KR100305699B1 - Manufacturing Method of Ultrafine Permanent Magnet Thin Film of Niodymium Iron Boron / Iron / Niodymium Iron Boron Thin Film Structure - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultrafine grain permanent magnet thin film having an NdFeB / Fe / NdFeB structure using Fe as a soft magnetic layer by a laser ablation method. the method, a composition for deposition of the magnetic layer around atomic percent (at.%) to _{Nd X Fe 90.98-X B 9.02} (25≤X≤32) of NdFeB-based targets and for the deposition of the soft magnetic pure iron (Fe) target Heating the single crystal (100) Si substrate temperature to a temperature of 620 ° C. or higher in the reaction chamber in a vacuum; After rotating the NdFeB-based target, the pure iron target and the (100) Si substrate, KrF laser beams were alternately irradiated to the above two targets in an energy density range of 3.08 J / cm ² for a period of time showing hard magnetism on the substrate. Depositing a NdFeB-based thin film having a thickness of 3.6 to 54 nanometers (nm) with a first layer, and depositing a soft magnetic pure iron thin film having a thickness of 15 to 112 nanometers with a second layer thereon, and then again having the same layer as that of the first layer. Depositing a 3.6-54 nanometer hard magnetic NdFeB-based thin film controlled in thickness to form a three-layer film; A method of manufacturing an ultrafine grain permanent magnetic thin film having a NdFeB / Fe / NdFeB structure, comprising: cooling a three-layer deposited (100) Si substrate at a cooling rate of 3 to 5 ^° C. per minute.

Description

Manufacturing method of ultra fine grain permanent magnet thin film of niobium iron boron / iron / niodymium iron boron thin film structure

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultrafine grain permanent magnet thin film having an NdFeB / Fe / NdFeB structure using Fe as a soft magnetic layer by laser ablation, and in particular, irradiating an excimer laser beam to a target mounted inside a reaction chamber. By applying laser ablation to produce thin films, the ultrafine grain permanent magnet of 3-layer structure of NdFeB / Fe / NdFeB which simultaneously increases coercive force and residual magnetization value through induction of exchange interaction by controlling process variables and thickness of thin film It can be formed on the (100) Si substrate which is the most commonly used at low cost in thin film production.

Since 1983, the discovery of bulk permanent magnetic alloys based on three-way Nd ₂ Fe ₁₄ B phase exhibiting excellent hard magnetic properties, The research to be derived has been actively conducted.

On the other hand, in 1988, it was slightly inferior to the characteristics of the bulk permanent magnet alloy based on the conventional Nd ₂ Fe ₁₄ B phase, but it was better than the ferrite permanent magnet, but better than the ferrite permanent magnet. (R. Coehoorn, DBde Mooij, JPWB Duchateau, and KHJ Buschow: J.de Phys., 49, (1988) C8-669, EFKneller and R. Hawig: IEEE Trans. Magn., 27) , (1991) 3583, S.Hirosawa, H.Kanekiyo, and M. Uehara: J. Appl. Phys., 73, (1993) 6488, RKMishra and V. Panchanathan: J. Appl. Phys., 75, (1994 6652, CJ Yang and EBPark: J. Magn. Magn. Mat., 80, (1997) 101, J. Ding, PGMcCormic, and R. Street: J. Magn. Magn. Mat., 124, (1994) 1, J. Ding, Y. Liu, R. Street, and PGMcCormic: J. Appl. Phys., 72, (1994) 1032).

The ultrafine composite permanent magnet has a nanometer-sized Nd ₂ Fe ₁₄ B phase that exhibits hard magnetic properties and a low-cost Fe, Fe ₃ B phase that exhibits soft magnetic properties. By generating exchange coupling between hard and soft magnetic grains simultaneously, high residual magnetization value and high coercive force are realized simultaneously to show high energy ((BH) _max ).

Recent advances in monolithic microwave integrated circuits (MMICs), however, have led to the miniaturization and lightweighting of microwave equipment, as magnets for bias magnetic fields for efficient MMICs, such as micromotors and microactuators. Research on thinning of the permanent magnet material, which is of interest due to the expectation of application in the field of micromechanics and microelectronics (micromechanics and microelectronics), is relatively less than bulk, and especially in the manufacture of ultrafine permanent magnet thin film. There is rare research on this.

The sputtering method has been mainly used as a conventional NdFeB-based thin film manufacturing method (FJCadieu, TDCheung, L. Wickramasekara and N. Kamprath: IEEE Trans. Mag. Mag-22 (1986) p752, KDAylesworth, ZR Zhao, DJSellmyer and GCHadjipanayis: J. Appl. Phys. 64, (1988) p.5742, SM Parhofer, J. Wecker, G.Gieres and L. Schultz: IEEE Trans. Mag. Mag-32 (5) ( 1966) p.4437)

However, these methods are relatively complex due to the presence of energy sources inside the reaction chamber, and the sputtering yields of the individual elements of the target are different. Therefore, accurate composition control in the production of three or more alloy thin films such as NdFeB in the manufacturing process is difficult. It is difficult.

It is an object of the present invention to irradiate an excimer laser beam to a target mounted inside a reaction chamber in which the method is recently developed, which is relatively advantageous for solving the problems of the thin film manufacturing method. laser ablation method (SBKrupanidhi, N.Maffei, D.Roy and CJPeng: J. Vac.Sci.Technol.A10 (4), (1992) p.1815, K.Tanaka, Y.Omata, Y.Nishikawa , Y. Yoshida, K. Nakamura: IEEE Trans. Journal on Magnetics in Japan. 6, 11 (1991) P. 1001, R. Seed and C. Victoria: IEEE Trans. Mag. 28, 5 (1992) P. 3216 By applying), NdFeB / Fe / NdFeB 3 layer structure ultra fine grain permanent magnet thin film which increases the coercive force and residual magnetism at the same time by controlling the process variables and the thickness of the thin film and inducing exchange interaction, It is intended to be formed on the most commonly used (100) Si substrate.

1 is a graph showing the magnetic properties of the NdFeB / Fe / NdFeB-based three-layer film prepared according to the method of the present invention

Figure 2 is another graph showing the magnetic properties of the NdFeB / Fe / NdFeB-based three-layer film prepared according to the method of the present invention

The present invention relates to a method for manufacturing a three-layer thin film using the laser ablation method, wherein the composition is Nd _X Fe _90.98-X B _9.02 (25≤X≤) in atomic percent (at.%) For deposition of the hard magnetic layer. 32) heating a single crystal (100) Si substrate temperature to a temperature of 620 ° C. or higher in a vacuum reaction chamber equipped with a pure iron (Fe) target to deposit an NdFeB-based target and a soft magnetic layer, and an NdFeB-based target and a pure iron target. And rotating the (100) Si substrate and irradiating the KrF laser beam alternately on the two targets in an energy density range of 3.08 J / cm ² to the first substrate exhibiting hard magnetism on the substrate. Depositing an NdFeB based thin film having a thickness of 3.6 to 54 nanometers (nm), and depositing a soft magnetic pure iron thin film having a thickness of 15 to 112 nanometers (nm) as a second layer thereon, and then again having the same thickness as that of the first layer. To form a three-layer film by depositing a hard magnetic NdFeB-based thin film of 3.6 to 54 nanometers And cooling the three-layer film deposited (100) Si substrate at a cooling rate of 3 to 5 ° C. per minute.

Referring to the operation of the present invention configured as described above is as follows.

In the present invention, the laser ablation method is applied to heat the (100) Si substrate to a temperature higher than at least 620 ° C., because the first layer and the third layer of the three-layer structure are heated when the temperature is lower than that. Absorbed particles from the NdFeB-based target to form the hard magnetic layer of the quenched on the substrate, the NdFeB amorphous phase (mainstream) is the mainstream of the thin film exhibits soft magnetic propertes (coercivity) is significantly small This is because it adversely affects the expression of exchange interactions.

The heating temperature of the (100) Si substrate is more preferably in the temperature range of 640 to 700 ° C. The reason is that when the temperature reaches 700 ° C or higher, the Nd ₂ Fe ₁₄ B hard magnetic grains grow excessively in the formed NdFeB-based thin film. Rather, because it adversely affects the magnetic properties.

On the other hand, after adjusting the heating temperature of the (100) Si substrate to a temperature range of 640 to 700 ° C., the NdFeB-based target and the pure iron target can be used to obtain economical use of the target during laser ablation and to obtain a uniform plume. And (100) Si substrate is preferably rotated for uniform thickness of the deposited thin film, more preferably 3 to 4 rpm.

The energy density of the KrF excimer laser beam irradiated to the rotated NdFeB-based target and the pure iron target is preferably 2.75 to 3.2 J / cm ² , because the deposition of the first layer is less than 2.75 J / cm ² . rate is 2.0 Å / S or less, cheungchak speed of the second layer is a 0.65 Å / S or less is not desirable the longer the Time productivity for producing a predetermined film thickness away from fast evaporation rate is above 3.5 J / cm ² Due to the lack of active crystallization of Nd ₂ Fe ₁₄ B, it adversely affects the magnetic properties of the first layer or the surface of the first layer or the second layer is remarkably rough, which makes it difficult to induce exchange interaction in the three-layer film structure. to be.

The composition of the NdFeB-based target used in the ablation is preferably Nd _X Fe _90.98-X B _9.02 (25≤X≤32). When it is 25 at.% Or less, the angular formation and the coercive force property are deteriorated, indicating soft magnetic properties. If it is more than.%, The light magnetic properties become good, but it is economically disadvantageous because a large amount of expensive rare earth element Nd is required.

In addition, the use of a target containing relatively high amounts of Fe or B causes excessive α-Fe in each thin film or increases the amorphous crystallization temperature, which adversely affects the hard magnetic properties.

In order to increase the coercive force and residual magnetization value by inducing exchange interaction between soft and hard magnetic layers in the structure of the three-layer film during ablation, the thickness of the second layer is controlled to 15 to 30 nanometers and the total volume of the three-layer film is controlled. It is preferable to control the thickness of the first layer film to 3.6 to 11 nanometers so that the volume ratio of the second layer film to 50 to 80%. When the thickness of the second layer is 15 nm or less, the volume of the second layer film is In order to satisfy the ratio of at least 50%, the thicknesses of the first and third layers should be 4 nanometers or less. The film thickness is so thin that the formation of Nd ₂ Fe ₁₄ B films with uniform thickness is not easy to obtain the magnetic properties. If the thickness of the second layer is more than 30 nanometers, the exchange interaction between the soft and hard magnetic layers is reduced, and thus the soft magnetic properties of pure iron, which is a soft magnetic layer, are not suitable for the purposes of the present invention. Volume ratio is less than 50% Be not less than 80% is because soft, hard magnetic interlayer exchange interaction is reduced to a disadvantage in achieving the object of the present invention.

In the present invention, when the NdFeB-based three-layer film is deposited under the above conditions, it is preferable to cool the substrate at a cooling rate of 3 to 5 ^° C. per minute, because if the cooling rate is higher than 5 ° C., the thin film is separated from the substrate surface. And cracking is caused, and if it is later than 3 ° C, it takes too much time for cooling and is unnecessary.

In addition, the target used in the present invention was produced by plasma arc melting with NdFeB alloy or pure iron in a predetermined composition, and the diameter of the target is preferably 20 to 50 mm, and the element is preferably high purity, but preferably 99.9% or more. Do.

As described above, when the thin film is grown by the laser ablation method by precisely controlling the substrate temperature, the laser beam energy density, the composition of the target, and the thickness of each layer, the exchange interaction is expressed, and the coercive force and residual magnetization value are simultaneously increased. An ultrafine permanent magnet thin film is obtained.

Hereinafter, the present invention will be described in detail through examples.

Example 1

After the initial vacuum of the reaction chamber of the laser ablation apparatus was 4x10 ^-6 Torr or less, a thin film was prepared by allowing the substrate temperature to reach 680 ° C. Nd with a diameter of 50mm and a thickness of 5mm on a target holder that can be mounted on a disc with three types of targets at intervals of 120 ° and can be deposited in order from the first layer to the third layer when manufacturing a three-layer film. _27.51 Fe _63.47 B _{9.02 The} target and the pure iron target were mounted so that the target at the time of ablation was tilted at 45 ° from the direction of the laser beam incident, so that the rotational speed of the target was 3.3 rpm.

The substrate was a 10 × 10 × 1 mm size (100) Si single crystal. The distance from the target center to the center of the substrate was fixed at 5 cm, and the rotation speed was 3 rpm. In this case, an equipment using Kr and F gas was used as an excimer laser beam generator having a wavelength of 248 nm.

After the laser beam energy density at the target surface is fixed at the pulse frequency (repetition rate) of the laser beam at 10 Hz, the KrF laser output combines two convex lenses with a focal length of 50 cm to determine the size of the beam at the target surface. The energy density was adjusted to 3.08 J / cm ² , and the value was confirmed using a laser power energy meter.

In the laser ablation process described above, A was controlled to 3.6 to 54 and B to 15 to 112 so that the volume fraction (B / (2A + B) in the structural formula below) of the pure iron Fe layer as the second layer was 51%. nm) [NdFeB] / (B nm) [Fe] / (A nm) [NdFeB] After forming a three-layer film, lowering the temperature to 300 ° C at a cooling rate of 3 to 5 ° C / min, and then in the chamber to room temperature. Cooled in.

Various characteristics of the three-layer film prepared by the above method were evaluated and the results are shown in Table 1 and FIG. 1. Among the properties, the film thickness was measured by "alpha-step" and the surface shape was observed by atomic force microscopy (AFM). Crystal orientation of thin films was evaluated by X-ray diffraction analysis, and magnetic properties were evaluated using a vibrating sample magnetometer (VSM).

In Table 1, the angular ratio and coercive force are measured values in a magnetic field of 16 kOe, and //, Indicates that the magnetic fields were applied in parallel and vertical directions with respect to the thin film plane during measurement.

As shown in Table 1 and FIG. 1, the angular ratio and the coercive force are sensitively changed according to the thickness of the pure iron (second layer), which is a soft magnetic layer. In particular, when the magnetic field is applied horizontally to the thin film surface, the change is Remarkable

In other words, as the thickness of pure iron decreases at 112 nanometers, the angular ratio and coercive force, which are evidence of the exchange interaction, tend to increase at the same time, and at 23 nanometer thickness, both values show the same tendency and then decrease.

The angular ratio and the coercive force obtained when the horizontal magnetic field is applied to the thin film surfaces of Inventive Examples 1, 2, and 3 are compared with the values of Comparative Example 1, which are hard magnetic monolayer films, respectively.

On the other hand, if the thickness of the first layer and the third layer is less than 15 nanometers or less, it is difficult to form a uniform thin film that can cause exchange interactions. If the thickness is more than 30 nanometers, the soft magnetic layer becomes larger than the effective distance of the exchange interaction force. The magnetic properties of the pure iron layer determined the characteristics of the entire film to show soft magnetic properties.

Eventually, when the thickness of pure iron (second layer) is in the range of 15 to 30 nanometers, the exchange interaction with the upper and lower hard magnetic layers (first layer and third layer) increases, and the entire three layer film is completely bonded by the exchange interaction force. This thickness is the optimal distance for developing exchange interactions. In this case, the crystal grain diameter of the uppermost layer (third layer) confirmed through AFM was 20-30 nanometers.

Example 2

As can be seen in Example 1, since the thickness of the pure iron (second layer) in the range of 15 to 30 nanometers in the three-layer film structure is the optimum distance for expressing the exchange and coral action, the square ratio and the coercivity increase simultaneously. (A nm) [NdFeB] / (23 nm) [Fe] changed the volume of pure iron to the total volume of the three-layer film by fixing the thickness of pure iron to 23 nanometers and adjusting the thickness of the first layer and the third layer appropriately. After the thin film was prepared by the same method as in Example 1, the effect of the volume fraction of pure iron on the magnetic properties of the thin film was analyzed by the same method as in Example 1, and then The results are shown in Table 2 and FIG. 2.

In Table 2, the angular ratio and coercive force are measured values in a magnetic field of 16 kOe, and //, Indicates that the magnetic fields were applied in parallel and vertical directions with respect to the thin film plane during measurement.

As shown in Table 2 and FIG. 2, the angular ratio and the coercive force are sensitively changed depending on the volume fraction of the pure iron (second layer), which is a soft magnetic layer. Remarkable

In other words, as the volume fraction of pure iron increases from 50% to about 80%, the angular ratio increases to show the characteristics closer to that of pure iron monolayer of Comparative Example 8, while the coercive force is increased even though the volume fraction of soft magnetic pure iron increases. Rather than approaching the pure iron properties of Comparative Example 8, the increase was rather increased and rapidly decreased at about 80%.

Therefore, in the range of 50-80% of the volume fraction of pure iron, the increase in the square ratio and the coercive force were simultaneously obtained by the expression of exchange interaction. The angular ratio and the coercive force obtained when the horizontal magnetic field is applied to the thin film surfaces of Inventive Examples 2, 4, 5, and 6 are increased by 2.4 times or more and 2.7 or more, respectively, when compared with those of Comparative Example 1, which is a hard magnetic monolayer. have.

On the other hand, when the volume fraction of pure iron is less than 50%, the exchange interaction is not sufficiently obtained, which shows the characteristics of the hard magnetic layer (first layer and the third layer). The magnetic properties of the pure iron layer determined the properties of the entire film, resulting in soft magnetic properties.

As a result, when the volume fraction of pure iron (second layer) is in the range of 50 to 80%, the exchange interaction with the upper and lower hard magnetic layers (first layer and third layer) increases, and the entire three layer membrane is completely bonded by the exchange interaction force. It is displayed.

In the results of Examples 1 and 2, the thin-film properties of the three-layer structure including the hard and soft magnetic properties were similar to those of the nano-sized Nd ₂ Fe ₁₄ B phase showing the hard magnetic properties in the material and the low price. The Fe and Fe ₃ B phases, which show soft magnetic properties, are simultaneously produced in a material with a certain volume ratio or higher to induce exchange coupling between hard and soft magnetic grains, thereby realizing high residual magnetization and high coercive force simultaneously. It is the same as the characterization mechanism of the ultrafine bulk permanent magnets, which represent the product (BH) _max .

As described above, the present invention applies a laser ablation to produce a thin film by irradiating an excimer laser beam to a target mounted inside the reaction chamber, thereby appropriately controlling process variables and the thickness of the thin film, thereby inducing coercive force and residual force. The ultrafine grain permanent magnet thin film of NdFeB / Fe / NdFeB three-layer structure, which simultaneously increases the magnetization value, can be formed on the (100) Si substrate which can be most commonly used at low cost in mass production.

Claims (4)

In the method of manufacturing a three-layer thin film using the laser ablation method, NdFeB having a composition of Nd _X Fe _90.98-X B _9.02 (25≤X≤32) in atomic percent (at.%) For the deposition of the hard magnetic layer Heating the single crystal (100) Si substrate temperature to a temperature of 620 ° C. or higher in a vacuum reaction chamber equipped with a pure iron (Fe) target to deposit a system target and a soft magnetic layer; After rotating an NdFeB-based target, a pure iron target, and a (100) Si substrate, a KrF laser beam was alternately irradiated to the above two targets in an energy density range of 3.08 J / cm ² to display a first magnet having hard magnetism on the substrate. A layer of NdFeB based thin film having a thickness of 3.6 to 54 nanometers (nm) was deposited on the layer, and a soft magnetic thin film of 15 to 112 nanometers thick on the second layer thereon, and then on the same thickness as that of the first layer. Depositing a controlled 3.6-54 nanometer hard magnetic NdFeB based thin film to form a three-layer film; A method of manufacturing an ultrafine grain permanent magnetic thin film having a NdFeB / Fe / NdFeB structure, comprising: cooling a three-layer deposited (100) Si substrate at a cooling rate of 3 to 5 ° C. per minute. The method of claim 1, wherein the (100) Si substrate is heated to a temperature range of 640 ~ 700 ℃ ultra fine grain permanent magnet thin film of the NdFeB / Fe / NdFeB structure. 3. The method of manufacturing an ultrafine grain permanent magnet thin film according to claim 1 or 2, wherein the KrF laser beam energy density is 2.75 to 3.2 J / cm ² . The ultrafine grain of the NdFeB / Fe / NdFeB structure according to claim 3, wherein the thickness of the second layer is 15 to 30 nanometers and the volume fraction of the second layer is 50 to 80% of the total volume of the three-layer film. Method for producing a permanent magnetic thin film.