Piezoelectric laminates and piezoelectric chips

Abstract

To obtain a piezoelectric laminate and a piezoelectric element that have both high piezoelectric constant and high withstand voltage.SOLUTION: In a piezoelectric laminate and a piezoelectric element including a lower electrode layer and a piezoelectric film in this order on a substrate, the piezoelectric film includes a perovskite oxide, and the piezoelectric film includes a first region in which the perovskite oxide is mainly composed of a first perovskite crystal in which a first angle between a (100) plane orientation or a (001) plane orientation and the normal direction to the plane of the substrate is 5° or more and 30° or less, and a second region that is provided between the first region and the lower electrode layer and in which the perovskite oxide is mainly composed of a second perovskite crystal in which a second angle between the (100) plane orientation or the (001) plane orientation of the perovskite oxide and the normal direction is less than 5°, and the thickness of the second region is 30 nm or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to piezoelectric laminates and piezoelectric elements. [Background technology]

[0002] Perovskite oxides such as lead zirconate titanate (Pb(Zr,Ti)O3, hereinafter referred to as PZT) are known as materials with excellent piezoelectric and ferroelectric properties. Piezoelectric materials made of perovskite oxides are used as piezoelectric films in piezoelectric elements that have a lower electrode, a piezoelectric film, and an upper electrode on a substrate. These piezoelectric elements are being developed into a variety of devices, including memory, inkjet heads (actuators), micromirror devices, angular velocity sensors, gyro sensors, ultrasonic elements (PMUT: Piezoelectric Micromachined Ultrasonic Transducer), and vibration power generation devices.

[0003] When applying piezoelectric elements to devices, higher piezoelectric properties lead to power savings, therefore, it is desirable for the piezoelectric element to have high piezoelectric properties.

[0004] Patent documents 1 and 2 propose stacking PZT in which the crystal axis is tilted by 5° or more from the normal direction of the substrate surface in order to obtain a high piezoelectric constant. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-307833 [Patent Document 2] Japanese Patent Publication No. 2011-181828 [Overview of the project] [Problems that the invention aims to solve]

[0006] As shown in Patent Documents 1 and 2, PZT films with tilted crystal axes can achieve high piezoelectric constants. On the other hand, our research has revealed that PZT films with crystal axes tilted by 5° or more have a lower dielectric strength compared to PZT films with crystal axes perpendicular to the substrate surface.

[0007] The technology disclosed herein has been made in view of the above circumstances, and aims to provide a piezoelectric laminate and piezoelectric element that achieve both a high piezoelectric constant and a high dielectric strength. [Means for solving the problem]

[0008] The following embodiments are included as specific means for solving the above problems.

[0009] The piezoelectric laminate of this disclosure is a piezoelectric laminate comprising a lower electrode layer and a piezoelectric film on a substrate in this order, wherein the piezoelectric film contains a perovskite-type oxide, and the piezoelectric film comprises a first region mainly composed of a first perovskite crystal in which the perovskite-type oxide has a first angle between the (100) plane orientation or (001) plane orientation and the normal direction of the substrate surface of 5° or more and 30° or less, and a second region provided between the first region and the lower electrode layer, mainly composed of a second perovskite crystal in which the perovskite-type oxide has a second angle between the (100) plane orientation or (001) plane orientation and the normal direction of the substrate of less than 5°, and the thickness of the second region is 30 nm or more.

[0010] In the piezoelectric laminate of this disclosure, it is preferable that the first angle in the first region of the piezoelectric film is 5° or more and 15° or less.

[0011] In the piezoelectric laminate of this disclosure, it is preferable that the piezoelectric film between the first region and the second region is substantially parallel to the substrate and does not have a grain boundary caused by lamination.

[0012] In the piezoelectric laminate of this disclosure, the piezoelectric film is preferably a sputtered film.

[0013] In the piezoelectric laminate of the present disclosure, it is preferable that the thickness of the first region of the piezoelectric film is 1 μm or more.

[0014] In the piezoelectric laminate of the present disclosure, in the first perovskite crystal in the first region, it is preferable that the plane orientation forming a first angle with the normal direction is the (100) plane orientation.

[0015] In the piezoelectric laminate of the present disclosure, it is preferable that the first perovskite crystal in the first region is a rhombohedral crystal.

[0016] In the piezoelectric laminate of the present disclosure, the perovskite-type oxide is represented by the general formula ABO3, where A is the A-site element, B is the B-site element, and O is the oxygen element. It is preferable that the main component of the A-site element is Pb.

[0017] In the piezoelectric laminate of the present disclosure, the perovskite-type oxide is a compound represented by the following general formula (1). Pb{(Zr x Ti 1-x ) 1-y B1 y}O3(1) 0 < x < 1, 0 < y < 0.4, It is preferable that B1 is one or more elements selected from V, Nb, Ta, Sb, Mo, and W.

[0018] In the piezoelectric laminate of the present disclosure, it is preferable that the Pb composition ratio in the second region is larger than the Pb composition ratio in the first region.

[0019] The piezoelectric element of the present disclosure includes the piezoelectric laminate of the present disclosure and an upper electrode layer provided on the piezoelectric film of the piezoelectric laminate.

Advantages of the Invention

[0020] According to the piezoelectric laminate and the piezoelectric element of the present disclosure, a high piezoelectric constant and a high withstand voltage can be achieved simultaneously.

Brief Description of the Drawings

[0021] [Figure 1] This is a cross-sectional view showing the layer configuration of a piezoelectric element according to one embodiment. [Figure 2] This is an explanatory diagram of the orientation state of the piezoelectric film. [Figure 3] This is a schematic diagram of the rocking curve of the first region of a piezoelectric film. [Figure 4] This is a schematic diagram of the rocking curve in the second region of a piezoelectric film. [Figure 5] This is the XRD chart for Example 2. [Figure 6] This is the rocking curve of the first region in Example 2. [Figure 7] This is the rocking curve of the second region in Example 2. [Modes for carrying out the invention]

[0022] Embodiments of the present invention will be described below with reference to the drawings. Note that, for ease of viewing, the layer thicknesses and their ratios in the following drawings have been modified as appropriate and do not necessarily reflect the actual layer thicknesses and ratios.

[0023] Figure 1 is a schematic cross-sectional view showing the layer structure of the piezoelectric laminate 5 and the piezoelectric element 1 equipped with the piezoelectric laminate 5 according to the first embodiment, and Figure 2 is a schematic diagram showing the orientation state of the piezoelectric film 15. As shown in Figure 1, the piezoelectric element 1 comprises a piezoelectric laminate 5 and an upper electrode layer 18. The piezoelectric laminate 5 comprises a substrate 10 and a lower electrode layer 12 and a piezoelectric film 15 containing a perovskite-type oxide laminated on the substrate 10. Here, "lower" and "upper" do not mean up and down in the vertical direction, but rather the electrodes arranged on the substrate 10 side with respect to the piezoelectric film 15 are called the lower electrode layer 12 and the electrodes arranged on the side opposite to the substrate 10 with respect to the piezoelectric film 15 are called the upper electrode layer 18.

[0024] The piezoelectric film 15 contains a perovskite-type oxide. In this specification, "contains a perovskite-type oxide" means that 80 mol% or more of the piezoelectric film 15 is a perovskite-type oxide. Preferably, the piezoelectric film 15 contains 90 mol% or more of a perovskite-type oxide. Furthermore, it is preferable that the piezoelectric film 15 consists of a perovskite-structured oxide (however, it contains unavoidable impurities).

[0025] The piezoelectric film 15 includes a first region 15a which forms the main part, and a second region 15b provided between the first region 15a and the lower electrode layer 12. Note that other layers, such as an orientation control layer, may be provided between the lower electrode layer 12 and the second region 15b.

[0026] As shown in Figure 2, the first region 15a mainly consists of a first perovskite crystal 17A in which the perovskite-type oxide constituting the first region 15a has a first angle α between the (100) or (001) plane orientation indicated by arrow A and the normal direction N of the surface 10a of the substrate 10 (hereinafter referred to as substrate surface a), which is 5° or more and 30° or less. Preferably, the first angle α is 5° or more and 15° or less.

[0027] As shown in Figure 2, the second region 15b mainly consists of a second perovskite crystal 17B in which the angle β between the (100) or (001) plane orientation indicated by arrow B and the normal direction N of the substrate surface 10a of the perovskite-type oxide constituting the second region 15b is 5° or less. The thickness tb of this second region 15b (see Figure 1) is 30 nm or more, and more preferably 100 nm or more and 500 nm or less. Note that the angle β may be 0°, in which case the (100) or (001) plane orientation is parallel to the normal direction N.

[0028] (100) Plane orientation is the normal direction of the (100) plane, <100> It means direction. Similarly, the (001) plane orientation is the normal direction of the (001) plane, <001> It indicates direction.

[0029] A first perovskite crystal 17A in which the first angle α between the (100) plane orientation and the normal direction N of the substrate surface 10a is 5° or more and 30° or less is a perovskite crystal with (100) plane preference orientation, i.e., a-axis orientation, in which the inclination angle of the a-axis from the normal direction is 5° or more and 30° or less. Similarly, a first perovskite crystal 17A in which the first angle α between the (001) plane orientation and the normal direction N of the substrate surface 10a is 5° or more and 30° or less is a perovskite crystal with (001) plane preference orientation, i.e., c-axis orientation, in which the inclination angle of the c-axis from the normal direction is 5° or more and 30° or less. If the first perovskite crystal 17A is (100) preferred orientation, arrow A in Figure 2 represents the (100) plane orientation, i.e., the a-axis. If the first perovskite crystal 17A is (001) preferred orientation, arrow A in Figure 2 represents the (001) plane orientation, i.e., the c-axis. Hereafter, arrow A will be referred to as crystal axis A. It is more preferable that the (100) plane orientation of the first perovskite crystal 17A has an inclination of a first angle α with respect to the normal direction N, i.e., a-axis orientation.

[0030] A second perovskite crystal 17B in which the second angle β between the (100) plane orientation and the normal direction N of the substrate surface 10a is less than 5° is a perovskite crystal with (100) plane preference orientation, i.e., a-axis orientation, and the inclination angle of the a-axis from the normal direction is less than 5°. Similarly, a second perovskite crystal 17B in which the second angle β between the (001) plane orientation and the normal direction N of the substrate surface 10a is less than 5° is a perovskite crystal with (001) plane preference orientation, i.e., c-axis orientation, and the inclination angle of the c-axis from the normal direction is less than 5°. When the second perovskite crystal 17B has (100) preference orientation, arrow B in Figure 2 represents the a-axis, and when the second perovskite crystal 17B has (001) preference orientation, arrow B in Figure 2 represents the c-axis. In the following, arrow B will be referred to as crystal axis B.

[0031] In this embodiment, the piezoelectric film 15 is composed of a number of columnar crystal grains 17 extending in the thickness direction, as shown in Figure 2. Even if the crystal grains 17 extend from the first region 15a to the second region 15b, as shown in Figure 2, the first region 15a mainly consists of a first perovskite crystal 17A in which the crystal axis A is tilted at a first angle α from the normal direction N, and the second region 15b mainly consists of a second perovskite crystal 17B in which the crystal axis B is tilted at a second angle β from the normal direction N.

[0032] As shown in Figure 2, it is preferable that the boundary AB between the first region 15a and the second region 15b in the piezoelectric film 15 does not have a clear grain boundary.

[0033] (100) plane-preferential orientation or (001) plane-preferential orientation means that, in the XRD (X-ray diffraction) chart, no other peaks attributable to the perovskite structure are observed between the (100) peak and the (200) peak, or between the (001) peak and the (002) peak, or, if other peaks attributable to the perovskite structure are present, the (100), (001), (200), or (002) peak is the largest.

[0034] Furthermore, if the perovskite crystal is rhombohedral, the (100) plane and the (001) plane are equivalent and indistinguishable. On the other hand, even if the perovskite crystal is tetragonal, if the lattice constants of the a-axis and c-axis are close, the 2θ positions of the (100) peak and the (001) peak will approximately coincide in a normal XRD analysis using a Cu (copper) tube and characteristic X-ray CuKα, making it difficult to distinguish between the two. Nevertheless, it is possible to confirm whether the orientation is (100) plane-preferential or (001) plane-preferential from the XRD chart obtained by a normal XRD measurement.

[0035] Perovskite structures can be tetragonal, orthorhombic, monoclinic, trigonal, or rhombohedral. In the piezoelectric laminate 5 and piezoelectric element 1 of this embodiment, the first perovskite crystal 17A is preferably tetragonal, rhombohedral, or a mixed crystal of tetragonal and rhombohedral crystals, and is particularly preferably rhombohedral. Piezoelectric perovskite oxides are said to exhibit high piezoelectric constants at and near the morphotropic phase boundary (MPB). For example, in PZT, a composition with a molar ratio of Zr / Ti = 52 / 48 is the MPB composition, and it is said that the piezoelectric constant is highest at this composition. In MPB, it is a mixed crystal of tetragonal and rhombohedral crystals, and it is said to be tetragonal when Zr / Ti < 0.52 and rhombohedral when Zr / Ti > 0.52.

[0036] Furthermore, whether a perovskite crystal is rhombohedral, tetragonal with (100)-preferential orientation, or tetragonal with (001)-preferential orientation can be determined from the XRD peak angles. When using a normal CuKα X-ray source, if the perovskite oxide is PZT and the perovskite crystal is rhombohedral, a single (200) peak occurs around 2θ = 44.5°. On the other hand, if the perovskite oxide is PZT and tetragonal, a (002) peak occurs around 44.8° and another (002) peak occurs around 45.5°. However, separation is difficult because the peak angles are close. For example, by performing higher-resolution XRD analysis using synchrotron radiation, the aforementioned peaks can be separated, and rhombohedral, (100)-preferentially oriented tetragonal, and (001)-preferentially oriented tetragonal crystals can be distinguished.

[0037] The thickness t of the piezoelectric film 15 is, for example, 0.2 μm to 5 μm, but is preferably 1 μm or more. Furthermore, it is preferable that the thickness ta of the first region 15a of the piezoelectric film 15 is 1 μm or more.

[0038] The thickness t of the piezoelectric film 15 can be estimated from the cross-sectional TEM image. The thickness t of the piezoelectric film 15 is the distance between the interface of the piezoelectric film 15 and two adjacent layers, in this example, the lower electrode layer 12 and the upper electrode layer 18. The method for measuring the thickness ta of the first region 15a and the thickness tb of the second region 15b of the piezoelectric film 15 will be described later.

[0039] The first angle α and the second angle β between the (100) or (001) plane orientation of the perovskite structure and the normal direction N of the substrate surface 10a are defined by values ​​calculated by rocking curve measurement using X-ray diffraction. Specifically, the first angle α is calculated from the split width of the (100) or (001) diffraction peak or the diffraction peak associated with (100) or (001) with respect to the first region 15a (see Example). Similarly, the second angle β is calculated from the split width of the (100) or (001) diffraction peak or the diffraction peak associated with (100) or (001) in the second region 15b (see Example). The diffraction peak associated with (100) or (001) is, for example, the (200) or (002) diffraction peak.

[0040] Figure 3 schematically shows the intensity profile A with respect to angle ω obtained when rocking curve measurement is performed on the first perovskite crystal 17A. Figure 4 schematically shows the intensity profiles B1 and B2 with respect to angle ω obtained when rocking curve measurement is performed on the second perovskite crystal 17B. In Figures 3 and 4, examples of rocking curves relating to the (200) or (002) diffraction peak that occurs at ω = 22.5° (hereinafter referred to as the reference position) are schematically shown for a perovskite crystal in which the crystal axis (a-axis or c-axis) is parallel to the normal direction N of the substrate surface 10a.

[0041] When the crystal axis is tilted with respect to the normal direction N, a peak appears in the rocking curve at a position shifted from the reference position. The difference in angle between the reference position and the peak position corresponds to the tilt angle of the (100) plane orientation or (001) plane orientation with respect to the normal direction N.

[0042] As shown in Figure 2, in the first perovskite crystal 17A, the crystal axis A is tilted at a first angle α with respect to the normal direction N. Therefore, in profile A of the rocking curve shown in Figure 3, peaks PA1 and PA2 are generated at positions more than 5° away from the reference position. Note that, as shown in Figure 2, the direction in which the crystal axis A is tilted is random, so in profile A, there are peaks PA1 and PA2 on the low-angle side and high-angle side, respectively, with respect to the reference position. Generally, the diffraction intensity is higher on the low-angle side, so peak PA1 is more intense than peak PA2. The first angle α is the angle difference between peak PA1, which is the highest of the two intensity peaks, and the reference position.

[0043] In the second perovskite crystal 17B, the crystal axis B is tilted at a second angle β with respect to the normal direction N. When the second angle β is 0°, that is, when the crystal axis B is parallel to the normal direction N, the rocking curve has a single peak PB0, as shown in profile B1 in Figure 4, and peak PB0 approximately coincides with the reference position. When the second angle β is greater than 0° and less than 5°, the rocking curve produces peaks PB1 and PB2 at positions less than 5° away from the reference position, as shown in profile B2 in Figure 4. Here again, the second angle β is the angle difference between peak PB1, which is the largest of the two peaks, and the reference position.

[0044] As shown in Figures 3 and 4, a first perovskite crystal 17A having a crystal axis A tilted at a first angle α and a second perovskite crystal 17B having a crystal axis B tilted at a second angle β can be distinguished by rocking curve measurement. In the piezoelectric film 15, the boundary between the first region 15a and the second region 15b is determined by repeatedly polishing the surface of the piezoelectric film 15 and measuring the rocking curve on the polished and exposed surface. When rocking curve measurement is performed on the actual piezoelectric film 15, the profile may show not only a single peak or two peaks, but also three or more peaks. In the profile obtained by rocking curve measurement, if there are multiple peaks, the angle difference between the largest peak and the reference position is defined as the angle between the crystal axis of the perovskite crystal and the normal direction N on the exposed surface where the rocking curve measurement was performed. If this angle is 5° or greater, the crystal constituting the exposed surface is considered to be mainly composed of the first perovskite crystal 17A, and the thickness position of the exposed surface is considered to be the first region 15a. On the other hand, if this angle is less than 5°, the crystal constituting the exposed surface is considered to be mainly composed of the second perovskite crystal 17B, and the thickness position of the exposed surface is considered to be the second region 15b.

[0045] Specifically, the first region 15a, which is mainly composed of the first perovskite crystal 17A, refers to the region in the profile obtained by rocking curve measurement that has the maximum peak at a position 5° or more away from the reference position. The second region 15b, which is mainly composed of the second perovskite crystal 17B, refers to the region in the profile obtained by rocking curve measurement that has the maximum peak at a position less than 5° from the reference position.

[0046] When the piezoelectric film 15 is polished in the thickness direction from the surface and a rocking curve is measured at each depth position, the region where the angular difference between the maximum peak of the profile and the reference position is 5° or more is the first region 15a, and the depth position where the maximum peak becomes less than 5° is considered to be the boundary AB between the first region 15a and the second region 15b. The thickness from the surface of the piezoelectric film 15 to boundary AB is defined as the thickness ta of the first region 15a, and the thickness from boundary AB to the boundary with the adjacent layer (in this case, the lower electrode layer 12) is defined as the thickness tb of the second region 15b. The method of polishing the piezoelectric film 15 may be physical polishing, dry etching, or chemical polishing using a chemical solution.

[0047] Perovskite oxides are represented by the general formula ABO3. In the general formula, A is an A-site element, which is one or more of the following elements: Pb, Ba (barium), La (lanthanum), Sr, Bi (bismuth), Li (lithium), Na (sodium), Ca (calcium), Cd (cadmium), Mg (magnesium), and K (potassium). In the general formula, B is a B-site element, which is one or more of the following elements: Ti, Zr, V (vanadium), Nb (niobium), Ta (tantalum), Cr (chromium), Mo (molybdenum), W (tungsten), Mn (manganese), Fe (iron), Ru, Co (cobalt), Ir, Ni (nickel), Cu (copper), Zn (zinc), Ga (gallium), In, tin, antimony (Sb), and lanthanide elements. In the general formula, O represents oxygen. While the A:B:O ratio is based on 1:1:3, deviations are permitted within the range that allows for a perovskite structure.

[0048] The perovskite-type oxide constituting the piezoelectric film 15 is preferably one in which the main component of the A site is Pb. Here, Pb being the main component of the A site means that Pb accounts for 80 at% or more of the A site.

[0049] As the perovskite oxide constituting the piezoelectric film 15, a lead zirconate titanate (PZT) - based material containing Pb, Zr, Ti, and O (oxygen) is more preferable. In particular, it is preferable that the perovskite oxide is a compound represented by the following general formula (1) containing an additive B at the B site of PZT. Pb{(Zr x Ti 1-x ) 1-y B1 y}O3(1) Here, B1 is preferably one or more elements selected from V (vanadium), Nb (niobium), Ta (tantalum), Sb (antimony), Mo (molybdenum), and W (tungsten). Most preferably, B1 is Nb. Here, 0 < x < 1 and 0 < y < 0.4. Also here, Pb:{(Zr x Ti 1+x ) 1-y B y}:O is based on 1:1:3, but may deviate within the range where a perovskite structure can be obtained.

[0050] B1 may be a single element such as only V or only Nb, or a combination of two or more elements such as a mixture of V and Nb, or a mixture of V, Nb, and Ta. When B1 is these elements, a very high piezoelectric constant can be realized in combination with the Pb of the A - site element.

[0051] In the piezoelectric film 15, it is preferable that the first region 15a and the second region 15b are composed of the same element. When the first region 15a and the second region 15b are composed of the same element, the composition ratios in the composition of both regions may be the same or different. When the piezoelectric film 15 contains a perovskite-type oxide in which the main component of the A site is Pb, it is preferable that the Pb composition ratio in the second region 15b is greater than the Pb composition ratio in the first region 15a. Although the detailed mechanism is unknown, when the Pb composition ratio of the second region 15b is greater than the Pb composition ratio of the first region 15a, a higher piezoelectric constant is obtained compared to when the Pb composition ratio of the second region 15b is less than or equal to the Pb composition ratio of the first region 15a (see Examples).

[0052] The piezoelectric film 15 is deposited using a plasma-based vapor deposition method, such as sputtering, ion plating, plasma CVD, and pulsed laser position deposition (PLD). By changing the deposition conditions during the deposition of the piezoelectric film 15, a first region 15a and a second region 15b with different crystal axis inclination directions can be formed continuously. When deposited using these vapor deposition methods, a piezoelectric film 15 can be obtained that is substantially parallel to the substrate 10 and does not have a grain boundary between the first region 15a and the second region 15b due to stacking. It is particularly preferable that the deposition method is sputtering and that the piezoelectric film 15 is a sputtered film.

[0053] When depositing the piezoelectric film 15 by sputtering, the inclination angle of the crystal axis with respect to the normal direction can be changed, for example, by changing the substrate temperature. The angle can be increased as the substrate temperature increases. Furthermore, the inclination angle can be changed not only by controlling the substrate temperature, but also by changing the gas pressure and / or the input power. When depositing the first region 15a and the second region 15b, the deposition conditions can be changed by depositing the second region 15b, stopping the deposition temporarily, and changing the substrate temperature before depositing the first region 15a, or by changing the substrate temperature while depositing the first region 15a.

[0054] The presence or absence of grain boundaries can be determined by the presence or absence of transverse lines approximately parallel to the substrate 10 in the TEM (Transmission Electron Microscope) image of the cross-section of the piezoelectric film 15. In other words, if no transverse lines approximately parallel to the substrate 10 are observed in the TEM image of the cross-section of the piezoelectric film 15, then it can be assumed that there are no grain boundaries. That is, when a film is deposited by this vapor phase growth method, the boundary AB between the first region 15a and the second region 15b cannot be identified by the TEM image or the like.

[0055] The piezoelectric film 15 may be formed by the sol-gel method. However, in the case of the sol-gel method, in order to form a piezoelectric film 15 with a certain thickness or more (for example, 500 nm or more), it is necessary to repeat coating and sintering multiple times. When fabricated by repeating coating and sintering multiple times, transverse streaks associated with grain boundaries due to lamination occur in the piezoelectric film. Cracks may occur starting from these grain boundaries due to long-term use of the piezoelectric element. On the other hand, if the piezoelectric film 15 is formed by vapor phase growth and is a grain-boundary-free film, the occurrence of cracks, streaks, and defects caused by thermal stress can be suppressed, and it exhibits high durability.

[0056] As shown in Figure 1, the piezoelectric film 15 may contain a pyrochlore phase 16 of about 20 nm or less at the interface between the piezoelectric film 15 and the lower electrode layer 12. Since the pyrochlore phase 16 can be a starting point for cracks, it is preferable to omit it. It is also possible to realize a piezoelectric film 15 that is almost free of the pyrochlore phase 16 by providing an orientation control layer or the like as an underlayer for the piezoelectric film 15 on the lower electrode layer 12. On the other hand, when the piezoelectric film 15 is directly formed on the lower electrode layer 12 made of Ir or the like, it is possible to suppress the pyrochlore phase 16 by the film formation conditions of the piezoelectric film 15, but it is difficult to completely eliminate it.

[0057] The sufficiently suppressed pyrochlore phase 16 is not uniformly formed on the surface of the lower electrode layer 12, but grows partially as shown in Figure 1. The thickness of the pyrochlore phase 16 is calculated from a TEM image taken. In the piezoelectric film 15, the contrast between the pyrochlore phase and the perovskite phase in the TEM image is different, so the region of the pyrochlore phase can be identified. The thickness of the pyrochlore phase is calculated as the average thickness because the pyrochlore phase is not uniformly formed on the surface of the lower electrode layer. The specific method for calculating the thickness of the pyrochlore phase 16 is the method described in Japanese Patent Application Publication No. 2010-034448.

[0058] The layers of the piezoelectric element 1, other than the piezoelectric film 15, will now be described.

[0059] , There are no particular restrictions on the substrate 10, and examples include silicon, glass, stainless steel, yttrium-stabilized zirconia, alumina, sapphire, and silicon carbide. As the substrate 10, a laminated substrate such as a silicon substrate with a thermal oxide film formed on the surface of a silicon substrate may also be used. In tetragonal perovskite crystals, a-axis orientation and c-axis orientation can be differentiated by using substrates with different coefficients of linear expansion.

[0060] The lower electrode layer 12 is an electrode for applying a voltage to the piezoelectric film 15. The main component of the lower electrode layer 12 is not particularly limited and can be a metal or metal oxide such as gold (Au), platinum (Pt), iridium (Ir), ruthenium (Ru), titanium (Ti), molybdenum (Mo), tantalum (Ta), aluminum (Al), copper (Cu), silver (Ag), or a combination thereof. ITO (Indium Tin Oxide), LaNiO3, and SRO (SrRuO3) may also be used. Various adhesion layers and seed layers may be included between the piezoelectric film 15 and the lower electrode layer 12, and between the lower electrode layer 12 and the substrate 10.

[0061] The upper electrode layer 18 is paired with the lower electrode layer 12 and is an electrode for applying a voltage to the piezoelectric film 15. The main component of the upper electrode layer 18 is not particularly limited, and in addition to the materials exemplified for the lower electrode layer 12, electrode materials commonly used in semiconductor processes such as chromium (Cr) and combinations thereof can be used. However, it is preferable to use an oxide conductor in the region that is in contact with the piezoelectric film 15. Specifically, this includes ITO, iridium oxide, and SRO, as well as LaNiO3 or doped ZnO. By providing an oxide conductor in the region of the upper electrode layer 18 that is in contact with the piezoelectric film 15, oxygen elements are less likely to escape from the piezoelectric film 15 compared to when a metal is in direct contact with the piezoelectric film 15, and the effect of suppressing the deterioration of piezoelectric properties can be obtained.

[0062] The layer thickness of the lower electrode layer 12 and the upper electrode layer 18 is not particularly limited, but is preferably about 50 nm to 300 nm, and more preferably 100 nm to 300 nm.

[0063] As described above, in the piezoelectric laminate 5 and piezoelectric element 1 of this embodiment, the piezoelectric film 15 contains a perovskite oxide, and the piezoelectric film comprises a first region 15a and a second region 15b provided between the first region 15a and the lower electrode layer 12. The first region 15a mainly consists of a first perovskite crystal in which the first angle α between the (100) plane orientation or (001) plane orientation and the normal direction is 5° or more and 30° or less, so a higher piezoelectric constant can be obtained compared to the case in which the main component is a perovskite crystal in which the (100) plane orientation or (001) plane orientation is substantially parallel to the normal direction. On the other hand, as previously described, piezoelectric films in which the orientation plane is tilted by 5° or more from the normal direction exhibit a high piezoelectric constant, but have the problem of low dielectric strength. However, the piezoelectric element 1 and piezoelectric laminate 5 of this embodiment are provided with a second region 15b on the lower electrode layer 12 side of the first region 15a, which is mainly composed of a second perovskite crystal with a thickness of 30 nm or more, and in which the second angle between the (100) plane orientation or (001) plane orientation and the normal direction is less than 5°. With this configuration, the piezoelectric element 1 and piezoelectric laminate 5 have a higher dielectric strength compared to the piezoelectric element provided with a piezoelectric film in which the crystal axis is tilted by 5° or more from the normal direction, as described in the section on the prior art. This is presumed to be because the provision of the second region 15b improves the adhesion between the piezoelectric film 15 and the adjacent layer on the lower electrode layer 12 side (the lower electrode layer 12 in the above example). In particular, the effect of improving adhesion is obtained by setting the thickness tb of the second region 15b to 30 nm.

[0064] If the first angle in the first region 15a of the piezoelectric film 15 is between 5° and 15°, a higher piezoelectric constant can be obtained.

[0065] In the first perovskite crystal 17A of the first region 15a, a higher piezoelectric constant is obtained when the angle between the (100) plane orientation and the normal direction is 5° or more and 30° or less, compared to when the angle between the (001) plane orientation and the normal direction is 5° or more and 30° or less.

[0066] When the first perovskite crystal 17A in the first region 15a is a rhombohedral crystal, a higher piezoelectric constant is obtained compared to when it is a different crystal system.

[0067] If the piezoelectric film 15 is substantially parallel to the substrate 10 between the first region 15a and the second region 15b and does not have a grain boundary caused by lamination, then the occurrence of cracks that would occur if there were a grain boundary can be suppressed, and high durability can be obtained.

[0068] If the piezoelectric film 15 is a sputtered film, it can be made into a film without grain boundaries.

[0069] If the thickness of the first region 15a of the piezoelectric film 15 is 1 μm or more, a large displacement can be obtained, resulting in a piezoelectric element suitable for practical use. [Examples]

[0070] The following describes specific examples and comparative examples of the piezoelectric elements of this disclosure. First, the manufacturing method of each example piezoelectric element will be described. An RF (Radio frequency) sputtering apparatus was used to deposit each layer. In describing the manufacturing method, the reference numerals of each layer of piezoelectric element 1 shown in Figure 1 will be used for explanation.

[0071] (Bottom electrode layer deposition) For Examples 1-8, 10, 11, 12 and Comparative Examples 1-4, a Si wafer with a thermal oxide film on its surface was used as the substrate 10, and a lower electrode layer 12 was formed on the thermal oxide film of the substrate 10. A two-layer structure was formed by sequentially stacking a TiW layer and an Ir layer from the substrate 10 side. The TiW layer was 20 nm thick, and the Ir layer was 150 nm thick. On the other hand, in Example 9, a YSZ (stabilized zirconia) substrate was used as the substrate 10. In Example 9, the lower electrode layer 12 was formed under the same conditions as in Example 1, except for the type of substrate 10.

[0072] The sputtering conditions for each layer were as follows. Note that the target-substrate distance of 100 mm and the substrate temperature of 350°C were common to all layers.

[0073] -TiW layer sputtering conditions- Target input power: 600W Ar gas pressure: 0.5 Pa

[0074] -Ir layer sputtering conditions- Target input power: 600W Ar gas pressure: 0.1 Pa

[0075] (Piezoelectric film deposition) For Examples 1-7 and Comparative Examples 1-4, a substrate 10 with the lower electrode layer 12 was placed in an RF sputtering apparatus, and a 2 μm thick Nb-doped PZT film was deposited as a piezoelectric film 15 using an Nb-doped PZT target with an Nb doping amount of 12 at% at the B site. The first region 15a and the second region 15b were created separately by varying the substrate temperature. When depositing the second region 15b, the substrate temperature was set to 525°C, and when depositing the first region 15a, the substrate temperature was set to a value in the range of 575-750°C to obtain the first angle α for each example shown in Table 1. The higher the substrate temperature, the larger the inclination angle from the normal direction of the crystal axis. The deposition time was adjusted so that the thickness ta of the first region 15a and the thickness tb of the second region 15b were the values ​​shown in Tables 1 to 3 for each example. Note that Tables 1 to 3 show the designed thickness, but the error between this and the actual deposited thickness is approximately ±5%. For Examples 8 and 9, in order to control the crystal system, a Ti chip was placed on the Nb-doped PZT target used in the piezoelectric film deposition of Examples 1 to 7, and the amount of Ti at the B site was adjusted to be greater than that of the MPB composition. Other than this, the procedure was the same as in Example 2. For Examples 10, 11, and 12, a target with a different Pb composition ratio from the Nb-doped PZT target used in the piezoelectric film deposition of Examples 1 to 7 was used for film deposition in the second region 15b. Other than this, the procedure was the same as in Example 2. For Examples 10, 11, and 12, the Pb composition ratios in the second region 15b were as shown in Table 3.

[0076] The common sputtering conditions for each embodiment during sputtering of the piezoelectric film 15 were as follows:

[0077] - Piezoelectric film sputtering conditions (common parts) - Target-to-substrate distance: 60mm Target input power: 500W Ar / O2 gas pressure: 0.3 Pa, Ar / O2 mixed atmosphere (O2 volume fraction 2.0%)

[0078] (Top electrode layer formation) Next, the substrate 10 after the piezoelectric film 15 was deposited was placed in the deposition chamber of the RF sputtering apparatus, and an ITO (Indium Tin Oxide) target was used to deposit a 200 nm thick ITO layer as the upper electrode layer 18. Before depositing the upper electrode layer 18, a lift-off pattern for the evaluation sample was created on the piezoelectric film 15, and the upper electrode layer 18 was formed on the lift-off pattern. The deposition conditions for the upper electrode layer 18 were as follows.

[0079] -Upper electrode layer sputtering conditions- Target-to-substrate distance: 100mm Target input power: 200W Vacuum level: 0.3 Pa, Ar / O2 mixed gas (O2 volume fraction 5%) Board setting temperature: RT (room temperature) Substrate temperature: Room temperature

[0080] (Formation of evaluation electrode patterns) After the formation of the upper electrode layer 18, the upper electrode layer 18 was patterned by lifting it off along the lift-off pattern using the lift-off method.

[0081] Through the above process, piezoelectric laminated substrates of each example were fabricated, each comprising a lower electrode layer 12, a piezoelectric film 15, and a patterned upper electrode layer 18 on a substrate 10.

[0082] <Measurement of piezoelectric constant> (Preparation of the sample for measurement) A cantilever was fabricated by cutting out a 2mm x 25mm strip from a laminated circuit board.

[0083] (measurement) Using a cantilever, and following the method described in I. Kanno et. al. Sensor and Actuator A 107(2003)68., a sine wave applied voltage of -10V ± 10V, i.e., a bias voltage of -10V and a sine wave applied voltage with an amplitude of 10V, is used to determine the piezoelectric constant d 31 [pm / V] was measured. The measurement results are shown in Tables 1-3.

[0084] <Measurement of dielectric breakdown voltage (withstand voltage)> (Preparation of the sample for measurement) A laminated substrate was diced into a 1-inch (25mm) square to fabricate a 1-inch square piezoelectric laminate. During the deposition of the upper electrode layer 18, a metal mask with a partially 400μm diameter circular opening was used to form a 400μm diameter circular upper electrode layer 18. A 1-inch square section with the circular upper electrode layer 18 at its center was then cut out and used as a sample for voltage withstand measurement.

[0085] (measurement) The lower electrode layer 12 was grounded, and a negative voltage was applied to the upper electrode layer 18 at a rate of change of -1 V / second. The voltage at which a current of 1 mA or more flowed was considered the withstand voltage. Ten samples were prepared for each example, and a total of ten measurements were taken. The average value (absolute value) is shown in Tables 1-3 as the withstand voltage [V].

[0086] <Tilt angle of the (100) or (001) plane orientation of the piezoelectric film> For the examples and comparative examples, rocking curve measurements were performed on the (200) or (002) peaks of the piezoelectric film (PZT) using a RIGAKU RINT-ULTIMAIII to measure the tilt angle of the (100) or (001) plane orientation. Specifically, rocking curve measurements were performed, and the tilt angle of the (100) or (001) plane orientation was determined from the shift of the peak from the reference position, using the (200) or (002) diffraction peak position when the crystal axis is not tilted as the reference position. Figure 5 shows the profile obtained by rocking curve measurement of the piezoelectric film of Example 2 in an unpolished state before forming the upper electrode layer. Figure 6 shows the profile obtained by rocking curve measurement of the piezoelectric film of Example 2 after polishing the piezoelectric film surface to 1900 nm.

[0087] In the profile shown in Figure 5, the first peak PA1 and the second peak PA2 are located near 10° and 30°, respectively. The reference position is 22.2°, and the deviation of the largest peak, the first peak PA1, from the reference position of 22.2°, i.e., the angular difference between the reference position and the angle of the first peak PA1, is approximately 10°. Since the angular difference is 5° or more, this is the first angle α, which means that the piezoelectric film surface is in the first region 15a.

[0088] The profile shown in Figure 6 appears to be almost a single peak, but there are two peaks, the first PB1 and the second PB2, located close together on either side of the reference point. The angular difference between the largest peak, the first peak PB1, and the reference point is approximately 2°. Since the angular difference is less than 5°, this is the second angle β, meaning that the position 1900 nm from the surface is the second region 15b.

[0089] For each embodiment, the first angle α and second angle β obtained by rocking curve measurement for the first region 15a and the second region 15b are shown in Tables 1 to 3.

[0090] <Crystalline System Measurement> The piezoelectric films 15 of Examples 2, 8, and 9 were identified by XRD analysis near the (200) and (002) peaks of the perovskite structure using synchrotron radiation. The results are shown in Table 2.

[0091] Table 1 shows the composition of the piezoelectric film 15 and the evaluation results of its piezoelectric properties for Examples 1-7 and Comparative Examples 1-4. [Table 1]

[0092] Comparative Examples 1 and 2 have piezoelectric films that do not have a second region 15b, and only have regions where the angle between the crystal axis and the normal direction N is 5° or more. Conversely, Comparative Example 3 has a piezoelectric film that only has regions where the angle between the crystal axis and the normal direction is less than 5°. Comparative Example 1 has a high piezoelectric constant but a low dielectric strength, while Comparative Example 3 has a high dielectric strength but a low piezoelectric constant.

[0093] As shown in Table 1, Examples 1 to 7, which have a second region 15b with a thickness of 30 to 500 nm, show increased dielectric strength compared to Comparative Examples 1 and 2, which do not have a second region 15b, and have a higher piezoelectric constant compared to Comparative Example 3, which does not have a first region 15a. In other words, Examples 1 to 7 achieve both a high piezoelectric constant and a high dielectric strength. Comparative Example 4 has a first region 15a and a second region 15b, but the thickness of the second region 15b is less than 30 nm. From these results, it is clear that when the thickness of the second region 15b is less than 30 nm, the effect of improving the dielectric strength cannot be obtained.

[0094] Table 2 shows the crystal system and piezoelectric properties evaluation results for the piezoelectric films of Examples 2, 8, and 9. [Table 2]

[0095] As shown in Table 2, when the crystalline system of the piezoelectric film is rhombohedral, as in Example 2, the piezoelectric constant was found to be higher than that of Examples 8 and 9, which are tetragonal. Furthermore, a comparison of Examples 8 and 9 showed that even though both are tetragonal, Example 8, which has a (100) preferred orientation, has a higher piezoelectric constant than Example 9, which has a (001) preferred orientation.

[0096] Table 3 shows the configuration of the piezoelectric films in Examples 2, 10-12, and the evaluation results of their piezoelectric properties. [Table 3]

[0097] As shown in Table 2, compared to Examples 10 and 11, where the Pb composition ratio (Pb / B site element) of the second region 15b is less than or equal to the Pb composition ratio of the first region 15a, a higher piezoelectric constant was obtained when the Pb composition ratio of the second region 15b was greater than that of the first region 15a, as in Examples 2 and 12. [Explanation of Symbols]

[0098] 1. Piezoelectric element 5 Piezoelectric laminate 10 circuit boards 12 Lower electrode layer 15 Piezoelectric film 15a 1st area 15b 2nd area 16 Pyrochlore phase 17 Columnar crystal grains 17A First Perovskite Crystal 17B Second Perovskite Crystal 18 Upper electrode layer AB Boundary between the first and second regions

Claims

1. A piezoelectric laminate comprising a lower electrode layer and a piezoelectric film on a substrate in this order, The piezoelectric film comprises a perovskite-type oxide, The piezoelectric film comprises a first region mainly composed of a first perovskite crystal in which the perovskite-type oxide has a first angle between the (100) or (001) plane orientation and the normal direction of the surface of the substrate of 5° or more and 30° or less, and a second region provided between the first region and the lower electrode layer, mainly composed of a second perovskite crystal in which the perovskite-type oxide has a second angle between the (100) or (001) plane orientation and the normal direction of the substrate of less than 5°. The thickness of the second region is 30 nm or more and 500 nm or less, and is 1 / 3 or less of the thickness of the first region. Piezoelectric laminate.

2. The piezoelectric laminate according to claim 1, wherein the first angle in the first region of the piezoelectric film is 5° or more and 15° or less.

3. The piezoelectric laminate according to claim 1 or 2, wherein the piezoelectric film between the first region and the second region is substantially parallel to the substrate and does not have a grain boundary caused by lamination.

4. The piezoelectric laminate according to any one of claims 1 to 3, wherein the piezoelectric film is a sputtered film.

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

6. In the first perovskite crystal of the first region, the plane orientation making a first angle with the normal direction is the (100) plane orientation, according to any one of claims 1 to 5. Electrical laminate.

7. The piezoelectric laminate according to any one of claims 1 to 6, wherein the first perovskite crystal in the first region is a rhombohedral crystal.

8. The aforementioned perovskite-type oxide has the general formula ABO ３ It is represented as follows, where A is the A-site element, B is the B-site element, and O is the oxygen element. The piezoelectric laminate according to any one of claims 1 to 7, wherein the main component of the A-site element is Pb.

9. The aforementioned perovskite-type oxide is a compound represented by the following general formula (1): P｡{(Cr ｘ Ti １－ｘ ) １－ｙ B1 ｙ }O ３ (1) 0<x<1, 0<y<0.4, The piezoelectric laminate according to any one of claims 1 to 7, wherein B1 is one or more elements selected from V, Nb, Ta, Sb, Mo, and W.

10. The piezoelectric laminate according to claim 8 or 9, wherein the Pb composition ratio in the second region is greater than the Pb composition ratio in the first region.

11. A piezoelectric laminate according to any one of claims 1 to 10, A piezoelectric element comprising an upper electrode layer provided on the piezoelectric film of the piezoelectric laminate.

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