JPH07318578A - Acceleration sensor and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a compact acceleration sensor which has a superior shock resistance and has a high sensitivity over a wide frequency by supporting a piezoelectric vibrator with a support via a conductive protrusion consisting of metal or ceramic being formed by performing flame spraying to the piezoelectric vibrator. CONSTITUTION:A piezoelectric vibrator 100 is provided with a bimorph piezoelectric element 1 which is formed by laminating a plate consisting of a piezoelectric material such as a piezoelectric ceramic plate 2 as a piezoelectric element. An electrode 4 is formed on the opposing main surface of each piezoelectric ceramic plate 2. A protrusion 3 consisting of molybdenum is mounted onto the electrode 4 in a line at the center of the opposing surface of the bimorph piezoelectric element 1 by the flame spraying method. The piezoelectric vibrator 100 is supported via a conductive protrusion. The conductive protrusion is superb in mechanical strength, can stably fix the piezoelectric vibrator 100, and has an improved shock resistance. Also, by supporting the piezoelectric vibrator 100 at the center, an edge part can be freely vibrated like a piezoelectric vibrator in cantilever structure, thus detecting the vibration at a high frequency region with a high sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor used for measuring acceleration, detecting vibration, and the like, and a manufacturing method thereof. More specifically, the present invention relates to a small and high-performance acceleration sensor and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller, and portable electronic devices such as notebook personal computers have become popular. In order to secure / improve the reliability of these electronic devices against impact, there is an increasing demand for small and high-performance acceleration sensors. For example, if a shock is applied during a write operation to a high-density hard disk, the head will be displaced. As a result, a data write error or head damage may occur. Therefore, it is necessary to detect the impact applied to the hard disk, stop the writing operation, and retract the head to a safe position.

Conventionally, as an acceleration sensor, one using a piezoelectric material such as a piezoelectric ceramic is known. These acceleration sensors can realize high detection sensitivity by utilizing the electromechanical conversion characteristics of the piezoelectric material. The piezoelectric type acceleration sensor converts a force due to acceleration or vibration into a voltage by a piezoelectric effect and outputs the voltage. As such an acceleration sensor, there is a cantilever type rectangular bimorph element as disclosed in Japanese Patent Laid-Open No. 2-248086. In the cantilever structure, as shown in FIG. 12, one end of the piezoelectric vibrator 11 having a bimorph structure is attached with a conductive adhesive 15
It is fixed with adhesive. The bimorph element having a cantilever structure has a low resonance frequency and is used for measuring acceleration having a relatively low frequency component. Also,
When measuring acceleration in a high frequency region, a rectangular bimorph element in which both ends of a piezoelectric vibrator 11 having a bimorph structure are fixed to a fixing member 13 with an adhesive 15 or the like as shown in FIG. By fixing both ends of the piezoelectric vibrator, the resonance frequency can be made relatively high.

[0004]

The above-mentioned cantilever structure acceleration sensor has high sensitivity to vibrations in a low frequency range, but it is difficult to detect vibrations in a high frequency range and has shock resistance. Has the disadvantage of being inferior to. On the other hand, the double-supported beam acceleration sensor has a wide frequency range that can be detected.
Although it has high impact resistance, it has a problem that sensitivity is low and miniaturization is difficult.

Further, in order to stabilize the sensitivity of the rectangular bimorph piezoelectric element, its resonance frequency must be stabilized. For that purpose, the fixed state must be stable, but in actuality it shifts to the part supported or fixed by a supporting member or fixing member such as metal due to stress generated mechanically or by temperature change. Occurs. For example, when fixing using an adhesive, the fixing position changes depending on the application range of the adhesive. Also, the fixing state changes due to the temperature change of the adhesive,
There are problems such as difficulty in obtaining a stable fixed state.

In order to obtain a stable fixed state of the piezoelectric element,
As disclosed in Japanese Patent Laid-Open No. 59-70923, a method of forming a cantilever structure by providing a slit in the central portion of a bimorph piezoelectric diaphragm and fixing the peripheral portion of the bimorph piezoelectric diaphragm has been adopted. There is. In this method, the area of the supporting portion other than the cantilever structure portion formed by the slit that contributes to the detection of acceleration is large, and the size of the entire element is large,
It is difficult to manufacture a small acceleration sensor.

In order to improve the sensitivity to acceleration, the displacement gradient at the supporting point has a finite value, rather than being completely fixed so that the displacement gradient of the piezoelectric element caused by vibration becomes zero at the fixed point. In this way, even if the same acceleration is applied, a large distortion is generated in the piezoelectric element, so that the output sensitivity is increased. However, as described above, in the conventional method, it is difficult to realize a stable supporting state, the state between supporting and fixing is easily changed depending on the manufacturing conditions, the variation of the resonance frequency of the piezoelectric element becomes large, and the acceleration There is a problem in that the variation in sensitivity with respect to is large.

Japanese Utility Model Laid-Open No. 5-23617 discloses a holding structure for a piezoelectric resonator, in which a rectangular parallelepiped metal projection is formed on the surface of a piezoelectric vibrator and a piezoelectric element is held through the projection. is doing. Unlike the acceleration sensor, the piezo-resonator of Japanese Utility Model Laid-Open No. 5-23617 is an element that utilizes the resonance phenomenon of the vibrator, and the metal protrusion is provided at the position of the vibration node so as not to hinder the resonance. Actual Kaihei 5-2
No. 3617 discloses a method such as brazing, welding, welding, or bonding as a method for forming the rectangular parallelepiped metal projection.

When the metal projection is formed by brazing, welding, or welding, the piezoelectric vibrator is heated to a high temperature when the projection is formed, so that the characteristics of the piezoelectric vibrator deteriorate. In particular, since piezoelectric ceramics have a low Curie temperature and low heat resistance, they are said to have large characteristic deterioration when exposed to high temperatures. The Curie temperature of the piezoelectric ceramic material used for the piezoelectric vibrator is 250 to
It is about 350 ° C. Half of the Curie temperature (Celsius)
When the piezoelectric vibrator is heated to the above temperature, that is, 125 to 175 ° C. or higher, the characteristics of the piezoelectric vibrator are significantly deteriorated. Therefore, when the projection is formed on the piezoelectric vibrator by a method involving heating at high temperature such as brazing or soldering, the characteristics of the piezoelectric vibrator are significantly deteriorated. FIG. 14 shows a change in piezoelectric constant when a piezoelectric ceramic having a Curie temperature of 300 ° C. is heated for 1 hour. The horizontal axis of FIG. 14 represents the heating temperature, and the vertical axis represents the normalized piezoelectric constant. It can be seen from FIG. 14 that the piezoelectric constant does not change when heated up to 140 ° C., but the piezoelectric constant decreases at higher temperatures. Although not shown in the figure, the higher the heating temperature, the shorter the piezoelectric constant in a short time. When the projection is actually formed on the piezoelectric vibrator by a method such as brazing or soldering, the characteristics of the piezoelectric vibrator are deteriorated.

Further, when the metal projection is formed on the piezoelectric vibrator by using an adhesive, the adhesive sticks out beyond the bonding surface between the piezoelectric vibrator and the projection, and the sticking-out of the adhesive does not occur. Since they are not constant, there is a problem that both characteristic variation and characteristic deterioration are large.

In principle, it is possible to form metal projections by plating without involving high temperatures. However, since it takes a long time to form a thick projection by plating, only a projection having a thickness of about several μm can be practically formed. When a piezoelectric vibrator made of piezoelectric ceramic is held through such a low-height protrusion, the surface of the piezoelectric ceramic has irregularities of 3 to 5 μm.
Even with a slight inclination, the piezoelectric vibrator comes into contact with a support or the like that supports the protrusion. When the piezoelectric vibrator comes into contact with other members, the position of the portion supporting the piezoelectric vibrator is equivalent to moving, and therefore the length from the supporting portion to the tip of the piezoelectric vibrator changes. As a result, the resonance frequency of the piezoelectric vibrator changes and the frequency characteristic also changes. Even when a protrusion is formed by printing using an organic material such as a conductive paste, it is difficult to form a thick protrusion as in the case of plating, and it has the same problem as plating. Further, since the protrusion formed by printing has low mechanical strength and low adhesion strength, it is difficult to stably hold the piezoelectric vibrator.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a small acceleration sensor which is excellent in impact resistance and has high sensitivity over a wide frequency range.

[0013]

An acceleration sensor of the present invention is a piezoelectric element having first and second main surfaces facing each other, and first and second piezoelectric elements formed on the first and second main surfaces. Two
And a piezoelectric vibrator having conductive projections made of metal or ceramic formed by thermal spraying on the first and second electrodes, and supporting the piezoelectric vibrator through the conductive projections. And a support for
The above object can be achieved.

The conductive protrusion may be formed at a central portion in the longitudinal direction of the piezoelectric vibrator.

The supporting body has a supporting member having a spring property, and the piezoelectric vibrator is supported by the supporting portion via at least one of the conductive protrusions on the first and second electrodes. It may have been done.

The piezoelectric vibrator may be press-fitted into the support, and may be supported by the support via the conductive protrusion of the piezoelectric vibrator.

The support may have a support portion made of a material having a hardness lower than that of the conductive protrusion, and the conductive protrusion may be pressed into the support portion.

The piezoelectric element is a bimorph piezoelectric element, a multi-layer piezoelectric element in which a large number of piezoelectric plates are bonded together, a single-layer piezoelectric element, a unimorph piezoelectric element in which a piezoelectric plate is bonded to a shim material, or a bimorph piezoelectric element sandwiching a shim material. It may be selected from the group consisting of an element and a piezoelectric element composed of a piezoelectric thin film formed on a substrate and an electrode.

The piezoelectric vibrator further has protrusions made of metal or ceramics formed by thermal spraying on both ends of the piezoelectric vibrator on at least one of the first and second electrodes in the longitudinal direction. You may.

The conductive protrusions may be symmetrically arranged on the first and second electrodes. The conductive protrusion may be a linear protrusion extending in the width direction of the piezoelectric vibrator.

The length in the longitudinal direction of the piezoelectric vibrator may be 3.5 times or more the length in the width direction.

The height of the conductive protrusion is 50 to 150.
It may be μm.

According to the method of manufacturing an acceleration sensor of the present invention, a piezoelectric element having first and second main surfaces facing each other, and first and second electrodes formed on the first and second main surfaces. The method includes the step of forming a conductive protrusion by thermal spraying a metal or ceramic on at least one electrode of a piezoelectric vibrator having a.

The method may further include the step of providing a support for supporting the piezoelectric element via the conductive protrusion.

The step of forming the conductive protrusion is a step of forming the conductive protrusion by spraying a metal or a ceramic through a mask having an opening at the center of the piezoelectric vibrator in the longitudinal direction. May be included.

The opening of the mask may be a linear opening extending in the width direction of the piezoelectric vibrator.

The conductive protrusions may be formed on each of the first and second electrodes.

The height of the conductive protrusion is 50 to 150.
It may be μm.

The support has a support member having a spring property, and the piezoelectric vibrator is supported by the support through at least one of the conductive protrusions on the first and second electrodes. May be done.

The support may have a support portion made of a material having a hardness lower than that of the conductive protrusion, and the conductive protrusion may be pressed into the support portion.

The step of forming projections by spraying a metal or a ceramic on both ends of the piezoelectric vibrator in the longitudinal direction on at least one of the first and second electrodes of the piezoelectric vibrator is further included. May be included.

[0032]

The piezoelectric vibrator of the acceleration sensor of the present invention has conductive projections made of metal or ceramic formed by thermal spraying, and is supported through the conductive projections.
Since the conductive protrusions formed by thermal spraying have excellent mechanical strength, the piezoelectric vibrator can be stably fixed,
Excellent impact resistance. Also, by supporting the piezoelectric vibrator at its central portion, the ends can freely vibrate like a piezoelectric vibrator having a cantilever structure, so that it has high sensitivity and vibration (acceleration) in a high frequency range. Can be detected.
Moreover, since the conductive protrusions are formed by thermal spraying, the piezoelectric body is not heated to a high temperature during processing. Therefore, the problem of thermal deterioration of the piezoelectric characteristics can be avoided. Furthermore,
Since the area required to fix the piezoelectric vibrator is small,
The size of the device can be reduced. Since the processing accuracy of the conductive protrusion by thermal spraying is high, it is possible to provide a manufacturing method having excellent reproducibility of piezoelectric characteristics and mass production stability. Further, since the conductive protrusion is formed on the electrode on the piezoelectric element, the electric charge generated by acceleration (vibration) can be easily taken out to the external electrode.

[0033]

【Example】

(Embodiment 1) FIG. 1 is a perspective view of a piezoelectric vibrator 100 constituting an acceleration sensor according to an embodiment of the present invention. The piezoelectric vibrator 100 shown in FIG. 1 has, as a piezoelectric element, a bimorph piezoelectric element 1 formed by laminating plates made of a piezoelectric material such as a piezoelectric ceramic plate 2. Electrodes 4 are formed on the opposing main surfaces of each piezoelectric ceramic plate 2. A protrusion 3 made of molybdenum, nichrome or the like is linearly formed on the electrode 4 by a thermal spraying method at the central portion of the opposing surface of the bimorph oscillator 1. In this embodiment, two linear protrusions 3 are provided on each surface in order to stably support the bimorph vibrator 1. Here, the width and thickness of the protrusions 3 and the distance between the two protrusions 3 are determined in consideration of vibration resistance and shock resistance, and stable influence and influence on the characteristics of the bimorph oscillator 1. . In this embodiment, the width of one linear protrusion is 0.2 mm, the interval is 0.3 mm, and the thickness is 0.1.
mm. Further, since the protrusion 3 is mechanically stable even if a supporting force is applied and also has a role as a lead wire, it is required to have stable electrical properties. The material of No. 3 was selected in consideration of conductivity, elastic modulus (hardness), rust resistance and the like.

In this embodiment, the length is 5 mm and the width is 0.7 m.
A piezoelectric ceramic plate 2 having a thickness of m and a thickness of 0.1 mm was used. Therefore, the thickness of the piezoelectric element 1 is 0.2 mm. In order to effectively generate flexural vibration, the length L of the piezoelectric vibrator is preferably 3.5 times or more the width W. It is more preferably 5 times or more. The protrusion 3 is preferably formed near the center of the piezoelectric vibrator in the longitudinal direction, and is preferably arranged symmetrically with respect to the center line in the longitudinal direction. If formed in the vicinity of the center in the longitudinal direction of the piezoelectric vibrator, the number and arrangement of the linear protrusions may be different between the two facing main surfaces (front and back) of the piezoelectric element, but it is preferable that they are the same.

The height of the protrusions is preferably 20 to 150 μm, more preferably 50 to 100 μm. The shape of each protrusion is not limited to a linear shape, and may be a dot shape.
Further, as shown in FIG. 11A, the dot-shaped protrusions may be arranged linearly, or as shown in FIG. 11B, within a region having a constant width D at the center in the longitudinal direction. It may be randomly arranged. The width D in which the protrusion 3 is formed is 200 to 8
It is preferably in the range of 00 μm, more preferably 200 to 500 μm. That is, the width D is in the range of 0.04 to 0.16 with respect to the length L of the piezoelectric ceramic plate 2 in the longitudinal direction,
More preferably, it is in the range of 0.04 to 0.1. If D / L is smaller than 0.04, impact resistance is lowered, and if it is larger than 0.1, sensitivity is lowered.

In the case of the acceleration sensor, if the detection frequency region is not sufficiently separated from the resonance frequency, there arises a problem that the detection sensitivity depends on the frequency. In order to obtain an acceleration sensor having linearity over a wide frequency range, it is necessary to use a piezoelectric vibrator having a high resonance frequency. The resonance frequency of the piezoelectric vibrator of this example is 20 kHz,
Acceleration in the frequency region of Hz to 10 kHz can be measured with high accuracy. The range of measurable acceleration is
It is 0 G to 1500 G, and has excellent linearity even for acceleration of 20 G or more.

The projection 3 is formed by using a thermal spraying method.
With the spraying method, sufficient adhesion strength can be obtained without heating the bimorph oscillator (piezoelectric element) to a high temperature, and protrusions with high mechanical strength can be easily formed in a short time. Become. A method of manufacturing a piezoelectric vibrator according to the present invention will be described with reference to FIG. 2 by taking the piezoelectric vibrator 100 shown in FIG. 1 as an example.

Electrodes 4a and 4b are formed on the main surfaces of the piezoelectric ceramic plate 2 which face each other. A voltage is applied between the electrodes 4a and 4b to polarize the piezoelectric ceramic plate 2 (S1 in FIG. 2). The two piezoelectric ceramic plates 2 are bonded to each other with the surface on which the electrode 4a is formed facing outward (S in FIG. 2).
2). This adhesive has a strong adhesive force such as epoxy resin,
It can be performed using an adhesive having a high elastic modulus. The adhesive is applied very thinly and does not hinder the vibration of the piezoelectric vibrator. Further, the both electrodes 4b adhered to each other are in a conductive state. The electrode 4b and the adhesive on the adhesion surface are omitted in the figure showing the structure after adhesion. The polarization directions of the two ceramic plates 2 are not limited to the directions indicated by the arrows in the figure, but may be directions facing each other. That is, the two piezoelectric ceramic plates 2 may be bonded with the electrode 4a inside.

Next, a metal mask (not shown) made of Invar or the like is placed on the electrodes 4a on the piezoelectric ceramic plate 2. The metal mask has an opening at a portion corresponding to the protrusion 3. By controlling the spraying time, the height of the protrusion can be adjusted. In this example, a metal mask having a thickness of 0.2 mm was used. With a plasma spray device,
Spray particles are sprayed onto the electrode 4a through a metal mask.
The projections 3 are formed on the electrodes 4a by the spray particles that have passed through the openings of the metal mask. Similarly, the thermal spray projection 3 is also formed on the other electrode 4a. Instead of the metal mask, a photolithography technique may be used to form the resist mask. A liquid type resist or a dry film resist can also be used as a material for forming the resist mask.

The piezoelectric ceramic plate on which the protrusion 3 is formed is cut into a predetermined size to obtain the piezoelectric vibrator 100.
The piezoelectric ceramic plate can be cut using a dicing device, a wire saw, or the like.

The thermal spraying process in this embodiment will be described with reference to FIG. First, argon gas and helium gas, which are carrier gases, and metal particles are supplied to the plasma spraying apparatus. In this example, the flow rates of the argon gas and the helium gas were 15 SLM and 3 SLM, respectively.
As the metal particles, molybdenum particles having an average particle diameter of 25 μm were used. Arc discharge (arc current 400 A, voltage 30 V) is generated in the plasma spraying apparatus to melt the metal particles, and the obtained metal sprayed particles 18 are emitted from the plasma torch 19. The thermal spray particles 18 emitted from the plasma torch 19 pass through the metal mask 16 and the piezoelectric ceramic plate 1
Sprayed on 5. As a result, the piezoelectric ceramic plate 15
A protrusion is formed in a portion of the upper metal mask 16 corresponding to the opening 17. During this time, the piezoelectric ceramic plate 15
It is left at room temperature.

In the thermal spraying method, fine particles such as a metal material and a ceramic material are passed through a plasma in a high temperature state to be in a high temperature molten state, and the fine particles in the high temperature / melted state are blown to a substrate together with a gas flow. The fine particle film is formed on the substrate.

Forming the protrusions 3 using the thermal spraying method has the following advantages.

(1) A thick film can be easily formed in a short time.

(2) The film obtained by the thermal spraying method (hereinafter referred to as the thermal sprayed film) is formed by successively depositing high-temperature fine particles, so that a film having high adhesion strength between the particles can be obtained.

(3) The individual particles are in a high temperature / melting state, but the amount of heat that each individual particle has is small, and since the particles are blown to the substrate together with the gas flow, the substrate temperature does not rise. Remarkably less than construction methods such as soldering, brazing and soldering.

In this embodiment, it is important that the protrusions are formed by the thermal spraying method.

The thermal spraying method for forming protrusions can form protrusions having sufficient adhesion strength on the bimorph oscillator without heating the bimorph oscillator (piezoelectric element) to a high temperature, and is mechanical A protrusion having high strength can be easily formed in a short time. Further, as for the thickness of the protrusion, a thick film having a thickness of 100 μm or more can be easily formed.

In fact, in the thermal spraying method, the rise in substrate temperature is
Speaking in connection with FIG. 14, the deterioration of characteristics starts at about 130 ° C.
The temperature of the bimorph oscillator when forming protrusions is sufficiently lower than that of conventional brazing, etc., and as a result, there is almost no effect on the characteristics of the bimorph oscillator. I was not able to admit.

Further, since a thick film of 100 μm or more can be formed, even when a strong acceleration is applied to the bimorph oscillator and the bimorph oscillator bends, the bimorph oscillator contacts the support member or the package (support). It is difficult to do so, and it is possible to stably detect a wide range of acceleration. Therefore, the original characteristics of the bimorph oscillator (piezoelectric element) could be fully utilized.

A longitudinal cross section of an acceleration sensor 200 using the piezoelectric vibrator 100 shown in FIG. 1 is shown in FIG. The length of the element 200 in this example is 6 mm and the thickness is 1.8.
mm and width 2.8 mm. The bimorph oscillator 1 is supported at the center by sandwiching the protrusion 3 formed on the bimorph oscillator 1 with the convex portion 7 provided on the package (holding body) from one side by the support member 6 having a spring property. And then put it in the package 5. The support member 6 having a spring property holds the bimorph oscillator 1 at a constant pressure and does not hinder the vibration of the bimorph oscillator 1. In addition, the applied pressure is due to external impact, strength of the bimorph oscillator 1,
Decide in consideration of sensitivity to acceleration.

When acceleration having the vertical component of FIG. 4 is applied to the acceleration sensor 200, a load is generated on the support portion at the center of the bimorph element 1 and the bimorph element 1 is distorted. Due to the piezoelectric effect of the bimorph element 1, electric charges are generated in the bimorph element 1 due to this strain and can be taken out to the outside through the electrode 4. Since the amount of electric charge generated is proportional to the magnitude of strain, that is, the magnitude of acceleration applied from the outside, the acceleration can be detected as an electric quantity.

The charges taken out through the external electrode 21 are amplified by the amplifier circuit 300 shown in FIG. 5, and the output signal from the amplifier circuit 300 can be used as a signal indicating acceleration. The amplifier circuit 300 of this embodiment is
Field effect transistor (a current-voltage conversion type amplifier circuit using FET 40. The gate of FET 40 is connected to the external electrode of acceleration sensor 200, the source is connected to power supply 42 via a resistor, and output terminal 44 is connected. The amplifier circuit used in this embodiment is not limited to the current-voltage conversion type amplifier circuit, and an optimum circuit may be configured according to the application of the acceleration sensor.

In the structure shown in FIG. 4, since the center of the bimorph vibrator 1 can support the support width narrowly and stably and firmly, a cantilever type of the same length for fixing only one end face is used. The resonance frequency is higher than that of the piezoelectric vibrator. Therefore, it is possible to measure up to a high frequency range, and distortion due to vibration is likely to occur from a position extremely close to the support position, and a large sensitivity to acceleration can be obtained.

Further, since the protrusion 3 can be formed with a highly accurate position by using a metal mask or the like, the variation in the supporting position can be reduced. Variations in the width and position of the support and the strength of the support vary depending on the coating amount and the temperature, compared to a support method using an adhesive or the like.

In addition, the protrusion 3 is formed on the electrode 4 of the bimorph vibrator 1 by using a material having conductivity, and plays a role of taking out the electric charge generated in the bimorph vibrator 1 by the acceleration. A conductive thin film 20a of silver palladium or the like is formed on the convex portion 7 of the package 5 by a method such as printing or plating, and the conductive thin film 20a is electrically connected to the external electrode 21a outside the package 5. There is. Further, the support member 6 having a spring property is made of a conductive metal, for example, a stainless alloy, and is brought into pressure contact with the protrusion 3 formed on the electrode 4 of the bimorph oscillator 1 to thereby cause the bimorph oscillator. It serves as a lead for taking out electric charges from one surface of the metal. A conductive thin film 20b that is electrically connected to the outside is formed on a portion of the package 5 that is in contact with the support member 6 having a spring property, and the electrode 4 on the other surface of the bimorph oscillator 1 is electrically connected to the external electrode 21b. To be done. In this way, the charges generated in the bimorph vibrator 1 due to acceleration can be easily taken out without using a conductive adhesive or the like, and characteristic variations due to variations in the application range of the conductive adhesive can be avoided. be able to.

The piezoelectric element for detecting the acceleration is not limited to the bimorph piezoelectric element, but may be a multilayer piezoelectric element in which a large number of piezoelectric plates are bonded together, a single-layer piezoelectric element, or a piezoelectric plate bonded to a shim material. A unimorph piezoelectric element may be used. Further, it may be a bimorph oscillator or one in which a shim material is sandwiched. Furthermore, a piezoelectric element composed of a piezoelectric thin film formed on a substrate and electrodes may be used. The piezoelectric material is not limited to the piezoelectric ceramic, but may be lithium niobate or the like. The material forming the protrusions 3 is not limited to molybdenum, but nickel-chromium alloy, stainless alloy, tungsten, brass, silver,
A metal such as a copper alloy or an aluminum alloy, or a conductive ceramic can be used. Further, the number of linear protrusions 3 is not limited to two on each surface, and may be one or three or more in consideration of the stability of the support and the supporting area, depending on the surface of the bimorph vibrator (piezoelectric element). Similar effects can be obtained with different numbers. Further, the shape of the protrusion 3 is not limited to the linear shape.

As described above, by using the thermal spraying method, a high adhesion strength can be obtained without heating the piezoelectric element to a high temperature, and a protrusion having a high mechanical strength which does not cause a large plastic deformation even if pressed from above and below is formed by the piezoelectric method. By providing the protrusion at the center of the element and stably supporting the protrusion having high mechanical strength, it is possible to realize a small-sized acceleration sensor having high sensitivity to acceleration, small variation in characteristics, and high reliability.

(Embodiment 2) FIG. 6 is a perspective view of a piezoelectric vibrator 400 constituting an acceleration sensor according to an embodiment of the present invention. As the piezoelectric element, the bimorph vibrator 1 formed by sandwiching and bonding the shim 8 between the piezoelectric ceramic plates 2 was used. As the shim 8, a phosphor bronze plate, a stainless plate, or the like can be used. The use of the shim 8 increases the mechanical strength of the piezoelectric element and facilitates mounting on a package. Electrodes 4 are formed on opposite sides of the piezoelectric element. In the center of each surface of the bimorph oscillator 1,
Nickel-chromium alloy or nickel-chromium-aluminum alloy with minute irregularities of several μm to several hundred μm, metal with relatively high hardness such as molybdenum, or conductive ceramics is linearly metal-projected by a method such as thermal spraying. It is attached as item 3. Here, the width and thickness of the protrusion 3 are determined in consideration of vibration resistance and impact resistance, stable holding, and influence on the characteristics of the piezoelectric element. The material of the protrusions 13 is required to be mechanically stable even if a force for holding is applied and to have stable electrical properties because it also serves as a lead wire. Determined in consideration of rust, conductivity, elastic modulus (hardness), etc.

FIG. 7 shows a supporting structure of the piezoelectric vibrator 400 of FIG. 6 in another acceleration sensor 500 of the present invention, which is a longitudinal sectional view of the piezoelectric vibrator 400. Package 5
The convex portion (support portion) of is formed of a resin such as PPS,
The distance between the two convex portions 7 is determined in consideration of the hardness and Young's modulus of the package and the protrusions so that the bimorph oscillator is stably supported. Piezoelectric vibrator 4
00 is press-supported by being press-fitted into the two convex portions 7 provided on the package 5. If a material having a hardness smaller than that of the protrusion is selected for the convex portion 7 of the package 5, fine irregularities at the contact portion at the tip of the protrusion 3 can bite into the convex portion of the package and be stably supported. Even if the area of the protrusion 3 is reduced to reduce the contact area between the piezoelectric vibrator 400 and the convex portion 7 of the package 5, which is the support portion, such mechanical coupling provides excellent vibration resistance and impact resistance. The piezoelectric vibrator 400 can be stably supported.

Electrode patterns electrically connected to the external electrodes are formed on the surfaces of the two convex portions 7 of the package 5 by a method such as plating, and the conductive protrusions come into contact with the electrode patterns 30. The electrodes 4 on both sides of the bimorph vibrator 1 are electrically connected to the external electrodes 31, and an output signal when acceleration is applied can be easily taken out.

In the above embodiment, the piezoelectric element is made of nickel.
A metal having a relatively high hardness such as a chromium alloy, a nickel-chromium-aluminum alloy, or molybdenum is formed as an electrically conductive protrusion, but similarly, a stainless alloy,
Metals such as tungsten, brass, copper alloys or aluminum alloys can be used. Further, the same effect can be obtained even if ceramic has conductivity. Further, in the above embodiment, the convex portion of the package is made of resin such as PPS,
Ceramic etc. may be used. Only the convex portion may be made of resin and the other package portion may be made of a material such as ceramic.

As described above, the acceleration sensor of this embodiment supports the piezoelectric vibrator by pressing the piezoelectric vibrator having the conductive protrusions into the support such as the package. By forming the support portion of the support body with a material having a hardness lower than that of the conductive protrusion, the conductive protrusion is pressed into the support portion. In addition, since the fine irregularities of several μm to several hundred μm on the surface of the conductive protrusion formed on the piezoelectric vibrator bites into the support portion, they are mechanically coupled effectively and stably support the piezoelectric vibrator. be able to.

As a result, it is possible to realize the support of the piezoelectric vibrator having excellent characteristics and stability, and to provide a small-sized acceleration sensor having high sensitivity to acceleration, small characteristic variation, and high reliability. be able to.

(Embodiment 3) FIG. 8 is a perspective view of a piezoelectric vibrator 600 of an acceleration sensor according to an embodiment of the present invention. In FIG. 8, the piezoelectric element is a bimorph vibrator 1 formed by laminating piezoelectric ceramic plates 2, and electrodes 4 are formed on each main surface of the piezoelectric ceramic plate 2. A protrusion made of molybdenum is linearly attached on the electrode 4 by a thermal spraying method at the center of the opposing surface of the bimorph oscillator 1. Further, at both ends of each surface of the bimorph oscillator 1, additional mass portions 9 that act as additional mass are linearly formed. In the bimorph element of this embodiment, molybdenum was used to form the additional mass portion 9 at the same time as the protrusion 3 for supporting the central portion by the thermal spraying method.

Here, the width and height of the linear projection 3 and the distance between the two lines allow stable support in consideration of vibration resistance and shock resistance, and influence on the characteristics of the piezoelectric element 1. And decide. Further, the material of the protrusions is mechanically stable even if a force for supporting is applied, and also serves as a lead wire, so that stable electrical properties are required, and rust resistance, It was determined in consideration of conductivity, elastic modulus (hardness) and the like. The method for forming the protrusions 3 uses a thermal spraying method that can obtain a sufficient adhesion strength without heating the piezoelectric vibrator to a high temperature and can easily obtain a protrusion having high mechanical strength at high speed. There is. Therefore, the characteristic deterioration of the piezoelectric vibrator is almost negligible, and the original characteristics of the piezoelectric vibrator can be utilized.

The additional mass portions 9 formed at both ends of the bimorph oscillator 1 improve the sensitivity to acceleration. The additional mass unit 9 determines a necessary sensitivity characteristic, and obtains a desired mass by changing the film thickness. The additional mass portion 9 can be formed at the same time when the central protrusion 3 is formed using a mask, and can be formed without increasing the number of manufacturing steps. The material forming the additional mass portion 9 satisfies the condition required for the material of the protrusion, and if a material having a high density is selected, a larger effect can be obtained.

FIG. 9 shows a supporting structure of the piezoelectric vibrator 600 of FIG. 8 in the acceleration sensor 700 of the present invention, and is a longitudinal sectional view of the piezoelectric vibrator 600. FIG. 10 shows X in FIG.
FIG. 6 is a cross-sectional view taken along the line X. The bimorph oscillator 1 is supported by being sandwiched by the support members 10 having spring properties from both sides via the protrusion 3 formed at the center of the bimorph oscillator 1, and the support member 10 is fixed to the package 5. The spring-supporting member 10 holds the piezoelectric vibrator 600 with a constant pressure, and stably and firmly holds the center of the piezoelectric vibrator 600 with a narrow support width without disturbing the vibration of the piezoelectric vibrator 600. Since it can be supported, distortion due to vibration is likely to occur from a position very close to the supporting position, and a large sensitivity to acceleration can be obtained.

Further, since the protrusion 3 can be formed with a highly accurate position by using a metal mask or the like, the variation in the supporting position can be reduced. The variation is smaller than that of a supporting method using an adhesive or the like in which the width and position of the support and the strength of the support vary depending on the coating amount and temperature.

The protrusion 3 is made of a conductive material and is formed on the electrode 4 of the piezoelectric vibrator 600, and plays a role of taking out the electric charge generated in the piezoelectric vibrator 600 by the acceleration. The support member 10 having a spring property has conductivity and also serves as a lead wire, and has a structure in which the electrodes 4 on both surfaces of the piezoelectric vibrator 600 are not short-circuited. A conductive pattern that maintains electrical continuity with the external electrodes is formed on the package where the support member 10 having the spring property is fixed. By fixing the support member 10 having the spring property to this part, The electrodes 4 on both sides of the piezoelectric vibrator 600 are electrically connected to external electrodes.

The support member 10 having the spring property may be fixed to the package by press fitting, or by a conductive adhesive material or the like. By sandwiching the piezoelectric vibrator 600 with the supporting member 10 having a spring property and then fixing it to the package, even a small piezoelectric element can be easily handled.

The piezoelectric element for detecting the acceleration is not limited to the bimorph piezoelectric element, but may be a multi-layer piezoelectric element in which a large number of piezoelectric plates are laminated, a single-layer piezoelectric element, or a piezoelectric plate attached to a shim material. A unimorph piezoelectric element may be used. Further, it may be a bimorph oscillator or one in which a shim material is sandwiched. Furthermore, a piezoelectric element composed of a piezoelectric thin film formed on a substrate and electrodes may be used. Further, the shape of the piezoelectric element is not limited to the rectangular shape and may be a disk shape. The piezoelectric material is not limited to piezoelectric ceramics,
It may be such as lithium niobate. The material forming the protrusions is not limited to molybdenum, but nickel.
A metal such as a chromium alloy, a stainless alloy, tungsten, brass, silver, a copper alloy or an aluminum alloy, or a conductive ceramic can be used. Further, the number of linear protrusions for supporting is not limited to one on each side, and the number of linear additional mass portions 9 is not limited to one on each end face, and may be plural or only one side. . further,
The shapes of the protrusion 3 for supporting and the additional mass portion 9 are not limited to the linear shape, and may be formed by forming a plurality of point-shaped protrusions. The additional mass portion 9 and the supporting projection 3 do not have to have the same thickness, and in order to increase the additional mass, the supporting projection is formed to have a predetermined thickness and then the supporting projection 3 is formed. It is also possible to form a metal or the like on the additional mass portion 9 by spraying only the additional mass portion 9 in which a large number of portions 3 are masks. Also,
The additional mass portion and the protrusion for supporting may not be the same material, and different materials may be separately formed.

As described above, by using the thermal spraying method, it is possible to obtain a protrusion having a high mechanical strength that can obtain a high adhesion strength without heating the piezoelectric vibrator to a high temperature and does not cause a large plastic deformation even if it is pressed from above and below. By providing this protrusion with high mechanical strength in the center of the piezoelectric vibrator and supporting it stably with a supporting member and fixing the supporting member to the package, high sensitivity to acceleration, small variation in characteristics, and high reliability We were able to realize a small acceleration sensor.

[0074]

The piezoelectric vibrator of the acceleration sensor of the present invention has conductive protrusions made of metal or ceramics formed by thermal spraying, and is supported by the package via the conductive protrusions. Since the conductive protrusions formed by thermal spraying have excellent adhesion and mechanical strength, it is possible to stably support the piezoelectric vibrator, and it is possible to provide an acceleration sensor with excellent impact resistance. Becomes Also, by supporting the piezoelectric vibrator at its center, the end can freely vibrate like a cantilever structure piezoelectric vibrator, so it has high sensitivity and vibration (acceleration) in the high frequency range.
It is possible to provide an acceleration sensor that can detect the. Moreover, since the piezoelectric vibrator can be fixed in a very small area, a small acceleration sensor can be provided. Furthermore, since the electrodes of the piezoelectric vibrator can be taken out of the package via the conductive protrusions, the element structure of the acceleration sensor can be simplified and downsized.

Further, according to the method of manufacturing the acceleration sensor of the present invention, since the conductive protrusion is formed by thermal spraying, the piezoelectric body is not heated to a high temperature during processing. Therefore,
It is possible to provide a method of manufacturing an acceleration sensor that does not cause thermal deterioration of piezoelectric characteristics in the manufacturing process. Further, since the conductive projections are processed with high precision by thermal spraying, it is possible to provide a manufacturing method having excellent reproducibility of piezoelectric characteristics and stability of mass production.

[Brief description of drawings]

FIG. 1 is a perspective view of a piezoelectric vibrator that constitutes an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the manufacturing process of the acceleration sensor according to the embodiment of the invention.

FIG. 3 is a schematic diagram showing a thermal spraying process in an example of the present invention.

FIG. 4 is a sectional view of an acceleration sensor according to an embodiment of the present invention.

FIG. 5 is a circuit diagram in an embodiment of the present invention.

FIG. 6 is a perspective view of a piezoelectric vibrator that constitutes an acceleration sensor according to the embodiment of the invention.

FIG. 7 is a sectional view of an acceleration sensor according to an embodiment of the present invention.

FIG. 8 is a perspective view of a piezoelectric vibrator that constitutes the acceleration sensor according to the embodiment of the invention.

FIG. 9 is a sectional view of an acceleration sensor according to an embodiment of the present invention.

10 is a cross-sectional view of the acceleration sensor of FIG. 9 taken along the line XX.

11A and 11B are plan views showing another embodiment of the arrangement of the protrusions of the present invention.

FIG. 12 is a diagram showing a structure of a conventional acceleration sensor.

FIG. 13 is a diagram showing another structure of a conventional acceleration sensor.

FIG. 14 is a diagram showing the temperature dependence of the piezoelectric constant of a ceramic piezoelectric material.

[Explanation of symbols]

 1 Bimorph vibrator 2 Piezoelectric ceramic plate 3 Protrusion 4 Electrode 100 Piezoelectric vibrator

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 41/22 (72) Inventor Shigeo Suzuki 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Takahiro Nishikura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Katsumi Imada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masanori Sumihara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Katsushi Takeda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsuda Electric Industry Co., Ltd. (72) Takashi Nojima, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (20)

[Claims] 1. A piezoelectric element having first and second main surfaces facing each other, first and second electrodes formed on the first and second main surfaces, and the first and second electrodes. An acceleration sensor comprising: a piezoelectric vibrator having a conductive protrusion formed of metal or ceramic formed on the electrode by thermal spraying; and a support body that supports the piezoelectric vibrator through the conductive protrusion. 2. The acceleration sensor according to claim 1, wherein the conductive protrusion is formed at a central portion in the longitudinal direction of the piezoelectric vibrator. 3. The supporting member has a supporting member having a spring property, and the piezoelectric vibrator includes the supporting portion via at least one of the conductive protrusions on the first and second electrodes. The acceleration sensor according to claim 2, which is supported by. 4. The acceleration sensor according to claim 1, wherein the piezoelectric vibrator is press-fitted into the support, and is supported by the support via the conductive protrusion of the piezoelectric vibrator. 5. The acceleration according to claim 4, wherein the support has a support portion made of a material having a hardness lower than that of the conductive protrusion, and the conductive protrusion is press-fitted into the support portion. Sensor. 6. The piezoelectric element is a bimorph piezoelectric element,
A multi-layer piezoelectric element in which a large number of piezoelectric plates are laminated, a single-layer piezoelectric element, a unimorph piezoelectric element in which a piezoelectric plate is attached to a shim material, a bimorph piezoelectric element in which a shim material is sandwiched, and a piezoelectric thin film formed on a substrate The acceleration sensor according to claim 1, wherein the acceleration sensor is selected from the group consisting of a piezoelectric element composed of an electrode and an electrode. 7. The piezoelectric vibrator comprises protrusions made of metal or ceramic formed by thermal spraying on both ends of the piezoelectric vibrator on at least one of the first and second electrodes in the longitudinal direction. The acceleration sensor according to claim 1, further comprising: 8. The conductive protrusions are the first and second conductive protrusions.
The acceleration sensor according to claim 1, wherein the acceleration sensor is symmetrically disposed on the electrodes. 9. The acceleration sensor according to claim 1, wherein the conductive protrusion is a linear protrusion extending in a width direction of the piezoelectric vibrator. 10. The acceleration sensor according to claim 1, wherein the length of the piezoelectric vibrator in the longitudinal direction is 3.5 times or more the length in the width direction. 11. The height of the conductive protrusion is 50 to 1
The acceleration sensor according to claim 1, which has a thickness of 50 μm. 12. A piezoelectric vibrator having at least a piezoelectric element having first and second main surfaces facing each other, and first and second electrodes formed on the first and second main surfaces. A method for manufacturing an acceleration sensor, which comprises a step of forming a conductive protrusion on one electrode by spraying a metal or a ceramic. 13. The method of manufacturing an acceleration sensor according to claim 12, further comprising the step of providing a support for supporting the piezoelectric element via the conductive protrusion. 14. The step of forming the conductive protrusions comprises:
The method of manufacturing an acceleration sensor according to claim 12, further comprising the step of forming a conductive protrusion by spraying a metal or a ceramic through a mask having an opening at the center of the piezoelectric vibrator in the longitudinal direction. 15. The opening of the mask is a linear opening extending in the width direction of the piezoelectric vibrator.
A method for manufacturing the acceleration sensor according to [1]. 16. The method of manufacturing an acceleration sensor according to claim 12, wherein the conductive protrusion is formed on each of the first and second electrodes. 17. The height of the conductive protrusions is 50 to 1
The method of manufacturing an acceleration sensor according to claim 12, wherein the acceleration sensor has a thickness of 50 μm. 18. The support body includes a support member having a spring property, and the piezoelectric vibrator includes the support portion via at least one of the conductive protrusions on the first and second electrodes. 14. The method of manufacturing an acceleration sensor according to claim 13, which is supported by. 19. The acceleration sensor according to claim 13, wherein the support has a support portion made of a material having a hardness lower than that of the conductive protrusion, and the conductive protrusion is press-fitted into the support portion. Manufacturing method. 20. A step of forming projections by spraying a metal or a ceramic on both ends in the longitudinal direction of the piezoelectric vibrator on at least one electrode of the first and second electrodes of the piezoelectric vibrator. 13. The method further comprising:
A method for manufacturing the acceleration sensor according to [1].