A method for characterizing the high-frequency damping factor of soft magnetic thin film materials

Abstract

This invention provides a method for characterizing the high-frequency damping factor of soft magnetic thin film materials. This method is specifically designed for characterizing the high-frequency damping factor of soft magnetic thin film materials in a swept-frequency mode, measuring magnetic spectra in the frequency range of 500 MHz–9 GHz. First, the imaginary part is fitted with a Lorentz peak to obtain the resonance linewidth Δ. f The resonance linewidth Δ is obtained by analyzing and converting the data as the external magnetic field changes. H With resonance frequency f The change from 0. Finally, the high-frequency damping factor is calculated using a linear fitting formula. The method provided by this invention reduces the resonant linewidth Δ in the frequency sweep mode. f Resonance linewidth Δ converted to sweep mode H This allows for the acquisition of the high-frequency damping factor of soft magnetic thin film samples using conventional linear fitting methods. Typically, the high-frequency damping factor of soft magnetic thin films needs to be characterized using ferromagnetic resonance spectra in swept field mode, and the swept field mode requires significantly more time than the swept frequency mode.

Description

Technical Field

[0001] The invention belongs to the field of soft magnetic film material testing, and relates to high-frequency magnetic spectrum analysis of soft magnetic films, specifically to an analytical calculation method for complex magnetic permeability of soft magnetic film materials and obtaining high-frequency damping factors of soft magnetic film materials. Background Art

[0002] The high-frequency damping factor of soft magnetic thin film materials is one of the key factors to measure the magnetic loss of materials in the microwave frequency band, and is also the main parameter to measure the quality factor of soft magnetic materials. Complex magnetic permeability is usually used to characterize the responsiveness of magnetic moments in soft magnetic materials to microwave signals, and is also called the magnetic spectrum. The magnetic spectrum is a complex number that varies with microwave frequency, in which the imaginary part is generally a resonance peak, indicating the loss of magnetic energy, and its resonance linewidth can be used to describe the damping factor. The magnetic spectrum of soft magnetic materials is one of the important parameters that determine their application in the microwave frequency band. As soft magnetic thin film materials have been widely used in micro-planar inductor cores or anti-electromagnetic interference devices in recent years, accurately characterizing the high-frequency damping factor of soft magnetic films is very critical for their application in high-frequency devices.

[0003] Usually, the damping factor is calculated using the resonant line width Δ at different frequencies. H First, the ferromagnetic resonance spectrum of the scanning mode is measured at a fixed microwave frequency, and the resonance line width Δ H Then change the microwave frequency to obtain the resonance line width at different frequencies. Finally, use the linear fitting relationship to analyze the damping factor. The relationship between the resonance line width and frequency is: ,in α is the damping factor, γ is the gyromagnetic ratio, f 0 is the microwave frequency, Δ H 0 represents the fitting intercept. The magnetic spectrum is a ferromagnetic resonance spectrum in the sweep mode when the external magnetic field is fixed, and its resonance line width is Δ f . Using the resonance line width Δ f When calculating the damping factor, the expression is: , where 4π M s is the saturation magnetization of the soft magnetic film, H k is the anisotropy field in the plane, H is the resonance field. Since usually 4π M s Much larger than the external magnetic field H , so the resonance line width Δ fThe linear change with the external magnetic field is not very obvious, and there is even no regularity. As shown in Table 1 below, the ferromagnetic resonance results of the sweeping field mode and the sweeping frequency mode can give the relationship between the resonance field and the resonance frequency, as well as the resonance line width. Compared with the results of the sweeping field mode, the magnetic spectrum results in the sweeping frequency mode can not only give the complex magnetic permeability of the soft magnetic film, but also the test time is relatively short, but it cannot directly give the damping factor well. Therefore, based on the magnetic spectrum in the sweeping frequency mode, how to obtain an accurate high-frequency damping factor is a very important task, which can not only analyze the high-frequency magnetic properties of soft magnetic film materials more quickly and accurately, but also can replace the ferromagnetic resonance test method in the sweeping field mode.

[0004] Table 1 Comparison of results between sweep mode and sweep frequency mode

[0005] , Table 1 H r is the resonance field, f r is the resonant frequency. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a calculation and analysis method to characterize the high-frequency damping factor of the soft magnetic film in view of the shortcomings of the prior art. The present invention realizes the analysis and transformation of the magnetic spectrum, and converts the resonance line width Δ f Converted into the resonance line width Δ in sweep mode H , and then the conventional linear fitting method is used to obtain the high-frequency damping factor of the soft magnetic film sample.

[0007] In order to solve the technical problem of the present invention, the following technical solution is adopted:

[0008] A method for characterizing the high-frequency damping factor of a soft magnetic thin film material, the specific method is as follows:

[0009] The first step is to obtain the magnetic spectrum of the sample under test; the port reflection parameter S of the short-circuited microstrip line is tested by a four-step method using a microwave transmission line fixture and a vector network analyzer. 11 , the magnetic spectrum of the soft magnetic film sample is calculated using the following formula:

[0010] ,in, K is a dimensionless coefficient, t is the thickness of the soft magnetic film sample, l and h are the length of the short-circuited microstrip line and the distance between the GS lines, l e is the remaining length of the short-circuited microstrip line after the sample is placed. S 11 empis the port reflection parameter when the microstrip line cavity is short-circuited, S 11 emp+field is the port reflection parameter when a constant magnetic field of at least 3000 Oe is applied to the short-circuited microstrip line cavity. S 11 sam is the port reflection parameter when the short-circuited microstrip line is placed in the sample, S 11 sam+field It is the port reflection parameter when a short-circuited microstrip line is placed in the sample and a steady magnetic field of at least 3000 Oe is applied;

[0011] The second step is to perform Lorentz peak fitting on the imaginary part of the magnetic spectrum to obtain the resonant frequency in the sweep mode. f 0 and the resonance line width Δ f ;

[0012] The third step is to obtain the resonance frequency based on the fitting results in the previous step. f 0With the external magnetic field H The change relationship is calculated and fitted using the Kittel formula, which is shown as follows:

[0013] By analyzing the fitting results, the saturation magnetization intensity 4π of the soft magnetic film sample is obtained. M s and the in-plane anisotropic field intensity H k , gyromagnetic ratio γ ;

[0014] The fourth step is to set the resonance line width Δ f Converted into the resonance line width Δ in sweep mode H , the conversion formula used is as follows:

[0015] , where the resonant frequency f 0 and the resonance line width Δ f The saturation magnetization intensity of the soft magnetic film can be obtained by fitting the magnetic spectrum. M s and the in-plane anisotropic field intensity H k The resonant frequency can be fitted by Kittel's formula f 0 and external magnetic field H The relationship between them is obtained;

[0016] Finally, using the resonance line width Δ H Resonance frequency f The linear relationship between 0: , the high-frequency damping factor of the soft magnetic film sample can be obtained by linear fittingα , where Δ H 0 represents the change of the resonance line width in the soft magnetic film.

[0017] The frequency range of the magnetic spectrum of the tested sample obtained in the first step is 500 MHz - 9 GHz.

[0018] The microwave transmission line fixture in the first step is a short-circuit microstrip line fixture. The present invention is suitable for characterizing the high-frequency damping factor of soft magnetic films such as Fe, Co, Ni and their alloys or oxide soft magnetic films such as YIG, TmIG, NiFe2O4, etc.

[0019] The present invention proposes a method for characterizing the high-frequency damping factor of soft magnetic film materials for measuring magnetic spectra in the frequency range of 500 MHz to 9 GHz in the sweep mode. First, the imaginary part is fitted with a Lorentz peak type to obtain the resonance line width Δ f As the external magnetic field changes, the resonance line width Δ is obtained through data analysis and conversion. H Table with resonant frequency f 0. Finally, the high-frequency damping factor is calculated using a linear fitting formula. The present invention provides a data conversion method to convert the resonance line width Δ f Converted into the resonance line width Δ in sweep mode H , so as to obtain the high-frequency damping factor of the soft magnetic film sample using the conventional linear fitting method α . Normally, the high-frequency damping factor of a soft magnetic film needs to be characterized by a ferromagnetic resonance spectrum in a sweeping field mode, and the scanning magnetic field mode takes more time than the scanning frequency. The present invention is an in-depth exploration of the experimental magnetic spectrum of a soft magnetic film, which reduces the steps of characterizing the high-frequency damping factor by a sweeping field mode method, and is conducive to quickly and accurately testing the high-frequency properties of soft magnetic film samples. The data conversion method provided by the present invention is also an extension and supplement to the method of testing magnetic spectra in a sweeping frequency mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The magnetic spectrum of the soft magnetic thin film material sample tested in Example 1 of the present invention;

[0021] Figure 2 is the resonance line width Δ obtained by fitting the magnetic spectrum in Example 1 of the present invention f With external magnetic field H The change relationship diagram of

[0022] Figure 3 is the resonance frequency obtained by fitting the magnetic spectrum in Example 1 of the present invention f 0 and external magnetic field H The change relationship diagram between

[0023] Figure 4 The resonance line width Δ is obtained by the conversion formula proposed in Example 1 of the present invention. H Resonance frequency f 0, and fitted with a linear relationship;

[0024] Figure 5 is the resonance line width Δ obtained by fitting the magnetic spectrum in Example 2 of the present invention f With external magnetic field H The change relationship diagram of

[0025] Figure 6 is the resonance frequency obtained by fitting the magnetic spectrum in Example 2 of the present invention f 0 and external magnetic field H The change relationship diagram between

[0026] Figure 7 The resonance line width Δ is obtained by the conversion formula proposed in Example 2 of the present invention. H Resonance frequency f 0, and fitted with a linear relationship. DETAILED DESCRIPTION

[0027] Example 1

[0028] A method for characterizing the high-frequency damping factor of soft magnetic thin film materials using the common Ni 80 Fe 20 The alloy soft magnetic film was used as a verification sample. The thickness of the sample was 80 nm and the sample was cut into squares with a side length of 5 mm.

[0029] The first step is to obtain the magnetic spectrum of the sample under test; the short-circuited microstrip line fixture and vector network analyzer equipment are used to test the port reflection parameter S of the short-circuited microstrip line through a four-step method. 11 , the magnetic spectrum of the soft magnetic film sample is calculated using the following formula:

[0030] ,in, K is a dimensionless coefficient, t is the thickness of the soft magnetic film sample, l and h are the length of the short-circuited microstrip line and the distance between the GS lines, l eis the length of the short-circuited microstrip line after the sample is placed. The four S obtained by the four-step method (existing technology, reference: Jinwu Wei, Jianbo Wang, Qingfang Liu, Xiaoyu Li, Derang Cao, and Xiaojun Sun, An induction method to calculate the complex permeability of soft magnetic films without a reference sample, Review of Scientific Instruments 2014, 85, 054705) 11 The parameters are: (1) S 11 emp is the port reflection parameter when the microstrip line cavity is short-circuited; (2) S 11 emp+field is the port reflection parameter when a 3000 Oe constant magnetic field is applied to the short-circuited microstrip line cavity, where the intensity of the magnetic field is greater than the anisotropy field of the soft magnetic film material; (3) S 11 sam is the port reflection parameter when the short-circuited microstrip line is placed in the sample; (4) S 11 sam+field It is the port reflection parameter when a short-circuited microstrip line is placed in the sample and a 3000 Oe constant magnetic field is applied, where the intensity of the magnetic field is greater than the anisotropy field of the soft magnetic film material. Figure 1 As shown in the figure, the magnetic spectrum with a frequency range of 500 MHz - 9 GHz is displayed, including the real part and the imaginary part. The black solid line represents the real part and the hollow icon represents the imaginary part. As the external magnetic field gradually increases, the resonant frequency of the magnetic spectrum moves to the high frequency, and the magnetic spectra are obtained when the external magnetic field is 300 Oe, 350 Oe, 400 Oe, 450 Oe, and 500 Oe. Figure 2 As shown in the figure, the external magnetic field increases from 100 Oe to 500 Oe, the resonance line width Δ f The change of is not big, and it is difficult to fit the accurate slope through the linear relationship and obtain the high-frequency damping factor. In order to obtain the accurate high-frequency damping factor, it is necessary to obtain the resonance line width Δ f Converted into the resonance line width Δ in sweep mode H .

[0031] The second step is to perform Lorentz peak fitting on the imaginary part of the magnetic spectrum to obtain the resonant frequency in the sweep mode. f 0 and the resonance line width Δf。

[0032] The third step is to obtain the resonance frequency based on the fitting results in the previous step. f 0With the external magnetic field H The change relationship is calculated and fitted using the well-known Kittel formula, which is shown as follows:

[0033] , in the above formula f 0 is the resonant frequency, γ is the gyromagnetic ratio, H k is the in-plane anisotropic field intensity, H is the strength of the applied magnetic field, 4π M s is the saturation magnetization; by analyzing the fitting results, the saturation magnetization of the soft magnetic film sample is obtained as 4π M s and the in-plane anisotropic field intensity H k , gyromagnetic ratio γ; like Figure 3 As shown in the solid line, the saturation magnetization intensity 4π can be obtained M s and the in-plane anisotropic field intensity H k Equivalent to 9225 Gauss, 11 Oe, and gyromagnetic ratio respectively γ Equal to 0.01857 GHz / Oe.

[0034] The fourth step is to set the resonance line width Δ f Converted into the resonance line width Δ in sweep mode H , the conversion formula used is as follows:

[0035] , where the resonant frequency f 0 and the resonance line width Δ f The saturation magnetization intensity of the soft magnetic film can be obtained by fitting the magnetic spectrum. M s and the in-plane anisotropic field intensity H k The resonant frequency can be fitted by Kittel's formula f 0 and external magnetic field H The relationship between them is obtained;

[0036] Finally, using the resonance line width Δ H Resonance frequency f The linear relationship between 0: , the high-frequency damping factor of the soft magnetic film sample can be obtained by linear fitting α, where Δ H 0 indicates the change of the resonance line width caused by factors such as inhomogeneity in the soft magnetic film.

[0037] Among them, the conversion formula f 0, Δ f 、4π M s , H k , γ are all known quantities, and then the linear relationship is used to fit the data. The fitting results are as follows Figure 4 As shown in the solid line, the slope of the fitting result is 6.21 Oe / GHz, and the high-frequency damping factor is equal to the slope value multiplied by ( γ / 4π), we can get Ni by substituting the data into 80 Fe 20 The high-frequency damping factor of the alloy soft magnetic film is 9.2×10 -3 .

[0038] Through the high-frequency damping factor data, the magnetic loss of the soft magnetic film material and the energy loss in the actual application scenario can be determined. 80 Fe 20 The alloy soft magnetic film was tested in sweeping field mode, and the resonance line width Δ H ,like Figure 4 As shown in the hollow five-pointed star, it can be seen that the results obtained in the two test modes are self-consistent, which also shows that the data conversion method proposed in the present invention is feasible.

[0039] Example 2

[0040] A method for characterizing the high-frequency damping factor of soft magnetic film materials. A common metal Co soft magnetic film is used as a verification sample. The thickness of the sample is 100 nm, and the sample is also cut into squares with a side length of 5 mm. The external magnetic field is changed from 100 Oe to 300 Oe, and the magnetic spectrum of the sample is measured. The frequency measurement range of the sample magnetic spectrum is 500 MHz - 9 GHz.

[0041] The first step is to obtain the magnetic spectrum of the sample under test; the short-circuited microstrip line fixture and vector network analyzer equipment are used to test the port reflection parameter S of the short-circuited microstrip line through a four-step method. 11 , the magnetic spectrum of the soft magnetic film sample is calculated using the following formula:

[0042] ,in, K is a dimensionless coefficient, t is the thickness of the soft magnetic film sample,l and h are the length of the short-circuited microstrip line and the distance between the GS lines, l e It is the remaining length after the sample is placed in the short-circuited microstrip line.

[0043] The four S obtained by the four-step method 11 The parameters are: (1) Port reflection parameters when the microstrip line cavity is short-circuited S 11 emp ; (2) Port reflection parameters when a 3500 Oe constant magnetic field is applied to the short-circuited microstrip line cavity S 11 emp+field , where the intensity of the magnetic field is greater than the anisotropy field of the soft magnetic film material; (3) The port reflection parameters when the short-circuited microstrip line is placed in the sample S 11 sam ; (4) Port reflection parameters when a short-circuited microstrip line is placed in the sample and a 3500 Oe constant magnetic field is applied S 11 sam+field , where the intensity of the magnetic field is greater than the anisotropy field of the soft magnetic film material.

[0044] By fitting the magnetic spectrum, the resonance line width Δ in the sweep mode is obtained. f and resonant frequency f 0, respectively Figure 5 and Figure 6 As shown. Figure 6 The saturation magnetization intensity 4π of the Co soft magnetic film can be obtained by fitting the Kittel formula. M s and the in-plane anisotropic field intensity H k Equivalent to 12789 Gauss, 9 Oe, and gyromagnetic ratio respectively γ Equal to 0.01873 GHz / Oe.

[0045] Using the conversion formula in this application, Figure 5 The resonance line width Δ f Converted into the resonance line width Δ in sweep mode H The result after conversion is as follows Figure 7 As shown, the linear fitting relationship can be used to fit the data well, and the slope can be obtained to be 12.28 Oe / GHz, and then the high-frequency damping factor is equal to the slope value multiplied by ( γ / 4π), the high-frequency damping factor of the metal Co soft magnetic film can be obtained by substituting it into the data to be 18.3×10 -3At the same time, as a comparison, the metal Co soft magnetic film was tested in the sweeping field mode, and the resonance line width Δ H ,like Figure 7 As shown in the hollow five-pointed star, it can be further verified that the results obtained in the two test modes are self-consistent.

[0046] Comparing the results of the two embodiments, it can be seen that the resonance line width Δ of different samples in the sweep mode f will show different changing patterns, such as Figure 2 and Figure 5 After data conversion, the resonance line width Δ H All of them show consistent linear variation patterns, such as Figure 4 and Figure 7 This also shows that the data conversion method proposed in the present invention has relatively wide applicability.

Claims

1. A method for characterizing the high-frequency damping factor of soft magnetic thin film materials, Features The specific method is as follows: The first step is to obtain the magnetic spectrum of the sample under test; the port reflection parameter S of the short-circuited microstrip line is tested by a four-step method using a microwave transmission line fixture and a vector network analyzer. 11 , the magnetic spectrum of the soft magnetic film sample is calculated using the following formula: ,in, K is a dimensionless coefficient, t is the thickness of the soft magnetic film sample, l and h are the length of the short-circuited microstrip line and the distance between the GS lines, l e is the remaining length of the short-circuited microstrip line after the sample is placed. S 11 emp is the port reflection parameter when the microstrip line cavity is short-circuited, S 11 emp+field is the port reflection parameter when a constant magnetic field of at least 3000 Oe is applied to the short-circuited microstrip line cavity. S 11 sam is the port reflection parameter when the short-circuited microstrip line is placed in the sample, S 11 sam+field It is the port reflection parameter when a short-circuited microstrip line is placed in the sample and a steady magnetic field of at least 3000 Oe is applied; The second step is to perform Lorentz peak fitting on the imaginary part of the magnetic spectrum to obtain the resonant frequency in the sweep mode. f 0 and the resonance line width Δ f ; The third step is to obtain the resonance frequency based on the fitting results in the previous step. f 0 With the external magnetic field H The change relationship is calculated and fitted using the Kittel formula, which is shown as follows: By analyzing the fitting results, the saturation magnetization intensity 4π of the soft magnetic film sample is obtained. M s and the in-plane anisotropic field intensity H k , gyromagnetic ratio γ ; The fourth step is to set the resonance line width Δ f Converted into the resonance line width Δ in sweep mode H , the conversion formula used is as follows: , where the resonant frequency f 0 and the resonance line width Δ f By fitting the magnetic spectrum, the saturation magnetization of the soft magnetic film is 4π M s and the in-plane anisotropic field intensity H k The resonant frequency can be fitted by Kittel's formula f 0 With external magnetic field H The relationship between them is obtained; Finally, using the resonance line width Δ H Resonance frequency f 0 The linear relationship between: , the high-frequency damping factor of the soft magnetic film sample is obtained by linear fitting α , where Δ H 0 Represents the change in the resonance line width in the soft magnetic film.

2. A method for characterizing the high-frequency damping factor of a soft magnetic thin film material according to claim 1, Features: The frequency range of the magnetic spectrum of the tested sample obtained in the first step is 500 MHz - 9 GHz.

3. A method for characterizing the high-frequency damping factor of a soft magnetic thin film material according to claim 1, Features: In the first step, the microwave transmission line fixture is a short-circuit microstrip line fixture.

4. A method for characterizing the high-frequency damping factor of a soft magnetic thin film material according to claim 1, Features: It is suitable for characterizing the high-frequency damping factor of soft magnetic films of Fe, Co, Ni and their alloys.

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