Method for simultaneously improving the remanence and coercivity of micron ndfeb-based permanent magnetic films

Abstract

The application provides a method for simultaneously improving the remanence and coercivity of a micrometer-scale NdFeB-based permanent thick film. The method is to introduce a combined layer during the growth of the NdFeB-based thick film, and the combined layer is arranged between hard magnetic layers, and the arrangement structure of the combined layer is: isolation layer / soft magnetic layer / isolation layer. The non-magnetic layer in the combined layer acts as an isolation layer to increase the coercivity to a certain extent, and the soft magnetic layer improves the remanence through long-range interaction between the hard magnetic layer and the thick film. The isolation layer is preferably Ta, and the soft magnetic layer is preferably Fe. When the combined layer is inserted into 7 layers, and the thickness of the soft magnetic layer is 80 nm, the remanence of the permanent thick film reaches 1.2 T, and the coercivity is maintained at above 1.5 T. The method provides performance guarantee for the use of the NdFeB-based permanent thick film in MEMS and micro permanent magnet motors.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet material preparation technology, and in particular provides a method for simultaneously improving the remanent magnetization and coercivity of micron-sized NdFeB-based permanent magnet thick films. Background Technology

[0002] Modern electronic components are developing towards miniaturization, integration, flexibility, and systematization. Developing high-performance permanent magnets for use in microelectromechanical systems (MEMS) is crucial for driving the operation of these components, such as electromagnetic sensors, actuators, and energy harvesters.

[0003] NdFeB-based permanent magnets have been applied in many macroscopic systems due to their excellent permanent magnetic properties, such as permanent magnet motors, loudspeakers, and magnetic resonance imaging (MRI) instruments. Moreover, compared to electromagnets, permanent magnets have lower heat loss and can generate stable and sufficiently large magnetic fields within a limited size range. Microelectromechanical systems (MEMS) are an industrial technology that integrates microelectronics and mechanical engineering, operating within the micrometer scale. Their fabrication processes are based on Si-based semiconductor and microelectronic processes. With the maturation of nanomaterial fabrication technology, it has become possible to prepare NdFeB-based permanent magnet thick films using magnetron sputtering. The NdFeB-based permanent magnet film sputtered on a Si substrate grows with its easy magnetization axis along the C-axis to obtain a high-performance, perpendicularly anisotropic permanent magnet thin film. Furthermore, this method is well-compatible with both semiconductor and microelectronic processes.

[0004] From the design perspective of magnetic microelectromechanical systems (MEMS), the engineering properties related to NdFeB-based permanent magnets include magnetic properties (including coercivity, saturation magnetization, remanent magnetization, and maximum energy product), thermal stability properties (including Curie temperature, maximum operating temperature, and remanence temperature coefficient), and chemical stability. The magnitude of coercivity determines the system's operating magnetic field, demagnetization resistance, and operating temperature range. The maximum energy product determines the system's output energy. Although magnetocrystalline anisotropy and saturation magnetization represent the theoretical limits of the material, the magnetic properties at the normal operating point of the permanent magnet cannot reach these limits. For example, in the absence of an external magnetic field, the magnetization (surface field) near the surface of a magnetized permanent magnet thin film is only 20%-50% of the remanence. While increasing the Fe content can typically increase saturation magnetization, this leads to a significant decrease in coercivity, and the remanence cannot be guaranteed. Leveraging the characteristics of magnetron sputtering for thin film fabrication, the performance of NdFeB-based permanent magnet thick films can be optimized by introducing buffer layers, capping layers, and isolation layers to achieve a sufficiently large surface field to meet application requirements. Summary of the Invention

[0005] To address the aforementioned issue of the trade-off between remanent magnetization and coercivity in micron-sized NdFeB-based permanent magnet thick films, this invention aims to provide a method for enhancing the remanent magnetization of NdFeB-based permanent magnet thick films while simultaneously improving the coercivity to a certain extent. This method can increase the remanent magnetization to a level where the saturation magnetization is less than 100 Am. 2 / kg NdFeB-based permanent magnet thick films, increased to over 100 Am 2 The method achieves a yield of / kg and maintains a coercivity of over 1.5T, providing a performance guarantee for the application of NdFeB-based permanent magnet thick films in MEMS and micro permanent magnet motors.

[0006] The technical solution of this invention is as follows:

[0007] A method for simultaneously improving the remanent magnetization and coercivity of micron-sized NdFeB-based permanent magnet thick films is characterized by inserting a non-magnetic / soft magnetic composite layer during the growth of a hard magnetic layer, such that the composite layer is located between the hard magnetic layers, and the composite layer is arranged in the following structure: isolation layer / soft magnetic layer / isolation layer.

[0008] in:

[0009] The isolation layer is a non-magnetic layer that prevents the metal from the soft magnetic layer from diffusing into the hard magnetic layer and also isolates adjacent hard magnetic layers. The isolation layer is composed of one or more of Ta, Mo, W, and Ti, and its thickness is ≥2nm.

[0010] The soft magnetic layer is one of Fe, Co, and Ni or an alloy thereof, and the thickness of the soft magnetic layer is 50-100 nm.

[0011] The hard magnetic layer is an NdFeB-based rare-earth permanent magnet material, Nd2Fe 14 B is the hard magnetic master phase, mainly composed of Nd, Fe and B. Some Nd can be replaced by one or more of Dy, Tb, Pr and Ce, and Fe can be partially replaced by one or more of Co, Ga and Nb; the total hard magnetic layer thickness is greater than 6 μm.

[0012] As a preferred technical solution:

[0013] The thickness of the isolation layer is 2-5nm, the thickness of the soft magnetic layer is 50-80nm, the thickness of the hard magnetic layer is 500nm-3μm, and the number of layers in the combined layer is 2-7.

[0014] The isolation layer is Ta, the soft magnetic layer is Fe, and the hard magnetic layer is preferably Nd-Dy-Fe-Co-B.

[0015] When the soft magnetic layer is Fe, the optimal thickness is 80 nm, and the optimal number of combined layers is 7, with each combined layer having a total thickness of 84 nm. The specific structure is [isolation layer (2 nm) / soft magnetic layer (80 nm) / isolation layer (2 nm)]; an 84 nm combined layer is inserted into every 0.75 μm hard magnetic layer, resulting in a total NdFeB-based permanent magnet thick film thickness of 6.688 μm (including a 50 nm buffer layer and a 50 nm capping layer). This structure and layer number scheme can maximize the remanent magnetization and improve the coercivity to a certain extent. The resulting micron-sized NdFeB-based permanent magnet thick film has a remanent magnetization of 100.01 Am. 2 / kg, with a coercivity of 1.55T.

[0016] This invention utilizes DC magnetron sputtering to prepare all layers in the following order: buffer layer (Ta) / hard magnetic layer / combined layer / ... / capping layer (Ta). The sputtering temperature is 500-600℃, the annealing temperature is 650-750℃, and the annealing time is 20-30 min. The NdFeB-based hard magnetic layer is sputtered using a self-made alloy target obtained through powder metallurgy.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention inserts a non-magnetic / soft magnetic composite layer into an NdFeB-based permanent magnet thick film. The non-magnetic layer serves two purposes: firstly, it isolates adjacent hard magnetic layers, allowing the NdFeB-based hard magnetic layer grains to preferentially align in the out-of-plane direction. From a macroscopic perspective, this reduces the surface roughness of the thick film. Secondly, at high temperatures, the diffusion of the soft magnetic layer into the hard magnetic layer affects the phase formation and orientation of the hard magnetic layer; therefore, the isolation layer also prevents the diffusion of the soft magnetic layer. Furthermore, stress occurs during film fabrication, and the insertion of the isolation layer causes the rare earth phase to aggregate near the non-magnetic layer, isolating the hard magnetic grains and the interaction between adjacent hard magnetic layers, thus improving intrinsic coercivity. The long-range magnetostatic interaction between the thicker hard magnetic layer and the thicker soft magnetic layer can significantly increase the remanent magnetization of the magnet. Compared to localized exchange coupling, the longer-range magnetostatic interaction is more beneficial for improving magnetic performance without decoupling. Therefore, the insertion of a soft magnetic layer of appropriate thickness is key to improving the remanent magnetization of the permanent magnet thick film without reducing coercivity. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an NdFeB-based multilayer thick film.

[0020] Figure 2 It is an in-plane and out-of-plane hysteresis loop of a Ta / NdDyFeCoB / Ta monolayer thick film with a thickness of 6μm.

[0021] Figure 3The out-of-plane hysteresis loop of the composite multilayer thick film Ta / (NdDyFeCoB / [Ta / Fe / Ta])x / NdDyFeCoB / Ta is when the combined layer thickness is 54nm and the number of layers is 2, 7 and 11 in Example 1.

[0022] Figure 4 The demagnetization curves near the coercivity of the composite multilayer thick film Ta / (NdDyFeCoB / [Ta / Fe / Ta])x / NdDyFeCoB / Ta are shown in Example 1 when the combined layer thickness is 54nm and the number of layers is 2, 7 and 11.

[0023] Figure 5 The out-of-plane hysteresis loop and its partial image are of the composite multilayer thick film with different thicknesses when the number of combined layers is 7 in Example 2: Ta / (NdDyFeCoB / [Ta / Fe / Ta]x nm)7 / NdDyFeCoB / Ta.

[0024] Figure 6 It is the out-of-plane and in-plane hysteresis loop of the composite multilayer thick film with 7 Fe layers directly inserted in Example 3: Ta / (NdDyFeCoB / Fe 80nm])7 / NdDyFeCoB / Ta.

[0025] Figure 7 The out-of-plane and in-plane hysteresis loops of the composite multilayer thick film with Nd-Fe-B hard magnetic layer composition in Example 4: Ta / (NdFeB / [Ta / Fe / Ta]84nm)7 / NdFeB / Ta. Detailed Implementation

[0026] 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.

[0027] like Figure 1 The diagram shows the structure of a NdFeB-based permanent magnet multilayer thick film. From the inside out, the layers are: substrate, buffer layer, (hard magnetic layer / combined layer)x, hard magnetic layer and capping layer. The combined layer consists of: isolation layer, soft magnetic layer and hard magnetic layer.

[0028] Example 1:

[0029] In this embodiment, a Si substrate is used, and an Nd2 target is used. 15.5 Dy 0.5 Fe 65 Co 10 B 10Using self-made alloy targets (hereinafter referred to as NDFCB), Ta metal targets, and Fe metal targets, the total thickness of the hard magnetic layer in the prepared NdFeB-based multilayer thick film was approximately 6 μm. A composite layer was uniformly inserted into the hard magnetic layer. The composite layer consisted of 2 nm Ta, 50 nm Fe, and 2 nm Ta layers, with 2, 7, and 12 layers inserted, respectively. That is, one composite layer was inserted for every 2 μm, 0.75 μm, and 0.5 μm thick hard magnetic layer grown. The effect of the number of composite layers inserted on the magnetic properties of the composite permanent magnet thick film was investigated.

[0030] Film-forming process and conditions:

[0031] Step (1) Buffer layer Ta: Deposition thickness 50nm, deposition temperature 30-300℃.

[0032] Step (2) NDFCB hard magnetic layer: deposition thickness of 6μm, 2μm and 0.75μm, deposition temperature of 500℃.

[0033] Step (3) Combination layer:

[0034] The isolation layer Ta has a deposition thickness of 2 nm and a deposition temperature of 300 °C.

[0035] Soft magnetic layer Fe: deposition thickness 50 nm, deposition temperature 300 °C.

[0036] The isolation layer Ta has a deposition thickness of 2 nm and a deposition temperature of 300 °C.

[0037] The NDFCB hard magnetic layer and composite layer are then grown repeatedly 2, 7 or 12 times.

[0038] Step (4) NDFCB hard magnetic layer: deposition thickness of 2μm, 0.75μm and 0.5μm, deposition temperature of 500℃.

[0039] Step (5) Capping layer Ta: Deposition thickness 50nm, deposition temperature 30-300℃.

[0040] Step (6) High-temperature annealing: Heat to 650℃ and hold for 20 minutes.

[0041] A total of three samples were prepared, designated as Examples 1-1, 1-2, and 1-3. Furthermore, as a comparison, to investigate the effect of the inserted composite layer on magnetic properties, a single-layer permanent magnet thick film without the inserted composite layer was also prepared in this example, designated as Example 1.

[0042] Figure 2 Example 1: In-plane and out-of-plane hysteresis loops of a single-layer NDFCB permanent magnet thick film.

[0043] Figure 3For Example 1, when the combined layer is [Ta 2nm / Fe ​​50nm / Ta 2nm], the out-of-plane hysteresis loops of Ta / (NdDyFeCoB / [Ta / Fe / Ta])x / NdDyFeCoB / Ta under different layer numbers are shown.

[0044] Figure 4 Example 1: Demagnetization curves near the coercivity of Ta / (NdDyFeCoB / [Ta / Fe / Ta])x / NdDyFeCoB / Ta under different layer numbers when the combined layer is [Ta 2nm / Fe ​​50nm / Ta 2nm].

[0045] Combination Figure 2 , 3 Table 1 summarizes the magnetic properties of the NDFCB composite permanent magnet thick films, showing the remanent magnetization and coercivity of the NDFCB composite permanent magnet thick films in Examples 1, 1-1, 1-2, and 1-3. The results show that the remanent magnetization and coercivity of the composite thick film are improved by inserting composite layers; the more layers inserted, the higher the remanent magnetization (decoupling occurs after inserting 12 layers, and the remanence decreases). The NDFCB composite permanent magnet thick film sample with 7 composite layers inserted exhibits higher coercivity and remanent magnetization. Therefore, Example 2 will be conducted with 7 composite layers inserted.

[0046] Table 1:

[0047]

[0048] Example 2

[0049] In this embodiment, the influence of the thickness of the soft magnetic layer in the composite layer on the magnetic properties of the composite permanent magnet thick film is investigated. Si is used as the substrate, and Nd is used as the target material. 15.5 Dy 0.5 Fe 65 Co 10 B 10 The self-made alloy target (hereinafter referred to as NDFCB), Ta metal target and Fe metal target, the hard magnetic layer thickness in the prepared NdFeB-based multilayer thick film is about 6 μm, the composite layer is uniformly inserted into the hard magnetic layer, the composite layer is composed of Ta, Fe and Ta, a total of 7 layers are inserted, the thickness of the isolation layer Ta is 2 nm, and the thickness of the soft magnetic layer Fe is 70 nm and 80 nm, respectively.

[0050] Film-forming process and conditions:

[0051] Step (1) Buffer layer Ta: Deposition thickness 50nm, deposition temperature 30-300℃.

[0052] Step (2) NDFCB hard magnetic layer: deposition thickness 0.75μm, deposition temperature 500℃.

[0053] Step (3) Combination layer: Isolation layer Ta: deposition thickness 2nm, deposition temperature 300℃.

[0054] Soft magnetic layer Fe: deposition thickness of 70nm or 80nm, deposition temperature of 300℃.

[0055] The isolation layer Ta has a deposition thickness of 2 nm and a deposition temperature of 300 °C.

[0056] The NDFCB hard magnetic layer and the composite layer were then grown repeatedly for a total of 7 cycles.

[0057] Step (4) NDFCB hard magnetic layer: deposition thickness 0.75μm, deposition temperature 500℃.

[0058] Step (5) Capping layer Ta: Deposition thickness 50nm, deposition temperature 30-300℃.

[0059] Step (6) High-temperature annealing: Heat to 650℃ and hold for 20 minutes.

[0060] Two samples were collected in total, designated as Examples 2-1 and 2-2. Furthermore, to investigate the effect of the soft magnetic phase thickness in the inserted composite layer on the magnetic properties, the above samples were compared with Examples 1 and 1-2.

[0061] Combination Figure 2 , 3 Table 2 summarizes the magnetic properties of the composite permanent magnet thick film, comparing the remanent magnetization and saturation magnetization of the NDFCB composite permanent magnet thick films in Examples 1, 1-2, 2-1, and 2-2. Comparing Examples 1 and 1-2, the results show that the remanent magnetization of the composite permanent magnet thick film increases with the increase of the soft layer thickness, while the coercivity remains above 1.5T. Compared to Example 1 without the composite layer insertion, the remanent magnetization increases from 62.62 Am. 2 / kg increased to 100.01Am 2 / kg, and the coercivity also increased from 1.35T to 1.55T, without any decoupling phenomenon.

[0062] Table 2:

[0063]

[0064] Example 3

[0065] This embodiment serves as a comparative example to Example 2-2, exploring the importance of the Ta layer in maintaining the coercivity in the composite layer. Using Si as the substrate, the hard magnetic layer in the NdFeB-based multilayer thick film is approximately 6 μm thick, with only a soft magnetic Fe layer inserted, for a total of 7 layers. The thickness of the soft magnetic Fe layer is 80 nm.

[0066] The film-forming process and conditions were the same as in Examples 2-2 above, resulting in a total of one sample: Example 3-1. (Combined) Figure 5 and Figure 6 The changes in saturation magnetization, remanent magnetization, and coercivity were analyzed in embodiments with and without a Ta isolation layer. The results show that although the saturation magnetization increased from 125.75 Am... 2 / kg increased to 133.86Am 2 / kg, but the remanent magnetization decreased from 113.67 Am. 2 / kg decreased to 51.84Am 2 / kg, and the coercivity is significantly reduced to 0.4T. Therefore, it can be concluded that the Ta isolation layer is extremely important in maintaining the magnitude of coercivity and remanence in the composite layer.

[0067] Example 4

[0068] This embodiment serves as a comparative example to Example 2-2, exploring the optimal selection of the hard magnetic layer. Si was used as the substrate, Nd-Fe-B as the hard magnetic layer, and Fe as the soft magnetic layer. The total thickness of the hard magnetic layer was 6 μm. Seven soft magnetic layers were inserted into the hard magnetic layer (the Fe layer was 80 nm thick), for a total of seven layers. A Ta layer with a thickness of 2 nm was used to isolate the hard and soft magnetic layers.

[0069] The film-forming process and conditions were the same as in Examples 2-2 above, but the number of samples was two, named Examples 4-1 and 4-2. Figure 2 , Figure 5 and Figure 7 The changes in saturation magnetization, remanent magnetization, and coercivity of embodiments with altered hard magnetic layers were analyzed. The results show that although the magnetic properties are still improved after the insertion of the intermediate layer—for example, the coercivity increases from 0.85 T to 1.25 T, and the remanent magnetization increases from 47.26 Am—the magnetic properties remain improved. 2 / kg increased to 81.01Am 2 / kg, saturation magnetization from 72.42 Am 2 / kg increased to 107.05Am 2 / kg. However, compared with Example 2-2 (hard magnetic layer is NdDyFeCoB) which also has 7 intermediate layers and Fe layer thickness of 80 nm, Example 4-2 has lower coercivity, remanent magnetization and saturation magnetization than Example 2-2. Therefore, the hard magnetic layer is preferably Nd-Dy-Fe-Co-B.

[0070] Matters not covered in this invention are common knowledge.

[0071] 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 simultaneously improving the remanent magnetization and coercivity of micron-based NdFeB permanent magnet thick films, characterized in that: The total thickness of the permanent magnet thick film is not less than 6 μm, and the thickness of a single hard magnetic layer is 500 nm - 3 μm; by inserting a non-magnetic / soft magnetic composite layer during the growth of the hard magnetic layer, the composite layer is positioned between the hard magnetic layers, and the composite layer arrangement structure is: isolation layer / soft magnetic layer / isolation layer; wherein, the thickness of the soft magnetic layer is 50-100 nm, and the thickness of the isolation layer is ≥ 2 nm.

2. The method according to claim 1, characterized in that: The isolation layer is one or more of Ta, Mo, W, and Ti.

3. The method according to claim 1, characterized in that: The soft magnetic layer is one of Fe, Co, and Ni or an alloy thereof.

4. The method according to claim 1, characterized in that: The isolation layer is Ta, the soft magnetic layer is Fe, and the hard magnetic layer is Nd-Dy-Fe-Co-B.

5. The method according to claim 4, characterized in that: The obtained micron-scale NdFeB-based permanent magnet thick film has a remanent magnetization of 100.01 Am. 2 / kg, with a coercivity of 1.55 T.

6. The method according to claim 1, characterized in that: All layers were prepared by DC magnetron sputtering in the following order: buffer layer / hard magnetic layer / combined layer / ... / capping layer. The sputtering temperature was 500-600 ℃, the annealing temperature was 650-750 ℃, and the annealing time was 20-30 min.

7. A micron-sized NdFeB-based permanent magnet thick film prepared by the method according to any one of claims 1 to 4 and 6, characterized in that: The micron-scale NdFeB-based permanent magnet thick film contains an NdFeB-based hard magnetic layer and a non-magnetic / soft magnetic composite layer. The remanence of the permanent magnet thick film is increased by 37%, and the coercivity is not less than 1.5 T.

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