JP6908322B2 - Piezoelectric element - Google Patents

Description

The present invention relates to a piezoelectric element, and more particularly to a piezoelectric element utilizing a high-sensitivity, low-noise transverse piezoelectric effect.

In recent years, smartphones, whose demand is rapidly expanding, are often used for microphones using MEMS (Micro Electro Mechanical System) technology, which is small and thin and has resistance to high temperature processing in the solder reflow process of assembly. Further, not only MEMS microphones but also other MEMS elements are rapidly becoming widespread in various fields.

Most of these types of MEMS elements are capacitive elements that capture the vibration displacement of the diaphragm due to acoustic pressure or the like as a capacitance change with the opposing fixed plate, convert it into an electric signal, and output it. However, the improvement of the signal-to-noise ratio of the capacitive element is becoming a limit due to the acoustic resistance caused by the flow of air in the gap between the diaphragm and the fixing plate.

Therefore, a piezoelectric element capable of extracting acoustic pressure or the like as a voltage change due to distortion of a single diaphragm composed of a piezoelectric thin film has been attracting attention.

By the way, in this type of piezoelectric element, it is known that when the piezoelectric thin film constituting the diaphragm is vibrated and displaced due to acoustic pressure or the like, the strain or stress applied to the piezoelectric thin film in the thickness direction of the piezoelectric thin film is in the opposite direction. .. FIG. 7 is an explanatory diagram schematically showing strain or stress applied to the piezoelectric thin film in a piezoelectric element having a general structure. In the piezoelectric element shown in FIG. 7, a piezoelectric thin film 3 is laminated on a silicon substrate 1 serving as a support substrate via an insulating film 2 made _{of a silicon oxide film (SiO 2).} Further, a slit (not shown) is formed to form a double-sided beam structure. A pair of electrodes 4 are formed on the front surface and the back surface of the piezoelectric thin film 3 so as to sandwich the piezoelectric thin film 3, and each of the electrodes 4 is connected to a wiring electrode 5.

In a piezoelectric element having such a structure, for example, when an acoustic pressure signal is applied from the silicon substrate 1 side as shown in FIG. 7, tensile stress is generated on the silicon substrate side of the piezoelectric thin film 3 in regions A and C. Tensile stress is generated on the surface side. On the other hand, in region B, compressive stress is generated on the silicon substrate side of the piezoelectric thin film, and tensile stress is generated on the surface side.

In the piezoelectric thin film sandwiched between the pair of electrodes in this way, the polarity of the generated voltage is reversed in the region bonded to the support substrate (silicon substrate 1) and the region separated from the region, and further, the surface of the piezoelectric thin film is further reversed. The polarities of the voltages generated on the side and the silicon substrate side are reversed, and an output signal cannot be obtained.

Therefore, in order to effectively utilize the energy generated in the piezoelectric thin film, a piezoelectric element as shown in FIG. 8 has been proposed (Patent Document 1). In the piezoelectric element shown in FIG. 8, a multilayer structure piezoelectric thin film 3a and 3b is fixed on a silicon substrate 1 serving as a support substrate via an insulating film 2, and the piezoelectric thin film 3a is piezoelectricized by electrodes 4a and 4b from above and below. The thin film 3b has a structure in which the electrodes 4b and 4c are sandwiched from above and below, respectively. Each of the piezoelectric thin film and the electrode has a rectangular planar structure, and has a cantilever structure in which one end is fixed to the silicon substrate 1 and the other end is a free end.

In such a piezoelectric element, when the piezoelectric thin film 3a is distorted by receiving acoustic pressure or the like, polarization occurs inside the piezoelectric thin film 3a, and a voltage signal is taken out from the wiring metal 5a connected to the electrode 4a and the wiring electrode 5b connected to the electrode 4b. Is possible. Similarly, when the piezoelectric thin film 3b is distorted, polarization occurs inside the piezoelectric thin film 3b, and it becomes possible to extract a piezoelectric signal from the wiring metal 5a connected to the electrode 4c and the wiring metal 5b connected to the electrode 4b. However, when forming a piezoelectric element having such a structure, it is necessary to repeatedly form an electrode and a piezoelectric thin film, which makes the manufacturing process long and complicated.

Japanese Patent No. 5707323

The piezoelectric element having the structure shown in FIG. 7 has a problem that the energy generated in the piezoelectric thin film due to the displacement of the piezoelectric thin film cannot be effectively utilized. Further, the piezoelectric element having the structure shown in FIG. 8 needs to repeatedly form an electrode and a piezoelectric thin film, which causes a problem that the manufacturing process becomes long and complicated. An object of the present invention is to solve such a problem and to provide a piezoelectric element which can effectively utilize the energy generated in a piezoelectric thin film and can be easily formed.

In order to achieve the above object, the invention according to claim 1 of the present application is a piezoelectric film using a transverse piezoelectric effect including a piezoelectric thin film laminated on a support substrate and a pair of electrodes arranged so as to sandwich the piezoelectric thin film. In the element, the piezoelectric thin film has both ends fixed to the support substrate and has a laminated structure including at least the first piezoelectric thin film and the second piezoelectric thin film. The crystal orientation direction showing each piezoelectricity is such that when one is upward and the other is downward, and a plurality of sets of the pair of electrodes arranged with a part of the piezoelectric thin film interposed therebetween are provided, and at least the first piezoelectricity is provided. The element, the second piezoelectric element, and the third piezoelectric element are formed, and the first piezoelectric element, the second piezoelectric element, and the third piezoelectric element are present from one end side of both ends. The first piezoelectric element and the second piezoelectric element, and the second piezoelectric element and the third piezoelectric element are continuously extended from the electrodes of the piezoelectric element. It is characterized in that it is connected in series by a unit.

According to the second aspect of the present application, in the piezoelectric element according to the first aspect, a dielectric film having no piezoelectric effect is laminated between the first piezoelectric thin film and the second piezoelectric thin film. It is a feature.

The invention according to claim 3 of the present application is characterized in that, in the piezoelectric element according to any one of claims 1 or 2, the piezoelectric thin film is a film that vibrates due to acoustic pressure .

The piezoelectric element of the present invention has a structure in which piezoelectric thin films having different crystal orientation directions indicating piezoelectricity (one is upward and the other is downward) are stacked, so that the voltage is opposite in the thickness direction of the piezoelectric thin film. Even when the above occurs, the voltage generated in the piezoelectric thin film whose crystal orientation direction is upward and the voltage generated in the piezoelectric thin film whose crystal orientation direction is downward can be superimposed and extracted, and the crystal orientation direction having piezoelectricity can be determined. There is an advantage that a large output signal can be obtained as compared with the case of using a single-layer film structure in one direction.

Further, in the case of a double-sided beam structure in which both ends of the piezoelectric thin film are fixed to a support substrate, a piezoelectric element is formed for each region partitioned by a bending point that is curved and deformed by vibration, and the voltage output from each piezoelectric element. By connecting so as to superimpose and output the signals, it is possible to superimpose and take out the voltage generated in each region, and there is an advantage that a larger output signal can be obtained.

In particular, when connecting a plurality of piezoelectric elements in series as a double-sided beam structure, if the structure is such that the piezoelectric elements are connected by an extension portion formed by extending the electrodes of the piezoelectric element, a through hole that affects the displacement of the piezoelectric thin film is used. It is preferable because it does not require a connecting means such as.

When the piezoelectric thin film of the present invention is formed by sandwiching a dielectric thin film having no piezoelectric characteristics, an output signal is output from the upper and lower surface sides of the thin film having a large stress relative to the central surface in the thickness direction of the thin film. Can be obtained, and improvement in characteristics can be expected. Further, for example, _{a structure in which the layers are laminated via a silicon oxide film (SiO 2} ) is preferable because the dielectric loss is smaller than that of the piezoelectric thin film.

When the piezoelectric thin film of the piezoelectric element of the present invention is set to a thickness that vibrates due to acoustic pressure and is used as an acoustic transducer, high sensitivity and improvement in the signal-to-noise ratio are expected.

It is a top view of the piezoelectric element of the 1st Example of this invention. It is sectional drawing of the piezoelectric element of 1st Example of this invention. It is explanatory drawing of the state in which the acoustic pressure signal is applied to the piezoelectric element of 1st Example, and the piezoelectric thin film is distorted. It is sectional drawing of the piezoelectric element of the 2nd Example of this invention. It is explanatory drawing of the state in which the acoustic pressure signal is applied to the piezoelectric element of 2nd Example, and the piezoelectric thin film is distorted. It is sectional drawing of the piezoelectric element of the 3rd Example of this invention. It is explanatory drawing of the conventional piezoelectric element. It is explanatory drawing of another conventional piezoelectric element.

The piezoelectric element of the present invention has a laminated structure in which a piezoelectric thin film laminated on a support substrate includes at least two layers of piezoelectric thin films, one of which has piezoelectricity and has an upward crystal orientation direction, and the other. The piezoelectric thin film has a piezoelectricity, and the crystal orientation direction is a downward film. Hereinafter, the case where the piezoelectric element of the present invention is configured as an acoustic transducer will be described in detail as an example.

FIG. 1 shows a plan view of the piezoelectric element having a cantilever structure according to the first embodiment of the present invention, and FIG. 2 shows a cross-sectional view of the piezoelectric element shown in FIG. 1 on the AA plane. As shown in FIG. 2, the piezoelectric element of this embodiment has a piezoelectric crystal orientation direction described later _{on a silicon substrate 1 serving as a support substrate via an insulating film 2 made of a silicon oxide film (SiO 2).} The piezoelectric thin films 3a and 3b to have are formed. Further, two slits 6a extending in the horizontal direction of the drawing of FIG. 1 and a slit 6b extending in the vertical direction of the drawing from the central portion thereof are formed, and a hole formed by removing a part of the back surface side of the silicon substrate 1. By communicating with 8, a cantilever structure is formed in which one end of the layer containing the piezoelectric thin film is supported on the silicon substrate 1 (support substrate) and the other end is a free end.

In the embodiment shown in FIGS. 1 and 2, the piezoelectric element C1 having a pair of electrodes 4a1 and 4b1 arranged with the piezoelectric thin films 3a and 3b sandwiched between them and a pair of electrodes arranged with the piezoelectric thin films 3a and 3b sandwiched between them. Piezoelectric elements C2 having 4a2 and 4b2 are formed so as to face each other. Further, in order to connect the two piezoelectric elements in series, the electrodes 4b1 and 4a2 are connected by the wiring metal 7. As a result, the piezoelectric element C1 and the piezoelectric element C2 are connected in series between the wiring electrode 5a and the wiring metal 5b. The electrode and the wiring metal can be formed of a metal thin film such as molybdenum (Mo), platinum (Pt), titanium (Ti), iridium (Ir), and ruthenium (Ru). In the present invention, it is not always essential that the two piezoelectric elements are arranged so as to face each other or connected in series, and any configuration may include one of the piezoelectric elements. Further, the planar shape of the piezoelectric element is not limited to the rectangle shown in FIG. 1, and can be variously changed such as a trapezoid, a triangle, and a polygon.

Next, the crystal orientation direction of the piezoelectric thin film of the present invention having piezoelectricity will be described. The piezoelectric thin film of this embodiment has a structure in which a film having a piezoelectricity having a crystal orientation direction facing upward and a film having a piezoelectricity facing downward are stacked, as shown by an arrow in FIG. 2 showing the crystal orientation direction (piezoelectric polarity) having piezoelectricity. .. Specifically, when the c-axis orientation, which is the crystal orientation showing the piezoelectricity of the piezoelectric thin film 3a made of aluminum nitride (AlN), is downward, the c-axis orientation of the piezoelectric thin film 3b made of aluminum nitride is upward. Or vice versa.

The crystal orientation is controlled by a well-known method. Specifically, when forming a thin film of aluminum nitride having a wurtzite structure by a reactive sputtering method using nitrogen or oxygen gas as a reactive gas, the substrate temperature, sputtering pressure, nitrogen or oxygen concentration, power density, and film thickness are determined. By setting appropriately, it is possible to form a film having good crystal orientation and uniform c-axis orientation.

Further, by changing the sputtering conditions, it is possible to laminate and generate an aluminum nitride thin film whose c-axis direction is changed by 180 degrees.

As shown in FIG. 2, the c-axis orientation is not limited to the case where the piezoelectric thin film is aligned in the vertical direction with respect to the surface of the piezoelectric thin film, and may deviate from the vertical direction. Further, the upward c-axis direction and the downward c-axis direction may be directions opposite to each other, and may not be 180 degrees different as shown in FIG. Needless to say, the sensitivity is highest when the difference is 180 degrees, which is preferable.

In the piezoelectric element configured in this way, when an acoustic pressure signal is applied as shown in FIG. 3, the piezoelectric thin film is displaced upward, and tensile stress is generated in the piezoelectric thin film 3a and compressive stress is generated in the piezoelectric thin film 3b. At this time, due to the transverse piezoelectric effect, an electric field is generated in the direction perpendicular to the stress in the spreading direction (horizontal direction in the drawing) of the piezoelectric thin film (vertical direction in the drawing).

Since the piezoelectric thin films 3a and 3b have a structure in which a film having piezoelectricity in the crystal orientation direction upward and a film having a downward crystal orientation are stacked, the direction of the electric field generated by the transverse piezoelectric effect due to the tensile stress of the piezoelectric thin film 3a and the piezoelectric thin film 3b. The direction of the electric field due to the compressive stress of is the same.

On the contrary, when the piezoelectric thin film is displaced downward, compressive stress is generated in the piezoelectric thin film 3a and tensile stress is generated in the piezoelectric thin film 3b between the two electrodes 4a1 and 4b1. Also in this case, the direction of the electric field generated by the piezoelectric thin film 3a and the direction of the electric field generated by the piezoelectric thin film 3b are the same. As a result, in any displacement, the voltage generated by the respective piezoelectric thin films is superimposed and output between the electrodes 4a1 and 4b1.

Similarly, even between the electrodes 4a2 and 4b2, when the piezoelectric thin film is displaced upward, tensile stress is generated in the piezoelectric thin film 3a, compressive stress is generated in the piezoelectric thin film 3b, and the voltage generated in each piezoelectric thin film is generated. Is weighted and output. When the piezoelectric thin film is displaced downward, compressive stress is generated in the piezoelectric thin film 3a, tensile stress is generated in the piezoelectric thin film 3b, and the voltages generated in the respective piezoelectric thin films are superimposed and output.

Further, since the electrode 4b1 and the electrode 4a2 are connected, the voltage generated by the two piezoelectric elements C1 and C2 is added and output between the wiring electrode 5a and the wiring electrode 5b.

As described above, the piezoelectric element of the present embodiment has a piezoelectric thin film having a laminated structure having different crystal orientation directions (one facing upward and the other facing downward), so that the crystal orientation direction having piezoelectricity can be changed. There is an advantage that a large output signal can be obtained as compared with the case of a single-layer structure having one direction.

Next, a second embodiment of the present invention will be described. FIG. 4 is a cross-sectional view of the piezoelectric element of the second embodiment of the present invention. As shown in FIG. 4, the piezoelectric element of this embodiment is piezoelectric, as in the first embodiment, via an insulating film 2 made _{of a silicon oxide film (SiO 2) on a silicon substrate 1 serving as a support substrate.} A piezoelectric thin film 3a and a piezoelectric thin film 3b having different crystal orientation directions are formed. In this embodiment, as shown in FIG. 1 described in the first embodiment, only the slit 6a extending in the lateral direction of the drawing is formed among the slits 6a and 6b, and a part of the back surface side of the silicon substrate 1 is removed. The difference is that the silicon substrate 1 (supporting substrate) has a double-sided beam structure in which both ends of the layer containing the piezoelectric thin film are supported by communicating with the pores 8 formed in the above.

Also, the arrangement of the electrodes is different. In the embodiment shown in FIG. 4, the electrodes 4a1 and 4a2 are formed on the back surface side of the piezoelectric thin film 3a, and the electrodes 4a1 are connected to the wiring electrodes 5a. The electrode 4a2 is not connected to the wiring electrode 5a or other electrodes, and is in a floating state. Further, an electrode 4b1 and an electrode 4b2 are formed on the surface side of the piezoelectric thin film 3b, the electrode 4b1 is not connected to the wiring electrode 5a or other electrodes and is in a floating state, and the electrode 4b2 is a wiring electrode 5b. Is connected to. Further, by setting the length of each electrode as shown in FIG. 4, the piezoelectric element C1 having the pair of electrodes 4a1 and 4b1 arranged so as to sandwich the piezoelectric thin films 3a and 3b, and the pair of electrodes 4a2 and 4b1 can be formed. A piezoelectric element C2 including the piezoelectric element C2 and a piezoelectric element C3 provided with a pair of electrodes 4a2 and 4b are formed. Further, the piezoelectric element C1 and the piezoelectric element C2 are connected in series by an electrode 4b1 (an extension portion that does not overlap the opposing electrode), and the piezoelectric element C2 and the piezoelectric element C3 are connected to the electrode 4a2 (an extension portion that does not overlap the opposing electrode). Are connected in series by. As a result, the piezoelectric elements C1, C2, and C3 are connected in series between the wiring electrode 5a and the wiring electrode 5b. The electrode and the wiring metal can be formed of a metal thin film such as molybdenum (Mo), platinum (Pt), titanium (Ti), iridium (Ir), and ruthenium (Ru). It is preferable that the connection is made by an extension portion because it is not necessary to form a connection means such as a through hole that affects the displacement of the piezoelectric thin film in the piezoelectric thin film.

Next, the crystal orientation direction showing the piezoelectricity of the piezoelectric thin film of the present invention will be described. The piezoelectric thin film of this embodiment has a structure in which a film having piezoelectricity and a film having a crystal orientation direction facing downward are stacked, as shown by an arrow in FIG. 4 showing the crystal orientation direction having piezoelectricity. Specifically, when the c-axis orientation showing the piezoelectricity of the piezoelectric thin film 3a made of aluminum nitride is downward, the c-axis orientation which is the crystal orientation of the piezoelectric thin film 3b made of aluminum nitride is upward. Or vice versa.

The crystal orientation is also controlled by a well-known method as in the first embodiment. Specifically, when forming a thin film of aluminum nitride having a wurtzite structure by a reactive sputtering method using nitrogen or oxygen gas as a reactive gas, the substrate temperature, sputtering pressure, nitrogen or oxygen concentration, power density, and film thickness are determined. By setting appropriately, it is possible to form a film having good crystal orientation and uniform c-axis orientation.

Further, by changing the sputtering conditions, it is possible to laminate and generate an aluminum nitride thin film whose c-axis direction is changed by 180 degrees.

The c-axis orientation is not limited to the case where the orientation is aligned perpendicular to the surface of the silicon substrate as shown in FIG. 4, and may deviate from the vertical direction. Further, the upward c-axis direction and the downward c-axis direction may be directions opposite to each other, and may not be 180 degrees different as shown in FIG. Needless to say, the sensitivity is highest when the difference is 180 degrees, which is preferable.

In the piezoelectric element configured in this way, when an acoustic pressure signal is applied as shown in FIG. 5, the piezoelectric thin film is displaced upward, and tensile stress and compressive stress are generated in the piezoelectric thin film 3a and the piezoelectric thin film 3b. Further, when the piezoelectric thin film is displaced downward, the opposite stress is generated. At this time, due to the transverse piezoelectric effect, an electric field is generated in the direction perpendicular to the stress in the spreading direction (horizontal direction in the drawing) of the piezoelectric thin film (vertical direction in the drawing).

Since the piezoelectric thin films 3a and 3b have a structure in which a film having piezoelectricity in the crystal orientation direction upward and a film having a downward crystal orientation are stacked, the direction of the electric field due to the compressive stress of the piezoelectric thin film 3a and the electric field due to the tensile stress of the piezoelectric thin film 3b The orientation is the same. Further, the direction of the electric field due to the tensile stress of the piezoelectric thin film 3a and the direction of the electric field due to the compressive stress of the piezoelectric thin film 3b are the same.

In the example shown in FIG. 5, two inflection points are generated by applying an acoustic pressure signal, and the region is divided into three regions depending on the direction of stress on the piezoelectric thin film. For example, when the piezoelectric thin film is displaced upward, the region A and the region C are curved and displaced downward in a convex shape, tensile stress is generated in the piezoelectric thin film 3a, and compressive stress is generated in the piezoelectric thin film 3b. On the other hand, in the region B, the piezoelectric thin film 3a is curved and displaced upward in a convex shape, and the piezoelectric thin film 3a is subjected to compressive stress, and the piezoelectric thin film 3b is subjected to tensile stress.

Since tensile stress is generated in the piezoelectric thin film 3a and compressive stress is generated in the piezoelectric thin film 3b between the two electrodes 4a1 and 4b1 in the region A, the direction of the electric field generated in the piezoelectric thin film 3a is generated in the piezoelectric thin film 3b. It is the same as the direction of the electric field. This is also the same as the direction of the electric field generated between the two electrodes 4b2 and 4b1 in the region C. On the other hand, in the region B, compressive stress is generated in the piezoelectric thin film 3a and tensile stress is generated in the piezoelectric thin film 3b between the two electrodes 4a2 and 4b1, and the direction of the electric field generated in the piezoelectric thin film 3a is generated in the piezoelectric thin film 3b. The direction of the electric field is the same as that of the electric field to be generated, and the direction is opposite to the direction of the electric field generated in the regions A and C.

By the way, as described above, the connection between the piezoelectric element C1 and the piezoelectric element C2 is via the electrode 4b1, and the connection between the piezoelectric element C2 and the piezoelectric element C3 is via the electrode 4a2. In the meantime, all the voltages generated by the three piezoelectric elements C1, C2 and C3 are added and output.

As described above, the piezoelectric element of the present embodiment has a piezoelectric thin film having a laminated structure having different crystal orientation directions (one facing upward and the other facing downward), so that the crystal orientation direction having piezoelectricity can be changed. There is an advantage that a large output signal can be obtained as compared with the case of using a single-layer film structure in one direction.

Next, a third embodiment of the present invention will be described. In the first and second embodiments, the piezoelectric thin film 3a and the piezoelectric thin film 3b are directly superposed, but it is also possible to form a laminated structure via a dielectric film having no piezoelectric characteristics. FIG. 6 is a cross-sectional view of the piezoelectric element of the third embodiment of the present invention in which the laminated structure of the piezoelectric thin film of the second embodiment is modified. The structure is such that the dielectric film 9 is laminated between the piezoelectric thin film 3a and the piezoelectric thin film 3b.

By selecting the dielectric film 9 from dielectrics that do not have piezoelectric characteristics, the magnitude of compressive stress or tensile stress is thin when an acoustic pressure signal or the like is applied to the piezoelectric thin film having a laminated structure to cause displacement. The structure can be such that the piezoelectric thin film is arranged only on the front surface portion or the back surface portion of the thin film which is relatively large with respect to the central surface in the thickness direction of. As a result, it is possible to form a piezoelectric element having a high ratio (sensitivity) of the output signal voltage to the applied acoustic signal pressure.

If a silicon oxide film (SiO ₂ ) is selected as the dielectric film 9, the dielectric loss (loss angle tan δ) of the dielectric film 9 can be made smaller than that of the dielectric thin film made of aluminum nitride. It is expected that the signal noise ratio will be improved, which is preferable.

The structure including the dielectric film 9 can also be applied to the laminated structure of the dielectric thin films having the cantilever structure shown in FIG.

Although the piezoelectric element of the present embodiment has been described above, the present invention is not limited to aluminum nitride as the piezoelectric thin film. For example, Young's modulus affects the characteristics of piezoelectric microphones for typical piezoelectric materials such as aluminum nitride, scandium aluminum nitride (Al _1-x Sc _x N), zinc oxide (ZnO), and lead zirconate titanate (PZT). Table 1 shows material constants such as rate and transverse piezoelectric strain coefficient.

Performance index corresponding to the signal-to-noise ratio shown in Table 1 (FOM) is represented by the ratio of the coupling coefficient (k ₃₁ ²⁾ and the loss angle (tan [delta), as the value is larger, at approximately proportional to the form to the value Improvement of signal-to-noise ratio can be expected. As shown in Table 1, aluminum nitride has a figure of merit 6 to 40 times larger than that of zinc oxide and lead zirconate titanate, indicating that it is a suitable material for piezoelectric transducers. _{Further, it is known that scandium aluminum nitride (Al 1-x} Sc _x N) obtained by adding scandium to aluminum nitride has a higher transverse piezoelectric strain coefficient than aluminum nitride. For example, the ratio of scandium is set to 35%. In this case, it can be expected that the performance index is improved about 7 times as much as that of aluminum nitride. Furthermore, it is also possible to use aluminum nitride or the like dotted with chromium (Cr) or the like.

It is desirable that the size of each electrode is optimized from the viewpoint of maximizing the signal-to-noise ratio. This wiring electrodes 5a, the capacity of the equivalent capacitor as seen from 5b when the C _out, of the electrodes so as to maximize the energy stored in the equivalent capacitor ^{_{(C out · V out 2/}} 2) You just have to decide the size. Further, the thickness and material of the dielectric film may be appropriately selected in order to obtain desired characteristics.

As an example, assuming that it is used as an acoustic microphone mounted on a smartphone, when the resonance frequency is 20 kHz with a double-sided beam structure, the length of the double-sided beam is 700 μm, the width is 1400 μm, and a piezoelectric thin film made of aluminum nitride. The total thickness may be 500 nm, the thickness of the electrode made of molybdenum may be 100 nm, the length of the portion of the electrodes 4a1 and 4b2 that functions as the electrode of the piezoelectric element may be 90 μm, and the length of the electrodes 4b1 and 4a2 may be 500 μm. .. The width of the slit is 1 μm. _{In the case of a structure in which a dielectric film made of SiO 2} is provided between the piezoelectric thin films, the thickness of each aluminum nitride is 330 nm, the thickness of the dielectric film is 540 nm, and the total film thickness is 1.2 μm or less. If so, it is preferable as a vibrating film. In the case of scandium aluminum nitride as the piezoelectric thin film, if it is 1.4 μm or less, it is preferable as a vibrating film.

When the bending displacement is caused by the vibration of the piezoelectric thin film, if the inflection point of the displacement is 2 or more, the number of piezoelectric elements is increased for each region partitioned by the inflection point, not limited to the above embodiment. A plurality of elements may be arranged in each region.

1: Silicon substrate 2: Insulating film, 3a, 3b: Piezoelectric thin film, 4a1, 4a2, 4b1, 4b2: Electrode, 5a, 5b: Wiring electrode, 6a, 6b: Slit, 7: Wiring metal, 8: Pore, 9: Dielectric film

Claims (3)

In a piezoelectric element utilizing a transverse piezoelectric effect, which comprises a piezoelectric thin film laminated on a support substrate and a pair of electrodes arranged so as to sandwich the piezoelectric thin film.
The piezoelectric thin film has both ends fixed to the support substrate and has a laminated structure including at least a first piezoelectric thin film and a second piezoelectric thin film. When the crystal orientation direction indicating the property is upward on one side and downward on the other side,
A plurality of sets of the pair of electrodes arranged so as to sandwich a part of the piezoelectric thin film are provided, and at least a first piezoelectric element, a second piezoelectric element, and a third piezoelectric element are formed.
The first piezoelectric element, the second piezoelectric element, and the third piezoelectric element are arranged side by side in order from one end side to the other end side of both ends.
The first piezoelectric element and the second piezoelectric element, and the second piezoelectric element and the third piezoelectric element are connected in series by an extension portion continuous from the electrode of the piezoelectric element. Piezoelectric element. The piezoelectric element according to claim 1, wherein a dielectric film having no piezoelectric effect is laminated between the first piezoelectric thin film and the second piezoelectric thin film . The piezoelectric element according to any one of claims 1 or 2, wherein the piezoelectric thin film is a film that vibrates due to acoustic pressure .

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