CN1892231A - Acceleration sensor and magnetic disk device using same - Google Patents

Abstract

The present invention provides an acceleration sensor comprising a vibrating element (2) formed by arranging a conductive film (26, 29) on the outer main surface of a rectangular parallelepiped piezoelectric substrate (21, 22), and a first vibrating element sandwiching a part thereof. 1 support member (3a, 3b), the first support member (3a, 3b) is made of elastic body, and the bending point of the vibration element is located in the support area (91) sandwiched by the first support member (3a, 3b). As a result, the region where strain occurs in the piezoelectric substrate (21, 22) becomes larger, the generated charge increases, and the output voltage increases, thereby improving the detection sensitivity of acceleration.

Description

Acceleration sensor and magnetic disk device using same

technical field

The present invention relates to an acceleration sensor using a piezoelectric substrate, and more particularly to a compact and highly sensitive acceleration sensor.

Background technique

Conventionally, acceleration sensors have been used for purposes such as detecting external shocks applied to electronic devices such as hard disk drives.

For example, there is known an acceleration sensor of the type in which charge detection electrodes are arranged on both main surfaces of a rectangular parallelepiped piezoelectric substrate to form a vibrating element, and its ends are supported by supporting members (for example, refer to JP-A 2000- Publication No. 321299, Shi Kaiping No. 7-36064).

In such an acceleration sensor, the vibrating element is deflected by the applied acceleration, thereby generating strain in the piezoelectric substrate, and charges are generated in the charge detection electrodes formed on both main surfaces of the piezoelectric substrate by the piezoelectric effect.

Acceleration is detected by the charge or the voltage generated between the charge detection electrodes according to the charge.

Which one of charge and voltage is used to detect acceleration depends on the acceleration detection device that uses the acceleration sensor to detect acceleration. Generally, the detection sensitivity of acceleration when detecting acceleration from the generated charge is called "charge sensitivity". The detection sensitivity of the acceleration when the voltage detects the acceleration is called "voltage sensitivity". As an acceleration sensor, it is desirable that both the charge sensitivity and the voltage sensitivity are relatively high.

For example, in an acceleration sensor in which one end in the longitudinal direction of a bimorph-type (bimorph) vibrating element in which two rectangular parallelepiped piezoelectric substrates are bonded in the thickness direction is sandwiched by a supporting member, if the pressure The piezoelectric constant of the electric substrate is D, the length of the free vibration region not clamped by the support member in the vibrating element is L, the width of the vibrating element is W, and the thickness of the vibrating element is T, then when the acceleration is applied induced force F when the output voltage V becomes

V＝(3/2)·D·L·F/(W·T)

The output voltage V is proportional to the length L of the free vibration region of the vibrating element, and inversely proportional to the width W and thickness T of the vibrating element.

Therefore, in order to improve the detection sensitivity of the acceleration of the acceleration sensor, it is necessary to increase the length L of the free vibration region of the vibration element and reduce the width W and thickness T of the vibration element, but the increase of the length L of the free vibration region of the vibration element will cause This results in an increase in the size of the acceleration sensor, and a reduction in the width and thickness T of the vibrating element leads to a reduction in mechanical strength and thus a reduction in reliability.

Contents of the invention

An object of the present invention is to provide a compact acceleration sensor with high acceleration detection sensitivity and reliability, and a magnetic disk drive using the acceleration sensor.

An acceleration sensor according to the present invention includes: a vibrating element in which charge detection electrodes facing each other are arranged on both principal surfaces of a rectangular parallelepiped piezoelectric substrate; and a first support member supporting the vibrating element. The vibrating element includes: a support region supported by contact with the first support member; and a free vibration region that is longer in the longitudinal direction than the support region and is not supported by the first support member. In addition, the first supporting member is made of an elastic body.

In the configuration of the present invention, since the first support member is made of an elastic body, strain due to deflection of the vibrating element is also generated in the portion located within the support region of the piezoelectric substrate. Therefore, compared with the case where the first support member is formed of a non-elastic body like the conventional acceleration sensor, the region where strain occurs in the piezoelectric substrate increases, the amount of generated charge increases, the output voltage increases, and the acceleration can be improved. detection sensitivity. Furthermore, since the length of the vibrating element is not increased, the size of the acceleration sensor is not increased, and since the width and thickness of the vibrating element are not reduced, there is no reduction in reliability due to insufficient mechanical strength.

The bending point of the vibrating element is located in the support area sandwiched by the first support member. Here, the "bending point" refers to a boundary between a deflected portion and a non-deflected portion of the vibrating element. Therefore, compared with the case where there is a bending point at the boundary between the support region and the free vibration region, that is, the case where the deflection starts from the boundary portion of the support region and the free vibration region, as in the conventional acceleration sensor, the generation of the piezoelectric substrate is less. The area of strain increases, the amount of charge generated increases, the output voltage increases, and the detection sensitivity of acceleration can be improved.

The modulus of elasticity of the first supporting member is preferably 10 MPa to 10 GPa. If the modulus of elasticity of the first supporting member is set within this range, the first supporting member is likely to be deformed by the force received from the vibrating element, and the vibrating element is likely to be deflected in the supporting region.

The acceleration sensor of the present invention preferably further includes a second support member supporting the first support member from a direction perpendicular to both principal surfaces of the piezoelectric substrate, and the modulus of elasticity of the first support member is lower than that of the first support member. 2 The modulus of elasticity of the supporting member is small.

In this way, if the second supporting member is also included and the elastic modulus of the second supporting member is set to be larger than that of the first supporting member, the second supporting member 4 is less likely to be deformed. Therefore, the problem that "the deformation of the vibrating element 2 itself is suppressed due to the deformation of the second supporting member and the detection sensitivity of the acceleration decreases" is less likely to occur.

The modulus of elasticity of the first support member is preferably 10 MPa to 10 GPa, and the modulus of elasticity of the second support member is preferably 10 GPa to 500 GPa.

In the acceleration sensor according to the present invention, the first supporting member may be configured to protrude further toward the region of the vibration element having the largest amplitude than the second supporting member.

Here, the "maximum amplitude region" refers to the region where the amplitude of the flexural vibration is the largest in the vibration element, and when the vicinity of one end in the longitudinal direction of the vibration element is used as the supporting region, the vibration amplitude becomes the largest near the other end. area. When the vicinity of the central portion in the longitudinal direction of the vibrating element is used as the support region, the vicinity of both end portions becomes the maximum amplitude region. When the vicinity of both end portions in the longitudinal direction of the vibrating element is used as the support region, the vicinity of the central portion becomes the region with the largest amplitude.

According to such a structure in which the first supporting member protrudes further toward the region of the vibration element having the maximum vibration amplitude than the second supporting member, there is a portion of the first supporting member that is not sandwiched by the second supporting member. Since this portion restricts the deflection of the vibrating element and generates some degree of deflection together with the vibrating element, deflection of the vibrating element occurs even at this portion. In addition, in the vibrating element, since the deflection starting from the end of the region sandwiched by the first supporting member and the end of the region sandwiched by the second supporting member in addition to the first supporting member Therefore, the region where the strain occurs in the piezoelectric substrate increases, the amount of generated charges increases, and the output voltage increases, which can improve the detection sensitivity of acceleration.

In the longitudinal direction of the vibrating element, when the length of the first support member protruding beyond the second support member is α, and the length of the free vibration region is β, it is desirable that 0.05≦α/(α +β)≤0.1.

It is desirable that the charge detection electrodes arranged opposite to each other on both main surfaces of the piezoelectric substrate are arranged on portions of the two main surfaces of the vibrating element, in the free vibration region and the support region, close to the free vibration region.

In this structure, on both main surfaces of the vibrating element, the charge detecting electrodes are arranged in the free vibration region and the part close to the free vibration region in the supporting region. Of course, no charge detection electrodes are arranged in the part of the support region away from the free vibration region. In the acceleration sensor of the present invention, when an acceleration is applied, since the piezoelectric substrate is strained and charges caused by the piezoelectric effect are generated in the part of the support region close to the free vibration region in addition to the free vibration region, therefore, by Charge detection electrodes are also arranged in the region near the free vibration region so that charges generated in the support region near the free vibration region are attracted to the charge detection electrodes in addition to the charges generated in the free vibration region. Therefore, the amount of charges accumulated in the charge detection electrodes increases, and the potential difference generated between the charge detection electrodes on both main surfaces of the vibrating element also increases. Since the charge and voltage generated by the applied acceleration increase, an acceleration sensor with high acceleration detection sensitivity can be obtained.

Furthermore, since the charge detection electrode is not arranged in the part of the support region far from the free vibration region, compared with the case where the charge detection electrode is also arranged in the part of the support region far from the free vibration region, the overall charge detection electrode As the area decreases, the capacitance between the charge detection electrodes on both main surfaces of the vibrating element also decreases.

If the amount of charge accumulated in the charge detection electrodes according to the applied acceleration is Q, the potential difference generated between the charge detection electrodes on the two main surfaces of the vibration element is V, and the charge detection electrodes on the two main surfaces of the vibration element The electrostatic capacitance between them is C, and then V=Q/C. Therefore, when the amount of charge Q is constant, if the electrostatic capacitance C decreases, the potential difference V increases. That is, by not disposing the charge detection electrode in the part away from the free vibration region in the supporting region, the amount of charge Q accumulated in the charge detection electrode hardly changes according to the applied acceleration, since the charge detection electrodes on both main surfaces of the vibration element The electrostatic capacitance C between them decreases, so the potential difference V generated between the charge detection electrodes on both main surfaces of the vibrating element increases. Accordingly, an acceleration sensor having high voltage sensitivity when detecting an applied acceleration from a change in voltage can be obtained.

In the longitudinal direction of the vibrating element, when the length of the part where the charge detection electrode is arranged in the support region is γ, and the length of the free vibration region is δ, it is desirable that 0.15≤γ/δ≤0.3 .

Furthermore, according to the acceleration sensor of the present invention, in the above configuration, the vibrating element may be provided in such a way that a plurality of piezoelectric substrates are stacked in the thickness direction, and the piezoelectric substrate and the two main substrates are connected between the piezoelectric substrates. The charge detection electrodes are also arranged on the surface (outer main surface) such that the charge detection electrodes face each other.

In this case, the charge detection electrodes arranged between the piezoelectric substrates are arranged in positions and shapes overlapping the charge detection electrodes arranged on the outer main surface of the vibrating element in the thickness direction. As a result, charges are generated in the charge detection electrodes disposed on both main surfaces of the piezoelectric substrates, and the amount of generated charges in the entire vibrating element increases. Therefore, the generated charges can be used to improve the charge sensitivity when detecting acceleration.

Furthermore, according to the acceleration sensor of the present invention, in the above configuration, the first lead-out electrode drawn from the charge detection electrode on one main surface of the piezoelectric substrate to one side surface may be arranged, and the first lead-out electrode drawn from the other main surface may be arranged. The charge detection electrode is led out to the second lead-out electrode on the other side surface.

In this case, all the charge detection electrodes are drawn out to both side surfaces of the vibrating element via the two lead-out electrodes, so that they can be easily electrically connected to the outside of the vibrating element. Thus, since there is no need to form a via hole or the like for electrically connecting the charge detection electrodes located between the layers of the piezoelectric substrate to the outside of the vibration element in the vibration element, a simple structure and a simplified manufacturing process can be obtained. Accelerometer.

Moreover, by being electrically connected to the outside of the vibration element on both sides of the vibration element, if the electrode is drawn out to the end surface of the vibration element to expose it, and the end surface of the vibration element is electrically connected to the outside of the vibration element In this case, the distance between the connecting parts to the outside of the vibrating element can be increased. This reduces the possibility of an electrical short between the first lead-out electrode and the second lead-out electrode when the lead-out electrode is connected to the outside of the vibrating element using fluid solder or a conductive adhesive. .

Furthermore, the magnetic disk device of the present invention is equipped with the acceleration sensor of the present invention in order to detect the acceleration applied to the magnetic disk device. The acceleration sensor always monitors the acceleration applied to the magnetic disk device, compares the acceleration data with a preset threshold value, and when it is judged that the threshold value is exceeded, the magnetic head is avoided, so that even the magnetic disk device is not damaged during data reading and writing. Even when strong acceleration is applied, damage to the magnetic disk device due to collision between the magnetic head and the magnetic disk can be prevented before failure occurs.

The above-mentioned or further other advantages, features, and effects of the present invention will be clarified through the description of the following embodiments with reference to the accompanying drawings.

Description of drawings

FIG. 1 is a perspective view schematically showing the appearance of an acceleration sensor according to an embodiment of the present invention;

2 is an external perspective view schematically showing a vibrating element used in an acceleration sensor according to an embodiment of the present invention;

Fig. 3 is a perspective view of the appearance of the first support member of the vibration detection element of Fig. 2;

4 is an external perspective view schematically showing a second supporting member used in the acceleration sensor according to the embodiment of the present invention;

Fig. 5 is a perspective view of the external appearance of the acceleration sensor shown in Fig. 1 after the sealing resin is removed;

Fig. 6 is the A-A ' line sectional view of Fig. 1;

7 is a cross-sectional view of an acceleration sensor according to another embodiment of the present invention;

8 is an external perspective view schematically showing a vibrating element and a first supporting member used in an acceleration sensor according to still another embodiment of the present invention;

Fig. 9 is an exploded perspective view of the vibrating element and the first supporting member shown in Fig. 8;

10 to 12 are respectively a perspective view, a plan view, and a bottom view schematically showing the piezoelectric substrate constituting the vibrating element shown in FIG.

13 to 15 are respectively a perspective view, a top view, and a bottom view schematically showing another piezoelectric substrate constituting the vibrating element shown in FIG. ;

16 is a cross-sectional view schematically showing an acceleration sensor according to still another embodiment of the present invention;

17 is a perspective view schematically showing the appearance of a vibrating element and a first supporting member used in the acceleration sensor shown in FIG. 16;

18 to 20 are respectively a perspective view, a top view, and a bottom view schematically showing the piezoelectric substrate constituting the vibrating element shown in FIG. 17 and the conductor films disposed on both main surfaces of the piezoelectric substrate, viewed from above;

21 to 23 are respectively a perspective view, a top view, and a bottom view schematically showing another piezoelectric substrate constituting the vibrating element shown in FIG. ;

24 is a cross-sectional view schematically showing an acceleration sensor according to still another embodiment of the present invention;

Fig. 25 is a perspective view schematically showing the appearance of a vibrating element and a first supporting member used in the acceleration sensor shown in Fig. 24;

26 to 28 are respectively a perspective view, a top view, and a bottom view schematically showing the piezoelectric substrate constituting the vibrating element shown in FIG. 25 viewed from above;

29 to 31 are respectively a perspective view, a plan view, and a bottom view schematically showing other piezoelectric substrates constituting the vibrating element shown in FIG. 25 viewed from above;

32 to 34 are diagrams showing simulation results of the distribution of charges generated on the surface of the vibrating element when an impact is applied to the acceleration sensor;

35 to 37 are partial cross-sectional views schematically showing the state of deformation of the vibration element 2;

38 is a graph showing simulation results of changes in detection sensitivity of acceleration when the extension amount of the first supporting member is changed in the acceleration sensor according to the embodiment shown in FIG. 7 of the present invention;

39 is a diagram showing simulation results of distribution of charges generated on the surface of the vibrating element when acceleration is applied to the acceleration sensor according to the embodiment shown in FIGS. 1 to 6 of the present invention;

40 is a graph showing simulation results of changes in voltage sensitivity when the amount of protrusion of the charge detection electrode into the supporting region is changed in the acceleration sensor according to the embodiment shown in FIGS. 8 to 15 of the present invention;

41 is an exploded perspective view showing a vibrating element and a first support member in an embodiment in which one charge detection electrode is disposed between two piezoelectric substrates in the acceleration sensor of the present invention;

42 is a perspective view showing the internal structure of the magnetic disk device on which the acceleration sensor is installed;

FIG. 43 is a block diagram showing a circuit for processing an acceleration detection signal of an acceleration sensor.

In the figure: 1-housing, 1a, 1b-lead electrodes, 1h-opening, 2-vibration element, 21, 22-piezoelectric substrate, 26-29-conductor film, 23-adhesive, 3a, 3b-first support member, 4-second support member, 4a, 4b-recess, 4h-through hole, 5-resin for sealing, 6a, 6b-conductive adhesive material, 7a, 7b-end of lead electrode , 8a, 8b-resin cofferdam, 91-support area, 92-free vibration area, C-charge detection electrode, E-extraction electrode.

Detailed ways

<Structure 1 of acceleration sensor>

FIG. 1 is a perspective view showing the appearance of an acceleration sensor according to an embodiment of the present invention. This acceleration sensor has a structure in which a vibrating element 2 (shown in FIG. 2 ) is accommodated in a case 1 having lead electrodes 1 a and 1 b , and an opening 1 h of the case 1 is sealed with a sealing resin 5 .

The case 1 is a rectangular parallelepiped container having an opening 1 h at one end. As the material, for example, a high-strength plastic material such as liquid crystal polymer (LCP), polyphenylene sulfide (PPS), or polyether ether ketone (PEEK), or a ceramic material such as alumina is preferably used.

Lead electrodes 1 a , 1 b that provide mechanical fixation and electrical connection of the acceleration sensor to a mounting substrate or the like are mounted in the housing 1 . The lead electrodes 1a and 1b are used for electrical connection and fixation with an external circuit wiring board (not shown) by solder or the like.

As a material of the lead electrodes 1a and 1b, for example, phosphor bronze or the like is used, and the thickness thereof is set to, for example, 0.1 to 0.5 mm. In addition, in the acceleration sensor of this embodiment, the lead electrodes 1a, 1b are integrally formed with the housing 1 by insert molding.

The sealing resin 5 is formed so as to close the opening 1 h of the housing 1 , and as a material of the sealing resin 5 , for example, epoxy resin or the like is used.

2 is an external perspective view schematically showing the vibrating element 2 used in the acceleration sensor of this embodiment and the first support members 3 a and 3 b for sandwiching one end side of the vibrating element 2 .

FIG. 3 is a perspective view showing the vibrating element 2 from another angle, and shows the first supporting members 3 a and 3 b in perspective.

The vibrating element 2 adopts a structure in which a rectangular parallelepiped piezoelectric substrate 21 covered with a pair of conductive films 26 and 27 on both main surfaces and a rectangular parallelepiped piezoelectric substrate 21 covered with a pair of conductive films 28 and 29 on both main surfaces. The electric substrate 22 is bonded via an insulating adhesive. Conductor films 27 and 28 are insulated from each other by adhesive 23 . This configuration is generally referred to as "bimorph".

The piezoelectric substrates 21 and 22 are polarized in the thickness direction so that the respective polarization directions are opposite, and piezoelectric ceramic materials such as lead zirconate titanate or lead titanate can be used as the material. The piezoelectric substrates 21 and 22 are formed, for example, in a rectangular parallelepiped shape with a length of 0.5 to 5.0 mm, a width of 0.2 to 1.0 mm, and a thickness of 0.1 to 1.0 mm.

The following manufacturing method is employed in manufacturing the piezoelectric substrates 21 and 22 . The manufacturing method includes: (1) adding a binder to the raw material powder and pressing it into shape, or using a ball mill to mix and dry the raw material powder with water and a dispersant, and adding a binder, a solvent, and a plasticizer (2) The process of firing the molded body at a peak temperature of 1100°C to 1400°C for 10 minutes to several hours to form a substrate, (3) ) A step of applying a voltage of 3 kV/mm to 15 kV/mm at a temperature of, for example, 60° C. to 150° C. to perform polarization treatment in the thickness direction of the substrate.

The conductive films 26, 27, 28, and 29 coated on the two main surfaces of the piezoelectric substrates 21, 22 are made of metals with good conductivity such as gold, silver, copper, chromium, nickel, tin, lead, aluminum, etc. The material is formed on both main surfaces of the piezoelectric substrates 21, 22 by vacuum coating or spraying (sputtering) method, or a predetermined conductor paste containing the above-mentioned metal material is applied to a predetermined shape by a known printing method or the like. pattern and clad by firing together at high temperature. The thickness is preferably in the range of 0.1 to 3 μm.

The adhesive 23 for bonding the piezoelectric substrates 21 and 22 is made of insulating materials such as glass cloth base epoxy resin, inorganic glass, and epoxy resin.

In bonding with glass cloth base epoxy resin, piezoelectric substrates are stacked up and down, and a laminate material (pre-preg) impregnated with epoxy resin between glass fibers is sandwiched between them. Heating compresses the epoxy resin to a predetermined thickness and cures it.

In bonding with inorganic glass, after printing and applying glass paste, the piezoelectric substrates are superimposed and a load is applied, while heating at 300 to 700° C. using a firing furnace to melt and integrate them. At the time of firing, if the firing is performed in a vacuum furnace in advance, the inclusion of air bubbles in the glass bonding interlayer can be suppressed. In particular, when bonding is performed at a high temperature of 300° C. or higher, the polarization of the piezoelectric substrate needs to be re-polarized after bonding due to depolarization.

The first support members 3 a and 3 b are members for sandwiching the vibrator element 2 from both main surface sides thereof. The region of the vibrator element 2 sandwiched between the first support members 3a and 3b is referred to as a "support region 91". The region of the vibrating element 2 that is not sandwiched between the first supporting members 3a and 3b is referred to as a "free vibration region 92".

The length of the free vibration region 92 in the longitudinal direction (x direction) is longer than the length of the support region 91 in the longitudinal direction (x direction).

The modulus of elasticity of the first supporting members 3a and 3b is preferably in the range of 10 MPa to 10 GPa, particularly preferably in the range of 1 to 10 GPa.

As a material of the first supporting members 3a and 3b, for example, a silicone resin or an epoxy-based resin having an elastic modulus of about 6 GPa is suitably used. Also, the thickness thereof is preferably 20 to 100 μm. It is desirable that the width direction (y direction) of the first supporting members 3a, 3b spans the entirety of the vibrating element 2, and it is desired that the longitudinal direction (x direction) is at a distance from one end of the vibrating element 2 (where the first supporting members 3a, 3b are installed). The end portion) is formed within the range of 0.5 to 1.5mm.

Next, a method of forming such first support members 3a, 3b will be described. (1) First, prepare a piezoelectric plate having a portion to be a plurality of piezoelectric substrates 21, 22, and print resin, which is the material of the first supporting members 3a, 3b, by screen printing on a predetermined position on each main surface of the plate. paste and let it solidify. Screen printing can be repeated as many times as necessary, or the surface of the cured resin paste can be ground to obtain thickness accuracy. (2) Next, the position of the cured resin paste is confirmed, and the piezoelectric plate is cut using a dicing saw or the like to obtain the first supporting members 3a, 3b and the vibrating element 2 having a predetermined length. Thereby, the vibrating element 2 to which the first support members 3a, 3b are mounted can be obtained.

The shape of the vibration element 2 thus obtained is, for example, 3 mm in length, 0.5 mm in width, and 0.3 mm in thickness. The length of the support region 91 sandwiched between the first support members 3 a and 3 b is 1 mm, and the length of the free vibration region 92 not sandwiched between the first support members 3 a and 3 b is 2 mm. In addition, in the following description, one end of the vibrating element 2 (the end on the side sandwiched by the first support members 3a, 3b) will be referred to as a "fixed end", and the other end will be referred to as a "free end". ".

FIG. 4 is an external perspective view of the second support member 4 used in the acceleration sensor of this embodiment.

The second support member 4 is provided in the vicinity of the opening 1 h in the case 1 , sandwiches the outer sides of the first support members 3 a , 3 b of the resonator element 2 , and serves as a member that supports the resonator element 2 .

A through hole 4h into which the vibrating element 2 is inserted is provided in the second support member 4 . The vibrating element 2 is inserted into the through hole 4h from the free end, and is further clamped by the second support member 4 by pressing the first support members 3a, 3b mounted on the fixed end side into the through hole 4h. The outer sides of the first supporting members 3a, 3b can fix the vibrating element 2 in the housing 1 .

In the second supporting member 4, recesses 4a, 4b for potting conductive adhesive materials 6a, 6b described later are provided, and recesses 4a, 4b are provided for protruding through the inside of the housing 1. The holes through which the ends 7a, 7b of the leading electrodes 1a, 1b are exposed.

FIG. 5 is a perspective view showing the sealing resin 5 of the acceleration sensor shown in FIG. 1 without removing it.

Parts of the conductor films 26 and 27 formed on the piezoelectric substrates 21 and 22 are formed to extend to the lateral peripheral edges of the piezoelectric substrates 21 and 22 as shown in FIG. Electrode E".

As shown in FIG. 5 , the lead electrodes E are electrically connected to the ends 7a, 7b of the lead electrodes 1a, 1b via the conductive adhesive materials 6a, 6b in the recesses 4a, 4b of the second support member 4 . Accordingly, the output voltage generated between the conductor films 26, 27 and the conductor films 28, 29 is output to the outside from the guide electrodes 1a, 1b.

The conductive adhesives 6a and 6b are adhesives containing a conductive filler in the adhesive resin, and the conductive filler is desirably a highly conductive metal such as silver or copper. Since it is desired that the adhesive resin be cured at a temperature lower than 300° C. in order to eliminate depolarization of the piezoelectric substrates 21 and 22 , for example, an epoxy resin or the like is suitably used.

In addition, the conductive adhesive materials 6a, 6b are suppressed from spreading during potting by the recesses 4a, 4b.

Furthermore, resin bank 8a, 8b is provided from the surface of the 2nd support member 4 to a pair of 1st support member 3a, 3b. Bank dams 8a, 8b suppress the flow of conductive adhesive material 6a (6b) to reach conductive adhesive material 6b (6a), thereby preventing short circuit between lead electrodes 1a, 1b.

Fig. 6 is a sectional view taken along line A-A' of Fig. 1 . The second support member 4 is provided in the vicinity of the opening 1h in the case 1, and is integrally formed as a part of the case 1 using the same material as the case 1 . If formed integrally in this way, manufacture becomes easy. In addition, the second support member 4 may be manufactured separately from the case 1 and the second support member 4 may be fitted into the opening 1 h of the case 1 .

The second support member 4 has a length d of 0.5 to 1.5 mm in the longitudinal direction (x direction) of the vibrating element 2, and sandwiches the outer sides of the first support members 3a, 3b with the length d.

One of the characteristics of the pressure sensor of this embodiment is that the first supporting members 3a, 3b are formed of elastic bodies. As a result, the first supporting members 3 a and 3 b deform according to the force received from the vibrating element 2 , and the vibrating element 2 may bend not only in the free vibration region 92 but also in the supporting region 91 . In this case, the bending point P of the vibration element 2 is located in the support area 91 sandwiched between the first support members 3a and 3b, as shown in FIGS. 36 and 37 . Accordingly, strain due to the deflection of the vibrating element 2 also occurs in the piezoelectric substrates 21 and 22 located in the support region 91 .

Therefore, compared with the case where there is a bending point P at the boundary between the support region 91 and the free vibration region 92 ( FIG. 35 ) as in the conventional acceleration sensor, the strain-generating region in the piezoelectric substrates 21 and 22 increases, resulting in The charge increases, the output voltage increases, which can improve the detection sensitivity of acceleration.

Moreover, since the length of the free vibration region of the vibrating element 2 is not increased, the acceleration sensor will not be increased in size, and the width and thickness of the vibrating element 2 will not be reduced, so reliability problems caused by insufficient mechanical strength will not be caused. reduce.

An additional feature of the pressure sensor of this embodiment is that the elastic modulus of the second support member 4 is set to be larger than the elastic modulus of the first support members 3a, 3b. It is desirable that the modulus of elasticity of the second support member 4 is twice or more than the modulus of elasticity of the first support members 3a, 3b. By setting the modulus of elasticity of the second supporting member 4 higher than that of the first supporting members 3 a and 3 b in this way, deformation is less likely to occur in the second supporting member 4 .

If the modulus of elasticity of the second supporting member 4 is equal to or smaller than the modulus of elasticity of the first supporting members 3a, 3b, when an impact is applied to the acceleration sensor, the first supporting member 3a , 3b, the second support member 4 will be significantly deformed. As a result, the impact originally applied to the vibrating element 2 is absorbed by the second supporting member 4 . Therefore, the deformation of the vibrating element 2 is reduced, and the detection sensitivity of the acceleration is reduced.

In this embodiment, since the elastic modulus of the second supporting member 4 is set larger than that of the first supporting members 3a, 3b, an impact is directly applied to the vibrating element 2, and the deformation of the vibrating element 2 increases. , can prevent the reduction of the detection sensitivity of the acceleration.

It is desirable that the value of the modulus of elasticity of the second supporting member 4 is about 10 to 500 GPa, preferably about 20 to 500 GPa, and particularly preferably about 20 to 400 GPa.

Here, a method of measuring the modulus of elasticity of the material of the first supporting members 3a and 3b and the material of the second supporting member 4 will be described.

An example of the modulus of elasticity is "modulus of elasticity in flexure (flexural modulus) Ef". The so-called flexural modulus of elasticity Ef refers to, when the stresses corresponding to the strains ε1=0.0005 and ε2=0.0025 of the specified two points are set as σ1 and σ2 respectively, the difference of the stress (ε2-ε1) is divided by the difference of the strain (ε2-ε1) σ2-σ1), the value after

Ef＝(σ2-σ1)/(ε2-ε1)

The unit of the flexural modulus of elasticity Ef is MPa.

In this specification, if there is no special problem, it will be implemented based on the standard of JIS K7171. JIS K7171 is a standard equivalent to ISO 178; 1993 (Plastics-Determination of flexible properties). That is, a test piece is prepared using the same material as that of the member whose modulus of elasticity is to be measured, and its modulus of elasticity is measured. Basically, make a standard test piece with a length of 80.0mm, a width of 10.0mm, and a thickness of 4.0mm, and set the distance L between fulcrums to 64mm, set the radius R1 of the indenter to 5.0mm, and set the radius R2 of the support table to 5.0mm, and measure the flexural modulus Ef under the conditions of temperature 23°C and humidity 50%RH.

As the material of the second supporting member 4, ceramic materials such as alumina can be used, but liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK) and the like can also be suitably used. modulus of elasticity of the resin.

By using a resin that is easy to process as the material of the second support member 4 in this way, the second support member 4 having a desired modulus of elasticity and shape can be easily formed, and an acceleration sensor with high detection sensitivity can be easily obtained. .

When the vibrating element 2 fixed as above is subjected to a physical impact (acceleration) from the outside, the free vibrating region 92 not sandwiched by the first support members 3a, 3b bends and passes through the bonded piezoelectric substrate 21. , 22 to generate strain to generate charges, so that between the conductive films 26 and 27 covering the two main surfaces of the piezoelectric substrate 21 and between the conductive films 28 and 29 covering the two main surfaces of the piezoelectric substrate 22 A potential difference is generated between them, and this is taken out as an output voltage to detect acceleration.

In addition, in the acceleration sensor of this embodiment, as shown in FIGS. 4 and 5 , the vibrating element 2 is fixed so as to be inclined relative to the horizontal direction, so that not only the vertical direction but also the impact from the lateral direction can be sensed. Specifically, the angle θ formed by the mounting surface (x-y plane) of the case 1 and the surface perpendicular to the principal surface of the vibrating element 2 (the angle on the acute angle side) is set within a range of 20° to 50° depending on the application.

<Structure of acceleration sensor 2>

7 is a cross-sectional view schematically showing an acceleration sensor according to another embodiment of the present invention. In addition, in the acceleration sensor of this embodiment, only the point which differs from the above-mentioned embodiment is demonstrated, the same reference numeral is used for the same component, and overlapping description is abbreviate|omitted.

The characteristic part of the acceleration sensor shown in FIG. 7 is that the first supporting members 3 a and 3 b protrude toward the free end which is the region of the largest vibration amplitude of the vibrating element 2 relative to the second supporting member 4 .

By adopting such a shape, the portion (indicated by α) of the first supporting members 3a, 3b that is not sandwiched by the second supporting member 4 restricts the deflection of the vibrating element 2, and at the same time generates a certain Such a degree of deflection, so even at this portion, the vibrating element 2 is deflected.

In addition, in the vibrating element 2, due to the deflection starting from the end portion (indicated by P1 in FIG. 37 ) of the region sandwiched by the first support members 3a, 3b, and The deflection starting from the end of the region sandwiched by the second supporting member 4 (indicated by P2 in FIG. 37 ) both occurs, so the region where strain is generated in the piezoelectric substrate and the charge is generated increases, The generated charge increases and the output voltage increases, thereby improving the detection sensitivity of acceleration.

Furthermore, in the acceleration sensor of the present embodiment, in the above configuration, the modulus of elasticity of the first support members 3 a and 3 b is set to be smaller than the modulus of elasticity of the second support member 4 .

Therefore, the portion (α) of the first supporting members 3a, 3b that is not sandwiched by the second supporting member 4 becomes more easily deflected together with the vibrating element 2, and even in the region sandwiched by the second supporting member 4 Inside, the vibrating element 2 can also be deflected by deforming the first supporting members 3a and 3b by the force received from the vibrating element. This increases the area where charges are generated due to strain in the piezoelectric substrates 21 and 22 , the generated charges increase, the output voltage increases, and the detection sensitivity of acceleration can be improved.

<Structure of Acceleration Sensor 3>

8 schematically shows a vibrating element 2 used in an acceleration sensor according to still another embodiment of the present invention and a first support member 3a that sandwiches both main surfaces of one end portion of the vibrating element 2 in the longitudinal direction (x direction). , 3b appearance perspective view. It is shown in a state where the first support members 3a, 3b shown by dotted lines are transmitted through.

9 is an exploded perspective view schematically showing the vibrating element 2 and the first supporting members 3 a and 3 b shown in FIG. 8 .

10, 11, and 12 are perspective views schematically showing the piezoelectric substrate 21 constituting the vibrating element 2 shown in FIG. Top view, bottom view.

13, 14, and 15 schematically show other piezoelectric substrates 22 constituting the vibrating element 2 shown in FIG. Perspective view, top view, bottom view.

In addition, the conductive film 26 is composed of the charge detection electrode C26 and the extraction electrode E26, and the conductive film 27 is composed of the charge detection electrode C27 and the extraction electrode E27. The conductive film 28 is composed of the charge detection electrode C28 and the extraction electrode E28, and the conductive film 29 is composed of the charge detection electrode C29 and the extraction electrode E29.

As shown in FIGS. 10, 11, and 12, on the upper surface of the rectangular parallelepiped piezoelectric substrate 21, there is a free vibration region 92 that is a region sandwiched by the first support members 3a, 3b to a free vibration region 92 that is formed by the first support members 3a, 3b. The charge detection electrode C26 is arranged in the middle of the support region 91 which is the sandwiched region, and the extraction electrode E26 drawn from the charge detection electrode C26 is arranged in the support region 91 and exposed to one side of the piezoelectric substrate 21 .

Furthermore, on the lower surface of the piezoelectric substrate 21, a charge detection electrode C27 is disposed on the way from the free vibration region 92 to the support region 91, and the extraction electrode E27 drawn from the charge detection electrode C27 is disposed in the support region 91 and exposed to the piezoelectric substrate 91. The other side surface of the substrate 21 .

Furthermore, the charge detection electrodes C26 and C27 are arranged to face each other via the piezoelectric substrate 21. When strain occurs in the piezoelectric substrate 21, charges of different signs are generated in the charge detection electrodes C26 and 27 due to the piezoelectric effect. Thereby, a potential difference is generated between the charge detecting electrodes C26, 27. In addition, the extraction electrodes E26, 27 have the function of electrically connecting the charge detection electrodes C26, 27 to the outside of the vibrating element 2, respectively, and are arranged in such a manner that they do not face each other through the piezoelectric substrate 21, so as to prevent a gap between the extraction electrodes E26, 27. A large electrostatic capacitance is generated between them.

Similarly, as shown in FIGS. 13, 14, and 15, on another rectangular parallelepiped piezoelectric substrate 22, a charge detection electrode C28 is disposed on the way from the free vibration region 92 to the support region 91, and the charge detection electrode C28 leads out from the charge detection electrode C28. The extraction electrode E28 is arranged in the supporting region 91 and exposed to one side surface of the piezoelectric substrate 22 . Furthermore, on the lower surface of the piezoelectric substrate 22, a charge detection electrode C29 is disposed on the way from the free vibration region 92 to the support region 91, and the extraction electrode E29 drawn from the charge detection electrode C29 is disposed in the support region 91 and exposed to the piezoelectric substrate. 22 on the side of the other side.

Furthermore, the charge detection electrodes C28 and 29 are arranged to face each other via the piezoelectric substrate 22, and when strain occurs in the piezoelectric substrate 22, charges of different signs are generated in the charge detection electrodes C28 and 29 due to the piezoelectric effect. , thereby generating a potential difference between the charge detection electrodes C28, 29. In addition, the extraction electrodes E28, 29 have the function of electrically connecting the charge detection electrodes C28, 29 to the outside of the vibrating element 2, respectively, and are arranged in such a manner that they do not face each other through the piezoelectric substrate 22, thereby preventing any damage between the extraction electrodes E28, 29. A large electrostatic capacitance is generated between them.

In addition, the piezoelectric substrates 21, 22 are attached so that the charge detection electrodes C27, C28 face each other via the insulating adhesive material 23, the lead-out electrodes E26, E28 are exposed to one side surface of the vibration element 2, and the lead-out electrode E27 , E29 are exposed on the other side of the vibration element 2 .

As shown in FIG. 8, the supporting region 91 located at one end of the vibrating element 2 is sandwiched by the first supporting members 3a, 3b, and the first supporting members 3a, 3b are sandwiched by the second supporting member 4. The support region 91 of the vibration element 2 is supported to function as an acceleration sensor. That is, the free vibration region 92 of the vibrating element 2 is deflected by the applied acceleration, thereby generating strain in the piezoelectric substrates 21 and 22, and generating strain in the charge detection electrodes C26, 27, 28, and 29 due to the piezoelectric effect. Charges thereby generate a potential difference between the charge detection electrodes C26 and 27 and between the charge detection electrodes C28 and 29 . In this way, acceleration can be detected from the generated charge or voltage.

As described above, the modulus of elasticity of the first supporting members 3 a and 3 b is preferably about 10 MPa to 10 GPa, and the modulus of elasticity of the second supporting member 4 is preferably about 10 to 500 GPa.

The lead electrodes E26, 28 are exposed to one side of the piezoelectric substrates 21, 22, and are connected to the end of the lead electrode 1a protruding to the vicinity of one side of the vibrating element 2 in the case 1 through the conductive adhesive 6a. 7a is electrically connected. Further, the lead electrodes E27 and 29 are exposed to the other side of the piezoelectric substrates 21 and 22, and are connected to the guide electrode 1b protruding to the vicinity of the other side of the vibrating element 2 in the housing 1 via the conductive adhesive 6b. The end 7b is electrically connected.

Accordingly, output voltages generated between the charge detection electrodes C26 and 27 and between the charge detection electrodes C28 and 29 are output to the outside through the guide electrodes 1a and 1b.

In addition, since the vibrating element 2 is mechanically fixed on the main surface and electrically connected on the side surface, the space is effectively used, and thus a smaller acceleration sensor can be formed.

<Structure 4 of the acceleration sensor>

In the above-mentioned embodiment, the structure in which one end of the vibrating element in the longitudinal direction is sandwiched by the supporting member is adopted, but a structure in which both ends of the vibrating element are sandwiched by the supporting member may also be adopted. The member clamps the structure near the central portion of the vibrating element.

16 is a cross-sectional view schematically showing an acceleration sensor according to still another embodiment of the present invention. FIG. 17 is an external perspective view schematically showing the vibrating element 2 and the first supporting members 3 a and 3 b used in the acceleration sensor shown in FIG. 16 . 18, 19, and 20 are perspective views schematically showing the piezoelectric substrate 21 constituting the vibrating element 2 shown in FIG. , top view, bottom view. 21, 22, and 23 schematically show other piezoelectric substrates 22 constituting the vibrating element 2 shown in FIG. Perspective view, top view, bottom view.

In addition, in this embodiment, only the point which differs from the said example is demonstrated, the same reference numeral is used for the same component, and the overlapping description is abbreviate|omitted.

The characteristic part of the acceleration sensor of this embodiment is that both ends in the longitudinal direction of the vibrating element 2 serve as support regions 91 sandwiched between the first support members 3a, 3b and the second support member 4, and the central part serves as a free vibration region. Area 92. Further, the length in the longitudinal direction of the free vibration region 92 is longer than the length of each supporting region 91 , and the central portion in the longitudinal direction of the free vibration region 92 becomes the region with the largest amplitude. Also in this case, by arranging the charge detection electrodes C26, 27, 28, and 29 halfway from the free vibration region 92 to the support region 91, the acceleration detection sensitivity can be improved by the same mechanism as in the above-mentioned example.

<Structure 5 of the acceleration sensor>

24 is a cross-sectional view schematically showing an acceleration sensor according to still another embodiment of the present invention. FIG. 25 is an external perspective view schematically showing the vibrating element 2 and the first supporting members 3 a and 3 b used in the acceleration sensor shown in FIG. 24 . 26, 27, and 28 are perspective views schematically showing the piezoelectric substrate 21 constituting the vibrating element 2 shown in FIG. , top view, bottom view. 29, 30, and 31 schematically show other piezoelectric substrates 22 constituting the vibrating element 2 shown in FIG. Perspective view, top view, bottom view.

In addition, also in this embodiment, only the point which differs from the above-mentioned example is demonstrated, the same reference numeral is used for the same component, and overlapping description is abbreviate|omitted.

The characteristic part of the acceleration sensor of this embodiment is that the central portion in the longitudinal direction of the vibrating element 2 is a support region 91 sandwiched by the first support members 3a, 3b and the second support member 4, and the two sides are free. Vibration area 92 . In addition, in this case, both end portions in the longitudinal direction of the vibrating element 2 become regions of maximum amplitude. Also in this case, by arranging the charge detection electrodes C26, 27, 28, and 29 halfway from the free vibration region 92 to the support region 91, the acceleration detection sensitivity can be improved by the same mechanism as in the above-mentioned example.

<Manufacturing example>

Next, a manufacturing example of the acceleration sensor of the present invention will be described.

First, a binder was added to the raw material powder of lead zirconate titanate, pressed, and fired at a peak temperature of 1200° C. for 24 hours to obtain a piezoelectric body.

Then, the block is cut with a wire saw, and both sides are ground with a lapping machine to produce piezoelectric mother substrates that become piezoelectric substrates once divided. The thickness of the piezoelectric mother substrate was set to be 100 μm.

Next, metal thin films divided to become conductor films 26 to 29 were formed on both main surfaces of the piezoelectric mother substrate by using a sputtering apparatus. Each metal thin film has a two-layer structure of chromium and silver, and after forming a chromium thin film with a thickness of 0.3 μm, a silver thin film is formed thereon with a thickness of 0.3 μm.

Next, the piezoelectric mother substrate was put into the polarization tank, and a voltage of 300V was applied for 10 seconds to perform polarization treatment on the piezoelectric mother substrate in the thickness direction.

Then, after forming a resist pattern on the surface of the metal thin film by the screen printing method, the metal thin film was dipped into an etching solution to form a pattern of the metal thin film, and then dipped in toluene to remove the resist layer.

Next, two piezoelectric mother substrates with metal thin film patterns formed on both main surfaces are placed in a vacuum oven, and a laminate material of epoxy resin containing glass fibers is sandwiched between them and bonded together, and a load is applied. And they were bonded by keeping under the condition of 180 degreeC for 2 hours. In addition, when laminating two piezoelectric mother substrates, the directions of polarization of the two piezoelectric substrates are opposite to each other.

Next, an epoxy resin to be the first supporting members 3 a and 3 b was applied to predetermined positions on the piezoelectric mother board using a screen printer, and was cured by holding at 150° C. for 2 hours.

Then, use a dicing saw to divide the piezoelectric mother substrate into individual pieces, and simultaneously obtain a plurality of vibration elements, as shown in FIG. 2.

Next, a housing 1 made of LCP (Liquid Crystal Polymer) including lead electrodes 1a, 1b made of phosphor bronze by insert molding, and a second support member 4 integrally formed near the opening 1h is prepared, as shown in FIG. 5 and 6, the vibrating element 2 covered with the first supporting members 3a, 3b is press-fitted into the through-hole 4h of the second supporting member 4 and fixed.

Next, as shown in FIG. 5 , use a dispenser (dispenser) to coat the vicinity of the central portion of the upper surface of the exposed first support members 3a, 3b and the vicinity of the central portion of the lower surface of the first support member 3b, respectively. The dams 8a, 8b, and the two sides of the vibrating element 2 exposed in the recesses 4a, 4b of the second support member 4 are coated with conductive adhesive materials 6a, 6b made of epoxy resin and silver filler, and Hold at 200° C. for 30 minutes to make it harden.

Then, as shown in FIG. 1, a sealing resin 5 made of epoxy resin is applied to the opening 1h of the case 1 using a dispenser to cover the vibrating element 2, the first support members 3a, 3b, the bank 8a, 8b, the conductive adhesives 6a, 6b and the second support portion 4 are kept at 150° C. for 2 hours to be cured to complete the acceleration sensor.

The electric characteristics were evaluated by applying a shock to the acceleration sensor produced in this way, and it was confirmed that the acceleration sensor had better characteristics than conventional ones.

<Simulation example 1>

32 , 33 , and 34 are diagrams showing simulation examples using the finite element method performed to confirm the effect of improving the pressure detection sensitivity of the acceleration sensor of the present invention.

The distribution of charges generated on the surface of the vibrating element 2 when an impact is applied to the acceleration sensor is indicated by a white area. Regions with a higher density of generated charges appear whiter.

In addition, in these simulations, the length of the vibrating element 2 is 3 mm, the width is 0.5 mm, and the thickness is 0.3 mm. The length of the support region 91 sandwiched by the first support members 3 a and 3 b is 1 mm. 1 The length of the free vibration region 92 sandwiched between the supporting members 3a and 3b is 2 mm, and the thickness of the supporting member 1 is 30 μm.

33 is a graph showing the simulation results of the acceleration sensor of the present invention shown in FIGS. 1 to 6. The left side of the dotted line is the support region 91, and the right side of the dotted line is the free vibration region 92. The modulus of elasticity of the first supporting member is 4GPa. , let the elastic modulus of the second supporting member be 500GPa.

32 is a diagram showing simulation results of a conventional acceleration sensor for comparison. The left side of the dotted line is the support region 91 , and the right side of the dotted line is the free vibration region 92 . The elastic modulus of the support member is 500 GPa.

In the conventional acceleration sensor shown in FIG. 32 , charges are generated almost only in the free vibration region 92 and are concentrated in the vicinity of the support region 91 . This means that no strain occurs in the piezoelectric substrates 21 , 22 in the support region 91 , that is, no deflection occurs in the vibrating element 2 in the support region 91 . It also shows that in the free vibration region 92 of the vibration element 2, the strain generated in the piezoelectric substrates 21, 22 becomes larger as it gets closer to the support region 91. On the contrary, almost no strain occurs near the free end of the vibration element 2, which can be considered as Caused by the difference in torque applied to each area. And it can be considered that the vicinity of the free end of the vibrating element is almost only functioning as a lead sinker.

In contrast, in the acceleration sensor of the present invention shown in FIG. 33 , charges are generated even in the vicinity of the free vibration region 92 in the support region 91 . This means that strain is also generated in the piezoelectric substrates 21 and 22 in the support region 91 , that is, the vibrating element 2 is deflected in the support region 91 . This is considered to be because the first supporting members 3a, 3b are made of elastic body and have a smaller modulus of elasticity than the second supporting member 4, so that the first supporting members 3a, 3b are easily vibrated by the force received from the vibrating element 2. deformation, so that the vibrating element 2 can be deflected even in the support region 91 .

35 , 36 , and 37 are partial cross-sectional views schematically showing states of deformation of the vibration element 2 in the acceleration sensor of the present invention and in a conventional acceleration sensor.

It can be considered that in the conventional acceleration sensor shown in FIG. 35, the deflection of the vibrating element 2 mainly occurs in a very limited range represented by L0 in the free vibration region 92, while in the conventional acceleration sensor shown in FIG. 36 In the acceleration sensor, the deflection of the vibrating element 2 occurs in a wide range indicated by L1 from the middle of the support region 91 to the free vibration region 92, and thus the simulation results shown in FIGS. 32 and 33 are obtained.

In this way, in the acceleration sensor of the present invention, since charges are also generated in a part of the supporting region 91, compared with the conventional acceleration sensor, since the generation region of charges in the vibrating element 2 becomes wider, the charge generated in the vibrating element 2 becomes larger. The charge amount is increased, so that the acceleration detection sensitivity can be improved without changing the size of the vibrating element 2 and without reducing the mechanical strength of the vibrating element 2 .

In the acceleration sensor of the present invention shown in FIGS. 1 to 6 , Table 1 shows the detection sensitivity to acceleration when the modulus of elasticity of the first support members 3a, 3b and the modulus of elasticity of the second support member 4 are changed. (Amount of charge generated at the charge detection electrode per acceleration of 1G) is the result of the simulation. In addition, various conditions other than the modulus of elasticity in this simulation were set as described above.

[Table 1] Modulus of elasticity of the first supporting member Modulus of elasticity of the second supporting member Modulus of elasticity of the supporting member Charge Sensitivity (pC/G) (GPa) (GPa) size relationship 3 3 1st = 2nd 0.282 3 30 No. 1 < No. 2 0.311 3 300 No. 1 < No. 2 0.313 30 3 No. 1 > No. 2 0.267 30 30 1st = 2nd 0.283 30 300 No. 1 < No. 2 0.287 300 3 No. 1 > No. 2 0.251 300 30 No. 1 > No. 2 0.260 300 300 1st = 2nd 0.269

In Table 1, when the modulus of elasticity of the first support member 3a, 3b is 3GPa, as the modulus of elasticity of the second support member 4 increases to 3GPa, 30GPa, 300GPa, the charge sensitivity also increases to 0.282, 0.311, 0.313. Similarly, when the modulus of elasticity of the first support members 3 a and 3 b is 30 GPa and 300 GPa, the charge sensitivity increases as the modulus of elasticity of the second support member 4 increases. From this, it can be seen that the charge sensitivity improves with an increase in the modulus of elasticity of the second supporting member 4 .

Furthermore, when the modulus of elasticity of the second support member 4 is 3 GPa, the charge sensitivity deteriorates to 0.282, 0.267, and 0.251 as the modulus of elasticity of the first support members 3a, 3b increases to 3GPa, 30GPa, and 300GPa. Similarly, when the modulus of elasticity of the second support member 4 is 30 GPa or 300 GPa, the charge sensitivity deteriorates as the modulus of elasticity of the first support members 3 a and 3 b increases. From this, it can be seen that the charge sensitivity is improved by decreasing the modulus of elasticity of the first supporting members 3a, 3b.

Furthermore, when the charge sensitivities in Table 1 are arranged from the smaller values, 0.251, 0.26, 0.267, 0.269, 0.282, 0.283, 0.287, 0.311, 0.313, 0.251, 0.26, 0.267 are the values of the first supporting members 3a, 3b. The charge sensitivity when the elastic modulus is larger than the elastic modulus of the second supporting member 4 (first > second), 0.269, 0.282, and 0.283 are the elastic modulus of the first supporting members 3a, 3b and the second supporting member The charge sensitivity when the elastic modulus of 4 is equal (1st = 2nd), 0.287, 0.311, 0.313 is the case where the elastic modulus of the first supporting member 3a, 3b is smaller than the elastic modulus of the second supporting member 4 Lower (1st<2nd) charge sensitivity. From this result, it can be confirmed that the dominant influence on the charge sensitivity is the magnitude relationship between the elastic modulus of the first supporting members 3a, 3b and the elastic modulus of the second supporting member 4, and by placing the first supporting members 3a, 3b The modulus of elasticity is set smaller than the modulus of elasticity of the second supporting member 4, thereby improving the detection sensitivity of acceleration.

34 shows the distribution of charges generated on the surface of the vibrating element 2 when an impact is applied to the acceleration sensor having a structure in which the first supporting members 3a and 3b shown in FIG. 7 protrude toward the free end more than the second supporting member 4 The simulation results.

In Fig. 34, the left side of the dotted line on the left side is the area sandwiched by the first support members 3a, 3b and the second support member 4, and the area between the left and right dotted lines is only supported by the first support member 4. In the region sandwiched by the members 3a and 3b, the free vibration region 92 is located on the right side of the dotted line on the right side.

In addition, in this simulation, the modulus of elasticity of the first support members 3 a and 3 b is set to 4 GPa, and the modulus of elasticity of the second support member 4 is set to 500 GPa, as in the case of FIG. 33 .

As can be seen from comparison with FIG. 33 , the region where charges are generated is further enlarged compared with the acceleration sensor having the structure shown in FIGS. 1 to 6 . That is, as in FIG. 37 schematically shows the deformation of the vibrating element 2 in the acceleration sensor of the structure shown in FIG. Generated within, so that the charge generation area is further widened.

Moreover, in the acceleration sensor with the structure shown in FIG. There is almost no deformation, and there is no problem that "the deformation of the vibration element 2 is suppressed by the deformation of the second supporting member 4, so that the detection sensitivity of the acceleration decreases".

38 is a graph showing simulation results showing changes in acceleration detection sensitivity when the protrusion amount α of the first supporting members 3 a and 3 b relative to the second supporting member 4 is changed in the acceleration sensor shown in FIG. 7 . In addition, β represents the length from the end faces of the first supporting members 3 a and 3 b to the free end of the vibrating element 2 .

In this graph, the horizontal axis represents the ratio of the protruding amount of the first supporting members 3a, 3b to the length from the end surface of the second supporting member 4 to the free end of the vibrating element 2 (α/(α+β in FIG. 7 )), and the vertical axis represents the detection sensitivity of acceleration (the amount of charge generated in the charge detection electrode per acceleration of 1G).

In addition, in this simulation, the length of the vibrating element 2 is set to 3 mm, the width to 0.5 mm, and the thickness to 0.3 mm, the thickness of the supporting member 1 is set to 30 μm, and the modulus of elasticity of the second supporting member 4 is set to 300 GPa. The length of the region sandwiched by the second supporting member 4 was calculated as 1 mm.

From this simulation, it was confirmed that, as shown in FIG. 38 , the acceleration detection sensitivity can be improved by protruding the first supporting members 3 a and 3 b toward the free end side with respect to the second supporting member 4 .

In particular, it can be seen that the acceleration detection sensitivity is higher when the first support members 3 a and 3 b are 1 GPa than when they are 10 GPa. In addition, as is clear from the graph shown in FIG. 38 , the detection sensitivity of acceleration can be further improved by desirably protruding the first support members 3 a , 3 b relative to the second support member 4 in a range of 5 to 10%.

<Simulation example 2>

39 is a diagram schematically showing the result of simulation of the distribution of charges generated on the surface of the vibrating element 2 when acceleration is applied to the acceleration sensor having the configuration shown in FIGS. 1 to 6 using the finite source method. Regions with higher densities of generated charges are shown by denser hatching.

In this simulation, the length of the vibrating element 2 is 3 mm, the width is 0.5 mm, and the thickness is 0.3 mm. The length of the support region 91 sandwiched by the first support members 3 a and 3 b is 1 mm. The length of the free vibration region 92 sandwiched between the members 3a and 3b is 2 mm, and the thickness of the first supporting members 3a and 3b is respectively 30 μm. Furthermore, the modulus of elasticity of the first support members 3 a and 3 b is set to 4 GPa, and the modulus of elasticity of the second support member 4 is set to 500 GPa.

In addition, in the drawing, the left side of the dotted line is the support region 91 , and the right side of the dotted line is the free vibration region 92 .

As can be seen from the results shown in FIG. 39 , it was confirmed that charges were generated not only in the free vibration region 92 but also in the portion close to the free vibration region 92 in the support region 91 . This means that strain is also generated in the piezoelectric substrate in the support region 91 , and the vibrating element 2 is deflected even in the support region 91 .

Furthermore, it was also confirmed that, on the contrary, in the tip portion of the free vibration region 92 or the portion on the opposite side of the free vibration region 92 in the support region 91, the vibration element 2 does not bend, and therefore no strain is generated in the piezoelectric substrate. , resulting in almost no charge.

In the acceleration sensor having the electrode structure shown in FIGS. 8 to 15 , charge detection electrodes C26 facing each other are arranged via piezoelectric substrates 21 and 22 on the way from the free vibration region 92 of the vibrating element 2 to the support region 91 . , 27, 28, 29. That is, the charge detection electrodes C26, 27, 28, and 29 are arranged in the part close to the free vibration region 92 in the support region 91, and the charge detection electrodes C26, 27, 29 are not arranged in the part far from the free vibration region 92 in the support region 91. 28, 29.

Since the charge detection electrodes C26, 27, 28, and 29 are also arranged in the part close to the free vibration area 92 in the support area 91, in addition to the charges generated in the free vibration area 92, the approach in the support area 91 is free. The charge generated in the part of the vibration region 92 is also attracted to the charge detection electrodes C26, 27, 28, 29, so that the amount of charge accumulated in the charge detection electrodes C26, 27, 28, 29 increases, and between the charge detection electrodes C26, 27 and The potential difference generated between the charge detection electrodes C28, 29 also increases. Since the charge and voltage generated by the applied acceleration increase, an acceleration sensor with high acceleration detection sensitivity can be obtained.

Moreover, since the charge detection electrodes C26, 27, 28, and 29 are not arranged in the part of the support region 91 far away from the free vibration region 92, if the charge detection electrode C26 is also arranged in the part of the support region 91 far from the free vibration region 92 , 27, 28, and 29, the areas of the charge detection electrodes C26, 27, 28, and 29 are reduced, thereby reducing the capacitance between the charge detection electrodes C26, 27 and between the charge detection electrodes C28, 29.

In addition, even if the charge detection electrodes C26, 27, 28, and 29 are not arranged in the part of the support region 91 away from the free vibration region 92, the charge detection electrodes C26 and 27 are arranged in the part of the support region 91 far from the free vibration region 92. , 28, 29, the charges accumulated in the charge detection electrodes C26, 27, 28, 29 hardly decrease.

Therefore, the potential difference generated between the charge detection electrodes C26 and 27 and between the charge detection electrodes C28 and 29 increases, and an acceleration sensor having high sensitivity (voltage sensitivity) when detecting an applied acceleration by a voltage can be obtained.

FIG. 40 shows the detection of acceleration when the amount γ of protrusion of the charge detection electrodes C26, 27, 28, and 29 into the support region 91 is changed in the acceleration sensor having the electrode structure shown in FIGS. 8 to 15. A graph of the results of a simulation of the variation in sensitivity.

In this graph, the horizontal axis represents the ratio of the protruding amount γ of the charge detection electrodes C26, 27, 28, and 29 into the support region 91 to the length δ of the free vibration region 92 of the vibrating element 2 (shown in FIGS. 10 to 15 ). The ratio γ/δ of γ to δ), and the vertical axis represents the voltage sensitivity (the voltage generated between the charge detection electrodes C26, 28 and the charge detection electrodes C27, 29 per acceleration of 1G). In addition, in this simulation, the length of the vibrating element 2 is set to 3 mm, the width to 0.5 mm, and the thickness to 0.3 mm, the length of the support region 91 is set to 1 mm, the length of the free vibration region 92 is set to 2 mm, and the first support member The thicknesses of 3a and 3b are 30 μm, and the elastic modulus of the second support member 4 is calculated as 300 GPa.

From the graph shown in FIG. 40, it can be confirmed that the degree varies depending on the modulus of elasticity of the first support members 3a, 3b, but it can be improved by extending the charge detection electrodes C26, 27, 28, 29 to the middle of the support region 91. voltage sensitivity.

Furthermore, the optimum value of the protrusion amount γ of the charge detection electrodes C26, 27, 28, and 29 into the support region 91 increases when the elastic modulus of the first support members 3a, 3b is small, and accordingly, the optimum value of The voltage sensitivity also tends to increase. This is considered to be because the first supporting members 3a, 3b are easily deformed by the force received from the vibrating element 2 when the elastic modulus of the first supporting members 3a, 3b becomes smaller, so that the vibration in the supporting region 91 The amount of deflection of the element 2 increases, and the region where the strain is generated in the piezoelectric substrates 21 and 22 in the support region 91 , that is, the region where the charge is generated, expands. Furthermore, it is preferable that the ratio of the projection amount γ of the charge detection electrodes C26, 27, 28, and 29 into the support region 91 to the length δ of the free vibration region 92 is in the range of 15 to 30%, and it can be confirmed that the acceleration can be further improved. detection sensitivity.

And, according to the acceleration sensor of this example, since the elastic modulus of the first supporting members 3a, 3b on the side contacting the vibrating element 2 is set smaller than the elastic modulus of the second supporting member 4, the acceleration can be further improved. detection sensitivity. That is, since the first support members 3a, 3b have a smaller elastic modulus than the second support member 4, the first support members 3a, 3b are easily deformed by the force received from the vibrating element 2, thereby supporting the region 91 The vibrating element 2 inside becomes easily deflected. Therefore, the region where strain occurs in the piezoelectric substrates 21 and 22 in the supporting region 91 increases, thereby increasing generated charges and output voltage, and further improving the detection sensitivity of acceleration. Furthermore, since the modulus of elasticity of the second supporting member 4 is set larger than that of the first supporting members 3 a and 3 b , deformation is less likely to occur in the second supporting member 4 . By making the second supporting member 4 less likely to deform, it is possible to suppress the second supporting member 4 from being significantly deformed and absorbing the shock when an impact is applied to the acceleration sensor, thereby suppressing the detection of "acceleration due to the reduced deformation of the vibrating element 2." Sensitivity drops."

Furthermore, according to the acceleration sensor of the present invention, the vibrating element 2 is laminated with the piezoelectric substrates 21, 22 in the thickness direction, and between the piezoelectric substrates 21, 22, the charge detection electrodes C26, C26, Charge detection electrodes C27 and 28 are also disposed in such a way that 29 faces each other. As a result, charges are generated in the charge detection electrodes C26, 27, 28, and 29 arranged on both main surfaces of the piezoelectric substrates 21, 22 according to the applied acceleration. , since the amount of charge generated in the entire vibration element 2 increases, the charge sensitivity can be improved.

Furthermore, according to the acceleration sensor of the present invention, in each of the piezoelectric substrates 21, 22, the first lead-out electrodes E26, 28 drawn out from the charge detection electrodes C26, 28 to one side surface are respectively arranged on one main surface, and Second extraction electrodes E27 and 29 drawn from the charge detection electrodes C27 and 29 to the other side surface are arranged on the other main surface. Thus, even in a structure in which the piezoelectric substrates 21, 22 are stacked in the thickness direction and the charge detection electrodes C27, 28 are arranged between the layers, all the charge detection electrodes C26, 27, 28, 29 can be connected via the extraction electrodes. E26, 27, 28, 29 are connected to the conductive adhesive 6a, 6b on both sides of the vibrating element 2, and then all the charge detection electrodes C26, 27, 28, 29 can be connected to each other via the guide electrodes 1a, 1b. External electrical connection for the accelerometer. Therefore, since there is no need to form via holes (via holes) or the like for electrically connecting the charge detection electrodes C27, 28 positioned between the layers to the outside in the vibrating element 2, an acceleration with a simple structure and a simplified manufacturing process can be obtained. sensor. Moreover, the lead-out electrodes E26, 27, 28, and 29 can be connected to the conductive adhesives 6a, 6b on both sides of the vibrating element 2. By exposing the end faces and connecting the end faces of the vibration element 2 to the conductive adhesives 6a, 6b, the distance between the conductive adhesives 6a, 6b can be increased. Thereby, the possibility of electric short circuit occurring between the 1st extraction electrode E26, 28 and the 2nd extraction electrode E27, 29 by the flow of the conductive adhesive 6a, 6b before hardening can be reduced.

In addition, this invention is not limited to the said embodiment, Various changes and improvements are possible in the range which does not deviate from the summary of this invention.

For example, in the example of the above-mentioned embodiment, a bimorph-shaped vibrating element in which two piezoelectric substrates are laminated is used, but more piezoelectric substrates may be stacked, or a single-body transistor may be used instead. (monomorph)-shaped or unimorph-shaped vibration element. In the case of a monomorph type, it is sufficient to reverse the polarization of the piezoelectric substrate in the thickness direction. In the case of a unimorph type, it is sufficient to cover one main surface of the piezoelectric substrate with a vibrating plate made of metal or the like. .

In the example of the embodiment described above, as shown in FIG. 9 , two charge detection electrodes C27 and 28 connected to mutually different potentials are arranged in a laminated body in which two piezoelectric substrates 21 and 22 are laminated. As for the configuration between the piezoelectric substrates 21 and 22, as shown in FIG. 41, a configuration in which the charge detection electrode C30 is arranged between the layers of the two piezoelectric substrates may also be employed. In this case, the charge detection electrodes C26 and 29 arranged on the outer main surfaces of the piezoelectric substrates 21 and 22 may be connected to the same potential so that the directions of polarization of the two piezoelectric substrates 21 and 22 are the same.

In addition, in the example of the above-mentioned embodiment, the structure in which both main surfaces of the vibrating element 2 are sandwiched by the first supporting members 3a, 3b is adopted, but only one main surface of the vibrating element 2 may be bonded using an adhesive or the like. The surface is fixed to the supporting member to support the vibrating element 2 .

In addition, in the example of the above-mentioned embodiment, the first support members 3a and 3b are formed by being divided into two parts 3a and 3b, but they may be integrally formed so as to surround the upper, lower, and side surfaces of the vibrating element 2 .

In addition, in the example of the above-mentioned embodiment, the support members are constituted by two members of different materials, the first support members 3a, 3b and the second support member 4, but the support member may be composed of a single material depending on circumstances. However, compared with the case where the elastic modulus of the first supporting members 3 a and 3 b is set to be smaller than that of the second supporting member 4 , it is considered that the detection sensitivity of the acceleration is lowered to some extent.

<disk device>

Fig. 42 is a perspective view showing the internal structure of the magnetic disk device.

The magnetic disk device (hereinafter referred to as HDD) has a rectangular box-shaped case 40 with an open top.

Housing 40 houses: a plurality of magnetic disks 41 as magnetic recording media; a spindle motor 43 that supports and rotates these magnetic disks 41; a magnetic head 42 that records/reproduces information on the magnetic disks 41; supports and positions the magnetic heads 42. head regulator (actuator) 45; circuit substrate 44 and the like. The acceleration sensor S of the present invention for detecting acceleration applied to the HDD is mounted on the circuit board 44 .

Furthermore, in the circuit board 44, as shown in FIG. 43 , include: an A/D conversion circuit 46 that converts an analog signal from the acceleration sensor S into a digital signal; 42 control circuit 47 for judging avoidance.

The acceleration sensor S constantly monitors the acceleration applied to the HDD, and the acceleration data is converted into a digital value by the A/D conversion circuit 46 and supplied to the control circuit 47 . The control circuit 47 compares the acceleration data with a preset threshold, and when it is judged that the acceleration data exceeds the threshold, sends an avoidance signal to the magnetic head actuator 45 to avoid the magnetic head 42 . Accordingly, when a strong acceleration is applied to the HDD during reading and writing of data, the magnetic head 42 can be dodged, and failure of the HDD can be prevented before failure occurs.

Claims (14)

1. An acceleration sensor comprising: a vibrating element in which mutually opposing charge detection electrodes are arranged on both principal surfaces of a rectangular parallelepiped piezoelectric substrate; and a first support member supporting the vibrating element, The vibrating element includes: a support area supported by contacting the first support member; and a free vibration area that is longer in the longitudinal direction than the support area and is not supported by the first support member, The first support member is made of elastic body. 2. The acceleration sensor according to claim 1, characterized in that, The bending point of the vibrating element is located in the support area. 3. The acceleration sensor according to claim 1, characterized in that, The modulus of elasticity of the first support member is 10 MPa to 10 GPa. 4. The acceleration sensor according to claim 1, characterized in that, further comprising a second support member supporting the first support member from a direction perpendicular to both principal surfaces of the piezoelectric substrate, The modulus of elasticity of the first support member is smaller than the modulus of elasticity of the second support member. 5. The acceleration sensor according to claim 4, characterized in that, The modulus of elasticity of the first support member is 10 MPa to 10 GPa, and the modulus of elasticity of the second support member is 10 GPa to 500 GPa. 6. The acceleration sensor according to claim 1, characterized in that, further comprising a second support member supporting the first support member from a direction perpendicular to both principal surfaces of the piezoelectric substrate, The first supporting member protrudes further toward a region of the vibrating element having a maximum vibration amplitude than the second supporting member. 7. The acceleration sensor according to claim 6, characterized in that, In the longitudinal direction of the vibrating element, when the length of the first support member protruding beyond the second support member is α, and the length of the free vibration region is β, 0.05≤α/(α+ β)≤0.1. 8. The acceleration sensor according to claim 1, characterized in that, The charge detection electrodes are arranged on the two main surfaces of the vibrating element, in the free vibration region and in the supporting region, which are close to the free vibration region. 9. The acceleration sensor according to claim 8, characterized in that, In the longitudinal direction of the vibrating element, when the length of the part where the charge detection electrode is arranged in the support region is γ, and the length of the free vibration region is δ, 0.15≤γ/δ≤0.3. 10. The acceleration sensor according to claim 1, characterized in that, A plurality of the piezoelectric substrates of the vibrating element are laminated in a thickness direction, and a charge detection electrode is disposed between the piezoelectric substrates so as to face the charge detection electrode via the piezoelectric substrate. . 11. The acceleration sensor according to claim 1, characterized in that, For each of the plurality of piezoelectric substrates, a first extraction electrode drawn from the charge detection electrode to one side surface is arranged on one main surface, and a first extraction electrode drawn from the charge detection electrode is arranged on the other main surface. The electrodes are led out to the second lead-out electrodes on the other side surface. 12. A magnetic disk device equipped with the acceleration sensor according to claim 1 for detecting an acceleration applied to the magnetic disk device. 13. The magnetic disk device according to claim 12, having: disk; a head for writing data to and reading data from the disk; and A head regulator that supports the head and performs its positioning. 14. The magnetic disk device according to claim 12, comprising: an A/D conversion circuit that converts an analog signal from the acceleration sensor into a digital signal; and A control circuit that makes a decision to avoid the magnetic head based on a signal from the A/D conversion circuit.

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