JP2009092396A - Vibration type sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibration type sensor having excellent reliability and detection accuracy, capable of stabilizing and amplifying a change of a resonance frequency caused by a disturbance, and detecting a physical quantity of the disturbance. <P>SOLUTION: This vibration type sensor 10 which is formed by inserting a part of a beam 12 into both of a weight 11 side root domain and a frame body 18 root domain relative to the beam 12 or into either domain, has vibrators 13 (13a, 13b, 13c, 13d) connected mutually on respective both ends in the longitudinal direction of the beam 12 and a support structure 12s, wherein the area of a cut surface vertical to the longitudinal direction of the beam is larger in the support structure 12s than in the vibrator 13, and measures the physical quantity of a disturbance from a resonance frequency of the vibrator 13 changing by a force caused by the disturbance. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vibration sensor that measures physical quantities of disturbances such as acceleration, angular acceleration, and contact force that cause distortion in a structure.

  Conventionally, sensors using semiconductor processing technology have been developed as means for measuring acceleration, angular acceleration, contact force, and the like. For example, in acceleration detection, a piezo type that detects the inertial force applied to the weight due to acceleration as a distortion of the beam using a structure in which the weight is supported by a beam, or a capacitance type that measures the movement of the weight as a change in capacitance Various methods have been developed, such as a vibration type that utilizes the fact that the resonance frequency of the vibration system changes due to strain applied to the beam.

  Among these methods, when a sensor is made smaller by using a semiconductor processing technique, a vibration method has been attracting attention as a method in which the resolution becomes higher as the sensor is made smaller. This is because the resonance frequency increases as the size of the structure decreases, so that the vibration type that detects the magnitude of acceleration from the amount of change becomes more advantageous as compared to other methods.

  For example, the vibration type sensor described in Patent Document 1 is configured such that a structure made of a weight and a beam made of a single crystal silicon integral structure is movable only in one axial direction, and the movement in the movable direction is controlled. The vibrator is made of a thin film to restrain it. This thin film is driven to resonate by electrostatic force, and when the resonance frequency of the vibrator at no load is 22 kHz, the resonance frequency of 40 Hz per 1 G changes, and measurement up to about 120 G can be performed.

Patent Document 2 proposes a method of processing all structures with single crystal silicon as means for improving reliability, which is a drawback of thin film vibrators. In this method, the rigidity in one direction of the beam supporting the weight is lowered by arranging the beam to be long, and the acceleration is measured from the change (± 10%) in the resonance frequency (6400 Hz) of the beam.
JP-A-7-191052 (paragraphs 0014, 0015, FIG. 1, FIG. 3, etc.) Japanese Patent Laid-Open No. 9-257830 (paragraphs 0037, 0044, 0045, FIGS. 1 to 6 etc.)

By the way, the above-described vibration type sensor utilizes the fact that the resonance frequency of the vibrator can be changed to about 10% by disturbance applied to the vibrator.
Therefore, in order to improve measurement accuracy and reduce the size, stress (distortion) generated in the vibrator by increasing the resonance frequency of the vibrator and efficiently transmitting the force applied to the weight to the vibrator when a disturbance is applied Is required to be large. The resonance frequency of the vibrator is proportional to the square root of its rigidity and inversely proportional to the square root of its mass. Further, the stress (strain) generated in the vibrator increases as the rigidity thereof decreases.

For this reason, in the vibration type sensor disclosed in Patent Document 1, a structure composed of a weight and a beam made of an integral structure of single crystal silicon is configured to be movable only in one axial direction, and the movement in the movable direction is constrained. As described above, the resonator is made of a thin film having a higher resonance frequency and lower rigidity as compared with single crystal silicon.
This method makes it possible to realize a highly sensitive sensor even if the force applied to the weight is reduced by reducing the size of the sensor, and can achieve both miniaturization and high sensitivity of the sensor, but the reliability of the thin film is a problem. Become.

Patent Document 2 proposes a method of processing all structures with single crystal silicon as means for improving reliability, which is a drawback of the thin film vibrator. In this method, the rigidity in one direction of the beam supporting the weight is reduced by increasing the length of the beam, and the acceleration is measured from the change in the resonance frequency of the beam. In this type of vibration type accelerometer, the resonance frequency that is inversely proportional to the square root of the mass of the mass and the strain applied to the beam that is proportional to the mass of the mass have a relationship in which the other becomes smaller and the other is smaller. It is necessary to increase the size in order to obtain the detection sensitivity.
For this reason, the reliability is high, but the detection sensitivity is inferior to that when a thin film is used.
In view of the above situation, an object of the present invention is to provide a vibration type sensor that can stabilize and amplify a change in resonance frequency due to a disturbance and can detect a physical quantity of the disturbance and has excellent reliability and detection accuracy.

  The vibration sensor according to the present invention includes a weight and a frame that is fixed to a measurement object, and one or more beams that support the weight with one end connected to the weight and the other end connected to the frame. And a vibration type sensor that measures the magnitude of the disturbance using the change of the position of the weight due to the disturbance applied to the measurement object, and includes both the weight-side root area and the frame-side root area of the beam. Or, it has a vibrator and a support structure which are formed through one part of the beam and are connected to each other at both ends in the longitudinal direction of the beam, and cut perpendicular to the longitudinal direction of the beam. The surface area of the support structure is larger than that of the vibrator, and the physical quantity of the disturbance is measured from the resonance frequency of the vibrator that changes due to the force caused by the disturbance.

  According to the present invention, not only the reliability can be improved, but also the detection sensitivity can be equal to or higher than that of a sensor of the same size using a thin film. Further, if it is composed of single crystal silicon alone, it is possible to realize a highly sensitive sensor that is not easily affected by temperature and whose measurement accuracy does not depend on temperature.

The vibration type sensor made as a monolithic silicon monolithic structure is inferior in detection sensitivity as compared with the thin film type, but outperforms the most important reliability of the sensor. Therefore, it is desirable to realize a vibration type sensor with a monocrystalline silicon integrated structure. The sensitivity of a vibration sensor made of a monocrystalline silicon monolithic structure is inferior to that of a thin film type. The load applied to the vibrator (the inertial force of the weight generated by acceleration) and the resonance frequency of the vibrator (the square root of the mass of the weight) Therefore, it is possible to realize a vibration type sensor having high reliability and high detection sensitivity if it can be controlled separately.
Specifically, the structure itself consisting of a weight and a beam that converts disturbances such as acceleration into force is not used as a vibrator, but a fine structure with a high resonance frequency is vibrated as an integral structure of single crystal silicon in a part of the beam. The amount of change in the resonance frequency of the vibrator equal to or greater than that of the thin film by amplifying the stress (strain) generated in the vibrator with respect to the stress generated in the beam by the support structure that is built as a child and pairs with the structure Can be obtained.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
<< First Embodiment >>
FIG. 1A is a top view showing the inside of a vibration sensor 10 to which the present invention is applied, and FIG. 1B is a right side view showing a usage state of the vibration sensor 10 of FIG. It is.
A vibration sensor 10 shown in FIG. 1 is used by being fixed to a structure of an object to be measured, and a physical quantity due to a disturbance applied to the structure, for example, accelerations a1 and a2 indicated by white arrows in FIG. This is a sensor that extracts and detects the change in the resonance frequency of the vibrator 13 (13a, 13b, 13c, 13d) from the displacement.
FIG. 3 is a top view of the inside of the vibration sensor 10 when accelerations a1 and a2 indicated by white arrows are applied to the weight 11 of the vibration sensor 10 fixed to the structure of the measurement object.

As shown in FIG. 1A, the vibration sensor 10 includes a vibration conversion structure 10A that converts a measurement object such as acceleration from a displacement of a weight 11 into a change in the resonance frequency of the vibrator 13, and a vibration conversion structure. The 10A vibrator 13 is vibrated at a resonance frequency, and a resonance circuit for detecting a change in the resonance frequency is provided.
Here, the vibration type sensor 10 is shown in FIG. 1B in order to prevent the influence of the vibration around the vibrator 13 on the vibration at a high frequency such as viscous damping and acoustic damping of the gas around the vibrator 13. In addition, the lids 10B and 10C formed of glass, a substrate and the like are hermetically sealed and used.
Here, in the central region of the lid 10B facing the weight 11 and the beam 12 of the vibration converting structure 10A shown in FIG. 1A, as shown in FIG. A vibration space P (shown by a broken line in FIG. 1 (b)) is formed so as not to hinder the movement of the beam 11 and the beam 12.
In addition, when the lids 10B and 10C are formed of glass, it is advantageous in that the inside of the vibration sensor 10 can be visually recognized.
As shown in FIG. 1 (a), the vibration converting structure 10A is manufactured as a monolithic structure of single crystal silicon, and is formed in the center part and has a weight 11 that generates an inertial force due to the acceleration of the measurement object, and the weight 11 Are formed by connecting one end to the four corner regions, and supporting the weight 11, and by connecting the other end of the four beams 12 to the four beams 12 and And a frame 18 that supports the weight 11.

The frame 18 surrounds the four beams 12 and the weight 11 and is formed in a middle shape. The frame 18 approaches the other end of the root area of the four beams 12 to the frame. Each of the four protrusions 14a protrudes. An insulated fixed electrode 14 is provided on the upper end surface of each projecting portion 14 a in the frame 18, and a vibrator electrode 15 is provided on the outer peripheral edge of the frame 18.
Further, the frame body 18 is formed with a pair of stoppers 16 and 16 projecting toward the weight 11 in the direction in which the disturbance is applied (left and right direction in FIG. 1A). When an overload is applied to 11, the weight 11 collides with the stopper 16 and stops, preventing an excessive inertia force and preventing the vibrator 13 from being overloaded.

As shown in FIG. 2 (a), which is an enlarged view of part D in FIG. 1 (a), the beam 12 has a through-hole 12n and a through-hole extending along the longitudinal direction at the other end which is a root area to the frame 18. A through hole 12m is formed in the center of the hole 12n along the short direction.
The region of the beam 12 outside the through hole 12n and close to the protruding portion 14a constitutes the vibrator 13a, and the region inside the through hole 12n and separated from the protruding portion 14a forms the support structure 12s. is doing.
Further, as shown in FIG. 2 (b), which is an enlarged view of the E portion in FIG. 1 (a), the beam 12 has a through hole 12n along the longitudinal direction at the other end which is a root region to the frame 18. And a through hole 12m of the amplitude amplifying mechanism along the short direction is formed in the center of the through hole 12n. The region of the beam 12 outside the through hole 12n and close to the protruding portion 14a constitutes the vibrator 13b, and the region inside the through hole 12n and separated from the protruding portion 14a forms the support structure 12s. is doing.

Similarly, the F portion of the beam 12 in FIG. 1A is symmetrical with the vibrator 13a and the support structure 12s shown in FIG. 2A with respect to the C2-C2 line in FIG. The vibrator 13 c and the support structure 12 s are formed at the other end of the root area to the frame 18. Similarly, the G portion of the beam 12 in FIG. 1A is symmetrical with the vibrator 13b and the support structure 12s shown in FIG. 2B with respect to the C2-C2 line in FIG. The vibrator 13d and the support structure 12s are formed at the other end of the root area to the frame 18.
The vibrator 13 and each support structure 12s are connected to each other at both ends in the longitudinal direction of the beam 12, and the vibrator 13 and each support structure 12s are juxtaposed.

Here, in the present embodiment, the through holes 12n and 12m drilled in the beam 12 are illustrated as T-shaped through holes in a top view. However, the end portions of the through holes 12n and 12m have three apexes. It is good also as a triangular-like through-hole (it shows with the dashed-two dotted line in Fig.2 (a)). As described above, the support structure 12 s has a configuration in which the second moment of section varies depending on the position of the beam 12 in the longitudinal direction.
Note that the T-shaped through holes 12n and 12m shown in the present embodiment are advantageous in that they have high strength against disturbance in the Z-axis direction (perpendicular to the plane of FIG. 1A).

<Detection principle when the detection target is acceleration>
As described above, as shown in FIG. 3A, the vibrator 13 and the support structure 12s have the bending moment in the beam 12 when the acceleration a1 of the white arrow due to the disturbance acts on the weight 11 to generate an inertial force. Is formed at the other end, which is the root region of the frame 18 with little change in the position of the beam 12, that is, with little displacement.
As shown in FIG. 3A, when acceleration a1 indicated by a white arrow is applied to the weight 11 of the vibration sensor 10, the position of the weight 11 changes in the direction of the acceleration a1 with respect to the frame body 18, and the weight 11 The inertial force is applied to the beam 12.

At this time, as shown in FIG. 2A, a moment M1a is applied to the beam 12 having the vibrator 13a, and a tensile force due to the moment M1a is applied to the vibrator 13a.
Here, since the through-hole 12m that is an amplitude amplifying mechanism is formed in the beam 12, the moment M1a is concentrated on the vibrator 13a around the fulcrum 12m1 of the through-hole, and the tensile force applied to the vibrator 13a is increased. Increasing and the displacement is amplified.
Similarly, as shown in FIG. 2B, a moment M1b is applied to the beam 12 having the vibrator 13b, and a compressive force due to the moment M1b is applied to the vibrator 13b.
Here, since the through-hole 12m which is an amplitude amplifying mechanism is formed in the beam 12, the moment M1b is concentrated on the vibrator 13b around the fulcrum 12m1 of the through-hole, and the compressive force applied to the vibrator 13b is increased. Increasing and the displacement is amplified.

Similarly, as shown in FIG. 3 (a), due to the moment applied to the beam 12 having the vibrator 13c, a tensile force is applied to the vibrator 13c so as to be extended and displaced, and the moment applied to the beam 12 having the vibrator 13d. Then, a compressive force is applied to the vibrator 13d to shorten the displacement.
On the other hand, as shown in FIG. 3B, when the acceleration a2 indicated by the white arrow is applied to the vibration sensor 10, the weight 11 is displaced in the direction of the acceleration a2 with respect to the frame 18, and the vibration is detected. A compressive force due to the moment is applied to the child 13a and the displacement is shortened, while a tensile force due to the moment is applied to the vibrator 13b and the displacement is extended. Similarly, a compressive force is applied to the vibrator 13c due to the moment applied to the beam 12 having the vibrator 13c, and the displacement is shortened, and a tensile force is applied to the vibrator 13d due to the moment applied to the beam 12 having the vibrator 13d. .

In this way, the bending moment applied to the beam 12 is converted into the tensile compression force applied to the vibrator 13 and the support structure 12s, and the tensile force applied to the vibrator 13 through the through-hole 12m of the amplitude amplification mechanism. Or the compression force is increased.
Next, an electrostatic driving method will be described as an example of a method of driving the vibrator 13 (13a, 13b, 13c, 13d) at its resonance frequency.
FIG. 4 is a conceptual diagram showing a method of driving the vibrator 13 by the electrostatic drive method at the resonance frequency.
In the case of electrostatic driving, if a single crystal silicon substrate having a low resistance of about 0.1 Ωcm is used, it can be used as an electrode material as it is.

When the vibrator 13 is vibrated at the resonance frequency, as shown in FIG. 4, a fixed electrode 14 electrically separated from the vibrator 13 is used, the vibrator 13 is grounded, and an alternating current is applied to the fixed electrode 14. Thus, an electrostatic force is applied between the vibrator 13 and the fixed electrode 14 to vibrate the vibrator. Note that a vibrator electrode 15 shown in FIG. 1A is used as an electrode of the vibrator 13.
Then, the resonance drive of the vibrator 13 is performed using a self-excited circuit or a PLL (Phase Locked Loop) circuit that shifts and vibrates the frequency so as to maximize the amplitude, and the resonance frequency is extracted by a counter. The acceleration of the detection target is calculated from the change in the following equation (1), (2).

また、加速度が加わり振動子１３ａに引張力Ｆが加わった場合の共振周波数をｆ_αｔとし、振動子１３ｂに圧縮力Ｆが加わった場合の共振周波数をｆ_αｃとした場合、振動子１３の共振周波数の変動量Δｆは、(２)式で表される。

なお、Ｆ：振動子に加わる力(引張力・圧縮力)［Ｎ］、Ｌ：振動子長［ｍ］(図２(ａ)参照)、Ｅ：振動子ヤング率［Ｎ／ｍ^２］、ｂ：振動子厚［ｍ］(図２(ａ)参照)、ｈ：振動子幅［ｍ］(図２(ａ)の紙面に垂直方向の寸法)、Ｉ：振動子の断面二次モーメント、Ａ：振動子断面積(ｈ×ｂ)、ρ：振動子密度［ｋｇ／ｍ^３］ The resonance frequency f ₀ of the vibrator 13 when no load is applied to the vibration sensor 10 is expressed by Expression (1).

Further, when the resonance frequency is f _αt when acceleration is applied and the tensile force F is applied to the vibrator 13a, and the resonance frequency is f _αc when the compression force F is applied to the vibrator 13b, the resonance of the vibrator 13 is obtained. The frequency variation Δf is expressed by equation (2).

F: force applied to the vibrator (tensile force / compression force) [N], L: vibrator length [m] (see FIG. 2A), E: vibrator Young's modulus [N / m ² ], b: vibrator thickness [m] (see FIG. 2A), h: vibrator width [m] (dimension in the direction perpendicular to the paper surface of FIG. 2A), I: cross-sectional secondary moment of the vibrator, A: vibrator cross-sectional area (h × b), ρ: vibrator density [kg / m ³ ]

Here, since the resonance frequency of the vibrator 13a to which the tensile force F is applied changes high, and the resonance frequency of the vibrator 13b to which the compression force F is applied changes to low, f _αt when the tensile force F is applied and By taking the difference from f _αc when the compressive force F is applied, the fluctuation amount Δf can be extracted as twice the amount of change compared to the case of the vibrator formed on the cantilever support.
As apparent from the equation (2), the resonance frequency of the vibrator 13 changes in proportion to the force F applied to the vibrator 13, so that the force F is obtained from the change in the resonance frequency, and the detection target is obtained from the force F. Can be calculated. This calculation is performed by executing a control program in the control device.
In this embodiment, the weight 11 is supported by four beams 12 arranged in an H shape, but may be supported by one beam or two or more parallel beams, and the number of beams is arbitrary. Can be selected.

In the acceleration detection of the vibration type sensor 10, the vibrator 13 is distorted by the inertial force of the weight 11 generated by the acceleration, and the magnitude of the acceleration is detected from the change amount Δf of the resonance frequency. Size is important. Therefore, the greater the length of the beam 12 that determines the size and strain value of the weight 11 that is the basis of the inertial force, the higher the sensitivity. Therefore, the vibration sensor 10 has a sub-millimeter order, that is, 0.5 mm of 1 mm or less. , 0.7 mm, etc.
However, with this size, the resonance frequency is only on the order of several thousand Hz, and therefore, only a change in resonance frequency of several hundred Hz can be obtained even if a change in resonance frequency of about ± 1% occurs in the acceleration detection range.

Therefore, in order to improve the sensitivity within the allowable range of distortion that does not break, it is necessary to increase the resonance frequency f ₀ of the vibrator 13. In the structure of this embodiment, the resonance frequency f ₀ of the vibrator 13 can be designed from the equation (1) regardless of the size of the weight 11 and the beam 12 from the equations (1) and (2). The resonance frequency f ₀ of the vibrator 13 can be increased by about two digits without changing the size of the beam 12.
For example, the thickness b (see FIG. 2A) of the vibrator 13 is set to several μm or more, the length L (see FIG. 2A) is shortened to several hundred μm or less, and both ends are fixed. In addition, 100,000 Hz or more can be realized as the resonance frequency f ₀ of the vibrator 13.

Further, since the chip size, that is, the dimension of the vibration sensor 10 is reduced by reducing the weight 11 and shortening the beam 12, the vibrator 13 (vibrator 23 described later) can be used as a mechanism for increasing a small force or a small moment. 33) and a pair of support structures 12s (support structures 22s and 32s described later). By providing the support structure 12s, the stress (strain) generated in the vibrator 13 (vibrators 23 and 33 described later) becomes smaller as the cross-sectional area of the vibrator 13 is made smaller than the cross-sectional area of the support structure 12s. Can be increased.
Further, the longer the center-to-center distance s (see FIG. 2A) in the thickness direction of the vibrator 13 (vibrators 23 and 33 described later) and the support structure 12s (support structures 22s and 32s described later) is vibrated. Tensile and compressive forces applied to the element 13 (vibrators 23 and 33 described later) can be increased, and the amount of change in resonance frequency can be increased.

<Modification 1>
Next, the vibrator 23 of the vibration sensor according to the first modification shown in FIG. 5 will be described. 5A is an enlarged view of a portion D of FIG. 1A showing the vibrator 23 of the vibration sensor according to the first modification, and FIG. 5B is a view of H in FIG. 5A. FIG.
In the vibrator 23 in the vibration sensor according to the first modification shown in FIG. 5 and the vibrator 33 in the vibration sensor according to the second modification shown in FIG. 7 described later, the vibrators 23 and 33 are used as the support structures 22s and 32s. The thickness is made thinner than that, i.e., b2 and b3 (refer to FIGS. 5A and 7A) corresponding to b (refer to FIG. 2A) of the formula (1) are decreased, and the width, that is, By narrowing h2 and h3 (see FIGS. 5B and 7B) corresponding to h (the dimension of the vibrator 13 in the direction perpendicular to the paper surface of FIG. 2A) in Expression (1), The cross-sectional area A of the equation (1) is reduced, and the stress (strain) generated in the vibrators 23 and 33 when acceleration is applied is increased.

The vibrator 23 in the vibration type sensor of the first modification shown in FIG. 5 is obtained by removing the upper surface side and the lower surface side of the vibrator 13 (see FIGS. 1A and 2) of the first embodiment, and the vibrator width. h2 (see FIG. 5B) is made thinner than that of the first embodiment, and the thickness dimension b2 (see FIG. 5A) is made smaller.
Since the other configuration is the same as the configuration of the first embodiment, the same components are shown by changing the tens digit to the twentieth symbol, and detailed description is omitted. .
FIG. 6 shows a case where the beam 22 and the weight 21 including the vibrator 23 of the vibration conversion structure 20A are provided in the center in the thickness direction of the vibration conversion structure 20A.
6A is a cross-sectional view taken along the line AA of FIG. 1A showing a state in which the vibration conversion structure 20A of the vibration sensor 20 of the first modification is hermetically sealed with the lids 20B and 20C. 6 (b) is a cross-sectional view taken along line BB in FIG. 1 (a), FIG. 6 (c) is a cross-sectional view taken along line C1-C1 in FIG. 1 (a), and FIG. ) Is a cross-sectional view taken along line C2-C2 of FIG.
As shown in FIG. 6, when the beam 22 including the vibrator 23 and the weight 21 are provided in the center portion in the thickness direction of the vibration conversion structure 20A (particularly, see FIG. 6B), the beam 22 is used. And the space for vibration of the weight 21 is formed in the vibration conversion structure 20A above and below the beam 22 and the weight 21, so that the lids 20B and 20C for hermetically sealing the vibration conversion structure 20A are flat plates. It is possible to form in the shape. In this configuration, when the vibration conversion structure 20A is formed of single crystal silicon and the lids 20B and 20C are formed of glass, the cost can be reduced.
The lid body 20B is provided with a conical connection hole 27 facing the fixed electrodes 24, 24, 24, 24 and the vibrator electrode 25 of the vibration converting structure 20A.

<Modification 2>
Next, the vibrator 33 of the vibration type sensor according to the second modification shown in FIG. 7 will be described. FIG. 7A is an enlarged view of a portion D in FIG. 1A showing the vibrator 33 of the vibration type sensor according to the second modification, and FIG. 7B is an I diagram in FIG. 7A. FIG.
The vibrator 33 in the vibration type sensor of the second modification shown in FIG. 7 is obtained by removing the upper surface side and the lower surface side of the vibrator 13 (see FIG. 1A and FIG. 2) of the first embodiment. h3 (see FIG. 7B) is made thinner than that of the first embodiment, the thickness dimension b3 (see FIG. 7A) is made smaller, and a through hole 12m which is an amplitude amplification mechanism is provided. There is no configuration. Since the other configuration is the same as the configuration of the first embodiment, the same component is shown by changing the tens digit to the thirty symbol, and the detailed description is omitted. .

Since the vibrator 33 according to the second modification does not have a through hole (22m in FIG. 5A) that is an amplitude amplification mechanism, the amplitude of the vibrator 33 is not amplified. More desirable.
Here, as a specific example, when the size of the beam 12 is width = 20 μm, thickness (perpendicular to the paper surface of FIG. 1A) = 100 μm, and length = 600 μm, the root region to the frame 18 Width h = 20 μm at the other end of the beam 12 (FIG. 1 (a), perpendicular to the paper surface of FIG. 2 (a), thickness direction for the beam), thickness b = 1 μm (see FIG. 2 (a), The center-to-center distance s between the vibrators 13 and 33 having the length L = 10 μm (the length direction for the beam) and the support structures 12s and 32s (FIGS. 2A and 7A). When the weight 11 is 1 mm square, the amount of change Δf of the resonance frequency f ₀ per 1 G (G: gravitational acceleration 9.880665 m / s ² ) is 28 kHz.
Assuming that the frequency change is measured by the counter, the minimum resolution is 1/140 G if the response is 200 Hz. In this case, the acceleration detection range is ± 3G.

<Modification 3>
Next, a vibration type sensor 10 ′ according to the third modification will be described with reference to FIG. FIG. 8 is a top view showing the vibration type sensor 10 ′ of the third modification.
The vibration type sensor 10 ′ according to the third modification shown in FIG. 8 is formed by making the length of the beam 12 ′ longer than the length of the beam 12 of the vibration type sensor 10 according to the first embodiment. Since the configuration other than this is the same as that of the first embodiment, the reference numerals of the same components are shown by attaching '(dash), and detailed description is omitted.
The vibration type sensor 10 ′ according to the third modification increases the moment due to the inertial force of the weight 11 ′ applied to the beam 12 ′ by elongating the beam 12 ′, so that the vibrator 13 ′ (13 a ′, 13 b ′, 13 c ′ , 13d ′) has an effect of increasing the tensile force and compressive force. When the beam 12 ′ is lengthened, the displacement of the weight 11 ′ increases, and the detection stability tends to decrease.

<Manufacturing method of vibration sensor>
Next, a method for manufacturing the vibration sensor 10 will be briefly described.
In the present embodiment, processing is performed by a process called a bulk micromachine. This is a general term for processes that process single crystal silicon as a structural material, but reliability is required because of the homogeneity of single crystal silicon material and the reproducibility of micro processing, that is, the accuracy of micro processing. This technology has become mainstream in the field.
The structure of this embodiment has two methods: a method using an SOI (Silicon On Insulator) wafer and a method of manufacturing a single crystal silicon substrate by bonding.

In the method using the SOI wafer, the structures such as the weight 11, the beam 12, and the frame 18 are processed by deep-RIE (Deep-Reaction Ion Etching) technology, and the box oxidation under the movable structure such as the weight 11 and the beam 12 is performed. After removing the film, it is manufactured by sealing with another substrate in a reduced-pressure atmosphere and sealing hermetically.
The reason why the hermetic sealing is performed in the reduced-pressure atmosphere is to exclude the influence of viscous attenuation and acoustic attenuation applied to the vibration of the vibrators 13, 23, and 33 by the gas around the vibrators 13, 23, and 33.

Therefore, since this airtightness is also a decisive factor for sensor performance, airtightness is often achieved by a metal package instead of airtight sealing at the wafer level. Wafer level packaging is desirable because it can be realized with low cost packages such as molding.
As a process not using an SOI wafer, there is a method of combining a bonding technique and a wafer polishing technique using a single crystal silicon wafer. An advantage of this method is that a more complicated three-dimensional structure can be manufactured by performing processing on both surfaces of the substrates to be bonded in advance and then bonding them.

    As an example, the widths h2 and h3 of the vibrators 23 and 33 (see FIGS. 5B and 7B) are the same as the widths k2 and k3 of the support structures 22s and 32s (FIGS. 5A and 7B). A case where the width is narrowed with respect to (a) will be described. In this process, the widths h2 and h3 of the vibrators 23 and 33 are previously narrower than the support structures 22s and 32s in the portion of the substrate on which the weights and beams 22 and 32 and the frames 28 and 38 are formed. Processing is performed from both sides of the substrate. In this state, it is bonded to a single crystal silicon substrate, a Pyrex (registered trademark) glass substrate, and the like, and weights, beams 22 and 32, frame bodies 28 and 38, and the like are bonded to the bonded substrates. The body 22s and 32s are processed. Another advantage of this process is that it is not necessary to remove the box oxide film required when using the SOI substrate (separation layer etching) to separate the weight, beam, and frame from the silicon substrate. As a result, not only can the separation layer removal step that yields the lowest yield in the manufacture of movable structures such as weights and beams be made unnecessary, but also facilities for the separation layer removal step are unnecessary, and production costs can be reduced.

<< Second Embodiment >>
Next, a vibration sensor according to a second embodiment will be described with reference to FIG. 9A is an enlarged view of a portion D in FIG. 1A showing the vibrator 43 of the vibration sensor according to the second embodiment, and FIG. 9B is a J direction of FIG. 9A. It is an arrow view.
In the vibration type sensor of the second embodiment, the detection axis direction of the acceleration to be detected is perpendicular to the plane of FIG. 9A (perpendicular to the plane with the weight, beam, and frame).
The overall configuration of the vibration sensor according to the second embodiment is the same as that of the vibration sensor 10 shown in FIG. 1A except for the fixed electrode described later. It is the structure which added the change to the body 42s. Since the configuration other than this is the same as that of the vibration type sensor of the first embodiment, the same constituent elements are shown by changing the tens digit of the first embodiment to the forty digits, Detailed description is omitted.

Since the acceleration of the vibration type sensor of the second embodiment is applied with acceleration in the direction perpendicular to the paper surface of FIG. 9, a bending moment in the direction perpendicular to the paper surface of FIG. Therefore, the vibrator 43 and the support structure 42s need to have different force points with respect to this bending moment in the wafer thickness direction.
In the configuration shown in FIG. 9, the vibrator 43 and the support structure 42 s are processed to reduce the thickness from different surfaces in the detection axis direction, that is, from the vibrator lower surface 43 b side and the support structure upper surface 42 s 1 and 42 s 1 side, respectively. By providing the slit-shaped through hole 42n, a separation structure between the vibrator 43 and the support structure 42s is realized in the beam 42.

As shown in FIG. 9 (a), both ends of the beam 42 in the short direction are processed and removed from above, and as shown in FIG. 9 (b), support structure upper surfaces 42s1, 42s1 lower than the beam upper surface 42a. The support structures 42s and 42s having the structure are formed. Further, the portion sandwiched between the support structures 42s and 42s in the beam 42 shown in FIG. 9A is processed and removed from below, and the vibrator lower surface 43b is higher than the beam lower surface 42b shown in FIG. 9B. The vibrator 43 is formed.
In this way, as shown in FIG. 9A, slit-shaped through holes 42n and 42n are formed, the thickness of the vibrator 43 and the support structure 42s is smaller than that of the beam 42, and the vibrator 43 And the support structure 42s are separated.

In addition, when detecting acceleration in the direction perpendicular to the paper surface of FIG. 9A by electrostatic drive, as shown in FIGS. 2 and 3, the transducer 43 is vibrated in the acceleration detection direction. A fixed electrode 44 (corresponding to the fixed electrode 14 in FIG. 1 (a)) is required on the lid 40B (corresponding to 10B in FIG. 1 (b)) to be joined to the structure 40A from the upper side of the paper in FIG. 9 (a). Become. In this case, it is necessary to form the fixed electrode 44 on the insulating film provided on the lid.
Here, since the size of the vibrator 43 is small, the electrostatic capacity thereof is small, and a change in the electrostatic capacity of the vibrator 43 cannot be detected unless the stray capacitance generated in the fixed electrode 44 is reduced. Therefore, it is necessary to design such that the size of the insulating film is made small and the insulating film under the electrode 44 is thickened.
In the second embodiment, the case has been described in which the vibrator 43 is processed and thinned from the beam lower surface 42b, and the support structure 42s is processed and thinned from the beam upper surface 42a. Can be processed and thinned from the beam upper surface 42a, and the support structure 42s can be processed and thinned from the beam lower surface 42b.

The configuration of the vibration sensor that detects the acceleration in the horizontal direction and the vertical direction with respect to the paper surface of FIG. 1A has been described in the first embodiment and the second embodiment.
According to the above configuration, since the vibrator that is the strain amplification mechanism is formed at the place where the maximum strain is generated by the disturbance, the change in the resonance frequency due to the acceleration is stably amplified, and is detectable and highly sensitive.
In addition, since the stopper is formed on the frame body, an excessive inertia force of the weight due to the disturbance can be prevented by bringing the weight into contact with the stopper, and an overload can be prevented from being applied to the vibrator.

In addition, a structure that concentrates stress on the vibrator realizes each function small, and a large number of sensors can be mounted together.
Since the vibrators can be processed by the same manufacturing apparatus only with different structures, for example, it is possible to create a configuration in which a physical quantity in the multi-axis direction is simultaneously detected in one substrate. Therefore, it is possible to easily make a multi-axis vibration type sensor having a plurality of detection axes with one chip, and it is possible to easily perform planar mounting.
In addition, even if the detection axis directions are different, the vibration sensors can be stacked and joined to make the size of the top view of FIG. 1A the same, so that a multi-axis vibration sensor with a small mounting area can be realized. .

In the above-described embodiment, the case where the vibrator and the support structure are formed in the frame-side root region of the beam is exemplified, but both the frame-side root region of the beam and the weight-side root region of the beam, or the beam You may form only in the weight side root area | region.
Moreover, although the said embodiment demonstrated and demonstrated the case where an acceleration was detected with a vibration type sensor, it is not limited to an acceleration, It can apply widely as a sensor which detects physical quantities, such as an angular acceleration and a pressure.
Therefore, according to the present invention, it is possible to realize a vibration sensor excellent in reliability and detection accuracy that can stabilize and amplify a change in resonance frequency due to a disturbance and detect a physical quantity of the disturbance.

(a) And (b) is a top view which shows the vibration-type sensor of 1st Embodiment of this invention, and a right view which shows the use condition of the vibration-type sensor of (a) figure. (a) And (b) is the D section enlarged view of FIG. 1, and the E section enlarged view of FIG. The top view which showed the vibration type sensor 10 when the acceleration a1 of a white arrow is added to the weight. (a) And (b) is the conceptual diagram which showed the method of driving a vibrator | oscillator by the electrostatic drive system with a resonant frequency. (a) And (b) is the D section enlarged view of FIG. 1 which showed the vibration type sensor of the deformation | transformation form 1, and the H direction arrow line view of (a) figure. (a) is the sectional view on the AA line of FIG. 1 which shows the state which sealed the vibration conversion structure of the vibration type sensor of the deformation | transformation form 1 with the cover body, (b) is B-B of FIG. 2 is a cross-sectional view taken along line B, (c) is a cross-sectional view taken along line C1-C1 in FIG. 1, and (d) is a cross-sectional view taken along line C2-C2 in FIG. (a) And (b) is the D section enlarged view of FIG. 1 which showed the vibration type sensor of the deformation | transformation form 2, and the I direction arrow line view of (a) figure. The top view which shows the vibration type sensor 10 'of the deformation | transformation form 3. FIG. (a) And (b) is the D section enlarged view of FIG. 1 which shows the vibration type sensor of 2nd Embodiment, and the J direction arrow line view of (a) figure.

Explanation of symbols

10, 10 'Vibration sensor 11 Weight 12, 22, 32, 42, 12' Beam 12n, 22n, 32n Through hole 12n, 12m, 22n, 22m Through hole (through hole of claim 6)
12s, 22s, 32s, 42s, 12s' support structure 13 (13a, 13b, 13c, 13d), 23, 33, 43, 13 'vibrator 18, 28, 38, 48, 18' frame 42n through hole ( (Through holes of claims 3 and 7)
43 vibrators (vibrators of claims 3 and 7)

Claims (11)

A weight and a frame fixed to the measurement object; and one or more beams supporting one end at one end of the frame and connected to the frame at the other end. A vibration type sensor that measures the magnitude of a disturbance using the fact that the weight changes position due to the applied disturbance,
The beam-side root region and the frame-side root region of the beam are formed so as to penetrate a part of the beam in one region thereof, and are connected to each other at both ends in the longitudinal direction of the beam. Having a vibrator and a support structure,
The area of the cut surface perpendicular to the longitudinal direction of the beam is larger in the support structure than in the vibrator,
A vibration type sensor that measures a physical quantity of the disturbance from a resonance frequency of the vibrator that changes due to a force caused by the disturbance. The vibration sensor according to claim 1, wherein the weight, the beam, and the frame are integrally formed from the same material. The detection axis direction of the disturbance is perpendicular to the longitudinal direction of the beam in a plane including the weight, the beam, and the frame, and
The vibrator and the support structure are separately formed by a through-hole penetrating a part of the beam in a direction perpendicular to a plane including the weight, the beam, and the frame. 2. The vibration type sensor according to 1. The detection axis direction of the disturbance is perpendicular to a plane including the weight, beam, and frame,
The vibrator and the support structure are separated by forming a through-hole penetrating the beam in a direction perpendicular to a plane including the weight, the beam, and the frame,
When the vibrator is thinly formed by processing from one surface of the beam with respect to the vertical direction of the plane including the weight, the beam, and the frame, the support structure is formed from the other surface of the beam. The support structure is processed and thinned from one surface of the beam when the vibrator is thinned by processing from the other surface of the beam. The vibration type sensor according to claim 1, wherein The through hole is formed in a slit shape of an elongated hole in a direction perpendicular to a plane including the weight, beam, and frame,
The vibration sensor according to claim 3, wherein the vibrator and the support structure have a parallel plate-like structure. The through hole is formed to penetrate in a direction perpendicular to a plane including the weight, beam, and frame,
The vibrator has a plate-like structure,
The vibration type sensor according to claim 3, wherein the support structure has a cross-sectional second moment that varies depending on a position in a longitudinal direction of the beam. The vibration sensor according to claim 6, wherein the through hole has a T-shaped shape in a top view. The vibrator and the support structure are separated by forming a slit-like shape of two elongated holes in which the through hole is parallel to the longitudinal direction of the beam, and
When the vibrator is thinly formed by machining from one side of the beam with respect to the vertical direction of the plane including the weight, beam, and frame, the support structure is machined from the other side of the beam. Or when the vibrator is processed and thinned from the other surface of the beam, the support structure is processed and thinned from one surface of the beam. The vibration sensor according to claim 4. The vibration sensor according to any one of claims 1 to 8, wherein the weight, the beam, and the frame are made of single crystal silicon. The plane including the weight, the beam, and the frame body is shared, and the vibration sensor having the different detection axis directions is integrally formed on the same substrate to enable multi-axis detection. The vibration type sensor according to any one of claims 1 to 9. The vibration type sensor according to any one of claims 1 to 9, wherein the vibration type sensors having different detection axis directions are stacked and joined to enable multi-axis detection. .

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