JPH1151962A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an acceleration sensor with high sensitivity without mounting a high resistance on a board, and without reducing the output voltage up to a low frequency region with regard to a given magnitude of acceleration. SOLUTION: An acceleration sensor is provided both with an piezoelectric element 100 having a piezoelectric body layer in which a plurality of piezoelectric bodies 4-1, 4-2, and 4-3 are laminated and electrodes 1a, 3a, 1b, and 3b that have been provided on the main opposed surfaces of the respective piezoelectric body layers 4-1, 4-2, and 4-3, and with a supporting body for supporting the piezoelectric element 100; and some of the piezoelectric bodies 4-1, 4-3 out of the piezoelectric body layers are polarized, and on both surfaces of the polarized piezoelectric bodies, electrodes 1a, 3a, 1b, 3b are provided, and the impedances formed by the polarized piezoelectric bodies and the electrodes on both surfaces thereof are electrically connected to each other in a parallel condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an acceleration sensor used for measuring acceleration, detecting vibration, and the like.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller, and portable electronic devices such as notebook computers have become widespread. In order to secure and improve the reliability of these electronic devices against impact, there is an increasing demand for high-performance acceleration (shock) sensors that are compact and surface mountable. For example, if an impact is applied during a writing operation to a high-density hard disk, a head displacement occurs. As a result, there is a possibility that a data write error or damage to the head may occur. Therefore, it is necessary to detect the impact applied to the hard disk, stop the write operation, and retract the head to a safe position.

[0003] In addition, there is an increasing demand for an acceleration sensor for detecting an impact of an airbag device for protecting an occupant from an impact at the time of a collision of an automobile, and for detecting an acceleration for controlling a suspension. For these acceleration sensors, further reduction in size and weight is required.

[0004] By the way, piezoelectric ceramics can be used as an acceleration sensor because when a force proportional to acceleration is applied to the piezoelectric ceramics, distortion occurs inside the piezoelectric ceramics and electric charges are generated on both sides of the piezoelectric ceramics. FIG. 38 shows a piezoelectric element 5 of a conventional piezoelectric acceleration sensor.
00 is a diagram showing a structure of a piezoelectric ceramic 50 on a plate or a disk and a metal plate are bonded,
Electrodes are formed on both upper and lower surfaces of the piezoelectric ceramic 50, and the electrode on one surface is divided into two and used as a drive electrode 52 and a detection electrode 51 at the time of self-diagnosis. When the piezoelectric element 500 flexes and vibrates in the vertical direction, electric charges are generated at the output electrode.

FIG. 39 shows a general signal processing circuit of a piezoelectric acceleration sensor. An acceleration sensor for measuring acceleration uses a source follower circuit using a field effect transistor (hereinafter, FET). In this source follower circuit, the impedance conversion efficiency is large, and the gain of the circuit is almost 0d.
B.

In the circuit of FIG. 39, the output frequency range on the low frequency side is determined by the time constant (1 / ωs) of the high-pass filter including the capacitance C11 of the acceleration sensor and the resistor Rh connected in parallel with the acceleration sensor. It is determined by the calculated cutoff frequency. And the cutoff frequency fhc of the high-pass filter is It is.

In general, the capacitance of a piezoelectric acceleration sensor depends on its shape, but a piezoelectric sensor manufactured using piezoelectric ceramic has a capacitance of several hundred pF. The resistance Rh is about 1 MΩ to about 10 MΩ when a general-purpose chip resistance is used as the gate of the resistance Rh. Therefore, in the case of a piezoelectric sensor using piezoelectric ceramic, the cutoff frequency is about several hundred Hz.

As described above, the lower limit of the measurable frequency of the piezoelectric acceleration sensor is determined by the capacitance of the acceleration sensor and the resistance value connected thereto, and the output lowers on the lower frequency side.

Next, the principle of the self-diagnosis will be described below.
The self-diagnosis pulse from the transmitter is applied to the piezoelectric element to the self-diagnosis drive electrode. The piezoelectric element vibrates by the self-diagnosis pulse, and the vibration causes the acceleration sensor to vibrate. At that time, charges corresponding to the magnitude of the vibration are generated in the detection electrodes, and are converted into voltages by the signal processing circuit. If the voltage detected as a result of the vibration generated by the self-diagnosis pulse is different from a predetermined value, the signal processing circuit is configured to diagnose that the acceleration sensor is abnormal and take measures when the abnormality is abnormal. As described above, a function of performing a self-diagnosis of a failure of the acceleration sensor can be added.

[0010]

The characteristics required when an acceleration sensor using piezoelectric ceramics is used to improve the safety of a safety device such as an air bag or the like on a rough road are as low as possible. Acceleration can be detected up to the frequency range, the detection sensitivity is excellent even in the detectable range, the pyroelectric effect is small, and self-diagnosis can be performed.

In order to be able to detect acceleration to the lowest possible frequency range, the above-mentioned cutoff frequency must be small. Therefore, it is necessary to increase the capacitance of the acceleration sensor and the resistance value connected thereto.

Therefore, by increasing the resistance Rh connected in parallel with the acceleration sensor, the cutoff frequency fh
There is a measure to reduce c and obtain a constant output up to low frequencies. However, resistors exceeding 10 MΩ are quite expensive and impractical.

Another problem is that a high resistance cannot be substantially obtained unless special attention is paid to a leakage current between wirings of a board to be mounted. A member such as a guard ring for preventing leakage current must be provided at the connection terminal of the resistor to the substrate. There is a problem that the leakage current between the wirings of the substrate changes due to a change in environment such as humidity, and the resistance value is apparently reduced.

Although the signal processing circuit shown in FIG. 39 can be easily integrated into an integrated circuit, a high resistance of 10 MΩ or more, such as Rh, can be very easily incorporated into an integrated circuit by current semiconductor technology. Have difficulty. Therefore, in addition to the acceleration sensor and the integrated circuit for signal processing, it is necessary to prepare and mount a high resistance separately, but this increases the number of mounted components, increases the mounting area, and reduces the size of impact detection devices and other devices. Hinders

On the other hand, there is a measure to increase the capacitance C11 of the acceleration sensor. When the material is the same, the capacitance of the piezoelectric acceleration sensor increases as the thickness of the piezoelectric body decreases, and increases as the area increases. It is sufficient to make the piezoelectric body thinner, but if it becomes thinner, the mechanical strength decreases and it becomes easier to crack,
There is also a problem that it becomes difficult to handle even in the process. In addition, when the area is increased, miniaturization becomes difficult. further,
Since the shape of the piezoelectric body determines the resonance frequency closely related to the measurement frequency band, there is a problem that the shape of the piezoelectric sensor cannot be easily changed. Therefore, it is necessary to consider another way to increase the capacity.

On the other hand, even if it can be detected in a predetermined frequency range, its sensitivity needs to be high. By the way, when the same piezoelectric ceramic is used, the amount of charge generated by vibration is constant, and Q (charge) = C (capacity) V (sensitivity). Become.

That is, in order to enable the acceleration sensor to detect the low frequency region as much as possible and to increase the sensitivity, it is necessary to increase the capacity and to have an appropriate size.

Regarding the sensitivity, if the charge generated during vibration is small, a two-stage amplifier must be used to amplify the signal, and the circuit becomes complicated. At the same time,
Since noise is similarly amplified, there is a problem that the signal-to-noise ratio deteriorates and the circuit becomes more complicated to prevent malfunction.

Further, when an oscillation pulse is applied to the driving electrode by a transmitter for self-diagnosis and the vibration is detected by the vibration detecting electrode by driving at a low frequency, the vibration detecting electrode is used as described above. Is small because the capacitance of the piezoelectric element of the vibration detection electrode portion is small. Since the vibration detection electrode is not provided on the entire surface of the piezoelectric element, the capacitance is further lower than the capacitance of the entire piezoelectric element. Further, the amount of electric charge generated in the vibration detection electrode also decreases according to the area.

When the output voltage at the low frequency of the vibration detection at the time of the self-diagnosis decreases, the accuracy of the self-diagnosis at the low frequency decreases. Therefore, there is a problem that self-diagnosis cannot be performed accurately in all frequency bands.

Also, if the area of the self-diagnosis electrode is too small, vibration cannot be detected, and if it is too large, the vibration becomes large, and there is a problem that the piezoelectric body is destroyed.
However, when the area of the self-diagnosis electrode is reduced and the distance between the self-diagnosis electrode and the detection electrode is increased, a portion of the element having no electrode is increased. When there is an electrode portion and an internal portion on the surface of the piezoelectric layer, warpage or undulation occurs in the piezoelectric element due to a difference in shrinkage, and a stable warp-free element cannot be obtained.

The present invention has been made in view of the above-mentioned various conventional problems, and without mounting a high resistance on a substrate,
It has high sensitivity to the magnitude of acceleration up to the low frequency range without a drop in output voltage, and can obtain flat frequency characteristics of output voltage, enabling self-diagnosis over a wide frequency range. It is an object of the present invention to provide a small-sized acceleration sensor which can be accurately performed and can easily extract a signal.

[0023]

Means for Solving the Problems The first invention (claim 1)
A) a piezoelectric element having a piezoelectric layer in which a plurality of piezoelectric bodies are stacked and electrodes provided on main opposing surfaces of each of the piezoelectric layers, and a support for supporting the piezoelectric element, Some of the piezoelectric layers in the piezoelectric layer are polarized, the electrodes are provided on both sides of the polarized piezoelectric body, and the impedance formed by the polarized piezoelectric body and the electrodes on both sides thereof is reduced. An acceleration sensor characterized by being electrically connected in parallel to each other.

According to a second aspect of the present invention (corresponding to claim 2), each of the piezoelectric layers has a rectangular shape, and the electrode present on at least one surface of the piezoelectric layer is divided into two. The two electrodes described above are provided substantially along the long side of the piezoelectric element, in the acceleration sensor according to the first aspect of the present invention.

According to a third aspect of the present invention (corresponding to claim 3), each of the piezoelectric layers has a rectangular shape, and the electrode present on at least one surface of the piezoelectric layer is divided into two. The two electrodes described above are provided substantially along the short side of the piezoelectric element, in the acceleration sensor according to the first aspect of the present invention.

According to a fourth aspect of the present invention (corresponding to claim 4), each of the piezoelectric layers has a disk shape, and the electrode present on at least one surface of the piezoelectric layer is divided into two, The acceleration sensor according to the first aspect of the present invention is characterized in that each of the two electrodes is provided concentrically.

According to a fifth aspect of the present invention (corresponding to claim 5), the piezoelectric element has a through-hole passing through the center of each of the disk-shaped piezoelectric layers. Acceleration sensor.

According to a sixth aspect of the present invention (corresponding to claim 6), the piezoelectric element is supported at substantially the center of a long side of each of the rectangular piezoelectric layers. 3 is an acceleration sensor according to the present invention.

A seventh aspect of the present invention (corresponding to claim 7) is the fourth or fifth aspect, wherein the piezoelectric element is supported substantially at the center of each of the disk-shaped piezoelectric layers. 3 is an acceleration sensor according to the present invention.

An eighth aspect of the present invention (corresponding to claim 8) is characterized in that the electrical connection between the electrode and another external electrode is made via the support. 1 to 7
Or the acceleration sensor of the present invention.

According to a ninth aspect of the present invention (corresponding to claim 9), one of the two electrodes is a driving electrode at the time of self-diagnosis, and the other is a vibration detecting electrode. 8 is an acceleration sensor according to the present invention.

A tenth aspect of the present invention (corresponding to claim 10)
The piezoelectric element has a rectangular shape, the electrode present on at least one surface of the piezoelectric layer is divided into two, and the support is supported substantially at the center of the long side of each piezoelectric layer. One of the two divided electrodes is a vibration detecting electrode and is disposed at the center of the surface of the piezoelectric element, and the other is a driving electrode at the time of self-diagnosis and is a surface of the piezoelectric element. An acceleration sensor according to a first aspect of the present invention, which is arranged at or near both ends in the longitudinal direction and connected to each other.

[0033] The eleventh invention (corresponding to claim 11) provides:
24 and 29. The driving electrodes are arranged at both ends of the surface F of the other piezoelectric layer of the piezoelectric element or in the vicinity of the both ends, respectively. An acceleration sensor according to a tenth aspect of the present invention, wherein the acceleration sensors are connected to each other also at F.

The twelfth invention (corresponding to claim 12) provides:
(Corresponding to FIGS. 31, 33, and 35) The driving electrodes are disposed at or near both ends of the surface F of the other piezoelectric layer of the piezoelectric element. A tenth aspect of the acceleration sensor according to the present invention, wherein the acceleration sensors are not connected to each other on the surface F.

According to a thirteenth aspect of the present invention (corresponding to claim 13),
The acceleration according to a tenth aspect of the present invention, wherein a dummy member that is not connected to the electrodes for vibration detection and the driving electrode disposed on the same surface of the piezoelectric layer is disposed between the electrodes. It is a sensor.

The fourteenth invention (corresponding to claim 14) provides:
The acceleration sensor according to any one of claims 10 to 13, wherein the vibration detection electrode and the drive electrode are connected to another external electrode via the support. is there.

That is, the acceleration sensor of the present invention utilizes the fact that the generation of electric charges is large near the surface of the piezoelectric element in the thickness direction of the piezoelectric element, and the electric charge is large near the center holding portion in the longitudinal direction. When a stress is applied to the piezoelectric element, the element bends and deforms, and the deformation in the vicinity of the center and the vicinity of the center increases, so that the electric charge generated by the piezoelectric effect is effectively used.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is an external view of a piezoelectric element used in an acceleration sensor according to an embodiment of the present invention. The piezoelectric element 100 includes a layer 4-1, a layer 4-2, and a layer 4-3.
It has a rectangular shape with a structure in which three layers of are laminated.
Each of the layers is made of a sheet-like ceramic mainly composed of lead zirconate titanate. The thickness of each of the layers 4-1 and 4-3 was 50 μm (preferably about 10 μm to 80 μm), and the thickness of the layer 4-2 was 100 μm. Since the ceramics in a sheet form are stacked and fired, each layer can be made thinner and the capacitance of each layer can be increased as compared with a case where a piezoelectric ceramic plate is bonded. On the upper surface of the layer 4-1, two electrodes 1a and 2a are formed separately, and both are provided in parallel with the longitudinal direction of the rectangle. Although not shown in the figure, an electrode 3 is provided on the bottom of the layer 4-3.
b (a part of the common electrode) is formed. The electrode 1a and the electrode 2b are also formed continuously on a part of the end face (the left front side in FIG. 1). Each of the electrodes is made of silver and has a thickness of 1000A (an angstrom; hereinafter the same) to 10,000A.
And

FIG. 2 is a sectional view of the electrode 1a of the piezoelectric element 100 taken along line XX '. FIG. 3 is a plan view of the electrodes of each layer. The electrode 1b and the electrode 2b formed between the layer 4-2 and the layer 4-3 are similarly divided in the same shape as the electrodes 1a and 2a provided on the surface of the layer 4-1, and have a rectangular shape. It is provided parallel to the direction. The electrode 1a is a layer 4-
2 and an electrode 1b formed between the layer 4-3 and the end face. Although not shown in FIG. 2, the electrode 2a is connected to the internal electrode 2b similarly to the electrode 1. Similarly, the electrode 3b on the bottom surface and the electrode 3a (a part of the common electrode) formed between the layers 4-1 and 4-2 are connected at an end face opposite to the electrode 1. The electrodes 1a, 2a, 1b, 2b are formed up to one end (left side in the figure) for connection. The electrodes 1b and 2b are slightly receded from the ends on the right side of the figure to prevent a short circuit with the connection part of the electrode 3. Electrode 3
Similarly, a and b are formed to the end on the right side of the figure for connection,
The left side is receding from the edge.

The layers 4-1 and 4-3 are polarized, and the directions of polarization are opposite to each other. Layer 4-2 is not polarized.

By connecting the respective electrodes as described above,
The impedance formed by the layer 4-1 and the electrodes 1a, 3a on both surfaces thereof, and the impedance formed by the layer 4-3 and the electrodes 1b, 3a on both surfaces thereof
The impedance formed by b is electrically connected in parallel. Therefore, the capacitance of the entire piezoelectric element is a value obtained by adding the capacitance of each layer. Further, since the layers are superimposed, it is sufficient to maintain a predetermined strength as a whole. Therefore, each layer can be formed of a thin layer, and the capacitance of each layer can be increased. In addition, since the respective capacitances are added, a larger capacitance can be obtained than a single-layer piezoelectric element having the same thickness.

FIG. 4 is a sectional view of an acceleration sensor using the piezoelectric element shown in FIGS. The piezoelectric element 100 is supported at its center in the longitudinal direction by the supports 7a and 7b, and is housed inside the container 12. The container 12 was formed of alumina. External electrodes 9a and 9b are provided outside the container 12.
c is provided. The external electrodes 9a, b, and c were formed by forming a solder layer on Ni. The external electrodes 9a, b, c are respectively connected to the electrodes 1a, 2a, 3b via the supports 7a, b.
And charge generated by the acceleration is transferred to the container 12.
Can be taken out.

FIG. 5 is a view showing a state in which the support 7a is attached to the piezoelectric element (the support 7a shows only the mounting end). The support 7a is provided with conductive layers 8a and 8b on the contact surface with the piezoelectric element as shown in the drawing. The conductive layers 8a and 8b are connected to the electrodes 1a and 2a on the surface of the piezoelectric element 100, respectively. Further, the conductive layers 8a and 8b are electrically connected to the external electrodes 9a and 9b, so that electric charges can be taken out. The conductive layer 8 and the electrodes 1a and 2a may be bonded using a conductive adhesive.

When the acceleration in the direction parallel to the substrate on which the acceleration sensor is mounted is detected by using the rectangular piezoelectric element, the piezoelectric element must be disposed substantially vertically on the mounting substrate. That is, the electrode surface of the piezoelectric element 100 must be substantially perpendicular to the mounting substrate. In the case of a rectangular piezoelectric element, even if the piezoelectric element is mounted vertically, the height of the acceleration sensor does not increase, so that a small acceleration sensor can be realized.

FIG. 6 is a diagram showing the operation principle of the acceleration sensor. When acceleration is applied in the up-down direction, the piezoelectric element 100 whose center is supported vibrates as shown in the figure.
At this time, the two layers on the surface side of the three layers are distorted such that one expands and one contracts. In the present embodiment, the layer 4-1 expands, the layer 4-3 contracts, and this strain generates charges. However, since the polarization directions of the layers 4-1 and 4-3 are opposite, charges of the same polarity are generated. To electrodes 1a and b, electrode 2
a, b and the electrodes 3a, b. Layer 4-
The charges generated in 1 and 4-3 will be added,
A large charge amount can be obtained.

As described above, the front and back surfaces of the piezoelectric element have large distortion. In the present embodiment, however, the sensitivity can be increased because the polarized piezoelectric layer is provided there. .

FIG. 7 is a block diagram of an acceleration detecting device having a self-diagnosis function using an acceleration sensor.
At the time of self-diagnosis, the electrodes 2a and 2b are used as driving electrodes, and the electrodes 1a and 1b are used as vibration detecting electrodes. The external electrode 9b is connected to a driving circuit 10a for driving a vibration for self-diagnosis. A drive AC voltage is generated from the drive circuit 10a and applied to the electrodes 2 and 3 as drive electrodes of the piezoelectric element via the external electrodes 9b and 9c. An electric field is generated inside the layers 4-1 and 4-3 by the AC voltage. Although the electric field is applied in the same direction, the polarization direction is different, so that distortion is generated in the opposite direction, and the entire piezoelectric element performs flexural vibration. As described above, electric charges are generated by the vibration, and the electric charges are detected by the electrodes 1a and 1b and the electrodes 3a and 3b which are the electrodes for detecting the vibration. The detected charges are input to external electrodes 9a and 9c connected to the impedance conversion circuit 10b. The impedance conversion circuit 10b is generally configured using an FET or the like. The output voltage from the impedance conversion circuit 10b is input to an acceleration detection circuit and an abnormality detection circuit 10c, where it is determined whether the piezoelectric element has an abnormality. In general, the abnormality detection circuit 10c includes a high-pass filter, a low-pass filter, a smoothing circuit, a comparator, and the like.
The abnormality diagnosis determines whether or not a voltage that matches a predetermined value is output from the impedance conversion circuit 10c with respect to the AC voltage input from the oscillator 10a. When there is an abnormality in the piezoelectric element, the abnormality detection circuit issues an instruction to perform a process at the time of abnormality.

Since the driving electrode portions are stacked, each layer is thin and the electric field is large, so that a large amplitude flexural vibration can be obtained only by inputting a small amplitude AC voltage from the oscillation circuit, and the self-diagnosis can be performed. Accuracy has improved.

Further, since the drive electrode is formed over the entire length in the longitudinal direction of the piezoelectric element, the entire piezoelectric element can be distorted. As a result, vibration could be generated efficiently, and self-diagnosis could be performed with high accuracy even at low voltage.

Further, the detection electrode portion is also laminated, so that a large capacitance can be obtained, and the vibration induced by the oscillation circuit with high sensitivity up to a low frequency region can be obtained without using a high resistance in the impedance conversion circuit. The self-diagnosis was able to be performed and highly accurate self-diagnosis was performed in a wide frequency range.

Even during normal acceleration detection, since the piezoelectric element 100 is formed by laminating thin layers and the formed capacitors are connected in parallel, the capacitance of the entire piezoelectric element becomes large. In addition, each layer can be thinned without impairing the mechanical strength of the entire piezoelectric element. Therefore, a sufficiently high sensitivity can be obtained even at a low-frequency acceleration,
It could be measured without using high resistance.

At the time of normal acceleration detection, the driving electrode 2
A higher sensitivity could be obtained by using both a and b and the electrodes 1a and 1b for vibration detection as electrodes for detecting acceleration and connecting them to an impedance conversion circuit.

The layer 4-2 is an unpolarized layer.
By providing this layer, the strength of the entire piezoelectric element could be maintained even when the layers 4-1 and 4-3 were extremely thin. The layer 4-2 also has the effect of increasing the capacitance.

The method of the piezoelectric element is not limited to the center support, but may be a cantilever supporting one end or a double-supporting beam supporting both ends.

The self-diagnosis circuit and the impedance conversion circuit are not limited to those shown in FIG.

The directions of polarization are not limited to the directions shown in the figure, but may be any directions as long as they are opposite to each other.

The electrodes 1a and 1b are used as drive electrodes, and the electrodes 2a and 2b are used as electrodes.
a and b may be used as detection electrodes.

The thicknesses of the layers need not all be the same, but it is preferable that the layers 4-1 and 4-3 have substantially the same thickness. The layer 4-2 may be thicker than other layers, in which case it contributes to an improvement in impact resistance.

(Embodiment 2) FIG. 8 is a sectional view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention. The piezoelectric element 102 has a rectangular shape and has three layers 14-1,
It has a structure in which layers 2 and 3 are stacked, and the layers 14-1 and 3 are polarized, and the polarization directions are the same. FIG.
FIG. 3 is a plan view of an electrode of a piezoelectric element. The electrodes 11a and 11b and the electrodes 12a and 12b are provided on the upper surface and the bottom surface of the piezoelectric element in parallel in the longitudinal direction, and are connected at the end surfaces. The electrodes 13a and 13b are provided on substantially the entire surface of the piezoelectric element except for the vicinity of an end face serving as a connection portion between the electrodes 11 and 12, and are connected on the side opposite to the connection portion between the electrodes 11 and 12. The capacitor formed by the layer 14-1 and the capacitor formed by the layer 14-3 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The layers 14-1, 2, and 3 were all manufactured using ceramics containing lead zirconate as a main component. Silver was used for the electrode.

Although the polarization directions of the layers 14-1 and 14-3 are the same, the connection directions of the electrodes are different from those in FIG. 2, so that the electrodes 11a and 11b have the same polarity even when flexural vibration occurs. Is generated, and the acceleration can be detected.

The layer 14-2 has a role of increasing the strength of the piezoelectric element 102 and improving the impact resistance.

In the first embodiment, the impedance formed by the middle unpolarized layer 4-2 and the electrodes 3a and 1b is the impedance formed by the piezoelectric layer 4-1 and the electrode 1a and the electrode 3a, and the impedance formed by the piezoelectric layer 4-1 and the electrode 3a. 4-3 and electrode 1b, electrode 3
The impedance formed by b is electrically connected in parallel, and the capacitance of the unpolarized layer 4-2 is also included in the capacitance of the entire device. However, since no charge is generated in the unpolarized layer 4-2 even when acceleration is applied,
The capacitance of this layer lowers the output voltage, resulting in lower sensitivity. However, since the layer 14-2 in the second embodiment has its opposite surface sandwiched between the electrodes 13a and 13b, the capacitance of this layer is smaller than the capacitance of the layers 14-1 and 14-2. Since it is not added, the sensitivity increases.

The self-diagnosis can be performed in the same manner as in FIG. 7, using the electrode 11 as a vibration detecting electrode and the electrode 12 as a driving electrode.

A conductive layer for extracting charges from the electrodes can be formed through the support in the same manner as in FIG.

(Embodiment 3) FIG. 10 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
Fig. 2 shows a plan view of the electrodes of each layer of the piezoelectric element.

The piezoelectric element 200 has a rectangular shape, and
It has a structure in which two or three layers are laminated. Layer 24-1,
2 are polarized in opposite directions.

The electrodes 21a and 22a are on the upper surface of the piezoelectric element 200, the electrode 23a is between the layers 24-1 and 24-2, the electrodes 21b and 22b are between the layers 24-2 and 24-3, 23b is provided on the lower surface. Electrodes 21a, 22a
Are formed to be substantially symmetrically divided right and left from the center in the longitudinal direction of the piezoelectric element. The electrodes 21b and 22b are also electrodes 21
a, 22a, and has substantially the same shape as the piezoelectric element 200.
The electrodes 21a and 21b and the electrodes 22a and 2
2b is connected. The electrodes 23a and 23b are provided on almost the entire surface of the piezoelectric element except for the connection between the electrodes 21 and 22, and are connected to each other on the short side surface.

By connecting such electrodes, the layer 24-1 is formed.
Is connected in parallel with the capacitor formed by the layer 24-3, so that the capacitance of the piezoelectric element can be increased. In addition, since the impact resistance can be increased by the laminated structure and the non-polarized layer 24-2, each layer can be thinned and the capacitance can be increased.

As shown in FIG. 11, the electrode 21 has a shape in which the upper part of the figure protrudes leftward from the center and the lower part is depressed rightward, and the electrode 22 is reversed. Such a bent shape is for facilitating extraction of electric charge from the electrode with one support. The piezoelectric element 200 is supported at the center in the longitudinal direction as in FIG. FIG. 12 is a diagram showing the configuration of the conductive layer on the surface of the support that contacts the electrode surface. Support 2
7 is provided with conductive layers 28a and 28b, which are in contact with the electrodes 21a and 22a, respectively, to establish electrical connection.
The conductive layers 28a and 28b are connected to the external electrodes of the container as in FIG. As a result, the charges generated on the electrodes 21a and 22a can be taken out.

In this electrode structure, it is only necessary to provide a space for separating the electrode only at the position of the support portion, and the electrode can be formed over the entire width of the other piezoelectric element surface. Can be efficiently increased.

The operation of detecting the acceleration when receiving the acceleration is the same as in FIG.

At the time of self-diagnosis, it is possible to use a circuit similar to that shown in FIG. 7 by using the electrode 21 as a vibration detecting electrode and the electrode 22 as a driving electrode. When an AC voltage is applied to the electrode 22 by an oscillating circuit, the entire piezoelectric element 200 generates flexural vibration with its center supported. This vibration is detected by the vibration detection electrode, and a failure diagnosis is performed based on the output voltage. Since both the vibration detection unit and the drive unit have a laminated structure, the capacitance is high and the self-diagnosis can be performed even at a low frequency.

The materials constituting the layers and the materials constituting the electrodes were the same as in the first embodiment.

The self-diagnosis may be performed using the electrode 21 as a driving electrode and the electrode 22 as a vibration detecting electrode.

Further, the electrodes 21a and 21b are not connected on the long side of the electrode, and the electrodes 2a are not formed along the edge of the long side as shown in FIG.
One connecting portion 21c is provided, and the electrodes 21a and 21
b and the electrodes 22a and 22b may be connected.

(Embodiment 4) FIG. 14 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
Fig. 2 shows a plan view of the electrodes of each layer of the piezoelectric element.

The piezoelectric element 300 is a disk having a through hole 35 at the center and has a structure in which three layers 34-1, 2 and 3 are laminated. Layers 34-1 and 34-2 are polarized in opposite directions.

The electrodes 31a and 32a are on the upper surface of the piezoelectric element 300, the electrode 33a is between the layers 34-1 and 34-2, the electrodes 31b and 32b are between the layers 34-2 and 34-3, and 33b is provided on the lower surface. Electrodes 31a, 32a
Are formed concentrically with the center of the piezoelectric element. The electrodes 31b and 32b have substantially the same shape as the electrodes 31a and 32a. The electrode 31a and the electrode 31b are connected at the end face of the inner peripheral portion of the piezoelectric element 300. Also, the electrodes 32a and 3
2b is connected at the end face of the outer peripheral portion of the piezoelectric element 300. The electrodes 33a and 33b are electrodes 31 and 32 of the piezoelectric element.
Are provided on almost the entire surface except for the connection portion, and are connected to each other on the side surface of the outer peripheral portion. By the connection of the electrodes, the capacitor formed by the layer 34-1 and the layer 34-3 are formed.
Is connected in parallel with the capacitor formed by the piezoelectric element, the capacitance of the piezoelectric element can be increased. In addition, since the impact resistance can be increased by the laminated structure and the non-polarized layer 34-2, each layer can be thinned and the capacitance can be increased. The materials constituting the layers and the electrodes were the same as in the first embodiment.

FIG. 16 is a sectional view of an acceleration sensor using the piezoelectric element 300. The piezoelectric element 300 penetrates through the through-hole 35 and is supported at the center by a support 37 that presses both sides of the piezoelectric element 300. The detection principle is the same as in FIG. 6, and when the piezoelectric element receives acceleration in the vertical direction in the figure,
The center is supported and the periphery vibrates flexibly. The acceleration generated can be detected by converting the generated distortion into electric charge. Since the layer 34-1 and the layer 34-3 are polarized in directions opposite to each other, charges having the same polarity are generated in the electrodes connected to each other in each layer.

The electrode 32a and the electrode 33c are
And is electrically connected by contact with a conductive layer (not shown in the figure) provided on the external electrode 39a, c.
To extract electric charges to the outside. The electrode 33b was connected to the external electrode 39b by wiring (not shown).

As a method that does not use means such as wiring with the electrode on the outer peripheral portion, the electrodes 31a and 31b provided on the surface of the piezoelectric element may be changed to another shape. FIG.
It is a top view of other electrode composition of the surface of a piezoelectric element. Electrode 2
A cutout was provided in a part of 1a, a connection portion 32c was provided to the center of the electrode 32a, and the other electrode configuration was the same as in FIG. By extending the connecting portion 32c to the center of the piezoelectric element, a conductive layer is provided on the support 37, and the conductive layer and the connecting portion 32c are provided.
By conducting c, electrical connection with the external electrode 39b can be obtained without using means such as wiring.
Although the shape of the electrode becomes complicated, since no means such as wiring is required, it is easy to manufacture the acceleration sensor and the size can be reduced.

The self-diagnosis can be performed in the same manner as in the method shown in FIG. At the time of self-diagnosis, an AC voltage is applied from an oscillation circuit to the electrode 33 using the electrode 32 as a driving electrode,
The entire piezoelectric element bends and vibrates. Vibration at this time,
The electrode 32 is converted into a voltage as a vibration detection electrode to perform a failure diagnosis. Because of the laminated structure of the thin layers, the capacitance was large and the self-diagnosis could be performed accurately even at a low frequency.

The acceleration sensor can be configured without providing a through hole in the piezoelectric element. That is, FIG.
FIG. 4 is a plan view of an electrode when a through hole is not provided in a piezoelectric element. The layer structure of the piezoelectric element other than the electrodes is the same as in FIG. The electrode 31 has a circular shape at the center of the piezoelectric element,
Are concentrically provided in a donut shape. Electrode 32a
Is an electrode 32b provided between the layer 34-2 and the layer 34-3
And a connection portion 32c at the edge of the outer peripheral portion. Electrode 3
In 1a, a narrow connecting portion 31d is extended to the outer peripheral portion. Electrode 3 formed between layer 34-2 and layer 34-3
Similarly, a connection portion 31c is provided in 1b, and the connection portion 31c and the connection portion 31d are electrically connected at the outer peripheral portion, and the electrodes 31a and 31b are electrically connected. The electrode 33a provided between the layer 34-1 and the layer 34-2 and the electrode 33b formed on the lower surface of the piezoelectric element are connected to the connecting portion 33 provided on the outer peripheral edge of the piezoelectric element.
c. In addition, a connection portion 32d for providing conduction from the electrode 32 and a support for supporting the center was provided as in FIG.

The electrode 32 may be a detection electrode, and the electrode 31 may be a drive electrode.

(Embodiment 5) FIG. 19 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
2 is a plan view of the electrodes of each layer of the piezoelectric element, and FIG.
FIG. 1 shows a plan view of a support of the acceleration sensor according to the embodiment.

One electrode 1a is provided at the center of the element along the long side of the piezoelectric element 100, and the other electrode 2a is provided at the periphery. The peripheral electrodes 2a are connected to each other by a connection portion 10 provided at one end. In this structure, if the inner electrode 1a is used as a drive electrode, the drive electrode is provided over the entire length along the long side and located at the center,
Compared with other electrode structures, uniform driving can be caused on the entire element, and self-diagnosis can be performed in a state closer to the state where acceleration is actually applied. The extraction from the electrode to the external electrode is performed by the conductive layers 8a and 8b provided on the support 7a.
Can be done through When connecting to the central electrode 1a, an insulating layer 9 may be provided on the electrode so as not to short-circuit with the peripheral electrode 2a. As the insulating layer, S
An SiO ₂ film, a Si ₃ N ₄ film, a polyimide film, or the like may be used. Alternatively, it may be formed by applying an insulating adhesive such as an epoxy resin or a silicon resin.

It is to be noted that the peripheral electrodes may be connected by drawing out to external electrodes without providing connection portions on the electrode surfaces.

(Embodiment 6) FIG. 22 is an external view of a piezoelectric element used in an acceleration sensor according to an embodiment of the present invention.

The piezoelectric element 100 includes layers 4-1 and 4-2,
It has a rectangular shape with a structure in which three layers including a layer 4-3 are stacked. Each of the layers is made of a sheet-like ceramic mainly composed of lead zirconate titanate. The thickness of each layer is 50 μm for layer 4-1 and layer 4-3, and 100 μm for layer 4-2.
And The thickness of the layer is preferably about 10 μm to 100 μm, and the total thickness is 150 μm to 350 μm
Is preferred. Since the ceramics in a sheet form are stacked and fired, each layer can be made thinner and the capacitance of each layer can be increased as compared with a case where a piezoelectric ceramic plate is bonded. On the upper surface of the layer 4-1, two electrodes 1a and 2
The electrode 1a is formed in the vicinity of the center of support by a vibration detecting electrode, and the electrode 2a is a driving electrode at the time of self-diagnosis and is formed at both ends in a rectangular longitudinal direction. The driving electrodes at both ends are connected by connecting portions formed along the long side of the piezoelectric element. Although not shown in the figure, an electrode 3b is formed on the bottom surface of the layer 4-3. The electrode 1a and the electrode 2b are also formed continuously on a part of the end face. Depending on the firing temperature, the internal electrode and the surface electrode were formed of silver palladium, and the end surface electrodes were formed of silver. FIG. 23 is a longitudinal sectional view of the piezoelectric element 100. FIG. 24 is a plan view of the electrodes of each layer. Layer 4-
The electrode 1b and the electrode 2b formed between the layer 2 and the layer 4-3 have substantially the same shape as the electrodes 1a and 2a provided on the surface of the layer 4-1. The electrode 2b is a driving electrode at the time of self-diagnosis and is connected to both ends in the longitudinal direction of the rectangle via the center of the long side of the piezoelectric element. Although not shown in FIG.
The electrode 1a is the electrode 1 formed between the layer 4-2 and the layer 4-3.
b at the end face, and the electrode 2a is connected to the internal electrode 2b. Similarly, the bottom electrode 3b, layer 4-1 and layer 4-2
The electrode 3a formed therebetween is connected on the opposite side to the electrode 1. The electrode 3a is slightly receded from the end to prevent a short circuit between the electrodes 1a and 1b or the connection between the electrodes 2a and 2b.

The layers 4-1 and 4-3 are polarized, and the directions of polarization are opposite to each other. Layer 4-2 is not polarized.

By connecting the respective electrodes as described above,
The impedance formed by the layer 4-1 and the electrodes on both surfaces thereof and the impedance formed by the layer 4-3 and the electrodes on both surfaces thereof are electrically connected in parallel. Therefore, the capacitance of the entire piezoelectric element is a value obtained by adding the capacitance of each layer. Since the layers are superimposed, it is sufficient to maintain a predetermined strength as a whole. As a result, each layer can be formed of a thin layer, and the capacitance of each layer can be increased. In addition, since the respective capacitances are added, a larger capacitance can be obtained than a single-layer piezoelectric element having the same thickness.

FIG. 25A is an external view of an acceleration sensor using the piezoelectric element shown in FIGS.
(B) is a sectional view thereof. The piezoelectric element 100 is supported at its center in the longitudinal direction by supports 7a and 7b,
Is housed inside. The container 12 was formed of alumina. Outside the container 12, external electrodes 9a, 9b and 9c are provided. The external electrodes 9a, b, and c were formed by forming a solder layer on Ni. The external electrodes 9a, b, and c are connected to the electrodes 1a, 2a, and 3b by conductive layers 8a, b, and c via supports 7a and b, respectively, so that charges generated by acceleration can be taken out of the container 12. it can.

FIG. 26 is a view showing the conductive layer of the support 7a. The support 7a is provided with conductive layers 8a and 8b on the contact surface with the piezoelectric element as shown. The conductive layers 8a and 8b are connected to the electrodes 1a and 2a on the surface of the piezoelectric element 100, respectively. Further, the conductive layers 8a and 8b
It is electrically connected to a and b and can take out electric charges to the outside. The conductive layer 8 and the electrodes 1a and 2a may be bonded using a conductive adhesive.

By using a rectangular piezoelectric element, as described with reference to FIG. 5, even if the piezoelectric element is mounted upright, the height of the acceleration sensor does not increase, so that a small acceleration sensor can be realized.

When acceleration is applied in the vertical direction,
As described with reference to FIG. 6, a large charge amount can be obtained.

As described above, the front and back surfaces of the piezoelectric element are greatly strained, but in the present embodiment, the sensitivity can be increased because the polarized piezoelectric layer is provided there. .

Also, the piezoelectric element has a large distortion near the center holding and a small distortion at the end. In this embodiment, however, an electrode for vibration detection is provided in a portion near the center holding. As a result, the sensitivity could be increased.

FIG. 27 is a block diagram of an acceleration detecting device having a self-diagnosis function using an acceleration sensor.
At the time of self-diagnosis, the electrodes 2a and 2b are used as driving electrodes, and the electrodes 1a and 1b are used as vibration detecting electrodes. The electrodes 3a and 3b are common electrodes and are grounded through the external electrode 9c. The external electrode 9b is provided with a driving circuit 10a for driving a vibration for self-diagnosis.
It is connected to the. A drive AC voltage is generated from the drive circuit 10a and applied to the electrodes 2 and 3 as drive electrodes of the piezoelectric element via the external electrodes 9b and 9c. An electric field is generated inside the layers 4-1 and 4-3 by the AC voltage. Although the electric field is applied in the same direction, the polarization direction is different, so that distortion is generated in the opposite direction, and the entire piezoelectric element performs flexural vibration. As described above, electric charges are generated by the vibration, and the electric charges are generated.
Detection is performed at a and b. The detected charges are input to external electrodes 9a and 9c connected to the impedance conversion circuit 10b. The impedance conversion circuit 10b is generally configured using an FET or the like. This impedance conversion circuit 1
The output voltage from 0b is input to an acceleration detection circuit and an abnormality detection circuit 10c, where it is determined whether or not the piezoelectric element has an abnormality. In general, the abnormality detection circuit 10c includes a high-pass filter, a low-pass filter, a smoothing circuit, a comparator, and the like. The abnormality diagnosis determines whether or not a voltage that matches a predetermined value is output from the impedance conversion circuit 10c with respect to the AC voltage input from the oscillator 10a. When there is an abnormality in the piezoelectric element, the abnormality detection circuit issues an instruction to perform a process at the time of abnormality.

Since the driving electrode portions are stacked, each layer is thin and the electric field is large. Therefore, a large amplitude flexural vibration can be obtained only by inputting a small amplitude AC voltage from the oscillation circuit, and the self-diagnosis can be performed. Accuracy has improved.

Further, since the detection electrode portion is also laminated, the capacitance can be increased, and the vibration induced by the oscillation circuit with high sensitivity up to a low frequency region can be obtained without using a high resistance in the impedance conversion circuit. The self-diagnosis was able to be performed and highly accurate self-diagnosis was performed in a wide frequency range.

Even during normal acceleration detection, since the piezoelectric element 100 is formed by laminating thin layers and each layer is connected in parallel, the capacitance of the entire piezoelectric element becomes large. In addition, each layer serving as a detection element can be thinned without impairing the mechanical strength of the entire piezoelectric element. Therefore, a sufficiently high sensitivity can be obtained even at a low-frequency acceleration,
It could be measured without using high resistance.

At the time of normal acceleration detection, the driving electrode 2
A higher sensitivity could be obtained by using both a and b and the electrodes 1a and 1b for vibration detection as electrodes for detecting acceleration and connecting them to an impedance conversion circuit.

The layer 4-2 is an unpolarized layer.
By providing this layer, the strength of the entire piezoelectric element could be maintained even when the layers 4-1 and 4-3 were extremely thin. The layer 4-2 also has the effect of increasing the capacitance.

Next, an acceleration sensor (layer 4-1 and layer 4-3 having a thickness of 50 μm and layer 4-2 having a thickness of 100 μm) manufactured using the electrodes (see FIG. 3) of the piezoelectric element used for the acceleration sensor of the first embodiment. And the piezoelectric element size is 1.3 mm × 8.0
mm × 0.2 mm, the size of the vibration detection electrode and the drive electrode was 0.5 mm × 7.8 mm), and an acceleration sensor formed using the electrodes of the piezoelectric element of the sixth embodiment (see FIG. 24). (Layers 4-1 and 4-3 have a thickness of 50 μm,
The layer 4-2 is set to 100 μm, and the piezoelectric element size is 1.3 mm.
× 8.0 mm × 0.2 mm, width of detection electrode 1.0 m
m, length 2mm, 3m around support point in longitudinal direction
m, 4 mm, 5 mm, and 6 mm. Drive electrode is 0.2
mm insulated portion was formed on the remaining portion).

Table 1 shows the area, the sensitivity, the product of the capacitance and the sensitivity, and the like of the manufactured acceleration sensors.

[0108]

[Table 1]

The sensitivity decreases as the capacitance increases, even for the same amount of generated charge. Comparing the acceleration sensor of the first embodiment and the acceleration sensor of the sixth embodiment having substantially the same capacity of the vibration detection unit from Table 1, a sensor having twice the sensitivity was obtained. For example, in the first embodiment and the sixth embodiment, the NO. This can be seen from a comparison with No. 3. In addition, the sensitivity was greatly improved in any of the sensors in which the length of the vibration detection section electrode was variously changed. The product of the capacitance and the sensitivity indicates the amount of generated charge. In the acceleration sensor according to the sixth embodiment, the generation of the charge is smaller than that in the first embodiment.
1.5 times or more. That is, by arranging the vibration detection electrode near the support, sensitivity is improved, noise can be reduced, and amplification can be performed with a single-stage amplifier, so that the circuit is simplified.

The self-diagnosis circuit and the impedance conversion circuit are not limited to those shown in FIG.

The directions of polarization are not limited to the directions shown in the figure, but may be any directions as long as they are opposite to each other.

(Embodiment 7) FIG. 28 (a) is a sectional view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention, and FIG. 28 (b) is a perspective view thereof.

The piezoelectric element 102 has a rectangular shape and has three layers 14.
-1, 2 and 3 are laminated, and the layer 14-
1, 3 are polarized, and the polarization directions are the same. FIG. 29 is a plan view of the electrodes of the piezoelectric element. Layer 14-
On the upper surface of 1, two electrodes 11 a and 12 a are divided and formed. The electrode 11 a is formed near the center of the support by a vibration detection electrode, and the electrode 12 a is a rectangular drive electrode for self-diagnosis. Are formed at both ends in the longitudinal direction of the piezoelectric element, and they are connected to each other via a connection portion near the center of the long side of the piezoelectric element. The electrodes 13a and 13b are provided on substantially the entire surface of the piezoelectric element except for the vicinity of an end face serving as a connection portion between the electrodes 11 and 12, and are connected on the side opposite to the connection portion between the electrodes 11 and 12. The layers 14-1 and 14-3 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The layers 14-1, 2, and 3 were all manufactured using ceramics containing lead zirconate as a main component. The electrode used was silver palladium. Although the polarization directions of the layer 14-1 and the layer 14-3 are the same, the connection direction of the electrodes is different from that of FIG. 2, so that the electrodes 11a and 11b generate electric charges of the same polarity even when subjected to flexural vibration. Thus, the acceleration can be detected.

The layer 14-2 has the function of increasing the strength of the piezoelectric element 102 and increasing the impact resistance.

In the first embodiment, the impedance formed by the middle unpolarized layer 4-2 and the electrodes 3a and 1b is the impedance formed by the piezoelectric layer 4-1 and the electrodes 1a and 3a, and the impedance formed by the piezoelectric layer 4-1 and the electrode 3a. 4-3 and electrode 1b, electrode 3
The impedance formed by b is electrically connected in parallel, and the capacitance of the unpolarized layer 4-2 is also included in the capacitance of the entire device. However, since no charge is generated in the unpolarized layer 4-2 even when acceleration is applied,
The capacitance of this layer lowers the output voltage, resulting in lower sensitivity. However, since the layer 14-2 in the seventh embodiment has its opposite surface sandwiched between the electrodes 13a and 13b, the capacitance of the layer 14-2 is smaller than that of the layer 14-.
1. The sensitivity is increased because the capacitance is not added to the capacitance of the layer 14-2.

The self-diagnosis can be performed in the same manner as in FIG. 7, using the electrode 11 as a vibration detecting electrode and the electrode 12 as a driving electrode.

A conductive layer for taking out charges from the electrodes can be formed through a support in the same manner as in FIG.

Using the electrodes of the piezoelectric element shown in FIG. 29 of this embodiment, the thickness of the layer 4-1 and the layer 4-3 is 50 μm,
-2: 100 μm, piezoelectric element size: 1.3 mm × 8.0
An acceleration sensor of mm × 0.2 mm was manufactured. Vibration detection electrode of the present embodiment, as in the sixth embodiment, the width 1.
The drive electrode for self-diagnosis was formed on the remaining portion by changing the length at 0 mm. 4 of the manufactured acceleration sensor
The output of the sensitivity at 0Hz and the self-diagnosis sensitivity at 1V input is
This is 25% higher than in the first embodiment, and the effect of not adding the capacitance of the non-polarized layer to the capacitance of the device was confirmed. Also,
By arranging the vibration detection electrode near the support, sensitivity is improved, noise can be reduced, and amplification can be performed with a single-stage amplifier, which has the effect of simplifying the circuit.

(Eighth Embodiment) FIG. 30 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
Fig. 2 shows a plan view of the electrodes of each layer of the piezoelectric element.

The piezoelectric element 200 has a rectangular shape, and
It has a structure in which two or three layers are laminated. Layer 24-1,
2 are polarized in opposite directions. Electrodes 21a, 22
a is on the upper surface of the piezoelectric element 200, and the electrode 23a is the layer 24-1.
And the layer 24-2, the electrodes 21b and 22b are connected to the layer 24-2.
The electrode 23b is provided on the lower surface between the layer and the layer 24-3. Two electrodes 21a and 22a are provided on the upper surface of the layer 4-1.
The electrode 21a is formed near the center of the support with a vibration detecting electrode, and the electrode 22a is a driving electrode at the time of self-diagnosis and is formed at both ends in a rectangular longitudinal direction. The piezoelectric elements are connected to each other via a connection near the center of the long side of the piezoelectric element. The electrode 21b is a vibration detection electrode, is formed near the center of the support, and is formed over the entire width of the piezoelectric layer. The electrodes 22b are driving electrodes at the time of self-diagnosis and are formed at both ends in the rectangular longitudinal direction. The electrodes 21a and 21
b, the electrodes 22a and 22b are connected. The electrodes 23a and 23b are provided on almost the entire surface except for the connection portions of the electrodes 21 and 22 of the piezoelectric element, and are connected at end faces on the long sides opposite to each other.

By the connection of such electrodes, the layer 24-1 is formed.
And the capacitor formed by the layer 24-3 are connected in parallel, so that the capacitance of the piezoelectric element can be increased. Further, since the electrode 21b is formed in the vicinity of the center of the support and is formed over the entire width of the piezoelectric layer, the amount of generated charges is increased, the sensitivity is further improved, and the noise is reduced as well as one step. The amplifier can be amplified and the circuit is simplified. In addition, since the impact resistance can be increased by the laminated structure and the non-polarized layer 24-2, each layer can be thinned and the capacitance can be increased.

The piezoelectric element 200 is supported at the center in the longitudinal direction as in FIG. 4 and has a conductive layer on the surface in contact with the electrode surface of the support as in FIG.

The operation of detecting the acceleration when receiving the acceleration is the same as in FIG.

At the time of self-diagnosis, it is possible to use a circuit similar to that shown in FIG. 7 using the electrode 21 as a vibration detecting electrode and the electrode 22 as a driving electrode.

The material forming each piezoelectric layer, the material forming the electrodes, and the element size were the same as in the first embodiment.

(Embodiment 9) FIG. 32 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
Fig. 2 shows a plan view of the electrodes of each layer of the piezoelectric element.

The piezoelectric element 300 has a rectangular shape, and includes the layers 34-1 and 34-1.
It has a structure in which two or three layers are laminated. Layer 34-1,
2 are polarized in opposite directions. Electrodes 31a, 32
a is on the upper surface of the piezoelectric element 300, and the electrode 33a is the layer 34-1.
Between the layer 34-2 and the electrodes 31b and 32b.
The electrode 33b is provided on the lower surface between the layer and the layer 34-3. Two electrodes 31a and 32a are provided on the upper surface of the layer 4-1.
The electrode 31a is formed near the center of the support by a vibration detecting electrode, and the electrode 32a is a driving electrode at the time of self-diagnosis and is formed at both ends in a rectangular longitudinal direction. The drive electrodes at both ends are connected to each other at a connection portion formed along the long side of the piezoelectric element. The electrode 31a and the electrode 32a are formed to be separated by a predetermined distance. The electrode 31b is constituted by a vibration detecting electrode near the center of the support, and the electrode 32b is a driving electrode at the time of self-diagnosis and is formed at both ends in a rectangular longitudinal direction. The electrodes 31a and 31b and the electrode 32
a and 32b are connected. The electrodes 33a and 33b are provided on almost the entire surface except for the connection portions of the electrodes 31 and 32 of the piezoelectric element, and are connected at the end faces on the long sides opposite to each other.

As described above, by providing a predetermined distance between the vibration detection electrode 31 and the self-diagnosis electrode 32, it is possible to arbitrarily change the area ratio between the vibration detection electrode and the self-diagnosis electrode.
By holding it, an appropriate capacitance can be realized, and the degree of freedom in circuit design of the system can be increased.

Embodiment 10 FIG. 34 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
FIG. 5 shows a plan view of the electrodes of each layer of the piezoelectric element.

The piezoelectric element 400 has a rectangular shape and includes the layers 44-1 and
It has a structure in which two or three layers are laminated. Layer 44-1,
2 are polarized in opposite directions. Electrodes 41a, 42
a is on the upper surface of the piezoelectric element 400, and the electrode 43a is the layer 44-1.
The electrodes 41b and 42b are provided between the layer 44-2 and the layer 44-2.
The electrode 43b is provided on the lower surface between the layer 44-3. Two electrodes 41a and 42a are provided on the upper surface of the layer 4-1.
The electrode 41a is a vibration detection electrode and is formed near the center of support, and the electrode 42a is a drive electrode for self-diagnosis and is formed at both ends in the rectangular longitudinal direction.

Further, portions without electrodes are formed outside the electrodes 42a and 42b. The electrode 41b is a vibration detecting electrode and is formed near the center of the support, and the electrode 42b is a driving electrode for self-diagnosis and is formed at both ends in a rectangular longitudinal direction. The electrodes 41a and 4a on the end face on the long side of the piezoelectric element 400
1b, the electrodes 42a and 42b are connected. The electrodes 43a and 43b are provided on almost the entire surface except for the connection portions of the electrodes 41 and 42 of the piezoelectric element, and are connected at end faces on the long sides opposite to each other.

By forming a portion without electrodes outside the electrodes 42a and 42b, a desired resonance frequency can be obtained without extremely increasing the resonance frequency determined by the total length of the piezoelectric element. The ratio of the area of the self-diagnosis detection electrode can be changed arbitrarily, and the degree of freedom in the system circuit design can be increased.

(Embodiment 11) FIG. 36 is an external view of a piezoelectric element of an acceleration sensor according to another embodiment of the present invention.
FIG. 7 shows a plan view of the electrodes of each layer of the piezoelectric element.

The piezoelectric element 500 has a rectangular shape and includes the layers 54-1 and 54-1.
It has a structure in which two or three layers are laminated. Layer 54-1,
2 are polarized in opposite directions. Electrodes 51a, 52
a is on the upper surface of the piezoelectric element 500, and the electrode 54a is the layer 54-1.
The electrodes 51b and 52b are between the layer 54-2 and the layer 54-2.
The electrode 54b is provided on the lower surface between the layer 54-3. Two electrodes 51a and 52a are provided on the upper surface of the layer 5-1.
The electrode 51a is formed in the vicinity of the center of the support by a vibration detection electrode, and the electrode 52a is a drive electrode at the time of self-diagnosis and is formed at both ends in a rectangular longitudinal direction. The connection is made at a connection portion formed along the long side of the piezoelectric element.

The electrode (dummy member) 53a is a dummy member that is not connected to either the vibration detection electrode or the self-diagnosis drive electrode. The electrode 51b is a vibration detection electrode and is formed near the center of the support. The electrode 52b is a drive electrode for self-diagnosis and is formed at both ends in the rectangular longitudinal direction. The electrode 53b (dummy member) is a dummy electrode that is not connected to any of the vibration detection electrode and the self-diagnosis drive electrode. The electrode 51 is located at the end face on the long side of the piezoelectric element 500.
a and 51b and the electrodes 52a and 52b are connected. The electrodes 54a and 54b are provided on almost the entire surface of the piezoelectric element except for the connecting portions of the electrodes 51 and 52, and are connected at opposite long side end surfaces.

The operation of detecting the acceleration when receiving the acceleration is the same as in FIG.

At the time of self-diagnosis, it is possible to use a circuit similar to that shown in FIG. 7 using the electrode 51 as a vibration detecting electrode and the electrode 52 as a driving electrode.

Further, by forming the dummy electrodes, it is possible to prevent warpage caused by a difference in firing shrinkage depending on the presence or absence of the electrodes of the piezoelectric element.

In all of the above embodiments, the piezoelectric layers are not limited to those mainly composed of lead zirconate titanate, but mainly composed of lead titanate, lead zirconate, lead lanthanate and the like. It may be something. Further, the electrode is not limited to silver, but may be gold, chromium, nickel, copper, or the like, or a laminate of these, or an alloy thereof. The material of the container is not limited to alumina, but may be metal or resin. The external electrode is not limited to silver-solder, but may be a reflowable material, such as silver brazing.

Note that the number of layers is not limited to three.
When the number of layers is further increased, the electrodes may be connected every other layer at an end face or the like.

For example, a five-layer structure as shown in FIGS. 40, 41 and 42 may be used. 40 is an exploded plan view of the electrode, FIG. 41 is a sectional view, and FIG. 42 is an external view.

In all of the above embodiments, it goes without saying that the acceleration detection circuit is not limited to the impedance conversion method.

As described above, without using electrical connection means such as wiring, it has a high capacitance, maintains a high sensitivity even at a low frequency, and can perform a self-diagnosis at a low frequency range with high accuracy. A small acceleration sensor has been realized.

[0145]

As described above, since the acceleration sensor has a laminated structure and high capacitance, it is not necessary to externally mount a high-resistance element on the substrate. It is not necessary to facilitate special members, etc., it has high sensitivity up to low frequency, it can perform self-diagnosis with high accuracy up to low frequency region, it is easy to take out charge from electrodes,
In addition, a small acceleration sensor without warpage in the laminated element was realized.

[Brief description of the drawings]

FIG. 1 is an external view of a piezoelectric element used for an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a piezoelectric element used for the acceleration sensor according to the first embodiment of the present invention.

FIG. 3 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the first embodiment of the present invention.

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

FIG. 5 is a plan view of a support of the acceleration sensor according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating an operation principle of the acceleration sensor according to the first embodiment of the present invention.

FIG. 7 is a block diagram of signal processing using the acceleration sensor according to the first embodiment of the present invention.

FIG. 8 is a sectional view of a piezoelectric element used in the acceleration sensor according to the second embodiment of the present invention.

FIG. 9 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the second embodiment of the present invention.

FIG. 10 is an external view of a piezoelectric element used for an acceleration sensor according to Embodiment 3 of the present invention.

FIG. 11 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the third embodiment of the present invention.

FIG. 12 is a plan view of a support of the acceleration sensor according to the third embodiment of the present invention.

FIG. 13 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the third embodiment of the present invention.

FIG. 14 is an external view of a piezoelectric element used for an acceleration sensor according to Embodiment 4 of the present invention.

FIG. 15 is a plan view of electrodes of a piezoelectric element used in an acceleration sensor according to Embodiment 4 of the present invention.

FIG. 16 is a sectional view of a piezoelectric element used in the acceleration sensor according to the fourth embodiment of the present invention.

FIG. 17 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to Embodiment 4 of the present invention.

FIG. 18 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the fourth embodiment of the present invention.

FIG. 19 is a plan view of electrodes of a piezoelectric element used in an acceleration sensor according to another embodiment of the present invention.

20 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the embodiment shown in FIG. 19;

21 is a plan view of a support of the acceleration sensor according to the embodiment shown in FIG. 19;

FIG. 22 is an external view of a piezoelectric element used for an acceleration sensor according to Embodiment 6 of the present invention.

FIG. 23 is a sectional view of a piezoelectric element used in the acceleration sensor according to the sixth embodiment of the present invention.

FIG. 24 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the sixth embodiment of the present invention.

FIG. 25 (a) is an external view of an acceleration sensor according to Embodiment 6 of the present invention. (B) It is sectional drawing of the acceleration sensor of Embodiment 6 of this invention.

FIG. 26 is a plan view of a support of the acceleration sensor according to the sixth embodiment of the present invention.

FIG. 27 is a block diagram of signal processing using the acceleration sensor according to the sixth embodiment of the present invention.

FIG. 28 is a sectional view of a piezoelectric element used in the acceleration sensor according to the seventh embodiment of the present invention.

FIG. 29 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the seventh embodiment of the present invention.

FIG. 30 is an external view of a piezoelectric element used for an acceleration sensor according to Embodiment 8 of the present invention.

FIG. 31 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the eighth embodiment of the present invention.

FIG. 32 is an external view of a piezoelectric element used in an acceleration sensor according to Embodiment 9 of the present invention.

FIG. 33 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the ninth embodiment of the present invention.

FIG. 34 is an external view of a piezoelectric element used in the acceleration sensor according to the tenth embodiment of the present invention.

FIG. 35 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the tenth embodiment of the present invention.

FIG. 36 is an external view of a piezoelectric element used for an acceleration sensor according to Embodiment 11 of the present invention.

FIG. 37 is a plan view of electrodes of a piezoelectric element used in the acceleration sensor according to the eleventh embodiment of the present invention.

FIG. 38 is a plan view of electrodes of a piezoelectric element used in a conventional acceleration sensor.

FIG. 39 is a diagram showing a general signal processing circuit used for an acceleration sensor.

FIG. 40 is an exploded plan view of electrodes of a piezoelectric element used in the acceleration sensor according to one embodiment of the present invention.

FIG. 41 is a sectional view of a piezoelectric element used in the acceleration sensor according to the embodiment of the present invention shown in FIG. 40;

FIG. 42 is an external view of a piezoelectric element used in the acceleration sensor according to the embodiment of the present invention shown in FIG. 40;

[Explanation of symbols]

1, 2, 3, 21, 22, 22, 31, 32, 33 Electrode 4, 24, 34 Layer 7, 27, 37 Support 8 Conductive layer 9 External electrode 100, 200, 300 Piezoelectric element 101, 301 Acceleration sensor

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Katsushi Takeda 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Katsunori Moriki 1006 Kadoma Kazuma Kadoma, Osaka Pref. (72) Inventor Kawa Osamu Osamu 1006 Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Junichi Kato 1006 Okadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (14)

[Claims] A piezoelectric element having a piezoelectric layer on which a plurality of piezoelectric bodies are stacked, and electrodes provided on main opposing surfaces of the piezoelectric layers; and a support for supporting the piezoelectric element; Some of the piezoelectric layers are polarized,
The electrodes are provided on both surfaces of the polarized piezoelectric material,
An acceleration sensor, wherein an impedance formed by the polarized piezoelectric body and electrodes on both surfaces thereof is electrically connected in parallel to each other. 2. Each of the piezoelectric layers has a rectangular shape, and an electrode present on at least one surface of the piezoelectric layer is divided into two, and each of the two electrodes is disposed on a long side of the piezoelectric element. The acceleration sensor according to claim 1, wherein the acceleration sensor is provided substantially along. 3. Each of the piezoelectric layers has a rectangular shape, and an electrode present on at least one surface of the piezoelectric layer is divided into two, and each of the two electrodes is connected to a short side of the piezoelectric element. The acceleration sensor according to claim 1, wherein the acceleration sensor is provided substantially along. 4. Each of the piezoelectric layers has a disk shape, and electrodes present on at least one surface of the piezoelectric layer are divided into two, and each of the two electrodes is provided concentrically. The acceleration sensor according to claim 1, wherein: 5. The acceleration sensor according to claim 4, wherein the piezoelectric element has a through hole penetrating a center of each of the disk-shaped piezoelectric layers. 6. The acceleration sensor according to claim 2, wherein the piezoelectric element is supported substantially at the center of a long side of each of the rectangular piezoelectric layers. 7. The acceleration sensor according to claim 4, wherein the piezoelectric element is supported substantially at the center of each of the disk-shaped piezoelectric layers. 8. The acceleration sensor according to claim 1, wherein the electrical connection between the electrode and another external electrode is made via the support. . 9. The acceleration sensor according to claim 2, wherein one of the two electrodes is a driving electrode during self-diagnosis, and the other is a vibration detecting electrode. 10. The piezoelectric element has a rectangular shape, an electrode present on at least one surface of the piezoelectric layer is divided into two, and the support is substantially a long side of each of the piezoelectric layers. Supported at the center, one of the two divided electrodes is a vibration detection electrode and is disposed at the center of the surface of the piezoelectric element, and the other is a driving electrode at the time of self-diagnosis and is a piezoelectric element of the piezoelectric element. 2. The acceleration sensor according to claim 1, wherein the acceleration sensor is arranged at or near both ends in the longitudinal direction of the surface and connected to each other. 11. The driving electrode is disposed at or near both ends of a surface F of another piezoelectric layer of the piezoelectric element, and the driving electrode on the surface F is also disposed on the surface F. 2. The device according to claim 1, wherein the devices are connected to each other.
0 acceleration sensor. 12. The driving electrode is disposed at or near both ends of a surface F of another piezoelectric layer of the piezoelectric element, and the driving electrode on the surface F is formed on the surface F. The acceleration sensor according to claim 10, wherein the acceleration sensors are not connected to each other. 13. A dummy member which is not connected to the vibration detecting electrode and the driving electrode disposed on the same surface of the piezoelectric layer and is not connected to the electrodes. 10. The acceleration sensor according to 10. 14. The method according to claim 10, wherein the vibration detecting electrode and the driving electrode are connected to another external electrode via the support. The acceleration sensor according to any one of the preceding claims.