JP2004184274A - Thin-film piezoelectric sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and low-cost thin-film piezoelectric sensor having superior heat resistance and proper piezoelectric properties. <P>SOLUTION: The thin-film piezoelectric sensor is made up so as to laminate an underlayer 2, a piezoelectric thin film layer 3 and an upper electrode 4 onto a surface of a substrate 1 in this order. By using for piezoelectric thin-film layer 3 thin film materials, such as aluminum nitride (AlN), zinc oxide (ZnO) or piezoelectric materials of similar effectiveness, for which Curie temperature points do not exist, the heat resistance and decay durability of the thin-film type piezoelectric sensor is improved. In addition, by controlling the degree of dipole orientation of crystals in the piezoelectric thin-film layer 3 are ensured to be not less than 75%, the piezoelectric properties are ensured. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a thin-film piezoelectric sensor that detects physical quantities such as acoustic emission, vibration, and acceleration by a piezoelectric ceramic thin-film element in a high-temperature environment such as inside an engine of an internal combustion engine or inside a plant such as a nuclear power plant. It is about.
[0002]
[Prior art]
2. Description of the Related Art A sensor is installed inside a structure to detect abnormalities in a structure that generates a high-temperature atmosphere, such as a pipe or a valve in a plant such as a nuclear power plant, or an engine of an internal combustion engine. For example, an acoustic emission sensor that detects acoustic emission, which is an elastic wave generated when a crack or a crack occurs, and a vibration sensor of a piezoelectric type that detects information on abnormal vibration and acceleration, are used. Various types such as a die, a cantilever type, a diaphragm type, and a shear type are known.
[0003]
Among these, the compression type thin film type piezoelectric sensor is composed of a pedestal, a pedestal side electrode, a piezoelectric body, a load body side electrode, and a laminated body in which a load body is sequentially laminated, and the lower surface of the pedestal is rigidly attached to an object to be measured. That is, it is used by being firmly attached. When vibration occurs in the measured object, the vibration is transmitted to the pedestal side of the sensor. The pedestal side of the sensor vibrates together with the object to be measured, but the load side has a delay in vibration due to inertial force, and a compression or tensile stress is generated in the piezoelectric body in proportion to the vibration acceleration. Then, charges or voltages proportional to the stress are generated on both sides of the piezoelectric body, and the two electrodes arranged on both sides of the piezoelectric body take out the electricity. The magnitude and acceleration of the vibration of the measured object can be detected by measuring the extracted electric output.
[0004]
Conventionally, as a piezoelectric body used in such a piezoelectric sensor, a piezoelectric body such as lead zirconate titanate or polyvinylidene fluoride described in Patent Documents 1 and 2 has been used. Such a piezoelectric material made of a piezoelectric material has a low Curie temperature at which polarization disappears, and its applicable limit temperature is about 300 ° C. at the maximum. Therefore, in order to keep the piezoelectric body at an appropriate temperature, Patent Document 3 discloses one in which the piezoelectric body is cooled by a Peltier element. However, since the Peltier element only has a function of generating a local temperature gradient, the Peltier element cannot be applied to a location where the temperature becomes high as a whole without a cooling mechanism attached to the outside.
[0005]
In addition, vibration such as acoustic emission is attenuated due to the nature of the vibration transmitting substance in the middle, or extraneous vibration is mixed in from the outside in the middle of the transmission path. It is desirable. However, as described above, conventional thin-film type piezoelectric sensors cannot withstand high temperatures, and measurement is performed by inducing vibration to a remote low-temperature environment via a vibration transmission rod, as described above. I was In this case, the vibration is attenuated, noise is mixed, and the vibration of the object to be measured cannot be measured sufficiently accurately.
[0006]
Thus, Patent Document 4 discloses a method of using a piezoelectric material having a high Curie temperature, such as lithium niobate, for a piezoelectric layer as a thin-film piezoelectric sensor that can withstand high temperatures. Lithium niobate has a Curie temperature of about 1140 ° C. and can be used in a high-temperature environment without cooling means. However, it is difficult to form a thin film, and if it is not a single crystal, piezoelectric characteristics cannot be obtained.
[0007]
In the high-temperature thin-film vibration sensor described in Patent Document 5, in order to solve these problems, zinc oxide or aluminum nitride is used as a piezoelectric ceramic having no Curie temperature and oriented in the c-axis direction. The thin film is a piezoelectric thin film element.
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 6-148011 (published May 27, 1994)
[0009]
[Patent Document 2]
JP-A-10-206399 (published August 7, 1998)
[0010]
[Patent Document 3]
JP-A-5-203665 (publication date: August 10, 1993)
[0011]
[Patent Document 4]
JP-A-5-34230 (publication date: February 9, 1993)
[0012]
[Patent Document 5]
JP-A-10-122948 (publication date May 15, 1998)
[0013]
[Problems to be solved by the invention]
However, a substance having a wurtzite crystal structure, such as zinc oxide or aluminum nitride, in Patent Document 5 is difficult to maintain the piezoelectric characteristics. Can't improve. In other words, although c-axis orientation is also a necessary factor for improving the piezoelectric characteristics, it is not possible to stably maintain the piezoelectric characteristics by itself, and even from experimental data, it is possible to produce a product having good piezoelectric characteristics. However, it is known that there is no reproducibility, and in some cases, no piezoelectricity is exhibited.
[0014]
This is because the piezoelectric sensor manufactured by the method of Patent Document 5 has the piezoelectric layer directly provided on the substrate, and cannot stably align the dipole directions of the crystal of the piezoelectric element. Even if a material having a high degree of dipole orientation can be produced, it is difficult to obtain a piezoelectric layer having a high degree of dipole orientation with good reproducibility. I can't keep it above. Therefore, there is a problem that the piezoelectric characteristics of the piezoelectric sensor are not maintained, and good pressure detection cannot be performed.
[0015]
Therefore, the present invention has been made in view of the above-mentioned conventional problems, and has as its object to reduce the thickness of a piezoelectric material having no Curie temperature and to assure the piezoelectric characteristics by orienting the polarity of the crystal in the thin film. It is an object of the present invention to provide a thin-film piezoelectric sensor which is small in size, does not require a cooling means, has excellent heat resistance, and is inexpensive, and detects acoustic emission, vibration or acceleration.
[0016]
[Means for Solving the Problems]
The present inventors have conducted various studies on a method for forming a thin film of a piezoelectric material having no Curie temperature, and as a result, the method comprises a sintered body of an oxide-based, carbon-based, nitrogen-based or boride-based ceramic or quartz glass. The above-mentioned object is achieved by forming a thin film by growing a piezoelectric ceramic in a single crystal state while controlling the polarity on an insulating substrate or a conductive substrate made of a heat-resistant metal material such as Inconel or SUS630. Have been achieved, and the present invention has been completed based on such findings.
[0017]
That is, the thin film type piezoelectric sensor according to the present invention can be used for an insulating substrate made of a sintered body of oxide, carbide, nitride or boride ceramic or quartz glass, or a heat resistant material such as Inconel or SUS630 equivalent. This is a high-temperature thin-film type piezoelectric sensor in which piezoelectric ceramics without Curie temperature are grown into a single crystal on a conductive substrate made of a conductive metal material to form a thin film. This is a compression type, cantilever type, diaphragm It can be used for various types of thin film type piezoelectric sensors such as a die type and a shear type.
[0018]
The thin film piezoelectric sensor of the present invention is a thin film piezoelectric sensor formed by laminating a first electrode layer, a piezoelectric layer, and a second electrode layer on a substrate surface in this order, wherein the piezoelectric layer has It is made of a piezoelectric material having no Curie temperature, and has a dipole orientation degree of 75% or more.
[0019]
The thin-film type piezoelectric sensor of the present invention is formed by forming a first electrode layer, a piezoelectric layer, and a second electrode layer on a substrate and laminating and integrating them, so that the structure is simple and small. Further, the piezoelectricity can be improved by making the first electrode layer function as a base layer for improving the dipole orientation degree of the piezoelectric layer.
[0020]
Further, the “piezoelectric material having no Curie temperature” is a material that has piezoelectric characteristics and does not cause polar dislocation with a rise in temperature, and examples thereof include a substance having a crystal structure of a wurtzite structure. . Specific examples of the substance having a wurtzite crystal structure include aluminum nitride (AlN) and zinc oxide (ZnO).
[0021]
Substances having a wurtzite crystal structure, such as aluminum nitride (AlN) and zinc oxide (ZnO), inherently have piezoelectricity due to the absence of symmetry in the crystal, and have a Curie temperature like a ferroelectric. In addition, since no polar dislocation occurs even at a high temperature, the piezoelectric property is not lost until the crystal is melted or sublimated. For example, the sublimation temperature of AlN is about 2000 ° C., which is sufficiently higher than the combustion temperature of 500 ° C. in an engine cylinder, and can be used without using a cooling device therein. Therefore, the piezoelectric layer made of such a piezoelectric material has excellent heat resistance, and does not deteriorate in piezoelectric characteristics even at a high temperature. Further, it is excellent in workability and is suitable for thinning.
[0022]
Further, the “degree of dipole orientation” is defined as the ratio of the polarity of the crystal column forming the electric dipole, which is positive or negative, in the same direction, in the same direction. If the directions of the polarities of the crystal columns are completely random, the piezoelectricity of each crystal column cancels each other, and the piezoelectricity disappears in the entire thin film. If the dipole orientation degree of the piezoelectric element is smaller than 75%, the apparent piezoelectric constant becomes less than half of that at the time when the dipole orientation degree is 100%, the piezoelectric characteristics of the piezoelectric layer are deteriorated, and good stress detection cannot be performed. However, if the piezoelectric layer is formed so that the degree of dipole orientation is 75% or more, good piezoelectricity can be maintained.
[0023]
Therefore, according to the above configuration, it is possible to obtain a small-sized, low-cost, thin-film piezoelectric sensor having excellent piezoelectricity and heat resistance.
[0024]
Further, in order to solve the above problems, the thin film piezoelectric sensor according to the present invention, in addition to the above-described configuration, may be configured such that the substrate is a sintered body of an oxide-based, carbide-based, nitride-based or boride-based ceramic or quartz. It is characterized by being an insulating substrate made of glass. According to this, the above-mentioned ceramic materials are excellent in heat resistance, easy to manufacture and inexpensive, and have high hardness and dense characteristics, so that a thin film piezoelectric sensor having high performance and excellent productivity is provided. Is obtained.
[0025]
Further, the substrate may be a conductive substrate made of a heat-resistant metal material. According to this, the substrate can be used as a substitute for a lead wire for extracting a signal from the first electrode layer, and the substrate can be processed into various shapes by ordinary machining.
[0026]
Further, in order to solve the above-mentioned problems, a thin-film piezoelectric sensor according to the present invention is characterized in that the piezoelectric layer is formed by a physical vapor deposition method.
[0027]
The “physical vapor deposition method” is a method in which a substance is evaporated by a physical method and condensed on a member on which a film is formed to form a thin film, and mainly refers to a sputtering method, a vacuum evaporation method, or the like. According to this method, the needle-like crystal columns of the piezoelectric material grow in a frost column shape, and a thin film of the piezoelectric material in a single crystal state can be formed.
[0028]
When stress is applied to this crystal column, positive and negative charges are generated at both ends of the crystal column to form an electric dipole, and at which end the positive charge is generated depends on the dipole of the crystal column. It depends on which direction you are facing. Therefore, in order to increase the degree of dipole orientation and to secure good piezoelectric properties in the thin film of the piezoelectric layer, it is necessary to control the dipole orientation of the crystal when performing the physical vapor deposition method. Specifically, after providing a first electrode layer having a function of adjusting the dipole orientation of the crystal of the piezoelectric layer on the substrate surface, when forming the piezoelectric layer by physical vapor deposition, the substrate temperature, the substrate target There is a method in which the inter-distance and the gas pressure are set to optimal values and the c-axis orientation of the crystal is aligned.
[0029]
Further, in order to solve the above-mentioned problems, the thin-film piezoelectric sensor according to the present invention is characterized in that a surface of the first electrode layer in contact with the piezoelectric layer is covered with a metal contained in the piezoelectric layer. And
[0030]
Here, “metal contained in the piezoelectric layer” refers to a main metal among components contained as a material of the piezoelectric layer. For example, when the piezoelectric layer is aluminum nitride, aluminum is used, and when the piezoelectric layer is oxidized, aluminum is used. In the case of zinc, it refers to zinc. Further, only the surface of the first electrode layer in contact with the piezoelectric layer may be covered with the metal contained in the piezoelectric layer, or the entire first electrode layer may be made of the metal contained in the piezoelectric layer. . Specifically, when the material of the piezoelectric layer is aluminum nitride, the material of the first electrode layer may be aluminum, and when the material of the piezoelectric layer is zinc oxide, the material of the first electrode layer may be zinc. .
[0031]
As a result, the degree of dipole orientation of the piezoelectric layer increases, and the degree of dipole orientation becomes 75% or more. Therefore, the piezoelectric characteristics of the piezoelectric layer can be maintained, and the thin-film piezoelectric sensor can perform good stress detection. .
[0032]
Further, in order to solve the above problems, the thin film type piezoelectric sensor of the present invention is characterized in that, in addition to the above configuration, the thickness of the piezoelectric layer is 0.1 μm or more and 100 μm or less.
[0033]
This is because if the thickness of the piezoelectric layer is thinner than 0.1 μm, it is difficult to form a continuous film, and short circuits are likely to occur when electrodes are arranged on the upper and lower sides. It is because it becomes. Therefore, when the thickness of the piezoelectric layer is within the above range, a thin-film type piezoelectric sensor capable of performing good stress detection can be manufactured in a short time.
[0034]
Further, in order to solve the above-mentioned problems, the thin-film piezoelectric sensor of the present invention is characterized in that, in addition to the above configuration, the second electrode layer is formed by being divided into two or more. .
[0035]
According to this, when stresses such as different pressures are applied depending on positions in the thin film type piezoelectric sensor, different stresses are generated by the respective electrodes, and different charges and voltages are generated on the respective electrodes. In the case of a cantilever-type or diaphragm-type piezoelectric sensor, detecting a difference in stress (that is, a difference between the electrodes) in a substrate on which a piezoelectric thin film is formed may be more effective in terms of sensitivity. Especially, in the case of a cantilever type, when the shear stress is detected instead of the bending stress, the difference can be re-detected by hardware, and high sensitivity can be obtained without being restricted by the dynamic range of each amplifier. Detection can be realized.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
One embodiment of the present invention will be described below with reference to FIG.
[0037]
The thin-film type piezoelectric sensor has a base layer (first electrode layer) 2, a piezoelectric thin-film layer (piezoelectric layer) 3, and an upper electrode (second electrode layer) 4 formed in this order on a substrate 1. It is.
[0038]
For each film formation, a physical vapor deposition method (PVD method), that is, a method in which a substance is evaporated by a physical method and condensed on a member to be formed into a thin film can be used. For example, vacuum evaporation methods such as resistance heating evaporation or electron beam heating evaporation, various sputtering methods such as DC sputtering, high frequency sputtering, RF plasma assisted sputtering, magnetron sputtering, ECR sputtering or ion beam sputtering, high frequency ion plating method, activation Various ion plating methods such as vapor deposition or arc ion plating, molecular beam epitaxy, laser ablation, ion cluster beam vapor deposition, and ion beam vapor deposition.
[0039]
FIG. 1 is a cross-sectional view of a thin film piezoelectric sensor according to one embodiment of the present invention, in which a substrate layer 1, a base layer 2 also serving as a lower electrode, a piezoelectric thin film layer 3, and an upper electrode 4 are sequentially laminated and integrated. Formed.
[0040]
The thin film type piezoelectric sensor is used by attaching the lower surface of the substrate 1 to an object to be measured. When vibration is generated in the measured object, the vibration is transmitted to the substrate 1 and the substrate 1 vibrates together with the measured object. However, the vibration of the opposite side of the measured object of the thin film type piezoelectric sensor is delayed due to inertial force. Compression or tensile stress is generated in the piezoelectric thin film layer 3 in proportion to the vibration acceleration. Then, a charge or a voltage proportional to the stress is generated in the piezoelectric thin film layer 3 on both sides of the piezoelectric thin film layer 3, and the underlayer 2 and the upper electrode 4 arranged on both sides of the piezoelectric thin film layer 3 take out the electricity, The magnitude and acceleration of the vibration of the measured object can be detected by measuring the extracted electric output.
[0041]
The substrate 1 generates stress by directly receiving vibration or pressure, and an insulating or conductive substrate can be used.
[0042]
As the insulating substrate, a sintered body of an oxide-based, carbide-based, nitride-based, or boride-based ceramic or a substrate made of quartz glass can be used. In particular, a substrate made of SiC (polycrystalline silicon carbide) is desirable, but other carbide-based ceramic substrates (for example, B ₄ A substrate made of C, TiC, WC, ZrC, NbC, HfC) or an oxide-based ceramic substrate (eg, Al ₂ O ₃ , ZrO ₂ , TiO ₂ , SiO ₂ Substrate, a nitride-based ceramic substrate (for example, a substrate made of cBN, AlN, and TiN), and a boride-based ceramic substrate (for example, TiB ₂ , ZrB ₂ , CrB ₂ , MoB). It is desired that these ceramic materials have excellent heat resistance, are easy to manufacture and inexpensive, and have high hardness and dense characteristics.
[0043]
The conductive substrate is preferably made of, for example, a heat-resistant metal material such as Inconel or SUS630. The surface of the conductive substrate is polished or chemically removed to improve the orientation of the crystal axis. It is desirable to perform mirror finishing by a conventional method.
[0044]
The underlayer 2 is a buffer layer between the piezoelectric thin film layer 3 formed thereon and the substrate 1, and plays a role in improving the orientation of dipoles and crystal axes of the piezoelectric thin film layer 3 and improving wettability with the substrate 1. have. The material of the underlayer 2 is TiN, MoSi ₂ , Si ₃ N ₄ , Cr, Fe, Mg, Mo, Nb, Ta, Ti, Zn, Zr, W, Pt, Al, Ni, Cu, Pd, Rh, Ir, Ru, Au or Ag. Two or more layers using a plurality of materials can be formed.
[0045]
The piezoelectric thin film layer 3 receives the stress generated by the substrate 1 and generates a charge or a voltage proportional thereto.
[0046]
The material of the piezoelectric thin film layer 3 is preferably aluminum nitride (AlN) or zinc oxide (ZnO), but is not limited thereto, and may be any piezoelectric material having no Curie temperature. A piezoelectric material having no Curie temperature does not lose piezoelectricity until the crystal melts or sublimes. Examples of the piezoelectric material having no Curie temperature include substances having a wurtzite crystal structure, and GaN in addition to AlN and ZnO. A material crystal having such a wurtzite crystal structure has piezoelectricity due to lack of symmetry, and has no Curie temperature because it is not a ferroelectric. Therefore, the piezoelectric thin film layer 3 made of such a piezoelectric material is excellent in heat resistance, does not deteriorate in piezoelectric characteristics even at high temperatures, and has a high piezoelectricity even when exposed to a high temperature close to 500 ° C. like a cylinder of an engine. It does not lose its function as a body. This eliminates the need for a cooling means for the piezoelectric thin film layer 3 and eliminates the restriction that the piezoelectric layer must be provided at a low temperature position, thereby simplifying the structure of the piezoelectric sensor.
[0047]
The dipole orientation of the piezoelectric thin film layer 3 is 75% or more, and preferably 90% or more. This is because, when the dipole orientation degree is smaller than 75%, the apparent piezoelectric constant becomes less than half of that at the time when the dipole orientation degree is 100%, the piezoelectric characteristics of the piezoelectric thin film layer 3 are deteriorated, and stress is favorably reduced. This is because detection becomes impossible. If the dipole orientation degree is 75% or more, sufficient piezoelectricity is maintained.
[0048]
In order for the dipole orientation degree of the piezoelectric thin film layer 3 to be 75% or more, it is necessary to easily align the first atoms when growing the crystal columns. On the other hand, a piezoelectric material having no Curie temperature, unlike a ferroelectric such as lead zirconate titanate, cannot be controlled by an external electric field after crystal formation, so that the piezoelectric material of the piezoelectric thin film layer 3 has a bipolar structure. In order to maintain the dipole orientation at 75% or more, the crystal of the piezoelectric thin film layer 3 must be controlled so that the dipole orientation at the time of forming the piezoelectric thin film layer 3 is 75% or more. Specifically, after providing the underlayer 2 having a function of adjusting the dipole orientation of the crystal of the piezoelectric layer on the substrate, when forming the piezoelectric thin film layer 3, the substrate temperature, the distance between the substrate targets, and the gas pressure are adjusted to optimal values. And the c-axis orientation of the crystal is uniformed, the degree of dipole orientation of the piezoelectric thin film layer 3 can be increased. As described above, in order to improve the piezoelectric characteristics, it is desirable to orient the crystal of the piezoelectric element in the c-axis direction.
[0049]
Further, the surface of the underlayer 2 on the side in contact with the piezoelectric thin film layer 3 is made of metal contained in the piezoelectric thin film layer 3 (Al when AlN is used for the piezoelectric thin film layer 3, and when ZnO is used for the piezoelectric thin film layer 3). With the configuration covered with Zn), the degree of dipole orientation of the piezoelectric thin film layer 3 can be further increased. At this time, when the underlying layer 2 has a multi-layer structure, it is desirable that the uppermost layer (the layer in contact with the piezoelectric thin film layer 3) be a metal contained in the piezoelectric thin film layer 3. Note that the dipole orientation degree is defined as a ratio of positive or negative polarities of crystal columns on the surface of the piezoelectric thin film layer 3 in the same direction.
[0050]
The upper electrode 4 detects the charge generated by the applied stress, and can be made of the same material as the underlayer 2. However, it is not necessary that the upper electrode 4 be the same, and the upper electrode 4 can be appropriately changed depending on the compatibility with the piezoelectric thin film layer 3. It may be selected, and the structure may be a single layer.
[0051]
Further, the thickness of the piezoelectric thin film layer 3 of the thin film type piezoelectric sensor of the present invention is desirably in the range of 0.1 μm to 100 μm, more preferably 0.5 μm to 20 μm, and more preferably 1 μm to 10 μm. More preferably, If the thickness is less than 0.1 μm, a short circuit easily occurs between the underlayer 2 and the upper electrode 4, and if the thickness is more than 100 μm, the deposition time becomes long.
[0052]
The present invention can be configured as the following thin film piezoelectric sensor.
[0053]
A dipole made of a piezoelectric thin film material with no Curie temperature on which a metal electrode is formed on an insulating substrate made of a sintered body of oxide, carbide, nitride, or boride ceramics or quartz glass A first high-temperature thin-film type piezoelectric sensor, wherein a piezoelectric ceramic thin film having an orientation degree of 90% or more and a metal electrode are further laminated and integrated thereon.
[0054]
A metal thin film serving as a buffer layer is formed on a conductive substrate made of a heat-resistant metal material such as Inconel or SUS630, and a dipole orientation degree made of a piezoelectric thin film material having no Curie temperature is 90% or more. A second high-temperature thin-film piezoelectric sensor, wherein a piezoelectric ceramic thin film and a metal electrode are further laminated and integrated thereon.
[0055]
In the first or second thin film type piezoelectric sensor, the piezoelectric thin film element uses a piezoelectric thin film element having a thickness of 0.1 μm to 0.1 mm.
[0056]
In the first or second thin film piezoelectric sensor, the piezoelectric thin film element is made of a thin film of aluminum nitride or zinc oxide.
[0057]
In the first or second thin film piezoelectric sensor, the metal thin film element formed on the piezoelectric ceramic thin film is divided into two or more metal electrodes.
(Embodiment 2)
An embodiment of the present invention will be described below with reference to FIG.
[0058]
In the thin film type piezoelectric sensor of the present invention, an underlayer (first electrode layer) 2, a piezoelectric thin film layer (piezoelectric layer) 3, and a plurality of divided upper electrodes (second electrode layers) 5 are formed on a substrate 1 in this order. It is formed by film formation.
[0059]
The materials and manufacturing methods of the substrate 1, the base layer 2, and the piezoelectric thin film layer 3 are the same as those of the first embodiment, but the piezoelectric thin film layer 3 of the present invention has the divided upper metal electrode 5 divided into two or more. It is formed.
[0060]
The material and manufacturing method of the divided upper metal electrode 5 are almost the same as those of the first embodiment. However, after the piezoelectric thin film layer 3 is formed, the separated electrode upper electrode 5 is formed using a pattern mask or the like. That is, in the first embodiment, the upper electrode 4 is formed as one continuous layer, whereas in the second embodiment, an arbitrary pattern mask is arranged on the surface of the piezoelectric thin film layer 3 on the substrate 1 when forming the film. By doing so, the divided upper electrode 5 divided into an arbitrary shape and number is manufactured.
[0061]
According to such a configuration, when a different stress is generated on the surface of the thin-film piezoelectric sensor depending on the location, the stress such as the pressure differs depending on the position of the divided upper electrode 5. As a result, different charges and voltages are generated on each of the divided upper electrodes 5, and the difference therebetween can be detected. That is, it is possible to detect to which part of the thin film piezoelectric sensor the stress is applied.
[0062]
Such a thin-film piezoelectric sensor can be used for detecting the direction of vibration by measuring the change in the temporal stress distribution. When a cantilever-type or diaphragm-type thin-film piezoelectric sensor is configured, by detecting the above-described stress difference, hardware-based difference detection becomes possible, and the dynamic range of each amplifier is limited. High sensitivity of the shear stress detection can be realized without the need.
[0063]
【Example】
On a surface of a quartz glass substrate having a diameter of 17 mm and a thickness of 1 mm, an underlayer of a circular aluminum thin film having a diameter of 3 mm is formed by a sputtering method, and an AlN (aluminum nitride) thin film having a thickness of about 1 micron is further formed thereon. Was produced by a sputtering method.
[0064]
By analyzing the X-ray diffraction pattern, it was found that the AlN had excellent crystallinity and was oriented in the c-axis direction. Further, the dipole orientation degree of the piezoelectric layer was 92%.
[0065]
Next, a circular aluminum electrode having a diameter of 3 mm was further formed as a top electrode on the surface of AlN by a sputtering method so as to overlap the bottom electrode.
[0066]
FIG. 3 shows a result of configuring a compression type thin film type piezoelectric sensor using the above thin film type piezoelectric sensor and performing vibration detection measurement. The horizontal axis indicates time, and the vertical axis indicates the voltage of generated electricity. In the measurement, the thin-film piezoelectric sensor is fixed to a metal structure, and a vibration generated by striking the metal structure with a hammer is given to the thin-film piezoelectric sensor at a time of 1.51 seconds on the horizontal axis. Was done. FIG. 3 shows that a large voltage was generated at about 1.519 seconds at substantially the same time, so that the thin film piezoelectric sensor thin film generated a voltage corresponding to the vibration. That is, the thin-film piezoelectric sensor had appropriate piezoelectric characteristics.
[0067]
【The invention's effect】
As described in detail above, the thin-film piezoelectric sensor of the present invention is a thin-film piezoelectric sensor formed by laminating a first electrode layer, a piezoelectric layer, and a second electrode layer on a substrate surface in this order. The piezoelectric layer is made of a piezoelectric material having no Curie temperature such as a substance having a wurtzite crystal structure (eg, aluminum nitride or zinc oxide), and has a dipole orientation degree of 75% or more. Configuration.
[0068]
According to the above configuration, it is possible to provide a thin-film piezoelectric sensor that guarantees piezoelectric characteristics, is small, does not require a cooling unit, has excellent heat resistance, and is inexpensive, and detects acoustic emission, vibration, or acceleration. .
[0069]
For the substrate, an oxide-based, carbide-based, nitride-based or boride-based ceramic sintered body or an insulating substrate made of quartz glass, or a conductive substrate made of a heat-resistant metal material, A thin-film piezoelectric sensor having excellent properties such as heat resistance and hardness is obtained.
[0070]
Further, if the piezoelectric thin film layer is formed by a physical vapor deposition method, needle-like crystal columns of a piezoelectric material having no Curie temperature grow into frost columns, and a single-crystal thin film of the piezoelectric material can be formed. Thus, a small-sized thin film piezoelectric sensor having a simple structure can be obtained. Further, when the thickness of the piezoelectric layer is 0.1 μm or more and 100 μm or less, stress can be detected well, and the piezoelectric layer can be manufactured in a short time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a laminated substrate of a thin-film piezoelectric sensor according to one embodiment of the present invention.
FIG. 2 is a cross-sectional view of a laminated substrate of a thin film piezoelectric sensor having a plurality of divided upper electrodes according to another embodiment of the present invention.
FIG. 3 is a graph showing a result of performing vibration detection measurement using the thin film piezoelectric sensor according to one embodiment of the present invention.
[Explanation of symbols]
1 substrate
2 Underlayer (first electrode layer)
3 Piezoelectric thin film layer (piezoelectric layer)
4 Upper electrode (second electrode layer)
5 split upper electrode (second electrode layer)

Claims (8)

A thin-film piezoelectric sensor formed by laminating a first electrode layer, a piezoelectric layer, and a second electrode layer in this order on a substrate surface,
A thin-film piezoelectric sensor, wherein the piezoelectric layer is made of a piezoelectric material having no Curie temperature, and has a dipole orientation degree of 75% or more. 2. The thin-film piezoelectric sensor according to claim 1, wherein the substrate is an insulating substrate made of a sintered body of an oxide-based, carbide-based, nitride-based, or boride-based ceramic or quartz glass. 2. The thin film piezoelectric sensor according to claim 1, wherein the substrate is a conductive substrate made of a heat-resistant metal material. 4. The thin film piezoelectric sensor according to claim 1, wherein the piezoelectric layer is formed by a physical vapor deposition method. 5. The thin-film piezoelectric sensor according to claim 1, wherein the piezoelectric layer is made of aluminum nitride or zinc oxide. The thin-film piezoelectric sensor according to claim 1, wherein a surface of the first electrode layer on a side in contact with the piezoelectric layer is covered with a metal included in the piezoelectric layer. . 7. The thin film type piezoelectric sensor according to claim 1, wherein the thickness of the piezoelectric layer is 0.1 μm or more and 100 μm or less. The thin-film piezoelectric sensor according to any one of claims 1 to 7, wherein the second electrode layer is formed by being divided into two or more.

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