Piezoelectric laminate, piezoelectric element, and method for manufacturing piezoelectric laminate

Abstract

This piezoelectric laminate comprises: a substrate; an oxide film formed on the substrate and containing zinc and oxygen as main elements; an electrode film formed on the oxide film; and a piezoelectric film, which is an alkaline niobium oxide film having a perovskite structure, formed on the electrode film and containing potassium, sodium, niobium, and oxygen.

Description

Technical Field

[0001] The present disclosure relates to a piezoelectric laminate, a piezoelectric element, and a method for manufacturing a piezoelectric laminate.

Background Art

[0002] Piezoelectric materials are widely used in functional electronic components such as sensors and actuators. As piezoelectric materials, lead-based materials, particularly PZT-based ferroelectrics represented by the composition formula Pb(Zr 1-x Ti x )O3, are widely used. Since PZT-based piezoelectric materials contain lead, they are not preferable due to concerns about their effects on the human body. Therefore, as lead-free piezoelectric materials, piezoelectric materials containing potassium, sodium, niobium, and oxygen have been proposed, and laminates having a piezoelectric film formed using such piezoelectric materials have been proposed (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described patented technology, it has been found that when an electric field is applied in the thickness direction of the piezoelectric film, dielectric breakdown is more likely to occur when the electric field is applied in one direction in the thickness direction than when the electric field is applied in the other direction in the thickness direction. That is, it has been found that the breakdown voltage of the piezoelectric film may vary depending on the direction of the applied electric field. This is a new problem that has become clear for the first time through the inventors' intensive research.

[0005] In addition, in the above-described patented technology, there was also a problem that when the film formation temperature of the piezoelectric film was lowered in an attempt to reduce the dielectric constant of the piezoelectric film, the crystal orientation of the piezoelectric film deteriorated.

[0006] An object of the present disclosure is to further improve the performance of a piezoelectric film containing potassium, sodium, niobium, and oxygen.

Means for Solving the Problems

[0007] According to one aspect of the present disclosure, a substrate, a oxide film formed on the substrate and containing zinc and oxygen as main elements, an electrode film formed on the oxide film, and a piezoelectric film formed on the electrode film, containing potassium, sodium, niobium, and oxygen and having a perovskite structure, are provided, together with a piezoelectric laminate and related technologies thereof.

Advantages of the Invention

[0008] According to the present disclosure, it becomes possible to further improve the performance of a piezoelectric film containing potassium, sodium, niobium, and oxygen.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0010] <Findings Obtained by the Inventor> In a laminate having a substrate, a lower electrode film formed on the substrate, a piezoelectric film (KNN film) formed on the lower electrode film and containing potassium (K), sodium (Na), niobium (Nb), and oxygen (O), and an upper electrode film formed on the KNN film, it is common to provide a film containing titanium (Ti) (for example, a Ti film) as an adhesion film that adheres these to each other between the substrate and the lower electrode film. In a piezoelectric element (piezoelectric device module) manufactured using such a laminate provided with such an adhesion film, it has been found that dielectric breakdown is more likely to occur when a positive voltage is applied than when a negative voltage is applied. Here, the application of a negative voltage in this specification means applying a negative voltage to the upper electrode film such that an electric field in the upward direction (from the lower electrode film toward the upper electrode film) in the thickness direction of the KNN film is generated between the upper electrode film and the lower electrode film with the upper electrode film side being negative and the lower electrode film side being grounded. Also, the application of a positive voltage in this specification means applying a positive voltage to the upper electrode film such that an electric field in the downward direction (from the upper electrode film toward the lower electrode film) in the thickness direction of the KNN film is generated between the upper electrode film and the lower electrode film with the upper electrode film side being positive and the lower electrode film side being grounded.

[0011] The inventors conducted intensive research on the above problems. As a result, they obtained the finding that Ti in the adhesion film may diffuse through the lower electrode film to the KNN film, and this may be a factor causing dielectric breakdown when a positive voltage is applied. This is because Ti easily spreads, for example, to the upper surface of the lower electrode film (the surface in contact with the KNN film) in the temperature environment during KNN film formation. Therefore, when a film containing Ti is provided as the adhesion film, Ti in the adhesion film diffuses to the piezoelectric film and combines with oxygen in the piezoelectric film (captures oxygen in the piezoelectric film), resulting in x TiO. As a result, oxygen defects (oxygen deficiencies, oxygen vacancies) are generated in the piezoelectric film, particularly near the interface between the piezoelectric film and the lower electrode film. In a piezoelectric element (piezoelectric device module) having such a piezoelectric film, when a positive voltage is applied, the oxygen defects in the piezoelectric film move through the piezoelectric film toward the lower electrode film side, thereby causing dielectric breakdown.

[0012] In addition, in a laminate provided with a Ti film as the adhesion film, in order to lower the dielectric constant of the piezoelectric film, attempts have been made to lower the film formation temperature of the piezoelectric film. However, there has also been a problem that when the film formation temperature of the piezoelectric film is lowered, the crystal orientation of the piezoelectric film deteriorates. For this reason, when a Ti film is provided as the adhesion film, in order to avoid a decrease in the orientation of the piezoelectric film, it is necessary to form the piezoelectric film at a high temperature (for example, exceeding 500°C). As a result, the dielectric constant of the piezoelectric film could not be sufficiently lowered. That is, a piezoelectric laminate having both a low dielectric constant and a high orientation could not be obtained.

[0013] The present disclosure has been made based on the above-described findings and problems obtained by the inventors.

[0014] <One aspect of the present disclosure> Hereinafter, one aspect of the present disclosure will be described with reference to the drawings.

[0015] (1) Configuration of the piezoelectric laminate As shown in FIG. 1, a laminate (laminated substrate) 10 having a piezoelectric film according to the present embodiment (hereinafter also referred to as a piezoelectric laminate 10) includes a substrate 1, an oxide film 5 formed on the substrate 1, a lower electrode film 2 formed on the oxide film 5, a piezoelectric film (piezoelectric thin film) 3 formed on the lower electrode film 2, and an upper electrode film 4 formed on the piezoelectric film 3.

[0016] As the substrate 1, a single-crystalline silicon (Si) substrate 1a having a surface oxide film (SiO2 film) 1b such as a thermal oxide film or a CVD (Chemical Vapor Deposition) oxide film, that is, an Si substrate having a surface oxide film can be preferably used. Further, as the substrate 1, as shown in FIG. 2, an Si substrate 1a having an insulating film 1d formed of an insulating material other than SiO2 on its surface can also be used. Further, as the substrate 1, an Si substrate 1a having an exposed Si (100) plane or Si (111) plane or the like on its surface, that is, an Si substrate having no surface oxide film 1b or insulating film 1d can also be used. Further, as the substrate 1, an SOI (Silicon On Insulator) substrate, a quartz glass (SiO2) substrate, a gallium arsenide (GaAs) substrate, a sapphire (Al2O3) substrate, or a metal substrate formed of a metal material such as stainless steel (SUS) can also be used. The thickness of the single-crystalline Si substrate 1a can be, for example, 300 μm or more and 1000 μm or less, and the thickness of the surface oxide film 1b can be, for example, 1 nm or more and 4000 nm or less.

[0017] The oxide film 5 is a film mainly composed of zinc and oxygen. The oxide film 5 can be formed using, for example, zinc oxide. The oxide film 5 can be a polycrystalline film or a single crystal film (hereinafter, the oxide film 5 is also referred to as the ZnO film 5). The composition ratio of Zn and O constituting the ZnO film 5 preferably satisfies the relationship of Zn:O = 1:1, but is not limited thereto, and there may be some variation. Crystals constituting the ZnO film 5 are often those in which the (0001) plane is parallel to the main surface of the substrate 1 (including crystals in which the (0001) plane is inclined at an angle within ±5° with respect to the main surface of the substrate 1), that is, it is preferable that the (0001) plane orientation is preferentially oriented. That the crystals constituting the ZnO film 5 are preferentially oriented in the (0001) plane orientation means that in the X-ray diffraction pattern obtained by X-ray diffraction (XRD) measurement, the diffraction peak due to the crystals oriented in the (0002) plane orientation is in the highest state. That is, the surface of the ZnO film 5 (the surface serving as the base for the lower electrode film 2) is preferably mainly composed of the ZnO (0001) plane. Incidentally, the ZnO film 5 can be formed using a sputtering method, an evaporation method, or the like. The ZnO film 5 functions as an adhesion film for enhancing the adhesion between the substrate 1 and the lower electrode film 2 described later.

[0018] The thickness of the ZnO film 5 can be, for example, 1 nm or more, preferably 2 nm or more. When the thickness of the ZnO film 5 is, for example, 1 nm or more, the ZnO film 5 can surely function as the above-described adhesion film, and when it is 2 nm or more, the ZnO film 5 can more surely function as the above-described adhesion film. Also, it is possible to surely enhance the orientation of the KNN film 3 described later. The upper limit of the thickness of the ZnO film 5 is not particularly limited, but from the viewpoint of suppressing a decrease in the productivity of the piezoelectric laminate 10, the thickness of the ZnO film 5 can be, for example, 50 nm or less, preferably 20 nm or less, more preferably 10 nm or less.

[0019] The lower electrode film 2 can be formed, for example, using platinum (Pt). The lower electrode film 2 becomes a polycrystalline film or a single crystal film (hereinafter, these are also referred to as Pt films). Among the crystals constituting the Pt film, there are many crystals whose (111) plane is parallel to the main surface of the substrate 1 (including crystals whose (111) plane is inclined at an angle within ±5° with respect to the main surface of the substrate 1). That is, it is preferable that the crystals constituting the Pt film are preferentially oriented in the (111) plane direction. For the crystals constituting the Pt film to be preferentially oriented in the (111) plane direction means that in the X-ray diffraction pattern obtained by XRD measurement, the diffraction peak due to the crystals oriented in the (111) plane direction is in the highest state. That is, the surface of the lower electrode film 2 (the surface that becomes the base of the piezoelectric film 3) is preferably mainly composed of the Pt(111) plane. The lower electrode film 2 can be formed using a sputtering method, an evaporation method, or the like. For example, by directly forming the lower electrode film 2 (Pt film) on a ZnO film 5 whose surface is mainly composed of the ZnO(0001) plane, a lower electrode film 2 whose surface is mainly composed of the Pt(111) plane can be easily obtained. In addition to Pt, the lower electrode film 2 can also be formed using various metals such as gold (Au), ruthenium (Ru), or iridium (Ir), or alloys mainly composed of these. The thickness of the lower electrode film 2 can be, for example, 100 nm or more and 400 nm or less.

[0020] The piezoelectric film 3 is, for example, an alkaline niobium oxide film containing potassium (K), sodium (Na), niobium (Nb), and oxygen (O). The piezoelectric film 3 can be formed using potassium sodium niobate (KNN). The piezoelectric film 3 becomes a polycrystalline film of KNN (hereinafter, also referred to as KNN film 3). The crystal structure of KNN is a perovskite structure. That is, the KNN film 3 has a perovskite structure. The KNN film 3 can be formed using techniques such as a sputtering method, a PLD (Pulsed Laser Deposition) method, or a sol-gel method. The thickness of the KNN film 3 can be, for example, 0.5 μm or more and 5 μm or less.

[0021] The crystal constituting the KNN film 3 is preferably preferentially oriented in the (001) plane orientation with respect to the main surface of the substrate 1 (when the substrate 1 is, for example, an Si substrate 1a having a surface oxide film 1b or an insulating film 1d, etc., the Si substrate 1a). That is, the surface of the KNN film 3 (the surface that becomes the base of the upper electrode film 4) is preferably mainly composed of the KNN (001) plane. For example, by directly forming the KNN film 3 on a Pt film (lower electrode film 2) whose surface is mainly composed of the Pt (111) plane, a KNN film 3 whose surface is mainly composed of the KNN (001) plane can be easily obtained.

[0022] In this specification, that the crystal constituting the KNN film 3 is oriented in the (001) plane orientation means that the (001) plane of the crystal constituting the KNN film 3 is parallel to the main surface of the substrate 1. Note that that the (001) plane of the crystal constituting the KNN film 3 is parallel to the main surface of the substrate 1 includes not only the case where the (001) plane is completely parallel to the main surface of the substrate 1, but also the case where the (001) plane is inclined within ±5°, preferably within ±3° with respect to the main surface of the substrate 1. Further, that the crystal constituting the KNN film 3 is preferentially oriented in the (001) plane orientation means that there are many crystals whose (001) plane is parallel to the main surface of the substrate 1. For example, it is preferable that 80% or more of the crystals in the crystal group constituting the KNN film 3 are oriented in the (001) plane orientation with respect to the main surface of the substrate 1. That is, the orientation ratio of the (001) plane orientation of the crystal constituting the KNN film 3 (hereinafter, also referred to as the "orientation ratio of the KNN film 3") is preferably, for example, 80% or more, and more preferably, for example, 90% or more. Note that the "orientation ratio" in this specification is a value calculated by the following (Equation 1) based on the peak intensity of the X-ray diffraction pattern (2θ / θ) obtained by X-ray diffraction (XRD) measurement with respect to the KNN film 3. (Equation 1) Orientation ratio (%) = {(diffraction peak intensity of (001) plane / (diffraction peak intensity of (001) plane + diffraction peak intensity of (110) plane))} × 100

[0023] As used in the above (Equation 1) and in this specification, the "diffraction peak of the (001) plane" refers to a diffraction peak in the X-ray diffraction pattern obtained by XRD measurement of the KNN film 3, which is caused by the crystal oriented in the (001) plane direction among the crystals constituting the KNN film 3 (i.e., the crystal whose (001) plane is parallel to the main surface of the substrate 1), and is a peak that appears within the range where 2θ is 20° or more and 23° or less. Also, as used in the above (Equation 1) and in this specification, the "diffraction peak of the (110) plane" refers to a diffraction peak in the X-ray diffraction pattern obtained by XRD measurement of the KNN film 3, which is caused by the crystal oriented in the (110) plane direction among the crystals constituting the KNN film 3 (i.e., the crystal whose (110) plane is parallel to the main surface of the substrate 1), and is a peak that appears within the range where 2θ is 30° or more and 33° or less.

[0024] Preferably, more than half of the crystals in the crystal group constituting the KNN film 3 have a columnar structure. The boundaries between the crystals constituting the KNN film 3, i.e., the grain boundaries present in the KNN film 3, preferably penetrate in the thickness direction of the KNN film 3. For example, in the KNN film 3, it is preferable that the grain boundaries penetrating in the thickness direction are more numerous than the grain boundaries not penetrating in the thickness direction of the KNN film 3.

[0025] The KNN film 3 may contain elements other than K, Na, Nb, and O, such as copper (Cu), manganese (Mn), lithium (Li), tantalum (Ta), and antimony (Sb), within a range of, for example, 5 at% or less (when a plurality of the above elements are added, the total concentration is 5 at% or less).

[0026] The upper electrode film 4 can be formed using various metals such as Pt, Au, aluminum (Al), Cu, or alloys thereof. The upper electrode film 4 can be formed using techniques such as sputtering, vapor deposition, plating, or the metal paste method. The upper electrode film 4 does not significantly affect the crystal structure of the KNN film 3 like the lower electrode film 2 does. Therefore, the material, crystal structure, and film formation technique of the upper electrode film 4 are not particularly limited. Note that between the KNN film 3 and the upper electrode film 4, an adhesion layer mainly composed of, for example, titanium (Ti), Ta, titanium oxide (TiO2), nickel (Ni), ruthenium oxide (RuO2), iridium oxide (IrO2), etc. may be provided to enhance their adhesion. The thickness of the upper electrode film 4 can be, for example, 100 nm or more and 5000 nm or less, and when an adhesion layer is provided, the thickness of the adhesion layer can be, for example, 1 nm or more and 200 nm or less.

[0027] As described above, in the piezoelectric laminate 10, between the substrate 1 and the lower electrode film 2, instead of a film containing Ti (for example, a Ti film) as an adhesion film (hereinafter, also simply referred to as an "adhesion film") that enhances the adhesion between them, a ZnO film 5 is provided. Zinc oxide (ZnO) is less likely to diffuse compared to Ti element and hardly diffuses through the lower electrode film 2 to the KNN film 3. Therefore, the above problems that occur when, for example, a Ti film is provided as the adhesion film do not occur. Also, since the Zn element is more inert than the Ti element, even if it diffuses to the KNN film 3, it is less likely to capture the O element in the KNN film 3 and less likely to cause oxygen defects in the KNN film 3.

[0028] In addition, by providing the ZnO film 5, it becomes possible to increase the number of KNN crystals in which the (001) plane is parallel to the main surface of the substrate 1 compared to the case where the Ti film is provided. That is, it becomes possible to reduce the number of KNN crystals in which the (001) plane is inclined at a predetermined angle with respect to the main surface of the substrate 1. Further, even when the (001) plane of the KNN crystal is inclined at a predetermined angle with respect to the main surface of the substrate 1, it becomes possible to reduce the inclination angle. As a result, when the ZnO film 5 is provided, the diffraction peak of the (001) plane has a narrower half-value width and a sharper peak, and the diffraction peak intensity of the (001) plane becomes higher than when the Ti film is provided. For example, by providing the ZnO film 5, it becomes possible to make the maximum intensity of the diffraction peak of the (001) plane 1000 cps or more and 1400 cps or less, preferably 1100 cps or more and 1350 cps or less.

[0029] On the other hand, when the Ti film is provided, the number of KNN crystals in which the (001) plane is inclined at a predetermined angle with respect to the main surface of the substrate 1 is larger than when the ZnO film 5 is provided, and the inclination angle is also larger. As a result of these, the diffraction peak of the (001) plane becomes a peak with a wide half-value width, and the peak intensity becomes low. In this case, the maximum intensity of the diffraction peak of the (001) plane is, for example, about 600 cps to 900 cps.

[0030] In addition, by providing the ZnO film 5, it becomes possible to obtain the KNN film 3 having a high orientation rate and a low relative permittivity. This is because it has been found that when the ZnO film 5 is provided, the KNN film 3 maintains the high orientation rate as described above even when the film formation temperature of the KNN film 3 is lowered (for example, to 500 ° C. or lower). This is a new finding first discovered by the inventors. Thus, since the ZnO film 5 is provided, the KNN film 3 can be formed at a low temperature without reducing the orientation (orientation rate) of the KNN film 3, so that the KNN film 3 can also be made into a film with a low relative permittivity. For example, when the lower electrode film 2 is grounded (zero potential) and a voltage of -1V to +1V is applied to the upper electrode film 4 with a triangular wave of a frequency of 3 kHz for measurement, the relative permittivity (ε r) can be, for example, 250 or more and 300 or less, preferably 250 or more and less than 300, more preferably 250 or more and 270 or less.

[0031] On the other hand, when the Ti film is provided, if the film formation temperature of the KNN film 3 is lowered (for example, to 500 °C or lower), the orientation of the KNN film 3 will deteriorate. Therefore, when the Ti film is provided, in order to prevent the deterioration of the orientation of the KNN film 3, it is necessary to form the KNN film 3 at a high temperature (for example, above 500 °C). As a result, the dielectric constant of the KNN film 3 will increase. In this case, the relative dielectric constant of the KNN film 3 is, for example, about 300 to 500.

[0032] In this way, by providing the ZnO film 5, it is possible to obtain a KNN film 3 having good orientation and low dielectric constant without causing the above problems, for example, a KNN film 3 having a high diffraction peak intensity of the (001) plane and a low dielectric constant.

[0033] (2) Configuration of piezoelectric element and piezoelectric device module Fig. 3 shows a schematic configuration diagram of a device module 30 (hereinafter also referred to as a piezoelectric device module 30) having the KNN film 3 in the present disclosure. The piezoelectric device module 30 includes at least an element (device) 20 (an element 20 having the KNN film 3, hereinafter also referred to as a piezoelectric element 20) obtained by shaping the above-described piezoelectric laminate 10 into a predetermined shape, and a voltage application unit 11a or a voltage detection unit 11b connected to the piezoelectric element 20. The voltage application unit 11a is a means for applying a voltage between the lower electrode film 2 and the upper electrode film 4 (between the electrodes), and the voltage detection unit 11b is a means for detecting the voltage generated between the lower electrode film 2 and the upper electrode film 4 (between the electrodes). As the voltage application unit 11a and the voltage detection unit 11b, various known means can be used.

[0034] By connecting the voltage application unit 11a between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric element 20 can function as an actuator. By applying a voltage between the lower electrode film 2 and the upper electrode film 4 with the voltage application unit 11a, the KNN film 3 can be deformed. By this deformation operation, various members connected to the piezoelectric element 20 can be actuated. In this case, examples of the uses of the piezoelectric element 20 include a head for an inkjet printer, a MEMS mirror for a scanner, a vibrator for an ultrasonic generator, and the like.

[0035] By connecting the voltage detection unit 11b between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric element 20 can function as a sensor. When the KNN film 3 deforms due to a change in some physical quantity, a voltage is generated between the lower electrode film 2 and the upper electrode film 4 due to the deformation. By detecting this voltage with the voltage detection unit 11b, the magnitude of the physical quantity applied to the KNN film 3 can be measured. In this case, examples of the uses of the piezoelectric element 20 include an angular velocity sensor, an ultrasonic sensor, a pressure sensor, an acceleration sensor, and the like.

[0036] As described above, in the piezoelectric laminate 10, since the ZnO film 5 is provided instead of the Ti film as the adhesion film, there are few oxygen defects present in the KNN film 3, particularly in the vicinity of the interface between the KNN film 3 and the lower electrode film 2. As a result, the piezoelectric element 20 obtained by processing the piezoelectric laminate 10 is less likely to undergo dielectric breakdown even when a positive voltage is applied.

[0037] (3) Manufacturing method of piezoelectric laminate, piezoelectric element, and piezoelectric device module The manufacturing methods of the above-described piezoelectric laminate 10, piezoelectric element 20, and piezoelectric device module 30 will be described.

[0038] First, prepare a substrate 1, and form a ZnO film 5 on one of the main surfaces of the substrate 1 by, for example, sputtering. For example, using a target material made of zinc oxide, in an atmosphere of a mixed gas of argon (Ar) gas and oxygen (O2) gas (hereinafter, also referred to as "Ar / O2 mixed gas atmosphere"), the ZnO film 5 is formed by RF sputtering.

[0039] As conditions for forming the ZnO film 5, the following conditions are exemplified. The film formation time of the ZnO film 5 can be appropriately set according to the thickness of the ZnO film 5. The film formation rate can be, for example, a rate at which a ZnO film with a thickness of 2.5 nm is formed in 30 seconds. Temperature (substrate temperature): 200 °C or higher, preferably 300 °C or higher, more preferably 500 °C or higher, and still more preferably 700 °C or lower Discharge power: 100 W or more and 500 W or less, preferably 200 W or more and 400 W or less Atmosphere: Ar / O2 mixed gas atmosphere Partial pressure of Ar gas with respect to O2 gas (Ar gas / O2 gas partial pressure ratio): 5 / 1 to 30 / 1, preferably 7 / 1 to 20 / 1, more preferably 10 / 1 to 15 / 1 Atmospheric pressure: 0.1 Pa or more and 0.5 Pa or less, preferably 0.2 Pa or more and 0.4 Pa or less

[0040] Under the above conditions, particularly under the above temperature conditions, by forming the ZnO film 5, the crystals constituting the ZnO film 5 can be preferentially oriented in the (0001) plane direction. That is, by forming the ZnO film 5 with the substrate 1 heated, it is possible to obtain a ZnO film 5 with high orientation. Further, by forming the ZnO film 5 under temperature conditions of, for example, 300 °C or higher, the orientation of the ZnO film 5 can be further enhanced. Also, by forming the ZnO film 5 under temperature conditions of, for example, 500 °C or higher, the orientation of the ZnO film 5 can be further enhanced.

[0041] As described above, the higher the film formation temperature of the ZnO film 5, the higher the orientation of the ZnO film 5 tends to be. However, even when the film formation temperature of the ZnO film 5 exceeds 700°C, the effect of enhancing the orientation of the ZnO film 5 reaches a plateau, while it takes time to lower the temperature in the atmosphere from the film formation temperature of the ZnO film 5 to the film formation temperature of the KNN film 3 described later, and as a result, the productivity of the piezoelectric laminate 10 may decrease. For this reason, the film formation temperature of the ZnO film 5 is preferably 700°C or lower.

[0042] Subsequently, a lower electrode film 2 (for example, a Pt film) is formed on the ZnO film 5 in which the crystal is preferentially oriented in the (0001) plane direction in advance, for example, by a sputtering method.

[0043] The following conditions are exemplified as the conditions for forming the lower electrode film 2. Temperature (substrate temperature): 200°C or higher, preferably 300°C or higher, more preferably 500°C or higher, still more preferably 700°C or lower Discharge power: 1000 W or more and 1500 W or less, preferably 1100 W or more and 1300 W or less Atmosphere: Ar gas atmosphere Atmospheric pressure: 0.1 Pa or more and 0.5 Pa or less, preferably 0.2 Pa or more and 0.4 Pa or less Film formation time: 3 minutes or more and 10 minutes or less, preferably 4 minutes or more and 8 minutes or less, more preferably 5 minutes or more and 6 minutes or less

[0044] Under the above conditions, particularly under the above temperature conditions, by forming a Pt film as the lower electrode film 2, the crystals constituting the Pt film can be preferentially oriented in the (111) plane direction. That is, by forming the Pt film in a state where the substrate 1 is heated, it is possible to obtain a Pt film with high orientation. Further, by forming the Pt film under temperature conditions of, for example, 300°C or higher, the orientation of the Pt film can be further enhanced. Further, by forming the Pt film under temperature conditions of, for example, 500°C or higher, the orientation of the Pt film can be further enhanced.

[0045] As described above, as the film formation temperature of the Pt film increases, the orientation of the Pt film tends to increase. However, even when the film formation temperature of the Pt film exceeds 700°C, the effect of enhancing the orientation of the Pt film reaches a plateau. On the other hand, it takes time to lower the temperature in the atmosphere from the film formation temperature of the Pt film to the film formation temperature of the KNN film 3 described later. As a result, the productivity of the piezoelectric laminate 10 may decrease. For this reason, the film formation temperature of the Pt film is preferably 700°C or lower.

[0046] Subsequently, a KNN film 3 is formed on the Pt film whose crystal has been preferentially oriented in the (111) plane direction in advance, for example, by sputtering. The composition ratio of the KNN film 3 can be adjusted by controlling the composition of the target material used during sputtering film formation. The target material can be produced by, for example, mixing K2CO3 powder, Na2CO3 powder, Nb2O5 powder, etc. and firing them. The composition of the target material can be controlled by adjusting the mixing ratio of K2CO3 powder, Na2CO3 powder, Nb2O5 powder, etc. When forming a KNN film 3 containing elements such as Cu or Mn, a target material in which Cu powder (or CuO powder), Mn powder (or MnO powder), etc. are mixed in a predetermined ratio may be used in addition to the above-mentioned respective powders.

[0047] The following conditions are exemplified as the conditions for forming the KNN film 3. Note that the film formation time can be appropriately set according to the thickness of the KNN film 3. Discharge power: 2000 W or more and 2400 W or less, preferably 2100 W or more and 2300 W or less Atmosphere: Ar gas + oxygen (O2) gas atmosphere Atmospheric pressure: 0.2 Pa or more and 0.5 Pa or less, preferably 0.2 Pa or more and 0.4 Pa or less Partial pressure of Ar gas with respect to O2 gas (Ar / O2 partial pressure ratio): 30 / 1 to 20 / 1, preferably 27 / 1 to 22 / 1 Film formation temperature: 430°C or more and 700°C or less Film formation rate: 0.5 μm / hr or more and 2 μm / hr or less, preferably 0.75 μm / hr or more and 1.5 μm / hr or less

[0048] By forming the KNN film 3 under the above-described conditions on the lower electrode film 2 in which the crystals are preferentially oriented in the (111) plane orientation in advance, it becomes possible to preferentially orient the crystals constituting the KNN film 3 in the (001) plane orientation. Thus, by forming the ZnO film 5 and the lower electrode film 2 while heating the substrate 1, that is, by forming the ZnO film 5 and the lower electrode film 2 at a high temperature, it becomes possible to enhance the orientation of the KNN film 3 formed on the lower electrode film 2. Thereby, for example, 80% or more of the crystals constituting the KNN film 3 can be oriented in the (001) plane orientation. That is, it is possible to obtain the KNN film 3 having the above-described orientation ratio of, for example, 80% or more.

[0049] Note that if the film formation temperatures of the ZnO film 5 and the lower electrode film 2 are each 200°C or higher, the film formation temperature of the lower electrode film 2 can also be made lower than the film formation temperature of the ZnO film 5. However, from the viewpoint of enhancing the orientation of the ZnO film 5 and the lower electrode film 2 and surely obtaining the KNN film 3 with high orientation, it is preferable to form both the ZnO film 5 and the lower electrode film 2 at a high temperature.

[0050] For example, by forming the ZnO film 5 and the lower electrode film 2 under temperature conditions of 300°C or higher, respectively, it becomes possible to surely orient, for example, 80% or more of the crystals constituting the KNN film 3 in the (001) plane orientation. That is, it is possible to surely obtain the KNN film 3 having the above-described orientation ratio of, for example, 80% or more.

[0051] Also, for example, by forming the ZnO film 5 and the lower electrode film 2 under temperature conditions of 500°C or higher, respectively, it becomes possible to orient, for example, 85% or more, preferably 90% or more of the crystals constituting the KNN film 3 in the (001) plane orientation. That is, it is possible to obtain the KNN film 3 having the above-described orientation ratio of, for example, 85% or more, preferably 90% or more.

[0052] When the piezoelectric element 20 functions as an actuator, the film formation temperature of the KNN film 3 is preferably 500°C or higher and 700°C or lower, and more preferably 540°C or higher and 700°C or lower. This makes it possible to reliably increase the breakdown voltage of the KNN film 3 when a positive voltage is applied.

[0053] When the piezoelectric element 20 functions as a sensor, the film formation temperature of the KNN film 3 is preferably 430°C or higher and 500°C or lower, and more preferably 440°C or higher and 470°C or lower. Since the ZnO film 5 is provided, even if the film formation temperature of the KNN film 3 is lowered in this way, it is possible to make the KNN film 3 a highly oriented film. Further, by forming the KNN film 3 at such a low temperature, it is possible to make the KNN film 3 a low dielectric constant film. That is, it is possible to obtain a KNN film 3 having both a high orientation rate and a low dielectric constant, which can be suitably used as a sensor.

[0054] Then, an upper electrode film 4 is formed on the KNN film 3, for example, by sputtering. The conditions for forming the upper electrode film 4 can be the same as the conditions for forming the lower electrode film 2 described above.

[0055] Under the above conditions, by forming the ZnO film 5, the lower electrode film 2 (Pt film), the KNN film 3, and the upper electrode film 4 on the substrate 1 in this order, a piezoelectric laminate 10 as shown in FIG. 1 is obtained.

[0056] The obtained piezoelectric laminate 10 is formed into a predetermined shape by etching or the like (microfabrication is performed into a predetermined pattern). Thereby, a piezoelectric element 20 as shown in FIG. 3 is obtained, and by connecting a voltage application unit 11a or a voltage detection unit 11b to the piezoelectric element 20, a piezoelectric device module 30 is obtained. As the etching method, for example, a dry etching method such as reactive ion etching or a wet etching method using a predetermined etching solution can be used.

[0057] When the piezoelectric laminate 10 is formed by dry etching, a photoresist pattern as an etching mask for dry etching is formed on the piezoelectric laminate 10 (for example, the upper electrode film 4) by a photolithography process or the like. As the etching mask, a noble metal film (metal mask) such as a chromium (Cr) film, a nickel (Ni) film, a platinum (Pt) film, or a Ti film may be formed by a sputtering method. Then, dry etching is performed on the piezoelectric laminate 10 (upper electrode film 4, KNN film 3, etc.) using a gas containing a halogen element as the etching gas. Note that the halogen element includes chlorine (Cl), fluorine (F), etc. As the gas containing a halogen element, BCl3 gas, SiCl4 gas, chlorine (Cl2) gas, CF4 gas, C4F8 gas, etc. can be used.

[0058] When the piezoelectric laminate 10 is formed by wet etching, a silicon oxide (SiO x ) film or the like as an etching mask for wet etching is formed on the piezoelectric laminate 10 (for example, the upper electrode film 4). Then, the piezoelectric laminate 10 is immersed in an etching solution containing an alkaline aqueous solution of a chelating agent and not containing hydrofluoric acid, and wet etching is performed on the piezoelectric laminate 10 (upper electrode film 4, KNN film 3, etc.). Note that as the etching solution containing an alkaline aqueous solution of a chelating agent and not containing hydrofluoric acid, an etching solution obtained by mixing ethylenediaminetetraacetic acid as a chelating agent, aqueous ammonia, and hydrogen peroxide water can be used.

[0059] (4) Effects According to this aspect, one or more of the following effects can be obtained.

[0060] (a) As the adhesion film that closely adheres the substrate 1 and the lower electrode film 2 to each other, instead of a film containing Ti (for example, a Ti film), a ZnO film 5 is provided, so that the adhesion can be maintained at the same level as or higher than that in the case where a Ti film is provided. Further, since zinc oxide is less likely to diffuse than Ti element, by forming the adhesion film with the ZnO film 5, the elements diffusing into the KNN film 3 can be reduced compared to the case where the adhesion film is formed with a Ti film. Thereby, generation of oxygen defects in the KNN film 3, particularly near the interface between the KNN film 3 and the lower electrode film 2, can be suppressed. As a result, the withstand voltage of the KNN film 3 when a positive voltage is applied can be increased, and a decrease in insulation performance when a positive voltage is applied can be avoided. That is, in the piezoelectric element 20 obtained by processing the above-described piezoelectric laminate 10, even when a positive voltage is applied, dielectric breakdown is less likely to occur.

[0061] For example, in a state where the piezoelectric laminate 10 (piezoelectric element 20) is heated so that its temperature becomes 200°C, while grounding the lower electrode film 2, a positive voltage is applied to the upper electrode film 4 so as to generate an electric field of 300 kV / cm (an electric field directed from the upper electrode film 4 to the lower electrode film 2) between the lower electrode film 2 and the upper electrode film 4 in a highly accelerated life test (Highly Accelerated Life Test, abbreviated as HALT). When this is done, the time from the start of voltage application until the KNN film 3 reaches dielectric breakdown can be made 1500 seconds or more. In this aspect, it is regarded that the KNN film 3 reaches dielectric breakdown when the leakage current density flowing through the KNN film 3 exceeds 30 mA / cm 2 .

[0062] Note that it has also been proposed to form a film that does not contain Ti and has a main component such as tantalum (Ta), tantalum oxide (Ta2O5), nickel (Ni), or a titanium oxide (TiO2) film as the adhesion film. However, these films have a problem that their adhesion is clearly weaker than that of a Ti film or the ZnO film 5. On the other hand, in this aspect, since the ZnO film 5 is provided as the adhesion film, the adhesion can be maintained at the same level as or higher than that of a Ti film.

[0063] (b) Further, since the ZnO film 5 is provided as an adhesion film for closely adhering the substrate 1 and the lower electrode film 2 to each other, it is possible to increase the amount of KNN crystals in which the (001) plane is parallel to the main surface of the substrate 1 compared to the case where the Ti film is provided. As a result, it becomes possible to make the KNN film 3 a film having a high diffraction peak intensity of the (001) plane. For example, the maximum intensity of the diffraction peak of the (001) plane can be set to 1000 cps or more and 1400 cps or less.

[0064] (c) Further, since the ZnO film 5 is provided as an adhesion film for closely adhering the substrate 1 and the lower electrode film 2 to each other, it becomes possible to make the KNN film 3 a film having both a high orientation rate and a low dielectric constant. This is because, by providing the ZnO film 5, it becomes possible to form the KNN film 3 at a low temperature without reducing the orientation rate of the KNN film 3. Since it becomes possible to form the KNN film 3 at a low temperature, it becomes possible to make the KNN film 3 a film having a low dielectric constant. For example, when the lower electrode film 2 is grounded and a voltage from -1V to +1V is applied as a triangular wave at a frequency of 3 kHz for measurement, the relative dielectric constant of the KNN film 3 can be set to 250 or more and 300 or less. The piezoelectric laminate 10 having such a KNN film 3 can be particularly preferably used for applications such as high-sensitivity sensors that require a low dielectric constant.

[0065] (d) By the orientation rate of the crystal constituting the KNN film 3 in the (001) plane direction being 80% or more, it becomes possible to obtain a piezoelectric element 20 in which the result of HALT under predetermined conditions is 1500 seconds or more, preferably 1600 seconds or more. Further, by the orientation rate of the crystal constituting the KNN film 3 in the (001) plane direction being 90% or more, it becomes possible to obtain a piezoelectric element 20 in which the result of HALT under predetermined conditions is 1800 seconds or more.

[0066] (e) Since the thickness of the ZnO film 5 is, for example, 1 nm or more, the ZnO film 5 can surely function as an adhesion film for closely adhering the substrate 1 and the lower electrode film 2 to each other. Thereby, it is possible to surely suppress the lower electrode film 2 from peeling off from the substrate 1 during the manufacturing process of the piezoelectric laminate 10, the piezoelectric element 20, and the piezoelectric device module 30, or when a voltage is applied. Further, since the thickness of the ZnO film 5 is, for example, 1 nm or more, it is possible to further enhance the orientation of the KNN film 3.

[0067] (f) By forming the ZnO film 5 and the lower electrode film 2 in a state where the substrate 1 is heated, that is, by forming the ZnO film 5 and the lower electrode film 2 at a high temperature, it is possible to enhance the orientation of the KNN film 3 formed on the lower electrode film 2. Further, it is possible to obtain a KNN film 3 with high orientation without performing annealing on the ZnO film 5 and the lower electrode film 2.

[0068] Here, it is also conceivable to form the ZnO film 5 and the lower electrode film 2 under a low temperature condition of less than 200 °C and then perform annealing on the ZnO film 5 and the lower electrode film 2. However, the inventors have confirmed that in this case, it is not possible to form a KNN film 3 with high orientation on the lower electrode film 2.

[0069] <Other aspects> As described above, one aspect of the present disclosure has been specifically described. However, the present disclosure is not limited to the above-described aspects, and various modifications can be made without departing from the gist thereof. Further, these aspects can be arbitrarily combined.

[0070] For example, the lower electrode film 2 can also be formed using a metal oxide such as strontium ruthenate (SrRuO3, abbreviated as SRO) or lanthanum nickelate (LaNiO3, abbreviated as LNO). When forming the lower electrode film 2 using a metal oxide, the crystal constituting the lower electrode film 2 preferably has a large number of crystals whose (001) plane is parallel to the main surface of the substrate 1 (including crystals whose (001) plane is inclined at an angle within ±5° with respect to the main surface of the substrate 1), that is, the crystal constituting the lower electrode film 2 is preferably preferentially oriented in the (001) plane direction. Also in this embodiment, by forming the lower electrode film 2 under the same temperature conditions as in the above-described embodiment, a lower electrode film 2 preferentially oriented in the (001) plane direction can be formed. Further, the lower electrode film 2 may be a single-layer film formed using the above-described various metals or metal oxides, or a laminate of a metal film formed using a metal such as Pt and a film made of SRO provided on the metal film, or a laminate of a metal film and a film made of LNO provided on the metal film. Also in this embodiment, the same effects as in the above-described embodiment can be obtained.

[0071] Also, for example, when forming the above-described piezoelectric laminate 10 into a piezoelectric element 20, as long as the piezoelectric element 20 produced using the piezoelectric laminate 10 can be applied to a desired use such as a sensor or an actuator, the substrate 1 may be removed from the piezoelectric laminate 10.

Example

[0072] Hereinafter, experimental results verifying the effects of the above-described embodiment will be described.

[0073] (a) Samples 1 to 16 of the piezoelectric laminate were produced, and evaluations were made regarding the orientation of the KNN film, the adhesion between the substrate and the lower electrode film, and the insulation property when a positive voltage was applied.

[0074] As a substrate, a Si substrate with a surface having a (100) plane orientation, a thickness of 610 μm, a diameter of 6 inches, and a thermal oxide film (SiO2 film) with a thickness of 200 nm formed on the surface was prepared. Then, on this substrate (on the thermal oxide film), a first adhesion film, a Pt film (thickness: 200 nm) as a lower electrode film, a KNN film (thickness: 2 μm) as a piezoelectric film, a RuO2 film (thickness: 10 nm) as a second adhesion film, and a Pt film (thickness: 100 nm) as an upper electrode film were successively formed to fabricate a piezoelectric laminate (Samples 1 to 16). The first adhesion film is a film for adhering the substrate and the lower electrode film, and the second adhesion film is a film for adhering the KNN film and the upper electrode film. As the first adhesion film, a ZnO film or a Ti film was formed. Also, the thickness of the first adhesion film was varied within the range of 0.5 nm or more and 50 nm or less.

[0075] The first adhesion film (ZnO film or Ti film) was formed by the RF magnetron sputtering method. The conditions for forming the first adhesion film were as follows. Among the following conditions, the film formation temperature means the temperature of the heater in the sputtering apparatus (the same applies to the conditions of other films). Also, when the film formation temperature is room temperature, it means forming the first adhesion film in a non-heated state. Also, the film formation time was appropriately changed according to the thickness of the first adhesion film to be formed. Film formation temperature: A predetermined temperature within the range of room temperature (for example, 28 °C) or more and 700 °C or less Atmosphere: Atmosphere of a mixed gas of Ar gas and O2 gas Introduced gas: Ar gas: 100 cc, O2 gas: 10 cc Atmospheric pressure: 0.2 Pa Discharge power: 300 W Film formation rate: The rate at which a first adhesion film with a thickness of 2.5 nm is formed in 30 seconds

[0076] The lower electrode film and the upper electrode film were formed by the RF magnetron sputtering method. The conditions for forming the lower electrode film and the upper electrode film were as follows. Film formation temperature: 300 °C Discharge power: 1200 W Introduced gas: Ar gas Atmospheric pressure: 0.3 Pa Film formation time: 5 minutes

[0077] The KNN film was formed by the RF magnetron sputtering method. As the sputtering target material for forming the KNN film, a (K 1-x Na x )NbO3 sintered body having a composition of (K+Na) / Nb = 0.8 to 1.2 and Na / (K+Na) = 0.4 to 0.7 was used. The target material was prepared by mixing K2CO3 powder, Na2CO3 powder, and Nb2O5 powder using a ball mill for 24 hours, pre-firing at 850°C for 10 hours, then pulverizing again with a ball mill, molding under a pressure of 200 MPa, and firing at 1080°C. The composition of the target material was controlled by adjusting the mixing ratio of K2CO3 powder, Na2CO3 powder, and Nb2O5 powder, and was measured by EDX (energy dispersive X-ray spectroscopy) before the film formation process.

[0078] The conditions for forming the KNN film were as follows. Film formation temperature: 550°C Discharge power: 2200 W Introduced gas: Mixed gas of Ar gas and O2 gas Atmospheric pressure: 0.3 Pa Ratio of partial pressure of Ar gas to O2 gas (Ar gas partial pressure / O2 gas partial pressure): 25 / 1 Film formation rate: 1 μm / hr

[0079] And for each sample, an evaluation of the orientation of the KNN film, an evaluation of the adhesion between the substrate and the lower electrode film, and an evaluation of the insulation property when a positive voltage was applied were performed. These evaluation results are shown in Table 1 below.

[0080]

Table 1

[0081] (Evaluation regarding orientation) The orientation of the KNN film was evaluated by measuring the orientation ratio of the crystals constituting the KNN film in the (001) plane direction. For each sample, XRD measurement was performed to obtain an X-ray diffraction pattern. The conditions for the XRD measurement were as follows. Device name: Bruker D8 DISCOVER (registered trademark, manufactured by Bruker) Output voltage: 50 kV Output current: 22 mA Thickness of the KNN film: 2 μm

[0082] Based on the peak intensity of the obtained diffraction pattern, it was calculated according to the above formula (Equation 1). The calculation results of the orientation ratio were as shown in Table 1 above.

[0083] As shown in Table 1, when the ZnO film was formed as the first adhesion film, by forming the ZnO film and the lower electrode film at a temperature of 200 °C or higher, the orientation of the KNN film could be enhanced, and it was confirmed that a KNN film with an orientation ratio of 80% or more as described above could be obtained. When the ZnO film and the lower electrode film were formed in a non-heated state or at a temperature below 200 °C, it was confirmed that the orientation of the KNN film could not be enhanced and the orientation ratio became less than 80%.

[0084] Also, as shown in Table 1, by forming the ZnO film as the first adhesion film and the lower electrode film at a temperature of 300 °C, it was confirmed that the orientation of the KNN film could be further enhanced compared to the case of forming at a temperature of 200 °C.

[0085] Also, as shown in Table 1, by forming the ZnO film as the first adhesion film and the lower electrode film at a temperature of 500 °C or higher (for example, 500 °C, 700 °C), the orientation of the KNN film could be further enhanced, and it was confirmed that a KNN film with an orientation ratio of 90% or more as described above could be obtained.

[0086] Furthermore, as shown in Table 1, when a Ti film was formed as the first adhesion film, it was confirmed that the orientation ratio of the KNN film could be less than 80% even when the film formation temperature of the Ti film and the lower electrode film was 500°C.

[0087] (Evaluation regarding adhesion) The evaluation of adhesion was performed by visually checking whether the lower electrode film was peeled off from the substrate (the presence or absence of film peeling). "None" in Table 1 means that no peeled portion of the lower electrode film from the substrate could be confirmed, and "Yes" means that a peeled portion of the lower electrode film from the substrate could be confirmed.

[0088] As shown in Table 1, it was confirmed that by making the thickness of the ZnO film as the first adhesion film 1 nm or more, it was possible to maintain an adhesion force equal to or greater than that in the case where a Ti film was provided as the first adhesion film. When the thickness of the ZnO film as the first adhesion film was less than 1 nm (for example, 0.5 nm), the adhesion force was weak, and it was confirmed that there was a portion where the lower electrode film was peeled off from the substrate. Also, when a Ti film with a thickness of 1 nm was provided as the first adhesion film, it was confirmed that there was a portion where the lower electrode film was peeled off from the substrate.

[0089] (Evaluation regarding insulation) The evaluation of insulation when a positive voltage was applied was performed by measuring the time from the start of voltage application until the KNN film reached dielectric breakdown when performing HALT in which a positive voltage was applied to the upper electrode film while grounding the lower electrode film so as to generate an electric field of 300 kV / cm (electric field directed from the upper electrode film to the lower electrode film) between the lower electrode film and the upper electrode film in a state where the temperature of each piezoelectric laminate (each sample) was heated to 200°C. Note that the leakage current density flowing through the KNN film was 30 mA / cm 2When it exceeded this value, it was considered that the KNN film had reached dielectric breakdown. The time until the KNN film measured by HALT under the above conditions reached dielectric breakdown is defined as the "HALT life". The HALT life of each sample is as shown in Table 1. Note that these HALT lives (measurement results) are the averages of the values measured at seven locations within 0.5 mmφ for each sample. The description "1800 seconds or more" in Table 1 means that dielectric breakdown did not occur even after 1800 seconds had elapsed since the start of voltage application.

[0090] As shown in Table 1, it was confirmed that the sample provided with the ZnO film as the first adhesion film was less likely to cause dielectric breakdown when a positive voltage was applied than the sample provided with the Ti film as the first adhesion film. That is, it was confirmed that the sample provided with the ZnO film had a longer HALT life than the sample provided with the Ti film.

[0091] Also, as shown in Table 1, by forming the ZnO film and the lower electrode film under temperature conditions of 200°C or higher, it was confirmed that a piezoelectric laminate (KNN film) with an orientation rate of the KNN film of 80% or more and a HALT life of 1500 seconds or more could be obtained.

[0092] Also, as shown in Table 1, by forming the ZnO film and the lower electrode film under temperature conditions of 300°C or higher, it was confirmed that the orientation of the KNN film was further improved and a piezoelectric laminate with a HALT life of 1600 seconds or more could be obtained.

[0093] Also, as shown in Table 1, it was confirmed that by forming the ZnO film and the lower electrode film under temperature conditions of 500°C or higher, a piezoelectric laminate with an orientation ratio of the KNN film of 90% and an HALT life of 1800 seconds or more can be obtained. When the thickness of the ZnO film is less than 1 nm (for example, 0.5 nm), it was confirmed that by forming the ZnO film and the lower electrode film under temperature conditions of 500°C or higher, a piezoelectric laminate with an orientation ratio of the KNN film of 85% or more and an HALT life of 1700 seconds or more can be obtained. However, when the thickness of the ZnO film is less than 1 nm, it has been confirmed that it is difficult to obtain a piezoelectric laminate with an orientation ratio of the KNN film of 90% or more and an HALT life of 1800 seconds or more even when the ZnO film and the lower electrode film are formed under temperature conditions of 500°C or higher.

[0094] (b) Also, samples 17 to 21 of the piezoelectric laminate were fabricated, and evaluations were made on the orientation ratio of the crystals constituting the KNN film in the (001) plane orientation, the diffraction peak intensity of the (001) plane of the KNN film, and the relative permittivity.

[0095] In samples 17 to 21, the thickness of the ZnO film or Ti film as the first adhesion film was made as shown in Table 2 below, and the film formation temperature of the first adhesion film was 500°C. Also, the film formation temperature of the lower electrode film was 500°C. Also, the film formation temperature of the KNN film was 460°C. Other methods and conditions were the same as those of samples 1 to 16 described above.

[0096]

Table 2

[0097] (Evaluation) For samples 17 to 21, the orientation ratio of the crystals constituting the KNN film in the (001) plane orientation, the diffraction peak intensity of the (001) plane of the KNN film, and the relative permittivity were evaluated.

[0098] The measurement of the orientation ratio of the crystals constituting the KNN film in the (001) plane orientation was performed under the same methods and conditions as the measurement of the orientation ratio of samples 1 to 16.

[0099] For the diffraction peak intensity of the (001) plane of the KNN film, XRD measurements were performed on each of Samples 17 to 21 to obtain an X-ray diffraction pattern (2θ / θ), and in the obtained X-ray diffraction pattern, the maximum intensity of the peak that appears within the range of 2θ from 20° to 23° was measured and calculated. The conditions for the XRD measurement were as follows. Apparatus name: Bruker D8 DISCOVER (registered trademark, manufactured by Bruker) Output voltage: 50 kV Output current: 22 mA Thickness of the KNN film: 2 μm

[0100] The relative permittivity was measured by applying a voltage from -1 V to +1 V to the upper electrode film 4 as a triangular wave with a frequency of 3 kHz with the lower electrode film 2 grounded.

[0101] The measurement results of the orientation ratio, diffraction peak intensity, and relative permittivity were as shown in Table 2 above. Note that "001 intensity" in Table 2 means the diffraction peak intensity of the (001) plane of the KNN film.

[0102] As shown in Table 2, by providing the ZnO film as the first adhesion film, it was confirmed that even when the film formation temperature of the KNN film was set to a low temperature (500 °C or lower, for example, 460 °C), the orientation of the KNN film did not deteriorate. That is, by providing the ZnO film, even when the KNN film was formed at a low temperature, it was confirmed that the maximum intensity of the diffraction peak of the (001) plane could be set to 1000 cps or more and 1400 cps or less, preferably 1100 cps or more and 1350 cps or less.

[0103] Also, it was confirmed that by forming the KNN film at a low temperature, the relative permittivity of the KNN film could be lowered. That is, it was confirmed that the relative permittivity could be set to 250 or more and 300 or less, preferably 250 or more and less than 300, more preferably 250 or more and 270 or less.

[0104] As shown in Table 2, it was confirmed that the KNN film can be formed at a low temperature without deteriorating the orientation of the KNN film by providing the ZnO film. That is, it was confirmed that the KNN film having both a high orientation ratio and a low dielectric constant can be obtained by providing the ZnO film. Such a KNN film can be particularly preferably used for applications of high-sensitivity sensors.

[0105] On the other hand, as shown in Table 2, when the Ti film was provided as the first adhesion film, it was confirmed that the orientation of the KNN film deteriorated when the KNN film was formed at a low temperature (500 °C or lower). That is, it was confirmed that the above-mentioned orientation ratio may be less than 80%, or the maximum intensity of the diffraction peak of the (001) plane may be less than 1000. In addition, in this case, it was also confirmed that the relative dielectric constant of the KNN film was about 300 to 500. That is, it was found that a KNN film having both a high orientation ratio and a low dielectric constant cannot be obtained when the Ti film is provided as the first adhesion film.

[0106] <Preferred Embodiment of the Present Disclosure> Hereinafter, preferred embodiments of the present disclosure will be appended.

[0107] (Supplementary Note 1) According to one aspect of the present disclosure, a substrate, a oxide film formed on the substrate and having zinc and oxygen as main elements, an electrode film formed on the oxide film, and a piezoelectric film formed on the electrode film and containing potassium, sodium, niobium, and oxygen and having a perovskite structure, is provided.

[0108] (Supplementary Note 2) The piezoelectric laminate according to Supplementary Note 1, preferably, the orientation ratio of the crystal constituting the piezoelectric film in the (001) plane orientation is 80% or more.

[0109] (Supplementary Note 3) The piezoelectric laminate according to Supplementary Note 1 or 2, preferably, When a positive voltage is applied to the upper electrode film, which is a film different from the electrode film and is provided on the piezoelectric film, at a temperature of 200 °C to generate an electric field of 300 kV / cm between the upper electrode film and the electrode film, the leakage current density flowing through the piezoelectric film from the start of voltage application is 30 mA / cm 2 until it exceeds, and the time is 1500 seconds or more, preferably 1600 seconds or more.

[0110] (Supplementary Note 4) The piezoelectric laminate according to Supplementary Note 1, preferably, The orientation ratio of the crystal constituting the piezoelectric film in the (001) plane direction is 90% or more.

[0111] (Supplementary Note 5) The piezoelectric laminate according to Supplementary Note 4, preferably, When a positive voltage is applied to the upper electrode film, which is a film different from the electrode film and is provided on the piezoelectric film, at a temperature of 200 °C to generate an electric field of 300 kV / cm between the upper electrode film and the electrode film, the leakage current density flowing through the piezoelectric film from the start of voltage application is 30 mA / cm 2 until it exceeds, and the time is 1800 seconds or more.

[0112] (Supplementary Note 6) The piezoelectric laminate according to any one of Supplementary Notes 1 to 5, preferably, With the electrode film grounded (at zero potential), when a voltage of -1 V to +1 V is applied to the upper electrode film, which is a film different from the electrode film and is provided on the piezoelectric film, in a triangular wave at a frequency of 3 kHz, the relative permittivity of the piezoelectric film measured is 250 or more and 300 or less.

[0113] (Supplementary Note 7) The piezoelectric laminate according to any one of Supplementary Notes 1 to 6, preferably, The thickness of the oxide film is 1 nm or more.

[0114] (Supplementary Note 8) The piezoelectric laminate according to any one of Supplementary Notes 1 to 7, preferably, An upper electrode film, which is an electrode film different from the electrode film, is provided on the piezoelectric film.

[0115] (Supplementary Note 9) According to another aspect of the present disclosure, A substrate, An oxide film formed on the substrate and having zinc and oxygen as main elements, A lower electrode film formed on the oxide film, A piezoelectric film formed on the lower electrode film, containing potassium, sodium, niobium, and oxygen, and having a perovskite structure, An upper electrode film formed on the piezoelectric film, and a piezoelectric element or a piezoelectric device module including the same are provided.

[0116] (Supplementary Note 10) The piezoelectric element or the piezoelectric device module according to Supplementary Note 9, preferably, The orientation ratio of the crystal constituting the piezoelectric film in the (001) plane direction is 80% or more.

[0117] (Supplementary Note 11) The piezoelectric element or the piezoelectric device module according to Supplementary Note 9 or 10, preferably, When a positive voltage is applied to the upper electrode film so as to generate an electric field of 300 kV / cm between the upper electrode film and the lower electrode film at a temperature of 200°C, the leakage current density flowing through the piezoelectric film from the start of voltage application is 30 mA / cm 2 The time until it exceeds is 1500 seconds or more, preferably 1600 seconds or more.

[0118] (Supplementary Note 12) The piezoelectric element or the piezoelectric device module according to Supplementary Note 9, preferably, The orientation ratio of the crystal constituting the piezoelectric film in the (001) plane direction is 90% or more.

[0119] (Supplementary Note 13) The piezoelectric element or piezoelectric device module according to Supplementary Note 12, preferably, When a positive voltage is applied to the upper electrode film so as to generate an electric field of 300 kV / cm between the upper electrode film and the lower electrode film at a temperature of 200° C., the leakage current density flowing through the piezoelectric film from the start of voltage application is 30 mA / cm 2 until it exceeds, and the time is 1800 seconds or more.

[0120] (Supplementary Note 14) According to still another aspect of the present disclosure, a step of forming an oxide film containing zinc and oxygen as main elements on a substrate; a step of forming an electrode film on the oxide film; a step of forming a piezoelectric film, which is an alkali niobium oxide film containing potassium, sodium, niobium, and oxygen and having a perovskite structure, on the electrode film, and a method for manufacturing a piezoelectric laminate is provided.

[0121] (Supplementary Note 15) The method according to Supplementary Note 14, preferably, in the step of forming the oxide film, the oxide film is formed under a temperature condition of 200° C. or higher, in the step of forming the electrode film, the electrode film is formed under a temperature condition of 200° C. or higher.

[0122] (Supplementary Note 16) The method according to Supplementary Note 14 or 15, preferably, in the step of forming the oxide film, the crystals constituting the oxide film are preferentially oriented in the (0001) plane orientation, in the step of forming the electrode film, the crystals constituting the electrode film are preferentially oriented in a predetermined orientation. Preferably, in the step of forming the electrode film, when forming a metal film as the electrode film, the crystals constituting the electrode film are preferentially oriented in the (111) plane orientation, and when forming a predetermined oxide film as the electrode film, the crystals constituting the electrode film are preferentially oriented in the (001) plane orientation.

Explanation of Reference Numerals

[0123] 1 Substrate 3 Piezoelectric film 10 Piezoelectric laminate

Claims

1. A substrate, A oxide film formed on the substrate, with zinc and oxygen as main elements, An electrode film formed on the oxide film, A piezoelectric film formed on the electrode film, containing potassium, sodium, niobium, and oxygen, and having a perovskite structure, and comprising: A piezoelectric laminate in which the crystals constituting the oxide film are preferentially oriented in the (0001) plane orientation.

2. The piezoelectric laminate according to claim 1, wherein the orientation ratio of the crystals constituting the piezoelectric film in the (001) plane orientation is 80% or more.

3. The piezoelectric laminate according to claim 1, wherein the orientation ratio of the crystals constituting the piezoelectric film in the (001) plane orientation is 90% or more.

4. When the electrode film is grounded and a voltage of -1V to +1V is applied to an upper electrode film, which is an electrode film different from the electrode film and is provided on the piezoelectric film, in a triangular wave of a frequency of 3 kHz for measurement, the relative permittivity of the piezoelectric film is 250 or more and 300 or less. The piezoelectric laminate according to any one of claims 1 to 3.

5. The piezoelectric laminate according to any one of claims 1 to 4, wherein the thickness of the oxide film is 1 nm or more.

6. The piezoelectric laminate according to any one of claims 1 to 5, wherein an upper electrode film, which is an electrode film different from the electrode film, is provided on the piezoelectric film.

7. A substrate, A oxide film formed on the substrate, with zinc and oxygen as main elements, A lower electrode film formed on the oxide film, A piezoelectric film formed on the lower electrode film, containing potassium, sodium, niobium, and oxygen, and having a perovskite structure, An upper electrode film formed on the piezoelectric film, and comprising: A piezoelectric element in which the crystals constituting the oxide film are preferentially oriented in the (0001) plane orientation.

8. The piezoelectric element according to claim 7, wherein the orientation ratio of the crystals constituting the piezoelectric film in the (001) plane orientation is 80% or more.

9. When a positive voltage is applied to the upper electrode film so as to generate an electric field of 300 kV / cm between the upper electrode film and the lower electrode film at a temperature of 200°C, the leakage current density flowing through the piezoelectric film from the start of voltage application is 30 mA / cm ２ The piezoelectric element according to claim 7 or 8, wherein the time until it exceeds is 1500 seconds or more.

10. The piezoelectric element according to claim 7, wherein the orientation ratio of the crystals constituting the piezoelectric film in the (001) plane orientation is 90% or more.

11. When a positive voltage is applied to the upper electrode film so as to generate an electric field of 300 kV / cm between the upper electrode film and the lower electrode film at a temperature of 200°C, the leakage current density flowing through the piezoelectric film from the start of voltage application is 30 mA / cm ２ The piezoelectric element according to claim 10, wherein the time until it exceeds is 1800 seconds or more.

12. A step of forming an oxide film mainly composed of zinc and oxygen on a substrate, A step of forming an electrode film on the oxide film, A step of forming a piezoelectric film, which is an alkali niobium oxide film containing potassium, sodium, niobium, and oxygen and having a perovskite structure, on the electrode film, and In the step of forming the oxide film, the oxide film is formed under a temperature condition of 200°C or higher, and a method for manufacturing a piezoelectric laminate in which the crystals constituting the oxide film are preferentially oriented in the (0001) plane orientation.

13. The method for manufacturing a piezoelectric laminate according to claim 12, wherein in the step of forming the electrode film, the electrode film is formed under a temperature condition of 200°C or higher.

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