JP2002207069A - Method for suppressing phase noise of high frequency carrier type magnetic field sensor and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for suppressing a phase noise of a high frequency carrier type magnetic field sensor and an apparatus therefor which enable detecting minute signals to a level of thermal fluctuation of a sensor element itself or thermal noise by reducing an SSB phase noise. SOLUTION: There are provided a signal generator 1, a first divider 2 connected to the signal generator 1, the sensor element 3 connected to the first divider 2, a series connection circuit which is connected in parallel to the sensor element 3 and is comprised of an attenuator 4 connected to the first divider 2 and a phase shifter 5, a second divider 6 connected to the sensor element 3 and the phase shifter 5, a preamplifier 7 connected to the second divider 6, and a spectrum analyzer 8 connected to the preamplifier 7. A carrier voltage is divided by the first divider 2 and adjusted with the use of the attenuator 4 and the phase shifter 5 so that an output signal of the phase shifter 5 becomes equal in amplitude and different by approximately 180 deg. in phase to a carrier component as an output signal of the sensor element 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency carrier type magnetic field sensor which suppresses a carrier component of an AM modulated wave output from a high frequency carrier type magnetic field sensor and reduces SSB phase noise of a carrier component in a sideband. The present invention relates to a phase noise suppression method and an apparatus thereof.

[0002]

2. Description of the Related Art Conventionally, there have been the following techniques disclosed in such fields.

(1) Shigeru Numazawa, Koichi Murakami, Hiroyuki Hojo: Journal of the Japan Society of Applied Magnetics, 9, 263 (1985) (2) Yoshikuni Kamo, Hiroshi Shimada: 13th Annual Meeting of the Japan Society of Applied Magnetics, 23aD- 6 (1989) (3) K.C. Mohri, T .; Kohzawa, K .; Ka
washima, H .; Yoshida, and L.M.
V. Panina: IEEE Trans. Mag
n. , 28, 3150 (1992) (4) Hiroaki Kikuchi, Masaaki Takezawa, Masahiro Yamaguchi, Kenichi Arai: Journal of the Japan Society of Applied Magnetics, 21, 789 (1997) (5) Koji Higa, Tsuyoshi Uchiyama, R. Shin, Toshio Mori,
Yasumoto Unoki, Kazumasa Kikuchi: Journal of the Japan Society of Applied Magnetics, 21, 6
49 (1997) (6) M.P. Senda, O .; Ishii, Y .; Kosh
imoto, andT. Toshima: IEEE T
rans. Magn. , 30, 4611 (1994). (7) M.P. Senda, Y .; Koshimoto: IE
EE Trans. Magn. , 33, 3379 (19
97) (8) K. Morikawa, Y. Nishibe, H. Yamadera, H. Nonomura, S. Takeuchi, and Y. Taga: Journal of the Japan Society of Applied Magnetics, 20, 553
(1996) (9) T.I. Morikawa, Y .; Nishibe,
H. Yamada, Y .; Nonomura, M .; T
akeuchi, and Y .; Taga: IEEE T
rans. Magn. , 33, 4367 (1997). Yamaguchi, M .; Takezawa
a, Y. H. Kim, K .; Ishiyama, M .; Ba
ba, K .; I. Arai, N .; Wako, and I .;
Abe: Procedings of Transd
ucers '99, 2P3.8 (1999) (11) Masaaki Takezawa: Doctoral Dissertation, Graduate School of Engineering, Tohoku University, p. 216 (1999) (12) Masaaki Takezawa, Noriyuki Ajishiro, Masahiro Yamaguchi, Ken-ichi Arai, Jiro Yamazaki: Materials of IEICE Magnetics Research Group, MAG-
99-189 (13) S.R. Uchiyama, M .; Masuda, a
nd Y. Sasaki: Jpn. J. Appl. Ph
ys. , 2,621 (1963) high-frequency carrier currents energized directly to the magnetic, highly sensitive magnetic field sensor using the skin effect studies to realize a thin film has been actively, so far 10 ^-10 Tesla There are reports that (T) units of AC magnetic field resolution were obtained.

[0004]

High-frequency carrier-type thin-film magnetic field sensors Although higher sensitivity is expected compared to existing magnetic field sensors, the output signal is very small and the theoretical minimum detection sensitivity is the magnetic moment. Determined by thermal fluctuations. This small magnetic field signal is amplified by a high-frequency carrier.
Modulated to produce a sideband signal, the minimum detection sensitivity of which was hitherto limited by the SSB phase noise level of the carrier.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a high-frequency carrier type magnetic field sensor capable of detecting a thermal fluctuation of a sensor element itself or a minute signal down to a thermal noise level by reducing SSB phase noise. It is an object of the present invention to provide a phase noise suppressing method and apparatus therefor.

[0006]

According to the present invention, there is provided a method for suppressing phase noise of a high-frequency carrier type magnetic field sensor, comprising the steps of: It is characterized in that the carrier and the SSB phase noise are suppressed by combining with the modulation wave.

[2] In a phase noise suppression device for a high-frequency carrier type magnetic field sensor, a signal generator, a first divider connected to the signal generator, a sensor element connected to the first divider, A series connection circuit of an attenuator and a phase shifter connected in parallel with the sensor element and connected to the first divider; a second divider connected to the sensor element and the phase shifter; A preamplifier connected to a divider; and a spectrum analyzer connected to the preamplifier. A carrier voltage is divided by the first divider, and an output signal of the phase shifter is an output signal of the sensor element. It is characterized in that the amplitude is adjusted using the attenuator and the phase shifter so that a certain carrier component has the same amplitude and a phase difference of approximately 180 °. That.

[0008]

Embodiments of the present invention will be described below in detail.

First, a description will be given of how to increase the sensitivity of the sensor element.

[0010] Chemically amplified negative resist ZP on a glass substrate
N1100 was applied at 3 μm and resist patterning was performed. Subsequently, the amorphous Co was formed by rf sputtering.
_{An 85} Nb ₁₂ Zr ₃ single layer film and a CoNbZr / Nb / CoNbZr laminated film in which the magnetic layer was divided into two by an Nb conductor layer were formed, and a strip-shaped magnetic field sensor element was manufactured by lift-off. FIG. 1 shows an external view of the strip-shaped magnetic field sensor element. FIG. 1A is a perspective view showing a single-layer film sensor, and FIG. 1B is a perspective view showing a multilayer film sensor.

The length L of the strip is 1 mm and the width W is 10,2.
It was changed to 0.50 μm. The thickness D of the single-layer film is 1 μm,
By 0.5μm per layer thickness D ₁ of the magnetic film in the laminated film, the thickness D ₂ of the interlayer conductor layer was 5 [mu] m.

As a manufacturing method, the magnetic anisotropy introduced at the time of forming the single-layer film and the laminated film should be 8 × 10 ⁻⁴ or less,
400 ° C. in a vacuum rotating magnetic field of 0 kA / m (1 kOe),
After relaxation by heat treatment for 2 hours, heat treatment was performed at 400 ° C. for 1 hour in a vacuum electrostatic magnetic field under the same conditions to introduce uniaxial anisotropy such that the width direction was the easy axis direction. Anisotropic magnetic field H _k after this in a static electric field heat treatment 400~500A /
m (5-6 Oe). While applying an external DC magnetic field H _dc in the longitudinal direction of the strip element, and applying a high frequency current 100 MHz, network analyzer (HP875
2A), the impedance of the device was measured by a reflection method. After the measurement, the magnetic domain structure of each sensor element was observed by the Pitter method.

When the magnetic film has an ideal uniaxial anisotropy, the internal impedance Z _i of the strip-like magnetic thin film is
Is divided into resistance R _i and reactance X _i, and Z _i = R _i + jX _i (1)

[0014]

(Equation 1)

The calculation is as follows. Where ρ is resistivity, l, w and t are length, width and thickness,
μ _er ′ and μ _er ″ are the real part and the imaginary part of the relative magnetic permeability calculated from the theory of the bias magnetic susceptibility. δ ^* is the skin depth and is expressed by the following equation.

[0016]

(Equation 2)

From equations (1) to (3),

[0018]

(Equation 3)

When a function F (H _dc ) of the external magnetic field is defined as follows, Z _i becomes

[0020]

(Equation 4)

It can be expressed as follows.

Here, a gradient of an impedance change with respect to an external magnetic field, that is, a differential value (∂Z _i / ∂H _dc ) with respect to an impedance external magnetic field is defined as a sensor gain, which is represented by the following equation. When the sensor gain is calculated by differentiating equation (10) with an external magnetic field,

[0023]

(Equation 5)

It is expressed as follows.

FIG. 2 shows a change in impedance of a magnetic field sensor element using a single-layer film with respect to an external magnetic field. FIG. 2 (a)
FIG. 2B shows the case where lift-off is used, and FIG. 2B shows the case where ion milling is used.

For comparison, the characteristics of devices of the same dimensions manufactured using ion milling are also shown. In the case of using a case and an ion milling using lift-off, the magnetic field strength is different from the impedance change amount is a maximum value is because the magnitude of the anisotropy field H _k of the magnetic film is different. Element width 2
At 0.5 μm, no difference was observed in the impedance change ΔZ due to the difference in the process. 10μ width
In the case of m, the impedance change amount of 9.5Ω was obtained in the element using the lift-off, whereas the impedance change amount was about 3Ω in the element using the ion milling.

FIG. 3 shows a photograph of the magnetic domain structure of the sensor element at a width of 10 μm. Line drawings are also shown. As shown in FIG. 3A, in the element using lift-off, a 180 ° domain wall parallel to the axial direction and a 90 ° domain wall at the end of the element were observed. In this reflux magnetic domain structure, the area of the main magnetic domain is dominant as compared with the area of the reflux magnetic domain, and it is apparent that the uniaxial anisotropy is induced in the width direction of the element by the heat treatment in the magnetic field. On the other hand, as shown in FIG. 3B, in the element using the ion milling, the 180 ° domain wall is not observed, but only the 90 ° domain wall is observed, and the uniaxial anisotropy is clearly deteriorated. This is considered to be the cause of the reduced amount of impedance change.

As a cause of the deterioration of the uniaxial anisotropy, the processing accuracy at the end of the element at the time of fine processing can be considered. FIG. 4 shows an enlarged photograph of the end of the element. FIG. 4A shows a case where lift-off is used, and FIG. 4B shows a case where ion milling is used. As shown in FIG. 4B, when ion milling is used, the taper is large and the shape is uneven, as compared with the case where lift-off is used. This disorder of the shape leads to an increase in the magnetostatic energy, and there is a possibility that a magnetic domain structure having a large return magnetic domain is adopted in order to suppress this.

FIG. 5 shows the change in sensor gain with respect to the element width of a sensor using a single-layer film and a laminated film together with calculated values. The calculated value was calculated based on the equation (11).
In the case of a single-layer film, the sensor gain increased with a decrease in the element width, which was in agreement with the calculated value. In the case of the laminated film, the sensor gain was increased as compared with the single-layer film, and high sensitivity was realized. When the width is 20 μm or less, the sensor gain is 100 kΩ / T
(10Ω / Oe) or more was obtained.

FIG. 6 is a view showing a photograph of the magnetic domain structure of the sensor element formed of a single-layer film, and FIG.
In the case of a width, FIG. 6B shows the case of a 20 μm width, and FIG.
Is 10 μm. FIG. 7 is a view showing a photograph of the magnetic domain structure of the sensor element formed by the laminated film, and FIG.
In the case of 0 μm width, FIG. 7B shows the case of 20 μm width.
(C) is 10 μm.

From these figures, in the magnetic domain structure of the laminated film, the return magnetic domain observed in the single layer film was not observed, and a 180 ° domain wall almost parallel to the axial direction was observed. This is presumably because magnetostatic coupling occurs at the ends between the divided magnetic layers, and the generation of magnetic poles and return magnetic domains is suppressed.

From the above, it has been clarified that the sensor gain can be increased by increasing the area of the return magnetic domain when the sensor element has a laminated structure.

FIG. 8 is a diagram showing an equivalent circuit of the measurement system. FIG. 8A shows an equivalent circuit of the carrier suppressing circuit of the present invention, and FIG. 8B shows a sensor element and a spectrum analyzer connected in series. An equivalent circuit of a system without a carrier suppression circuit is shown.

In FIG. 8A, reference numeral 1 denotes a signal generator (H
P8656B), 2 is a first divider (KDI D29)
35), 3 is a sensor element, 4 is an attenuator (HP84)
94A), 5 is a phase shifter (HLS-JJ-1), 6 is a second divider (KDI D2935), 7 is a preamplifier (HP87405), and 8 is a spectrum analyzer (HP8561E).

In FIG. 8B, 11 is a signal generator (HP8656B), 12 is a sensor element, and 13 is a spectrum analyzer (HP8561E).

As described above, in the high-frequency carrier type magnetic field sensor, the magnetic field to be measured is detected by measuring the output in the sideband of the AM modulated wave. The carrier suppression circuit
It is intended to reduce only the carrier component of the AM modulated wave from the sensor element 3 and measure the sideband with high sensitivity.
The carrier voltage was divided by the second divider 6 and adjusted using the attenuator 4 and the phase shifter 5 so that the signal at the point B and the carrier component at the point A had the same amplitude and a phase difference of almost 180 °.

FIG. 9 shows frequency spectra at points A and C in the carrier suppression circuit. The detection limit of the sideband is the size of the sideband is the SSB of the carrier component.
It is determined under the condition equal to the magnitude of the phase noise. SSB phase noise is noise caused by fluctuations in the frequency of an oscillator that supplies carriers. By canceling the carrier component by the carrier suppression circuit, the SSB phase noise of the carrier component is reduced from −120 dBm to −13 in FIG.
Since the signal is reduced to 3 dBm, it is possible to detect a signal in a smaller sideband. The signals at the points A and B were combined, and the combined signal amplified by the preamplifier 7 having a gain of 24 dBNF 6.5 dB was measured by the spectrum analyzer 8.

The sensor element used for the measurement has a length of 5 mm,
This is a stacked structure of CoNbZr / Cr / CoNbZr with an element width of 50 μm. The thickness of CoNbZr is 0.5 μm, and the thickness of the nonmagnetic interlayer is 10 nm. A carrier signal having a frequency of 370 MHz and a voltage of 3 V was applied to the sensor element, and the sensor output when a small alternating magnetic field having a frequency of 500 kHz was applied to the sensor element was measured. During the measurement of the small AC magnetic field, a DC bias magnetic field of 400 A / m (5 Oe) was applied so that the sensor gain of the sensor element was maximized.

FIG. 10 shows the sensor output with respect to a minute AC magnetic field when a carrier suppression circuit is used and in a system in which a sensor element and a spectrum analyzer are connected in series. In a system in which a sensor element and a spectrum analyzer are connected in series, the magnetic field detection resolution is 2.0 × 10 ^-8
T (2.0 × 10 ⁻⁴ Oe). This means that the SSB phase noise at the carrier frequency is -118 dBm,
This is because in a magnetic field of 0 × 10 ⁻⁸ T or less, the output of the sideband of the AM modulation wave from the sensor element is buried in the SSB phase noise. On the other hand, it is considered that the SSB phase noise could be reduced to -161 dBm by using the carrier suppression circuit. The noise floor of the spectrum analyzer is -140 dBm
This is the detection limit. As a result, FIG.
8.5 × 10 ⁻¹¹ T in the measurement system using the circuit of FIG.
A magnetic field detection resolution of (8.5 × 10 ⁻⁷ Oe) was obtained.

As described above, in the present invention, a sensor element is newly manufactured by using lift-off as a fine processing process. As a result, in a single-layer film having a width of 10 μm, an impedance change amount about three times as large as that obtained by using ion milling was obtained. Further, a sensor element having a laminated structure was manufactured, and a sensor gain of 100 kΩ /
T (10Ω / Oe) was realized. Furthermore, a carrier suppression circuit was proposed as a highly sensitive magnetic field measurement method, and 8.5 × 10
A small alternating magnetic field of ^-11 T (8.5 × 10 ^-2 Oe) was successfully detected.

It should be noted that the present invention is not limited to the above-described embodiment, but various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0042]

As described above, according to the present invention, the following effects can be obtained.

(A) As a microfabrication process, a sensor element was manufactured by using lift-off, and an element whose size was reduced to 10 μm in width obtained an impedance variation three times or more as compared with the conventional one.

(B) By stacking the sensor elements, the area of the return magnetic domain was reduced, and the sensor gain was improved.

(C) In the laminated structure, the element is 10 μm wide.
100Ω / T, even when downsized to m and 1mm long
A sensor gain of (10Ω / Oe) was obtained.

(D) By reducing the SSB phase noise using the carrier suppression circuit, 8.5 × 10 ^-11 T
(8.5 × 10 ⁻⁷ Oe) enables detection of a very small magnetic field. As described above, the present invention provides a high-frequency carrier-type sensor that operates at room temperature, has higher sensitivity than a conventional sensor, and can be a promising candidate for a next-generation magnetic recording head, and operates at room temperature. The emergence of an ultra-sensitive magnetic field sensor that opens the door will open the way to the creation of new industries.

[Brief description of the drawings]

FIG. 1 is an external view of a strip-shaped magnetic field sensor element according to the present invention.

FIG. 2 is a diagram showing a change in impedance with respect to an external magnetic field of a magnetic field sensor element using a single-layer film according to the present invention.

FIG. 3 is a view showing a photograph of a magnetic domain structure of a sensor element with a width of 10 μm showing an example of the present invention.

FIG. 4 is a view showing an enlarged photograph of an element end showing an example of the present invention.

FIG. 5 is a diagram illustrating a change in sensor gain with respect to an element width of a sensor using a single-layer film and a stacked film according to an embodiment of the present invention, together with a calculated value.

FIG. 6 is a view showing a photograph in which a magnetic domain structure of a sensor element having a single-layer film according to an embodiment of the present invention is observed.

FIG. 7 is a view showing a photograph in which a magnetic domain structure of a sensor element using a laminated film according to an embodiment of the present invention is observed.

FIG. 8 is a diagram showing an equivalent circuit of the measurement system.

FIG. 9 is a diagram illustrating frequency spectra at points A and C in the carrier suppression circuit according to the embodiment of the present invention.

FIG. 10 is a diagram showing a sensor output with respect to a small AC magnetic field in a case where a carrier suppression circuit according to an embodiment of the present invention is used and in a system in which a sensor element and a spectrum analyzer are connected in series.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Signal generator 2 1st divider 3 Sensor element 4 Attenuator 5 Phase shifter 6 2nd divider 7 Preamplifier 8 Spectrum analyzer

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Satoshi Suzuki 2-205 F-term (reference) 2G017 AA01 AD51 AD63 AD65

Claims (2)

[Claims] 1. An AM-modulated wave modulated by an external magnetic field is added to a carrier component and a component having a phase opposite to that of a carrier component.
A phase noise suppressing method for a high-frequency carrier type magnetic field sensor, characterized in that only a carrier component is reduced, thereby reducing phase noise and enabling high sensitivity measurement of a sideband. 2. A signal generator, (b) a first divider connected to the signal generator, (c) a sensor element connected to the first divider, and (d) a sensor element connected to the first divider. A series connection circuit of an attenuator and a phase shifter connected in parallel with the sensor element and connected to the first divider; (e) a second divider connected to the sensor element and the phase shifter; A) a preamplifier connected to the second divider; and (g) a spectrum analyzer connected to the preamplifier; and (h) a carrier voltage divided by the first divider. A high-frequency carrier-type magnetic element, wherein the output signal is adjusted using the attenuator and the phase shifter so that the amplitude is equal to the carrier component which is the output signal of the sensor element, and the phase is different by approximately 180 °. Phase noise suppression apparatus of the sensor.