WO2014147866A1

WO2014147866A1 - High-frequency electromagnetic field measurement device

Info

Publication number: WO2014147866A1
Application number: PCT/JP2013/074059
Authority: WO
Inventors: 遠藤　恭; 山口　正洋; 島田　寛; 翔室賀
Original assignee: 国立大学法人東北大学
Priority date: 2013-03-18
Filing date: 2013-09-06
Publication date: 2014-09-25
Also published as: JP6327614B2; JPWO2014147866A1

Abstract

[Problem] To provide a high-frequency electromagnetic field measurement device that can separate the impact of a high-frequency electromagnetic field and the impact of a high-frequency electric field, that are generated by the input of a high-frequency signal, and that can measure a high-frequency electromagnetic field with high precision. [Solution] A magnetic force sensor (21) is formed from the cantilever of a magnetic force microscope (11) and can detect a magnetic field. A current line (12) is formed from a coil and is disposed so as to be adjacent to an object of measurement (1). A carrier guide means (13) inputs a high-frequency carrier signal to the object of measurement (1), and a reference wave guide means (14) is configured so as to input a high-frequency reference wave signal to the current line (12). Further, the potential when the carrier signal is input to the object of measurement (1) from the carrier guide means (13) is made to match the potential of the magnetic force sensor (21). The magnetic force microscope (11) has a placement stand (22) onto which the object of measurement (1) is placed, a displacement measurement means (23) for measuring the displacement of the magnetic force sensor (21), and a scanning means (24) for scanning the magnetic force sensor (21).

Description

High frequency electromagnetic field measuring device

The present invention relates to a high-frequency electromagnetic field measuring apparatus.

In recent years, with the progress of miniaturization of analog high-frequency integrated circuits (Radio Frequency Integrated Circuit: RFIC) for portable information terminals, the minimum wiring pitch has become narrower, and problems such as crosstalk between wires and electromagnetic noise have occurred. The possibility to do is increasing. In addition, on an RFIC chip that processes high-frequency signals used in wireless communication, electromagnetic noise generated in the digital circuit is mixed into the analog circuit due to an increase in the digital circuit area and a mixture of the digital and analog circuits, and electromagnetic interference (Electromagnetic Interference: EMI) is causing problems. As a countermeasure for this EMI problem, it is important to specify the source, propagation path, and mixing destination of electromagnetic noise generated in the chip. For this reason, it is effective to measure the high-frequency magnetic field generated on the chip. is there.

Conventionally, as a method of measuring a magnetic field near a high frequency generated on a chip, a shielded loop coil type magnetic field probe, a magneto-optical probe, a superconducting quantum interferometer (Superducting Quantum Interference Device: SQUID), a giant magnetoresistance type (Giant Magnetismistance): There is a method using a GMR) sensor (for example, see Non-Patent Documents 1 to 4). However, in the methods described in Non-Patent Documents 1 to 4, although the measurement frequency band exceeds 0.5 GHz, the spatial resolution of the detection sensor is only approximately several tens of μm. For this reason, an RFIC chip having a minimum wiring pitch of about submicron has a problem that it is difficult to detect a magnetic field component generated by a current flowing through the fine signal wiring and constituent elements.

Therefore, in order to satisfy both the submicron spatial resolution and the high-frequency characteristics in the gigahertz band, the present inventors pay attention to the probe of a magnetic force microscope (MFM) as a detection sensor and beat the field ( A high-frequency near-field magnetic field measurement method using a “Beating field” method has been developed (see Japanese Patent Application No. 2012-083425). In this field beat system, two sinusoidal signals with slightly different frequency bands are input to a high-frequency transmission line such as a coplanar waveguide (CPW), and a field beat (beat signal) is input on the line. The magnetic field near the high frequency is measured by the MFM probe.

As the two sinusoidal signals, when the input carrier signal and the reference wave signal CPW, the force F _M acting on the probe of a magnetic force microscope by the magnetic field generated by the CPW is represented by (1) (See Non-Patent Document 5, for example).

Here, m the magnetic moment of the probe, H _Z vertical (Z) direction of the magnetic field components, H _C is the magnetic field component of the carrier signal, theta _C vertical (Z) direction of angle of the magnetic field component of the carrier signal, H _ref is the magnetic field component of the reference wave signal, θ _ref is the angle in the vertical (Z) direction of the magnetic field component of the reference wave signal, f _Res is the resonance frequency of the probe (cantilever), t is the time, and f ₀ is the frequency of the carrier signal. And an intermediate value (frequency) of the frequency of the reference wave signal, and δ is a phase.

Further, as two sinusoidal signals, when the input carrier signal and the reference wave signal CPW, the force F _E acting on the probe of a magnetic force microscope by an electric field generated on the CPW is represented by equation (2) (See, for example, Non-Patent Document 6).

Here, ε is the dielectric constant, S is the area of the cantilever, h is the distance (lift height) between the tip of the probe and the CPW, V _CPW is the CPW potential, V _tip is the probe potential, and Z is the CPW characteristic. Impedance, E _C is the electric field component of the carrier wave signal, and E _ref is the electric field component of the reference wave signal.

There is a method of measuring a magnetic field in the vicinity of a high frequency by an amplitude modulation method or a frequency modulation method using a high frequency magnetic force microscope (HF-MFM). However, in a state where a circuit in an IC chip is actually operated, a wiring or a power line It is not possible to directly measure the magnetic field resulting from the current flowing through For this reason, it cannot be used for failure analysis of IC chips.

The conventional near-field high-frequency magnetic field measurement method can satisfy both sub-micron spatial resolution and high-frequency characteristics in the gigahertz band at the same time. There is a problem that the influence of the magnetic field and the influence of the high frequency electric field cannot be separated, and the measurement accuracy of the high frequency magnetic field is lowered.

The present invention has been made paying attention to such problems, and can separate the influence of the high-frequency magnetic field generated by the input of the high-frequency signal from the influence of the high-frequency electric field, and can measure the high-frequency magnetic field with high accuracy. An object of the present invention is to provide a high-frequency electromagnetic field measuring apparatus.

In order to achieve the above object, a high-frequency electromagnetic field measurement apparatus according to the present invention is a high-frequency electromagnetic field measurement apparatus for measuring a high-frequency magnetic field emitted from a measurement object to which a high-frequency signal is input, and is based on magnetic action A magnetic force sensor capable of detecting a magnetic field using vibration; a current line disposed in proximity to the measurement object; a carrier introduction means for inputting a high-frequency carrier signal to the measurement object; and the current line And a reference wave introducing means configured to be able to change the frequency of the reference wave signal to be inputted, and the carrier wave signal is transferred from the carrier introducing means to the measurement object. The input potential is configured to be equal to the potential of the magnetic force sensor.

The high-frequency electromagnetic field measuring apparatus according to the present invention can measure a high-frequency magnetic field generated by a measurement object to which a high-frequency signal is input as follows. That is, a high frequency carrier signal is input to the measurement object by the carrier introduction means to generate a high frequency magnetic field having a certain intensity and frequency. Further, the reference wave introducing means inputs a high-frequency reference wave signal to a current line arranged close to the object to be measured, thereby generating a high-frequency magnetic field having a certain intensity and frequency. At this time, by changing the frequency of the reference wave signal by the reference wave introducing means, the frequency of the high-frequency magnetic field generated by the measurement object and the frequency of the high-frequency magnetic field generated by the current line are slightly shifted, Magnetic beats (beat signals) including each high-frequency magnetic field can be generated. By making the frequency of the beat signal close to the resonance frequency of the magnetic force sensor, a high frequency magnetic field can be measured.

At this time, since the potential when the carrier wave signal is input from the carrier wave introducing means to the measurement object is equal to the potential of the magnetic force sensor, the high frequency generated together with the high frequency magnetic field by the input of the high frequency signal The force received by the magnetic force sensor from the electric field can be suppressed. Thereby, the influence by a high frequency magnetic field and the influence by a high frequency electric field can be isolate | separated, and a high frequency magnetic field can be measured with high precision. It is preferable that the potential when the carrier signal is input from the carrier introduction means to the object to be measured and the potential of the magnetic force sensor are exactly the same because the closer to the same value, the higher the magnetic field measurement accuracy. However, some deviation may occur in the circuit configuration. For this reason, even if these electric potentials are not exactly the same, it is sufficient that they are almost equal.

The high-frequency electromagnetic field measuring apparatus according to the present invention increases the effect of separating a high-frequency magnetic field and a high-frequency electric field, and further improves measurement accuracy. It is preferable to align the phase and amplitude with the phase and amplitude of the potential of the magnetic force sensor. In order to align the phases, for example, a phase adjuster or the like can be used.

The high-frequency electromagnetic field measuring apparatus according to the present invention includes a magnetic force microscope, the magnetic force sensor includes a cantilever of the magnetic force microscope, and the magnetic force microscope includes a mounting table on which the measurement object is placed; It is preferable to have displacement measuring means for measuring displacement due to vibration of the magnetic force sensor, and scanning means for scanning the magnetic force sensor relative to the measurement object. In this case, the force that the magnetic force sensor receives from the high-frequency magnetic field can be measured by the displacement measuring means. Further, a two-dimensional distribution of a high-frequency magnetic field generated on a measurement object such as a circuit can be obtained by scanning with a scanning unit. Thereby, the generation source, propagation path, mixing destination, etc. of electromagnetic noise on the measurement target can be specified, which can contribute to the solution of the EMI problem.

In the high-frequency electromagnetic field measuring apparatus according to the present invention, it is preferable that the current line is made of a coil, the cantilever is made of an insulator, and a magnetic film is formed on the surface of the tip of the tip. In this case, the coil mainly generates a high-frequency magnetic field, and the insulator cantilever beam is not affected by the high-frequency electric field, so that the high-frequency magnetic field can be measured with high accuracy. The electric field that can eliminate the influence is a high-frequency electric field of 100 MHz or more, and in particular, the influence of the electric field in the GHz order can also be removed. The cantilever may have a magnetic film formed on the surface of the beam opposite to the probe in order to increase the measurement accuracy of the high-frequency magnetic field. In addition, an AC power source for applying an alternating magnetic field to the current line and a magnetization of the magnetic material of the magnetic film of the cantilever are reattached so that the magnetization of the magnetic material of the magnetic film of the cantilever can be AC demagnetized. A DC power source for generating a DC magnetic field in the current line may be provided so as to be magnetized.

Further, in the high frequency electromagnetic field measuring apparatus according to the present invention, the current line may be an open transmission line, and the cantilever may be made of silicon. In this case, the open-type transmission line mainly generates a high-frequency electric field, and the silicon cantilever is easily affected by the high-frequency electric field. Can do. The cantilever is not limited to silicon but may be made of other conductive materials, but silicon is particularly preferable because of good workability. Note that the high-frequency electromagnetic field measuring apparatus according to the present invention may be configured such that both the high-frequency magnetic field and the high-frequency electric field can be measured, and the current line can be switched between the coil and the open transmission line. The cantilever may also be configured to be switchable between an insulator and a magnetic film formed on the tip of the tip and a silicon one.

The high-frequency electromagnetic field measuring apparatus according to the present invention, when the reference wave signal is input while changing the frequency by the reference wave introducing means, from the displacement due to the vibration of the magnetic force sensor measured by the displacement measuring means, Obtaining the amplitude when the magnetic force sensor vibrates at the resonance frequency, obtaining the frequency of the reference wave signal by the reference wave introducing means at that time, and obtaining the obtained amplitude of the magnetic force sensor and the frequency of the reference wave signal And analyzing means for calculating the amplitude and frequency of the high-frequency signal emitted from the measurement object in response to the input of the carrier wave signal. In this case, the high-frequency signal emitted from the measurement object to which the high-frequency signal is input can be quantitatively grasped by the analyzing means. When measuring a high-frequency magnetic field, the high-frequency magnetic field can be quantitatively obtained using the equation (1). Further, at the time of measuring the high frequency electric field, the high frequency electric field can be quantitatively obtained using the formula (2).

In the high-frequency electromagnetic field measuring apparatus according to the present invention, the magnetic force sensor may be made of an insulator. In this case, since the insulating magnetic force sensor is not affected by the high frequency electric field, the high frequency magnetic field can be measured with high accuracy.

According to the present invention, it is possible to provide a high-frequency electromagnetic field measuring apparatus capable of separating the influence of a high-frequency magnetic field generated by the input of a high-frequency signal and the influence of a high-frequency electric field and measuring the high-frequency magnetic field with high accuracy. .

It is a block diagram which shows the high frequency electromagnetic field measuring device of embodiment of this invention. It is a circuit diagram of the measurement system of the high frequency electromagnetic field measuring apparatus shown in FIG. It is a block diagram which shows the modification for a high frequency electric field detection of the high frequency electromagnetic field measuring apparatus of embodiment of this invention. It is a circuit diagram of the measurement system of the high frequency electromagnetic field measuring apparatus shown in FIG. 1A is a perspective view showing the overall configuration of a high-frequency magnetic field measuring apparatus using a field beat method, and FIG. 1B is a measurement of a coplanar waveguide (CPW) used for the measurement. It is an enlarged plan view showing a position, and (c) an enlarged sectional view. 6 is a combined spectrum of a carrier wave signal and a reference wave signal used in measurement of a high-frequency magnetic field by the measurement apparatus shown in FIG. When a high-frequency magnetic field is measured by the measuring apparatus shown in FIG. 5, (a) a graph showing the vibration amplitude value of the probe when the frequency of the carrier signal is 100 MHz, (b) the frequency of the carrier signal is 100 MHz and 2 GHz. 6 is a graph showing the relationship between the vibration amplitude value of the probe near the resonance frequency of the cantilever and the current value of the carrier wave signal. It is a graph which shows the relationship between the frequency of a carrier wave signal, the vibration amplitude value of a probe, and Q value when a high frequency magnetic field is measured with the measuring apparatus shown in FIG. It is a graph which shows the relationship between the position of the probe with respect to CPW, and the vibration amplitude value of the probe when the frequency of the carrier wave signal is 100 MHz and 2 GHz when the high frequency magnetic field is measured by the measuring apparatus shown in FIG. FIG. 6 is a perspective view showing an overall configuration of a high-frequency magnetic field measurement apparatus improved from FIG. 5A with respect to the high-frequency electromagnetic field measurement apparatus according to the embodiment of the present invention. When the high-frequency magnetic field is measured by the measuring device shown in FIG. 10 and the measuring device shown in FIG. 5A, the position of the probe with respect to the CPW and the vibration amplitude value of the probe when the frequency of the carrier signal is 2 GHz. It is a graph which shows the relationship. When the high-frequency magnetic field is measured using a Ni—Fe coated cantilever and an uncoated cantilever using the measurement apparatus shown in FIG. 10, the position of the probe with respect to the CPW when the frequency of the carrier signal is 2 GHz It is a graph which shows the relationship with the vibration amplitude value of a probe. Relationship between the probe position relative to the CPW and the magnetic field (Hz) × magnetic field gradient (dHz / dz) when the frequency of the carrier wave signal is 1.1 GHz when the high-frequency magnetic field is measured by the measuring apparatus shown in FIG. It is a graph which shows. When a high frequency magnetic field is measured by the field beat method using the high frequency electromagnetic field measuring apparatus shown in FIG. 1, (a) when there is no carrier signal, (b) the amplitude of the carrier signal is 9 dBm, and (c) the carrier signal. (D) carrier wave signal amplitude is 15 dBm, (e) carrier wave signal amplitude is 18 dBm, and (f) carrier wave signal amplitude is 21 dBm, probe vibration amplitude (upper stage) and phase (lower stage) It is a graph which shows the measurement result of). It is a graph which shows the change of the peak value of the vibration amplitude of a probe with respect to the amplitude of a carrier wave signal when measuring a high frequency magnetic field by a field beat method using the high frequency electromagnetic field measuring device shown in FIG. It is a graph which shows the relationship between the frequency of a reference wave signal, and the peak value of the vibration amplitude of a probe when a high frequency magnetic field is measured by the field beat method using the high frequency electromagnetic field measuring apparatus shown in FIG. (A) The high-frequency electromagnetic field measuring apparatus according to the embodiment of the present invention shown in FIG. 1, (b) the high-frequency electromagnetic field measuring apparatus according to the embodiment shown in FIG. 3, (c) shown in FIG. 5 (a). FIG. 11 is a measurement principle diagram of a high-frequency magnetic field measurement apparatus using a field beat method, and (d) an improved high-frequency magnetic field measurement apparatus shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 16 show a high-frequency electromagnetic field measuring apparatus according to an embodiment of the present invention.
As shown in FIG. 1, a high-frequency electromagnetic field measurement apparatus 10 is a high-frequency electromagnetic field measurement apparatus 10 for measuring a high-frequency magnetic field generated by a measurement object 1 to which a high-frequency signal is input, and includes a magnetic force microscope 11 and a current. Line 12, carrier wave introducing means 13, reference wave introducing means 14, and computer 15 are provided.

The measurement object 1 includes, for example, active elements such as transistors and diodes, passive elements such as capacitors and inductors, power supply circuits, LSI chips, and high-frequency transmission lines.

The magnetic force microscope 11 (MFM) includes a magnetic force sensor 21, a mounting table 22, a displacement measuring unit 23, and a scanning unit 24. The magnetic force sensor 21 includes an insulating cantilever provided with a probe 21b at the tip of a beam 21a. In the magnetic force sensor 21, a magnetic film is formed on the surface of the probe 21b and the surface of the beam 21a opposite to the probe 21b. The magnetic force sensor 21 is configured to be able to detect a magnetic field using vibration caused by a magnetic action. In particular, the magnetic force sensor 21 is preferably made of a material having a soft magnetic property with a high magnetic permeability or a material having a coercive force of about 50 to 100 Oe and a magnetic permeability.

The mounting table 22 is composed of a stepping motor drive stage, and is provided so that the measuring object 1 can be mounted thereon. The mounting table 22 is configured such that the height can be adjusted in a state where the measuring object 1 is placed. The displacement measuring means 23 includes a laser 23a, an optical position sensor (PSD) 23b, and a detection circuit 23c. The displacement measuring means 23 applies the light from the laser 23 a to the magnetic force sensor 21, receives the reflected light by the optical position sensor 23 b, and sends the signal to the detection circuit 23 c, whereby the displacement due to the vibration of the magnetic force sensor 21. Can be measured.

The scanning means 24 is composed of a piezo element driving type stage, to which the magnetic force sensor 21 is attached. The scanning unit 24 is configured to be able to move the magnetic force sensor 21 in a horizontal plane with respect to the measurement object 1.
The current line 12 is formed by a one-turn or two-turn circular or semi-circular coil (Coil), and is disposed in the vicinity of the measurement object 1.

As shown in FIGS. 1 and 2, the carrier introduction means 13 includes a signal generator (SG) 25 that transmits a high-frequency carrier signal and a splitter (Power Splitter) 26 that divides the transmitted carrier signal into two. is doing. The carrier wave introduction means 13 inputs one signal divided by the splitter 26 to the measurement object (DUT) 1 and inputs the other signal to the magnetic force sensor 21 via the phase adjuster 27 and the bypass capacitor 28. It is configured as follows. Thereby, the high frequency electromagnetic field measuring apparatus 10 is configured such that the potential when the carrier wave signal is input to the measurement object 1 and the potential of the magnetic force sensor 21 are equal.

As shown in FIGS. 1 and 2, the reference wave introducing means 14 has a signal generator 29 that transmits a high-frequency carrier signal, and is configured to be able to input a high-frequency reference wave signal to the current line 12. The reference wave introducing means 14 is configured to be able to change the frequency of the input reference wave signal.

As shown in FIG. 1, the computer 15 is connected to the detection circuit 23c of the displacement measuring means 23 via the lock-in amplifier 30, and the carrier wave introducing means 13 and the reference wave introducing means via the lock-in amplifier 30 and the frequency mixer 31. 14. Thus, the high frequency electromagnetic field measuring apparatus 10 generates a reference signal by mixing the carrier wave signal from the carrier wave introducing means 13 and the reference wave signal from the reference wave introducing means 14 by the frequency mixer 31, and the lock-in amplifier 30. It is sent to the computer 15 in synchronism with the displacement data from the detection circuit 23c to perform high-sensitivity measurement.

Further, the computer 15 has analysis means (not shown) and control means (not shown), and is connected to the mounting table 22 and the scanning means 24 via the

controllers

32 and 33, respectively. When the analysis means inputs the reference wave signal while changing the frequency by the reference wave introducing means 14, the magnetic force sensor 21 vibrates at the resonance frequency from the displacement caused by the vibration of the magnetic force sensor 21 measured by the displacement measuring means 23. In addition, the amplitude of the reference wave signal obtained by the reference wave introduction means 14 at that time is obtained. Further, based on the obtained amplitude of the magnetic force sensor 21 and the frequency of the reference wave signal, the amplitude and frequency of the high-frequency signal emitted from the measurement object 1 by the input of the carrier wave signal are calculated. The control means adjusts the height of the mounting table 22 to control the distance between the measurement object 1 and the probe 21b, and horizontally moves the scanning means 24 to measure the measurement object 1 in the horizontal plane. The position is controlled.

Next, the operation will be described.
The measurement principle of the high frequency electromagnetic field measuring apparatus 10 is shown in FIG. The high-frequency electromagnetic field measuring apparatus 10 can measure a high-frequency magnetic field generated by the measurement object (DUT) 1 to which a high-frequency signal is input as follows. That is, a high-frequency carrier signal is input to the measurement object 1 by the carrier introduction means 13 to generate a high-frequency magnetic field (H) having a certain intensity and frequency. Further, the reference wave introducing means 14 inputs a high frequency reference wave signal to the current line 12 arranged close to the measurement object 1 to generate a high frequency magnetic field (H) having a certain intensity and frequency. At this time, the frequency of the reference wave signal is changed by the reference wave introducing means 14 so that the frequency of the high frequency magnetic field generated by the measurement object 1 and the frequency of the high frequency magnetic field generated by the current line 12 are slightly shifted. This makes it possible to generate a beat (beat signal) of a magnetic field including each high-frequency magnetic field. By making the frequency of the beat signal close to the resonance frequency of the magnetic force sensor 21 composed of a cantilever, a high-frequency magnetic field can be measured.

At this time, the displacement measuring means 23 measures the displacement received by the magnetic force sensor 21 from the high-frequency magnetic field. Based on the measured data, the analyzing means inputs a high-frequency signal using equation (1). The high-frequency magnetic field generated by the measured object 1 can be obtained quantitatively.

Further, the high frequency electromagnetic field measuring apparatus 10 is configured such that the potential when the carrier wave signal is input from the carrier wave introducing means 13 to the measurement object 1 is equal to the potential of the magnetic force sensor 21, and the phase adjustment is performed. Since the phase and amplitude of these potentials are aligned by the capacitor 27 and the bypass capacitor 28, the force received by the magnetic force sensor 21 from the high-frequency electric field generated together with the high-frequency magnetic field by the input of the high-frequency signal can be suppressed. Thereby, the influence by a high frequency magnetic field and the influence by a high frequency electric field can be isolate | separated, and a high frequency magnetic field can be measured with high precision. In addition, since the coil of the current line 12 mainly generates a high frequency magnetic field and the insulator cantilever beam 21a which is the magnetic force sensor 21 is not affected by the high frequency electric field, the high frequency magnetic field can be measured with higher accuracy. it can.

The high-frequency electromagnetic field measuring apparatus 10 can obtain a two-dimensional distribution of a high-frequency magnetic field generated on the measurement object 1 such as a circuit by performing measurement while scanning with the scanning unit 24. Thereby, the generation source, propagation path, mixing destination, etc. of the electromagnetic noise on the measurement object 1 can be specified, which can contribute to the solution of the EMI problem.

As shown in FIG. 1, the high-frequency electromagnetic field measuring apparatus 10 has a DC power source 41 for generating a DC magnetic field on the current line 12 and an AC power source 42 for applying an alternating magnetic field to the current line 12. You may do it. In this case, by using the AC power source 42 to make the current line 12 a high frequency magnetic field source, the magnetization of the magnetic material of the magnetic film of the magnetic force sensor 21 can be AC demagnetized. In addition, by using the DC power source 41 to make the current line 12 a DC magnetic field generation source, the magnetization of the magnetic material of the magnetic film of the magnetic force sensor 21 can be re-magnetized and saturated.

Further, as shown in FIGS. 3 and 4, the current line 12 is formed of an open type transmission line, and the cantilever of the magnetic force sensor 21 may be made of silicon. The measurement principle of the high frequency electromagnetic field measuring apparatus 10 at this time is shown in FIG. In this case, the open transmission line mainly generates a high-frequency electric field (E), and the silicon cantilever is susceptible to the influence of the high-frequency electric field. Can be measured. Further, the high-frequency electric field can be obtained quantitatively using the formula (2). The high-frequency electromagnetic field measuring apparatus 10 shown in FIGS. 3 and 4 can be used for high-frequency electric field measurement in a memory or the like.

Furthermore, the high frequency electromagnetic field measuring apparatus 10 may be configured such that the current line 12 can be switched between a coil and an open transmission line so that both a high frequency magnetic field and a high frequency electric field can be measured. Further, the cantilever may be made of an insulator, and may be configured to be switchable between a silicon film formed on the surface of the tip 21b and a silicon film.
Hereinafter, an experiment for verifying the principle of the high-frequency electromagnetic field measuring apparatus 10 was performed.

[Measurement of high-frequency magnetic field by field beat method]
The high frequency magnetic field was measured using the field beat method. A coplanar waveguide (CPW) was produced as the measurement object 1. For the production of CPW, electron beam lithography, DC magnetron sputtering and lift-off methods were used. The produced CPW has a one-port shape with one end terminated, and the structure is Cr (5 nm) laminated on a glass substrate (Glass sub .; thickness: 550 μm, relative dielectric constant εr: 7.0). ) / Cu (300 nm) / Cr (5 nm). The CPW line length is 7800 μm, the signal line (SL; Signal Line) width is 5 μm, the ground line (GL; Ground Line) width is 50 μm, and the gap width between the signal line and the ground line is 6 μm. The characteristic impedance of CPW is 189Ω. As shown in FIGS. 5B and 5C, as a position display at the time of measurement, a point approximately 400 to 600 μm from the short-circuit point at the center of the CPW signal line is set as the origin.

As the magnetic force sensor 21, an MFM cantilever coated with Ni-Fe was used. The cantilever has a resonance frequency of about 28 kHz, a spring constant of 1.3 to 1.4 N / m, a Q value of 80, and a tip radius of the probe 21b of 40 to 50 nm. The cantilever fixes the magnetization in the vertical direction before measurement. As measurement conditions, the distance between the probe (MTM tip) 21b and the CPW (Lift Height) is 500 nm, the carrier wave signal is 9.15 mA, 100 MHz and 2 GHz, the reference wave signal is 9.15 mA, 100 MHz and 2 GHz, The bandwidth of the lock-in amplifier 30 was 80 Hz.

For the measurement, the apparatus shown in FIG. 5 (a) was used. The measurement principle of the measurement apparatus shown in FIG. 5 (a) is shown in FIG. 17 (c). The apparatus of FIG. 5A differs from the high-frequency electromagnetic field measuring apparatus 10 in the following points. First, the carrier wave signal and the reference wave signal shifted by the resonance frequency of the cantilever from the frequency of the carrier wave signal are simultaneously input to the CPW of the measurement object (DUT) without using the current line 12. A high frequency magnetic field is generated by the beat of the field. Further, the output from the function generator (FG) 51 is used as a reference signal for the lock-in amplifier 30. Note that the output frequency of the function generator 51 is set to several hundred kHz or less so as to include the resonance frequency of the cantilever.

First, the spectrum after synthesizing the carrier wave signal and the reference wave signal via the power combiner 52 was evaluated. As an example, FIG. 6 shows a spectrum when the frequency of the carrier signal is 100 MHz. As shown in FIG. 6, two narrow-bandwidth spectra are observed at 100 MHz and 100.028 MHz. On the other hand, no spectrum is observed in the vicinity of 28 kHz corresponding to the frequency difference. This result is the same in all cases where the frequency of the carrier signal is changed from 10 MHz to 10 GHz. Therefore, it was confirmed that even if a carrier wave signal and a reference wave signal are input on the CPW line to generate a beat component of the field, no signal is synthesized in a low frequency band near the resonance frequency band of the cantilever. It was also confirmed that the line widths of these spectra were sufficiently narrow compared to the cantilever resonance frequency band.

Next, a high frequency magnetic field was measured by this beat component. As an example, FIG. 7A shows the measurement result of the vibration amplitude value of the probe 21b when the frequency of the carrier wave signal is 100 MHz. The measurement position of the probe 21b is the center of the gap between the CPW signal line and the ground line. As shown in FIG. 7A, it was confirmed that the vibration amplitude value of the probe 21b was the maximum in the vicinity of 28 kHz corresponding to the resonance frequency of the cantilever. From this result, it can be said that the beat of the field caused by the two high-frequency signals can be detected by the MFM probe 21b.

Further, when the frequency of the carrier signal is 100 MHz and 2 GHz, the relationship between the vibration amplitude value of the probe 21b in the vicinity of 28 kHz corresponding to the resonance frequency of the cantilever and the current value of the carrier signal is examined, and the result is shown in FIG. ). The measurement position of the probe 21b is the center of the gap between the CPW signal line and the ground line. As shown in FIG. 7B, it was confirmed that when the current value of the carrier signal was increased, the vibration amplitude value near the resonance frequency of the cantilever increased linearly. This is because the amplitude intensity of the waveform due to the beat of the magnetic field generated on the CPW increases as the current of the carrier signal increases, and the MFM probe 21b follows the envelope of the high-frequency signal formed by the beat. This is probably due to this.

Next, the high frequency magnetic field due to the field beat was measured while changing the frequency of the carrier signal. FIG. 8 shows the relationship between the frequency of the carrier wave signal and the vibration amplitude value and Q value of the probe 21b at this time. The measurement position of the probe 21b is the center of the gap between the CPW signal line and the ground line. As shown in FIG. 8, the vibration amplitude value is almost constant up to around 2 GHz and is 0.60 to 0.75 nm. Further, it was confirmed that at 2 GHz or more, it rapidly decreased to near 0.08 nm and then decreased logarithmically. Further, it was confirmed that the Q value was almost constant regardless of the frequency band, and the value was about 350.

Next, when the frequency of the carrier wave signal was 100 MHz and 2 GHz, the high frequency magnetic field due to the beat of the field was measured while moving the probe 21b in the cross-sectional direction of the CPW. The relationship between the position of the probe 21b and the vibration amplitude value of the probe 21b at this time is shown in FIG. As shown in FIG. 9, it was confirmed that the vibration amplitude value of the probe 21 b decreased with a decrease in the detection area (Detection Area) where the CPW signal line, the ground line, and the cantilever overlap. This suggests that the cantilever detects not only a high-frequency magnetic field but also a high-frequency electric field.

[Separation of magnetic field and electric field by field beat method]
The apparatus shown in FIG. 5A was improved and an attempt was made to separate a high-frequency magnetic field and a high-frequency electric field by a field beat method. As the measurement object 1, CPW shown in FIG. 5 was used. As the magnetic force sensor 21, a cantilever coated with the same Ni—Fe as in FIG. The apparatus used for the measurement is shown in FIG. Moreover, the measurement principle of this measuring apparatus is shown in FIG. The apparatus of FIG. 10 differs from the apparatus of FIG. 5A in that the potential when the carrier wave signal is input to the CPW and the potential of the cantilever are equalized by the splitter 26, the phase adjuster 27, and the bypass capacitor 28. Has been. Thus, the configuration is closer to that of the high-frequency electromagnetic field measuring apparatus 10.

Using the apparatus shown in FIG. 10, when the frequency of the carrier wave signal was 2 GHz, the high frequency magnetic field due to the beat of the field was measured while moving the probe 21b in the CPW cross-sectional direction. The relationship between the position of the probe 21b and the vibration amplitude value of the probe 21b at this time is shown in FIG. 11 ("improved" in the figure; black circle). For comparison, the result of 2 GHz in FIG. 9 measured with the apparatus in FIG. 5A is also shown (“before improvement” in the figure; white circle). As shown in FIG. 11, in the result of the apparatus shown in FIG. 10, there is no correlation between the vibration amplitude value of the probe 21b and the detection area where the CPW signal line and ground line overlap the cantilever. From this, it is considered that the influence of the high frequency electric field can be suppressed by configuring the potential when the carrier wave signal is input to the CPW and the potential of the cantilever to be equal.

Next, the same measurement was performed using an uncoated cantilever, and the result is shown in FIG. 12 (“Non coated” in the figure). For comparison, the results of a cantilever coated with Ni—Fe in FIG. 11 are also shown (“Ni—Fe” in the figure). As shown in FIG. 12, it was confirmed that the vibration amplitude value of the probe 21b is substantially constant in a cantilever that is not magnetically coated. Since the cantilever that is not magnetically coated is considered not to be affected by the high-frequency magnetic field, it can be said from the results shown in FIG. 12 that the apparatus shown in FIG. 10 can suppress the influence of the high-frequency electric field.

Next, using the apparatus shown in FIG. 10, when the frequency of the carrier wave signal was 1.1 GHz, the high frequency magnetic field due to the beat of the field was measured while moving the probe 21b in the cross-sectional direction of the CPW. From the measurement results, the magnetic field (Hz) × magnetic field gradient (dHz / dz) is obtained using the equation (1), and the relationship between the obtained value and the position of the probe 21b is shown in FIG. The magnetic force sensor 21 is a cantilever coated with Ni—Fe. As shown in FIG. 13, it was confirmed that the value of the magnetic field × magnetic field gradient had a maximum value or a minimum value in the vicinity of the boundary between the CPW ground line or the signal line and the gap. From this, it is considered that the gradient of the high-frequency magnetic field could be detected by the apparatus shown in FIG.

Thus, it can be said that a high-frequency magnetic field can be detected by configuring the potential when the carrier wave signal is input to the CPW and the potential of the cantilever to be equal. For this reason, even in the high frequency electromagnetic field measuring apparatus 10 having the same configuration, it is considered that only the high frequency magnetic field can be detected by separating the influence of the high frequency magnetic field and the influence of the high frequency electric field.

Using the high frequency electromagnetic field measuring apparatus 10, the high frequency magnetic field was measured by the field beat method. As the measurement object 1, CPW shown in FIG. 5 was used. Further, as the magnetic force sensor 21, an MFM cantilever in which the surface of the probe 21b and the surface of the beam 21a opposite to the probe 21b are coated with Ni—Fe is used. The frequency of the reference wave signal flowing through the coil of the current line 12 is 1000 MHz, the amplitude is 12 dBm, the frequency of the carrier wave signal flowing through the CPW of the measurement object 1 is 1000.02797 MHz, the amplitude is 9, 12, 15, 18, 21 dBm, A high frequency magnetic field was generated by the beat of the field, and the vibration amplitude and phase of the probe 21b were measured.

These measurement results are shown in FIG. 14 together with the results when there is no carrier signal. FIG. 14A shows the measurement results when there is no carrier signal, and FIGS. 14B to 14F show the measurement results when the amplitude of the carrier signal is 9, 12, 15, 18, 21 dBm, respectively. 14A to 14F, the upper graph shows the probe vibration amplitude, and the lower graph shows the phase measurement result. FIG. 15 shows changes in the peak value of the vibration amplitude of the probe 21b with respect to the amplitude of the carrier signal. As shown in FIG. 14, it was confirmed that the vibration amplitude of the probe 21b was maximized at 27.7 kHz near the resonance frequency of the cantilever by the field beat method. Further, as shown in FIG. 15, it was confirmed that when the amplitude of the carrier wave signal was increased, the vibration amplitude in the vicinity of the resonance frequency of the cantilever increased substantially linearly.

Next, the amplitude of the reference wave signal was set to 18 dBm, the amplitude of the carrier wave signal was set to 12 dBm, and the frequency of the reference wave signal and the carrier wave signal was changed to measure the high frequency magnetic field by the field beat method. FIG. 16 shows the relationship between the frequency of the reference wave signal at this time and the peak value of the vibration amplitude of the probe 21b. As shown in FIG. 16, it was confirmed that the high frequency electromagnetic field measurement apparatus 10 can be used to measure a high frequency magnetic field by a field beat method. In FIG. 16, when the frequency of the reference wave signal is 1 to 1.3 GHz, the vibration amplitude of the probe 21b is large, which depends on the high frequency characteristics of the measurement system, By improving the connector or the like, the high-frequency characteristics can be improved.

As described above, it was confirmed that the high frequency electromagnetic field measuring apparatus 10 can detect the high frequency magnetic field. Further, the high frequency electromagnetic field measuring apparatus 10 is configured so that the potential when the carrier wave signal is input to the CPW and the potential of the cantilever are equal, so that the influence of the high frequency electric field is suppressed and only the high frequency magnetic field is detected. It is thought that.

The high-frequency electromagnetic field measuring apparatus according to the present invention can be used as a high-frequency magnetic force microscope, a high-frequency electromagnetic noise measuring instrument, and a spin element measuring apparatus. When used as a high-frequency magnetic force microscope, the measurable frequency band can be expanded to a high frequency of at least 6 to 7 GHz and a maximum of 10 GHz. When used as a high-frequency electromagnetic noise measuring instrument, the spatial resolution can be increased to 1 μm or less, and electromagnetic noise on an LSI chip can be measured. Further, when used as a spin element measuring apparatus, the behavior of a minute magnetic material can be directly observed.

DESCRIPTION OF SYMBOLS 1 Measurement object 10 High frequency electromagnetic field measuring apparatus 11 Magnetic force microscope 21 Magnetic force sensor 21a Beam 21b Probe 22 Mounting stand 23 Displacement measuring means 23a Laser 23b Optical position sensor 23c Detection circuit 24 Scanning means 12 Current line 13 Carrier introduction means 25 Signal generator 26 Splitter 27 Phase adjuster 28 Bypass capacitor 14 Reference wave introducing means 29 Signal generator 15 Computer 30 Lock-in amplifier 31

Frequency mixer

32, 33 Controller

Claims

A high-frequency electromagnetic field measuring device for measuring a high-frequency magnetic field generated by a measurement object to which a high-frequency signal is input,
A magnetic force sensor capable of detecting a magnetic field using vibration caused by magnetic action;
A current line disposed in proximity to the measurement object;
Carrier wave introduction means for inputting a high frequency carrier wave signal to the measurement object;
A reference wave introduction means configured to be able to input a high frequency reference wave signal to the current line, and to be able to change the frequency of the input reference wave signal;
A high-frequency electromagnetic field measuring apparatus, wherein a potential when the carrier signal is input from the carrier introduction means to the measurement object is equal to a potential of the magnetic force sensor.
Have a magnetic force microscope,
The magnetic force sensor comprises a cantilever of the magnetic force microscope,
The magnetic force microscope includes a mounting table on which the measurement object is placed, a displacement measuring unit that measures displacement due to vibration of the magnetic force sensor, and a scan that relatively scans the magnetic force sensor with respect to the measurement object. Having a means,
The high-frequency electromagnetic field measuring apparatus according to claim 1, wherein
The current line comprises a coil;
The high-frequency electromagnetic field measuring apparatus according to claim 2, wherein the cantilever is made of an insulator, and a magnetic film is formed on a surface of a probe at the tip.
An AC power source for applying an alternating magnetic field to the current line so that the magnetization of the magnetic material of the magnetic film of the cantilever can be AC demagnetized;
A DC power source for generating a DC magnetic field in the current line so as to remagnetize the magnetization of the magnetic material of the magnetic film of the cantilever,
The high frequency electromagnetic field measuring apparatus according to claim 3, wherein the high frequency electromagnetic field measuring apparatus is provided.
The current line consists of an open transmission line,
The high frequency electromagnetic field measuring apparatus according to claim 2, wherein the cantilever is made of silicon.
When the reference wave signal is input while changing the frequency by the reference wave introducing means, the magnetic force sensor vibrates at a resonance frequency from the displacement caused by the vibration of the magnetic force sensor measured by the displacement measuring means. Obtaining the amplitude, obtaining the frequency of the reference wave signal by the reference wave introducing means at that time, and by inputting the carrier signal based on the obtained amplitude of the magnetic force sensor and the frequency of the reference wave signal The high-frequency electromagnetic field measuring apparatus according to claim 2, further comprising an analysis unit that calculates an amplitude and a frequency of a high-frequency signal emitted from the measurement object.
The high frequency electromagnetic field measuring apparatus according to claim 1, wherein the magnetic force sensor is made of an insulator.