Piezoelectric film substrate and method for manufacturing piezoelectric film substrate

Abstract

This piezoelectric film substrate 100 comprises a substrate 1, a seed layer 2, a lower electrode layer 3, an adjustment layer 4, a piezoelectric layer 5, and an upper electrode layer 6. The seed layer 2 contains a zirconium oxide formed by an epitaxial growth layer on the substrate 1 composed of a (100) silicon single crystal. The lower electrode layer 3 contains at least one among iridium and platinum formed by an epitaxial growth layer on the seed layer 2. The adjustment layer 4 contains a metal oxide having a perovskite structure formed by an epitaxial growth layer on the lower electrode layer 3. The piezoelectric layer 5 is composed of bismuth ferrite preferentially oriented to (100) on the adjustment layer 4.

Description

Piezoelectric film substrate and method for manufacturing the same

[0001] The present invention relates to a piezoelectric film substrate and a method for manufacturing a piezoelectric film substrate, and more particularly to a piezoelectric film substrate on which a piezoelectric layer made of bismuth ferrite is formed, and a method for manufacturing a piezoelectric film substrate.

[0002] Conventionally, a method for forming a bismuth ferrite film has been known (see, for example, Patent Document 1).

[0003] In the above-mentioned Patent Document 1, bismuth ferrite (BiFeO ３ In the method described in Patent Document 1, a platinum (Pt) layer is formed on a silicon oxide layer formed on a substrate surface by thermal oxidation. Then, a bismuth ferrite crystal film is formed on the platinum layer by electron cyclotron resonance (ECR) plasma sputtering under conditions in which the substrate temperature during film formation is in the range of 420°C to 460°C.

[0004] JP 2010-7121 A

[0005] However, in the method for forming a bismuth ferrite film described in Patent Document 1, the film must be formed by ECR plasma sputtering under conditions in which the substrate temperature during film formation is in the range of 420°C to 460°C. Therefore, if the ECR plasma sputtering method is used and the substrate temperature deviates from the relatively narrow range of 420°C to 460°C, it is believed that the formation of a piezoelectric bismuth ferrite film will be insufficient. For example, if the substrate temperature is higher than 460°C, excessive iron oxide may be precipitated, causing problems such as current leakage. Furthermore, if the substrate temperature is lower than 420°C, it is believed that the piezoelectric properties may be reduced. Here, it is difficult to directly measure the actual substrate temperature during film formation. Furthermore, the temperature set as the heating temperature in the film formation apparatus may differ from the actual substrate temperature. Therefore, if the substrate temperature range during film formation is narrow, it is believed that it is difficult to easily form a piezoelectric bismuth ferrite film. Therefore, it is desired to easily form a piezoelectric layer made of bismuth ferrite by using a method other than ECR plasma sputtering and by broadening the range of substrate temperatures during film formation.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a piezoelectric film substrate and a method for manufacturing a piezoelectric film substrate that can easily form a piezoelectric layer made of bismuth ferrite.

[0007] In order to achieve the above object, a piezoelectric film substrate according to a first aspect of the present invention comprises a substrate made of (100) silicon single crystal, a seed layer containing zirconium oxide formed on the substrate by an epitaxial growth layer, a lower electrode layer containing at least one of iridium and platinum formed on the seed layer by an epitaxial growth layer, an adjustment layer containing a metal oxide having a perovskite structure formed on the lower electrode layer by an epitaxial growth layer, a piezoelectric layer composed of bismuth ferrite with a (100) preferred orientation on the adjustment layer, and an upper electrode layer.

[0008] As described above, the piezoelectric film substrate according to a first aspect of the present invention includes a seed layer containing zirconium oxide formed on a substrate by epitaxial growth, a lower electrode layer containing at least one of iridium and platinum formed on the seed layer by epitaxial growth, an adjustment layer containing a metal oxide having a perovskite structure formed on the lower electrode layer by epitaxial growth, and a piezoelectric layer composed of bismuth ferrite with a (100) preferred orientation on the adjustment layer. Because the seed layer, lower electrode layer, and adjustment layer are each formed in this order by epitaxial growth, a piezoelectric layer composed of bismuth ferrite can be formed with a (100) preferred orientation on the adjustment layer with good crystal orientation formed by epitaxial growth in this order from the substrate. Therefore, by forming a film on the adjustment layer with good crystal orientation, a piezoelectric layer composed of bismuth ferrite with good piezoelectric properties can be formed without carefully setting conditions such as temperature during film formation. As a result, a piezoelectric layer composed of bismuth ferrite can be easily formed.

[0009] In the piezoelectric film substrate according to the first aspect, the piezoelectric layer is preferably made of bismuth ferrite formed by epitaxial growth on an adjustment layer. This configuration allows the piezoelectric layer made of bismuth ferrite to be formed by epitaxial growth on an adjustment layer with good crystal orientation formed by epitaxial growth on the substrate. Therefore, a piezoelectric layer made of bismuth ferrite with better piezoelectric properties can be formed by epitaxial growth without having to carefully set conditions such as temperature during film formation.

[0010] In the piezoelectric film substrate according to the first aspect, the seed layer preferably contains yttria-stabilized zirconia as zirconium oxide. This configuration allows the seed layer to have a stabilized crystalline structure by containing stabilized zirconia (zirconium oxide). This stabilizes the crystalline structure of the seed layer, further improving the crystalline orientation of the lower electrode layer formed on the seed layer. As a result, a lower electrode layer with better crystalline orientation can be formed, making it easier to form a piezoelectric layer made of bismuth ferrite.

[0011] In the piezoelectric film substrate according to the first aspect, the lower electrode layer preferably includes an iridium layer formed on the seed layer and a platinum layer formed on the iridium layer. By forming the platinum layer on the iridium layer formed on the seed layer, the platinum layer can be easily epitaxially grown to match the crystal orientation of the seed layer. Therefore, the lower electrode layer can be easily epitaxially grown with an aligned crystal orientation.

[0012] In the piezoelectric film substrate according to the first aspect, the adjustment layer preferably contains strontium and ruthenium. By forming the adjustment layer from a metal oxide containing strontium and ruthenium, the crystal orientation of the piezoelectric layer containing bismuth ferrite formed on the adjustment layer can be improved. Furthermore, since the metal oxide containing strontium and ruthenium is a relatively stable substance, processing can be easily performed when using the resulting piezoelectric film to produce devices such as piezoelectric elements.

[0013] In the piezoelectric film substrate according to the first aspect, the adjustment layer preferably contains lanthanum and nickel. By forming the adjustment layer from a metal oxide containing lanthanum and nickel, the crystal orientation of the piezoelectric layer containing bismuth ferrite formed on the adjustment layer can be improved. Furthermore, since metal oxides containing lanthanum and nickel are relatively unstable substances and easily react with other substances, the adjustment layer can be easily etched.

[0014] In the piezoelectric film substrate according to the first aspect, the piezoelectric layer is preferably made of bismuth ferrite doped with manganese. By configuring in this manner, the piezoelectric properties of bismuth ferrite can be improved by adding manganese to bismuth ferrite. Therefore, by adding manganese, it is possible to effectively and easily form a piezoelectric layer made of bismuth ferrite with improved piezoelectric properties.

[0015] In the piezoelectric film substrate according to the first aspect, the piezoelectric layer preferably has a relative dielectric constant of 150 or less in a frequency band of 1 kHz or more. Here, the figure of merit of the piezoelectric thin film is expressed as the value obtained by dividing the square of the piezoelectric constant (piezoelectric stress constant) by the dielectric constant. Therefore, by configuring the piezoelectric layer to have a relative dielectric constant of 150 or less in a frequency band of 1 kHz or more, as in the present invention, a piezoelectric layer with a sufficiently small relative dielectric constant and a good figure of merit can be obtained.

[0016] In order to achieve the above object, a method for manufacturing a piezoelectric film substrate according to a second aspect of the present invention includes the steps of forming a seed layer containing zirconium oxide by epitaxial growth on a substrate made of (100) silicon single crystal, forming a lower electrode layer containing at least one of iridium and platinum by epitaxial growth on the seed layer, forming an adjustment layer containing a metal oxide having a perovskite structure by epitaxial growth on the lower electrode layer, forming a piezoelectric layer composed of bismuth ferrite with a (100) preferred orientation on the adjustment layer, and forming an upper electrode layer.

[0017] A method for manufacturing a piezoelectric film substrate according to a second aspect of the present invention includes the steps of epitaxially growing a seed layer containing zirconium oxide on a (100) silicon single crystal substrate, epitaxially growing a lower electrode layer containing at least one of iridium and platinum on the seed layer, epitaxially growing an adjustment layer containing a metal oxide having a perovskite structure on the lower electrode layer, and forming a piezoelectric layer made of bismuth ferrite with a (100) preferred orientation on the adjustment layer. Since the seed layer, lower electrode layer, and adjustment layer are each formed in this order by epitaxial growth, the piezoelectric layer made of bismuth ferrite can be formed with a (100) preferred orientation on the adjustment layer with good crystal orientation formed in this order by epitaxial growth on the substrate. Therefore, by forming a film on the adjustment layer with good crystal orientation, a piezoelectric layer made of bismuth ferrite with good piezoelectric properties can be formed without carefully setting conditions such as temperature during film formation. As a result, it is possible to provide a method for manufacturing a piezoelectric film substrate that allows for easy formation of a piezoelectric layer made of bismuth ferrite.

[0018] In the method for manufacturing a piezoelectric film substrate according to the second aspect, the step of forming the piezoelectric layer preferably includes a step of forming the piezoelectric layer while heating the substrate on which the adjustment layer has been formed at a temperature of 400° C. or higher and 500° C. or lower. Here, since the adjustment layer with good crystal orientation is formed by epitaxial growth, a piezoelectric layer made of bismuth ferrite exhibiting piezoelectricity can be formed even when film formation is performed at a wider temperature range of 400° C. or higher and 500° C. or lower. Therefore, the appropriate temperature range during film formation can be set to a wider temperature range of 400° C. or higher and 500° C. or lower, making it easier to form a piezoelectric layer made of bismuth ferrite.

[0019] In this case, the step of forming the piezoelectric layer preferably includes a step of forming a piezoelectric layer made of bismuth ferrite by sputtering while the substrate is heated to a temperature of 400° C. or more and 500° C. or less. With this configuration, the piezoelectric layer made of bismuth ferrite can be formed by sputtering while the temperature of the substrate 1 is kept in a wider range of 400° C. or more and 500° C. or less, and therefore the sputtering conditions for forming the piezoelectric layer can be set relatively easily.

[0020] According to the present invention, as described above, a piezoelectric layer made of bismuth ferrite can be easily formed.

[0021] FIG. 1 is a cross-sectional view showing a piezoelectric film substrate according to a first embodiment. FIG. 2 is a schematic view for explaining epitaxial growth. FIG. 3 is a schematic view showing a perovskite structure. FIG. 4 is a schematic view showing the configuration of a sputtering apparatus. FIG. 5 is a flow chart for explaining a method for manufacturing a piezoelectric film substrate according to a first embodiment. FIG. 6 is a view for explaining (100) preferred orientation when a bismuth ferrite film is formed at 400° C. according to the first embodiment. FIG. 7 is a view for explaining orientation in epitaxial growth when a bismuth ferrite film is formed at 400° C. according to the first embodiment. FIG. 8 is a view for explaining (100) preferred orientation when a bismuth ferrite film is formed at 500° C. according to the first embodiment. FIG. 9 is a cross-sectional view showing a piezoelectric film substrate according to a second embodiment. FIG. 10 is a cross-sectional view showing a piezoelectric film substrate according to a third embodiment. FIG. 11 is a view for explaining the configuration of a sputtering apparatus according to a third embodiment. FIG. 10 is a diagram for explaining the (100) preferred orientation when a film of manganese-added bismuth ferrite according to the third embodiment is formed at 400° C. FIG. 11 is a diagram for explaining the orientation in epitaxial growth when a film of manganese-added bismuth ferrite according to the third embodiment is formed at 400° C. FIG. 12 is a diagram for explaining the (100) preferred orientation when a film of manganese-added bismuth ferrite according to the third embodiment is formed at 500° C. FIG. 13 is a diagram for explaining the orientation in epitaxial growth when a film of manganese-added bismuth ferrite according to the third embodiment is formed at 500° C.

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] First Embodiment The configuration of a piezoelectric film substrate 100 according to a first embodiment of the present invention will be described with reference to FIGS.

[0024] (Configuration of Piezoelectric Film Substrate) The piezoelectric film substrate 100 is a piezoelectric film substrate that is divided into a plurality of individual pieces, each of which becomes a device. The devices are, for example, MEMS (Micro Electro Mechanical Systems) devices. The MEMS devices are also used, for example, as sensors or actuators.

[0025] 1, the piezoelectric film substrate 100 includes a substrate 1, a seed layer 2, a lower electrode layer 3, an adjustment layer 4, a piezoelectric layer 5, and an upper electrode layer 6. In the piezoelectric film substrate 100, the seed layer 2, the lower electrode layer 3, the adjustment layer 4, the piezoelectric layer 5, and the upper electrode layer 6 are arranged so as to be stacked in this order on the substrate 1.

[0026] The substrate 1 is a (100) silicon single crystal. The substrate 1 is disk-shaped and made of single crystal silicon. The substrate 1 has a crystal orientation in which the crystal orientation (plane orientation) on the main surface is (100). The substrate 1 has a thickness of, for example, about 300 μm or more and about 725 μm or less. The seed layer 2 is a thin film containing zirconium oxide. Zirconium oxide is an oxide of zirconium (Zr) and is also called zirconia. Specifically, in the first embodiment, the seed layer 2 contains yttria-stabilized zirconia (YSZ) as the zirconium oxide. The seed layer 2 functions, for example, as a seed layer (seed crystal layer) for aligning the crystal orientation of the film to be stacked with a desired orientation. The seed layer 2 may also function as an insulating layer.

[0027] As shown in FIG. 2 , the seed layer 2 includes zirconium oxide formed by epitaxial growth on the substrate 1 made of (100) silicon single crystal. Epitaxial growth refers to the growth of crystals on the single crystal substrate 1 with an aligned orientation so that the growing crystals follow the regularity of the atomic arrangement of the crystal of the substrate 1. The epitaxial growth layer refers to a crystalline film obtained by epitaxial growth. In epitaxial growth, a crystalline film grows with its crystal axes aligned both in the direction perpendicular to the main surface of the substrate 1 and in the in-plane direction of the main surface of the substrate 1. By epitaxial growth, a film is formed on the single crystal substrate 1 with an aligned crystal orientation, thereby forming the seed layer 2 made of single crystal yttria-stabilized zirconia. The seed layer 2 is a thin film formed by sputtering while the substrate 1 is heated to a temperature of several hundred degrees Celsius so that the resulting crystals grow epitaxially. In the seed layer 2, a crystalline film of yttria-stabilized zirconia is formed by epitaxial growth in a cube-on-cube relationship with respect to the silicon crystal of the substrate 1. "Cube-on-cube" means that a crystal having a cubic structure grows epitaxially with the in-plane and in-plane crystal orientations aligned. That is, in the first embodiment, the seed layer 2 having a (100) crystal orientation, which is the common orientation, is formed on the substrate 1 having a (100) crystal orientation. In this specification, the terms "epitaxial growth" and "single crystal" are used as broad concepts that may include not only a perfect crystal structure but also some lattice defects.

[0028] As shown in FIG. 1 , the lower electrode layer 3 includes iridium (Ir) and platinum (Pt) formed by epitaxial growth on a seed layer 2 on a substrate 1. The lower electrode layer 3 is formed as a single crystal by epitaxial growth. Specifically, in the first embodiment, the lower electrode layer 3 is a multilayer film including an iridium layer 3 a and a platinum layer 3 b, each of which is formed as a single crystal by epitaxial growth. In the lower electrode layer 3, the iridium layer 3 a is formed on the seed layer 2, and the platinum layer 3 b is formed on the iridium layer 3 a. The iridium layer 3 a is composed of single-crystal iridium formed by epitaxial growth. Similarly, the platinum layer 3 b is composed of single-crystal platinum formed by epitaxial growth.

[0029] In the lower electrode layer 3, the iridium layer 3a and the platinum layer 3b are each a single-crystal crystalline film grown with the crystal axes aligned both in the direction perpendicular to the main surface of the substrate 1 and in the in-plane direction of the main surface of the substrate 1, similar to the seed layer 2. The iridium layer 3a and the platinum layer 3b are each a thin film formed by sputtering while the substrate 1 is heated to a temperature of several hundred degrees Celsius so that the crystals to be produced grow epitaxially. Similarly to the seed layer 2, the iridium layer 3a and the platinum layer 3b are each formed as a crystalline film having a (100) crystal orientation by cube-on-cube epitaxial growth.

[0030] The adjustment layer 4 includes a metal oxide having a perovskite structure. In the first embodiment, the adjustment layer 4 includes strontium (Sr) and ruthenium (Ru) as metal elements. Specifically, the adjustment layer 4 includes strontium ruthenate (SrRuO) containing strontium and ruthenium. ３ The adjustment layer 4 is made of a material such as SiO2 (sintered body) and a silicon dioxide (SiO2) film. The adjustment layer 4 adjusts the crystal orientation of the piezoelectric layer 5. The adjustment layer 4 functions as a seed layer (seed crystal layer) for adjusting the crystal orientation of the piezoelectric layer 5 to a desired orientation.

[0031] 3, in the perovskite structure, metal elements are located at the A site, which is each vertex of a cubic crystal, and at the B site, which is the body center, and oxygen (O) is located at the face center of each face centered on the B site. In the strontium ruthenate of the adjustment layer 4, strontium is located at the A site of the perovskite structure, and ruthenium is located at the B site.

[0032] As shown in FIG. 1 , the adjustment layer 4 is formed on the substrate 1 by epitaxial growth on the lower electrode layer 3. That is, the adjustment layer 4 is composed of single-crystal strontium ruthenate formed by epitaxial growth. Like the seed layer 2 and the lower electrode layer 3, the adjustment layer 4 is a single-crystal crystalline film grown with its crystal axes aligned both in the direction perpendicular to the main surface of the substrate 1 and in the in-plane direction of the main surface of the substrate 1. The adjustment layer 4 is a thin film formed by sputtering, for example, while the substrate 1 is heated to a temperature of several hundred degrees Celsius so that the resulting crystals grow epitaxially. Like the seed layer 2 and the lower electrode layer 3, the adjustment layer 4 is formed as a crystalline film with a (100) crystal orientation by cube-on-cube epitaxial growth.

[0033] The piezoelectric layer 5 is formed on the substrate 1 by forming a layer of bismuth ferrite (BiFeO ３:BFO). Specifically, the piezoelectric layer 5 is composed of bismuth ferrite with a (100) preferred orientation so as to have a (100) crystal orientation. The piezoelectric layer 5 is composed of bismuth ferrite formed by epitaxial growth on the adjustment layer 4 on the substrate 1. The piezoelectric layer 5 also contains ferroelectric bismuth ferrite. The piezoelectric layer 5 is composed of single-crystal bismuth ferrite formed by epitaxial growth. Like the seed layer 2, the lower electrode layer 3, and the adjustment layer 4, the piezoelectric layer 5 is a single-crystal crystalline film grown with its crystal axes aligned both in the direction perpendicular to the main surface of the substrate 1 and in the in-plane direction of the main surface of the substrate 1. The piezoelectric layer 5 is a thin film formed by sputtering while the substrate 1 is heated at a temperature of 400° C. to 500° C. so that the resulting crystals grow epitaxially. The piezoelectric layer 5 is formed as a crystalline film with a (100) crystal orientation by cube-on-cube epitaxial growth. The bismuth ferrite constituting the piezoelectric layer 5 has a perovskite structure shown in Fig. 3, with bismuth (Bi) located at the A site and iron (Fe) located at the B site.

[0034] The upper electrode layer 6 is formed on the substrate 1 and on the piezoelectric layer 5. The upper electrode layer 6 is made of titanium (Ti), gold (Au), platinum (Pt), or iridium dioxide (IrO ２ The upper electrode layer 6 may be formed of a material such as silicon dioxide. The upper electrode layer 6 may be formed of the same material as the lower electrode layer 3, or may be formed of a material different from that of the lower electrode layer 3. The material of the upper electrode layer 6 is not particularly limited. The upper electrode layer 6 may be a single layer or a multilayer. An adjustment layer such as a buffer layer may be provided between the piezoelectric layer 5 and the upper electrode layer 6. The upper electrode layer 6 may be polycrystalline or single-crystalline. The upper electrode layer 6 may be amorphous. An insulating layer such as a silicon oxide layer may be formed on the upper electrode layer 6.

[0035] Here, the thickness of the seed layer 2 is 2 nm or more and 100 nm or less. The thickness of the lower electrode layer 3 (iridium layer 3a and platinum layer 3b) is 50 nm or more and 500 nm or less. The thickness of the adjustment layer 4 is 2 nm or more and 40 nm or less. The thickness of the lower electrode layer 3 is greater than the thickness of the adjustment layer 4. If the thickness of the lower electrode layer 3 is too small, the resistance increases and the effect as an electrode layer is reduced. Therefore, by making the thickness of the lower electrode layer 3 greater than the thickness of the adjustment layer 4, it is possible to suppress a decrease in the characteristics as an electrode layer due to an increase in the electrical resistance of the lower electrode layer 3. Furthermore, if the thickness of the adjustment layer 4 is increased, it is thought that the crystallinity will deteriorate. Furthermore, if the thickness of the adjustment layer 4 is increased, the series resistance component will increase. Therefore, by making the thickness of the adjustment layer 4 smaller than the thickness of the lower electrode layer 3, it is possible to form an adjustment layer 4 with good crystallinity and suppress an increase in the series resistance component.

[0036] <Sputtering Apparatus> As shown in FIG. 4 , in the first embodiment, the piezoelectric layer 5 is formed by sputtering using a sputtering apparatus 101. The sputtering apparatus 101 is configured to sputter target particles (sputtered particles) from a target member 102 containing bismuth and iron, which are materials for the piezoelectric layer 5, and to deposit the sputtered particles on the substrate 1 on which the adjusting layer 4 has been formed, thereby forming a thin film of the sputtered particles from the target member 102 on the adjusting layer 4. The sputtering apparatus 101 includes a mounting table 11, a heating device 12, a film formation chamber 13, and a vacuum pump 14. Sputtering is performed with the film formation chamber 13 evacuated by the vacuum pump 14. Note that the term "vacuum" used here refers to a pressure lower than atmospheric pressure.

[0037] The sputtering apparatus 101 is configured to, for example, pump argon (Ar) and oxygen (O ２) is introduced. The sputtering apparatus 101 then applies a voltage to a target member 102 disposed in the deposition chamber 13 to generate plasma within the deposition chamber 13. Charged particles (e.g., argon ions) in the plasma collide with the target member 102, causing sputter particles containing bismuth and iron to be emitted (knocked out) from the target member 102. The emitted sputter particles then adhere to the substrate 1 (piezoelectric film substrate 100) placed on the mounting table 11, forming a thin film on the surface of the adjustment layer 4 of the substrate 1, thereby depositing the piezoelectric layer 5.

[0038] In the sputtering apparatus 101, the heating device 12 is configured to heat the substrate 1 placed on the mounting table 11. Specifically, the heating device 12 has a heating surface along the main surface of the substrate 1 on the side where the substrate 1 is placed. The heating device 12 includes, for example, an electric heating wire. In the sputtering apparatus 101, sputtering is performed on the substrate 1 placed in the film formation chamber 13 and heated by the heating device 12. The heating device 12 is controlled to maintain the substrate 1 at a predetermined temperature during sputtering. The predetermined temperature is, for example, a temperature between 400°C and 500°C. Note that in the sputtering apparatus 101, the temperature measured and displayed as the internal temperature of the sputtering apparatus 101 does not necessarily represent the actual temperature of the substrate 1 during film formation. Due to disturbances such as plasma generated during film formation, the heating temperature set in the sputtering apparatus 101 and the actual temperature of the substrate 1 differ from each other.

[0039] The sputtering apparatus 101 includes a control device 15. The control device 15 controls each part of the sputtering apparatus 101. The control device 15 includes, for example, an arithmetic unit including a CPU (Central Processing Unit) and a storage device such as a flash memory. The control device 15 controls sputtering by the sputtering apparatus 101 based on programs and parameters stored in the storage device. The control device 15 controls the application of voltage to the target member 102, the operation of the vacuum pump 14, and the operation of the heating device 12.

[0040] (Method for manufacturing piezoelectric film substrate) Next, a method for manufacturing the piezoelectric film substrate 100 will be described with reference to Fig. 5. The method for manufacturing the piezoelectric film substrate 100 is a method for manufacturing a piezoelectric film substrate that is divided into a plurality of individual pieces that each become a device.

[0041] 5, the method for manufacturing the piezoelectric film substrate 100 includes step S1, which is a step of preparing the substrate 1, step S2, which is a step of forming the seed layer 2, step S3, which is a step of forming the lower electrode layer 3, step S4, which is a step of forming the adjustment layer 4, step S5, which is a step of forming the piezoelectric layer 5, and step S6, which is a step of forming the upper electrode layer 6. In the method for manufacturing the piezoelectric film substrate 100 according to the first embodiment, steps S1 to S6 are performed in this order. The steps from step S1 to step S6 do not have to be performed consecutively unless otherwise specified.

[0042] First, in step S1, in the process of preparing a substrate 1, a substrate 1 made of (100) silicon single crystal is prepared.

[0043] Next, in step S2, in the step of forming the seed layer 2, the seed layer 2 containing zirconium oxide is formed by epitaxial growth on the substrate 1. Specifically, in a state in which the substrate 1 is heated to a temperature of several hundred degrees Celsius, the seed layer 2 made of yttria-stabilized zirconia as zirconium oxide is formed by epitaxial growth by sputtering.

[0044] Next, in step S3, in the process of forming the lower electrode layer 3 on the substrate 1, the lower electrode layer 3 including an iridium layer 3a and a platinum layer 3b is formed by epitaxial growth so as to be stacked on the seed layer 2 on the substrate 1. In the process of forming the lower electrode layer 3, the iridium layer 3a is formed so as to grow epitaxially on the seed layer 2 with the substrate 1 heated to a temperature of, for example, several hundred degrees Celsius. Then, after the iridium layer 3a is formed, the platinum layer 3b is formed so as to grow epitaxially on the iridium layer 3a with the substrate 1 heated to a temperature of, for example, several hundred degrees Celsius.

[0045] Then, in step S4, in the process of forming adjustment layer 4, after the lower electrode layer 3 is formed, adjustment layer 4 containing a metal oxide having a perovskite structure is formed by epitaxial growth on lower electrode layer 3 on substrate 1 by sputtering. In the process of forming adjustment layer 4, for example, while substrate 1 is heated to cause epitaxial growth, single-crystal adjustment layer 4 made of strontium ruthenate containing strontium and ruthenium is deposited.

[0046] Then, in step S5, in the process of depositing the piezoelectric layer 5 on the adjustment layer 4, the piezoelectric layer 5 made of (100)-preferentially oriented bismuth ferrite is formed on the adjustment layer 4 formed on the substrate 1. In step S5, the piezoelectric layer 5 made of bismuth ferrite is formed by epitaxial growth on the adjustment layer 4. In step S5, the piezoelectric layer 5 is formed by sputtering while the substrate 1 on which the adjustment layer 4 has been formed is heated at a temperature of 400°C or higher and 500°C or lower. Specifically, the piezoelectric layer 5 is deposited by sputtering using sputter particles from the target member 102 while the substrate 1 on which the adjustment layer 4 has been formed, placed in the deposition chamber 13 of the sputtering device 101, is heated by the heating device 12 to a temperature of 400°C or higher and 500°C or lower. The control device 15 of the sputtering device 101 performs sputtering by applying a voltage to the target member 102 for, for example, a preset period of time until the piezoelectric layer 5 is deposited to a predetermined thickness.

[0047] In the first embodiment, in the process of forming the piezoelectric layer 5 on the adjustment layer 4 in step S5, the piezoelectric layer 5 made of bismuth ferrite is further formed by epitaxial growth on the seed layer 2, the lower electrode layer 3, and the adjustment layer 4, each of which is formed as an epitaxially grown layer on the substrate 1. That is, the crystal orientation in each layer from the substrate 1 to the bismuth ferrite of the piezoelectric layer 5 is aligned by epitaxial growth. In other words, in the first embodiment, the seed layer 2, the lower electrode layer 3, and the adjustment layer 4, each made of a single crystal material, are formed on the single crystal substrate 1, and the piezoelectric layer 5 made of bismuth ferrite is formed on the multilayer single crystal film, each of which has an aligned orientation.

[0048] Then, in step S6, the process of forming the upper electrode layer 6 on the substrate 1, after the piezoelectric layer 5 is formed, the upper electrode layer 6 is formed on the piezoelectric layer 5 on the substrate 1 by sputtering. For example, the process of forming the upper electrode layer 6 is performed without heating the substrate 1 (piezoelectric film substrate 100). The piezoelectric film substrate 100 is manufactured by steps S1 to S6. Note that the sputtering processes in steps S2 to S6 may be performed using different sputtering apparatuses, or some of the sputtering processes in steps S2 to S6 may be performed using a common sputtering apparatus. Even in this case, the sputtering processes in steps S2 to S6 may be performed in different chambers, or may be performed in a common chamber using a shutter that shields the target.

[0049] Thereafter, when processing into a shape for a device is performed, for example, photolithography is used to process the lower electrode layer 3, the adjustment layer 4, the piezoelectric layer 5, and the upper electrode layer 6 into a shape for the device. In the case of photolithography, wet etching using an etching solution or dry etching using an etching gas is used to remove unnecessary portions and leave necessary portions, thereby processing the piezoelectric film substrate 100 into a shape for the device. Furthermore, when the piezoelectric film substrate 100 is divided into individual pieces for the device, the piezoelectric film substrate 100 is cut into the individual pieces for the device using, for example, a blade.

[0050] Example of First Embodiment With reference to FIGS. 6 to 9, the crystal orientation of the piezoelectric layer 5 in the piezoelectric film substrate 100 according to an example of the first embodiment will be described.

[0051] As shown in FIG. 6 , when the piezoelectric layer 5 was formed with the substrate 1 heated to 400°C, the degree of (100) orientation (angle) was high. The degree of crystalline orientation was measured using X-ray diffraction intensity as an indicator. When the piezoelectric layer 5 was formed with the substrate 1 heated to 400°C, a diffraction peak was detected at an angle corresponding to the (100) crystal orientation, confirming that the piezoelectric layer 5 was formed with a (100) preferred orientation. As shown in FIG. 7 , when the piezoelectric layer 5 made of bismuth ferrite according to the first embodiment was formed with the substrate 1 heated to 400°C, the degree of the same angle (orientation) as the orientation of the single-crystal silicon of the substrate 1 was high. That is, when the orientation of the piezoelectric layer 5 was measured by X-ray diffraction, as shown in FIG. 7 , a diffraction peak was detected at an angle corresponding to the (100) direction of the single-crystal silicon of the substrate 1. Therefore, it was confirmed that the piezoelectric layer 5 made of single-crystal bismuth ferrite was formed by cube-on-cube epitaxial growth in a state in which the piezoelectric layer 5 had the same crystal orientation as the single-crystal silicon of the substrate 1 .

[0052] 8, when the piezoelectric layer 5 was formed with the substrate 1 heated to 500°C, the degree of (100) orientation (angle) was increased, similar to when the substrate 1 was heated to 400°C. That is, when the piezoelectric layer 5 was formed with the substrate 1 heated to 500°C, a diffraction peak was detected at an angle corresponding to the (100) crystal orientation, confirming that the piezoelectric layer 5 was formed with a (100) preferred orientation. Therefore, in the first embodiment, the piezoelectric layer 5 is formed of bismuth ferrite with a (100) preferred orientation when the substrate 1 is heated to a temperature in the range of 400°C to 500°C. Furthermore, as shown in FIG. 9, when the piezoelectric layer 5 formed of bismuth ferrite according to the first embodiment was formed with the substrate 1 heated to 500°C, the degree of the same angle (orientation) as the orientation of the single-crystal silicon of the substrate 1 was increased, similar to when the substrate 1 was heated to 400°C. 9, even when the temperature of the substrate 1 is heated to 500°C, a diffraction peak is detected at an angle indicating the (100) direction of the single crystal silicon of the substrate 1, and it was confirmed that the piezoelectric layer 5 made of single crystal bismuth ferrite is formed by cube-on-cube epitaxial growth in a state having the same crystal orientation as the orientation of the single crystal silicon of the substrate 1. That is, in the first embodiment, the piezoelectric layer 5 made of epitaxially grown bismuth ferrite is formed when the temperature of the substrate 1 is in the range of 400°C to 500°C.

[0053] <Relative dielectric constant> With reference to Table 1 below, the relative dielectric constant ε of the piezoelectric film substrate 100 according to the first embodiment is ｒ As shown in Table 1, in the first embodiment, when the temperature of the substrate 1 during the deposition of the piezoelectric layer 5 was heated to 400° C. and when the temperature was heated to 500° C., the piezoelectric layer 5 had a relative dielectric constant ε of 150 or less in a frequency band of 1 kHz or more. ｒ It is difficult to accurately measure the temperature of the substrate 1 during film formation, and the temperature may be different from the value set as the heating temperature during film formation in the sputtering apparatus 101. In addition, the relative dielectric constant ε ｒis calculated by the following formula (1). where C represents the capacitance and ε ０ represents the dielectric constant of a vacuum. The capacitance C was measured using an LCR meter. In the example of Table 1, the relative dielectric constant ε measured at 100 kHz where the value of capacitance C stabilizes is ｒ In addition, S represents the electrode area, and d represents the film thickness of the piezoelectric layer 5. In the examples of Table 1, the film thickness of the piezoelectric layer 5 ranged from 400 nm to 1000 nm.

[0054] (Effects of First Embodiment) In the first embodiment, the following effects can be obtained.

[0055] As described above, the first embodiment includes the seed layer 2 containing zirconium oxide formed by epitaxial growth on the substrate 1, the lower electrode layer 3 containing at least one of iridium and platinum formed by epitaxial growth on the seed layer 2, the adjustment layer 4 containing a metal oxide having a perovskite structure formed by epitaxial growth on the lower electrode layer 3, and the piezoelectric layer 5 made of bismuth ferrite with a (100) preferred orientation on the adjustment layer 4. As a result, the seed layer 2, the lower electrode layer 3, and the adjustment layer 4 are each formed in this order by epitaxial growth, so that the piezoelectric layer 5 made of bismuth ferrite can be formed with a (100) preferred orientation on the adjustment layer 4 with good crystal orientation formed by epitaxial growth in this order on the substrate 1. Therefore, by forming a film on the adjustment layer 4 with good crystal orientation, it is possible to form the piezoelectric layer 5 made of bismuth ferrite with good piezoelectric properties without having to carefully set conditions such as temperature during film formation. As a result, the piezoelectric layer 5 made of bismuth ferrite can be easily formed.

[0056] Furthermore, in the first embodiment, as described above, the piezoelectric layer 5 is made of bismuth ferrite formed by epitaxial growth on the adjustment layer 4. This allows the piezoelectric layer 5 made of bismuth ferrite to be formed by epitaxial growth on the adjustment layer 4, which has good crystal orientation and is formed by epitaxial growth on the substrate 1. Therefore, the piezoelectric layer 5 made of bismuth ferrite, which exhibits better piezoelectric properties, can be formed by epitaxial growth without having to carefully set conditions such as temperature during film formation.

[0057] Furthermore, in the first embodiment, as described above, the seed layer 2 contains yttria-stabilized zirconia as zirconium oxide. This stabilizes the crystal structure of the seed layer 2 by containing stabilized zirconia (zirconium oxide). Therefore, the crystal structure of the seed layer 2 is stabilized, and the crystal orientation of the lower electrode layer 3 formed on the seed layer 2 can be further improved. As a result, a lower electrode layer 3 with better crystal orientation can be formed, and the piezoelectric layer 5 made of bismuth ferrite can be more easily formed.

[0058] Furthermore, in the first embodiment, as described above, the lower electrode layer 3 includes an iridium layer 3 a formed on the seed layer 2 and a platinum layer 3 b formed on the iridium layer 3 a. Thus, by forming the platinum layer 3 b on the iridium layer 3 a formed on the seed layer 2, it is possible to easily form the platinum layer 3 b epitaxially grown so as to follow the crystal orientation of the seed layer 2. Therefore, it is possible to easily form the lower electrode layer 3 epitaxially grown with an aligned crystal orientation.

[0059] Furthermore, in the first embodiment, as described above, the adjustment layer 4 contains strontium and ruthenium. Thus, by forming the adjustment layer 4 from a metal oxide containing strontium and ruthenium, it is possible to improve the crystal orientation of the piezoelectric layer 5 containing bismuth ferrite formed on the adjustment layer 4. Furthermore, because the metal oxide containing strontium and ruthenium is a relatively stable substance, processing can be easily carried out when producing a device such as a piezoelectric element using the produced piezoelectric film.

[0060] Furthermore, in the first embodiment, as described above, the piezoelectric layer 5 has a relative dielectric constant of 150 or less in a frequency band of 1 kHz or more. Here, the figure of merit of a piezoelectric thin film is expressed as the value obtained by dividing the square of the piezoelectric constant (piezoelectric stress constant) by the dielectric constant. Therefore, by configuring the piezoelectric layer 5 to have a relative dielectric constant of 150 or less in a frequency band of 1 kHz or more, as in the first embodiment, a piezoelectric layer 5 with a sufficiently small relative dielectric constant and a good figure of merit can be obtained.

[0061] Furthermore, in the manufacturing method of the piezoelectric film substrate 100 according to the first embodiment, as described above, the step of forming the piezoelectric layer 5 (step S5) includes a step of forming the piezoelectric layer 5 while heating the substrate 1 on which the adjustment layer 4 has been formed at a temperature of 400° C. or higher and 500° C. or lower. Here, because the adjustment layer 4 with good crystal orientation is formed by epitaxial growth, the piezoelectric layer 5 made of bismuth ferrite exhibiting piezoelectricity can be formed even when the film is formed at a wider temperature range of 400° C. or higher and 500° C. or lower. Therefore, the appropriate temperature range during film formation can be set to a wider temperature range of 400° C. or higher and 500° C. or lower, making it easier to form the piezoelectric layer 5 made of bismuth ferrite.

[0062] Furthermore, in the manufacturing method of the piezoelectric film substrate 100 according to the first embodiment, as described above, the step of forming the piezoelectric layer 5 (step S5) includes a step of forming the piezoelectric layer 5 made of bismuth ferrite by sputtering while the substrate 1 is heated at a temperature of 400° C. or higher and 500° C. or lower. This allows the piezoelectric layer 5 made of bismuth ferrite to be formed by sputtering while the temperature of the substrate 1 is kept in a wider range of 400° C. or higher and 500° C. or lower, making it possible to set the sputtering conditions for forming the piezoelectric layer 5 relatively easily.

[0063] [Second Embodiment] Next, the configuration of a piezoelectric film substrate 200 according to a second embodiment will be described with reference to Fig. 10. In the second embodiment, unlike the first embodiment in which the adjustment layer 4 contains strontium and ruthenium, the adjustment layer 204 contains lanthanum and nickel. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted.

[0064] As shown in FIG. 10 , in the second embodiment, the piezoelectric film substrate 200 includes an adjustment layer 204. The adjustment layer 204 includes a metal oxide having a perovskite structure, similar to the adjustment layer 4 in the first embodiment. In the second embodiment, the adjustment layer 204 includes lanthanum (La) and nickel (Ni) as metal elements. Specifically, the adjustment layer 204 is made of lanthanum nickelate (LaNiO) containing lanthanum and nickel. ３ The adjustment layer 204 is formed of lanthanum nickel oxide (LNO). The lanthanum nickel oxide of the adjustment layer 204 has a perovskite structure, with lanthanum located at the A site and nickel located at the B site of the perovskite structure. The adjustment layer 204 adjusts the crystal orientation of the piezoelectric layer 5, similar to the adjustment layer 4.

[0065] Similarly to the adjustment layer 4 of the first embodiment, the adjustment layer 204 is formed on the substrate 1 by epitaxial growth on the lower electrode layer 3. That is, the adjustment layer 204 is composed of single-crystal lanthanum nickelate formed by epitaxial growth. Similar to the seed layer 2 and the lower electrode layer 3, the adjustment layer 204 is a single-crystal crystalline film grown with its crystal axes aligned both in the direction perpendicular to the main surface of the substrate 1 and in the in-plane direction of the main surface of the substrate 1. The adjustment layer 204 is formed, for example, by sputtering while the substrate 1 is heated to a temperature of several hundred degrees Celsius so that the resulting crystals grow epitaxially. The adjustment layer 204 is formed as a crystalline film with a (100) crystal orientation by cube-on-cube epitaxial growth.

[0066] Other configurations of the second embodiment are the same as those of the first embodiment. That is, in the second embodiment, the piezoelectric layer 5 is made of bismuth ferrite (BiFeO ３ It is composed of: BFO.

[0067] [Effects of the Second Embodiment] In the second embodiment, as described above, the adjustment layer 204 contains lanthanum and nickel. Thus, by forming the adjustment layer 204 from a metal oxide containing lanthanum and nickel, it is possible to improve the crystal orientation of the piezoelectric layer 5 containing bismuth ferrite formed on the adjustment layer 204. Furthermore, since a metal oxide containing lanthanum and nickel is a relatively unstable substance and easily reacts with other substances, the adjustment layer 204 can be easily etched. Other effects of the second embodiment are similar to those of the first embodiment.

[0068] 11 and 12, the configuration of a piezoelectric film substrate 300 according to a third embodiment will be described. In the third embodiment, manganese is added to the bismuth ferrite that constitutes the piezoelectric layer 305. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0069] As shown in FIG. 11 , the piezoelectric film substrate 300 of the third embodiment includes a piezoelectric layer 305. The piezoelectric layer 305 is a bismuth ferrite (BiFeO ) layer formed on the adjustment layer 4 by epitaxial growth, similar to the piezoelectric layer 5 of the first embodiment. ３ In the third embodiment, the piezoelectric layer 305 is made of bismuth ferrite with manganese (Mn) added thereto.

[0070] As shown in FIG. 12 , in the third embodiment, the piezoelectric layer 305 is formed by sputtering using the sputtering apparatus 101, as in the first embodiment. In the third embodiment, the piezoelectric layer 305 is formed of manganese-doped bismuth ferrite by sputtering using a target member 302 containing bismuth (Bi) and iron (Fe) as well as manganese. The manganese-doped bismuth ferrite is crystallized in a state in which some of the iron located at the B site of the perovskite structure shown in FIG. 3 is replaced with manganese. In the third embodiment, as in the first embodiment, the substrate 1 on which the adjustment layer 4 has been formed is heated to a temperature of 400° C. or higher and 500° C. or lower by the heating device 12, and the piezoelectric layer 305 is formed by sputtering. Like the piezoelectric layer 5, the piezoelectric layer 305 is formed as a single-crystal crystalline film having a (100) crystal orientation by cube-on-cube epitaxial growth.

[0071] (Example of Third Embodiment) Next, with reference to FIGS. 13 to 16, the crystal orientation of the piezoelectric layer 305 in the piezoelectric film substrate 300 according to an example of the third embodiment will be described.

[0072] As shown in Fig. 13, when the manganese-added piezoelectric layer 305 was deposited with the substrate 1 heated to 400°C, the degree of (100) orientation (angle) was increased. That is, when the manganese-added piezoelectric layer 305 was deposited with the substrate 1 heated to 400°C, a diffraction peak was detected at an angle corresponding to the (100) crystal orientation, confirming that the piezoelectric layer 305 was formed with a (100) preferred orientation. Then, as shown in Fig. 14, when the manganese-added piezoelectric layer 305 was deposited with the substrate 1 heated to 400°C, the degree of the same angle (orientation) as the orientation of the single-crystal silicon of the substrate 1 was increased. That is, similarly to the first embodiment, when manganese is added, and the orientation of the piezoelectric layer 305 is measured by X-ray diffraction, a diffraction peak is detected at an angle indicating the (100) direction of the single crystal silicon of the substrate 1, and the piezoelectric layer 305 made of single crystal bismuth ferrite to which manganese has been added is formed by cube-on-cube epitaxial growth in a state having the same crystal orientation as the orientation of the single crystal silicon of the substrate 1.

[0073] 15 , when the piezoelectric layer 305 to which manganese was added was formed while the temperature of the substrate 1 was heated to 500° C., the degree of (100) orientation (angle) was also increased, as in the case of heating to 400° C. That is, when the piezoelectric layer 305 to which manganese was added was formed while the temperature of the substrate 1 was heated to 500° C., a diffraction peak was detected at an angle corresponding to the (100) crystal orientation, confirming that the piezoelectric layer 305 was formed with a (100) preferred orientation. Therefore, in the third embodiment, similar to the first embodiment, the piezoelectric layer 305 is formed of bismuth ferrite formed with a (100) preferred orientation when the temperature of the substrate 1 is in the range of 400° C. or higher and 500° C. or lower. 16 , when the piezoelectric layer 305 made of manganese-doped bismuth ferrite according to the third embodiment was formed with the substrate 1 heated to 500° C., the degree of the same angle (orientation) as the orientation of the single crystal silicon of the substrate 1 increased, as in the case of heating to 400° C. As shown in FIG. 16 , even when heated to 500° C., a diffraction peak was detected at an angle indicating the (100) direction of the single crystal silicon of the substrate 1, confirming that the piezoelectric layer 305 made of manganese-doped single crystal bismuth ferrite was formed by cube-on-cube epitaxial growth in a state having the same crystal orientation as the orientation of the single crystal silicon of the substrate 1. That is, in the third embodiment, the piezoelectric layer 305 made of bismuth ferrite was formed by epitaxial growth at a temperature range of 400° C. to 500° C., as in the first embodiment.

[0074] <Relative dielectric constant> With reference to Table 2 below, the relative dielectric constant ε of the piezoelectric film substrate 300 according to the third embodiment is ｒ As shown in Table 2, in the third embodiment, similarly to the first embodiment, when the temperature of the substrate 1 during the deposition of the piezoelectric layer 305 was heated to 400° C. and when the temperature was heated to 500° C., the piezoelectric layer 305 had a relative dielectric constant ε of 150 or less in a frequency band of 1 kHz or more. ｒ It has the following characteristics. In the third embodiment, the relative dielectric constant ε is calculated by the formula (1) in the same way as in the first embodiment. ｒ In the example of Table 2, the relative dielectric constant ε measured at 100 kHz where the value of the capacitance C is stable is also calculated. ｒ The film thickness of the piezoelectric layer 305 was in the range of 400 nm to 1000 nm.

[0075] The other configurations of the third embodiment are similar to those of the first embodiment.

[0076] [Effects of the Third Embodiment] In the third embodiment, as described above, the piezoelectric layer 305 is made of bismuth ferrite to which manganese has been added. Thus, by adding manganese to bismuth ferrite, the properties of the bismuth ferrite as a piezoelectric material can be improved. Therefore, by adding manganese, it is possible to effectively and easily form the piezoelectric layer 305 made of bismuth ferrite whose properties as a piezoelectric material have been improved. Other effects of the third embodiment are similar to those of the first embodiment.

[0077] (Modifications) The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above-mentioned embodiments, and includes all modifications (modifications) within the meaning and scope of the claims.

[0078] For example, in the first to third embodiments, the seed layer 2, the lower electrode layer 3, the adjustment layer 4 (204), the piezoelectric layer 5 (305), and the upper electrode layer 6 are each formed by sputtering. However, the present invention is not limited to this. In the present invention, any of the seed layer, the lower electrode layer, the adjustment layer, the piezoelectric layer, and the upper electrode layer may be formed by a method other than sputtering. For example, any of the seed layer, the lower electrode layer, the adjustment layer, the piezoelectric layer, and the upper electrode layer may be formed by vacuum deposition, PLD (pulsed laser deposition), CVD (chemical vapor deposition), a sol-gel method, or the like. Note that when any of the seed layer, the lower electrode layer, the adjustment layer, the piezoelectric layer, and the upper electrode layer is formed by sputtering, the sputtering method is not limited, and may include DC sputtering, RF sputtering, magnetron sputtering, ECR plasma sputtering, and ion beam sputtering. Furthermore, the type of gas used for sputtering is not limited.

[0079] Furthermore, in the first to third embodiments, examples have been shown in which the lower electrode layer 3 includes an iridium layer 3a and a platinum layer 3b, but the present invention is not limited to this. In the present invention, the lower electrode layer may be configured to include either platinum or iridium. Alternatively, the lower electrode layer may be configured from an alloy of platinum and iridium. Alternatively, elements other than platinum and iridium may be added to the lower electrode layer.

[0080] Furthermore, in the first to third embodiments, examples were shown in which the adjustment layer 4 contained strontium and ruthenium, or lanthanum and nickel, but the present invention is not limited to this. In the present invention, the adjustment layer may be configured to contain a metal element other than strontium, ruthenium, lanthanum, and nickel. Furthermore, the adjustment layer may not have the function of adjusting the crystal orientation of the piezoelectric layer. Furthermore, the adjustment layer may be multi-layered.

[0081] In the first to third embodiments, the seed layer 2 contains yttria-stabilized zirconia as zirconium oxide, but the present invention is not limited to this. In the present invention, the seed layer may contain zirconium oxide (ZrO ２ The seed layer may be made of zirconium oxide to which an element other than yttrium is added.

[0082] In the first to third embodiments, the piezoelectric layer 5 (305) has a relative dielectric constant of 150 or less in a frequency band of 1 kHz or more, but the present invention is not limited to this. In the present invention, the piezoelectric layer may have a relative dielectric constant of more than 150 in a frequency band of 1 kHz or more.

[0083] Furthermore, in the first to third embodiments, an example was shown in which the piezoelectric layer 5 (305) made of bismuth ferrite was formed while the substrate 1 was heated to a temperature of 400°C or higher and 500°C or lower, but the present invention is not limited to this. In the present invention, the piezoelectric layer made of bismuth ferrite may be formed while the substrate is heated to a temperature higher than 500°C. Note that, if the substrate temperature is high during film formation, the thermal load on the film formation apparatus increases, so the substrate temperature during film formation is preferably 500°C or lower. Furthermore, if film formation is performed while the substrate is heated to 550°C or higher, excessive iron oxide may be precipitated, which may cause problems such as current leakage, so the substrate temperature is preferably lower than 550°C.

[0084] Furthermore, in the first to third embodiments, examples have been shown in which the seed layer 2, the lower electrode layer 3, the adjustment layer 4 (204), the piezoelectric layer 5 (305), and the upper electrode layer 6 are each formed by cube-on-cube epitaxial growth, but the present invention is not limited to this. In the present invention, any of the seed layer, the lower electrode layer, the adjustment layer, the piezoelectric layer, and the upper electrode layer may be formed by epitaxial growth other than cube-on-cube. For example, any of the seed layer, the lower electrode layer, the adjustment layer, the piezoelectric layer, and the upper electrode layer may be epitaxially grown with its orientation rotated 45 degrees relative to the underlying layer.

[0085] In the first to third embodiments, the thickness of the piezoelectric layer 5 (305) is 400 nm to 1000 nm, but the present invention is not limited to this. In the present invention, the thickness of the piezoelectric layer may be less than 400 nm or greater than 1000 nm.

[0086] In the third embodiment, the piezoelectric layer 305 is made of bismuth ferrite doped with manganese, but the present invention is not limited to this. In the present invention, the piezoelectric layer may be made of bismuth ferrite doped with a metal element other than manganese. In this case, the bismuth ferrite may be substituted for the bismuth located at the A site of the perovskite structure, or the iron located at the B site may be substituted for the bismuth ferrite.

[0087] Furthermore, in the first to third embodiments, examples have been shown in which the piezoelectric layer 5 (305) is made of bismuth ferrite formed by epitaxial growth, but the present invention is not limited to this. In the present invention, the piezoelectric layer may be made of bismuth ferrite with a preferred orientation on an adjustment layer. That is, the piezoelectric layer may be made of polycrystalline bismuth ferrite with a (100) preferred orientation, rather than single-crystal bismuth ferrite. When the piezoelectric layer is made of bismuth ferrite with a (100) preferred orientation, a film is formed in which the crystal axis is aligned in a direction perpendicular to the main surface of the substrate.

[0088] REFERENCE SIGNS LIST 1 substrate 2 seed layer 3 lower electrode layer 3a iridium layer 3b platinum layer 4, 204 adjustment layer 5, 305 piezoelectric layer 6 upper electrode layer 100, 200, 300 piezoelectric film substrate

Claims

1. A piezoelectric film substrate comprising: a substrate made of (100) silicon single crystal; a seed layer containing zirconium oxide formed on the substrate by epitaxial growth; a lower electrode layer containing at least one of iridium and platinum formed on the seed layer by epitaxial growth; an adjustment layer containing a metal oxide having a perovskite structure formed on the lower electrode layer by epitaxial growth; a piezoelectric layer composed of bismuth ferrite with a (100) preferred orientation on the adjustment layer; and an upper electrode layer.

2. The piezoelectric film substrate according to claim 1, wherein the piezoelectric layer is made of bismuth ferrite formed on the adjustment layer by epitaxial growth.

3. The piezoelectric film substrate according to claim 1 or 2, wherein the seed layer contains yttria-stabilized zirconia as zirconium oxide.

4. The piezoelectric film substrate according to claim 1 or 2, wherein the lower electrode layer includes an iridium layer formed on the seed layer and a platinum layer formed on the iridium layer.

5. The piezoelectric film substrate according to claim 1 or 2, wherein the adjustment layer contains strontium and ruthenium.

6. The piezoelectric film substrate according to claim 1 or 2, wherein the adjustment layer contains lanthanum and nickel.

7. The piezoelectric film substrate according to claim 1 or 2, wherein the piezoelectric layer is made of bismuth ferrite to which manganese has been added.

8. The piezoelectric film substrate according to claim 1 or 2, wherein the piezoelectric layer has a relative dielectric constant of 150 or less in a frequency band of 1 kHz or more.

9. A method for manufacturing a piezoelectric film substrate, comprising the steps of: forming a seed layer containing zirconium oxide by epitaxial growth on a substrate made of (100) silicon single crystal; forming a lower electrode layer containing at least one of iridium and platinum by epitaxial growth on the seed layer; forming an adjustment layer containing a metal oxide having a perovskite structure by epitaxial growth on the lower electrode layer; forming a piezoelectric layer composed of (100) preferentially oriented bismuth ferrite on the adjustment layer; and forming an upper electrode layer.

10. A method for manufacturing a piezoelectric film substrate as described in claim 9, wherein the step of forming the piezoelectric layer includes a step of forming the piezoelectric layer while heating the substrate on which the adjustment layer is formed at a temperature of 400°C or higher and 500°C or lower.

11. A method for manufacturing a piezoelectric film substrate as described in claim 10, wherein the step of forming the piezoelectric layer includes a step of forming the piezoelectric layer made of bismuth ferrite by sputtering while heating the substrate at a temperature of 400°C or higher and 500°C or lower.

Images