JP2011181764A - Piezoelectric-body element and method of manufacturing the same - Google Patents

Abstract

Provided is a piezoelectric element that does not contain lead and can improve the temperature dependence of piezoelectric characteristics.
A piezoelectric element includes a piezoelectric layer and an upper electrode and a lower electrode stacked on the front and back surfaces thereof. The piezoelectric layer 20 is formed by laminating five piezoelectric layers 21 to 25 having different compositions in the film thickness direction, the compositions of which differ stepwise, and the center plane ( It is formed so as to be symmetric with respect to a level plane indicated by a one-dot chain line C in FIG. Among these piezoelectric films 21 to 25, for example, the piezoelectric films 21 and 25 are made of BZT-50% BCT, the piezoelectric films 22 and 24 are made of BZT-45% BCT, and the piezoelectric film 23 is BZT-40% BCT. With this configuration, the temperature dependence of the piezoelectric characteristics of the piezoelectric layer 20 is averaged and significantly improved.
[Selection] Figure 2

Description

  The present invention relates to a piezoelectric element, a manufacturing method thereof, various sensors using the same, and the like.

Piezoelectric materials are generally widely used in various fields as substances that can significantly convert electrical energy and mechanical energy. At present, most of such piezoelectric materials that have been put into practical use due to their superiority in various viewpoints such as piezoelectric characteristics and productivity are PZT (Pb (Ti, Zr) O ₃ : lead zirconate titanate). It is not an exaggeration to say that it was used. However, since PZT contains a large amount of lead, which is a harmful heavy metal, in its composition, its use has been severely regulated in recent years from the viewpoint of environmental problems, and the application of such regulation is also demanded for piezoelectric materials. is there. For this reason, the development of lead-free (non-lead) piezoelectric materials having excellent characteristics comparable to PZT has become an urgent issue, and various proposals have been made so far. Piezoelectric materials that can be substituted are not yet widely recognized and permeated worldwide. Under such circumstances, Patent Document 1 proposes a lead-free piezoelectric material made of an oxide solid solution containing Ba (barium) and Ca (calcium) as elements instead of lead.

JP 2009-215111 A

Here, BZT-δ% BCT (described in abbreviations in Patent Document 1), which is a lead-free piezoelectric material proposed in Patent Document 1, has an extremely large piezoelectric coefficient (d ₃₃ ). It has performance that surpasses so-called soft PZT. However, the piezoelectric property is maximum at a temperature corresponding to a crystal layer boundary (Morphotropic Phase Boundary: MPB, a boundary between a tetragonal phase and a rhombohedral phase in a phase diagram as shown in FIG. 1 of Cited Reference 1). The temperature corresponding to the MPB is a rate of change with respect to the content ratio (composition ratio) of BZT and BCT in BZT-δ% BCT as shown in the phase diagram described in FIG. Tend to be excessive. Due to this, even if the composition ratios of BZT and BCT are slightly different, the temperature dependence of the piezoelectric coefficient (d ₃₃ ) of BZT-δ% BCT changes. In other words, the piezoelectric characteristics change with temperature. In a use environment where the ambient (atmosphere) temperature varies, it is difficult to control the piezoelectric characteristics as desired.

  Therefore, the present invention has been made in view of such circumstances, and provides a piezoelectric element that does not contain lead (with no lead) and that can improve the temperature dependence of piezoelectric characteristics, and a method for manufacturing the same. The purpose is to do.

  In order to solve the above problems, a piezoelectric element according to the present invention is a lead-free piezoelectric material having a crystal phase boundary (Morphotropic Phase Boundary: MPB) (particularly, a mixture, a mixed composition, a solid solution, and a composite including a plurality of compounds) ), And the piezoelectric layer includes a plurality of portions having different compositions.

  In such a configuration, the piezoelectric layer includes a plurality of parts having different compositions, for example, a multilayer thin film (laminated thin film), and a compound or a composition of each film (each layer: the same shall apply hereinafter) Since the composition (ratio) is formed of materials different from each other, even if a lead-free piezoelectric material having a temperature dependency of piezoelectric characteristics depending on the composition ratio is used, such as the piezoelectric material described in Patent Document 1, Since the temperature dependence of the piezoelectric characteristics of the films is different from each other, the piezoelectric characteristics of the entire piezoelectric layer are averaged (flattened against temperature changes), and as a result, the temperature dependence of the piezoelectric characteristics can be reduced.

  Specifically, even when the piezoelectric layer is formed so that the composition of the piezoelectric layer is continuously or intermittently different in the thickness direction, for example, a single layer whose boundary is not clear as the piezoelectric layer, The composition (ratio) is continuously changing in the thickness direction, or as described above, the piezoelectric layer is a multilayer thin film in which a plurality of thin films are laminated in the thickness direction (stacking direction), and , Films having different compositions (for example, gradually different in stages) can be mentioned.

  Further, it is preferable that the composition of the piezoelectric layer is formed so as to be symmetric with respect to the center plane in the thickness direction.

  In general, characteristics of a piezoelectric element (piezoelectric layer), such as dielectric constant, Curie temperature, coercive electric field, and remanent polarization, tend to vary depending on internal stress of the piezoelectric layer. A piezoelectric layer formed on a substrate such as a semiconductor substrate is likely to generate in-plane two-dimensional stress during film formation, that is, a physical property difference between the piezoelectric layer and its base, for example, a lattice Due to differences in constants, thermal expansion coefficients, etc., compressive stress or tensile stress may be generated inside the film during the film cooling process after high-temperature film formation. In this case, it may be difficult to form a piezoelectric layer having desired characteristics, and when the piezoelectric element is used after being separated from the substrate (individualized or individualized), In some cases, the stress remaining inside the film is released, and a shape change (deformation) that causes the piezoelectric element to warp may occur.

  In contrast, if the composition (ratio) of the film forming the piezoelectric layer differs in the thickness direction (direction perpendicular to the surface direction of the piezoelectric layer), the crystal structure, crystallite structure, domain structure, etc. Therefore, the compressive stress or tensile stress that can be generated inside each film can also be different in the thickness direction of the piezoelectric layer (however, the mechanism of action is not limited to this). Therefore, as in the present invention, if the composition of the piezoelectric layer is formed so as to be symmetric with respect to the center plane in the thickness direction, the piezoelectric layer as a whole has a compressive stress or tensile stress. It can be canceled (can be canceled) in the thickness direction with respect to the center plane. As a result, it is possible to average the characteristics of the piezoelectric layer, and thus the entire piezoelectric element, and to suppress the shape change.

  Alternatively, the piezoelectric layer may be configured to include a plurality of portions having different half-value widths of 2θ peaks in X-ray diffraction analysis.

  In this case, according to the knowledge of the present inventor, in the piezoelectric layer, the X-ray diffraction analysis shows that the half-value width of the 2θ peak on the same reflecting surface is different (in the case of a multilayer thin film, the X-ray diffraction analysis). (Films having different half-widths of 2θ peaks in the film) have different stresses (compressive stress or tensile stress) that can be generated therein, and in particular, the greater the half-width of the 2θ peaks in the X-ray diffraction analysis, Tend to be alleviated. Therefore, if the portion (film) that easily contracts in the piezoelectric layer is formed so that the half-value width of the 2θ peak in the X-ray diffraction analysis is larger, the internal stress of the portion can be further reduced. However, it is possible to suppress a shape change such as a warp that may occur in the piezoelectric layer and thus the piezoelectric element.

  In other words, the piezoelectric element according to the present invention has a piezoelectric layer made of a lead-free piezoelectric material having a crystal phase boundary from the viewpoint of effectively suppressing such a change in shape. The layer is useful even if it includes a plurality of portions having different half-widths of 2θ peaks in X-ray diffraction analysis.

  More specifically, it is possible to exemplify those formed such that the half width of the 2θ peak in the X-ray diffraction analysis of the piezoelectric layer increases in the thickness direction from one surface to the other surface. For example, when a piezoelectric film is formed by forming a piezoelectric film on a semiconductor substrate (which may have a base film formed so as to be in contact with the piezoelectric layer), generally, the upper part of the film, that is, The part farther from the semiconductor substrate (part formed later) has a higher degree of contraction, and conversely, the part closer to the substrate surface (part formed earlier) is restricted by the substrate surface. . Therefore, in this case, the piezoelectric element is removed from the substrate by forming the film so that the full width at half maximum of the 2θ peak in the X-ray diffraction analysis of the portion is increased toward the top of the film constituting the piezoelectric layer. Warpage (shape change) when peeled and separated into pieces can be more effectively suppressed.

More specifically, as a lead-free piezoelectric material, a binary compound or a pseudo-binary compound (for example, a perovskite complex oxide containing two different compounds, or an oxide thereof as a main component) composition), for _{example, Ba (Ti 1-x Zr} x) O 3 and _{(Ba 1-y M y)} TiO 3 ( where, M represents, Mg, Ca, at least one element of Sr.) And the phase diagram (Ba (Ti _1-x Zr _x ) O ₃ and (Ba _{1- y My} ) TiO _{3 has} a composition ratio as one axis (for example, the horizontal axis), and temperature is the other axis (for example, the vertical axis) In the state diagram)), those having a phase boundary between two phases among the three phases of cubic, rhombohedral and tetragonal are mentioned.

  The method for manufacturing a piezoelectric element according to the present invention is a method for effectively manufacturing the piezoelectric element according to the present invention, which is made of a lead-free piezoelectric material having a crystal phase boundary on a semiconductor substrate, and Forming a piezoelectric layer including a plurality of portions (films) having different compositions (ratio).

Specifically, in the step of forming the piezoelectric layer, a portion (film) made of a binary compound or a pseudo binary compound is formed as the piezoelectric layer, and the binary compound or pseudo binary is formed. As the raw material of the ternary compound, two kinds of materials composed of the first compound and the second compound constituting the compound may be used. At this time, the raw material of the binary compound or the pseudo-binary compound is not particularly limited, and the lead-free piezoelectric material forming the piezoelectric layer is, for example, the Ba (Ti _1-x Zr _x ) O ₃ described above. and (Ba _1-y M _y) is a TiO _3, consists case of depositing its piezoelectric layer, for example, various vapor deposition (growth) method, _{etc., Ba (Ti 1-x Zr} x) O 3 target and materials, and a target material consisting of _{(Ba 1-y M y)} TiO 3, may be used to prepare separately, single or various compositions (composition ratio, stoichiometry) Ba having a ( A sintered body containing Ti _1-x Zr _x ) O ₃ and (Ba _{1- y My} ) TiO ₃ may be used.

  In the step of forming the piezoelectric layer, it is also preferable to adjust the formation rate of the piezoelectric layer (deposition rate: for example, the unit is Å / sec). When the piezoelectric layer is formed into a film, if the formation rate is gradually decreased intermittently or intermittently, the half width of the 2θ peak in the X-ray diffraction analysis of the piezoelectric layer described above becomes the thickness of the piezoelectric layer. A piezoelectric element including a piezoelectric layer formed so as to increase from one surface to the other surface in the vertical direction can be more effectively manufactured.

  Here, “adjusting the formation rate of the piezoelectric layer” means changing (variing) the formation rate of the piezoelectric layer without making the composition of the entire piezoelectric layer uniform (constant). This means that portions having different compositions from each other are formed, or portions having different half-widths of 2θ peaks in the X-ray diffraction analysis are formed in the piezoelectric layer. In addition, as a method for adjusting the formation rate of the piezoelectric layer, for example, when forming a piezoelectric layer made of a piezoelectric thin film using various vapor deposition methods, each of the above-described piezoelectric layer forming materials (target materials) ) To change the amount of each material ion, chemical species, vapor, etc. generated per unit time, or to change the amount of each material vapor reaching the substrate on which the piezoelectric layer is formed, For example, when physical vapor deposition (PVD) such as sputtering is used, various parameters of the film formation conditions, for example, the type and composition of process (atmosphere) gas in the film formation chamber (for example, oxygen (Partial pressure), sputtering applied voltage, high-frequency power output, and T-S distance (target-substrate distance).

  In addition, as described above, the method for manufacturing a piezoelectric element according to the present invention is a piezoelectric body made of a lead-free piezoelectric material having a crystal phase boundary on a semiconductor substrate from the viewpoint of effectively suppressing the shape change of the piezoelectric element. In the step of forming the piezoelectric layer including the step of forming the layer, a method of adjusting the formation rate of the piezoelectric layer may be used.

  According to the piezoelectric element and the manufacturing method thereof of the present invention, since the piezoelectric layer made of a lead-free piezoelectric material having a crystal phase boundary (MPB) includes a plurality of portions having different compositions, the entire piezoelectric layer As a result, the piezoelectric properties of the piezoelectric element can be averaged to improve the temperature dependence thereof, so that the excellent piezoelectric properties of the piezoelectric element can be stably maintained and desired even in an environment where the ambient temperature fluctuates. It becomes possible to control to.

It is a schematic sectional drawing which shows the structure of one Embodiment of the piezoelectric element by this invention. It is a schematic sectional drawing which shows the structure of other one Embodiment of the piezoelectric element by this invention. It is a schematic sectional drawing which shows the structure of another one Embodiment of the piezoelectric element by this invention. Is a graph showing the temperature characteristic of the piezoelectric coefficient d ₃₃ of the piezoelectric film 21 to 25 and the piezoelectric layer 20 composed of those shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Furthermore, the following embodiment is an illustration for explaining the present invention, and is not intended to limit the present invention only to the embodiment. Furthermore, the present invention can be variously modified without departing from the gist thereof.

  FIG. 1 is a schematic sectional view showing the configuration of an embodiment of a piezoelectric element according to the present invention. The piezoelectric element 10 includes a piezoelectric layer 20 and an upper electrode 31 and a lower electrode 32 that are stacked on the front surface and the back surface, respectively. The material of the upper electrode 31 and the lower electrode 32 is not particularly limited and may be any conductive material suitable for controlling the crystal orientation of the piezoelectric layer 20, for example, Pt (platinum), Au (gold), Cu (Copper), Ti (titanium), etc. are mentioned, These may be used independently and may be used in multiple combination (mixing).

On the other hand, the piezoelectric layer 20 is mainly composed of, for example, a non-lead-based (not containing Pb) perovskite complex oxide represented by the chemical formula ABO ₃ —CDO ₃ (first and second compounds, respectively). It consists of a ternary compound or a pseudo binary compound. Here, A to D represent cations. As A and C, Mg (magnesium), Ca (calcium), Ba (barium), Sr (strontium), K (potassium), Na (sodium), Li ( Examples include at least one element selected from lithium), La (lanthanum), and Cd (cadmium). B and D include Ti (titanium), Zr (zirconium), Ta (tantalum), and Nb ( At least one element selected from niobium).

More specifically, as the material of the piezoelectric layer _{20, Ba (Ti 1-x} Zr x) O 3 and _{(Ba 1-y M y)} TiO 3 ( where, M is, Mg, Ca, among Sr At least one kind of element.) Or those containing them as a main component are preferred. More specifically, Ba (Ti _0.8 Zr _0.2 ) O ₃ — (Ba _0.7 Ca _0.3 ) TiO ₃ ( Hereinafter, it is abbreviated as “BZT-αBCT”, and this BZT-αBCT is described as a representative example of the piezoelectric layer 20), or one containing it as a main component. In this BZT-αBCT, in the chemical formula “ABO ₃ -CDO ₃ ”, “A” is Ba, “B” is Ti and Zr, “C” is Ba and Ca, and “D”. Is Ti.

  Further, the piezoelectric layer 20 has a state diagram (in the above example, a state diagram in which the composition ratio of BZT-αBCT is uniaxial (for example, horizontal axis) and the temperature is the other axis (for example, vertical axis); In the phase diagram similar to that described in FIG. 1, each of the three phases, cubic, rhombohedral and tetragonal, has a phase boundary of two phases, that is, a crystal phase boundary (MPB). It is formed with the material which has.

  Further, the piezoelectric layer 20 has, for example, a composition in the film thickness direction (thickness direction; a direction perpendicular to the extending surface of the piezoelectric layer 20, that is, the vertical direction in the drawing), that is, an example of BZT-αBCT. In "BZT" and "BCT" (first and second compounds respectively), the content ratio (mixing ratio, composition ratio; hereinafter, for example, containing 60 mass% BZT and 40 mass% BCT, in other words, , Α = 40% by mass is described as “BZT-40% BCT”.) Includes a plurality of different parts.

  FIG. 2 is a schematic cross-sectional view showing the configuration of another embodiment of the piezoelectric element according to the present invention. The piezoelectric element 10 of this embodiment has a piezoelectric layer 20 with piezoelectric films 21 to 25. The piezoelectric element 10 is configured in the same way as the piezoelectric element 10 shown in FIG. Among these piezoelectric films 21 to 25, the piezoelectric films 21 and 25 are made of BZT-50% BCT, the piezoelectric films 22 and 24 are made of BZT-45% BCT, and the piezoelectric film 23 is made of BZT. Consists of -40% BCT. That is, the piezoelectric layer 20 is formed by stacking five piezoelectric films 21 to 25 which are five layers having different compositions in the film thickness direction, and their compositions differ stepwise (discontinuously). In addition, in the film thickness direction, it is formed so as to be symmetric with respect to the center plane (level plane indicated by a virtual one-dot chain line C in FIG. 2). In other words, the piezoelectric films 21 and 25 and the piezoelectric films 22 and 24 are formed so as to be symmetric with respect to the reference film (piezoelectric film 23) of the piezoelectric layer 20.

Here, FIG. 4 is a graph showing the temperature characteristic of the piezoelectric coefficient d ₃₃ of the piezoelectric film 21 to 25 and the piezoelectric layer 20 composed of them (the change with respect to temperature), the piezoelectric film 21 and 25 (BZT −50% BCT), the piezoelectric films 22 and 24 (BZT−45% BCT), the piezoelectric film 23 (BZT−40% BCT), and the piezoelectric coefficient d ₃₃ of the piezoelectric layer 20 at a temperature of 20 ° C. to 70 ° C. The graphs are plotted every 10 ° C. in the range of ° C., and the line graphs connecting the plotted data are indicated by the lines L ₅₀ , L ₄₅ , L ₄₀ , and L _v , respectively, as a guide. From these data, when the piezoelectric films 21 to 25 have different compositions, the temperature dependence of the piezoelectric coefficient is relatively large. On the other hand, the piezoelectric layer 20 that is a laminated body (multilayer thin film) As a whole, the temperature dependence of the piezoelectric coefficient is averaged (flattened) to be small, and it is understood that the influence of temperature on the piezoelectric characteristics of the piezoelectric layer 20 is significantly improved.

  Based on this action and effect, for example, the piezoelectric element 10 shown in FIG. 2 is the same as the piezoelectric element 20 shown in FIG. 2 except that the composition of the piezoelectric layer 20 provided in the piezoelectric element 10 shown in FIG. Similarly to the piezoelectric layer 20 provided on the piezoelectric layer 20, if the composition is symmetric with respect to the central plane in the film thickness direction, the temperature dependence of the piezoelectric characteristics of the piezoelectric layer 20 as a whole is significantly reduced. It becomes possible to do.

  The piezoelectric element 10 having such a configuration is formed on a growth substrate 50 (semiconductor substrate) using a known thin film process. As the growth substrate 50, for example, a silicon single crystal substrate prepared such that the (100) plane is the substrate surface can be suitably used. Further, as a thin film process for forming the piezoelectric element 10, for example, a PVD method such as a sputtering method, a chemical vapor deposition method (CVD method) such as a plasma CVD method, a thermal CVD method, or an MOCVD method, etc. Vapor phase deposition method or liquid phase growth method such as sol-gel method is suitable.

  In particular, when the piezoelectric layer 20 made of BZT-αBCT is formed by performing a PVD method such as a sputtering method, for example, FIG. 1 (a) of Japanese Patent Application Laid-Open No. 2009-256721 by the present applicant and Using the sputtering target having the shape described in (b), the carousel-type sputtering apparatus described in FIGS. 2 (a) and 2 (b) can be used. In this case, it is also preferable that a sputtering target for BZT and a sputtering target for BCT are separately prepared as the sputtering target and installed on the side wall of the chamber of the carousel type sputtering apparatus.

  In order to form the piezoelectric layers 20 having different compositions in the film thickness direction of the piezoelectric element 10 shown in FIGS. 1 and 2, using these individual BZT sputtering targets and BCT sputtering targets, sputtering of each sputtering target is performed. An appropriate method for changing the rate (the amount of each material ion or chemical species generated per unit time) can be used.

  Such techniques include, for example, changing the type and composition (for example, oxygen partial pressure) of process (atmosphere) gas in the chamber of a carousel type sputtering apparatus for film formation, sputtering voltage applied for film formation, Examples include a method of changing the high-frequency output, and further the T-S distance (target-substrate distance). Further, the area (volume of the surface layer) on which the sputtering targets for BZT and BCT are sputtered may be changed. In this case, a part or all of each sputtering target is shielded by using, for example, an open / close shutter or the like. Or each sputtering target may be moved between a sputtered position and a non-sputtered position, or a movable or rotatable sputtering target that can be moved between such positions (e.g., respectively It is also preferable to use a disc-shaped rotating sputtering target formed by bonding semi-disc-shaped sputtering targets for BZT and BCT. A sputtering target made of a sintered body of BZT-αBCT may be used. In this case, a plurality of sintered sputtering targets of BZT-αBCT having compositions having different αs may be used.

  Further, as described above, the film formation rate (formation rate) of the piezoelectric layer 20 can be changed appropriately and sequentially by changing the sputtering rate of the sputtering target. Here, FIG. 3 is a schematic cross-sectional view showing the configuration of still another embodiment of the piezoelectric element according to the present invention. The piezoelectric element 10 of this embodiment includes a piezoelectric layer 20 and a piezoelectric film 26. The piezoelectric element 10 is configured in the same manner as the piezoelectric elements 10 and 10 shown in FIG. 1 and FIG. The piezoelectric layer 20 is formed so that the respective film formation rates gradually decrease (slow) from the piezoelectric film 26 close to the growth substrate 50 toward the piezoelectric film 30 farthest from the growth substrate 50. These piezoelectric films 26 to 30 are sequentially laminated.

  According to the knowledge of the present inventor, in the piezoelectric layer 20 composed of the piezoelectric films 26 to 30 formed by stacking the film formation rate in this way, the piezoelectric film 26 is directed toward the piezoelectric film 30. The full width at half maximum of the 2θ peak in each X-ray diffraction analysis is gradually increased. This is because, even when the compositions of the piezoelectric films 26 to 30 are the same or substantially the same, the structure and size of crystallites and domains, or the degree of a-axis orientation and c-axis orientation, due to different film formation rates. It is inferred as one of the factors that the (ratio) is different (however, the action is not limited to this). In each of the piezoelectric films 26 to 30 thus formed, the half-value width of the 2θ peak in the X-ray diffraction analysis is gradually increased stepwise, so that the stress (internal stress) generated inside each film. Even when the piezoelectric element 10 is peeled off from the growth substrate 50 and separated into pieces, the upper portion of the film (piezoelectric film) is smaller than when the entire piezoelectric layer 20 is formed at the same film formation rate. 30) can be remarkably reduced, and deformation such as warping of the piezoelectric element 10 can be suppressed.

  Based on this effect, for example, the piezoelectric layer 20 provided in the piezoelectric element 10 shown in FIG. 1 is shown in FIG. 3 except that the film forming rate in the film thickness direction is gradually reduced gradually. If formed in the same manner as the piezoelectric layer 20 provided in the piezoelectric element 10, the half-value width of the 2θ peak in the X-ray diffraction analysis is one surface of the piezoelectric layer 20 (the bottom surface of the piezoelectric layer 20, the growth substrate 50. Side, lower electrode 32 side) toward the other surface (upper surface of the piezoelectric layer 20), the upper electrode 31 side can be configured to gradually and gradually increase. It is possible to prevent a change in shape when it is peeled off from 50 and separated into individual pieces.

Further, an intermediate thin film 40 (underlying film) may be interposed between each piezoelectric element 10 shown in FIGS. 1 to 3 and the growth substrate 50. Examples of the intermediate thin film 40 include ZrO ₂ (zirconium oxide). By providing the intermediate thin film 40 in this manner, there is an advantage that the lower electrode 32 formed thereon can be prevented from being peeled off and the piezoelectric layer 20 can be easily epitaxially grown. For example, in the piezoelectric element 10 of each embodiment, SiO ₂ is formed on a Si substrate as the growth substrate 50, ZrO ₂ having (100) orientation is formed thereon, and then (100) orientation is provided. For example, a Pt electrode can be formed as the lower electrode 32. Further, when, for example, SrRuO ₃ (strontium ruthenate) having (100) orientation is used as the material of the uppermost film of the intermediate thin film 40 which is the base of the piezoelectric layer 20, the piezoelectric layer 20 is crystallized in the c-axis direction. It becomes easy to adjust the grain size of the columnar crystal particles obtained by the growth to a predetermined value or less, and in this case, the stress of the piezoelectric layer 20 after film formation may be significantly reduced.

  In addition, as above-mentioned, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the limit which does not change the summary. For example, each piezoelectric layer 20 may be composed mainly of columnar crystal grains epitaxially grown in the c-axis direction. However, the crystal structure is not a perfect (001) single-oriented film, and c-axis oriented crystals and a-axis oriented crystals are mixed appropriately so that crystal particles are ideally closely packed on the lower electrode 32. It may be a thin film. In each piezoelectric layer 20, the crystal structure may be adjusted so that the difference between the lattice constant of the a-axis oriented crystal and the lattice constant of the c-axis oriented crystal falls within an appropriate range.

  Further, the piezoelectric layer 20 shown in FIG. 2 and the piezoelectric layer 20 shown in FIG. 3 may be applied in combination. That is, the piezoelectric films 21 to 25 constituting the piezoelectric layer 20 shown in FIG. 2 are formed from the piezoelectric film 21 toward the piezoelectric film 25 so that the film formation rate gradually decreases (slows). The half width of the 2θ peak in the X-ray diffraction analysis may be gradually increased from the piezoelectric film 21 toward the piezoelectric film 25. Further, a shrinkage restricting substrate may be bonded onto the upper electrode 31.

  In addition, when the piezoelectric layer 20 is a composition including a plurality of compounds having different Curie points (temperatures), the content of a compound having a higher Curie point is higher than the content of a compound having a lower Curie point. Then it is useful. For example, in the case of BZT-αBCT, α> 50 mass% is preferable. Furthermore, the means for verifying whether or not the half width of the 2θ peak in the X-ray diffraction analysis of each film of the piezoelectric layer 20 is a desired value as intended (as set) is not particularly limited. For example, in FIG. 3, the piezoelectric films 30, 29, 28, and 27 are sequentially removed, and for each film removal process, the value of the 2θ peak in the X-ray diffraction analysis (the peak is obtained by appropriate fitting or the like). Qualitative / quantitative measurement is possible), and the half-value width of the 2θ peak in the X-ray diffraction analysis of each piezoelectric film is estimated by measuring the difference between the measured values.

  As described above, according to the piezoelectric element and the manufacturing method thereof of the present invention, the temperature dependency of the piezoelectric characteristics of the piezoelectric layer and thus the piezoelectric element can be improved by appropriately changing the composition in the thickness direction of the piezoelectric layer. It can be improved, and the shape change when the piezoelectric element is separated from the substrate and separated into pieces can be prevented, so that the gyro sensor, actuator, frequency filter, and nonvolatile memory equipped with the piezoelectric element are mounted. It can be widely and effectively used for all kinds of equipment, devices, modules, systems, devices, etc., such as light modulators and acoustic elements, and their production, and does not contain lead, thus contributing to environmental measures It is possible to fully respond to environmental regulations.

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric element 20 ... Piezoelectric layer 21-25 ... Piezoelectric film 26-30 ... Piezoelectric film 31 ... Upper electrode 32 ... Lower electrode 40 ... Intermediate thin film (underlayer film)
50 ... Growth substrate (semiconductor substrate, substrate)
L ₄₀ , L ₄₅ , L ₅₀ , L _v ... Reference line indicating temperature change of piezoelectric coefficient

Claims (14)

Comprising a piezoelectric layer made of a lead-free piezoelectric material having a crystal phase boundary;
The piezoelectric layer includes a plurality of portions having different compositions.
Piezoelectric element. The piezoelectric layer is formed such that the composition is continuously or intermittently different in the thickness direction of the piezoelectric layer.
The piezoelectric element according to claim 1. The piezoelectric layer is formed so that the different compositions are symmetric with respect to the center plane in the thickness direction of the piezoelectric layer.
The piezoelectric element according to claim 1 or 2. The piezoelectric layer includes a plurality of portions having different half-value widths of 2θ peaks in X-ray diffraction analysis.
The piezoelectric element according to claim 1. It has a piezoelectric layer made of a lead-free piezoelectric material having a crystal phase boundary,
The piezoelectric layer includes a plurality of portions having different half-value widths of 2θ peaks in X-ray diffraction analysis.
Piezoelectric element. The piezoelectric layer is formed such that the half width of the 2θ peak in the X-ray diffraction analysis increases from one surface to the other surface in the thickness direction of the piezoelectric layer.
The piezoelectric element according to claim 1. The lead-free piezoelectric material is a binary compound or a pseudo binary compound,
The piezoelectric element according to claim 1. The lead-free piezoelectric _{material, Ba (Ti 1-x Zr} x) O 3 and _{(Ba 1-y M y)} TiO 3 ( where, M represents, Mg, Ca, at least one of Sr.) And in the phase diagram, each of the three phases of cubic, rhombohedral and tetragonal has a phase boundary of two phases.
The piezoelectric element according to claim 1. The piezoelectric layer is formed on a semiconductor substrate,
A base film formed between the piezoelectric layer and the semiconductor substrate;
The piezoelectric element according to claim 1. Forming a piezoelectric layer made of a lead-free piezoelectric material having a crystal phase boundary and including a plurality of portions having different compositions on a semiconductor substrate;
The manufacturing method of the piezoelectric element containing this. In the step of forming the piezoelectric layer, as the piezoelectric layer, a portion made of a binary compound or a pseudo binary compound is formed, and as a raw material of the binary compound or pseudo binary compound , Using two kinds of materials comprising each of the first compound and the second compound constituting the binary compound or pseudo-binary compound,
The method for manufacturing a piezoelectric element according to claim 10. In the step of forming the piezoelectric layer, the formation rate of the piezoelectric layer is adjusted.
The method for manufacturing a piezoelectric element according to claim 10 or 11. Forming a piezoelectric layer made of a lead-free piezoelectric material having a crystal phase boundary on a semiconductor substrate;
In the step of forming the piezoelectric layer, the formation rate of the piezoelectric layer is changed.
A method for manufacturing a piezoelectric element. In the step of forming the piezoelectric layer, the formation rate is gradually or continuously reduced gradually.
The method for manufacturing a piezoelectric element according to claim 12 or 13.

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