WO2010023766A1

WO2010023766A1 - Displacement sensor

Info

Publication number: WO2010023766A1
Application number: PCT/JP2008/065692
Authority: WO
Inventors: 昌弘石杜
Original assignee: パイオニア株式会社
Priority date: 2008-09-01
Filing date: 2008-09-01
Publication date: 2010-03-04

Abstract

A displacement sensor has a first electrode, a second electrode and a movable structure and detects displacement of the movable structure. The first electrode has comb teeth formed according to a predetermined cycle on the same surface. The second electrode has comb teeth arranged alternately with the comb teeth of the first electrode on the same surface. The movable structure has an opposed surface parallel to the first and second electrodes at predetermined intervals and is displaced in an inplane direction. The movable structure, in the opposed surface, has first areas at each cycle equal to the cycle and second areas which are adjacent to the first areas and arranged alternately with the first areas. Then, the first and second electrodes form capacitors with the first and second areas. A capacitance per the unit area of a capacitor formed of the first area and the first electrode is different from that per the unit area of a capacitor formed of the second area and the first electrode.

Description

Displacement sensor

The present invention relates to a displacement sensor that measures the displacement of a movable part based on a change in capacitance.

An electrostatic capacitance type displacement sensor that detects the displacement of the movable structure (movable electrode) based on the detected capacitance value is known. For example, Non-Patent Document 1 describes a capacitance-type displacement sensor in which comb-shaped electrodes in which linear electrodes are periodically arranged are formed below the movable structure. Patent Document 1 describes a technique for realizing a capacitor by forming concave and convex grooves in a movable structure.

Japanese Patent Laid-Open No. 10-332384

However, the displacement sensor described in Non-Patent Document 1 or the like may cause a phase error or a capacitance error due to processing variations or misalignment. In this case, the displacement sensor is affected by these errors, and the accuracy (sensitivity) of displacement measurement decreases. Further, since the cycle of the electrodes used in this displacement sensor is set to be equal to or greater than the maximum displacement of the movable structure, it is impossible to detect a highly sensitive displacement when the maximum displacement is large. Non-Patent Document 1 does not describe any of these problems.

In addition, the capacitor described in Patent Document 1 is used only as an actuator and is not used as a sensor.

Examples of problems to be solved by the present invention include the above. It is an object of the present invention to realize high-resolution detection even for large displacements while reducing phase errors and capacitance errors caused by processing variations and misalignment in a capacitance type displacement sensor. And

According to the first aspect of the present invention, there is provided a displacement sensor that measures displacement based on a change in capacitance, the first electrode having comb teeth formed on the same surface according to a predetermined period, and the first electrode A second electrode having comb teeth that are alternately arranged on the same plane as the comb teeth of the electrode, and a facing surface parallel to the first and second electrodes at a predetermined interval, and the surface of the facing surface A movable structure that is displaced inwardly, the movable structure being adjacent to the first region and the first region arranged at the predetermined period on the facing surface. And a second region formed alternately with each other, and the capacitance per unit area of the capacitor formed by the first region and the first electrode is the second region. Different from the capacitance per unit area of the capacitor formed by the first electrode And wherein the door.

It is a figure which shows an example of the exploded perspective view of a displacement sensor. It is a figure which shows an example of sectional drawing of a displacement sensor. It is a figure which shows the structure of the capacitor | condenser part of a displacement sensor. It is a figure which shows the graph of the electrostatic capacitance and the change of a voltage value with respect to the displacement amount. It is a figure which shows an example of the system which detects a displacement amount. It is a figure which shows an example of the graph of the change of the output voltage value with respect to displacement. It is the figure shown about the alignment shift. It is a figure which shows an example of sectional drawing of the displacement sensor in Example 2. FIG. It is a figure which shows an example of the disassembled perspective view of the displacement sensor in Example 3. FIG. It is the figure which expanded a part of displacement sensor in Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Movable structure 2 Support substrate 3 Frame part 4 Support spring 10 Electrode pair 11 Concavity and convexity part 15 Detection part 20

Electrode foil

100, 100a-100e Displacement sensor

In one aspect of the present invention, a displacement sensor that measures displacement based on a change in capacitance, the first electrode having comb teeth formed on the same surface according to a predetermined period, and the first electrode A second electrode having comb teeth that are alternately arranged on the same plane as the comb teeth of the electrode, and a facing surface parallel to the first and second electrodes at a predetermined interval, and within the surface of the facing surface A movable structure that is displaced in a direction, wherein the movable structure has a first region that is arranged at the predetermined period on the facing surface, and is adjacent to the first region and the first region. Second regions formed alternately, and the capacitance per unit area of the capacitor formed by the first region and the first electrode is the second region and the second region. It differs from the capacitance per unit area of the capacitor formed by the first electrode.

The above displacement sensor has a first electrode, a second electrode, and a movable structure, and detects the displacement of the movable structure. The first electrode has a plurality of comb teeth formed on the same surface according to a predetermined cycle. The second electrode has comb teeth that are alternately arranged on the same plane as the comb teeth of the first electrode. The movable structure has a facing surface parallel to the first and second electrodes at a predetermined interval, and is displaced in the in-plane direction. The movable structure is formed on the opposite side, the first region arranged at the same period as the period of the comb teeth of the first electrode, adjacent to the first region, and alternately arranged with the first region. And a second region. The first and second electrodes form a capacitor with the first and second regions. The capacitance per unit area of the capacitor formed by the first region and the first electrode is different from the capacitance per unit area of the capacitor formed by the second region and the first electrode. . In other words, the capacitance per unit area of the capacitor formed by the first region and the second electrode is equal to the capacitance per unit area of the capacitor formed by the second region and the second electrode. Different. By doing so, the displacement sensor can differentially detect the displacement based on the capacitance detected from the first electrode and the capacitance detected from the second electrode. Further, by performing differential detection, in-phase noise based on temperature fluctuations, vibrations, and the like can be removed. Furthermore, by arranging the comb teeth of the first electrode and the comb teeth of the second electrode alternately, the displacement sensor also reduces phase errors and capacitance errors due to processing variations and misalignment. can do.

In one aspect of the displacement sensor, the facing surface has a concavo-convex structure, the first region is a convex portion of the concavo-convex structure, and the second region is a concave portion of the concavo-convex structure.

In a preferred example of the above displacement sensor, the convex portion and the concave portion are the same member. The capacitance of the capacitor is inversely proportional to the distance between the pair of electrodes constituting the capacitor. Therefore, according to this aspect, the displacement sensor has a capacitance per unit area of the capacitor formed by the first region and the first electrode, and a unit of the capacitor formed by the second region and the first electrode. A difference can be provided between the capacitance per area.

In another aspect of the above displacement sensor, the first region is defined by an electrode foil formed on the movable structure. In this aspect, the electrode foil is periodically formed on the surface facing the first and second electrodes of the movable structure. This electrode foil is formed, for example, by a method such as vapor deposition of metal particles through a mask, sputtering, or etching. Thereby, for example, the displacement sensor can perform differential detection by making the movable structure an insulator. Furthermore, by appropriately selecting the electrode foil to be bonded, the rate of change in capacitance with respect to the displacement can be increased. That is, the displacement sensor can perform differential detection with high sensitivity.

In another aspect of the above displacement sensor, the predetermined period is smaller than the maximum displacement of the movable structure in the direction in which the comb teeth are arranged. In this embodiment, the period of the comb teeth is reduced, and the rate of change in capacitance with respect to the amount of displacement is increased. Thereby, the displacement sensor can perform differential detection with high sensitivity. In addition, the output voltage value obtained by converting the capacitance detected from the first electrode and the capacitance detected from the second electrode into a voltage value and differentially amplifying it, and its fluctuation cycle By counting, the displacement sensor can appropriately detect a large displacement larger than the comb tooth period.

In another mode of the above displacement sensor, the first capacitance that is electrically connected to the first and second electrodes and is detected from the first electrode, and the detection is performed from the second electrode. And a detection unit that detects the amount of displacement of the movable structure based on the second capacitance.

In another aspect of the displacement sensor, the detection unit converts the first capacitance and the second capacitance into voltage values and differentially amplifies the output voltage values. Based on this, the amount of displacement is detected. In this aspect, the detection unit calculates the output voltage value by converting the first capacitance and the second capacitance into voltage values and differentially amplifying them. This output voltage value changes periodically based on the amount of displacement. Further, the cycle of the output voltage value has a correspondence relationship with the cycle of the voltage line arrangement. Therefore, the detection unit can appropriately detect the displacement amount by monitoring the output voltage value.

In another aspect of the displacement sensor, the detection unit detects a displacement based on the number of fluctuation periods of the output voltage value and the output voltage value. By doing in this way, the detection part can detect a displacement appropriately also with respect to the large displacement more than the period of the arrangement | sequence of a voltage line.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Example 1]
(Outline configuration)
FIG. 1 shows an example of an exploded perspective view of a displacement sensor 100 in the present embodiment. FIG. 2 shows an example of a cross-sectional view taken along a cutting plane AA ′ of the displacement sensor 100. As shown in FIGS. 1 and 2, the displacement sensor 100 includes a movable structure 1, a support substrate 2, a frame portion 3, a support spring 4, and an electrode pair 10.

The displacement sensor 100 is a sensor that detects the displacement of the movable structure 1 in the x-axis direction. The displacement sensor 100 performs differential detection based on the capacitance detected from the electrode pair 10 as will be described later.

The movable structure 1 is a member (electrode) that can be displaced in the x-axis direction and the y-axis direction shown in FIG. The movable structure 1 is connected to the support spring 4 and is displaced within the space defined by the frame portion 3. The movable structure 1, the frame portion 3, and the support spring 4 are made of, for example, a silicon substrate, and more specifically, are formed by performing MEMS (Micro Electro Mechanical Systems) processing on the silicon substrate.

An uneven portion 11 is formed on the lower surface of the movable structure 1, that is, on the surface (facing the surface) facing the electrode pair 10 and the support substrate 2. The concavo-convex portion 11 includes a convex portion 11a and a concave portion 11b. The concavo-convex part 11 is arranged so as to face the electrode pair 10 in parallel, that is, to face each other. Thereby, the uneven part 11 and the electrode pair 10 form a capacitor. That is, the concavo-convex portion 11 made of a silicon material functions as a capacitor electrode. In this embodiment, the concavo-convex portion 11 is made of the same member as the movable structure 1. In addition, the convex part 11a corresponds to the 1st area | region in this invention, and the recessed part 11b corresponds to the 2nd area | region in this invention.

The frame 3 is connected to the support spring 4 and is formed so as to surround the movable structure 1. As shown in FIG. 2, the frame portion 3 is joined to the support substrate 2 so that the concavo-convex portion 11 and the electrode pair 10 face each other. Specifically, the frame portion 3 and the support substrate 2 are bonded using a bonding technique such as anodic bonding, fusion bonding, direct bonding, or plasma activated bonding.

The support substrate 2 is made of glass, for example, and has a rectangular recess (indentation) 7 on the upper surface portion facing the movable structure 1. The recess 7 of the support substrate 2 has a larger area than the lower surface of the movable structure 1 as shown in FIG. In the support substrate 2, the electrode pair 10 is disposed in the recess 7.

The electrode pair 10 includes a first electrode 10a and a second electrode 10b. The first electrode 10a has a comb-tooth structure. That is, the surface of the first electrode 10a has a plurality of comb teeth 10ax that are located in parallel with the xy plane in FIG. 1 and extend in the negative direction of the y-axis. Similar to the first electrode 10a, the second electrode 10b has a comb-tooth structure. That is, the surface of the second electrode 10b has a plurality of comb teeth 10bx that are located in parallel with the xy plane in FIG. 1 and extend in the positive direction of the y-axis.

As shown in FIGS. 1 and 2, the comb teeth 10ax of the first electrode 10a and the comb teeth 10bx of the second electrode 10b are alternately arranged on the same plane (xy plane), that is, comb each other. It arrange | positions so that the space between teeth may be filled. Further, the direction in which the comb teeth 10ax and 10bx are arranged coincides with the direction in which the displacement is detected (hereinafter simply referred to as “detection direction”). The electrode pair 10 is made of, for example, platinum and chromium, or aluminum, or platinum and titanium.

(Capacitor structure and differential detection)
FIG. 3 is an example of an enlarged view of a part of the capacitor formed by the electrode pair 10 and the uneven portion 11. In FIG. 3, for convenience of illustration, only the convex portion 11a of the concave and convex portion 11 is illustrated. As shown in FIG. 3, the plurality of comb teeth 10 ax of the first electrode 10 a are formed with a predetermined period P. Similarly, the plurality of comb teeth 10bx of the second electrode 10b are formed with the same period P. As described above, the comb teeth 10ax of the first electrode 10a and the comb teeth 10bx of the second electrode 10b are arranged alternately in the x direction on the same plane.

The concavo-convex portion 11 is formed with a period P as shown in FIG. In the present embodiment, the convex portion 11a faces the comb teeth 10ax in a state where the movable structure 1 is not displaced. That is, each convex part 11a has the largest overlap (opposite area) in the xy plane with the comb teeth 10ax of the first electrode 10a. And the recessed part 11b opposes the comb-tooth 10bx of the 2nd electrode 10b in the state without a displacement.

The capacitor formed by the electrode pair 10 and the concavo-convex portion 11 has a predetermined capacitance. Hereinafter, the capacitance of the capacitor formed by the first electrode 10a and the concavo-convex portion 11 is expressed as “first capacitance C1”. Similarly, the capacitance of the capacitor formed by the second electrode 10b and the concavo-convex portion 11 is expressed as “second capacitance C2”.

The values of the first capacitance C1 and the second capacitance C2 change when the movable structure 1 is displaced. This will be described with reference to FIG. FIG. 4A shows an example of a graph of changes in the first capacitance C1 and the second capacitance C2 due to the displacement of the movable structure 1. In Fig.4 (a), a horizontal axis shows the displacement amount of the movable structure 1, and a vertical axis | shaft shows an electrostatic capacitance. Here, the “displacement amount” indicates a value (distance) by which the movable structure 1 is displaced in the detection direction, that is, the x-axis direction in which the comb teeth 10ax and 10bx are arranged.

Here, the distance between the electrode pair 10 and the convex portion 11a is smaller than the distance between the electrode pair 10 and the concave portion 11b. The electrostatic capacity is inversely proportional to the distance between the pair of electrodes constituting the capacitor, and the convex portion 11a is the same member as the concave portion 11b. Accordingly, the capacitance per unit area of the capacitor formed by the convex portion 11 a and the electrode pair 10 is larger than the capacitance per unit area of the capacitor formed by the concave portion 11 b and the electrode pair 10. In the present embodiment, the first electrode 10a faces the convex portion 11a and forms a capacitor with the convex portion 11a in a state where there is no displacement. Accordingly, the first capacitance C1 takes the maximum value “Cmax” as shown in FIG. 4A in a state where there is no displacement. On the other hand, in a state where there is no displacement, the second electrode 10b is opposed to the recess 11b and forms a capacitor with the recess 11b. Therefore, the second capacitance C2 takes the minimum value “Cmin” in a state where there is no displacement. Note that the phases of the capacitances C1 and C2 in a state where there is no displacement are not limited to those in FIG. 4 and may be set to any state.

As the amount of displacement increases, the area of the capacitor formed by the first electrode 10a and the recess 11b (that is, the area where the first electrode 10a and the plurality of recesses 11b face each other) increases, and the first The area of the capacitor formed by the electrode 10a and the convex portion 11a (that is, the area where the first electrode 10a and the plurality of concave portions 11b face each other) decreases. Therefore, the first capacitance C1 decreases until the displacement amount reaches P / 2, that is, until the area where the comb teeth 10ax of the first electrode 10a face the recess 11b is maximized. The first capacitance C1 takes the minimum value Cmin when the displacement is P / 2. Then, as shown in FIG. 4A, the first capacitance C1 alternately takes a maximum value Cmax and a minimum value Cmin every time the displacement amount increases by P / 2. Similarly, the second capacitance C2 alternately takes the maximum value Cmax and the minimum value Cmin every time the displacement amount increases by P / 2. Therefore, as shown in FIG. 4A, the first capacitance C1 is 180 degrees out of phase with the second capacitance C2.

The displacement sensor 100 measures the displacement of the movable structure 1 based on the detected first capacitance C1 and second capacitance C2. FIG. 5 shows an example of a system for calculating the displacement amount. As shown in FIG. 5, the detection unit 15 is arranged in the system. The detector 15 is electrically connected to the first electrode 10a and electrically connected to the second electrode 10b. The detection unit 15 detects the first capacitance C1 from the first electrode 10a, and detects the second capacitance C2 from the second electrode 10b. The detection unit 15 calculates the displacement amount of the movable structure 1 based on the detected first capacitance C1 and second capacitance C2. That is, the detection unit 15 differentially detects the displacement amount of the movable structure 1 based on the first capacitance C1 and the second capacitance C2.

First, the detection unit 15 converts the first capacitance C1 and the second capacitance C2 into voltage values, respectively. FIG. 4B shows a graph in which the first capacitance C1 and the second capacitance C2 shown in FIG. 4A are converted into voltage values (CV conversion). Hereinafter, the voltage value calculated from the first capacitance C1 is expressed as a voltage value “V1”, and the voltage value calculated from the second capacitance C2 is expressed as a voltage value “V2”. The voltage value is inversely proportional to the capacitance. Accordingly, as shown in FIG. 4B, when the first capacitance C1 is larger than the second capacitance C2, the voltage value V1 becomes smaller than the voltage value V2. Similarly, when the second capacitance C1 is smaller than the second capacitance C2, the voltage value V1 is larger than the voltage value V2.

Next, the detection unit 15 differentially amplifies the voltage value V1 and the voltage value V2. FIG. 6A shows a voltage value obtained by differential amplification after converting the first capacitance C1 and the second capacitance C2 into voltage values (hereinafter simply referred to as “output voltage value”). An example of a graph of

As described above, in a state where there is no displacement, the first capacitance C1 takes the maximum value Cmax, and the second capacitance C2 takes the minimum value Cmin. That is, in this case, the voltage value V1 takes the minimum value, and the voltage value V2 takes the maximum value. Therefore, the output voltage value takes the minimum value “Vmin” in a state where there is no displacement. The first capacitance C1 decreases and the second capacitance C2 increases until the amount of displacement reaches P / 2 from the state where there is no displacement. That is, the voltage value V1 increases and the voltage value V2 decreases. Therefore, in this case, the output voltage value increases. When the displacement amount is P / 2, the output voltage value takes the maximum value “Vmax”. Thereafter, the output voltage value decreases again, and takes the minimum value Vmin when the displacement amount is P. Thus, since the phase of the first electrostatic capacitance C1 and the second electrostatic capacitance C2 is 180 degrees different, the output voltage value has a maximum value Vmax and a minimum value every time the displacement amount changes by P / 2. The value Vmin is alternately taken. That is, the output voltage value periodically changes as the displacement amount changes. The output voltage value changes periodically every time the displacement amount changes by the period P. Accordingly, the detection unit 15 stores a map of the output voltage value and the displacement as shown in FIG. 6A in the memory in advance, and estimates the displacement amount by comparing with the detected output voltage value. Can do. Furthermore, since the detection unit 15 performs differential detection based on the first capacitance C1 and the second capacitance C2, it removes common-mode noise caused by temperature fluctuations, vibrations, changes in airflow, and the like. be able to. That is, the detection unit 15 can measure the displacement by performing differential detection without being affected by the common-mode noise.

In addition, the detection unit 15 detects an error (hereinafter referred to as “alignment error”) caused by a positional relationship deviation (alignment deviation) between the electrode pair 10 and the concavo-convex part 11 that occurs during manufacturing by the above-described differential detection. Can be reduced. This will be described with reference to FIG. FIG. 7 is an example showing the positional relationship between the electrode pair 10 and the concavo-convex portion 11 when alignment misalignment occurs. Specifically, in FIG. 7A, unlike the present embodiment, the first electrode 10a and the second electrode 10b are arranged close to each other without being close to each other (hereinafter referred to as “comparative example”). 5 shows the positional relationship between the electrode pair 10 and the concavo-convex portion 11 when an alignment shift occurs. FIG. 7B shows the positional relationship between the electrode pair 10 and the concavo-convex portion 11 when an alignment shift occurs in this embodiment. Note that the phase between the capacitances C1 and C2 and the phase of the output voltage value in a state where there is no displacement may be set arbitrarily. For example, in addition to the case where the phase difference is 180 ° as described above, an arbitrary phase difference can be provided in consideration of the offset. In this case, it is necessary to consider that a phase offset is necessary and that the output voltage value is reduced. However, the phase may be set within a possible range where an output voltage value necessary for detection can be obtained.

As shown in FIGS. 7A and 7B, in the comparative example and this example, the electrode pair 10 is shifted by the inclination α with respect to the concavo-convex portion 11. At this time, in the comparative example, due to the misalignment, the convex portion 11a and the first electrode 10a, which should originally completely face each other, are caused by the misalignment rather than the area where the first electrode 10a is no longer opposed on the xy plane. The area where the convex portion 11a and the second electrode 10b, which should not be opposed to each other, are opposed to each other in the xy plane is larger.

On the other hand, in the present embodiment, the area where the convex portion 11a that should originally completely face due to misalignment and the first electrode 10a do not face each other, and should originally be opposed due to misalignment. The area where the non-convex convex portion 11a and the second electrode 10b are opposed to each other is the same. Therefore, the displacement sensor 100 according to the present embodiment forms a reverse phase in which the first capacitance C1 and the second capacitance C2 are shifted by 180 degrees even when there is an alignment shift compared to the comparative example. The difference between the maximum value Cmax and the minimum value Cmin can be increased. Therefore, the displacement sensor 100 can reduce alignment errors.

Further, the displacement sensor 100 is configured by alternately arranging the comb teeth 10ax of the first electrode 10a and the comb teeth 10bx of the second electrode 10b in the x-axis direction, thereby processing the electrode pair 10 in the manufacturing process. Variation is reduced. Specifically, when the electrode pair 10 is manufactured using a process technique such as photolithography, the comb teeth 10ax of the first electrode 10a and the comb teeth 10bx of the second electrode 10b are alternately arranged. Thus, the electrode pair 10 is simultaneously formed using one mask. As a result, variations in processing occur in the first electrode 10a and the second electrode 10b substantially the same. In other words, even when a deviation occurs in processing, the capacitance that can be held by the first electrode 10a and the capacitance that can be held by the second electrode 10b are substantially the same. Therefore, the displacement sensor 100 can reduce the influence of processing variations in displacement detection by performing differential detection using the electrode pair 10 manufactured in this way. In particular, even when the period P of the comb teeth 10ax and 10bx is created within a range of 50 μm, for example, by MEMS (Micro Electro Mechanical Systems) processing, it is possible to manufacture the displacement sensor 100 with high accuracy.

Further, in the present embodiment, the period P is set to be equal to or less than the maximum displacement amount (hereinafter simply referred to as “maximum displacement”) in the x-axis direction (detection direction) in which the comb teeth are arranged. Note that the maximum displacement is constrained by the space or the like partitioned by the frame portion 3 as described above. By configuring the period P to be equal to or less than the maximum displacement in this way, the detection unit 15 can, for example, determine the number of times the minimum value Vmin is reached again, that is, the number of fluctuation periods of the output voltage value and the final output voltage value. Based on this, it is possible to detect a large displacement of the period P or more. That is, even when the period P is designed to be sufficiently smaller than the maximum displacement, the detection unit 15 can also measure the large displacement of the movable structure 1 by counting the number of fluctuation periods of the output voltage value. Therefore, the displacement sensor 100 can be used as a linear encoder.

In addition, when the period P is designed to be small, the ratio of the capacitance change to the displacement increases. That is, as shown in FIG. 4A, the smaller the value of the period P, the larger the rate of change of the first capacitance C1 and the second capacitance C2 with respect to the same displacement amount. Therefore, the detection unit 15 can measure the large displacement of the movable structure 1 with high resolution by making the period P smaller than the maximum displacement.

FIG. 6B shows a graph of the actual measurement value of the output voltage value with respect to the displacement amount of the movable structure 1. FIG. 6B shows the measurement by moving the movable structure 1 every 20 nm, and the period P of the comb teeth 10ax of the first electrode 10a and the comb teeth 10bx of the second electrode 10b at this time is 20 μm. It is. As shown in FIG. 6B, the output voltage value has a waveform with a period P (= 20 μm). Therefore, the detection unit 15 can calculate the displacement amount with high accuracy based on the number of fluctuation periods of the output voltage value and the output voltage value after displacement.

As described above, the displacement sensor according to the present invention includes the first electrode, the second electrode, and the movable structure, and detects the displacement of the movable structure. The first electrode has a so-called comb tooth structure, and has a plurality of comb teeth formed on the same surface according to a predetermined cycle. The second electrode has a comb-tooth structure, and has a plurality of comb teeth that are alternately arranged on the same plane as the comb teeth of the first electrode. The movable structure has a facing surface parallel to the first and second electrodes at a predetermined interval, and is displaced in the in-plane direction. A movable structure has a convex part arrange | positioned with the period same as the period of the said several comb tooth in a facing, and the recessed part adjacent to a convex part and formed in a line with a convex part alternately. The first and second electrodes form a concavo-convex portion and a capacitor. The capacitance per unit area of the capacitor formed by the convex portion and the first electrode is different from the capacitance per unit area of the capacitor formed by the concave portion and the first electrode. In other words, the capacitance per unit area of the capacitor formed by the convex portion and the second electrode is different from the capacitance per unit area of the capacitor formed by the concave portion and the second electrode. By doing so, the displacement sensor can differentially detect the displacement based on the capacitance detected from the first electrode and the capacitance detected from the second electrode. Further, by performing differential detection, in-phase noise based on temperature fluctuations, vibrations, and the like can be removed. Furthermore, by arranging the comb teeth of the first electrode and the comb teeth of the second electrode alternately, the displacement sensor also reduces phase errors and capacitance errors due to processing variations and misalignment. can do.

[Example 2]
In the displacement sensor 100 according to the first embodiment, the support substrate 2 has a recess 7 having a larger area than the lower surface of the movable structure 1. However, the configuration of the displacement sensor 100 to which the present invention is applicable is not limited to this.

FIG. 8 is a cross-sectional view of the displacement sensor 100a according to the second embodiment. As shown in FIG. 8, in the displacement sensor 100a, the upper surface of the support substrate 2 (the surface on the side facing the movable structure 1) is flat, and does not have the concave portion 7 as in the first embodiment. The support substrate 2 is connected to the frame portion 3 at the edge of the upper surface. An electrode pair 10 is disposed on the upper surface of the support substrate 2. The movable structure 1 and the support spring 4 are arranged with a predetermined distance with respect to the support substrate 2 and the electrode pair 10. That is, the lower surface of the movable structure 1 and the support spring 4, that is, the surface facing the support substrate 2 is recessed from the lower surface of the frame portion 3. Even in such a configuration, the displacement sensor 100a can detect the displacement of the movable structure 1 appropriately.

[Example 3]
In the displacement sensor 100 of Example 1, only one pair of electrode pairs 10 is arranged on the support substrate 2. However, the configuration of the displacement sensor 100 to which the present invention can be applied is not limited to this, and the displacement sensor 100 may include a plurality of electrode pairs 10.

FIG. 9 shows an example of an exploded perspective view of the displacement sensor according to the third embodiment. Specifically, FIG. 9A shows an exploded perspective view of a displacement sensor 100b in which two pairs of electrodes 10 for measuring the amount of displacement in the x-axis direction are arranged. FIG. 9B shows an exploded perspective view of a displacement sensor 100c in which two pairs of electrodes 10x that measure the amount of displacement in the x-axis direction and two pairs of electrodes 10y that measure the amount of displacement in the y-axis direction are arranged. .

As shown in FIG. 9A, the displacement sensor 100b includes a plurality of electrode pairs 10 that detect the amount of displacement in the same axial direction, whereby a higher-resolution sensor can be configured. Further, for example, one electrode pair 10 is used for measuring the positive direction of the x-axis and the other electrode pair 10 is used for measuring the negative direction of the x-axis. It is also detected whether it is displaced in the negative direction.

Further, as shown in FIG. 9B, the displacement sensor 100c includes an electrode pair 10x for detecting the displacement amount in the x-axis direction and an electrode pair 10y for detecting the displacement amount in the y-axis direction. Have both. Thereby, the displacement sensor 100c can measure the displacement amount of the movable structure 1 in the x-axis direction and the y-axis direction which is the vertical direction.

[Example 4]
In the embodiment described above, the movable structure 1 has the concavo-convex portion 11 on the lower surface, and the concavo-convex portion 11 and the electrode pair 10 form a capacitor. However, the configuration of the displacement sensor 100 to which the present invention can be applied is not limited to this, and the movable structure 1 does not necessarily have the uneven portion 11.

FIG. 10 shows an example of an enlarged view of the capacitor portion of the displacement sensor in the fourth embodiment. In the displacement sensor 100d shown in FIG. 10A, the movable structure 1 does not have an uneven portion on its lower surface. Instead, the movable structure 1 is formed with electrode foils 20 such as metal thin films that form electrodes on the lower surface thereof in a predetermined cycle. For example, the electrode foil 20 is formed in a region corresponding to a convex portion, and can be specifically formed by evaporating metal particles through a mask. Further, it can be formed by etching after the lift-off method or metal thin film formation. Thereby, the 1st area | region which consists of electrode foil 20 is divided. In FIG. 10A, the electrode foil 20 is disposed so as to face the first electrode 10a in a state where there is no displacement. Therefore, the electrode foil 20 is arranged for each period P. In Example 4, the movable structure 1 is an insulator such as lead zirconate titanate.

By configuring the displacement sensor 100d in this way, the first electrode 10a and the second electrode 10b form a capacitor with the electrode foil 20 and have a capacitance. On the other hand, the first electrode 10 a and the second electrode 10 b do not have a capacitance with the movable structure 1. Therefore, as shown in FIG. 10A, in the state where there is no displacement, the first electrode 10a is opposed to the electrode foil 20, so that a capacitor is formed and a predetermined capacitance is generated. On the other hand, the second electrode 10b does not oppose the electrode foil 20, but opposes the movable structure 1 made of an insulator member, so that the capacitance is zero. Accordingly, also in the fourth embodiment, the displacement sensor 100d can perform differential detection based on the first electrostatic capacitance C1 and the second electrostatic capacitance C2. Further, by appropriately selecting the member of the electrode foil 20, the displacement sensor 100d can increase the maximum value Cmax of the capacitance, and the difference between the maximum value Cmax and the minimum value Cmin (here, 0) is obtained. Can be bigger. Therefore, the displacement sensor 100d can detect the displacement amount with higher accuracy.

On the other hand, in the displacement sensor 100e in FIG. 10B, a concave space for fitting the electrode foil 20 is formed on the lower surface of the movable structure 1 in accordance with a predetermined cycle. Therefore, the lower surface of the movable structure 1 and the lower surface portion of the electrode foil 20 are configured on the same surface. Therefore, the movable structure 1 and the electrode foil 20 do not have a concavo-convex structure facing the movable structure 1. Even if comprised in this way, the displacement sensor 100e can detect differentially based on the 1st electrostatic capacitance C1 and the 2nd electrostatic capacitance C2 similarly to the displacement sensor 100d.

The present invention can be used for a displacement sensor for detecting a displacement amount. Further, it can be widely applied to acceleration sensors, pressure sensors, force sensors and the like.

Claims

A displacement sensor that measures displacement based on a change in capacitance,
A first electrode having comb teeth formed according to a predetermined period on the same surface;
A second electrode having comb teeth arranged alternately on the same plane as the first electrode comb teeth;
A movable structure having facing surfaces parallel to the first and second electrodes at a predetermined interval, and being displaced in an in-plane direction of the facing surfaces,
The movable structure has a first region arranged at the predetermined period on the facing side;
A second region adjacent to the first region and formed alternately with the first region,
The capacitance per unit area of the capacitor formed by the first region and the first electrode is the capacitance per unit area of the capacitor formed by the second region and the first electrode. Displacement sensor characterized by being different from
The displacement sensor according to claim 1, wherein the facing surface has a concavo-convex structure, the first region is a convex portion of the concavo-convex structure, and the second region is a concave portion of the concavo-convex structure. .
The displacement sensor according to claim 2, wherein the convex portion and the concave portion are the same member.
The displacement sensor according to claim 1, wherein the first region is partitioned by an electrode foil formed in the movable structure.
5. The displacement sensor according to claim 1, wherein the predetermined period is smaller than a maximum displacement of the movable structure in a direction in which the comb teeth are arranged.
Electrically connected to the first and second electrodes and based on a first capacitance detected from the first electrode and a second capacitance detected from the second electrode The displacement sensor according to claim 1, further comprising a detection unit that detects a displacement amount of the movable structure.
The detection unit detects the displacement amount based on an output voltage value calculated by converting the first capacitance and the second capacitance into a voltage value and differentially amplifying the voltage value. The displacement sensor according to claim 6.
The displacement sensor according to claim 7, wherein the detection unit detects a displacement amount based on a fluctuation period number of the output voltage value and the output voltage value.