JP6044021B2 - Noise suppression member - Google Patents

Description

  The present invention relates to a noise suppressing member for blocking electromagnetic waves radiated from a circuit.

  In a circuit of an electronic device such as a mobile phone, there is a problem that electromagnetic waves radiated from the circuit cause electromagnetic interference. In recent years, high-density mounting of circuit boards and components has been progressing in response to demands for miniaturization and high performance of electronic devices, and the distance between circuit boards and components has been reduced. The problem of interference has become serious. As one of the countermeasures against such electromagnetic interference, a noise suppression sheet prepared by dispersing ferrite powder in a binder has been conventionally arranged in the vicinity of a circuit (for example, see Patent Document 1), In the vicinity, a noise suppression sheet prepared by sintering ferrite powder is disposed (for example, see Patent Document 2).

: JP 2010-97969 A : JP 2009-290075 A

  Since the noise suppression sheets described in Patent Document 1 and Patent Document 2 are too thin, the electromagnetic interference suppression effect is reduced in proportion to the thickness and may be damaged. It becomes. For this reason, when arrange | positioning a noise suppression sheet | seat in the vicinity of a circuit, there existed a subject that the mounting of a circuit board might be obstructed. In addition, when the circuit is a radio frequency integrated circuit (RFIC), not only electromagnetic waves radiated from the circuit but also signals generated in the communication frequency band are blocked, and there is a concern that communication quality may be degraded. There was also a problem.

  The present invention has been made in view of such problems, and it is an object of the present invention to provide a noise suppression member that does not hinder mounting of a circuit board and that can maintain good communication quality while suppressing electromagnetic interference. It is said.

Noise suppression member according to the present invention is a noise suppression member for blocking electromagnetic waves radiated from the circuit, has a ferromagnetic resonance frequency, comprising a magnetic thin film which is disposed close to the circuit, the ferromagnetic The sum of the magnetic resistance inside the magnetic thin film and the magnetic resistance of the leakage magnetic flux path from the magnetic thin film is configured to be 0 in a frequency band equal to or higher than the resonance frequency, and the communication frequency band of the circuit is The magnetic thin film is included in a predetermined frequency range in which the shielding effect is negative .

Noise suppression member according to the present invention is made from the magnetic thin film, the magnetic thin film is preferably the real part of the relative permeability in the ferromagnetic resonance frequency or higher frequency band is soft magnetic thin film serving as a negative. In this case, the soft magnetic thin film is preferably made of one or more materials selected from NiFe, CoFeB, CoCrNb, CoZrNb, NiFeNb, CoZrO, CoAlO, and CoPdAlO. The soft magnetic thin film preferably has a thickness of 100 nm to 5 μm. Moreover, it is preferable that the space | interval of the said soft-magnetic thin film and the said circuit is 2 micrometers-10 micrometers.

  By using the noise suppression member of the present invention, the noise suppression member can be easily mounted on the circuit board. Moreover, since the shielding effect becomes negative at frequencies near the communication frequency band, the shielding effect becomes positive at frequencies other than the vicinity of the communication frequency band while maintaining good communication quality without blocking the signal. Electromagnetic interference can be effectively suppressed by blocking electromagnetic waves radiated from the circuit. As described above, according to the present invention, it is possible to provide a noise suppression member that does not hinder the mounting of the circuit board and that can satisfactorily maintain communication quality while suppressing electromagnetic interference.

It is a side view which shows the outline | summary of the bandpass filter using the magnetic thin film of the noise suppression member of embodiment of this invention. It is a graph which shows the frequency characteristic of the relative permeability of the magnetic thin film made from CoZrNb of the noise suppression member of embodiment of this invention. It is a perspective view which shows the measurement system of the shield effect of the noise suppression member of embodiment of this invention. It is a circuit diagram which shows the magnetic network around a signal wire | line of the noise suppression member of embodiment of this invention. It is a graph which shows the frequency characteristic of shielding effect SE of the noise suppression member of embodiment of this invention. It is a graph which shows the frequency characteristic of magnetoresistance of the noise suppression member of embodiment of this invention.

Hereinafter, the noise suppression member of embodiment of this invention is demonstrated in detail based on drawing.
As shown in FIGS. 1 and 3, a coplanar transmission line B (an example of a circuit) connected to a ground is disposed on a glass epoxy substrate A. . The dimensions of the coplanar line B were designed such that the signal line width was 160 μm, the thickness was 35 μm, the ground gap was 30 μm, and the characteristic impedance matched to 50Ω when the DC resistance was ignored. On this coplanar line B, a magnetic thin film (Co ₈₅ Zr ₃ Nb ₁₂ film, CoZrNb film) D having a thickness of 0.25 μm formed on a glass substrate (Glass) C having a thickness of 2 mm is formed with the coplanar line B and a magnetic film. The thin films were placed close together. A magnetic thin film (Magnetic film) D forms a noise suppressing member according to the embodiment of the present invention.

The composition ratio of CoZrNb is not limited to Co ₈₅ Zr ₃ Nb ₁₂ . Further, as the magnetic thin film D, soft magnetic thin films such as NiFe, CoFeB, CoCrNb, CoZrNb, NiFeNb, CoZrO, CoAlO, and CoPdAlO can be used. The film thickness is not limited to 0.25 μm and may be in the range of 100 nm to 5 μm.

The frequency characteristics of this magnetic thin film D are shown in FIG. As shown in FIG. 2, the relative permeability (Relactive Pemeability) is about 700 at 0.1 GHz, the ferromagnetic resonance frequency _{f r} is 1.1 GHz. The shielding effect of the magnetic thin film D was measured using a network analyzer (Network Analyzer) E manufactured by Agilent. As shown in FIG. 3, 0 dBm of power is input from one end of the coplanar line B from the port 1 (Port 1) of the network analyzer E, and the other end is terminated by a 50Ω resistor, and is disposed above the coplanar line B. A signal was detected at port 2 (Port 2) of the network analyzer E by using a shielded loop coil type magnetic field probe F. The shielding effect (SE) was evaluated by the following formula (1).

Here, H _wo , V _wo, and s _{wo 12} indicate the magnetic field strength, the induced voltage at the probe, and the transmission coefficient when there is no magnetic thin film D, respectively. H _m , V _m, and s _m12 indicate the magnetic field strength, the induced voltage at the probe, and the transmission coefficient when the magnetic thin film D is disposed, respectively.

As shown in FIG. 4, the shielding effect was calculated using a magnetic circuit including the leakage magnetic flux of the magnetic thin film D as a model. In order to understand the phenomenon of magnetic flux passing through the magnetic thin film D in a specific frequency band, the frequency characteristics of the magnetoresistance inside and outside the magnetic thin film D were considered. Here, R ′ _m and R ″ _m indicate the real part and the imaginary part of the magnetic resistance in the magnetic thin film D, respectively. R _lp and R _lv indicate the reluctance of leakage flux from the magnetic thin film D, respectively. R _dl and R _dv indicate the magnetic resistance around the signal line. The permeance method was used to derive R _lp and R _lv . At this time, it was assumed that the conduction current flowing through the signal line was a constant value with respect to the frequency, and the influence of the eddy current on the shielding effect in the magnetic thin film D was small.

  As shown in FIG. 5, the measured value (Meas.) And the calculated value (Calc.) Of the shielding effect are compared to examine the validity of this model, and the mechanism of the bandpass filter using the magnetic thin film D is examined. Demonstrated. The shielding effect is 2 to 4 dB up to 1.1 GHz which is the ferromagnetic resonance frequency of the magnetic thin film D, and the shielding effect of the magnetic thin film D is obtained. On the other hand, the shielding effect decreased monotonically from 1.1 to 1.5 GHz, and increased after reaching a minimum. At 1.5 GHz, the shielding effect is negative, and the magnetic flux passes through the magnetic thin film D in this frequency band. In addition, the calculated values tend to agree well with the measured values, and in particular, the frequency band that transmits the magnetic flux substantially agrees.

FIG. 6 shows the frequency characteristics of the magnetic resistance (Reluctance) inside and outside the magnetic thin film D. The black solid line (R ′ _m ) in FIG. 6 indicates the real part of the magnetic resistance inside the magnetic thin film D, and the gray solid line (R ₁ ) indicates the magnetic resistance in the leakage magnetic flux path. As shown in FIG. 6, the magnetic permeability inside the magnetic resistance becomes negative in the frequency range because the relative permeability of the magnetic thin film D becomes negative at a film-specific ferromagnetic resonance frequency of 1.1 GHz or higher. Monotonously decreases. As a result, there is a predetermined frequency band ft in which the sum of the magnetic resistance of the magnetic thin film D and the magnetic resistance of the leakage flux path is zero in a frequency band _equal to or higher than the ferromagnetic resonance frequency inherent in the film. Therefore, in the magnetic thin film D and the leakage magnetic flux path, a phenomenon occurs in which the magnetic circuit is close to the resonance phenomenon of the electric circuit, and the magnetic flux and the leakage magnetic flux flowing in the film increase. As shown in FIG. Became negative. At this time, it is preferable that the communication frequency band of the high-frequency integrated circuit is included in a predetermined frequency range W in which the shielding effect of the magnetic thin film D is negative. If comprised in this way, although electromagnetic waves radiated | emitted from the circuit are interrupted | blocked, electromagnetic interference can be suppressed effectively, although communication quality is favorably maintained without being interrupted | blocked.

  The present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. Nor.

A substrate B coplanar line C glass substrate D magnetic thin film E network analyzer F shielded loop coil type magnetic field probe _ft predetermined frequency band W predetermined frequency range

Claims (5)

A noise suppressing member for blocking electromagnetic waves radiated from a circuit,
A magnetic thin film having a ferromagnetic resonance frequency and disposed in close proximity to the circuit;
In the frequency band equal to or higher than the ferromagnetic resonance frequency , the sum of the magnetoresistance in the magnetic thin film and the magnetoresistance of the leakage magnetic flux path from the magnetic thin film is configured to be 0 ,
The noise suppression member , wherein a communication frequency band of the circuit is included in a predetermined frequency range in which the shielding effect of the magnetic thin film is negative . Consisting of the magnetic thin film,
The magnetic thin film, the noise suppression element according to claim 1, wherein the real part of the relative permeability in the ferromagnetic resonance frequency or higher frequency band is soft magnetic thin film serving as a negative. The noise suppressing member according to claim 2 , wherein the soft magnetic thin film is made of one or more materials selected from NiFe, CoFeB, CoCrNb, CoZrNb, NiFeNb, CoZrO, CoAlO, and CoPdAlO. The noise suppression member according to claim 2 , wherein the soft magnetic thin film has a thickness of 100 nm to 5 μm. 5. The noise suppression member according to claim 2 , wherein an interval between the soft magnetic thin film and the circuit is 2 μm to 10 μm.