Patent Description:
The present disclosure relates to a piezoelectric element having a vibration region, a piezoelectric device, and a method for manufacturing a piezoelectric element.

A piezoelectric element having a vibration region has conventionally been proposed (see, for example, Patent Document <NUM>). Specifically, the piezoelectric element has a configuration in which a piezoelectric film and an electrode film electrically connected to the piezoelectric film are laminated on a support member. In the piezoelectric element, a recess is formed in the support member, and a part of the piezoelectric film and the electrode film constitutes is a floating region floating from the support member. Further, in this piezoelectric element, the floating region is divided into a plurality of regions by forming slit in the floating region, thereby forming vibration regions. Each vibration region is in a state of being cantilevered by the support member. Each vibration region has a substantially triangular planar shape, and the mass of one end on the support member side is made heavier than the mass of the other end opposite to one end.

Patent Document <NUM> shows a piezoelectric device with multiple vibrating regions with different sizes to control the low-frequency roll-off.

In Patent Document <NUM>, the low-frequency roll-off is controlled by the selection of the number and size of openings in the sensor membrane or electronic processing.

By the way, in the piezoelectric element as described above, there is a demand for improving a detection accuracy on a low frequency side. An object of the present disclosure is to provide a piezoelectric element, a piezoelectric device, and a manufacturing method of a piezoelectric element, which can improve the detection accuracy.

According to one aspect of the present disclosure, a piezoelectric element includes a support member and a vibrating portion. The vibrating portion has a support region supported by the support member, and a plurality of vibration regions, one end portion side of which is supported by the support region, and the other end portion side of which is opposite to the one end portion is floating from the support member. The plurality of vibration regions includes a vibration region in which a mass on the one end portion side is heavier than the mass on the other end portion side, and which serves as a pressure detection section configured to output a first detection signal based on the charge of the piezoelectric film, and a vibration region in which a mass on the other end portion side is heavier than the mass on one end portion side, and which serves as an acceleration detection section configured to output a second detection signal based on the charge of the piezoelectric film.

According to this configuration, in the acceleration detection section, the mass of the other end portion side is made heavier than the mass of the one end portion side. Therefore, the acceleration detection section has a low-frequency roll-off frequency than that in the pressure detection section. Therefore, when the frequency of the pressure to be detected is less than the predetermined threshold value, the pressure is detected using the second detection signal from the acceleration detection section, thereby improving the detection accuracy on the low frequency side.

According to another aspect of the present disclosure, a piezoelectric device includes the above-described piezoelectric element and a control section that performs predetermined processing. The control section calculates a frequency of the applied pressure based on the first detection signal and the second detection signal, compares the calculated frequency with a predetermined threshold value, detects the pressure based on the second detection signal when it is determined that the calculated frequency is less than the predetermined threshold value, and detects the pressure based on the first detection signal when it is determined that the calculated frequency is equal to or greater than the predetermined threshold value.

According to this configuration, the control section detects the pressure based on the second detection signal when determining that the frequency of the calculated pressure is less than the predetermined threshold value. Therefore, it is possible to improve the detection accuracy on the low frequency side.

According to another aspect of the present disclosure, a piezoelectric device includes a piezoelectric element and a control section that performs predetermined processing. The piezoelectric element has a support member and a vibrating portion. The vibrating portion is disposed on the support member and has a piezoelectric film and an electrode film electrically connected to the piezoelectric film, and a support region supported by the support member, and a plurality of vibration regions, one end portion side of which is supported by the support region, and the other end portion side of which is opposite to the one end portion is floating from the support member. A plurality of piezoelectric elements includes a piezoelectric element having a vibration region in which a mass on the one end portion side is larger than the mass on the other end portion side and serves as a pressure detection section that outputs a first detection signal based on the charge of the piezoelectric film, and a piezoelectric element having a vibration region in which a mass on the other end portion side is larger than the mass on the one end portion side and serves as an acceleration detection section that outputs a second detection signal based on the charge of the piezoelectric film. The control section calculates a frequency of the applied pressure based on the first detection signal and the second detection signal, compares the calculated frequency with a predetermined threshold value, detects the pressure based on the second detection signal when it is determined that the calculated frequency is less than the predetermined threshold value, and detects the pressure based on the first detection signal when it is determined that the calculated frequency is equal to or greater than the predetermined threshold value.

According to this configuration, in the acceleration detection section, the mass of the other end portion side is made heavier than the mass of the one end portion side. Therefore, the acceleration detection section has a low-frequency roll-off frequency than that in the pressure detection section. The control section detects the pressure based on the second detection signal when determining that the frequency of the calculated pressure is less than the predetermined threshold value. Therefore, it is possible to improve the detection accuracy on the low frequency side.

According to another aspect of the present disclosure, a manufacturing method of the above-described piezoelectric element includes preparing a support member, forming a piezoelectric film and an electrode film on the support member, forming a vibrating region constituent part by forming a slit that penetrates the piezoelectric film and reaches the support member, and forming a vibrating portion having a vibrating region by forming a recess portion on the opposite side of the support member from the piezoelectric film side and floating the vibrating region constituent part. When configuring the vibrating region by forming the slit, the slit is formed so that the vibration region in which a mass on the one end portion side is made heavier than the mass on the other end portion side and serving as the pressure detection section is configured, and the vibration region in which a mass on the other end portion side is made heavier than the mass on the one end portion side and serving as the acceleration detection section is configured.

According to this configuration, the pressure detection section and the acceleration detection section are formed in the same process by adjusting the shape of the slit. Therefore, the manufacturing process can be simplified.

A reference numeral in parentheses attached to each component or the like indicates an example of correspondence between the component or the like and specific component or the like described in an embodiment below.

Embodiments of the present disclosure will be described below with reference to the drawings. In the following embodiments, the same reference numerals are assigned to parts that are the same or equivalent to each other for description.

The configuration of a piezoelectric device S10 of the first embodiment will be described with reference to <FIG>. In addition, the piezoelectric device S10 of the present embodiment is preferably used to detect pressure such as sound pressure of <NUM> to <NUM>, which is an audible range, and is preferably used by being mounted on a smart phone, an AI speaker, or the like. Also, the piezoelectric device S10 of the present embodiment is installed in an electronic device or the like that exhibits a wake-up function that can obtain an output according to displacement without a power source and is preferably used to detect the displacement.

As shown in <FIG>, the piezoelectric device S10 of the present embodiment includes a piezoelectric element <NUM> and a circuit board <NUM> having a control section <NUM>. The piezoelectric element <NUM> and the circuit board <NUM> are accommodated in a casing <NUM>. First, the configuration of the piezoelectric element <NUM> of the present embodiment will be described.

As shown in <FIG>, the piezoelectric element <NUM> includes a support member <NUM> and a vibrating portion <NUM>, and has a rectangular planar shape. The support member <NUM> includes a support substrate <NUM> having one surface 11a and the other surface 11b, and an insulating film <NUM> formed on the one surface 11a of the support substrate <NUM>. The support substrate <NUM> is made of, for example, a silicon substrate, and the insulation film <NUM> is made of an oxide film or the like.

The vibrating portion <NUM> is arranged on the support member <NUM> and has a piezoelectric film <NUM> and an electrode film <NUM> electrically connected to the piezoelectric film <NUM>. The piezoelectric film <NUM> is made of, for example, lead-free piezoelectric ceramics such as scandium aluminum nitride (ScAlN) or aluminum nitride (AIN). The electrode film <NUM> is made of molybdenum, copper, platinum, titanium, or the like.

In the present embodiment, the piezoelectric film <NUM> has a lower piezoelectric film <NUM> and an upper piezoelectric film <NUM> laminated on the lower piezoelectric film <NUM>. Further, the electrode film <NUM> includes: a lower electrode film <NUM> arranged below the lower piezoelectric film <NUM>, an intermediate electrode film <NUM> arranged between the lower piezoelectric film <NUM> and the upper piezoelectric film <NUM>, and an upper electrode film <NUM> arranged on the upper piezoelectric film <NUM>. That is, the vibrating portion <NUM> has a bimorph structure in which the lower piezoelectric film <NUM> is sandwiched between the lower electrode film <NUM> and the intermediate electrode film <NUM>, and the upper piezoelectric film <NUM> is sandwiched between the intermediate electrode film <NUM> and the upper electrode film <NUM>. The vibrating portion <NUM> then outputs a detection signal corresponding to a capacitance between the lower electrode film <NUM> and the intermediate electrode film <NUM> and a capacitance between the intermediate electrode film <NUM> and the upper electrode film <NUM>.

Each electrode film <NUM> is formed in each vibration region <NUM>, which will be described later, of the vibrating portion <NUM>. Each electrode film <NUM> is appropriately connected to a wiring (not shown) formed in a support region 21a, which will be described later, of the vibrating portion <NUM>, and is connected to the circuit board <NUM> via an electrode portion (not shown) formed in the support region 21a.

Further, the vibrating portion <NUM> of the present embodiment includes a base film <NUM> on which the lower piezoelectric film <NUM> and the lower electrode film <NUM> are disposed. That is, the piezoelectric film <NUM> and the electrode film <NUM> are disposed on the support member <NUM>, with the base film <NUM> interposed between the piezoelectric film <NUM> and the electrode film <NUM>. The base film <NUM> is not necessarily required, but it is provided to facilitate crystal growth when the lower piezoelectric film <NUM> and the like are formed. In the present embodiment, the base film <NUM> is made of aluminum nitride or the like. The piezoelectric film <NUM> has a thickness of about <NUM>, and the base film <NUM> has a thickness of about several tens of nm. That is, the base film <NUM> is extremely thin with respect to the piezoelectric film <NUM>.

In the support member <NUM>, a recess portion 10a is formed for floating an inner edge side of the vibrating portion <NUM>. The recess portion 10a corresponds to a recess. Therefore, the vibrating portion <NUM> has a structure with a support region 21a arranged on the support member <NUM> and a floating region 21b connected to the support region 21a and floating on the recess portion 10a. The recess portion 10a according to the present embodiment has a flat rectangular shape at the opening end at a side closer to the vibrating portion <NUM>. Therefore, the shape of the inner edge of the support region 21a is a rectangle having first to fourth sides <NUM> to <NUM>.

The floating region 21b includes a slit <NUM> that penetrates the floating region 21b in a thickness direction. In the present embodiment, the slit <NUM> divides the floating region 21b into six regions, and each divided region is cantilevered by the support region 21a. Each of the six divided regions functions as the vibration region <NUM>. Each vibration region <NUM> is composed of the same constituent elements, and functions are divided according to the planar shape, although the details will be described later. Each vibrating region <NUM> vibrates to change the electric charge of the piezoelectric film <NUM>, so that the electrode film <NUM> outputs a detection signal corresponding to the electric charge.

The configuration of each vibration region <NUM> in the present embodiment will be described below. Hereinafter, the end of each vibration region <NUM> that is a fixed end on the side of the support region 21a is referred to as one end portion <NUM>, and the end of each vibration region <NUM> that is a free end on the side opposite to the support region 21a is referred to as the other end portion <NUM>. In the following description, the surface of the vibration region <NUM> on the opposite side from the support member <NUM> is defined as one surface 22a of the vibration region <NUM>, and the surface of the vibration region <NUM> on the support member <NUM> side is defined as the other surface 22b of the vibration region <NUM>.

In the present embodiment, each of the six vibration regions <NUM> has a substantially triangular planar shape. Two vibration regions <NUM> of the six vibration regions <NUM> are formed such that the mass on the one end portion <NUM> side is heavier than the mass on the other end portion <NUM> side. In the present embodiment, the two vibration regions <NUM> have a substantially triangular planar shape as described above and are formed so that the one end portion <NUM> side is composed of one side connecting two apex angles and the other end portion <NUM> side is composed of one apex angle. In the two vibration regions <NUM>, the width of the one end portion <NUM> side is larger than the width of the other end portion <NUM> side in the direction (hereinafter also simply referred to as the normal direction) normal to the one surface 22a and the other surface 22b of the vibration region <NUM>. The width in the present embodiment is the length along the surface direction of the vibration region <NUM> in the direction intersecting with the extending direction of the vibration region <NUM> from the support region 21a side.

Such a vibrating region <NUM> vibrates according to the pressure directly applied to the vibration region <NUM> and outputs a detection signal based on the vibration. In other words, the vibration region <NUM> has a larger mass on the one end portion <NUM> side than on the other end portion <NUM> side, and outputs a detection signal corresponding to a state in which a uniformly distributed load is applied. In the following description, such a vibration region <NUM> is referred to as a pressure detection section 220a, and a detection signal output from the pressure detection section 220a is referred to as a first detection signal. The pressure detection section 220a has a smaller mass on the other end portion <NUM> side than the mass on the one end portion <NUM> side compared to the acceleration detection section 220b, which will be described later.

Four vibration regions <NUM> among the six vibration regions <NUM> are formed so that the mass on the other end portion <NUM> side is heavier than the mass on the one end portion <NUM> side. In the present embodiment, the four vibration regions <NUM> have a substantially triangular planar shape (in other words, a substantially trapezoidal planar shape) as described above and are formed so that the one end portion <NUM> side is composed of one apex angle and the other end portion <NUM> side is composed of the remaining two apex angle. In the four vibration regions <NUM>, the width on the side of the other end portion <NUM> is wider than the width on the side of the one end portion <NUM> in the normal direction.

Compared with the pressure detection section 220a, the vibration region <NUM> has a larger mass on the other end portion <NUM> side, so that the vibration region <NUM> is less likely to vibrate due to the pressure directly applied to the vibration region <NUM>. Such vibration region <NUM> outputs a detection signal corresponding to the acceleration based on the pressure applied to the entire piezoelectric element <NUM>. In other words, the vibration region <NUM> has a mass on the other end portion <NUM> side larger than that on the one end portion <NUM> side, and outputs a detection signal corresponding to a state in which a tip load is applied. In the following description, such a vibration region <NUM> is referred to as an acceleration detection section 220b, and a detection signal output from the acceleration detection section 220b is referred to as a second detection signal. The detection signal corresponding to the acceleration based on the pressure applied to the entire piezoelectric element <NUM> is a signal based on a vibration due to pressure applied to the entire piezoelectric element <NUM>, an air vibration, a vibration due to the weight of the other end portion <NUM> side, and the like. In addition, since the mass of the other end portion <NUM> side of the vibration region <NUM> is made heavier than the mass of the one end portion <NUM> side, the pressure that escapes through the slit <NUM> between the adjacent vibration regions <NUM> makes it difficult for the vibration regions <NUM> to vibrate.

As described above, the piezoelectric element <NUM> of the present embodiment is configured to have two pressure detection sections 220a and four acceleration detection sections 220b. In other words, the piezoelectric element <NUM> of the present embodiment is a so-called composite sensor. In the piezoelectric element <NUM> of the present embodiment, the pressure detection section 220a outputs a first detection signal based on the pressure directly applied to the vibration region <NUM>, and the acceleration detection section 220b output the second detection signal based on the pressure or the like applied to the entire piezoelectric element <NUM>. In the present embodiment, the four pressure detection sections 220a are connected in series and output one first detection signal. Similarly, the two acceleration detection sections 220b are connected in series and output one second detection signal.

Here, in the pressure detection section <NUM>, the mass of the one end portion <NUM> side is larger than the mass of the other end portion <NUM> side, and in the acceleration detection section 220b, the mass of the other end portion <NUM> side is larger than the mass of the one end portion <NUM> side. Therefore, as shown in <FIG>, the pressure detection section 220a and the acceleration detection section 220b have different low-frequency roll-off frequencies fr1 and fr2 and resonance frequencies f1 and f2. Specifically, the low roll-off frequency fr2 of the second detection signal output from the acceleration detection section 220b is lower than the low roll-off frequency fr1 of the first detection signal output from the pressure detection section 220a. For example, the low-frequency roll-off frequency fr2 of the second detection signal is approximately <NUM>, and the low-frequency roll-off frequency fr1 of the first detection signal is approximately <NUM>. Also, the resonance frequency f2 of the acceleration detection section 220b is lower than the resonance frequency f1 of the pressure detection section 220a. For example, the resonance frequency f2 of the acceleration detection section 220b is approximately <NUM>, and the resonance frequency f1 of the pressure detection section 220a is approximately <NUM>.

In <FIG>, the output of the first detection signal output from the pressure detection section 220a when the frequency is <NUM> is used as a reference (that is, <NUM> dB). Further, detailed numerical values of the low-frequency roll-off frequencies fr1 and fr2 and the resonance frequencies f1 and f2 can be appropriately changed by adjusting the width of the other end portion <NUM> side of the vibration region <NUM> and the like. However, when the pressure detection section 220a and the acceleration detection section 220b are configured with the magnitude relationship between the masses of the one end portion <NUM> and the other end portion <NUM> defined as described above, the low-frequency roll-off frequency fr2 of the second detection signal is lower than the low-frequency roll-off frequency fr1 of the first detection signal.

The pressure detection section 220a and the acceleration detection section 220b of the present embodiment are provided with one end portion <NUM> side supported by the first side <NUM> and the third side <NUM> facing each other in the support region 21a. Specifically, the first side <NUM> is provided with one pressure detection section 220a and two acceleration detection sections 220b. Specifically, one pressure detection section 220a is provided at a position including the center of the first side <NUM>. The two acceleration detection sections 220b are provided on the first side <NUM> so as to interpose the pressure detection section 220a. Similarly, the third side <NUM> is provided with one pressure detection section 220a and two acceleration detection sections 220b. Specifically, one pressure detection section 220a is provided at a position including the center of the third side <NUM>. The two acceleration detection sections 220b are provided on the third side <NUM> so as to interpose the pressure detection section 220a.

The above is the configuration of the piezoelectric element <NUM> in this embodiment.

The circuit board <NUM> performs predetermined processing and has the control section <NUM> in the present embodiment. The control section <NUM> is composed of a microcomputer having a CPU, storage units such as a ROM, a RAM, and a nonvolatile RAM, and is connected to the piezoelectric element <NUM>. The control section <NUM> is configured so that the CPU reads and executes a program from the ROM or the non-volatile RAM to execute various control operations. Various data (for example, initial values, lookup tables, maps, etc.) used for program execution are stored in advance in the ROM or non-volatile RAM. The storage medium such as the ROM is a non-transitory tangible storage medium. CPU is an abbreviation for Central Processing Unit, ROM is an abbreviation for Read Only Memory, RAM is an abbreviation for Random Access Memory.

The control section <NUM> of the present embodiment calculates the frequency of the applied pressure based on the first detection signal output from the pressure detection section 220a and the second detection signal output from the acceleration detection section 220b. For example, the control section <NUM> calculates the frequency of the applied pressure by performing Fourier analysis based on the first detection signal and the second detection signal.

Then, when the control section <NUM> determines that the calculated frequency is equal to or higher than the predetermined threshold value, the control section <NUM> detects the applied pressure using the first detection signal. Further, when the control section <NUM> determines that the calculated frequency is less than the predetermined threshold value, the control section <NUM> detects the applied pressure using the second detection signal. The predetermined threshold value is set based on the low-frequency roll-off frequency fr1 of the pressure detection section 220a and is set to <NUM> in the present embodiment, for example.

As shown in <FIG>, the casing <NUM> includes a printed circuit board <NUM> on which the piezoelectric element <NUM> and a circuit board <NUM> are mounted, and a lid <NUM> fixed to the printed circuit board <NUM> in a manner to accommodate the piezoelectric element <NUM> and the circuit board <NUM>. In the present embodiment, the printed circuit board <NUM> corresponds to a mounted member.

Although not illustrated, the printed circuit board <NUM> has a configuration in which a wiring portion, a through-hole electrode, and the like are appropriately formed, and electronic components such as a capacitor (not illustrated) are also mounted as necessary. In the piezoelectric element <NUM>, the other surface 11b of the support substrate <NUM> is mounted on one surface 101a of the printed circuit board <NUM>, with a bonding member <NUM>, such as an adhesive, interposed between the other surface 11b and the one surface 101a. The circuit board <NUM> is mounted on the one surface 101a of the printed circuit board <NUM> via a bonding member <NUM> made of a conductive member. The piezoelectric element <NUM> and the circuit board <NUM> are electrically connected via a bonding wire <NUM>. The lid <NUM> is made of metal, plastic, resin, or the like, and is fixed to the printed circuit board <NUM> to accommodate the piezoelectric element <NUM> and the circuit board <NUM>, in which a bonding member, such as an adhesive (not illustrated), is interposed between the lid <NUM> and the circuit board <NUM>.

Further, in the present embodiment, a through hole 101b is formed in a portion of the printed circuit board <NUM> that faces the vibration region <NUM> to allow the inside and outside of the casing <NUM> to communicate with each other. Specifically, the through hole 101b has a substantially cylindrical shape, and is formed such that its central axis matches up with a center of the vibrating portion <NUM> in the normal direction.

The above is the configuration of the piezoelectric device S10 in the present embodiment. Next, the operation of the piezoelectric device S10 will be described.

When pressure is applied to the piezoelectric device S10 of the present embodiment, the pressure is introduced into the recess portion 10a through the through hole 101b while the piezoelectric device S10 vibrates as a whole. Since the charge of the piezoelectric film <NUM> changes when the pressure detection section 220a and the acceleration detection section 220b vibrate, the pressure detection section 220a and the acceleration detection section 220b output the first and second detection signals according to the change in the charge. Specifically, the pressure detection section 220a outputs the first detection signal based on the pressure introduced into the recess portion 10a from the through hole 101b. The acceleration detection section 220b outputs the second detection signal based on the pressure or the like applied to the entire piezoelectric device S10 (that is, the entire piezoelectric element <NUM>).

The control section <NUM> performs the operations described above. Specifically, the control section <NUM> calculates the frequency of the applied pressure based on the first detection signal and the second detection signal. Then, when the calculated frequency is less than a predetermined threshold value, the pressure is detected using the second detection signal, and when the calculated frequency is greater than or equal to the predetermined threshold value, the pressure is detected using the first detection signal.

The following describes a method of manufacturing the piezoelectric element <NUM> with reference to <FIG> are cross-sectional views of a portion corresponding to <FIG>.

First, as illustrated in <FIG>, the base film <NUM>, the piezoelectric film <NUM>, the electrode film <NUM>, and the like are formed on the support member <NUM> having the support substrate <NUM> and the insulating film <NUM>. That is, a material in which the recess portion10a and the slit <NUM> are not formed in the piezoelectric element <NUM> illustrated in <FIG> is prepared. The piezoelectric film <NUM>, the electrode film <NUM> configured in the process of <FIG> are portions that form the vibrating portion <NUM>. Therefore, in <FIG>, the same reference numerals as those of the one surface 22a and the other surface 22b of the vibration region <NUM> are attached.

Next, as illustrated in <FIG>, anisotropic dry etching is performed using a mask (not illustrated) to form the slit <NUM> that penetrate the piezoelectric film <NUM> and reach the support member <NUM>. As a result, a vibration region constituent part <NUM> to be the vibration region <NUM> is configured by forming the recess portion 10a to be described later. In addition, when the vibration region <NUM> is configured, the slit <NUM> is formed so as to configure the pressure detection section 220a in which the mass on the one end portion <NUM> side is heavier than the mass on the other end portion <NUM> side and the acceleration detection section 220b in which the mass on the other end portion <NUM> side is heavier than the mass on the one end portion <NUM> side. That is, in the present embodiment, the pressure detection section 220a and the acceleration detection section 220b are separated only by the shape of the slit <NUM> and have the same configuration other than the planar shape.

The vibration region constituent part <NUM> is a portion to be the vibration region <NUM> with the formation of the recess portion 10a. For this reason, in the drawing, the one surface and the other surface of the vibration region constituent part <NUM> are given the same reference numerals as the one surface 22a and the other surface 22b of the vibration region <NUM>, respectively.

Subsequently, as illustrated in <FIG>, etching is performed using a mask (not illustrated) to penetrate the insulating film <NUM> from the other surface 11b of the support substrate <NUM> and reach the base film <NUM>, thereby forming the recess portion 10a. In the present embodiment, after the support substrate <NUM> is removed by anisotropic dry etching, the insulating film <NUM> is removed by isotropic wet etching to form the recess portion 10a. As a result, the vibration region constituent part <NUM> floats from the support member <NUM> to form the vibration region <NUM>, and the piezoelectric element <NUM> illustrated in <FIG> is manufactured.

In addition, since the slit <NUM> is formed as described above, the configured vibration region <NUM> is configured to have the pressure detection section 220a and the acceleration detection section 220b. In this step, although not illustrated, a protective resist or the like covering the upper piezoelectric film <NUM> and the upper electrode film <NUM> may be disposed to form the recess portion 10a. According to this configuration, when forming the recess portion 10a, it can suppress that the vibration region <NUM> is destroyed. The protective resist is removed after the recess portion 10a is formed.

According to the present embodiment described above, the piezoelectric device S10 has the pressure detection section 220a and the acceleration detection section 220b. Therefore, the detection accuracy can be improved. That is, when the piezoelectric element <NUM> includes only the pressure detection section 220a in which the mass on the one end portion <NUM> side is larger than the mass on the other end portion <NUM> side, the detection signal output from the pressure detection section 220a is shown in <FIG>. In <FIG>, the output when the frequency is <NUM> is referred to as the reference (that is, <NUM> dB).

As shown in <FIG>, the detection signal is a constant signal containing white noise at frequencies higher than <NUM>, but the detection signal becomes a signal whose <NUM>/f noise increases as the frequency decreases at frequencies lower than <NUM>. That is, the detection accuracy of the detection signal from the pressure detection section 220a decreases as the frequency decreases. The cause of this phenomenon is that when the pressure is at a low frequency, the mass on the one end portion <NUM> side of the pressure detection section 220a is made heavier than the mass on the other end portion <NUM> side, so the pressure coming out of the slit <NUM> has a greater influence.

Therefore, in the present embodiment, in addition to the pressure detection section 220a, the acceleration detection section 220b is provided. Further, In the acceleration detection section 220b, the mass of the other end portion <NUM> side is made heavier than the mass of the one end portion <NUM> side, and the low-frequency roll-off frequency fr2 of the second detection signal is lower than the low-frequency roll-off frequency fr1 of the first detection signal. Then, the piezoelectric device S10 detects the pressure based on the second detection signal when the pressure is less than the predetermined threshold value. Therefore, in the piezoelectric device S10 of the present embodiment, the low-frequency pressure that lowers the detection accuracy of the pressure detection section 220a is detected based on the second detection signal from the acceleration detection section 220b. can be improved. Therefore, it is possible to improve detection accuracy on the low frequency side. Further, by improving detection accuracy on the low frequency side, AOP (abbreviation of Acoustic Over Point) can be improved.

A second embodiment will be described. In the present embodiment, the piezoelectric element <NUM> is provided with a temperature detection section, as compared with the first embodiment. Descriptions of the same configurations and processes as those of the first embodiment will not be repeated hereinafter.

In the piezoelectric element <NUM> of the present embodiment, as shown in <FIG>, the support region 21a of the piezoelectric element <NUM> is provided with a temperature detection section <NUM>. The temperature detection section <NUM> is composed of a temperature sensitive resistor or the like whose resistance value changes according to the temperature.

The control section <NUM> of the present embodiment is connected to the temperature detection section <NUM> and performs predetermined temperature correction based on the temperature detection signal from the temperature detection section <NUM>. Specifically, the vibration region <NUM> is configured by laminating the piezoelectric film <NUM> and the electrode film <NUM> as described above. Therefore, the vibration region <NUM> may warp when the ambient temperature changes due to the use environment or the like because the piezoelectric film <NUM> and the electrode film <NUM> have different coefficients of linear expansion. Therefore, the control section <NUM> calculates the warp of the vibration region <NUM> from the temperature detection signal, performs temperature correction based on the calculated warp, and detects the pressure.

In the present embodiment, the relationship between the temperature and the warp of the vibration region <NUM> is calculated in advance by experiments or the like, and auxiliary data regarding the temperature and the warp of the vibration region <NUM> is stored in the control section <NUM>. Then, the control section <NUM> calculates the warp of the vibration region <NUM> based on the temperature detection signal and the auxiliary data and performs temperature correction for calculating a correction signal that reduces the influence of the warp from the first detection signal and the second detection signal and detect the pressure using the correction signal. The direction and magnitude of the warp of the vibration region <NUM> change depending on the temperature, the material and thickness of the piezoelectric film <NUM> and the electrode film <NUM>, and the like. Therefore, the auxiliary data is preferably created in consideration of the actual material, thickness, etc. of the piezoelectric film <NUM> and the electrode film <NUM>.

According to the present embodiment described above, the piezoelectric element <NUM> is provided with the pressure detection section 220a and the acceleration detection section 220b. Since the control section <NUM> detects the pressure based on the predetermined threshold value, it is possible to prevent the detection accuracy from deteriorating.

A third embodiment will be described. The present embodiment differs from the first embodiment in the configurations of the pressure detection section 220a and the acceleration detection section 220b. Descriptions of the same configurations and processes as those of the first embodiment will not be repeated hereinafter.

In the piezoelectric element <NUM> of the present embodiment, as shown in <FIG>, four pressure detection sections 220a and two acceleration detection sections 220b are formed. Specifically, the first side <NUM> is provided with one acceleration detection section 220b on the fourth side <NUM> side and one pressure detection section 220a on the second side <NUM> side. A portion including the boundary between the first side <NUM> and the second side <NUM> is provided with one pressure detection section 220a. The third side <NUM> is provided with one acceleration detection section 220b on the second side <NUM> side and one pressure detection section 220a on the fourth side <NUM> side. A portion including the boundary between the third side <NUM> and the fourth side <NUM> is provided with one pressure detection section 220a.

According to the present embodiment described above, the piezoelectric element <NUM> is provided with the pressure detection section 220a and the acceleration detection section 220b. Since the control section <NUM> detects the pressure based on the predetermined threshold value, it is possible to prevent the detection accuracy from deteriorating. As in the present embodiment, the number of pressure detection sections 220a and acceleration detection sections 220b can be changed as appropriate.

A fourth embodiment will be described. The present embodiment differs from the third embodiment in the arrangements of the pressure detection section 220a and the acceleration detection section 220b. The other configurations of the present embodiment are similar to those of the third embodiment, and therefore a description of the similar configurations will not be repeated.

As shown in <FIG>, in the piezoelectric element <NUM> of the present embodiment, the four pressure detection sections 220a are collectively arranged in one region with respect to a virtual line K connecting two predetermined locations on the inner edge side of the support region 21a. Also, in the piezoelectric element <NUM>, two acceleration detection sections 220b are collectively arranged in the other region with respect to the virtual line K.

The virtual line K in the present embodiment is a polygonal line that connects a central portion C of the floating region 21b and two locations on the inner edge portion of the support region 21a. However, the virtual line K may be a straight line, or may be a line that does not pass through the central portion C.

A fifth embodiment will be described. In the present embodiment, the configuration of the piezoelectric device S10 is changed from the first embodiment. Descriptions of the same configurations and processes as those of the first embodiment will not be repeated hereinafter.

In the piezoelectric device S10 of the present embodiment, as shown in <FIG>, the through hole 101b is formed in a portion facing the pressure detection section 220a and is not formed in a portion facing the acceleration detection section 220b. That is, in the through holes 101b of the present embodiment, the distance between the opposing side surfaces is narrower than that in the first embodiment.

A partition wall <NUM> is arranged around the through hole 101b of the printed circuit board <NUM>. Specifically, the partition wall <NUM> is arranged on the printed circuit board <NUM> so that a first space S1 surrounded by the pressure detection section 220a and the printed circuit board <NUM> and a second space S2 surrounded by the acceleration detection section 220b and the printed circuit board <NUM> are divided. In other words, the printed circuit board <NUM> is provided with the partition wall <NUM> that separates a portion facing the pressure detection section 220a from a portion facing the acceleration detection section 220b. The partition wall <NUM> is configured by, for example, placing a potting material made of a resin material at a predetermined location on the printed circuit board <NUM>. Further, the separation here includes the case where the first space S1 and the second space S2 are communicated with each other through a gap or the like.

A sixth embodiment will be described hereafter. In the present embodiment, the configuration of the piezoelectric device S10 is changed from the fifth embodiment. Descriptions of the same configurations and processes as those of the fifth embodiment will not be repeated hereinafter.

In the piezoelectric device S10 of the present embodiment, as shown in <FIG>, the recess portion 10a is formed so as to have a partition wall <NUM> that separates the first space S1 and the second space S2. In other words, the recess portion 10a has the partition wall <NUM> that separates the first space S1 surrounded by the pressure detection section 220a and the support member <NUM> and the second space S2 surrounded by the acceleration detection section 220b and the support member <NUM>. In other words, the partition wall <NUM> is arranged in the space within the recess portion 10a so as to separate the first space S1 on the side of the pressure detection section 220a from the second space S2 on the side of the acceleration detection section 220b. In addition, the partition wall <NUM> in the fifth embodiment is not formed in the present embodiment. Moreover, the partition wall <NUM> of the present embodiment is composed of the support substrate <NUM> and the insulating film <NUM>.

According to the present embodiment described above, the piezoelectric element <NUM> is provided with the pressure detection section 220a and the acceleration detection section 220b. Since the control section <NUM> detects the pressure based on the predetermined threshold value, it is possible to prevent the detection accuracy from deteriorating. Moreover, even if the partition wall <NUM> is provided in the piezoelectric element <NUM>, the same effects as those of the fifth embodiment can be obtained.

Although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to such embodiments or structures, the scope of the invention only being defined by the claims.

For example, in the first embodiment, the pressure detection section 220a and the acceleration detection section 220b may be arranged on different support members <NUM>. That is, in the first embodiment, two piezoelectric elements <NUM> may be provided, one of the piezoelectric elements <NUM> may be provided with the pressure detection section 220a, and the other piezoelectric element <NUM> may be provided with the acceleration detection section 220b. In such a configuration, the through hole 101b may be formed so as to communicate with the recess portion 10a of the piezoelectric element <NUM> in which the pressure detection section 220a is formed.

Further, in each of the above-described embodiments, the control section <NUM> does not have to be provided on the circuit board <NUM>. For example, the control section <NUM> may be provided in another circuit section arranged outside casing <NUM>.

In each of the embodiments described above, the number of pressure detection sections 220a and acceleration detection sections 220b can be changed as appropriate. For example, one pressure detection section 220a and one acceleration detection section 220b may be formed.

For example, in each of the above embodiments, the vibrating portion <NUM> may include at least one layer of the piezoelectric film <NUM> and at least one layer of the electrode film <NUM>. The planar shape of the piezoelectric element <NUM> does not have to be a rectangular shape but may be a polygonal shape, such as a pentagonal shape or a hexagonal shape. Furthermore, the planar shape of the floating region 21b may be a polygonal shape such as a substantially pentagonal shape or a substantially hexagonal shape instead of the substantially rectangular shape.

Furthermore, in the above-described first to fifth embodiments, as shown in <FIG>, a through hole 102a may be formed in the lid <NUM>. In addition, when forming the through hole 102a in the lid <NUM> in the fifth embodiment, the lid <NUM> should just be equipped with the partition wall.

Further, each of the above embodiments may be combined as appropriate. For example, the second embodiment may be combined with the third to sixth embodiments, and the temperature detection section <NUM> may be provided. The third embodiment may be combined with the fifth and sixth embodiments, and the numbers of the pressure detection sections 220a and the acceleration detection sections 220b may be changed. The fourth embodiment may be combined with the fifth and sixth embodiments to collectively arrange the pressure detection sections 220a and collectively arrange the acceleration detection sections 220b. The fifth embodiment may be combined with the sixth embodiment, and the partition wall <NUM> may be arranged on the printed circuit board <NUM> and the partition wall <NUM> may be arranged on the piezoelectric element <NUM>.

Claim 1:
A piezoelectric element for detecting pressure, comprising:
a support member (<NUM>); and
a vibrating portion (<NUM>) disposed on the support member and having a piezoelectric film (<NUM>) and an electrode film (<NUM>) electrically connected to the piezoelectric film, wherein
the vibrating portion (<NUM>) has a support region (21a) supported by the support member, and a plurality of vibration regions (<NUM>), one end portion (<NUM>) side of which is supported by the support region, and the other end portion (<NUM>) side of which is opposite to the one end portion (<NUM>) is floating from the support member, and
the plurality of vibration regions includes
a vibration region in which a mass on the one end portion side is heavier than the mass on the other end portion side, and which serves as a pressure detection section (220a) configured to output a first detection signal based on a charge of the piezoelectric film, and
a vibration region in which a mass on the other end portion side is heavier than the mass on one end portion side, and which serves as an acceleration detection section (220b) configured to output a second detection signal based on a charge of the piezoelectric film.