JP2011223422A - Physical quantity sensor and microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic field detection type physical quantity sensor that is improved in detection sensitivity, and a microphone.SOLUTION: In a microphone 1 comprising a magnetic field generation unit 10 which generates a magnetic field to be detected, a magnetic field detection unit 4 which outputs an electric signal corresponding to a first directional component Hx of the magnetic field to be detected, and a vibrating thin film 3 which vibrates the magnetic field generation unit 10 and magnetic field detection unit 4 relatively in a second direction (y) crossing a first direction (x) according to vibration input from the outside, the magnetic field generation unit 10 comprises a first magnetic field generation unit 11 which is arranged on one side of the magnetic field detection unit 4 in the second direction y and generates a first magnetic field H1 between a pair of magnetic poles, and a second magnetic field generation unit 13 which is arranged on the other side of the magnetic field detection unit 4 in the second direction y and generates a second magnetic field H2 between the pair of magnetic poles. Consequently, the magnetic field to be detected which is a composite magnetic field of the first magnetic field H1 and second magnetic field H2 whose first directional components are opposite in direction is generated between the first magnetic field generation unit 11 and second magnetic field generation unit 13.

Description

  The present invention relates to a physical quantity sensor that detects physical quantities such as displacement, velocity, and acceleration, and a microphone that detects sound waves.

  2. Description of the Related Art Conventionally, many physical quantity sensors have been proposed that detect a displacement, speed, acceleration, and the like by converting a physical change of a material itself generated according to an external force into an electric signal. This physical quantity sensor is applied in various fields. For example, a microphone that detects a sound wave is known as one of the application examples.

  As this microphone, a capacitor type that outputs a change in electrostatic capacity accompanying the displacement of the diaphragm due to sound waves as an electric signal is most often used. In recent years, attempts have been made to reduce the size by using MEMS (Micro Electro Mechanical Systems) technology. However, when the diaphragm area is reduced, the capacitance of the capacitor is reduced, so that the detection sensitivity of sound waves is lowered. Therefore, it is impossible to achieve both size reduction and high S / N ratio.

  In contrast to this condenser microphone, a magnetic field detection microphone has been proposed in which the magnetic field strength is detected by a magnetoresistive element that is displaced together with the vibrating membrane (see, for example, Patent Document 1). As shown in FIG. 22A, this microphone is configured to include a pair of magnets that form a gradient magnetic field, and a vibration film that relatively moves the magnetoresistive element and the magnet in response to sound waves. When the magnetic field around the magnetoresistive element changes with relative movement between the magnetoresistive element and the magnet, the change in resistance of the magnetoresistive element is output as an electrical signal.

JP-A-8-84398

By the way, in order to improve the detection sensitivity in the microphone described in Patent Document 1, it is preferable to dispose the magnetoresistive element at a location where the magnetic field gradient of the gradient magnetic field is steep. In this regard, if the magnetoresistive element is arranged close to the magnet, it is considered that the magnetic field gradient of the gradient magnetic field around the magnetoresistive element is increased and the detection sensitivity can be improved. However, when the magnetoresistive element is brought close to the magnet, the rate of change in resistance of the magnetoresistive element decreases as the magnetic field intensity around the magnetoresistive element increases, and the detection sensitivity of the magnetic field intensity decreases. On the other hand, if the distance between the pair of magnets is shortened, the magnetic field gradient in the vicinity of these magnets can be increased, but the magnetic field strength also increases in a region where the magnetic field gradient is large, and the detection sensitivity cannot be improved. If the magnetic field strength around the magnetoresistive element becomes too large, the magnetoresistive element is magnetically saturated and the magnetic field strength cannot be detected. Further, if the magnetoresistive element is placed away from the magnetic pole so as not to saturate, the magnetic field gradient becomes small and sensitivity cannot be obtained.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic field detection type physical quantity sensor and a microphone capable of improving detection sensitivity.

In order to solve the above problems, the present invention proposes the following means.
That is, the physical quantity sensor according to the present invention includes a magnetic field forming unit that forms a detected magnetic field in space, a magnetic field detecting unit that outputs an electric signal corresponding to a first direction component of the detected magnetic field, and an external displacement input. And a movable part that relatively displaces the magnetic field forming unit and the magnetic field detecting unit in a second direction intersecting the first direction, wherein the magnetic field forming unit is configured to detect the magnetic field. A second magnetic field is generated between a first magnetic field generating unit that generates a first magnetic field between magnetic poles disposed on one side in the second direction of the magnetic field and a magnetic field that is disposed on the other side in the second direction of the magnetic field detecting unit. A second magnetic field generating unit, and the detected magnetic field is a combined magnetic field of the first magnetic field and the second magnetic field between the first magnetic field generating unit and the second magnetic field generating unit. Each of the first magnetic field and the second magnetic field in the detected magnetic field Wherein the first direction component of is opposite to each other.
According to the physical quantity sensor having such a configuration, each first direction component of the first magnetic field and the second magnetic field becomes a gradient magnetic field having a magnetic field gradient that decreases as the distance from the magnetic field generation unit increases. Since the first direction components of the first magnetic field and the second magnetic field are opposite to each other, the first direction component of the detected magnetic field, which is a combined magnetic field of the first magnetic field and the second magnetic field, is In the vicinity of the magnetic field generating portion, the magnetic field is the reverse magnetic field having the largest magnetic field strength. Therefore, the magnetic field gradient of the first direction component of the detected magnetic field becomes steep. Thereby, the amount of change in the magnetic field strength detected when the magnetic field detector is displaced can be increased. In addition, since the first direction component is zero near the middle of each magnetic field generation unit, the magnetic field detection unit can be arranged in a range where the magnetic field strength is low, and the magnetic field detection unit can be used in a region where detection sensitivity is high. it can. Therefore, it is possible to improve the detection sensitivity of the physical quantity sensor.

In the physical quantity sensor according to the present invention, a magnetic field zero point at which a first direction component of the detected magnetic field becomes 0 by canceling out the first magnetic field and the second magnetic field in the detected magnetic field. And the magnetic field zero point is included on the locus of the magnetic field detection unit when the magnetic field detection unit is relatively displaced with respect to the magnetic field formation unit.
As a result, the magnetic field detection unit is arranged in the region where the magnetic field strength is the lowest, so that the magnetic field detection unit whose detection sensitivity decreases as the surrounding magnetic field strength increases can be used with high detection sensitivity. Accordingly, the difference between the magnetic field intensity at the location where the magnetic field detection unit is disposed and the magnetic field intensity at which the magnetic field detection unit is magnetically saturated can be increased, so that the range of detectable magnetic field intensity can be widened. .

Furthermore, in the physical quantity sensor according to the present invention, the pair of magnetic poles in the first magnetic field generation unit are arranged to face each other via a first magnetic gap located on one side in the second direction, and the second magnetic field generation unit The pair of magnetic poles in FIG. 2 are disposed to face each other via a second magnetic gap located on the other side in the second direction, and the magnetic field detection unit is configured so that the first magnetic gap and the second It is located within the gap of two magnetic gaps.
As a result, a detected magnetic field is formed by the first magnetic field that is the leakage magnetic field from the first magnetic gap and the second magnetic field that is the leakage magnetic field from the second magnetic gap, and the magnetic field of the first direction component in this detected magnetic field. Since the magnetic field detector is arranged in a region where the gradient is steep and the magnetic field strength is small, the detection sensitivity can be further improved.

In the physical quantity sensor according to the present invention, the first direction is a separation direction of the pair of magnetic poles of the first magnetic field generation unit and the second magnetic field generation unit, and the second direction is the The direction is perpendicular to the first direction.
Thereby, since the magnetic field intensity of the first direction component of each of the first magnetic field and the second magnetic field can be maximized, the first magnetic field and the second magnetic field cancel each other, so that the magnetic field gradient of the detected magnetic field Can be made larger. In addition, this magnetic field gradient is the steepest in the separation direction of the first magnetic field generation unit and the second magnetic field generation unit orthogonal to the first direction, so that the direction is the second direction in which the magnetic field detection unit relatively moves. Thus, the detection sensitivity of the magnetic field strength can be further improved.

The microphone according to the present invention is a microphone using the physical quantity sensor according to any one of the above, wherein the movable portion is relative to the second direction with respect to any one of the magnetic field forming portion and the magnetic field detecting portion. A vibration thin film stretched so as to vibrate, wherein the first magnetic field generation unit and the second magnetic field generation unit are each composed of a pair of magnetic thin films disposed along the vibration thin film, Any one of the magnetic field detection units is fixed to the vibration thin film.
According to the microphone having such a configuration, since the physical quantity sensor is used, a magnetic field change can be detected with high sensitivity by the magnetic field detection unit when the magnetic field forming unit and the magnetic field detection unit are relatively moved. In addition, since the movable part and the magnetic field generating part are each composed of a thin film, it can be easily manufactured using the MEMS technology, and the manufacturing cost can be reduced, the quality can be stabilized, and the manufacturing efficiency can be improved.

  According to the physical quantity sensor of the present invention, by changing the magnetic field gradient of the first direction component of the detected magnetic field to be detected by the magnetic field detector, the change in the magnetic field strength detected when the magnetic field detector is displaced is changed. The amount can be increased. In addition, since the magnetic field intensity in the range where the magnetic field detection unit is disposed can be kept low, the magnetic field detection unit can be used in a region where detection sensitivity is high. As a result, the detection sensitivity of the physical quantity sensor can be improved. Also, according to the microphone of the present invention, the magnetic field change can be detected with high sensitivity by the magnetic field detection unit, so that it is possible to detect sound waves with high sensitivity based on this magnetic field change.

It is a top view of the microphone of a 1st embodiment. It is AA sectional drawing of FIG. It is a schematic diagram of the magnetic circuit which the magnetic field formation part of 1st Embodiment comprises. It is a figure explaining the manufacturing method of the microphone of a 1st embodiment. It is a figure explaining the manufacturing method of the microphone of a 1st embodiment. It is a figure explaining the manufacturing method of the microphone of a 1st embodiment. It is a figure explaining the to-be-detected magnetic field formed of a 1st magnetic field and a 2nd magnetic field. It is a graph which shows the relationship between the magnetic field intensity around a magnetoresistive element, and resistance change rate. It is a top view of the microphone of a 2nd embodiment. It is AA sectional drawing of FIG. It is a figure explaining the manufacturing method of the microphone of a 2nd embodiment. It is a top view of the microphone of a modification. It is AA sectional drawing of FIG. It is a schematic diagram which shows the other structure of a magnetic field formation part. It is a schematic diagram which shows the other structure of a magnetic field formation part. It is a schematic diagram which shows the other structure of a magnetic field formation part. It is a schematic diagram which shows the other structure of a magnetic field formation part. It is a top view which shows the other structure of a magnetic field formation part. It is a schematic diagram which shows the other structure of a magnetic field formation part. It is a schematic plan view which shows the other structure of a magnetic field formation part. (A) The schematic diagram which shows a structure of an Example, (b) It is a graph which shows a magnetic field gradient. It is the schematic diagram which shows the (a) structure of a comparative example, (b) It is a graph which shows a magnetic field gradient.

Next, the microphone according to the first embodiment will be described with reference to FIGS. As shown in FIG. 1 and FIG. 2, the microphone 1 according to the present embodiment is integrated with a support substrate 2 as a base, a magnetic field forming unit 10 disposed on the support substrate 2, and the magnetic field forming unit 10. A formed vibration thin film (movable part) 3 and a magnetic field detector 4 fixed on the vibration thin film 3 are provided. That is, the microphone 1 is configured to detect the sound wave by converting the displacement of the vibration thin film 3 according to the sound wave into an electric signal by the magnetic field detection unit 4.
In the following description, the left-right direction in FIGS. 1 and 2 is referred to as a first direction x, and the depth direction in FIG. 1 (vertical direction in FIG. 2) perpendicular to the first direction x is referred to as a second direction y.

The support substrate 2 is formed of a silicon substrate, and a through hole 2a (see FIG. 2) penetrating in the second direction y is formed in the center in plan view.
As shown in detail in FIG. 2, the magnetic field forming unit 10 includes a first magnetic field generating unit 11 composed of a pair of permanent magnets 12A and 12B arranged to face each other via a first magnetic gap G1, and a second magnetic gap G2. And a pair of connecting yokes 15A and 15B for connecting the first magnetic field generating unit 11 and the second magnetic field generating unit 13 to each other. Has been.

  The permanent magnets 12A and 12B are arranged so as to form a rectangular thin film in plan view and extend in the first direction x, and the permanent magnet 12A on one side in the first direction x (left side in FIGS. 1 and 2) is The permanent magnet 12B arranged in the first direction x the other side (the right side in FIGS. 1 and 2) is arranged with the north pole facing the first magnetic gap G1 and the south pole facing the first magnetic gap G1. That is, the opposing direction of the pair of magnetic poles is arranged along the first direction x. The pair of permanent magnets 12A and 12B are formed to be bent so that the end on the first magnetic gap G1 side is one step higher than the end on the opposite side.

  The yokes 14A and 14B are made of a soft magnetic material such as a Ni-Fe alloy, for example, and form a rectangular thin film having substantially the same shape as the permanent magnets 12A and 12B in plan view, and extend in the first direction x. Is arranged. The yokes 14A and 14B are arranged on the support substrate 2 so as to overlap the permanent magnets 12A and 12B in the second direction y.

  The connecting yokes 15A and 15B are thin film members made of a soft magnetic material such as a Ni-Fe alloy, for example, like the yokes 14A and 14B. One connecting yoke 15A includes the permanent magnet 12A and the yoke 14A. The first direction x is connected in the second direction y on one side, and the other connection yoke 15B connects the permanent magnet 12B and the yoke 14B in the second direction y on the other side in the first direction x. Thereby, on the support substrate 2, the yokes 14A and 14B, the connection yokes 15A and 15B, and the permanent magnets 12A and 12B are arranged to be laminated in this order. Further, the first magnetic gap G1 and the second magnetic gap G2 are spaced apart in the second direction y by the thickness of the connecting yokes 15A and 15B and the bending of the permanent magnets 12A and 12B.

  In such a magnetic field forming unit 10, as shown in FIG. 3, the magnetic fields generated by the permanent magnets 12A and 12B pass through the connecting yokes 15A and 15B and the yokes 14A and 14B, so that these permanent magnets 12A and 12B, A magnetic circuit using the connecting yokes 15A and 15B and the yokes 14A and 14B as magnetic paths is configured. As a result, a first magnetic field H1 is generated from the first magnetic gap G1 as a leakage magnetic field by a pair of magnetic poles of the N pole of the permanent magnet 12A and the S pole of the permanent magnet 12B. Further, from the second magnetic gap G2, a second magnetic field H2 is generated as a leakage magnetic field by a pair of magnetic poles of the S pole generated in the yoke 14A and the N pole generated in the yoke 14B.

  As shown in FIGS. 1 and 2, the vibration thin film 3 is made of a flexible thin film having a circular shape in plan view, such as alumina, and a part of the circular periphery is a pair of connections in the magnetic field forming unit 10. The upper surfaces of the yokes 15A and 15B and the upper surface of the support substrate 2 are fixed. Thereby, the vibration thin film 3 can be relatively vibrated in the second direction y with respect to the magnetic field forming unit 10 between the first magnetic field generation unit 11 and the second magnetic field generation unit 13.

  As shown in FIGS. 1 and 2, the magnetic field detector 4 includes a magnetoresistive element 4 a whose electric resistance varies according to a change in magnetic field strength in a specific direction, and a pair of electrode pads 4 b formed on the support substrate 2. , 4b and a pair of lead portions 4c, 4c for electrically connecting the electrode pads 4b, 4b and the magnetoresistive element 4a. As the magnetoresistive element 4a, various elements such as MR (Magneto-resistive) element, GMR (Giant Magneto-resistive) element, TMR (Tunnel-type Magneto-resistive) element, and Hall element can be used. The magnetoresistive element 4a is fixed to a portion corresponding to the first magnetic gap G1 and the second magnetic gap G2 on the surface of the vibration thin film 3 facing the second direction y. That is, the magnetoresistive element 4a is fixed in the second direction. As viewed in the direction of the arrow y (when viewed from the second direction y), the first magnetic gap G1 and the second magnetic gap G2 are disposed so as to be positioned in the respective gaps. As a result, the first magnetic gap G1 of the first magnetic field generator 11 is located on one side in the second direction y (upper side in FIG. 2) of the magnetoresistive element 4a, and the other side in the second direction y (lower side in FIG. 2). 2nd magnetic gap G2 of the 2nd magnetic field generation part 13 is located in. The specific direction coincides with the first direction x, that is, the magnetoresistive element 4a is arranged such that the rate of change in resistance fluctuates due to a magnetic field change in the first direction x.

  A constant bias current is applied to the magnetoresistive element 4a, and the output voltage of the magnetoresistive element 4a at this time is extracted to the outside as an electrical signal through the lead portions 4c and 4c and the electrode pads 4b and 4b. When the magnetic field strength in the first direction x around the magnetoresistive element 4a changes, the resistance change rate of the magnetoresistive element 4a changes, and the change in the resistance change rate is taken out as an output voltage. It is going to detect the change of. Further, as shown in FIG. 3, the magnetoresistive element 4a is disposed at a magnetic field zero point P, which will be described in detail later, and detects a magnetic field between the first magnetic field generating unit 11 and the second magnetic field generating unit 13. As a magnetic field, a first direction component Hx of the detected magnetic field is detected.

  Next, a manufacturing method of the microphone 1 by the MEMS technology will be described with reference to FIGS. In addition, in each figure of FIGS. 4-6, the upper figure shows the top view and the lower figure has shown the longitudinal cross-sectional view. First, a support substrate 2 made of a silicon substrate is prepared (FIG. 4A), and a recess 2b is formed on the upper surface of the support substrate 2 by deep-RIE etching (FIG. 4B). Thereafter, a pair of yokes 14A, 14B of a soft magnetic thin film (magnetic thin film) made of Fe—Ni alloy is formed in the recess 2b (FIG. 4C), and the connecting yoke 15A, 14B is formed on these yokes 14A, 14B. 15B is formed (FIG. 4D). Next, a first sacrificial film 21 having a circular shape in plan view is formed in Cu in the recess 2b (FIG. 4E), and planarization polishing is performed on the upper surfaces of the first sacrificial film 21 and the connecting yokes 15A and 15B. (FIG. 4 (f)).

  Then, the vibration thin film 3 having a larger diameter than this is formed on the first sacrificial film 21 with alumina (FIG. 5A). At this time, a part of the lower surface of the vibration thin film 3 is fixed on the connection yokes 15A and 15B. Next, electrode pads 4b and 4b and lead portions 4c and 4c made of Cu—Au alloy are formed (FIG. 5B), and a spin valve type magnetoresistive element 4a is formed at the center of the upper surface of the vibration thin film 3 (FIG. 5). (C)). Thereafter, a resist film 22 is formed on the upper surfaces of the connection yokes 15A and 15B, and then a plating base sputter Cu 23a is formed on the entire upper surface (FIG. 5D), and a second sacrificial film 23 is formed of Cu on the entire upper surface. (FIG. 5 (e)).

  Subsequently, the resist film 22 is removed, and planarization polishing is performed on the upper surface of the second sacrificial film 23 (FIG. 6A). Thereafter, a pair of thin ferromagnetic thin films (magnetic thin films) 24 made of CoCrPt is formed on the connection yokes 15A and 15B and the second sacrificial film 23 by sputtering (FIG. 6B), and the first direction. By applying a magnetic field to x, the ferromagnetic thin film 24 is magnetized to form a pair of permanent magnets 12A and 12B (FIG. 6C). Next, through-holes 2a are formed by etching from the lower surface of the support substrate 2 by Deep-RIE (FIG. 6D), and then the first sacrificial film 21 and the second sacrificial film 23 are removed (FIG. 6). (E)). Thereby, the microphone 1 of this embodiment can be obtained. In the microphone 1, the single magnetic field forming unit 10 and the magnetic field detection unit 4 may be manufactured on the support substrate 2 by the manufacturing method using the MEMS technology described above. It can also be manufactured in a state where a large number of magnetic field forming units 10 and magnetic field detecting units 4 are connected on the substrate 2. Thereby, reduction of manufacturing cost and improvement of manufacturing efficiency can be aimed at.

  In the microphone 1 configured as described above, when the sound wave is transmitted to the vibration thin film 3, the vibration thin film 3 vibrates in the second direction y. At this time, the magnetoresistive element 4 a of the magnetic field detector 4 is displaced in the second direction y with the vibration of the vibration thin film 3. Then, a change in the resistance change rate of the magnetoresistive element 4a based on the magnetic field strength of the first direction component Hx of the detected magnetic field is taken out from the electrode pads 4b and 4b as an output voltage, and sound waves are detected based on this output voltage. Done.

  Here, the first direction component Hx of the detected magnetic field detected by the magnetoresistive element 4a will be described with reference to FIG. As shown in FIG. 7A, the first direction component H1x of the first magnetic field H1 and the first direction component H2x of the second magnetic field H2 are opposite to each other. In addition, the first direction component H1x of the first magnetic field H1 becomes a maximum in the first magnetic gap G1, and becomes a gradient magnetic field in which the magnetic field strength decreases toward the other side in the second direction y (the lower side in FIG. 7). Similarly, the first direction component H2x of the second magnetic field H2 becomes a maximum in the second magnetic gap G2, and becomes a gradient magnetic field in which the magnetic field strength decreases toward one side in the second direction y (upper side in FIG. 7). That is, the first direction component H1x of the first magnetic field H1 and the first direction component H2x of the second magnetic field H2 have a magnetic field gradient and a magnetic field direction opposite to each other.

  Therefore, the first direction component Hx of the detected magnetic field, which is a combined magnetic field of the first direction component H1x of the first magnetic field H1 and the first direction component H2x of the second magnetic field H2, has a magnetic field having a reverse magnetic field gradient. By interfering with each other, the magnetic field gradient in the second direction y of the first direction component Hx of the detected magnetic field can be made steeper than in the case of the first magnetic field H1 alone or the second magnetic field H2.

  Further, the first direction component H1x of the first magnetic field H1 and the first direction component H2x of the second magnetic field H2 cancel each other, so that the absolute value of the first direction component Hx of the detected magnetic field, which is a composite magnetic field of these. Is smaller than that of the first magnetic field H1 alone or the second magnetic field H2 alone. Further, between the first magnetic gap G1 and the second magnetic gap G2, the first direction component H1x of the first magnetic field H1 and the first direction component H2x of the second magnetic field H2 cancel each other out equally, thereby detecting the detection target. A magnetic field zero point P where the first direction component Hx of the magnetic field is 0 is formed.

As described above, in the microphone 1, the magnetic field gradient of the first direction component Hx of the detected magnetic field can be made steep. As a result, the amount of change in the magnetic field strength when the magnetoresistive element 4a is displaced by the unit length can be increased, so that the detection sensitivity of the sound wave can be improved.
In general, as shown in FIG. 8, for example, as shown in FIG. 8, the magnetoresistive element 4a has a decreasing rate of resistance as the absolute value of the surrounding magnetic field strength increases, so that the detection sensitivity decreases, and the magnetic field strength becomes too high. It becomes magnetically saturated and the magnetic field strength cannot be detected. On the other hand, in the microphone 1, since the absolute value of the magnetic field strength of the first direction component Hx of the detected magnetic field can be kept low as described above, the magnetoresistive element 4a is used in a region with high detection sensitivity. It is possible to improve the detection sensitivity of sound waves. In addition, since the magnetoresistive element 4a is less likely to be magnetically saturated, the range of detectable magnetic field strength can be widened.

  In particular, in the present embodiment, the magnetoresistive element 4a is disposed on the magnetic field zero point P at which the magnetic field strength of the first direction component Hx of the detected magnetic field becomes zero. In this case, the magnetic field strength applied can be minimized. Thereby, since the resistance change rate of the magnetoresistive element 4a can be maintained high, the magnetic field detection sensitivity can be further improved. In addition, since the difference between the magnetic field intensity at the location where the magnetoresistive element 4a is disposed and the magnetic field intensity at which the magnetoresistive element 4a is magnetically saturated can be increased, the range of detectable magnetic field intensity can be broadened. .

Further, the separation direction of the pair of magnetic poles facing each other through the first magnetic gap G1 in the first magnetic field generation unit 11 coincides with the first direction x, and further, in the second magnetic field generation unit 13 through the second magnetic gap G2. Since the separation direction of the pair of magnetic poles facing each other coincides with the first direction x, the magnetic field strengths of the first direction components H1x and H2x of the first magnetic field H1 and the second magnetic field H2 can be maximized. In this case, since the magnetic field gradient is steepest in the second direction y orthogonal to the first direction x, the second direction y in which the magnetoresistive element 4a is displaced is set to a direction orthogonal to the first direction x. Further, the detection sensitivity of the magnetic field strength can be further improved.
Moreover, since the vibration thin film 3 and the magnetic field formation part 10 are each comprised from the thin film, the microphone 1 can be easily manufactured using MEMS technology, and reduction of manufacturing cost and improvement of manufacturing efficiency can be aimed at.

Next, a microphone according to the second embodiment will be described with reference to FIGS. 9 to 11. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
As shown in FIGS. 9 and 10, the magnetic field forming unit 40 in the microphone 30 of the second embodiment includes a first magnetic field generating unit 11 including a pair of permanent magnets 12A and 12B and a first magnetic field generating unit 11 including a pair of yokes 14A and 14B. The two magnetic field generators 13 are directly stacked in the second direction y. Thus, the first magnetic gap G1 and the second magnetic gap G2 are spaced apart in the second direction y only by the bending of the permanent magnets 12A and 12B.

  The magnetic field forming unit 40 is disposed on the support substrate 2 via a yoke base 32 having a through hole 32a in the center in plan view, and a peripheral portion is sandwiched between the support substrate 2 and the yoke base 32. A vibration thin film (movable part) 33 is provided. The vibration thin film 33 has a circular shape in plan view, and an element placement portion 33a is provided at the center of the vibration thin film 33 so as to rise in a truncated cone shape on one side in the second direction y (upper side in FIG. 10). . The magnetoresistive element 4a is placed on the surface of the element placement portion 33a on one side in the second direction y.

  Next, an example of a method for manufacturing the microphone 30 having the above configuration will be described with reference to FIG. First, a support substrate 2 made of a silicon substrate is prepared, a first sacrificial film 41 having a truncated cone shape made of Cu is formed on the support substrate 2, and alumina is formed on the entire area of the support substrate 2 and the first sacrificial film 41. A vibration thin film 33 is formed (FIG. 11A). Next, the yoke base 32 is laminated on the vibration thin film 33, the magnetoresistive element 4a is provided on the element mounting portion 33a of the vibration thin film 33, and the electrode pads 4b and 4b and the lead portions 4c and 4c are formed (FIG. 11 (b)).

  Thereafter, a second sacrificial film 42 made of Cu is formed to the same height as the yoke base 32, and yokes 14A and 14B of soft magnetic thin films (magnetic thin films) are formed on the yoke base 32, and these yokes 14A and 14B are formed. With the resist 43 formed thereon, a third sacrificial film 44 is formed of Cu over the entire upper surface (FIG. 11C). After this, the resist 43 is removed, and then the third sacrificial film 44 is planarized and polished to form a pair of ferromagnetic thin films (magnetic thin films) 45 made of CoCrPt by sputtering (FIG. 11D). .

Then, through-holes 2a are formed by etching from the lower surface of the support substrate 2 by Deep-RIE, and a magnetic field is applied in the first direction x, whereby the ferromagnetic thin film 45 is magnetized to form a pair of permanent magnets. Using the magnets 12A and 12B, the first sacrificial film 41, the second sacrificial film 42, and the third sacrificial film 44 are removed (FIG. 11E). Thereby, the microphone 30 of this embodiment can be obtained.
In the microphone 30 of the second embodiment having such a configuration, the absolute value of the magnetic field strength can be kept low while increasing the magnetic field gradient of the first direction component Hx of the detected magnetic field, as in the first embodiment. The sensitivity of detecting sound waves can be improved by increasing the magnetic field detection sensitivity of the magnetoresistive element 4a.

The microphones 1 and 30 of the embodiment have been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention.
For example, as a modified example, the microphone 50 may be configured such that the magnetic field forming unit 60 (see FIG. 13) is displaced with respect to the magnetoresistive element 4a as shown in FIGS. In this microphone 50, a yoke plating 51 is formed on the support substrate 2, and the periphery of the vibration thin film 52 having a circular shape in plan view is fixed to the upper surface of the yoke plating 51, and the other direction y of the vibration thin film 52 in the second direction y is fixed. A magnetic field forming unit 60 is fixed to the center of the surface facing the side. As in the second embodiment, the magnetic field forming unit 60 includes a first magnetic field generation unit 11 composed of a pair of permanent magnets 12A and 12B and a second magnetic field generation unit 13 composed of a pair of yokes 14A and 14B, which are directly stacked vertically. It is set as the structure. In addition, an element mounting portion 2b for mounting the magnetoresistive element 4a is formed at the center of the support substrate 2, whereby the first magnetic gap G1 and the second magnetic gap G2 in the magnetic field forming portion 60 are formed. The magnetoresistive element 4a is located in the area between.

  In the microphone 50, the magnetic field forming unit 60 is displaced in the second direction y as the vibration thin film 52 vibrates in the second direction y by sound waves. Then, the magnetic field around the magnetoresistive element 4a provided on the support substrate 2 side changes, and a voltage change based on the electric resistance variation is taken out as an electric signal. Also by this, like the microphones 1 and 30 of the embodiment, the magnetic field detection sensitivity by the magnetoresistive element 4a can be increased, and the sound wave detection sensitivity can be improved.

In the embodiment, the second direction y is a direction orthogonal to the first direction x, but the second direction y may be a direction that intersects at least the first direction x.
Furthermore, although the magnetoresistive element 4a does not necessarily have to be arranged at the magnetic field zero point P, in order to minimize the magnetic field intensity around the magnetoresistive element 4a, it is within the range of the amplitude of the magnetoresistive element 4a, that is, It is preferable that the magnetic resistance element 4a is disposed so that the magnetic field zero point P is included on the locus of the magnetoresistive element 4a when the magnetic resistance element 4a is displaced with respect to the magnetic field forming unit 10.

  Moreover, as a structure of the magnetic field formation part 10, various structures as shown in FIG. 14 are employable. That is, as shown in FIG. 14A, the first magnetic field generator 11 may be composed of a pair of permanent magnets 71, 71, and the second magnetic field generator may be composed of a pair of yokes 72, 72. As shown in FIG. 14B, the first magnetic field generator 11 and the second magnetic field generator 13 may be composed of a pair of permanent magnets 71 and 71. Further, as shown in FIG. 14C, the first magnetic field generator 11 may be composed of a pair of permanent magnets 71, 71, and the second magnetic field generator 13 may be composed of a permanent magnet 71 and a yoke 72. . 14D and 14E, each of the first magnetic field generation unit 11 and the second magnetic field generation unit 13 may include a permanent magnet 71 and a yoke 72. Furthermore, as shown in FIG. 14 (f), the first magnetic field generator 11 may be composed of a permanent magnet 71 and a yoke 72, and the second magnetic field generator 13 may be composed of a pair of yokes 72, 72. .

  Further, the magnetic field forming unit 10 may have a configuration in which the permanent magnet 71 and the yoke 72 are arranged apart from each other without providing the connection yokes 15A and 15B as shown in FIG. That is, as shown in FIG. 15A, the first magnetic field generator 11 and the second magnetic field generator 13 may be configured by a pair of permanent magnets 71 and 71, respectively. Further, as shown in FIG. 15B, the first magnetic field generator 11 may be composed of a pair of permanent magnets 71, and the second magnetic field generator 13 may be composed of a permanent magnet 71 and a yoke 72. Further, as shown in FIG. 15C, the first magnetic field generator 11 and the second magnetic field generator 13 may each include a permanent magnet 71 and a yoke 72.

In addition, in the magnetic field formation part 10, as shown in FIG. 16, the structure which has arrange | positioned the permanent magnet 71 so that the polarization direction may follow the 2nd direction y may be sufficient.
That is, as shown in FIG. 16A, the first magnetic field generating unit 11 and the second magnetic field generating unit 13 are each composed of a pair of permanent magnets 71 and 71 arranged to face each other with the polarization direction along the second direction y. May be. At this time, as shown in FIG. 16 (b), the permanent magnet 71 of the first magnetic field generation unit 11 and the permanent magnet 71 of the second magnetic field generation unit 13 may be connected by a connection yoke 73. Further, as shown in FIG. 16C, a yoke 72 may be arranged in place of some permanent magnets 71.
14 to 16, the first direction component H1x of the first magnetic field H1 and the second direction component H2x of the second magnetic field H2 whose directions and magnetic field gradients are opposite to each other are obtained. The first direction component Hx of the detected magnetic field having a steep magnetic field gradient and a small absolute value of the magnetic field strength can be formed.

Furthermore, the distance between the magnetic poles in each of the first magnetic gap G1 and the second magnetic gap G2 (the dimension in the first direction x of each of the first magnetic gap G1 and the second magnetic gap G2), the first magnetic gap G1, and the second magnetic gap G1. The separation distance in the second direction y of the two magnetic gaps G2 is more preferably set to the same dimension. Thereby, the magnetic field gradient of the first direction component Hx of the detected magnetic field can be made the steepest.
In the microphones 1 and 30 of the embodiment, the permanent magnets 12A and 12B are used for the magnetic field forming units 10 and 40, but an electromagnet may be used instead.

  Further, for example, as shown in FIG. 17, the tips of the permanent magnets 12A and 12B of the first magnetic field generator 11 facing the first magnetic gap G1 and the second magnetic gaps of the yokes 14A and 14B of the second magnetic field generator 13 are provided. The tip facing G2 may have a sharp shape toward the magnetoresistive element 4a. In this case, since the magnetic field strength is increased by the concentration of the first magnetic field H1 and the second magnetic field H2, the magnetic field gradient of the first direction component Hx of the detected magnetic field can be further increased.

Furthermore, for example, as shown in FIG. 18, the tip of the permanent magnets 12 </ b> A and 12 </ b> B of the first magnetic field generation unit 11 that faces the first magnetic gap G <b> 1 may be narrow in plan view. Similarly, the end of the second magnetic field generator 13 facing the second magnetic gap G2 in the yokes 14A and 14B may be narrowed. Also by this, the magnetic field gradient of the first direction component Hx of the detected magnetic field can be increased by concentrating the magnetic field.
For example, as shown in FIG. 19, in the magnetic field forming unit 10, each of the first magnetic field generating unit 11 and the second magnetic field generating unit 13 is composed of a single permanent magnet 71, and these permanent magnets 71 have opposite polarization directions. It may be a configuration arranged as a direction. Even in this case, as shown in FIG. 19 (a), the first direction component H1x of the first magnetic field H1 and the second magnetic field H2 of the first magnetic field H1 whose directions and magnetic field gradients are opposite to each other outside the permanent magnets 71 and 71. A second direction component H2x can be formed. Accordingly, as shown in FIG. 19B, the first direction component Hx of the detected magnetic field having a large magnetic field gradient and a low absolute value of the magnetic field strength can be formed.

Furthermore, for example, as shown in FIG. 20, the facing direction of the first magnetic gap G1 and the facing direction of the second magnetic gap G2 may intersect in plan view. Even in this case, the first direction component H1x of the first magnetic field H1 and the second direction component H2x of the second magnetic field H2 have opposite directions and magnetic field gradients, respectively. Therefore, the magnetic field gradient of the first direction component Hx of the detected magnetic field can be increased.
Furthermore, a magnetic sensor such as a Hall element or a flux gate may be used in place of the magnetoresistive element 4a in the magnetic field detection unit 4. The present invention is not limited to the microphones 1, 30, and 50, and can be widely applied to all physical quantity sensors such as an acceleration sensor, an angular velocity sensor, a pressure sensor, a vibration sensor, and a displacement sensor.

An evaluation simulation was performed on the effect of the microphone of the present invention.
(Example)
As shown in FIG. 21 (a), the distance between the magnetic poles (one N pole and the other S pole) of the permanent magnets 81a and 81b is set to be 2xdμm and is opposed to the first direction x to constitute the first magnetic field generating unit 81. did. In addition, the magnetic poles (one S pole and the other N pole) of the pair of permanent magnets 82a and 82b are placed in the first direction at a location 2 yd μm apart on the other side in the second direction y (y direction) of the first magnetic field generator 81. A second magnetic field generation unit 82 was configured to be disposed opposite to x, and connected to the first magnetic field generation unit 81 by a connection yoke 83. Then, the magnetic field strength in the first direction x when the magnetoresistive element 84 was displaced in the second direction y was measured. The result is shown in FIG.

(Comparative example)
As shown in FIG. 22A, the permanent magnets 85 and 86 are arranged in the first direction x with an interval of 2 × dμm. Then, the magnetoresistive element 84 is disposed by separating the magnetoresistive element 84 from the magnetic pole surfaces of the permanent magnets 85 and 86 by yd μm in the second direction y, and the magnetoresistive element 84 is displaced in the second direction y. The magnetic field strength in the direction x was measured. The result is shown in FIG. In this comparative example and the above example, the measurement was performed with (xd, yd) = (1.5 μm, 1.5 μm), (2.5 μm, 2.5 μm).

(Evaluation of Examples and Comparative Examples)
From FIG. 21B and FIG. 22B, it can be seen that the magnetic field gradient is greater in the example than in the comparative example. Also, it can be seen that the absolute value of the magnetic field gradient around the magnetoresistive element 84 is much smaller in the example than in the comparative example. Furthermore, in the comparative example, even when the distance between the permanent magnets 85 and 86 is shortened, the magnetic field strength at the location where the magnetoresistive element 84 is arranged is large. However, in the embodiment, regardless of the distance between the permanent magnets 81a, 81b, 82a and 82b. The magnetic field intensity at the location where the magnetoresistive element 84 was disposed was zero. Therefore, it has been found that the embodiment corresponding to the present invention can achieve both an increase in magnetic field gradient and a decrease in magnetic field strength. Thereby, the operation and effect described above in the embodiment could be verified.

DESCRIPTION OF SYMBOLS 1 ... Microphone, 3 ... Vibration thin film (movable part), 4 ... Magnetic field detection part, 4a ... Magnetoresistive element, 10 ... Magnetic field formation part, 11 ... 1st magnetic field generation part, 12A ... Permanent magnet, 12B ... Permanent magnet, 13 2nd magnetic field generation part, 14A ... Yoke, 14B ... Yoke, 15A ... Connection yoke, 15B ... Connection yoke, 30 ... Microphone, 33 ... Vibration thin film (movable part), 40 ... Magnetic field formation part, 50 ... Microphone, 52 ... Vibration thin film (movable part), 60 ... magnetic field forming part, 71 ... permanent magnet, 72 ... yoke, 73 ... connection yoke, 81 ... first magnetic field generating part, 81a ... permanent magnet, 81b ... permanent magnet, 82 ... second magnetic field Generating part, 82a ... permanent magnet, 82b ... permanent magnet, 83 ... connecting yoke, 84 ... magnetoresistive element, 85 ... permanent magnet, 86 ... permanent magnet, G1 ... first magnetic gap, G2 ... second magnetic gap, H ... 1st magnetic field, H1x ... 1st direction component of 1st magnetic field, H2 ... 2nd magnetic field, H2x ... 1st direction component of 2nd magnetic field, Hx ... 1st direction component of detected magnetic field, P ... Magnetic field zero point, x ... first direction, y ... second direction

Claims (5)

A magnetic field forming unit for forming a detected magnetic field in space;
A magnetic field detector that outputs an electrical signal corresponding to a first direction component of the detected magnetic field;
A physical quantity sensor comprising a movable unit that relatively displaces the magnetic field forming unit and the magnetic field detection unit in a second direction intersecting the first direction in response to an external displacement input,
The magnetic field forming part is
A first magnetic field generator that generates a first magnetic field between magnetic poles disposed on one side in the second direction of the magnetic field detector;
A second magnetic field generator for generating a second magnetic field between the magnetic poles arranged on the other side in the second direction of the magnetic field detector,
The detected magnetic field is a combined magnetic field of the first magnetic field and the second magnetic field between the first magnetic field generating unit and the second magnetic field generating unit, and the first magnetic field in the detected magnetic field and The physical quantity sensor, wherein the first direction components of the second magnetic field are opposite to each other. In the detected magnetic field, a magnetic field zero point where the first direction component of the detected magnetic field becomes 0 is formed by canceling out the first magnetic field and the second magnetic field,
The physical quantity sensor according to claim 1, wherein the magnetic field zero point is included on a locus of the magnetic field detection unit when the magnetic field detection unit is relatively displaced with respect to the magnetic field forming unit. The pair of magnetic poles in the first magnetic field generation unit are disposed to face each other via a first magnetic gap located on one side in the second direction,
The pair of magnetic poles in the second magnetic field generation unit are disposed to face each other via a second magnetic gap located on the other side in the second direction,
3. The physical quantity sensor according to claim 1, wherein the magnetic field detection unit is located in a gap between the first magnetic gap and the second magnetic gap in the second direction arrow. The first direction is a separation direction of a pair of the magnetic poles in each of the first magnetic field generation unit and the second magnetic field generation unit,
The physical quantity sensor according to any one of claims 1 to 3, wherein the second direction is a direction orthogonal to the first direction. A microphone using the physical quantity sensor according to any one of claims 1 to 4,
The movable part is a vibration thin film stretched to be capable of relative vibration in the second direction with respect to either the magnetic field forming part or the magnetic field detection part,
Each of the first magnetic field generation unit and the second magnetic field generation unit includes a pair of magnetic thin films disposed along the vibration thin film,
One of the magnetic field formation part and the magnetic field detection part is fixed to the vibration thin film.

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