JP2007010377A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor of small size with high acceleration detection sensitivity and reliability. <P>SOLUTION: This acceleration sensor is equipped with a vibration element made by disposing principal surface electrodes on two principal surfaces of a strip-like piezoelectric substrate and support members for sandwiching a part thereof. The support members are made of elastic bodies. A bend point of the vibration element is positioned in a support area where the vibration element is sandwiched between the support members. Because of this, an area of the piezoelectric substrate where strain is developed is enlarged, generated electric charge increases to increase an output voltage, and acceleration detection sensitivity can be enhanced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an acceleration sensor, and more particularly to a small and highly sensitive acceleration sensor.

  Conventionally, acceleration sensors have been used for applications such as detecting external impacts on electronic devices such as hard disk drives, and both ends of vibration elements with main surface electrodes formed on both main surfaces of a strip-shaped piezoelectric substrate. An acceleration sensor of a type in which a main surface is sandwiched between support members is known. (For example, see Patent Document 1).

In such an acceleration sensor, the piezoelectric element is distorted by bending of the vibration element due to the applied acceleration, and a potential difference is generated between the main surface electrodes formed on both main surfaces of the piezoelectric substrate due to charges generated by the piezoelectric effect. The acceleration is detected by taking this out as an output voltage.
JP 2000-32299 A (FIG. 1)

  However, in the conventional acceleration sensor as described above, it is necessary to increase the length of the vibration element or reduce the width and thickness of the vibration element in order to improve the detection sensitivity of acceleration. For example, the output voltage V generated when an acceleration force F is applied to an acceleration sensor in which one end of a bimorph type vibration element in which two piezoelectric substrates are bonded together is sandwiched by a support member is expressed by the piezoelectric constant of the piezoelectric substrate as D When the length of the portion of the vibration element not sandwiched by the support member (length of the free region) is L, the width of the vibration element is W, and the thickness of the vibration element is T, V = (3/2) · D L / (W · T) · F, which is proportional to the length L of the free region of the vibration element and inversely proportional to the width W and thickness T of the vibration element. Therefore, in order to improve the acceleration detection sensitivity of the acceleration sensor, it is necessary to increase the length L of the free area of the vibration element and reduce the width W and thickness T of the vibration element. An increase in the length L causes an increase in the size of the acceleration sensor, and a decrease in the width W and the thickness T of the vibration element causes a problem that the mechanical strength is lowered and the reliability is lowered.

  The present invention has been devised in view of the problems in the conventional techniques as described above, and an object of the present invention is to provide a small acceleration sensor with high acceleration detection sensitivity and reliability.

  The acceleration sensor according to the present invention is an acceleration sensor comprising: a vibration element in which main surface electrodes are arranged on both main surfaces of a strip-shaped piezoelectric substrate; and a support member that sandwiches a part of the vibration element. The member is made of an elastic body, and the bending point of the vibration element is located in a support region sandwiched by the support member.

  According to the acceleration sensor of the present invention, in the above configuration, the support member is disposed so that the inner side is in contact with both main surfaces of the vibration element, and the first support member sandwiches the vibration element. A second support member that is in contact with the outside of the member and sandwiches the first support member, and the elastic modulus of the first support member may be smaller than the elastic modulus of the second support member. .

  Furthermore, the acceleration sensor of the present invention comprises a support member and main surface electrodes arranged on both main surfaces of the strip-shaped piezoelectric substrate, and a support region in which both main surfaces of the piezoelectric substrate are sandwiched by the support member, and An acceleration sensor comprising a vibration element having a maximum amplitude region in which the amplitude of flexural vibration is maximized, wherein the support member is disposed so that the inner surfaces thereof are in contact with both main surfaces of the vibration element, and holds the vibration element. A first support member and a second support member that is in contact with the outside of the first support member and sandwiches the first support member, and the first support member has an amplitude of the vibration element with respect to the second support member. It is characterized by extending toward the maximum area.

Furthermore, the acceleration sensor of the present invention may be configured such that, in the above configuration, the elastic modulus of the first support member is smaller than the elastic modulus of the second support member.

  In the acceleration sensor of the present invention, the support member is made of an elastic body, and the bending point of the vibration element is located in the support region sandwiched by the support member. Here, the bending point is a boundary between a portion where the vibration element is bent and a portion where the bending is not generated. By positioning the bending point in the support region, the piezoelectric substrate positioned in the support region is also distorted by the bending of the vibration element. Therefore, compared to the case where a bending point exists at the boundary between the support region and the free region as in the conventional acceleration sensor, the region where the distortion occurs in the piezoelectric substrate becomes larger, and the generated charge increases and the output voltage increases. In addition, the acceleration detection sensitivity can be increased. Further, since the length of the free region of the vibration element is not increased, the acceleration sensor is not increased in size, and the width and thickness of the vibration element are not decreased, so that reliability is not deteriorated due to insufficient mechanical strength.

  The acceleration sensor according to the present invention has a first support member that is arranged so that the inner surfaces thereof are in contact with both main surfaces of the vibration element and sandwiches the vibration element, and a first contact member that is in contact with the outer side of the first support member. The support portion may be configured from the second support member that sandwiches the support member, and the elastic modulus of the first support member may be smaller than the elastic modulus of the second support member, thereby increasing the detection sensitivity of acceleration. it can. The reason is considered as follows. That is, since the first support member has a smaller elastic modulus than the second support member, the first support member is easily deformed by the force received from the vibration element, and the vibration element is bent in the support region. As a result, the piezoelectric substrate located in the support region is also distorted by the bending of the vibration element. This causes distortion in the piezoelectric substrate as compared with the case where a bending point exists at the boundary between the support region and the free region as in the conventional acceleration sensor, that is, when the bending starts from the boundary between the support region and the free region. The area becomes larger, the generated charge increases, the output voltage increases, and the acceleration detection sensitivity can be increased. In addition, since the elastic modulus of the second support member is set to be larger than that of the first support member, the second support member is hardly deformed, and the deformation of the second support member causes the vibration element 2 to be deformed. The problem that the deformation is suppressed and the acceleration detection sensitivity is reduced does not occur.

  In the acceleration sensor of the present invention, the support member is arranged so that the inner side is in contact with both main surfaces of the vibration element, the first support member sandwiching the vibration element, and the first support member in contact with the outer side of the first support member. The second support member sandwiches the support member, and the first support member extends toward the maximum amplitude region of the vibration element with respect to the second support member. Here, the maximum amplitude region is a region where the amplitude of flexural vibration is maximum in the vibration element. When the vicinity of one end in the longitudinal direction of the vibration element is used as the support region, the vicinity of the other end is the vibration element. When the vicinity of the center in the longitudinal direction is the support region, the vicinity of both ends is the maximum amplitude region, and when the vicinity of both ends of the vibration element is the support region, the vicinity of the center is the maximum amplitude region. According to such an acceleration sensor of the present invention, the portion of the first support member that is not sandwiched between the second support members bends to some extent together with the vibration element while restricting the bending of the vibration element. Also, the bending of the vibration element occurs. In the vibration element, the bending starts from the end of the region sandwiched by the first support member, and the end of the region sandwiched by the second support member in addition to the first support member starts. Since both the bending and the bending occur, a region where distortion occurs in the piezoelectric substrate is increased, the generated charge is increased, the output voltage is increased, and the acceleration detection sensitivity can be increased.

  Furthermore, the acceleration sensor according to the present invention is sandwiched by the second support member in the first support member when the elastic modulus of the first support member is smaller than the elastic modulus of the second support member in the above configuration. The unsupported portion can be more easily bent with the vibration element, and the first support member can be easily deformed by the force received from the vibration element even in the region sandwiched by the second support member, and the vibration element can be bent. As a result, the region where distortion occurs in the piezoelectric substrate is further increased, the generated charge is increased, the output voltage is increased, and the acceleration detection sensitivity can be increased. In addition, since the elastic modulus of the second support member is set to be larger than that of the first support member, the second support member is hardly deformed, and the deformation of the second support member causes the vibration element 2 to be deformed. The problem that the deformation is suppressed and the acceleration detection sensitivity is reduced does not occur.

  Hereinafter, the acceleration sensor of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an external perspective view schematically showing an acceleration sensor according to an embodiment of the present invention. The acceleration sensor shown in the figure generally has a structure in which a vibration element 2 is housed in a case 1 having lead electrodes 1a and 1b, and an opening 1h is sealed with a sealing resin 5. .

  The rectangular parallelepiped case 1 for housing the vibration element 2 is a container body having an opening 1h on one end side, and examples of the material include liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK). ) Etc. are used.

  Lead electrodes 1a and 1b are attached to the case 1, and are electrically connected and fixed to an external circuit wiring board by solder or the like. The lead electrodes 1a and 1b are made of, for example, phosphor bronze, and the thickness thereof is set to 0.1 to 0.5 mm, for example. In the acceleration sensor of this embodiment, the lead electrodes 1a and 1b are integrally formed with the case 1 by insert molding.

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

  FIG. 2 is an external perspective view schematically showing the vibration element 2 used in the acceleration sensor of the present embodiment and the first support members 3a and 3b that sandwich one end side of both main surfaces of the vibration element 2. FIG. FIG. 3 is a perspective view illustrating the first support members 3a and 3b in FIG. The vibration element 2 shown in the figure includes a strip-shaped piezoelectric substrate 21 having a pair of main surface electrodes 21a and 21b attached to both main surfaces, and a strip having a pair of main surface electrodes 22a and 22b attached to both main surfaces. A piezoelectric substrate 22 is bonded to each other via an adhesive 23 and has a structure generally called a bimorph shape.

  The piezoelectric substrates 21 and 22 are polarized in the thickness direction, and are made of, for example, a piezoelectric ceramic material such as lead zirconate titanate or lead titanate. The dimensions are 0.5 to 5.0 mm in length and width. Is set to a strip shape having a thickness of 0.2 to 1.0 mm and a thickness of 0.1 to 1.0 mm.

  The piezoelectric substrates 21 and 22 are manufactured by adding a binder to the raw material powder and pressing it, or mixing and drying the raw material powder with water and a dispersant using a ball mill, and adding a binder, a solvent, a plasticizer, and the like. A step of forming a sheet by a method such as molding by a doctor blade method, a step of baking at a peak temperature of 1100 ° C. to 1400 ° C. for several tens of minutes to several hours, and forming a substrate, for example, 60 ° C. to 150 ° C. A manufacturing method including a step of applying a polarization treatment by applying a voltage of 3 kV / mm to 15 kV / mm at a temperature is employed.

  The main surface electrodes 21a, 21b, 22a, 22b attached to both main surfaces of the piezoelectric substrates 21, 22 are made of, for example, highly conductive materials such as gold, silver, copper, chromium, nickel, tin, lead, and aluminum. These metal materials are deposited and formed on both main surfaces of the piezoelectric substrates 21 and 22 by a conventionally known vacuum deposition or sputtering method, or a predetermined conductor containing the above-described metal material. The paste is applied to a predetermined pattern by a conventionally known printing method or the like, and is applied and formed by baking at a high temperature.

  The adhesive 23 for bonding the piezoelectric substrates 21 and 22 is made of an insulating material such as a glass cloth base epoxy resin, inorganic glass, or epoxy resin, or a conductive material such as a conductive adhesive or a metal sheet. In bonding with a glass cloth base epoxy resin, a piezoelectric substrate is superimposed on the top and bottom with a prepreg material impregnated with an epoxy resin between glass fibers, and heated while being pressed to a predetermined thickness. Compress and cure. In joining with inorganic glass, glass paste is printed and applied, and then superposed and melted and integrated using a firing furnace while applying a load. In a baking furnace, it is heated to 300 to 700 ° C. If firing is performed in a vacuum furnace, mixing of bubbles in the glass bonding intermediate layer can be suppressed. When bonding is performed at a high temperature of 300 ° C. or higher, the polarization of the piezoelectric substrate is depolarized. Therefore, it is necessary to perform polarization processing after bonding.

  The elastic modulus of the first support members 3a and 3b is preferably about 10 MPa to 10 GPa, and particularly preferably about 1 to 10 GPa. Therefore, as the material of the first support members 3a and 3b, for example, an epoxy resin having an elastic modulus of about 6 GPa is preferably used. Further, the thickness is 20 to 100 μm, the width direction is formed over the entire vibration element 2, and the length direction is formed over a range of 0.5 to 1.5 mm from one end of the vibration element 2. . In forming the first support members 3a and 3b, first, a sheet in which two piezoelectric mother substrates to be the piezoelectric substrates 21 and 22 are joined is prepared, and screen printing is performed at predetermined positions on both main surfaces of the sheet. Print and cure the resin paste with If necessary, screen printing may be repeated a plurality of times, or the surface of the cured resin paste may be polished to obtain thickness accuracy. Then, while confirming the position of the cured resin paste, the first support members 3a, 3b and a vibrating element 2 are cut using a dicing saw or the like so that the vibration elements 2 are obtained. The vibration element 2 to which 3b is attached can be obtained.

  The shape of the vibration element 2 obtained in this way is, for example, a length of 3 mm, a width of 0.5 mm, a thickness of 0.3 mm, a length of the support region sandwiched between the first support members 3a and 3b, and a first support member. The length of the free region not sandwiched between 3a and 3b is 2 mm. In the following description, one end of the vibration element 2 (the end on the side sandwiched between the first support members 3a and 3b) is referred to as a fixed end, and the other end is referred to as a free end.

  As described above, the first support members 3a and 3b are formed of an elastic body, and the bending point of the vibration element 2 is positioned in the support region sandwiched between the first support members 3a and 3b. The piezoelectric substrates 21 and 22 located in the region are also distorted by the bending of the vibration element 2. Therefore, compared to the case where a bending point exists at the boundary between the support region and the free region as in the conventional acceleration sensor, the region where the distortion occurs in the piezoelectric substrate becomes larger, and the generated charge increases and the output voltage increases. In addition, the acceleration detection sensitivity can be increased. In addition, since the length of the free region of the vibration element 2 is not increased, the acceleration sensor is not increased in size, and the width and thickness of the vibration element 2 are not decreased, so that reliability is deteriorated due to insufficient mechanical strength. Absent.

  FIG. 4 is an external perspective view of the second support member 4 used in the acceleration sensor of the present embodiment. The second support member 4 is provided with a through-hole 4h into which the vibration element 2 is inserted, and outside of the first support members 3a and 3b attached to one end portions of both main surfaces of the inserted vibration element 2. The vibration element 2 is supported by sandwiching. The elastic modulus of the second support member 4 is larger than the elastic modulus of the first support members 3a and 3b, and the value is preferably about 10 to 500 GPa, particularly about 20 to 400 GPa. Therefore, as the material of the second support member 4, a liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), or a ceramic material such as alumina is used. Further, the second support member 4 is configured to sandwich the outside of the first support member with a length of 0.5 to 1.5 mm in the longitudinal direction of the vibration element 2. The second support member 4 is provided in the vicinity of the opening 1 h in the case 1. However, if the second support member 4 is integrally formed as a part of the case 1 using the same material as the case 1, manufacturing becomes easy. Further, recesses 4a and 4b for potting conductive adhesive materials 6a and 6b, which will be described later, are provided. In the recesses 4a and 4b, lead electrodes 1a and 1b extending through the inside of the case 1 are provided. The end portions 7a and 7b are exposed.

  By inserting the vibration element 2 described above into the through hole 4h of the second support member 4 from the free end side and press-fitting the first support members 3a and 3b attached to the fixed end side into the through hole 4h. The outer sides of the first support members 3 a and 3 b that sandwich both main surfaces of the vibration element 2 are further sandwiched by the second support member 4 and fixed to the case 1.

  In the vibration element 2 fixed in this way, when a physical impact is applied from the outside, the free region not sandwiched between the first support members 3a and 3b is bent, and the bonded piezoelectric substrates 21 and 22 are distorted. As a result, electric charges are generated, and a potential difference is generated between the main surface electrodes 21a and 21b applied to both main surfaces of the piezoelectric substrate 21 and between the main surface electrodes 22a and 22b applied to both main surfaces of the piezoelectric substrate 22. The acceleration is detected by taking this as an output voltage.

  The vibration element 2 is fixed so as to be inclined with respect to the horizontal direction, and can sense not only the vertical direction but also an impact from the horizontal direction. Specifically, an angle formed by a surface perpendicular to the main surface serving as the mounting surface of the case 1 and the main surface of the vibration element 2 (an angle on an acute angle side) is 20 to 50 ° depending on the application. Set by range.

  5 is a view excluding the sealing resin of the acceleration sensor shown in FIG. 1, and FIG. 6 is a cross-sectional view taken along the line A-A 'of FIG.

  Part of the main surface electrodes 21 a, 21 b, 22 a, and 22 b extends to the side peripheral edges of the piezoelectric substrates 21 and 22, and this extended portion extends in the case 1 to the vicinity of the side surface of the vibration element 2. Since the lead electrodes 1a and 1b are electrically connected to the end portions 7a and 7b through the conductive adhesives 6a and 6b, the main surface electrodes 21a and 21b and the main surface electrodes 22a and 22b are connected. The generated output voltage is output to the outside from the lead electrodes 1a and 1b. Since the vibration element 2 is fixed on the main surface and is electrically connected on the side surface, the fixed region of the vibration element 2 is efficiently reduced, and the acceleration sensor is made smaller. The conductive adhesives 6a and 6b are attached to the recesses 4a and 4b, and the spread when potting is performed is suppressed.

  Resin weirs 8a and 8b are provided from a predetermined region on the surface of the second support member 4 on the opening 1h side of the case 1 to a predetermined region on the surface of the pair of first support members 3a and 3b on the opening 1h side of the case 1. Even if the conductive adhesives 6 a and 6 b formed near one side surface of the vibration element 2 flow, the flowed conductive adhesive materials 6 a and 6 b reach the other side surface of the vibration element 2. Is suppressed, and occurrence of a short circuit between the lead electrodes 1a and 1b is reduced.

  In the pressure sensor of the present embodiment, the elastic modulus of the first support members 3a and 3b is smaller than the elastic modulus of the second support member 4, and therefore the force that the first support members 3a and 3b receive from the vibration element 2 It is possible to easily deform the vibrating element 2 in the support region, and the electric charge due to the distortion of the piezoelectric substrate is generated in the support region, and the deformation of the second support member is suppressed, and the acceleration caused thereby is reduced. Since the detection sensitivity does not decrease, the acceleration detection sensitivity can be increased.

  FIGS. 7A and 7B show the vibration element 2 when a shock is applied to the acceleration sensor in the simulation by the finite element method performed to confirm the effect of increasing the pressure detection sensitivity of the acceleration sensor of the present invention. FIG. 6 is a diagram showing the distribution of charges generated on the surface of the film, and the region where the density of generated charges is higher is displayed in white. In these simulations, the length of the vibration element 2 is 3 mm, the width is 0.5 mm, the thickness is 0.3 mm, the length of the support region sandwiched between the first support members 3a and 3b is 1 mm, and the first support is provided. The length of the free region not sandwiched between the members 3a and 3b was 2 mm, and the thickness of the support member 1 was 30 μm. FIG. 7B is a diagram showing a simulation result of the acceleration sensor according to the present embodiment. The left side of the broken line is a support region sandwiched between the first support members 3a and 3b and the second support member 4 and the broken line. The right side is a free region, and the elastic modulus of the first support member is 4 GPa and the elastic modulus of the second support member is 500 GPa. FIG. 7A is a diagram showing a simulation result of a conventional acceleration sensor for comparison. The left side of the broken line is a support area sandwiched by the support member, and the right side of the broken line is a free area. The elastic modulus of the support member is 500 GPa.

  In the conventional acceleration sensor shown in FIG. 7A, electric charges are generated almost only in the free region and are concentrated in the vicinity of the support region. This indicates that no distortion occurs in the piezoelectric substrates 21 and 22 within the support region, that is, no deflection occurs in the vibration element 2 within the support region. In addition, the distortion generated in the piezoelectric substrates 21 and 22 in the free region of the vibration element 2 is larger in the vicinity of the support region, and conversely, almost no distortion is generated in the vicinity of the free end of the vibration element 2. This is thought to be due to the difference in the moment of force applied to the place. The vicinity of the free end of the vibration element seems to function only as a weight.

  On the other hand, in the acceleration sensor of the present embodiment shown in FIG. 7B, electric charges are generated even in the vicinity of the free region in the support region sandwiched between the first and second support members. This indicates that the piezoelectric substrates 21 and 22 in the support region are also distorted, that is, the vibration element 2 is also bent in the support region. This is because the first support members 3 a and 3 b have a smaller elastic modulus than the second support member 4, and thus the first support members 3 a and 3 b are easily deformed by the force received from the vibration element 2, so It is thought that this is because the vibration element 2 can be bent.

  FIG. 8 is a partial cross-sectional view schematically showing the deformation state of the vibration element 2 in the acceleration sensor of the present invention and the conventional acceleration sensor. In the conventional acceleration sensor shown in FIG. 8A, the vibration element 2 is mainly bent in a very limited range indicated by L0 in the free region, whereas in FIG. In the acceleration sensor of this embodiment shown in FIG. 7, since the bending of the vibration element 2 occurs in a wide range indicated by L1 from the middle of the support area to the free area, the acceleration sensor shown in FIGS. It is thought that the simulation result was obtained.

  As described above, in the acceleration sensor according to the present embodiment, charges are generated even in a part of the support region. Therefore, the charge generation region in the vibration element 2 is wider than that in the conventional acceleration sensor. Since the amount of generated charges increases, the acceleration detection sensitivity can be increased without changing the size of the vibration element 2 and without reducing the mechanical strength of the vibration element 2.

In the acceleration sensor according to the present embodiment, the detection sensitivity of the acceleration when the elastic modulus of the first support members 3a and 3b and the elastic modulus of the second support member 4 are changed (the amount of charge generated in the main surface electrode per 1G acceleration). Table 1 shows the result of simulating the change in (). Various conditions other than the elastic modulus in this simulation are as described above. It was confirmed that the acceleration detection sensitivity was improved by decreasing the elastic modulus of the first support members 3a and 3b and increasing the elastic modulus of the second support member 4.

  FIG. 9 is a cross-sectional view similar to FIG. 6 schematically showing an acceleration sensor according to another embodiment of the present invention. In the acceleration sensor of the present embodiment, only differences from the above-described embodiment will be described, and the same components will be denoted by the same reference numerals and redundant description will be omitted.

  The characteristic part of the acceleration sensor shown in FIG. 9 is that the first support members 3 a and 3 b are extended toward the maximum amplitude region of the vibration element 2, that is, the free end with respect to the second support member 4. is there. By adopting such a shape, the portions of the first support members 3a and 3b that are not sandwiched between the second support members 4 are bent to some extent together with the vibration elements while restricting the bending of the vibration elements. In this case, the vibration element is bent. Further, in the vibration element, the second support member 4 is sandwiched in addition to the bending starting from the end of the region sandwiched by the first support members 3a and 3b and the first support members 3a and 3b. As a result, both the deflection starting from the end of the region where the current occurs and the piezoelectric substrate are distorted, the region where charges are generated increases, the generated charges increase, the output voltage increases, and the acceleration Detection sensitivity can be increased.

  Furthermore, the acceleration sensor according to the present embodiment has the above-described configuration in which the elastic modulus of the first support members 3a and 3b is smaller than the elastic modulus of the second support member 4, so that the first support member The portions of 3a and 3b that are not sandwiched by the second support member 4 are more easily bent together with the vibration element 2, and the first support is also provided by the force received from the vibration element even in the region sandwiched by the second support member 4. The members 3a and 3b are deformed and the vibration element 2 can be bent. As a result, a region where electric charges are generated due to distortion in the piezoelectric substrates 21 and 22 is further increased, the generated electric charges are increased and the output voltage is increased, and the acceleration detection sensitivity can be further increased.

FIG. 7C is a simulation result showing a distribution of electric charges generated on the surface of the vibration element 2 when an impact is applied to the acceleration sensor shown in FIG. 9. The region sandwiched between the members 3a and 3b and the second support member 4, the region between the left and right broken lines is the region sandwiched only by the first support members 3a and 3b, and the right side is freer than the right broken line. It is an area. In this simulation, the elastic modulus of the first support members 3a and 3b is 4 GPa and the elastic modulus of the second support member 4 is 500 GPa, as in the case of FIG. As is clear from comparison with FIG. 7B, it can be seen that the region where charges are generated is further increased as compared with the acceleration sensor of the above-described embodiment. That is, FIG. 8C schematically shows a state of deformation of the vibration element 2 in the acceleration sensor of the present embodiment. The bending of the vibration element 2 over a wide range as indicated by L2 in FIG. It is considered that the generation region of electric charges has become wider due to the occurrence.

  Moreover, in the acceleration sensor of the present embodiment, since the elastic modulus of the second support member 4 is set larger than the elastic modulus of the first support members 3a and 3b, the second support member 4 is hardly deformed. There is no problem that the deformation of the vibration element 2 is suppressed by the deformation of the second support member 4 and the detection sensitivity of the acceleration is reduced.

  FIG. 10 is a graph showing simulation results showing changes in acceleration detection sensitivity when the extension amounts of the first support members 3a and 3b relative to the second support member 4 are changed in the acceleration sensor shown in FIG. In this graph, the horizontal axis indicates the amount of extension of the first support members 3a and 3b (La / Lb in FIG. 9), and the vertical axis indicates the acceleration detection sensitivity (the amount of charge generated in the main surface electrode per 1G of acceleration). ). In this simulation, the length of the vibration element 2 is 3 mm, the width is 0.5 mm, the thickness is 0.3 mm, the thickness of the support member 1 is 30 μm, the elastic modulus of the second support member 4 is 300 GPa, and the second support. The length of the region sandwiched between the members 4 was calculated as 1 mm. From this simulation, it was confirmed that the acceleration detection sensitivity could be increased by extending the first support members 3a and 3b toward the free end side with respect to the second support member 4. As is apparent from the graph shown in FIG. 10, the acceleration detection sensitivity is further increased by setting the extension amount of the first support members 3a and 3b to the second support member 4 in the range of 5 to 10%. be able to.

  In addition, this invention is not limited to embodiment mentioned above, A various change and improvement are possible in the range which does not deviate from the summary of this invention.

  For example, in the above-described embodiment, is a bimorph type vibration element in which two piezoelectric substrates are bonded together, but a larger number of piezoelectric substrates may be laminated, or conversely, a monomorph type may be used.

  In the above-described embodiment, the structure in which the vicinity of one end in the longitudinal direction of the vibration element is sandwiched by the support member is used. However, the structure may be such that both ends of the vibration element are sandwiched by the support member. A structure in which the vicinity of the center portion is sandwiched between the support members may be used.

  Furthermore, in the above-described embodiment, the first support member is divided into two parts 3a and 3b. However, the first support member may be integrally formed so as to surround the upper and lower surfaces and side surfaces of the vibration element 2.

1 is an external perspective view schematically showing an acceleration sensor according to an embodiment of the present invention. It is an appearance perspective view showing typically a vibration element used for an acceleration sensor concerning one embodiment of the present invention. It is the external appearance perspective view which saw through the 1st support member of the vibration detection element of FIG. It is an external appearance perspective view which shows typically the 2nd supporting member used for the acceleration sensor which concerns on one Embodiment of this invention. FIG. 2 is a diagram excluding a sealing resin of the acceleration sensor shown in FIG. 1. FIG. 2 is a cross-sectional view taken along line A-A ′ of FIG. 1. It is a figure which shows the simulation result of the distribution of the electric charge which generate | occur | produces on the surface of the vibration element 2 when an impact is given to an acceleration sensor. 3 is a partial cross-sectional view schematically showing how a vibration element 2 is deformed. FIG. It is sectional drawing which shows typically the acceleration sensor which concerns on other embodiment of this invention. It is a graph which shows the simulation result of the change of the detection sensitivity of an acceleration when the extension amount of the 1st support member is changed in the acceleration sensor which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Case 1a, 1b ... Lead electrode 1h ... Opening part 2 ... Vibrating element 21,22 ... Piezoelectric substrate 21a, 21b, 22a, 22b ... Main surface electrode 23 ... Adhesive 3a, 3b ... 1st support member 4 ... 2nd support member 4a, 4b ... Recess 4h ... Through-hole 5 ... Resin for sealing 6a, 6b ... Conductive adhesion Material 7a, 7b ... End of lead electrode 8a, 8b ... Resin weir

Claims (4)

In an acceleration sensor including a vibration element in which main surface electrodes are arranged on both main surfaces of a strip-shaped piezoelectric substrate, and a support member that sandwiches a part of the vibration element,
The acceleration sensor according to claim 1, wherein the support member is made of an elastic body, and a bending point of the vibration element is located in a support region sandwiched by the support member.   The support member is disposed so that the inner surfaces thereof are in contact with both main surfaces of the vibration element, and sandwiches the vibration element. The first support member is in contact with the outer side of the first support member and sandwiches the first support member. The acceleration sensor according to claim 1, further comprising: a second support member configured such that an elastic modulus of the first support member is smaller than an elastic modulus of the second support member. The main surface electrodes are arranged on both main surfaces of the support member and the strip-shaped piezoelectric substrate, and the main region of the piezoelectric substrate is sandwiched by the support member and the amplitude at which the amplitude of the flexural vibration is maximized. In an acceleration sensor comprising a vibration element having a maximum area,
The support member is disposed so that the inner surfaces thereof are in contact with both main surfaces of the vibration element, and sandwiches the vibration element. The first support member is in contact with the outer side of the first support member and sandwiches the first support member. An acceleration sensor, wherein the first support member extends toward the maximum amplitude region of the vibration element with respect to the second support member.   The acceleration sensor according to claim 3, wherein an elastic modulus of the first support member is smaller than an elastic modulus of the second support member.

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