JP4869111B2 - High-frequency magnetic thin film and high-frequency magnetic device using the same - Google Patents

Description

  The present invention relates to a high-frequency magnetic thin film in which a ferromagnetic thin film and an antiferromagnetic thin film are laminated and a high-frequency magnetic device using the same, and more specifically, it is suitable for application to a high frequency region with low eddy current loss. The present invention relates to improvement of a high-frequency magnetic thin film.

  In information communication, for example, cellular phones and wireless LANs, the frequency band used has reached the order of GHz, and further higher frequencies are expected in the future. For this reason, the request | requirement of high frequency is strong also with respect to the magnetic material used by a circuit, and the magnetic thin film which has a high magnetic permeability also in the GHz order has been requested | required.

As one method of increasing the magnetic permeability of magnetic thin films, ferromagnetic films and antiferromagnetic films are stacked, and a large uniaxial magnetic anisotropy is induced by exchange coupling between the two, thereby making the ferromagnetic film ferromagnetic. There is a method of increasing the resonance frequency, for example, there is a “high frequency device” described in Patent Document 1 below. This is a thin film with a bilayer structure obtained by alternately laminating a ferromagnetic film and an antiferromagnetic film. By utilizing the fact that an exchange bias magnetic field is generated by a ferromagnetic-antiferromagnetic exchange interaction. Yes.
JP 2003-257739 A

  By the way, the magnitude of the exchange bias magnetic field described above depends on the composition and film thickness of the ferromagnetic film and the antiferromagnetic film, and in order to increase the exchange bias magnetic field, the ferromagnetic film or the antiferromagnetic film has a certain thickness. It is necessary to. However, when the material used for the ferromagnetic film or the antiferromagnetic film is a metal, if the film thickness is large, eddy current loss becomes significant under high frequency. For this, a method using a non-metallic oxide material as a ferromagnetic film or an antiferromagnetic film can be considered. However, since the saturation magnetic moment Ms of the oxide material is small, a large magnetic permeability cannot be expected. For this reason, in order to ensure the absolute value of the magnetic permeability, a metallic magnetic material having a large saturation magnetic moment Ms is preferable, and it is advantageous if the film thickness can be reduced in order to reduce eddy current loss.

  On the other hand, it is suggested that magnetic exchange coupling exists between the ferromagnetic film and the antiferromagnetic film even in a state where there is no static exchange bias magnetic field, that is, the exchange bias magnetic field is zero. Research results have been reported (see S. Queste et al., Journal of Magnetism and Magnetic Materials 288 (2005) 60-65). It is not clear how this interaction affects the high-frequency characteristics of permeability, but if there is any exchange coupling between the ferromagnetic film and the antiferromagnetic film, it will also affect the permeability characteristics. Can be considered. As a result, even if the thickness of the antiferromagnetic film is reduced in order to make the exchange bias magnetic field zero, the high frequency characteristics of the magnetic permeability can be improved by using the ferromagnetic-antiferromagnetic exchange coupling, and the antiferromagnetic property can be improved. There is a possibility that eddy current loss can be reduced by reducing the thickness of the film.

  The present invention focuses on the above points, and its purpose is to reduce the eddy current loss by suppressing the thickness of the film, and to obtain a high-frequency magnetic thin film capable of obtaining good high-frequency characteristics, and a high-frequency using the same It is an object of the present invention to provide a magnetic device for use.

In order to achieve the above object, the present invention provides a high-frequency magnetic thin film having a laminated film in which a ferromagnetic layer and an antiferromagnetic layer are laminated, and when the thickness of the antiferromagnetic layer is reduced, The thickness of the antiferromagnetic layer is set so that the exchange bias magnetic field or exchange coupling strength obtained from the magnetic characteristics becomes substantially zero .

One of the main forms, together with the use of _Co 70 _{Fe 30} as a pre-Symbol ferromagnetic layer, if used MnIr as the antiferromagnetic layer, characterized in that the further thickness of MnIr layer 5nm or less.

  In another embodiment, the ferromagnetic layer is made of a material containing at least one of Fe, Co and Ni, an alloy material containing at least two of Fe, Co and Ni, or Fe, A multi-component alloy material containing at least one of Co and Ni and other elements, and as the antiferromagnetic layer, a material containing at least one of Mn, Fe, Co and Ni, or An oxide material containing at least one of Mn, Fe, Co, and Ni, an alloy material containing at least two of Mn, Fe, Co, and Ni, or an alloy containing the alloy material and an oxide An oxide material or a multi-component alloy oxide material containing the alloy oxide material and other elements is used.

In another embodiment, as the ferromagnetic layer, Fe, FeSiAl, FeAlO, FeN, FeCo, FeCoB, FeCoAlO, FeCoSi, NiFe, CoNiFe,
Together using either, as the antiferromagnetic _{layer, FeMn, MnNi, MnIr, CrMnPt} , MnRu, MnRh, MnRuRh, Mn 3 Ir, Mn 3 Ru, Mn 3 Rh, NiMn, PtMn, PdPtMn, NiO, α- One of Fe ₂ O ₃ and CoO is used.

  The high-frequency magnetic device of the present invention is characterized by using any one of the above-described high-frequency magnetic thin films. The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

  According to the present invention, although the thickness of the antiferromagnetic layer is reduced, the exchange coupling between the ferromagnetic layer and the antiferromagnetic layer is increased, and the ferromagnetic resonance frequency is increased. For this reason, good high frequency characteristics can be obtained while reducing eddy current loss.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples.

First, a first embodiment showing the basic configuration of the present invention will be described with reference to FIGS. FIG. 1 shows the laminated structure of this example. In the figure, a buffer layer 12 is formed on the main surface of a substrate 10, and a ferromagnetic layer 14 and an antiferromagnetic layer 16 are alternately formed in N / 2 layers, and N layers are formed as a whole. . In other words, N / 2 layers of the bilayer thin film 17 of the ferromagnetic layer 14 and the antiferromagnetic layer 16 are formed. A cap layer 18 is further formed on the uppermost layer as an anti-oxidation protective film. As the substrate 10, a Si wafer having a SiO ₂ film 11 formed on its main surface is used. For example, Cu is used as the buffer layer 12 and the cap layer 18. For example, Co ₇₀ Fe ₃₀ is used as the ferromagnetic layer 14, and MnIr is used as the antiferromagnetic layer 16, for example.

  It is known that the direct current magnetization curve of the bilayer thin film 17 obtained by alternately laminating the ferromagnetic layer 14 and the antiferromagnetic layer 16 as described above is shifted as shown in FIG. In FIG. 2, the vertical axis represents the magnetization M and the horizontal axis represents the magnetic field H, and the graph is shifted in the -H direction as a whole. This shift is caused by exchange coupling between the ferromagnetic layer 14 and the antiferromagnetic layer 16, and this shift amount is defined as an exchange bias magnetic field He.

  Here, when the thickness tF of the ferromagnetic layer 14 is constant, the exchange bias magnetic field He depends on the thickness tAF of the antiferromagnetic layer 16 and generally exhibits the behavior shown in FIG. In the figure, the vertical axis represents the exchange bias magnetic field He, and the horizontal axis represents the thickness tAF of the antiferromagnetic layer 16. As shown in the figure, the exchange bias magnetic field He suddenly rises from a certain thickness of the antiferromagnetic layer 16 to reach a peak, and thereafter decreases slightly as the thickness increases, but is a value above a certain value. It has become.

  In conventional high-frequency permeability using exchange coupling, the thickness tAF of the antiferromagnetic layer 16 is set so as to be in the region WB after the peak where a constant exchange bias magnetic field He occurs. On the other hand, in this embodiment, the thickness tAF of the antiferromagnetic layer 16 is set so that the exchange bias magnetic field He is in the area WA before the peak. In this region, the exchange bias magnetic field He suddenly decreases from the peak and becomes zero. As will be described in detail in the examples described later, even in the region where the exchange bias magnetic field He is zero, the ferromagnetic layer 14 and the antiferromagnetic layer 16 are exchange-coupled. Therefore, the magnetic permeability can be secured up to the GHz order band. Further, in the region WA, since the antiferromagnetic layer 16 is thin, the thickness of the entire magnetic thin film can be suppressed, and the eddy current loss can be reduced well.

  Next, a second embodiment of the present invention will be described. In this embodiment, samples are manufactured for the case where the antiferromagnetic layer 16 has the thickness of the region WA in FIG. 3 and the thickness of the region WB, and the magnetic characteristics are compared.

Table 1 shows various conditions of the sample of this example and the sample of the comparative example according to the background art. The materials are the same for both, but the film thickness conditions of the ferromagnetic layer 14 and the antiferromagnetic layer 16 are set as shown in the following table. Specifically, the thickness of the antiferromagnetic layer 16 is 2.5 nm in this embodiment and 10 nm in the comparative example, and the thickness tF of the ferromagnetic layer 14 and the number N of layers are stacked so that the magnetic permeability characteristics are substantially the same. Adjusted.

  When the frequency dependence of the magnetic permeability was measured for each sample as described above, the result as shown in FIG. 4 was obtained. In the figure, (A) shows the measurement result of the sample of this example, and (B) shows the measurement result of the sample of the comparative example. In the figure, the vertical axis represents magnetic permeability, and the horizontal axis represents frequency. As is clear by comparing these, almost the same frequency dependence is shown. As described above, according to this example, although the total film thickness of the antiferromagnetic layer 16 is less than or equal to one quarter of that of the comparative example, substantially the same permeability can be obtained up to the high frequency side. As a comparative example, the results are comparable.

Next, Embodiment 3 of the present invention will be described. In this embodiment, the change in the strength of exchange coupling when the thickness tF of the ferromagnetic layer 14 is constant and the thickness tAF of the antiferromagnetic layer 16 is changed is examined. The magnetic thin film shown in FIG. 1 was produced using a magnetron sputtering technique. Co ₇₀ Fe ₃₀ was selected as the ferromagnetic layer 14 and its thickness tF was kept constant at 50 nm. On the other hand, MnIr was used as the antiferromagnetic layer 16, and the film thickness was changed from 0 to 20 nm to obtain a sample. Note that a silicon substrate was used as the substrate 10, and Cu was used as the buffer layer 12 and the cap layer 18. After film formation, heat treatment was applied for 1 hour in a magnetic field of 1 kOe. In addition, the heat processing temperature at this time is 200 to 340 degreeC.

  FIG. 5 is a graph showing the relationship between the exchange coupling strength Jc (vertical axis) between the ferromagnetic layer 14 and the antiferromagnetic layer 16 and the film thickness tAF (horizontal axis) of the antiferromagnetic layer 16. In the figure, “◯” is the value of exchange coupling strength Jc determined from the exchange bias magnetic field He, and “●” is the value of exchange coupling strength Jc determined from ferromagnetic resonance. As can be seen from these graphs, in the case of the exchange coupling strength Jc determined from the exchange bias magnetic field He (static magnetic characteristics), Jc increases with an increase in the antiferromagnetic layer thickness tAF, and reaches a maximum at about 5 to 7 nm. However, it gradually decreases after that. For convenience, the thickness tAF of the antiferromagnetic layer 16 at which the exchange coupling strength Jc determined from the exchange bias magnetic field He is maximized is defined as the critical thickness.

  On the other hand, in the case of the exchange coupling strength Jc obtained from ferromagnetic resonance (dynamic magnetic characteristics), the value of Jc increases as the thickness tAF of the antiferromagnetic layer 16 decreases even below the critical thickness. (Refer to area WA). This indicates that exchange coupling exists between the ferromagnetic layer 14 and the antiferromagnetic layer 16 even below the critical thickness, and the strength Jc is larger below the critical thickness.

  In the case of the background art, the thickness tAF of the antiferromagnetic layer 16 is generally adjusted so that the exchange bias magnetic field He, that is, the exchange coupling strength Jc determined from the static magnetic characteristics is maximized (region WB). reference). In contrast, in the present embodiment, the thickness tAF of the antiferromagnetic layer 16 is adjusted so that the strength of exchange coupling Jc determined from ferromagnetic resonance, that is, dynamic magnetic characteristics, is maximized. As described above, by using the large ferromagnetic layer-antiferromagnetic interlayer exchange coupling in the region WA, excellent high-frequency permeability characteristics can be obtained.

  As shown in FIG. 5, when the thickness tAF of the antiferromagnetic layer 16 is reduced in the application area WA of the present invention with respect to the application area WB of the background art, the thickness is exchange bias. This is a region in which the strength of exchange coupling determined from the magnetic field He starts to decrease, and good high-frequency permeability characteristics can be obtained in this range. More preferably, the strength of exchange coupling determined from ferromagnetic resonance is the maximum. It is convenient to set the thickness tAF of the antiferromagnetic layer 16 so that the exchange bias magnetic field is near zero.

Next, Embodiment 4 of the present invention will be described with reference to FIG. In this example, the change in permeability when the thickness tAF of the antiferromagnetic layer 16 is constant and the thickness tF of the ferromagnetic layer 14 is changed is examined. As in the previous example, a sample was prepared using a magnetron sputtering technique. MnIr was used as the antiferromagnetic layer 16 and its thickness tAF was kept constant at 2 nm. On the other hand, Co ₇₀ Fe ₃₀ was selected as the ferromagnetic layer 14, and the thickness tF was changed to 100, 20, and 10 nm to obtain samples. The substrate 10 is silicon, and the buffer layer 12 and the cap layer 18 are Cu. The point that the heat treatment is performed in the magnetic field of 1 kOe for 1 hour after the film formation and the heat treatment temperature is 200 ° C. to 340 ° C. is the same as in Example 3.

  FIG. 6 is a graph showing the frequency characteristics of the magnetic permeability of each sample obtained as described above. In the figure, the vertical axis represents the magnetic permeability, the horizontal axis represents the frequency, the black mark represents the real part of the magnetic permeability, and the white mark represents the imaginary part of the magnetic permeability. The thickness tF of the ferromagnetic layer 14 is 100 nm for (A), 20 nm for (B), and 10 nm for (C). As shown in these graphs, when the ferromagnetic layer thickness tAF is 100 nm (see FIG. 1A), the magnetic permeability is about 250 and the ferromagnetic resonance frequency is about 3.5 GHz. Similarly, when the ferromagnetic layer thickness tAF is 20 nm (see FIG. 5B), the magnetic permeability is about 100, the ferromagnetic resonance frequency is about 6 GHz, and when the ferromagnetic layer thickness tAF is 10 nm (same as above). As shown in FIG. 2C, a high frequency characteristic having a magnetic permeability of about 40 and a ferromagnetic resonance frequency of about 8 GHz was obtained.

  As described above, according to the present example, although the thickness tAF of the antiferromagnetic layer 16 is only 2 nm, good magnetic permeability is obtained in the high frequency region. That is, a region where the thickness tAF of the antiferromagnetic layer 16 is less than the critical thickness and the exchange coupling strength Jc obtained from the exchange bias magnetic field He is substantially zero, that is, a region where the exchange bias magnetic field is substantially zero is used. As a result, it is possible to obtain good high frequency characteristics while suppressing the thickness of the antiferromagnetic layer 16 and reducing eddy current loss.

  Conventionally, in order to increase the ferromagnetic resonance frequency of a ferromagnetic-antiferromagnetic bilayer thin film, a larger static exchange bias magnetic field has been advantageous. However, as shown in the above-described embodiments, the exchange coupling between the ferromagnetic layer and the antiferromagnetic layer is rather important for increasing the frequency of the ferromagnetic resonance frequency, and strong for increasing the frequency of the ferromagnetic resonance frequency. It is most suitable to set the thickness of the antiferromagnetic layer 16 so that the exchange coupling between the magnetic layer and the antiferromagnetic layer is maximized, and the static exchange bias magnetic field is substantially zero in that region. It was issued. Furthermore, since the exchange coupling between the ferromagnetic layer and the antiferromagnetic layer becomes strong, not only the antiferromagnetic layer 16 but also the thickness of the ferromagnetic layer 14 can be reduced. The ferromagnetic layer 14 is often a metal, and the loss due to eddy current can be further reduced by making the metal layer thin.

In addition, this invention is not limited to the Example mentioned above, A various change can be added in the range which does not deviate from the summary of this invention. For example, the following are also included.
(1) The materials, shapes, and dimensions shown in the above embodiments are merely examples, and can be appropriately changed so as to achieve the same effect. For example, in the above embodiment, Co ₇₀ Fe ₃₀ is used as the ferromagnetic layer 14 and MnIr is used as the antiferromagnetic layer 16, but the material may be appropriately selected.
For example, the following materials can be considered.
a, ferromagnetic layer 14: a material containing at least one of Fe, Co and Ni, an alloy material containing at least two of Fe, Co and Ni, or of Fe, Co and Ni Multi-component alloy materials containing at least one kind and other elements, such as Fe, FeSiAl, FeAlO, FeN, FeCo, FeCoB, FeCoAlO, FeCoSi, NiFe, CoNiFe, etc.
b, antiferromagnetic layer 16: a material containing at least one of Mn, Fe, Co and Ni, an oxide material containing at least one of Mn, Fe, Co and Ni, or Mn, Alloy material containing at least two of Fe, Co, Ni, alloy oxide material containing the alloy material and oxide, or multi-component alloy oxide material containing the alloy oxide material and other elements , for _{example, FeMn, MnNi, MnIr, CrMnPt} , MnRu, MnRh, MnRuRh, Mn 3 Ir, Mn 3 Ru, Mn 3 Rh, NiMn, PtMn, PdPtMn, NiO, α-Fe 2 O 3, CoO , etc.,
(2) The combination of the material of the ferromagnetic layer 14 and the material of the antiferromagnetic layer 16 is not particularly limited. The critical thickness shown in FIG. 5 differs depending on the material and thickness tF of the selected ferromagnetic layer 14 and the antiferromagnetic layer 16.
(3) The high-frequency magnetic thin film of the present invention may be applied to various high-frequency magnetic devices. For example, it can be applied to a high frequency inductor, a transformer, an antenna, and the like. Specifically, the planar inductor for high frequency having the multilayer film and the conductor coil of the present invention, the transmission line having the multilayer film and the conductor line of the present invention, the high frequency filter using the ferromagnetic resonance of the multilayer film of the present invention, and the present invention. It can be applied to a high-frequency antenna having a laminated film and a metal casing. Figure 7 is an example is shown, and spiral conductor pattern 30 through the SiO ₂ film 20 is formed on the main surface of the magnetic thin film for high frequencies 50 shown in FIG. 1, whereby the high-frequency The inductor is configured.
(4) In the above embodiment, the thickness tAF of the antiferromagnetic layer 16 is adjusted so that the exchange coupling strength Jc determined from the dynamic magnetic characteristics is maximized. There is no problem.

  According to the present invention, good high frequency characteristics can be obtained while reducing eddy current loss, and therefore, it is particularly suitable for a high frequency device in a frequency band of the GHz order.

It is principal sectional drawing which shows the laminated structure of the high frequency magnetic thin film of Example 1 of this invention. It is a graph which shows the direct current | flow magnetization curve of the magnetic thin film of 1 of the said Example. 6 is a graph showing the relationship between the exchange bias magnetic field He and the thickness tAF of the antiferromagnetic layer 16 in Example 1. It is a graph which compares and shows the magnetic permeability of the sample in Example 2 of this invention, and the sample of background art. It is a graph which shows the relationship between the strength Jc of the exchange coupling in Example 3 of this invention, and the thickness tAF of the antiferromagnetic layer 16. FIG. It is a graph which shows the frequency characteristic of the magnetic permeability when the thickness tF of the ferromagnetic layer 14 in Example 4 of this invention is changed. It is a perspective view which shows an example of the device to which the magnetic thin film for high frequencies of this invention is applied.

Explanation of symbols

10: substrate 11: SiO ₂ film 12: buffer layer 14: ferromagnetic layer 16: antiferromagnetic layer 17: bilayer thin film 18: cap layer 20: SiO ₂ film 30: conductor pattern 50: magnetic thin film for high frequency H: magnetic field He: exchange bias magnetic field M: magnetization N: number of stacked layers tF: ferromagnetic layer thickness tAF: antiferromagnetic layer thickness WA, WB: film thickness region

Claims (5)

In a high-frequency magnetic thin film having a laminated film in which a ferromagnetic layer and an antiferromagnetic layer are laminated,
When the thickness of the antiferromagnetic layer is reduced, the thickness of the antiferromagnetic layer is set so that the exchange bias magnetic field or exchange coupling strength obtained from the static magnetic characteristics is substantially zero. A high-frequency magnetic thin film characterized by With use of _Co 70 _{Fe 30} as the ferromagnetic layer, said anti when the ferromagnetic layer using MnIr as, high frequency magnetic thin film according to claim 1 Symbol mounting, characterized in that the further thickness of MnIr layer 5nm or less . As the ferromagnetic layer,
A material containing at least one of Fe, Co and Ni, or
An alloy material containing at least two of Fe, Co and Ni, or
A multi-component alloy material containing at least one of Fe, Co, and Ni and other elements;
And using
As the antiferromagnetic layer,
A material containing at least one of Mn, Fe, Co, Ni, or
An oxide material containing at least one of Mn, Fe, Co, Ni, or
An alloy material containing at least two of Mn, Fe, Co and Ni, or
An alloy oxide material containing the alloy material and an oxide, or
A multi-component alloy oxide material containing the alloy oxide material and other elements;
The magnetic thin film for high frequency according to claim 1 or 2 , wherein As the ferromagnetic layer,
Fe, FeSiAl, FeAlO, FeN, FeCo, FeCoB, FeCoAlO, FeCoSi, NiFe, CoNiFe,
And using either
As the antiferromagnetic layer,
_{FeMn, MnNi, MnIr, CrMnPt,} MnRu, MnRh, MnRuRh, Mn 3 Ir, Mn 3 Ru, Mn 3 Rh, NiMn, PtMn, PdPtMn, NiO, α-Fe 2 O 3, CoO,
4. The magnetic thin film for high frequency according to claim 3 , wherein any one of the above is used. High-frequency magnetic device, characterized in that using the high frequency magnetic thin film as claimed in any one of claims 1-4.

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