A method for producing a low-oxygen homogeneous target material for growing ndfeb thin films

Abstract

The application relates to a preparation method of a low-oxygen-content homogeneous target material for growing an NdFeB film, and particularly relates to the technical field of permanent magnet material preparation. The application relates to a preparation method of a low-oxygen-content homogeneous target material for growing an NdFeB film, which adopts a burn injection method of master alloy batching and a split mold to prepare the low-oxygen-content homogeneous target material for growing the NdFeB film. The master alloy is adopted to replace single elements for batching, so that the batching error caused by the large difference in the atomic ratio of the three elements when high-purity Nd, Fe and B are directly smelted is effectively avoided, and the accuracy and repeatability of the target material composition are improved. The low-oxygen-content and high-uniformity sputtering target material can ensure that the NdFeB film obtains the ideal component ratio in design, reduces the interference of harmful elements, obtains good phase formation quality, and greatly improves the residual magnetism. The split mold of the composite material is adopted to cast the target material, so that the mold cost can be greatly reduced, and the target material cracking is prevented.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet material preparation technology, specifically relating to a method for preparing a low-oxygen-content homogeneous target for growing NdFeB thin films. Background Technology

[0002] Since its discovery in the 1980s, NdFeB permanent magnets have been the superior permanent magnet material with the highest magnetic energy product, and have been widely used in many fields such as motors, generators, and nuclear magnetic resonance.

[0003] With the continuous advancement of emerging information technology fields such as semiconductor technology, micro-nano fabrication technology, and Internet of Things (IoT) technology, novel microelectromechanical systems (MEMS) such as micromirrors, current sensors, and energy harvesters are emerging in large numbers. This has fueled a growing interest in the fabrication and integration of micro- and nano-permanent magnets, leading to extensive research on high-performance permanent magnet materials and fabrication methods for MEMS. While permanent magnet materials possess the ability to generate magnetic fields over long distances, the magnetic field strength decreases significantly with distance. In device design, achieving stronger magnetic fields, greater magnetic forces, or more efficient electromechanical energy conversion often requires substantial magnetic energy. The permanent magnets used in microelectromechanical systems (MEMS) typically range in size from a few micrometers to hundreds of micrometers.

[0004] Therefore, the size control of permanent magnets, their compatibility with micro / nano fabrication processes, and the feasibility of mass production have become key factors in selecting magnet fabrication processes. NdFeB (neodymium iron boron) thin films prepared by magnetron sputtering exhibit significant technical advantages in all three aspects, thus showing great application potential in the field of magnetic micro-motor systems.

[0005] However, although high-performance NdFeB thin films share similar compositions with bulk NdFeB magnets, their magnetic properties largely depend on the quality of the target material due to the technical characteristics of NdFeB thin film preparation. From raw materials to the target material and then to the NdFeB thin film, multiple processes are involved. During these processes, Nd and B elements are highly susceptible to oxidation, leading to a sharp decrease in the magnetic properties of the final NdFeB thin film. Furthermore, because the sputtering rates of different elements in the target material vary, the target composition requirements for NdFeB thin films differ from those for bulk NdFeB magnets. In addition, magnetron sputtering technology itself suffers from low target utilization and a tendency for the target material to crack during use. For large-scale production of permanent magnet NdFeB thin films, high-performance targets must not only possess low oxygen content and adjustable composition but also have a short preparation cycle. Current sintering methods, primarily based on powder metallurgy, suffer from drawbacks such as large single-batch feeding, poor adjustment flexibility, and long preparation cycles.

[0006] Therefore, in order to further optimize the magnetic properties of NdFeB thin films and promote their widespread application, it is essential to develop a novel target preparation process for growing NdFeB thin films to address the aforementioned challenges simultaneously. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a homogeneous target material with low oxygen content for growing NdFeB thin films.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing a low-oxygen-content homogeneous target for growing NdFeB thin films, comprising a casting method of master alloy feedstock and a split mold for preparing the low-oxygen-content homogeneous target for growing NdFeB thin films.

[0010] Furthermore, the master alloy ingredients include master alloy 1, master alloy 2 and master alloy 3, and the mass proportion of any one of master alloy 1, master alloy 2 or master alloy 3 shall not be less than 10% of the total mass of the master alloy ingredients, and the oxygen content of the master alloy shall be less than 150 ppm.

[0011] Furthermore, the elements in the master alloy are Nd, Fe, and B as the core. Nd can be completely or partially replaced by one or more of Pr, La, and Ce, and Fe can be partially replaced by one or more of Al, Ga, Nb, or Co.

[0012] Furthermore, the atomic proportions of Nd, Fe, and B in the master alloy composition are 15%, 75%, and 10%, respectively.

[0013] Furthermore, the total content of Nd, Pr, La, and Ce elements in the master alloy 1 accounts for more than 20% of the atomic ratio of the master alloy 1, and the total content of Fe, Co, Al, Ga, Cu, and Nb elements in the balance is greater than 7 and less than 8 in atomic ratio with B element.

[0014] Furthermore, the total content of Fe, Co, Al, Ga, Cu and Nb elements in the master alloy 2 accounts for more than 80% of the atomic ratio of the master alloy 2, and the total content of Nd, Pr, La and Ce elements in the balance has an atomic ratio of greater than 1 and less than 2 with that of B element.

[0015] Furthermore, in the master alloy 3, the B element accounts for more than 12% of the atomic ratio of the master alloy 3, and the atomic ratio of the total content of Nd, Pr, La, and Ce elements to the total content of Fe, Co, Al, Ga, Cu, and Nb elements in the balance is greater than 0.15 and less than 0.25.

[0016] Furthermore, the atomic ratios of Nd, Pr, La, and Ce elements in the master alloy composition are between 13% and 17%, the atomic ratios of Fe, Co, Al, Ga, Cu, and Nb elements in the master alloy composition are between 72% and 78%, and the atomic ratio of B element in the master alloy composition is between 8% and 12%.

[0017] Furthermore, the mixed master alloy is cast into a split mold and solidified using a vacuum melting method, wherein the vacuum melting method is electric arc melting, induction melting, or suspension melting.

[0018] Furthermore, the split mold should consist of two parts: an annular sidewall and a flat bottom plate. The material of the annular sidewall is pure iron, low carbon steel, or stainless steel, and the material of the flat bottom plate is quartz glass, alumina, or boron nitride ceramic.

[0019] Beneficial effects of this invention:

[0020] 1. By using a master alloy instead of individual elements for batching, the proportioning error caused by the large difference in the atomic ratio of the three elements when directly melting high-purity Nd, Fe and B is effectively avoided, thus improving the accuracy and repeatability of the target material composition.

[0021] 2. Because the melting point of the master alloy is lower than that of refractory element B and transition element Fe, but higher than that of rare earth element Nd, all raw materials melt within a relatively small time window during the melting process. This results in significantly less difference in volatilization loss among the three elements compared to melting elemental raw materials. The unique melting point characteristics of the master alloy significantly reduce the differences in volatilization loss among elements during melting, ensuring the uniformity and consistency of the material.

[0022] 3. The stirring during the smelting process further homogenizes the master alloy, improving the quality and performance of the target material.

[0023] 4. Compared with traditional powder metallurgy preparation methods, direct casting eliminates processes such as powder preparation, molding, and high-temperature sintering, greatly saving time and improving production efficiency.

[0024] 5. It avoids the reaction between multiple processes and oxygen or water vapor in the environment, effectively controls the oxygen content of the casting target material, making it basically the same as the oxygen content of the master alloy, and reduces the influence of harmful elements such as oxygen.

[0025] 6. Sputtering targets with low oxygen content and high uniformity can ensure that NdFeB films achieve the ideal composition ratio as designed, significantly reduce the interference of harmful elements, thereby obtaining good phase quality and ultimately greatly improving remanence.

[0026] 7. Using composite material split molds to cast the target material can significantly reduce mold costs and prevent the target material from cracking. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the split mold used in Example 1.

[0028] Figure 2 The initial morphology of the target material is obtained by casting.

[0029] Figure 3 The difference in microstructure between cast targets made from rapidly solidified cast sheets as the master alloy and cast targets made from single-element materials.

[0030] Figure 4 This is a comparison of the hysteresis loops of thin films prepared from low-oxygen targets cast using rapidly solidified cast sheets as the master alloy and from single-element cast targets.

[0031] Reference numerals: 101, stainless steel annular sidewall; 201, quartz glass base plate. Detailed Implementation

[0032] The preparation method of the present invention will be described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and are not intended to limit it in any way.

[0034] A low-oxygen-content homogeneous target for growing NdFeB thin films was prepared using a master alloy formulation casting method and a split mold. The master alloy formulation includes master alloy 1, master alloy 2, and master alloy 3. The mass proportion of any one of master alloy 1, master alloy 2, or master alloy 3 should not be less than 10% of the total mass of the master alloy formulation, and the oxygen content of the master alloy is less than 150 ppm. The elements in the master alloy formulation are Nd, Fe, and B as the core. Nd can be wholly or partially replaced by one or more of Pr, La, and Ce, and Fe can be partially replaced by one or more of Al, Ga, Nb, or Co.

[0035] Table 1 shows the composition values ​​of master alloy 1, master alloy 2, and master alloy 3. Compared with the target composition range, master alloy 1 has a higher rare earth content than the target content in the target material; master alloy 2 has a higher total content of Fe, Co, Al, Ga, Cu, and Nb than the target content of the corresponding elements in the target material; and master alloy 3 has a higher B content than the target content in the target material. The design principle for the three master alloy compositions is that, after removing elements with higher contents than the target content in the target material, the proportions of the remaining alloy components should be as close as possible to the proportions of the corresponding elements in the target alloy.

[0036] Example 1

[0037] In this embodiment, we investigate the differences in target microstructure between the target material cast using a casting method with rapidly solidified cast sheets as the master alloy and the target material cast using elemental Nd, Fe, and B as raw materials, and compare the magnetic properties obtained by growing a 500 nm NdFeB hard magnetic thin film.

[0038] The casting method for preparing master alloy feedstock and the process of preparing thin films using target materials:

[0039] Step (1) involves preparing a master alloy feedstock in a rapid solidification casting furnace using pure Nd, electrolytically pure Fe (99.9% purity), and bulk pure B (99.5% purity). Based on the experimentally determined atomic ratio of the target target material Nd:Fe:B = 15%:75%:10%, three master alloy compositions were designed as shown in Table 1. The required mass of master alloys for refining 150g of target target material is, in order: Master alloy 1: 50.04g, Master alloy 2: 50.77g, and Master alloy 3: 49.18g.

[0040] Step (2) After assembling the weighed master alloy and the combined mold, place them in a high-frequency induction melting furnace and heat them in an Ar atmosphere of 0.5 atmospheres for 8 minutes until all raw materials melt. After stirring thoroughly with a boron nitride stirrer for 8 minutes, quickly pour the alloy melt into the split mold and wait for it to solidify and cool to form the target material.

[0041] Figure 1 This is a schematic diagram of the split mold used. The split mold consists of two parts: an annular sidewall and a flat bottom plate. The annular sidewall is made of stainless steel, and the flat bottom plate is made of quartz glass.

[0042] Step (3) After the target material has cooled, remove it. Figure 2 To obtain the initial morphology of the target material for casting, a circular disc with a diameter of 55 mm and a thickness of 6 mm was made by wire cutting and grinding, and then loaded into a high-vacuum magnetron sputtering system for coating.

[0043] Step (4) Prepare a 500 nm thick NdFeB thin film. Film preparation conditions: Ta buffer layer: deposition thickness 50 nm, NdFeB hard magnetic layer: deposition thickness 500 nm, Ta capping layer: deposition thickness 50 nm. Deposition temperature 450℃, after deposition, the temperature is directly raised to 750℃ and held for 10 minutes.

[0044] Figure 3 The study shows the difference in microstructure between the rapidly solidified cast sputtering target material made from the master alloy and the single-element cast sputtering target material. The master alloy cast sputtering target material exhibits a uniform microstructure, consisting of a main NdFeB phase with a small amount of Nd-rich phase. In contrast, the single-element cast sputtering target material shows a distinct lamellar structure, which, upon analysis, is identified as a highly B-rich phase, indicating a non-uniform compositional distribution.

[0045] Figure 4The comparison of hysteresis loops is shown between thin films prepared from low-oxygen targets cast from rapidly solidified cast sheets as master alloys and thin films prepared from single-element cast targets.

[0046] Table 2 below compares the magnetic properties of thin films grown using two types of targets: one using a single-element casting target and the other using a master alloy casting target. It is evident that the remanence and energy product of the thin films prepared using the master alloy casting target are significantly higher than those prepared using the single-element casting target.

[0047] Table 1 shows the composition values ​​of master alloy 1, master alloy 2 and master alloy 3.

[0048] Table 1

[0049] Master alloy name Master alloy 1 Master alloy 2 Master alloy 3 <![CDATA[ Nd Atom%]]> 22 10 14 Fe atomic% 69 83 72 B atoms % 9 7 14

[0050] Table 2

[0051]

[0052] Matters not covered in this invention are common knowledge.

[0053] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for producing a low-oxygen homogeneous target material for growing NdFeB thin films, characterized by: The method comprises the following steps: preparing a low-oxygen homogeneous target material for growing a NdFeB thin film by using a mother alloy batching pouring method and a split mold; the mother alloy batching comprises a mother alloy 1, a mother alloy 2 and a mother alloy 3, the mother alloy 1, the mother alloy 2 and the mother alloy 3 are prepared by using Nd, Fe and B in a rapid solidification ingot furnace; any mass ratio of the mother alloy 1, the mother alloy 2 or the mother alloy 3 should not be less than 10% of the total mass of the mother alloy batching, and the oxygen content of the mother alloy is less than 150 ppm. The elements of the mother alloy batching are centered on Nd, Fe and B, Nd can be replaced by one or more of Pr, La and Ce in whole or in part, and Fe can be replaced by one or more of Al, Ga, Nb or Co in part; the total content of Nd, Pr, La and Ce in the mother alloy 1 is more than 20% of the atomic ratio of the mother alloy 1, the total content of Fe, Co, Al, Ga and Nb and the atomic ratio of B are greater than 7 and less than 8; the total content of Fe, Co, Al, Ga and Nb in the mother alloy 2 is more than 80% of the atomic ratio of the mother alloy 2, the total content of Nd, Pr, La and Ce and the atomic ratio of B are greater than 1 and less than 2; the content of B in the mother alloy 3 is more than 12% of the atomic ratio of the mother alloy 3, the total content of Nd, Pr, La and Ce and the total content of Fe, Co, Al, Ga and Nb are greater than 0.15 and less than 0.25; the atomic ratio of Nd, Pr, La and Ce is between 13% and 17% in the mother alloy composition, the atomic ratio of Fe, Co, Al, Ga and Nb is between 72% and 78% in the mother alloy composition, and the atomic ratio of B is between 8% and 12% in the mother alloy composition; the mixed mother alloy is poured into a split mold by a vacuum melting method to form a solidification, the split mold should be composed of a ring-shaped side wall and a flat bottom plate, the material of the ring-shaped side wall is pure iron, low-carbon steel or stainless steel, and the material of the flat bottom plate is quartz glass, alumina or boron nitride ceramic.

2. The method of claim 1, wherein the method further comprises: The atomic ratio of Nd, Fe and B in the mother alloy batching is 15%, 75% and 10%.

3. The method of claim 1, wherein the method further comprises: The vacuum melting method is electric arc melting, induction melting or suspension melting.

Images