JP7474649B2 - Vibration power generation element - Google Patents

Description

The present invention relates to a vibration power generation element.

A vibration power generation device has been proposed that can efficiently sense the vibration acceleration of the frequency to be detected and can generate power efficiently (see, for example, Patent Document 1). Each of the multiple power generation sections formed on a vibrator supported by a frame section is composed of a lower electrode, a piezoelectric thin film, and an upper electrode, and the composite voltage obtained between the lower electrode and the upper electrode, which corresponds to the vibration of the vibrator, is output as the output voltage.

JP 2017-017939 A

In piezoelectric vibration power generation elements, if bulk piezoelectric ceramics are used for the piezoelectric body placed on the vibration plate, there is a problem that it is easily damaged by bending deformation. On the other hand, there is a method of using a piezoelectric layer with the polarization direction of a ferroelectric thin film aligned as a structure that is resistant to bending deformation. Silicon single crystals that can be finely processed are generally used for the substrate on which the piezoelectric layer is formed. In a configuration in which a piezoelectric layer is formed on a substrate, substrate heating and/or post-annealing at high temperatures for the purpose of improving crystallinity and grain growth is required to improve the properties of the film. For this reason, Pt and/or a platinum group alloy that is chemically stable at high temperatures is formed on the substrate as a lower electrode layer. A piezoelectric layer is generally formed on the lower electrode, an upper electrode is formed on the piezoelectric layer, and the piezoelectric layer is generally sandwiched between the electrodes.

However, when substrate heating and/or post-annealing is performed, precious metals such as platinum (Pt) or palladium (Pd) alloys are used for the lower electrode that constitutes the power generation unit, increasing the cost of the entire device. On the other hand, if a precious metal is not used for the lower electrode, components of the substrate material and the piezoelectric layer diffuse near the interface during heat treatment processes such as post-annealing, resulting in a deterioration of characteristics. In addition, the silicon single crystal substrate that forms the piezoelectric layer is a brittle material, and is therefore prone to breakage when bent.

Therefore, the present invention aims to provide a vibration power generation element that can reduce costs while improving characteristics and mechanical robustness.

Means for solving the problem

The vibration power generating element of the present invention is
a metal substrate that is elastically deformable and supported in a cantilevered manner by a support member and extends with respect to the support member;
a piezoelectric layer formed on the substrate via a dielectric layer;
a first comb-teeth electrode and a second comb-teeth electrode formed on the piezoelectric layer,
the first comb-tooth electrode and the second comb-tooth electrode are arranged such that a plurality of first comb-tooth portions constituting the first comb-tooth electrode and a plurality of second comb-tooth portions constituting the second comb-tooth electrode are alternately adjacent to each other in an extension direction of the support member ,
a width b of each of the first comb tooth portion and the second comb tooth portion is greater than a thickness tp of the piezoelectric layer,
a ratio r=(ε _p /ε _a ) of the dielectric constant ε _p of the piezoelectric layer to the dielectric constant ε _a of the dielectric layer is within a range of 50 to 300;
The thickness t _a of the dielectric layer is in the range of 1 to 3 μm,
the thickness t _p of the piezoelectric layer is within the range of 10 to 50 μm and is within the range of {2867·r ^−0.98 }+{11.2·ln(r)−68}t _a +{37·r ^−0.6 }t _a ² or more;
A distance a between the first comb-tooth portion and the second comb-tooth portion is included in the range of 100t _a +10t _p or less, and is larger than the width b of each of the first comb-tooth portion and the second comb-tooth portion .

In a vibration power generation element of this configuration, a dielectric layer is formed between the substrate and the piezoelectric layer (ferroelectric layer). This prevents the electric field component parallel to the thickness direction of the piezoelectric layer from becoming the main component when a voltage is applied between the first comb-tooth electrode and the second comb-tooth electrode. Therefore, when an electric field sufficiently stronger than the coercive electric field of the piezoelectric layer is applied between adjacent first and second comb-tooth portions on the piezoelectric layer, it becomes possible to align the direction of spontaneous polarization inside the piezoelectric layer in a surface direction perpendicular to the thickness direction of the piezoelectric layer or in the extension direction of the substrate.

This allows the piezoelectric layer to function as a piezoelectric body with polarization aligned in the plane direction. Then, stress is applied to the piezoelectric layer in parallel with the polarization direction in response to bending deformation of the metal substrate that constitutes the cantilever beam, and a voltage can be generated between a first comb electrode having a plurality of first comb portions and a second comb electrode having a plurality of second comb portions due to the piezoelectric longitudinal effect.

In this way, with a vibration power generation element of this configuration, it is possible to form a piezoelectric layer by forming electrodes only on the film surface of the ferroelectric layer, making it possible to perform heat treatment without the need to use precious metals as electrodes.

FIG. 2 is a top view of the vibration power generating element according to an embodiment of the present invention. 2 is a cross-sectional view of the vibration power generating element taken along line II-II in FIG. 1 . FIG. 4 is a schematic diagram showing an electric field in a piezoelectric layer when a voltage is applied between comb-tooth electrodes. FIG. 11 is a diagram showing the relationship between the thicknesses of the dielectric layer and the piezoelectric layer and the dielectric constant ratio at which the electric field ratio reaches a threshold value. 11 is a diagram showing the relationship between the thickness of the dielectric layer, the spacing between the comb teeth, and the thickness of the piezoelectric layer at which the electric field ratio reaches a threshold value.

(composition)
The vibration power generating element according to one embodiment of the present invention shown in FIGS. 1 and 2 includes a substrate 10, a piezoelectric layer 20 formed on the substrate 10 via a dielectric layer 102, and a first comb-tooth electrode 41 and a second comb-tooth electrode 42 formed on the piezoelectric layer 20.

(substrate)
The substrate 10 is made of, for example, a flexible or elastically deformable, generally rectangular metal plate material having a thickness of 20 to 200 μm. The substrate 10 is preferably made of heat-resistant stainless steel containing Al, and a dielectric layer 102 having a thickness of 1 μm or more and mainly composed of aluminum oxide (Al ₂ O ₃ ) is formed on the surface. This dielectric layer 102 can prevent the components of the substrate 10 and the piezoelectric layer 20 from diffusing, even when the piezoelectric layer 20 is subjected to a heat treatment together with the substrate 10.

(Fixing method)
The substantially rectangular plate-like substrate 10 is joined or adhered to a support member 11 at one end of its lower surface (the other main surface opposite to the main surface on which the piezoelectric layer 20 is formed), so that the substrate 10 is supported in a cantilevered state by the support member 11 and extends in a first specified direction (X direction) with the support member 11 as a reference. The support member 11 may be formed of a resin clamp that holds the substrate 10 on which the piezoelectric layer 20 is formed, or a mechanical fixing mechanism such as a base and a screw for attaching the substrate 10 to the base.

(Piezoelectric materials)
From the viewpoints of application to a living body and environmental load at the time of disposal, the piezoelectric layer 20 is preferably made of a lead-free piezoelectric ceramic material. The piezoelectric layer 20 is made of a thin film of a lead-free piezoelectric material whose main components are, for example, barium titanate ( _BaTiO3 ), ( _{KxNa1 -x )} NbO3 _, ( _Bi0.5Na0.5 ) _TiO3 , or ( _Bi0.5K0.5 ) _TiO3 .

(Configuration of Piezoelectric Layer and Dielectric Layer)
The thickness t _p of the piezoelectric layer 20 is adjusted to be within the range of 10 to 50 μm, for example. This is because if the thickness t _p of the piezoelectric layer 20 exceeds 50 μm, mechanical damage such as cracks will easily occur in the piezoelectric layer 20 due to bending deformation of the substrate 10. Also, if the thickness t _p of the piezoelectric layer 20 is less than 10 μm, the generated energy will decrease.

It is preferable to form the dielectric layer 102 having a dielectric constant ε _a lower than the dielectric constant ε _p of the piezoelectric layer 20. This is to prevent the electric field component in the thickness direction (Z direction) of the piezoelectric layer 20 from becoming the main _component when a voltage is applied between the first comb-tooth electrode 41 and the second comb-tooth electrode 42, and further between the adjacent first comb-tooth portions 412 and second comb-tooth portions 422, so that the electric field strength in the surface direction (direction parallel to the main surface) becomes the coercive electric field E c of the piezoelectric layer 20 during polarization treatment of the piezoelectric layer 20.

The thickness t _a of the dielectric layer 102 is adjusted to fall within the range of 1 to 3 μm. This is to facilitate its formation while achieving the effect of controlling the electric field component. In Fig. 3, the electric field direction component in the piezoelectric layer 20 when a voltage is applied between the adjacent first comb tooth portion 412 and second comb tooth portion 422 is diagrammatically shown by an arrow pointing in that direction.

(Explanation of Interdigital Electrodes)
The first comb-tooth electrode 41 has a first base portion 411 extending in the extension direction (+X direction) of the substrate 10 based on a support point by the support member 11, and a plurality of first comb-tooth portions 412 extending from the first base portion 411 in a direction (-Y direction) perpendicular to the extension direction of the substrate 10. The second comb-tooth electrode 42 has a second base portion 421 extending in the extension direction (+X direction) of the substrate 10 based on a support point by the support member 11, and a plurality of second comb-tooth portions 422 extending from the second base portion 421 in a direction (+Y direction) perpendicular to the extension direction of the substrate 10. The first comb-tooth electrode 41 and the second comb-tooth electrode 42 are made of a conductor such as a metal. Since the first comb-tooth electrode 41 and the second comb-tooth electrode 42 do not entirely cover the upper surface of the piezoelectric layer 20, the material costs are reduced even if the first comb-tooth electrode 41 and/or the second comb-tooth electrode 42 are made of a precious metal.

(Relationship between piezoelectric vibration energy generation and dimensional parameters)
There is a relationship represented by relational equation (01) among the beam length L of the substrate 10, which is the length of the range in the longitudinal direction (X direction) of the substrate 10 over which the multiple first comb-tooth portions 412 and the multiple second comb-tooth portions 422 exist, the overlap length w _e of the first comb-tooth portion 412 and the second comb-tooth portion 422 in the transverse direction (Y direction) of the substrate 10, the piezoelectric constant d ₃₃ of the piezoelectric longitudinal effect of the piezoelectric layer 20, the thickness t _p and dielectric constant ε _p of the piezoelectric layer 20, the dielectric constant ε ₀ of a vacuum, the widths b of the first comb-tooth portion 412 and the second comb-tooth portion 422, the distance a between the first comb-tooth portion 412 and the second comb-tooth portion 422, and the stress T applied to the piezoelectric layer 40 due to bending deformation in the extension direction of the substrate 20 and the generated energy U ₃₃ corresponding to the potential difference between the first comb-tooth electrode 41 and the second comb-tooth electrode 42 corresponding to the stress T.

U ₃₃ ={d ₃₃ ² /(2ε _p ε ₀ )}(w _e t _p L)T ² {a/(a + b)} ...(01).

Relationship formula (01) represents the energy generated by the piezoelectric longitudinal effect, since the substrate 10 has a cantilever structure in which stress is applied in a direction parallel to the polarization axis of the piezoelectric layer 20 (second specified direction).

(In the case of the piezoelectric transverse effect)
Although not shown, a conventional vibration power generation element has a structure in which a piezoelectric layer is sandwiched between a pair of electrodes from above and below, and the polarization direction is the thickness direction of the piezoelectric layer, while the direction in which stress is applied to the piezoelectric layer is perpendicular to the polarization direction. This is a piezoelectric transverse effect element, and the power generation energy of the piezoelectric transverse effect has a piezoelectric constant _d31 in relational expression (01), making the term a/(a+b) unnecessary. Therefore, the power generation energy _U31 is expressed by relational expression (02).

U ₃₁ = {d ₃₁ ² / (2 _{ε p} ε ₀ )} T ² ( w _e t _p L ) (02).

In the case of piezoelectric ceramics, the relationship of the piezoelectric constant _d33 ≈ 2 × _d31 generally exists due to the relationship of the Poisson's ratio of the material. Therefore, when the same stress is applied to the substrate 10 and the piezoelectric layer 20, in order for the generated energy _U33 due to the longitudinal piezoelectric effect to be greater than the generated energy _U31 due to the transverse piezoelectric effect, the relationship expressed by the inequality 4a/(a+b) > 1 must be established from the relationship (01) and the relationship (02). That is, in order for the relationship _U33 > _U31 to be established, the relationship expressed by the inequality b/a < 3 must be established between the electrode width b of each of the first comb-tooth portion 412 of the first comb-tooth electrode 41 and the second comb-tooth portion 422 of the second comb-tooth electrode 42 and the interval a between the first comb-tooth portion 412 and the second comb-tooth portion 422.

(Effect of dielectric layer)
By focusing on the fact that the dielectric constant ε _a of the dielectric layer 102 (diffusion barrier layer) is smaller than the dielectric constant ε _p of the piezoelectric layer 20 when the piezoelectric layer 20 formed on the substrate 10 is heat-treated, the piezoelectric layer 20 formed on the substrate 10 can be made to function as a piezoelectric longitudinal effect element as a whole by controlling the thickness t _a .

The ratio r = (ε _p /ε _a ) of the dielectric constant ε _p of the piezoelectric layer 20 to the dielectric constant ε _a of the dielectric layer 102 is within the range of 50 to 300. The width b (size in the longitudinal direction of the substrate 10) of each of the first comb-tooth portion 412 and the second comb-tooth portion 422 is larger than the thickness t _p of the piezoelectric layer 20.

During polarization processing to align the polarization direction of the piezoelectric layer 20 formed on the main surface of the metal substrate 10 via the dielectric layer 102 in the in-plane direction (X direction), a voltage is applied between the first comb-tooth electrode 41 and the second comb-tooth electrode 42 formed on the surface of the piezoelectric layer 20. At this time, a potential difference is also generated between the first comb-tooth electrode 41 and the second comb-tooth electrode 42 and the substrate 10. For this reason, it is necessary to align the direction of the electric field between the first comb-tooth electrode 41 and the second comb-tooth electrode 42 in the in-plane direction of the piezoelectric layer 20.

According to the FEM analysis, when the electrode width b is larger than the thickness t _p of the piezoelectric layer 20, the electric field direction is distributed almost uniformly in the thickness direction of the piezoelectric layer 20 below each of the first comb-tooth electrode 41 and the second comb-tooth electrode 42, and the electric field direction is distributed almost uniformly in the in-plane direction of the piezoelectric layer 20 between the first comb-tooth electrode 41 and the second comb-tooth electrode 42 regardless of the depth position of the piezoelectric layer 20. On the other hand, according to the same FEM analysis, when the electrode width b is smaller than the thickness t _p of the piezoelectric layer 20, the electric field direction is distributed non-uniformly in the thickness direction of the piezoelectric layer 20. Therefore, under the condition of b>t _p , in order to align the directions of the spontaneous polarization of the piezoelectric layer 20 by polarization processing, it is sufficient to adjust the electric field intensity E ap between the adjacent first comb-tooth portion 412 and the second comb-tooth portion 422 so that the magnitude of the component E _x of the electric _field in the longitudinal direction (X direction) of the piezoelectric layer 20 is equal to or larger than E _c .

(Definition of E _ap and explanation of electric fields E _x and E _z )
When a voltage V is applied between the first comb-tooth electrode 41 and the second comb-tooth electrode 42, the electric field strength E _ap between the first comb-tooth portion 412 and the second comb-tooth portion 422, which are adjacent to each other at a distance a in the longitudinal direction of the substrate 10, is V/a. If the component of the electric field in the thickness direction (Z direction) of the piezoelectric layer 20 is E _z and the component of the electric field in the longitudinal direction (X direction) of the piezoelectric layer 20 is E _x , then from the viewpoint of aligning the polarization direction of the piezoelectric layer 20 in the x direction, the magnitude of the X-direction component E _x of the electric field needs to be equal to or greater than the coercive electric field E _c of the piezoelectric layer 20. E _x and E _z can be calculated by simulation using the finite element method.

(Definition of electric field strength ratio R)
Here, the X-direction component E _x of the electric field is the average value of the X-direction component E x of the electric field at a plurality of locations of the piezoelectric layer 20 (for example, at a plurality of different depth locations from the surface of the piezoelectric layer 20 between the first comb tooth portion 412 and the second comb tooth portion 422) between the first comb tooth portion 412 and the second comb tooth portion 422. For example, E _x > E _c is required as a condition for aligning the polarization direction of the piezoelectric layer 20 in the _x direction. Since the size of Ex is smaller than E _ap in a comb-tooth electrode pattern, in order to make E _x larger than E _c and perform polarization processing, the size of E _ap needs to be larger than the electric field strength in the structure in which the film is sandwiched between electrodes. Therefore, E _ap is set to three times E c as a manufacturing condition for applying a sufficient magnitude of E _x . In reality, E _ap may be selected to be large enough to apply an electric field to the piezoelectric film without discharging between the comb tooth electrodes. Since the magnitude of E _x varies depending on the electrode pattern dimensions of the comb electrode and the shape and dimensions of the piezoelectric film, it is necessary to determine the shapes of the electrodes and piezoelectric film such that E _x is equal to or greater than E _c . If the electric field intensity ratio R = E _x /E _ap is defined as E _ap ≧3E _c , then in order to satisfy the manufacturing condition, the electric field intensity ratio R = E _x /E _ap is 1/3 or more.

In FIG. 4, the ratio r=( _εp / _εa ) of the dielectric constant _εp of the piezoelectric layer 20 to the dielectric constant _εa of the dielectric layer 102 is 50, 100, and 300, respectively, and approximate curves representing the relationship between the thickness t _a of the dielectric layer 102 and the thickness t _p of the piezoelectric layer 20 at which the electric field intensity ratio R is 1/3 or more are shown by a solid line, a dashed line, and a double-dashed line, respectively.

The approximation curves shown by the solid line, the dashed line, and the double-dashed line, respectively, are expressed by the relational expressions (11), (12), and (13), respectively.

t _p =α ₀ (r = 50) +α ₁ (r = 50)t _a +α ₂ (r = 50)t _a ²
= 63 - 26t _a + 3t _a ² ... (11).

t _p =α ₀ (r = 100) +α ₁ (r = 100)t _a +α ₂ (r = 100)t _a ²
= 32 - 16.5t _a + 2.5t _a ² ... (12).

t _p =α ₀ (r = 300) +α ₁ (r = 300)t _a +α ₂ (r = 300)t _a ²
= 11 - 6 _{t a} + _t ² ... (13).

From the relations (11) to (13), the zeroth-order coefficient α ₀ (r), the first-order coefficient α ₁ (r), and the second-order coefficient α ₂ (r) are approximated as functions of the dielectric constant ratio r by the relations (14), (15), and (16), respectively.

α ₀ (r) = 2867 · r ^-0.98 ... (14).

α ₁ (r) = 11.2 · ln(r) − 68 (15).

α ₂ (r) = 37 · r ^-0.6 (16).

Therefore, the relationship between the thickness t _a of the dielectric layer 102 and the thickness _{t p} of the piezoelectric layer 20 at which the electric field intensity ratio R is 1/3 or more, corresponding to the ratio r = (ε _p /ε _a ) of the dielectric constant ε _p of the piezoelectric layer 20 to the dielectric constant ε _a of the dielectric layer 102, is expressed by relational equation (17).

t _p ≧α ₀ (r) + α ₁ (r) t _a + α ₂ (r) t _a ²
= {2867 · r ^-0.98 } + {11.2 · ln(r) - 68} t _a + {37 · r ^-0.6 } t a ² ... (17).

In FIG. 5, _{approximate curves} representing the relationship between the thickness _tp of the piezoelectric layer 20 at which the electric field intensity ratio R is 1/3 or more and the spacing a between the first comb tooth portion 412 and the second comb tooth portion 422 are shown by a solid line, a dashed line, and a double-dashed line, respectively, when the thickness t a of the dielectric layer 102 is 1 μm, 2 μm, and 3 μm, respectively.

The approximation curves shown by the solid line, the dashed line, and the double-dashed line are expressed by the equations (21), (22), and (23), respectively.

a = β ₀ (t _a = 1) + β ₁ (t _a = 1) t _p
= 100 + 10t _p ... (21).

a = β ₀ (t _a = 2) + β ₁ (t _a = 2) t _p
= 200 + 10t _p ... (22).

a = β ₀ (t _a = 3) + β ₁ (t _a = 3) t _p
= 300 + 10t _p ... (23).

From the relations (21) to (23), the zeroth-order coefficient β ₀ (t _a ) and the first-order coefficient β ₁ (t _a ) are approximated as functions of the thickness t _a of the dielectric layer 102 by the relations (24), (25) and (26), respectively.

β ₀ (t _a ) = 100t _a ... (24).

β ₁ (t _a ) = 10 (25).

Therefore, the relationship between the thickness t _a of the dielectric layer 102 where the electric field intensity ratio R is ⅓ or more and the comb tooth portion interval a corresponding to the thickness t _p of the piezoelectric layer 20 is expressed by relational expression (27).

a≦ _β0 (t _a )+ _β1 (t _a )t _p
= 100t _a + 10t _p ... (27).

(Production method)
A method for manufacturing a vibration power generating element according to one embodiment of the present invention will be described.

(Film formation by AD method)
In a vacuum, a lead-free piezoelectric ceramic powder having a particle size of, for example, about 1 μm, specifically, barium titanate (BaTiO ₃ ) powder, is sprayed from a nozzle onto a substantially rectangular plate-shaped substrate 10 made of heat-resistant stainless steel containing Al, and is caused to collide with the substrate 10, thereby forming a film by aerosol deposition (AD). By this AD method, a piezoelectric layer 20 having a desired thickness of 10 to 50 μm is formed.

(Flexibility and Adhesion Strength of AD Membrane)
The film formed by the AD method (as-deposited film) is firmly bonded to the substrate 10 due to the anchor effect. This strong bond is maintained even in the piezoelectric layer 20 in its final state. This reduces the possibility that the piezoelectric layer 20 will crack or peel off from the substrate 10 when the vibration power generation element is bent and deformed. Thus, the AD method is a suitable method for obtaining a piezoelectric layer 20 that has flexibility.

(Adjustment of Crystal Grain Size of Piezoelectric Layer)
The fine structure of the as-deposited film is smaller than the grain size of the powder used in the AD method, and is finely sized to about several tens of nm, so that the piezoelectricity is low, and therefore it is necessary to promote the crystal grain growth by heat treatment. On the other hand, since the destruction of ceramics generally occurs at the grain boundary, a microcrystalline structure with many grain boundaries is preferable to improve the strength of the piezoelectric layer 20. The as-deposited film is heat-treated at 800 to 1200°C for 1 to 4 hours so that the average crystal grain size of the crystals constituting the piezoelectric layer 20 is 100 nm or more from the viewpoint of improving the piezoelectric properties, and the average crystal grain size of the crystals constituting the piezoelectric layer 20 is 2000 nm or less from the viewpoint of ensuring the strength of the piezoelectric layer 20.

(Formation of Dielectric Layer (Diffusion Barrier Layer))
In the heat treatment process, a dielectric layer 102 containing an oxide of Al ( _Al2O3 ) as a main component is formed between the substrate 10 and the _{piezoelectric} layer 20. This allows the dielectric layer 102 to function as a diffusion barrier layer that suppresses diffusion of components between the stainless steel substrate 10 and the piezoelectric layer 20, and prevents the substrate 10 and the piezoelectric layer 20 from reacting when heat treated at a high temperature of 900°C or higher. A dielectric layer 102 having a thickness of 1 μm or more may be formed in advance on the main surface of the stainless steel substrate 10, or the piezoelectric layer 20 may be directly formed on the main surface of the stainless steel substrate 10 containing Al, and then the piezoelectric layer 20 may be heat-treated to form the dielectric layer 102.

(Formation of comb-tooth electrodes)
A first comb-tooth electrode 41 and a second comb-tooth electrode 42 are formed on the piezoelectric layer 20 after the heat treatment. The first comb-tooth electrode 41 and the second comb-tooth electrode 42 are made of a conductive film and have a thickness of, for example, 0.4 to 0.6 μm. The conductive film can be formed by, for example, a sputtering method or a vapor deposition method. The first comb-tooth electrode 41 and the second comb-tooth electrode 42 are not limited to an Au film, and may be a metal film made of other metals, such as a Cu film or a Cu alloy film, or may have a multi-layer structure such as Au/Ni/Ti.

(Polarization treatment)
The as-deposited film and the heat-treated film obtained by heat-treating the as-deposited film are polycrystalline structures, so that the direction of electric polarization is random as it is. Therefore, in order to align the direction of polarization, a voltage (predetermined voltage) equal to or greater than the electric field strength at which polarization is inverted is applied to the heat-treated film between the first comb-tooth electrode 41 and the second comb-tooth electrode 42. If the dielectric layer 102 is not formed between the substrate 10 and the piezoelectric layer 20, and if the thickness t _a of the dielectric layer 102 is excessively small compared to the thickness t _p of the piezoelectric layer 20, the thickness direction (Z direction) component of the electric field of the piezoelectric layer 20 tends to be the main component, so it is desirable that the thickness t _a of the dielectric layer 102 is 1 μm or more. By making the dielectric constant ε _a of the dielectric layer 102 (diffusion barrier layer) smaller than the dielectric constant ε _p of the piezoelectric layer 20, the surface direction component or the second specified direction component (Y direction component) of the electric field in the piezoelectric layer 20 becomes the main component.

In addition, forming a dielectric layer 102 with a thickness of more than 3 μm on the main surface of a metal substrate 10 such as stainless steel is not realistic in terms of production efficiency because the film formation rate is slow with a thin film formation method. Although it is possible to form a dielectric layer 102 with a thickness of more than 3 μm with a thick film formation method such as the AD method, from the viewpoint of improving power generation energy, thickening the piezoelectric layer 20 has a greater effect on improving performance than thickening the dielectric layer 102. For this reason, the thickness of the dielectric layer 102 is adjusted to 3 μm or less. In addition, by using a stainless steel base material containing Al as a method for forming the dielectric layer 102, it is possible to form the dielectric layer 102 by thermal oxidation of the Al contained in the base material, and the coating grows thick even during the heat treatment process of the piezoelectric layer 102, and the effect of improving the adhesion strength between the piezoelectric layer 102 and the dielectric layer 20 is achieved.

This produces a vibration power generation element according to one embodiment of the present invention (see Figures 1 and 2).

10: substrate, 11: support member, 20: piezoelectric layer (ferroelectric layer), 41: first comb electrode, 42: second comb electrode, 102: dielectric layer (diffusion barrier layer), 411: first base portion, 412: first comb portion, 421: second base portion, 422: second comb portion.

Claims (1)

a metal substrate that is elastically deformable and supported in a cantilevered manner by a support member and extends with respect to the support member;
a piezoelectric layer formed on the substrate via a dielectric layer;
a first comb-teeth electrode and a second comb-teeth electrode formed on the piezoelectric layer,
the first comb-tooth electrode and the second comb-tooth electrode are arranged such that a plurality of first comb-tooth portions constituting the first comb-tooth electrode and a plurality of second comb-tooth portions constituting the second comb-tooth electrode are alternately adjacent to each other in an extension direction of the support member ,
a width b of each of the first comb tooth portion and the second comb tooth portion is greater than a thickness tp of the piezoelectric layer,
a ratio r=(ε _p /ε _a ) of the dielectric constant ε _p of the piezoelectric layer to the dielectric constant ε _a of the dielectric layer is within a range of 50 to 300;
The thickness t _a of the dielectric layer is in the range of 1 to 3 μm,
the thickness t _p of the piezoelectric layer is within the range of 10 to 50 μm and is within the range of {2867·r ^−0.98 }+{11.2·ln(r)−68}t _a +{37·r ^−0.6 }t _a ² or more;
a distance a between the first comb tooth portion and the second comb tooth portion is within a range of 100t _a +10t _p or less and is greater than the width b of each of the first comb tooth portion and the second comb tooth portion;
A vibration power generation element characterized by:

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