JPH1118445A - Piezoelectric type generator and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric type generator and a manufacturing method thereof, which generates electricity by utilizing the mechanical vibratory energy of an engine used in an automobile or the like. SOLUTION: This piezoelectric type generator 200 is provided with an electric circuit 105 for charging electricity generated from a plurality of piezoelectric elements 205 in a storage battery 150. The respective piezoelectric elements involves a piezoelectric membrane, a supporting member for supporting the piezoelectric membrane, and a cantilever shape whose remaining capacity is preformed so as to be warped upwards, in order to prevent collision with a substrate. The piezoelectric membrane is constituted of a PZT, and the supporting member is formed out of nitride. An electric circuit 105 is provided with a DC/AC converter 130, which converts the direct current generated from the piezoelectric elements into an alternating current, a potential transformer 140, and a diode 160 which prevents current from being discharged from the storage battery 150. When an engine vibrates, a current is generated by stresses generated at the piezoelectric membrane and is charged in the storage battery 150 through the electric circuit 105.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric generator and a method of manufacturing the same, and more particularly, to a piezoelectric generator that generates electricity by using vibration energy of a mechanical vibration source and a method of manufacturing the same. About.

[0002]

2. Description of the Related Art Piezoelectric phenomena exist in a certain specific crystal group. Generally, the piezoelectric phenomenon involves a positive piezoelectric effect and a reverse piezoelectric effect. The positive piezoelectric effect refers to the generation of an electric charge when a force or stress is applied to the piezoelectric material, and the reverse piezoelectric effect refers to the effect of generating a stress and causing a displacement when a current flows through the piezoelectric material. Therefore, mutual conversion between electrical energy and mechanical energy is possible by the piezoelectric phenomenon.
Among the above-mentioned piezoelectric phenomena, the positive piezoelectric effect is widely used in the field of sensors for detecting mechanical changes as a form of electric current,
The inverse piezoelectric effect is mainly used as an actuator principle.

Since the discovery of the piezoelectricity of piezoelectric materials, sensors have been developed that use the positive voltage effect to sense mechanical changes. An example is the "piezoelectric acceleration sensor" entitled U.S. Pat.
No. 4,131. The Nakayama Shiro sensor includes a piezoelectric polymer membrane element and a membrane wall, and measures acceleration applied to the membrane wall using current generated by deformation of the piezoelectric element. Another example of a sensor utilizing piezoelectricity is U.S. Pat. No. 4,904,499 issued by Miura Shinsuke et al. As "Measuring device for viscosity and specific gravity of liquid", and Holm-named as "multidimensional force sensor". Many are disclosed in U.S. Pat. No. 5,083,466 to Kennedy, James W. and others.

An example of a sensor for measuring knocking and vibration of an engine by attaching a piezoelectric element to an automobile engine is called "vibration sensor" in US Pat. No. 4,672,839 by Takeuchi Tadashi et al. U.S. Pat. No. 4,6 granted to Entenmann Robert et al. And assigned to Robert Bosch Gmbh under the name "sensor"
No. 60,410 and the like.

In recent years, various studies have been made on piezoelectric generators that generate useful electric energy from stress applied to piezoelectric elements by more positively utilizing the positive piezoelectric effect. One example of such a piezoelectric generator is disclosed in U.S. Pat. No. 5,341,062 by Cero, Jr., Joseph T., et al., Entitled "Piezoelectric Generator". Charles G. Triplet, entitled "Car-mounted Piezoelectric Generator"
U.S. Pat. No. 4,504,761 to T. discloses a piezoelectric generator mounted on a vehicle tire that generates electricity using the stress applied to the tire as the vehicle wheels rotate. Also, under the name of “wind generator and speedometer”
U.S. Pat. No. 5,223,763 to David B. Chang discloses a piezoelectric generator that generates electricity from piezoelectric elements by eddy currents.

FIG. 1 schematically shows a tire on which the piezoelectric generator of the triplet is mounted. Referring to FIG.
Lett's piezoelectric generator includes a piezoelectric array having a number of piezoelectric elements 12 mounted on top of an inner wall 22 of an automobile tire 20, and a member 14 for applying a stress to the piezoelectric elements 12. Each time the tire 20 rotates, each of the stress members 14 comes into contact with the corresponding piezoelectric element 12 to apply a stress during the running of the automobile, and thereby the piezoelectric element 12 generates electricity. The current generated from the piezoelectric element 12 is electrically connected to a battery or an electric system of the vehicle.

FIG. 2 shows a piezoelectric generator in the window that generates electricity using wind. Referring to FIG. 2, the window generator includes a conduit 30 for guiding the wind, and vortices 42A-4.
A partition 40 for forming 2D is provided. A large number of piezoelectric elements 50A to 50F are arranged at a predetermined distance apart from each other on the path where the wind is guided, and the piezoelectric elements 50A to 50F are stressed by eddies 42A to 42F. Therefore, electricity is generated in the piezoelectric elements 50A to 50F that are stressed by the eddies 42A to 42F.

[0008]

However, in spite of its usefulness, a piezoelectric generator which actively generates useful electric energy from mechanical energy by utilizing the piezoelectric phenomenon and uses it is presently available. Not much research has been done. Further, since the processing of the piezoelectric element is difficult and the efficiency is not so high, there are many problems to be solved for practical use.

An object of the present invention is to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a piezoelectric generator that generates electricity by using vibration energy of a mechanical vibration source. To provide.

Another object of the present invention is to provide a piezoelectric generator having a piezoelectric element having a structure for effectively generating electricity and an electric circuit.

Still another object of the present invention is to provide a method for manufacturing the piezoelectric generator.

[0012]

In order to achieve the above object, a piezoelectric generator according to the present invention is provided with a piezoelectric thin film, and attached to the piezoelectric thin film, and deformed by vibration of a mechanical vibration source together with the piezoelectric thin film. A piezoelectric thin film support member having a supporting portion that is integrally formed on one side of the deformed portion to be raised and the deformed portion and supports the piezoelectric thin film and the deformed portion,
A plurality of piezoelectric elements provided on a wafer attached to a mechanical vibration source to generate electricity from the mechanical energy of the mechanical vibration source; and for charging a storage battery with the electricity generated from the piezoelectric element. And an electric circuit.

According to another feature of the present invention, the piezoelectric thin film and the deformed portion and the support portion of the piezoelectric thin film support member each have a substantially hexahedral shape, and a part of the piezoelectric element acts as a cantilever. As described above, the length of the piezoelectric thin film and the length of the deformed portion are formed sufficiently longer than the length of the support portion. Residual stress is formed in the cantilever portion of the piezoelectric element so as to warp upward. The size of the piezoelectric element is determined so that the product of the amount of charge generated from one piezoelectric element and the number of piezoelectric elements processed on the wafer is maximized. The piezoelectric thin film is preferably Z
The piezoelectric thin film support member is made of one selected from the group consisting of nO, PZT, and PLZT, and the piezoelectric thin film support member is made of nitride. A first electrode is formed below the piezoelectric thin film and a second electrode is formed above the piezoelectric thin film in order to transfer electric charges generated from the piezoelectric thin film to the storage battery. Said first and said platinum, tantalum,
Alternatively, it is constituted by any one selected from the group consisting of platinum and tantalum.

According to still another feature of the present invention, the electric circuit includes a high voltage coil having one side electrically connected to the piezoelectric element and the other side grounded, and both sides electrically connected to an anode and a cathode of the storage battery, respectively. A transformer with a low voltage coil connected to the power supply. The electric circuit is provided with a DC / AC converter for converting DC generated from the piezoelectric element into AC, and a diode for preventing current from being discharged from the storage battery through the transformer.

The manufacturing method according to the present invention comprises the steps of: i) forming a piezoelectric thin film having a step of forming a first electrode and a second electrode; and ii) forming the piezoelectric thin film on which the first electrode and the second electrode are formed. A piezoelectric thin-film support, comprising: a deformable portion attached to a thin film and deformed by the vibration of a mechanical vibration source together with the piezoelectric thin film; and a supporting portion integrally formed on one side of the deformable portion to support the piezoelectric thin film and the deformable portion. Forming a plurality of piezoelectric elements provided on a wafer mounted on a mechanical vibration source to generate electricity from mechanical vibration energy of the mechanical vibration source, the method comprising: Forming an electrical circuit for charging the storage battery with electricity generated from the elements.

[0016]

When the mechanical vibration source vibrates, a current is generated by the stress generated in the piezoelectric thin film, and the current is charged in the storage battery through the electric circuit. According to the present piezoelectric generator, useful electric energy can be effectively generated from wasted mechanical vibration energy and used for an electric system or the like.

[0017]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 3 is a schematic diagram for explaining the basic concept of the piezoelectric generator according to the present invention. The piezoelectric generator 200 is attached to a mechanical vibration source 100 such as an automobile engine. When the mechanical vibration source 100 vibrates, a displacement is applied to the piezoelectric element 205 of the piezoelectric generator 200 to generate a current. The piezoelectric generator 200 is electrically connected to a storage battery 150, and a current generated from the piezoelectric generator 200 charges the storage battery 150.

FIG. 4 is a schematic view showing an example in which the piezoelectric generator according to the present invention is applied to an engine. Referring to FIG. 4, a piezoelectric generator 200 of the present invention includes a plurality of piezoelectric elements 20.
5 and an electric circuit 105 for charging the storage battery 150 with electricity generated from the piezoelectric element 205. The plurality of piezoelectric elements 205 are provided on a wafer mounted on top of the engine 100 of the automobile. The engine 100 is provided with a normal AC generator 11 by a belt or the like.
0 is concatenated. The alternator 110 does not require electricity in the vehicle's electrical system 120 to reduce the running output of the vehicle when driven, or can run idle without being driven when the storage battery is fully charged. It has become. Unlike the alternator 110, the piezoelectric generator 200 of the present invention uses mechanical energy wasted by the vibration of the engine 100, so that the output of the vehicle is not reduced during power generation. The generator 200 operates prior to or with the alternator 110.

As shown in FIG. 4, the electric circuit 105 includes a DC / AC converter 130, a transformer 140, and a diode 160. First and second terminals 148 and 156 are electrically connected to the piezoelectric element 205. The first and second terminals 148 and 156 are further connected to ground and the DC / AC
The DC generated by the piezoelectric generator 200 is electrically connected to the DC / AC converter 1.
30 and is converted to an alternating current. In addition, the DC /
The AC converter 130 is electrically connected to a high voltage coil 142 of the transformer 140 through a third terminal 132, and the high voltage coil 142 is grounded through a fourth terminal 146, and is generated from the piezoelectric generator 200. DC /
The AC converted by the AC converter 130 flows through the high voltage coil 142. Meanwhile, the low voltage coil 144 of the transformer 140 is connected to the anode and the cathode of the storage battery 150 through fifth and sixth terminals 152 and 154, respectively.

The diode 160 is connected to the sixth terminal 15.
4 and the anode of the diode 160 is
The cathode of the diode 160 is connected to the low voltage coil 144. The diode 160 prevents current from being discharged from the storage battery 150 through the transformer 140.

The sixth terminal 154 of the low voltage coil 144
And the cathode of the storage battery 150 forms a first connection point CN1, and the cathode of the diode 160 and the anode of the storage battery 150
A connection point CN2 is formed. The first and second connection points CN
The first and second output terminals 112 and 114 of the AC generator 110 are connected to 1 and CN2, respectively. An anode and a cathode power supply terminal of an electric system 120 including electric components of a vehicle are connected to the first and second connection points CN1 and CN2 to supply current.

FIG. 5 schematically shows a piezoelectric element used in a piezoelectric generator according to the present invention. As shown in FIG. 5, the piezoelectric element 205 of the piezoelectric generator 200 of the present invention is
10, a first electrode 2 formed below the piezoelectric thin film 210
13, a second electrode 215 formed on the piezoelectric thin film 210 corresponding to the first electrode 213, and the first electrode 21
3, a piezoelectric thin film support member 220 (hereinafter, also referred to as a support member) that supports the piezoelectric thin film 210. The piezoelectric thin film 210 has a substantially hexahedral shape having a length L, a thickness T1, and a width B. The piezoelectric thin film 210
The constituents of ZnO, PZT (Pb (Zr, Ti) O ₃ ), or PLZ
T (Pb, La) (Zr, Ti) O ₃ ) or the like is used. Desirably PZ
The piezoelectric thin film 210 is formed using T. PZT is
It is a complete solid solution of PbZrO ₃ and PbTiO ₃ , and its crystal structure exists in a cubic paraelectric phase at high temperature, and at normal temperature, the crystal structure is orthorhombic antiferroelectric phase and rhombohedral according to the composition ratio of Zr and Ti. It is present in a tetrahedral ferroelectric phase and a tetragonal ferroelectric phase.

The first electrode 213 and the second electrode 215 are formed using platinum Pt, tantalum Ta, or platinum-tantalum Pt-Ta having excellent electrical conductivity. The first electrode 213 and the second electrode 215 are connected to the piezoelectric thin film 210.
To transfer the charge generated from

The piezoelectric thin film 210 on which the first electrode 213 and the second electrode 215 are formed is supported by a piezoelectric thin film supporting member 220. The support member 220 is made of nitride SiNx.
Formed using The piezoelectric thin film support member 220 has a substantially L-shaped cross section, and is attached to the piezoelectric thin film 210 and is deformed together with the piezoelectric thin film 210 by the vibration of the engine 100 of the vehicle. The piezoelectric thin film 210 includes the first and second electrodes 213 and 215 integrally formed on the side of the piezoelectric thin film 210, and a supporting portion 220B that supports a deformable portion 220A attached to the piezoelectric thin film 210. The deformation part 220A
Has a substantially hexahedral shape having a length L1, a thickness T2, and a width B. The support portion 220B has a length L2, a thickness TS2.
And a hexahedral shape having a width B. As shown in FIG. 5, the length L1 of the deformed portion 220A is formed sufficiently longer than the length L2 of the support portion 220B.
05 acts as a piezoelectric cantilever of length L1, thickness TC, and width B.

Recently, OMRON of Japan
M. Sakata etc. has a piezoelectric element 20 having a shape as shown in FIG.
The following equation was proposed to measure the piezoelectric constant of 5:

(Equation 1) Here, d ₃₁ : piezoelectric constant L1: length of piezoelectric cantilever Q: electric charge B: width of piezoelectric cantilever TC: thickness of piezoelectric cantilever E: Young's modulus of support member δ: displacement of piezoelectric thin film L: piezoelectric element The charge amount Q is the charge amount detected from the charge amplifier when measuring the piezoelectric constant, and the displacement amount δ is the displacement amount of the cantilever-shaped piezoelectric thin film 210.

Equation 1 is summarized below with respect to the detected charge amount Q.

(Equation 2) As can be seen from Equation 2, the charge amount Q in order to directly proportional to the piezoelectric constant d _31, in order to increase the charge amount Q, it is desirable to use a piezoelectric material the piezoelectric constant d ₃₁ is large. In the present invention, a material having a relatively large piezoelectric constant d ₃₁ in the range of 80 pC / N to 220 pC / N is used as the piezoelectric thin film 210.

The length L2 of the support portion 220B of the support member 220 is formed sufficiently smaller than the total length L of the piezoelectric element 205. Therefore, it can be assumed that the value of L1 is similar to L for simplicity of interpretation. For convenience of calculation, it is assumed that the piezoelectric constant d ₃₁ is 100 pC / N.

In Equation (1), the Young's modulus of the piezoelectric thin film 210 is ignored, assuming that the thickness T1 of the piezoelectric thin film 210 is sufficiently smaller than the thickness T2 of the support member. However, in interpreting the vibration of the piezoelectric element 205 of the present invention, the thickness of the first and second electrodes 213 and 215 formed on the lower and upper portions of the piezoelectric thin film 210 is ignored, but the thickness of the piezoelectric thin film 210 is ignored. The effective Young's modulus in the double layer is used without ignoring T1. Let the Young's modulus of the piezoelectric thin film be E1,
Assuming that the Young's modulus of the support member is E2, the effective Young's modulus E _eq in the double layer is as shown in Equation 3.

(Equation 3)

FIG. 6 shows a simple mechanical model for interpreting the vibration characteristics of the piezoelectric element used in the present invention. Referring to FIG. 6, cantilever-shaped piezoelectric element 20
The mechanical model of 5 comprises a mass having a mass m, a spring having a spring constant k, and a damper having a damping coefficient c. The spring and the damper are connected to the mass body in parallel. Assuming that the displacement of the mass body is x, an external force F = Asin (ωt) (where A is the amplitude of the vibration source, ω is the frequency of the vibration source,
The equation of motion of the mass body when (t is time) acts is as follows:

(Equation 4)

The solution of the above-mentioned differential equation in equation (4) is as shown in equation (5).

(Equation 5) Here, δ is the relative displacement of the piezoelectric element 205, A is the amplitude of the vibration source, ζ is the damping ratio, and γ is the ratio between the frequency ω of the vibration source and the natural frequency ω _n of the mechanical model, that is, the vibration indicates the number ratio ω / ω _n.

The natural frequency ω _n of the mechanical model is given by
It is like.

(Equation 6) Here, K _eq indicates the effective spring constant, and M _eq indicates the effective mass.

Physical properties such as Young's modulus and density of PZT and nitride constituting the cantilever are made of existing published materials, and the thickness of the piezoelectric thin film 210 and the deformed portion 220A are set to 1 μm. Table 1 summarizes the materials used for the calculations.

[Table 1]

Table 2 shows the types and ranges of variables adopted to desirably implement the present invention.

[Table 2]

Table 3 shows the natural frequency ω _n of the cantilever-shaped piezoelectric element 205 obtained by calculation, and FIG. 7 schematically shows the result.

[Table 3] As can be seen from Table 3, the natural frequency ω of the piezoelectric element 205
_n is inversely proportional to the square of its length L, independent of its width B.

In the present invention, Equation 2 is used to determine the size of the piezoelectric element 205 that generates the maximum charge.
Referring to Equation 2, the most important variable for maximizing the product of the number of piezoelectric elements 205 that can be processed on a circular wafer having a certain area and the amount of electric charge generated from each piezoelectric element 205 is piezoelectric element 205. It can be seen that the length is L.

FIG. 8 shows the amount of electric charge Q generated from one piezoelectric element 205 when the amplitude A of the vibration is 0.5 mm with respect to the length L and the width B of the piezoelectric element 205. As can be seen from FIG. 8, the generated charge amount Q is linearly proportional to the width B of the piezoelectric element 205. Also, referring to the point P in FIG.
It can be seen that when the width B of Sample No. 5 is 100 μm and the length L is 1000 μm, a charge amount of about 2 nC is generated every oscillation cycle.

FIG. 9 shows the number N of the piezoelectric elements 205 that can be processed to a fixed area on an 8-inch Si-wafer with respect to the length L and the width B of the piezoelectric elements 205. FIG.
The charge amount Q generated from the two piezoelectric elements (see FIG. 8) and the piezoelectric element 205 that can be processed on an 8-inch Si-wafer.
Schematically shows the product of the number N (see FIG. 9). Referring to FIG. 10, the amount of electric charge generated when a piezoelectric array composed of a cantilever piezoelectric element 205 micro-machined into one 8-inch Si-wafer at 1 kHz is 0.648C per second at the maximum. Therefore, a current of 648 mA is generated.

In the piezoelectric generator 200 according to the present invention, the physical properties important for increasing the charge generation amount Q are the piezoelectric constant d ₃₁ of the piezoelectric thin film 210 and the Young's modulus E 2 of the piezoelectric thin film supporting member 220. As can be seen from Equation 2, the generated charge amount Q increases in direct proportion to the piezoelectric constant d ₃₁ of the piezoelectric thin film 210 and the Young's modulus E2 of the support member 220.

The deformation of the cantilever-shaped piezoelectric element 205 due to its own weight is 0.678 μm by calculation, which is negligible. On the other hand, when the amplitude of the vibration is 0.5 mm, the displacement amount δ of the piezoelectric
37 μm at the time of 0 μm (= 500 μm × 0.07
4) is reached. However, the displacement amount δ of the piezoelectric element 205 is a very large value when compared with the thickness of the sacrificial layer serving as a movement space, and the piezoelectric element 205 is undesirably damaged due to collision with a substrate during operation. The result comes. Therefore, the Young's modulus E of the support member 220 is
There is a limit to reducing the value by reducing the value of 2, even though the amount of charge generation increases. For the reasons described above, the Young's modulus E of the support member 220 of the present invention is
2 is actually 200 × 10 ⁹ N / m to 400 × 10 ⁹ N
/ M.

Further, although the thickness TC of the piezoelectric element 205 can be reduced to increase the amount of generated electric charge Q, there is a limit in reducing the thickness TC of the piezoelectric element 205. On the other hand, it is expected that the above-mentioned problems can be solved to some extent by the shrinkage of the volume generated during the process of PZT crystallization. In the piezoelectric generator 200 according to the present invention, the piezoelectric element 20
The thickness TC of the piezoelectric element 205 is reduced as much as possible.
In order to more effectively prevent the collision with the substrate, a residual stress is generated in the piezoelectric thin film supporting member 220 in advance, and the piezoelectric element 205 is warped upward after the sacrificial layer is removed.

The piezoelectric array comprising the piezoelectric elements according to the invention is manufactured by micromachining. The piezoelectric array is a MEMS (Mic) for manufacturing a piezoelectric thin film directly on a Si-wafer.
The piezoelectric array is manufactured using a RoElectro Mechanical System, and in order to extend the mechanical fatigue life, the piezoelectric array is made of S
The i-wafer itself is manufactured by surface micromachining rather than volume micromachining where cracks are likely to occur.

Hereinafter, a method for manufacturing the above-described piezoelectric element 205 will be described in detail with reference to the drawings. 11A to 1
FIG. 1D is a manufacturing process diagram of the piezoelectric element 205 shown in FIG. 5.
11A to 11D, the same members as those in FIG. 5 are denoted by the same reference numerals.

Referring to FIG. 11A, first, the light substrate 3
A sacrificial layer 305 is formed on the lower layer 00 by using a low pressure chemical vapor deposition method (LPCVD). The sacrificial layer 305 is made of phosphor silicate glass (PSG) and has a thickness of about 1.0 to 5.0 μm. Next, the support member 2
A portion of the sacrificial layer 305 is etched and removed in consideration of the position where the 20 support portions 220B are formed.

Referring to FIG. 11B, a support layer 219 is formed on the substrate 300 and the sacrificial layer 305 by using a low pressure chemical vapor deposition method. The support layer 21
9 is formed using a nitride so as to have a thickness of 0.5 to 2.0 μm, preferably about 1.0 μm. The support layer 219 is patterned on the support member 220 later. A first electrode layer 212 is formed on the support layer 219. The first electrode layer 212 is made of platinum Pt, tantalum Ta, or platinum-tantalum Pt-Ta having excellent electric conductivity.
Metal such as 0.1 to 1.0 μm, preferably 0.1 to 1.0 μm using a sputtering method or a chemical vapor deposition method.
It is formed to have a thickness of about μm. First electrode layer 2
12 is patterned on the first electrode 213 later.

A piezoelectric layer 209 is formed on the first electrode layer 212 using a sol-gel method, a chemical vapor deposition method, or a sputtering method. The piezoelectric layer 209 is Z
Using piezoelectric materials such as nO, PZT and PLZT,
It is formed so as to have a thickness of about 0.5 to 2.0 μm. Preferably, the piezoelectric layer 209 is formed of PZT to have a thickness of about 1.0 μm using a sol-gel method. Next, the piezoelectric layer 209 is heat-treated using a rapid thermal processing (RTA) method, and is then polled. Piezoelectric layer 2
09 is patterned on the piezoelectric thin film 210 later.

The second electrode layer 2 is formed on the piezoelectric layer 209.
14 are formed. The second electrode layer 214 is the first electrode layer 21
2 is formed to have a similar thickness using the same material and method. The second electrode layer 214 will be
5 is patterned.

Referring to FIG. 11C, the second electrode layer 2
After applying a first photoresist (not shown) on the upper portion of the substrate 14, the second electrode layer 214, the piezoelectric layer 209, the first electrode layer 212, and the support are formed using the first photoresist as an etching mask. By patterning the layer 219, the second electrode 215 and the piezoelectric thin film 21 each having a square shape are formed.
0, the first electrode 213 and the support member 220 are formed. Next, a second photoresist is applied to the top and sides of the resultant by 1.5 to 2.0 μm using a spin coating method.
A protective layer 310 having a thickness of about m is formed. The protective layer 310 is formed on the piezoelectric thin film 210 on which the first electrode 213 and the second electrode 215 are formed while the sacrificial layer 305 is removed later.
Perform the function of protecting

Referring to FIG. 11D, the sacrificial layer 305
Is etched away using hydrogen fluoride (HF) vapor or potassium hydroxide (KOH) vapor. Then
After the protective layer 310 is etched and removed, the substrate 30
0 is separated to complete the piezoelectric element 205.

Hereinafter, the operation of the piezoelectric generator according to the present invention will be described. When the engine 100 of the automobile operates, the piston reciprocates in the cylinder, thereby generating vibration. When the vehicle engine 100 vibrates, a periodic external force is applied to the cantilever-shaped piezoelectric element 205 of the piezoelectric generator 200 mounted on the upper part of the vehicle engine 100, and the piezoelectric element 205 is displaced. Due to the displacement generated in the piezoelectric element 205, a current is generated in the piezoelectric element 205 due to its positive piezoelectric effect.

In the piezoelectric generator 200 according to the present invention, the thickness TC of the piezoelectric element 205 is reduced by generating residual stress in the piezoelectric thin film supporting member 220 in advance and warping the piezoelectric element 205 upward after removing the sacrificial layer. The collision of the piezoelectric element 205 with the substrate is more effectively prevented while being as thin as possible. The size of the piezoelectric element 205 is determined so that the product of the amount of electric charge generated from one piezoelectric element 205 and the number of the piezoelectric elements 205 processed on the wafer is maximized, thereby effectively generating electricity.

The electric current generated from the piezoelectric element 205 charges the storage battery 150 of the vehicle by the electric circuit 105. The DC generated from the piezoelectric element 205 is converted to AC by the DC / AC converter 130 of the electric circuit 105. The alternating current is applied to the high voltage coil 1 of the transformer 140.
42 and the low voltage coil 1 of the transformer 140
44 is connected to a cathode and an anode of the storage battery 150, respectively, and is charged with electricity. The transformer 140 and the storage battery 15
0 by the diode 160 provided between
Discharge of the current from 50 through the transformer 140 is prevented. Also, the storage battery 150 is connected to a normal AC generator 110 of a vehicle and is supplied with current from the AC generator. The alternator 110 does not require electricity in the vehicle's electrical system 120 to reduce the running power of the vehicle when driven, or can run idle without being driven when fully charged. ing. The piezoelectric generator 200 of the present invention
By utilizing the mechanical energy wasted by the vibration of zero, unlike the alternator 110, in order not to reduce the output of the vehicle during the power generation, the piezoelectric generator 200 of the present invention uses the alternator 110. Instead of or with the alternator 110.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to the embodiments, and a person having ordinary knowledge in the technical field to which the present invention belongs departs from the spirit and spirit of the present invention. Rather, the invention could be modified or changed.

[0053]

As described above, useful electric energy can be generated from mechanical vibration energy wasted by the piezoelectric generator according to the present invention. In addition, by selecting the shape, size, and physical properties of the piezoelectric elements used in the piezoelectric generator so that the maximum amount of charge is generated on the same area of the wafer, electricity is generated effectively. It is possible to do. Further, the electric circuit provided by the piezoelectric generator according to the present invention can effectively charge the storage battery with electricity generated from the piezoelectric element.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a conventional piezoelectric generator mounted on a tire.

FIG. 2 is a schematic diagram illustrating a conventional piezoelectric generator that generates electricity using wind.

FIG. 3 is a schematic diagram illustrating a basic concept of a piezoelectric generator according to the present invention.

FIG. 4 is a schematic view showing a piezoelectric generator according to an embodiment of the present invention.

FIG. 5 is a perspective view showing a piezoelectric element used in the piezoelectric generator of FIG. 4;

6 is a schematic diagram showing a mechanical model for interpreting the vibration characteristics of the piezoelectric element of FIG.

7A to 7C are graphs schematically showing natural frequencies of the piezoelectric element of FIG. 5;

8 is a graph schematically showing an amount of electric charge generated from the piezoelectric element of FIG.

FIG. 9 is a graph schematically showing the number of piezoelectric elements that can be processed on a wafer having a certain area.

FIG. 10 is a graph schematically showing a total charge amount generated from a wafer having a fixed area.

11A to 11D are manufacturing process diagrams of the piezoelectric element shown in FIG.

[Explanation of symbols]

 Reference Signs List 105 electric circuit 110 alternator 120 electric system 130 DC / AC converter 140 transformer 142 high voltage coil 144 low voltage coil 150 storage battery 160 diode 200 piezoelectric generator 205 piezoelectric element 213, 215 first and second electrodes 210 piezoelectric Thin film 220 Piezoelectric thin film support member

Claims (20)

[Claims] 1. A piezoelectric thin film, a deformed portion formed under the piezoelectric thin film, and deformed by the vibration of a mechanical vibration source together with the piezoelectric thin film, and a piezoelectric thin film integrally formed on one side of the deformed portion. Each of the piezoelectric thin film support members has a support portion for supporting the deformation portion, and is provided on a wafer attached to a mechanical vibration source to generate electricity from mechanical vibration energy of the mechanical vibration source. A piezoelectric generator comprising: a number of piezoelectric elements; and an electric circuit for charging a storage battery with electricity generated from the piezoelectric elements. 2. A method according to claim 1, wherein a first electrode is formed below the piezoelectric thin film and a second electrode is formed above the piezoelectric thin film in order to transfer electric charges generated from the piezoelectric thin film to the storage battery. The piezoelectric generator according to claim 1, wherein: 3. The device of claim 2, wherein the first and second electrodes are each made of one selected from the group consisting of platinum, tantalum, and platinum-tantalum. Piezoelectric generator. 4. The piezoelectric generator according to claim 1, wherein the mechanical vibration source is an engine. 5. The piezoelectric thin film and a deformed portion and a support portion of the piezoelectric thin film support member each have a substantially hexahedral shape, and the piezoelectric thin film has a shape such that a part of the piezoelectric element acts as a cantilever. 2. The piezoelectric generator according to claim 1, wherein the length and the length of the deformable portion are formed sufficiently longer than the length of the support portion. 3. 6. The piezoelectric generator according to claim 5, wherein residual stress is formed in the cantilever portion of the piezoelectric element so as to warp upward. 7. The piezoelectric generator according to claim 1, wherein the piezoelectric thin film is made of one selected from the group consisting of ZnO, PZT, and PLZT. 8. The piezoelectric generator according to claim 1, wherein the piezoelectric thin film supporting member is made of nitride. 9. The piezoelectric constant of the piezoelectric thin film is 80 pC / N.
2. The method according to claim 1, wherein the pressure is from 220 to 220 pC / N.
4. The piezoelectric generator according to claim 1. 10. The piezoelectric generator according to claim 1, wherein the piezoelectric thin film supporting member has a Young's modulus of 200 × 10 ⁹ N / m to 400 × 10 ⁹ N / m. 11. The piezoelectric element according to claim 1, wherein the size of the piezoelectric element is determined so that the product of the amount of electric charge generated from one piezoelectric element and the number of piezoelectric elements processed on a wafer is maximized. Piezoelectric generator. 12. The electric circuit has a first terminal electrically connected to the piezoelectric element, a second terminal electrically connected to the piezoelectric element on one side, and a grounded second terminal on the other side, and a first terminal electrically connected to the first terminal on the other side.
2. A transformer comprising a high voltage coil electrically connected to a terminal and grounded on the other side and a low voltage coil electrically connected on both sides to an anode and a cathode of the storage battery, respectively. 4. The piezoelectric generator according to claim 1. 13. The electric circuit according to claim 12, wherein the electric circuit further comprises a DC / AC converter provided to the first terminal for converting a direct current generated from the piezoelectric element into an alternating current. Piezoelectric generator. 14. The electric circuit for preventing a current from being discharged from the storage battery through the transformer,
The piezoelectric generator according to claim 12, further comprising a diode provided between the storage battery and the transformer. 15. forming a piezoelectric thin film having a step of forming a first electrode under the first electrode and a step of forming a second electrode thereon; and ii) forming the piezoelectric thin film on which the first electrode and the second electrode are formed. A piezoelectric thin-film support, comprising: a deformable portion attached to a thin film and deformed by the vibration of a mechanical vibration source together with the piezoelectric thin film; Forming a plurality of piezoelectric elements provided on a wafer mounted on a mechanical vibration source to generate electricity from mechanical vibration energy of the mechanical vibration source; and forming the piezoelectric element. Forming an electric circuit for charging the storage battery with the electricity generated from the battery. 16. The step of forming the piezoelectric thin film supporting member includes forming a sacrificial layer on the substrate using a low pressure chemical vapor deposition method and etching and removing a part of the sacrificial layer. The method according to claim 15, wherein the method is performed after the step (c). 17. The method of claim 15, wherein forming the sacrificial layer is performed using phosphor silicate glass to have a thickness of about 1.0 to 5.0 μm. A method for manufacturing the piezoelectric generator according to the above. 18. The step of forming the piezoelectric element includes protecting the upper and side portions of the piezoelectric thin film on which the first electrode and the second electrode are formed and the side portion of the piezoelectric thin film support member using a photoresist. The method of claim 15, further comprising forming a layer and etching the sacrificial layer using hydrogen fluoride vapor. 19. The step of forming the piezoelectric thin film supporting member may include forming the nitride by using a low-pressure chemical vapor deposition method.
The method of claim 14, wherein the forming is performed to have a thickness of 2.0 μm. 20. The step of forming the piezoelectric thin film member,
2. The method according to claim 1, wherein the step is performed using a sol-gel method, a chemical vapor deposition method, or a sputtering method.
5. The method for manufacturing a piezoelectric generator according to item 4.