preferably, the circular holes have different diameters, with the small aperture being 0.02mm~0.1mm, which can suppress local overpressure, produce laminar flow effect, and reduce steam turbulence kinetic energy; the large aperture being 0.2mm~0.5mm can ensure the overall flow rate and achieve a stable evaporation rate; the large and small apertures in the circular holes can be adjusted according to the needs of coating speed, thickness, etc., and the device has strong versatility.

[0010] Furthermore, the chromium content in the nickel-chromium alloy is 20wt%~22wt%, the diameter of the seamless pipe is 25mm, the pipe wall thickness is 0.05~0.5mm, and the aspect ratio is 5:1~10:1.

[0011] Furthermore, the chamber surface of the evaporation body has a Ti-Al2O3 coating, and the coating thickness is 2-5 μm. The Ti-Al2O3 coating provided on the chamber surface not only enhances the corrosion resistance and oxidation resistance of the chamber, but also improves the surface hardness and prolongs the service life of the equipment.

[0012] Furthermore, the evaporation source is Bi2Te3-1wt%Te, and the above setting can compensate for the preferential loss of Te during the evaporation process and maintain the stoichiometric ratio of the evaporated material.

[0013] Another object of the present invention is to provide a method for preparing a vapor deposition device for evaporating a bismuth telluride film, comprising the following steps: 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N at a mass ratio of 99:1, mix the two and place them in a vacuum melting furnace, maintain the vacuum degree at 0.01Pa, and melt at 620℃ for 2h; keep the solidification rate at 0.05K / s, cool to room temperature, crush the product into 200 mesh, put it into a mold, and isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm, put it into a vacuum sintering furnace, heat it to 450℃ at 5℃ / min, keep it warm for 2h, and then cool it to room temperature with the furnace to obtain; when the evaporation source is used for evaporation coating, after the current is turned on to 3A~3.5A, the tellurium bismuth alloy begins to evaporate from the small holes to form a uniform film.

[0014] 2) Preparation of the evaporation body: Select a nickel-chromium alloy seamless tube with a diameter of 25 mm, an aspect ratio of 5:1-10:1, and a thickness of 0.05-0.5 mm, deposit a Ti-Al2O3 coating with a thickness of 2-5 μm inside the seamless tube, and use laser drilling to form 2-10 evenly distributed circular holes 20 mm away from one end of the seamless tube, with a hole diameter of 0.02-0.5 mm; or select a nickel-chromium alloy seamless tube with a diameter of 25 mm, an aspect ratio of 5:1-10:1, and a thickness of 0.05-0.5 mm, deposit a Ti-Al2O3 coating with a thickness of 2-5 μm inside the seamless tube, and use laser drilling to form 2-10 evenly distributed circular holes with a hole diameter of 0.02-0.5 mm on the surface of the seamless tube in the middle area of ​​the two evaporation sources; 3) Use high temperature ceramic glue to fix the evaporation source at one end of the chamber away from the circular hole, cure at 250°C for 30 minutes, use a spinning machine to shrink the two ends and flatten the two ends after shrinking to form an integrally formed electrode. The high temperature ceramic glue is selected from Aremco Ceramabond 571 of Aremco Products, Inc.

[0015] Furthermore, there are 6 circular holes, which are distributed in two rows along the length direction of the seamless pipe, and the distance between two adjacent holes is 1 mm.

[0016] Furthermore, the compression amount of each shrinking process is 3% to 5%; the flattening process is specifically carried out in two stages, firstly maintaining the pressure at 50 MPa for 20 seconds, and then impact loading at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz for 3 times.

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. The thermal evaporation device provided by the present invention can solve the problems of material sputtering, short life of evaporation source, uncontrollable parameters, etc. in traditional evaporation, and also significantly improves the film quality and durability of the equipment, and has broad application prospects. First, the evaporation body and the electrode are integrally formed, which reduces the assembly steps and improves the overall stability and reliability of the equipment. At the same time, it also reduces the contact resistance, improves the current transmission efficiency, improves the overall mechanical strength and stability of the equipment, reduces the risk of damage caused by vibration or impact, and avoids the problem of burning that is easy to occur in traditional materials.

[0018] 2. Nickel-chromium alloy seamless pipes have excellent high temperature resistance and mechanical strength, and can work stably for a long time in high temperature environments. Combined with the setting of special surface coatings, it not only enhances the corrosion resistance and oxidation resistance of the chamber, but also improves the surface hardness, extends the service life of the equipment, and improves the mechanical strength and electrical connection stability of the equipment.

[0019] 3. The evenly distributed circular holes and the corresponding arrangement of the circular holes and the evaporation source help to achieve uniform heating and evaporation of the evaporation source, ensure the uniformity and consistency of the thin film deposition, and effectively control the evaporation rate and steam volume; the evaporation source is prepared by vacuum melting and isostatic pressing process, which also ensures the purity and density of the raw materials, improves the quality of the final product, and enhances the performance of the material. The present invention has achieved a generational leap in performance in the field of thermoelectric thin film evaporation through the trinity innovation of materials, structure, and process. The technical indicators of the equipment have reached the international leading level, providing a disruptive technology platform for the industrialization of the next generation of high-performance thermoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic plan view of a thermal evaporation device prepared in Example 1 of the present invention; Figure 2 A schematic plan view of a thermal evaporation device prepared in Example 2 of the present invention; Figure 3 A schematic plan view of a thermal evaporation device prepared in Example 3 of the present invention; Figure 4 This is a SEM morphology image of a Bi2Te3 thin film prepared by thermal evaporation in Example 3 of the present invention; Figure 5 A schematic plan view of a thermal evaporation device prepared in Example 4 of the present invention; Wherein: 1-electrode, 2-circular hole, 3-evaporation body, 4-bismuth telluride evaporation source, 5-substrate. DETAILED DESCRIPTION

[0021] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0022] It should be noted that the reference to "embodiment" in this document means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0023] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0024] Example 1 In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in two rows along the length direction of the seamless tube, and the circular holes have the same size. The schematic diagram of the device is shown in FIG. Figure 1 , the preparation method of the evaporation device is as follows: 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N at a mass ratio of 99:1, mix the two and place them in a vacuum melting furnace, maintain the vacuum degree at 0.01Pa, and melt at 620℃ for 2h; keep the solidification rate at 0.05K / s, cool to room temperature, crush the product into 200 mesh, and then put it into a mold, isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm, put it into a vacuum sintering furnace, heat it to 450℃ at 5℃ / min, keep it at this temperature for 2h, and then cool it to room temperature with the furnace; 2) Preparation of the evaporation body: Select a nickel-chromium alloy (chromium content is 20wt%) seamless tube with a diameter of 25mm, an aspect ratio of 5:1, and a thickness of 0.05mm, deposit a layer of Ti-Al2O3 coating with a thickness of 2μm inside the seamless tube, and use laser drilling to form 6 evenly distributed circular holes 20mm away from one end of the seamless tube. The diameter of the circular holes is 0.1mm, and the distance between adjacent circular holes is 0.5mm; 3) Use Aremco Ceramabond 571 to fix the prepared evaporation source at one end of the chamber away from the circular hole, so that the surface of the evaporation source is parallel to the length direction of the evaporation body, and cure it at 250°C for 30 minutes. Use a spinning machine to shrink the two ends, and the compression amount of each pass is 3%. Flatten the two ends after shrinking to form electrodes. The flattening is carried out in two stages. First, maintain the pressure at 50MPa for 20s, and then impact load 3 times at 100MPa with a pulse width of 0.5s and a frequency of 2Hz.

[0025] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film. During the evaporation process, the working temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.2℃. The evaporation film forming rate was relatively stable. The film thickness uniformity deviation was measured to be ≤1.3%, and the product composition was stable. After continuous coating of 200 pieces, the evaporation device was still able to work stably.

[0026] Example 2 In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in three rows along the length direction of the seamless tube, and the circular holes have different sizes. The schematic diagram of the device is shown in FIG. Figure 2 , wherein the diameter of the large circular hole is 0.5 mm, and the diameter of the small circular hole is 0.02 mm. The preparation method of the evaporation device is as follows: 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N at a mass ratio of 99:1, mix the two and place them in a vacuum melting furnace, maintain the vacuum degree at 0.01Pa, and melt at 620℃ for 2h; keep the solidification rate at 0.05K / s, cool to room temperature, crush the product into 200 mesh, and then put it into a mold, isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm, put it into a vacuum sintering furnace, heat it to 450℃ at 5℃ / min, keep it at this temperature for 2h, and then cool it to room temperature with the furnace; 2) Preparation of the evaporation body: Select a nickel-chromium alloy (chromium content is 22wt%) seamless tube with a diameter of 25mm, an aspect ratio of 10:1, and a thickness of 0.5mm, deposit a layer of Ti-Al2O3 coating with a thickness of 5μm inside the seamless tube, and use laser drilling to form 6 circular holes at 20mm from one end of the seamless tube, with a distance of 1mm between adjacent circular holes; 3) Use Aremco Ceramabond 571 to fix the prepared evaporation source at one end of the chamber away from the circular hole, so that the surface of the evaporation source is perpendicular to the length direction of the evaporation body. Curing at 250℃ for 30min, using a spinning machine to shrink the two ends, each compression amount is 5%, and the two ends after shrinking are flattened to form electrodes. The flattening is carried out in two stages, first at 50MPa for 20s, and then at 100MPa with a pulse width of 0.5s and a frequency of 2Hz for 3 times.

[0027] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film. During the evaporation process, the working temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.5℃. The evaporation film formation rate was relatively stable. The measured film thickness uniformity deviation was ≤1%. The product was relatively stable. After continuous coating of 500 pieces, the evaporation device was still able to work stably.

[0028] Example 3 In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in three rows along the length direction of the seamless tube, and the circular holes have the same size and a diameter of 0.5 mm. The schematic diagram of the device is shown in FIG. Figure 3 , the preparation method of the evaporation device is as follows: 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N at a mass ratio of 99:1, mix the two and place them in a vacuum melting furnace, maintain the vacuum degree at 0.01Pa, and melt at 620℃ for 2h; keep the solidification rate at 0.05K / s, cool to room temperature, crush the product into 200 mesh, and then put it into a mold, isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm, put it into a vacuum sintering furnace, heat it to 450℃ at 5℃ / min, keep it at this temperature for 2h, and then cool it to room temperature with the furnace; 2) Preparation of the evaporation body: Select a nickel-chromium alloy (chromium content is 21wt%) seamless tube with a diameter of 25mm, an aspect ratio of 8:1, and a thickness of 0.1mm, deposit a layer of Ti-Al2O3 coating with a thickness of 3μm inside the seamless tube, and use laser drilling to form 6 evenly distributed circular holes 20mm away from one end of the seamless tube, with a distance of 2mm between adjacent circular holes; 3) Use Aremco Ceramabond 571 to fix the prepared evaporation source at one end of the chamber away from the circular hole in a manner that the surface is perpendicular to the length direction of the evaporation body, and cure it at 250°C for 30 minutes. Use a spinning machine to shrink the two ends, with a compression amount of 4% per pass. Flatten the two ends after shrinking to form electrodes. The flattening is carried out in two stages. First, maintain the pressure at 50 MPa for 20 seconds, and then impact load 3 times at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz.

[0029] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film, wherein the substrate 5 was close to the circular hole and parallel to the tube, and the distance from the tube was 2cm. During the evaporation process, the operating temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.1°C. The evaporation film formation rate was relatively stable. The film thickness uniformity deviation was measured to be ≤1.4%. The product was relatively stable and the film formation speed was relatively fast. After continuous coating of 500 pieces, the evaporation device was still able to work stably. Figure 4It can be seen from the SEM image that the film is composed of evenly distributed nanoparticles. Most of these nanoparticles are hexagonal flake structures with a particle size of about 50nm, and the edges of the grains are clearly visible. Combined with XPS measurement calculations, it is shown that the Bi:Te atomic ratio in the product is 2:3.

[0030] Example 4 In this embodiment, a bismuth telluride film evaporation device is prepared, wherein the evaporation body is provided with 6 circular holes distributed in two rows along the length direction of the seamless tube, and the circular holes have different sizes. The schematic diagram of the device is shown in FIG. Figure 5 , wherein the diameter of the large circular hole is 0.4 mm, and the diameter of the small circular hole is 0.08 mm. The preparation method of the evaporation device is as follows: 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N at a mass ratio of 99:1, mix the two and place them in a vacuum melting furnace, maintain the vacuum degree at 0.01Pa, and melt at 620℃ for 2h; keep the solidification rate at 0.05K / s, cool to room temperature, crush the product into 200 mesh, and then put it into a mold, isostatically press it at 200MPa for 20min to prepare 2 green billets with a diameter of 24mm and a thickness of 4mm, put them into a vacuum sintering furnace, heat them to 450℃ at 5℃ / min, keep them at this temperature for 2h, and then cool them to room temperature with the furnace; 2) Preparation of the evaporation body: Select a nickel-chromium alloy (chromium content is 22wt%) seamless tube with a diameter of 25mm, an aspect ratio of 8:1, and a thickness of 0.1mm, deposit a layer of Ti-Al2O3 coating with a thickness of 3μm inside the seamless tube, and use laser drilling to form 6 evenly distributed circular holes with a distance of 2mm between adjacent circular holes in the middle of the seamless tube; 3) Use Aremco Ceramabond 571 to fix the prepared evaporation source at both ends of the chamber so that the surface of the evaporation source is perpendicular to the length direction of the evaporation body, cure at 250°C for 30 minutes, and use a spinning machine to shrink the two ends. The compression amount for each pass is 4%, and the two ends after shrinking are flattened to form electrodes. The flattening is carried out in two stages. First, the pressure is maintained at 50MPa for 20s, and then the impact loading is performed 3 times at 100MPa with a pulse width of 0.5s and a frequency of 2Hz.

[0031] The evaporation device was used to prepare a 2cm×2cm bismuth telluride film. During the evaporation process, the working temperature change in the chamber of the device was monitored by an infrared thermal imager and was ≤0.4°C. The evaporation film formation rate was relatively stable. The measured film thickness uniformity deviation was ≤1%. The product was relatively stable. After continuous coating of 1,500 pieces, the evaporation device was still able to work stably.

[0032] Comparative Example 1 A bismuth telluride film evaporation device, wherein the evaporation body is provided with two circular holes distributed in three rows along the length direction of a seamless tube, and the diameter of the circular holes is 1.5 mm. The evaporation device is obtained by the preparation method of Example 4, wherein no Ti-Al2O3 coating is deposited inside the seamless tube. A 2cm×2cm bismuth telluride film is prepared by the evaporation device. During the evaporation process, the maximum value of the working temperature change in the chamber of the device monitored by an infrared thermal imager is 2°C, the evaporation film forming rate is relatively stable, and the film thickness uniformity deviation is measured to be 4.3%. The early coating product is stable, and part of the coating falls off after continuous coating of 1000 sheets.

[0033] Comparative Example 2 A bismuth telluride film evaporation device, the main preparation method is the same as that of Example 1, the difference is that the evaporation circular hole on the evaporation body is replaced by a slit of 10 mm long and 2 mm wide, and the evaporation source uses 4N Bi2Te3 powder placed in a quartz evaporation boat. The 2cm×2cm bismuth telluride film is prepared using the evaporation device. During the evaporation process, the maximum change of the working temperature in the chamber of the device is 5°C monitored by an infrared thermal imager, and the evaporation film formation rate is relatively stable; the film thickness uniformity deviation is measured to be about 5.9%, the composition of the first few batches of products is stable, and the stability of the subsequent bismuth telluride film deteriorates, and impurities such as oxygen and carbon begin to appear.

[0034] The above is a detailed introduction to a thermal evaporation device with a controllable evaporation rate for evaporating bismuth telluride film. The above content is a further detailed description of the present invention in combination with a specific preferred embodiment, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, its architecture can be flexible and can derive a series of products. Just making a few simple deductions or substitutions should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims

1. A thermal evaporation device with controllable evaporation rate for evaporating bismuth telluride film, comprising an evaporation body made of conductive material, an evaporation source and electrodes located at both ends of the evaporation body, characterized in that: A chamber is provided inside the evaporation body, the evaporation source is fixed at one end of the chamber, a plurality of circular holes are provided at the end of the evaporation body away from the evaporation source, the diameter of the circular holes is 0.02-0.5 mm, the evaporation body and the electrode are integrally formed, and the evaporation source is Bi2Te3-1wt%Te.

2. The thermal evaporation device according to claim 1, characterized in that: The evaporation body is made of a seamless tube made of a nickel-chromium alloy, and the electrode is made of two ends of the seamless tube by shrinking and flattening to form an integral body.

3. The thermal evaporation device according to claim 1, characterized in that: The number of the circular holes is 2 to 10 and they are evenly arranged at one end of the evaporation body.

4. The thermal evaporation device according to claim 2, characterized in that: The chromium content in the nickel-chromium alloy is 20wt%-22wt%, the diameter of the seamless pipe is 25mm, the pipe wall thickness is 0.05-0.5mm, and the aspect ratio is 5:1-10:

1.

5. The thermal evaporation device according to claim 1 or 2, characterized in that: The chamber surface of the evaporation body is provided with a Ti-Al2O3 coating, and the coating thickness is 2-5 μm.

6. The thermal evaporation device according to any one of claims 1 to 3, characterized in that: The distance between adjacent circular holes in the circular holes is 0.5-2 mm.

7. The thermal evaporation device according to claim 6, characterized in that: The diameters of the plurality of circular holes are different, wherein the diameter of the small hole in the circular hole is 0.02 mm to 0.1 mm, and the diameter of the large hole is 0.2 mm to 0.5 mm.

8. A method for preparing a thermal evaporation device for evaporating a bismuth telluride film according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) Preparation of evaporation source: Weigh Bi2Te3 powder and Te powder with a purity of 4N at a mass ratio of 99:1, mix the two and place them in a vacuum melting furnace, maintain the vacuum degree at 0.01Pa, and melt at 620℃ for 2h; keep the solidification rate at 0.05K / s, cool to room temperature, crush the product into 200 mesh, and then put it into a mold, isostatically press it at 200MPa for 20min to obtain a green body with a diameter of 24mm and a thickness of 4mm, put it into a vacuum sintering furnace, heat it to 450℃ at 5℃ / min, keep it at this temperature for 2h, and then cool it to room temperature with the furnace to obtain; 2) Preparation of the evaporation body: Select a nickel-chromium alloy seamless tube with a diameter of 25 mm, an aspect ratio of 5:1-10:1, and a thickness of 0.05-0.5 mm, deposit a Ti-Al2O3 coating with a thickness of 2-5 μm inside the seamless tube, and use laser drilling to form 2-10 evenly distributed circular holes 20 mm away from one end of the seamless tube, with a circular hole diameter of 0.02-0.5 mm; 3) Use high-temperature ceramic glue to fix the evaporation source at the end of the chamber away from the circular hole, cure it at 250°C for 30 minutes, use a spinning machine to shrink the two ends and flatten the two ends after shrinking to form an integrated electrode.

9. The method for preparing a thermal evaporation device for evaporating a bismuth telluride film according to claim 8, characterized in that: There are 6 circular holes, which are distributed in two rows along the length direction of the seamless pipe, and the distance between two adjacent holes is 1 mm.

10. The method for preparing a thermal evaporation device for evaporating a bismuth telluride film according to claim 8, characterized in that: The compression amount of each shrinking process is 3% to 5%; the flattening process is specifically carried out in two stages, firstly maintaining the pressure at 50 MPa for 20 seconds, and then impact loading 3 times at 100 MPa with a pulse width of 0.5 seconds and a frequency of 2 Hz.

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