JP5853846B2 - Piezoelectric element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piezoelectric element in which an electrode, a seed layer, and a piezoelectric thin film are formed in this order on a substrate, and a method for manufacturing the piezoelectric element.

Conventionally, piezoelectric materials including Pb (Zr, Ti) O ₃ (lead zirconate titanate; PZT) have been used as electromechanical transducers for application to actuators and sensors.

  Conventionally, bulk materials have been used as piezoelectric bodies, but in recent years, thin-film piezoelectric bodies have been studied due to the need for miniaturization, high density, and low cost. By reducing the thickness of the piezoelectric body, high-precision processing using semiconductor process technology such as film formation and photolithography can be performed, and miniaturization and high density can be realized. In addition, since the piezoelectric bodies can be collectively processed on a large-area wafer, the cost can be reduced. In particular, when a piezoelectric body is used as an actuator for an ink jet head, it is necessary to mount nozzles at a high density in order to increase the definition of a printed image. Therefore, downsizing of the piezoelectric element is important.

A piezoelectric material such as PZT is generally an ABO ₃ type oxide, and it is known that a good piezoelectric effect is exhibited when the crystal has a perovskite type structure. FIG. 9 schematically shows the crystal structure of PZT. The perovskite structure is, for example, a tetragonal crystal of Pb (Zr _x , Ti _1-x ) O ₃ , where Pb atoms are located at each vertex of the tetragonal crystal, and Ti atoms or Zr atoms are located at the body center. In this structure, an O atom is located in the heart.

  Further, the characteristics vary greatly depending on the direction of crystal orientation of the piezoelectric body relative to the electric field direction. FIG. 10 schematically shows the difference in piezoelectric effect due to the difference in crystal orientation of the piezoelectric body. When the piezoelectric body is in the (100) orientation, that is, when the polarization direction P of the piezoelectric body is the (100) direction and this direction is a direction perpendicular to the substrate, the piezoelectric body is applied when an electric field is applied in the direction perpendicular to the substrate. Since the polarization direction P and the application direction E of the electric field are aligned, the magnitude of the electric field is completely converted into the deformation force of the piezoelectric body, and the piezoelectric body is efficiently deformed in the direction perpendicular to the substrate. On the other hand, when the piezoelectric body is in the (111) orientation, the (100) direction, which is the polarization direction P of the piezoelectric body, intersects the electric field application direction E, so that the electric field magnitude is completely converted into the deformation force of the piezoelectric body. In other words, the amount of deformation of the piezoelectric body in the direction perpendicular to the substrate is reduced.

  As described above, the (100) orientation of the piezoelectric body is higher in the (100) orientation than in the piezoelectric material. However, from the viewpoint of fatigue characteristics and ease of processing, other crystal orientations such as the (111) orientation are possible. May be preferred. In any case, to obtain stable characteristics, it is important to control the crystal orientation of the piezoelectric body.

  Piezoelectric materials (piezoelectric thin films) are known for chemical film formation methods such as CVD (Chemical Vapor Deposition), physical film formation methods such as sputtering and ion plating, and liquid layer growth methods such as sol-gel methods. It has been. In these film forming methods, it is necessary to sequentially form an adhesion layer, a lower electrode, a piezoelectric body, an upper electrode and the like on a substrate such as Si. Therefore, the characteristics of each film are affected by the underlying layer.

  When a PZT film is formed by sputtering, although depending on conditions such as argon (Ar) gas pressure, a crystal structure of a pyrochlore layer having no piezoelectricity is often obtained at a substrate temperature of about 400 ° C. or lower. In the sol-gel method or the like, it is necessary to sinter at a high temperature of about 700 ° C. after applying the raw material liquid on the base. For this reason, platinum (Pt) having high temperature stability and high conductivity is often used as the lower electrode. Pt has the property of being easily self-aligned in the (111) direction.

  The thin film PZT has a perovskite structure as described above, and has a high piezoelectric characteristic when it is (100) oriented. However, since PZT is affected by the underlying Pt, PZT on the (111) oriented Pt Is difficult to form with (100) orientation. If PZT is formed with a (111) orientation or a pyrochlore phase is mixed, the piezoelectric characteristics of PZT will deteriorate.

Therefore, in Patent Document 1, for example, a main insulator layer made of PZT is provided on an electrode via a sub-insulator layer made of titanate (for example, PLT; (Pb, La) TiO ₃ ). PLT is more likely to have a (100) orientation than PZT and has a perovskite structure. Therefore, the PLT layer is formed on Pt as a seed layer, and PZT is formed on the seed layer. It is considered that the piezoelectric properties can be improved by improving the crystallinity and orientation of the film.

JP-A-6-89986 (refer to claim 1, paragraph [0101], FIG. 1 etc.)

  However, when PLT is formed with (100) orientation on Pt with (111) orientation, the lattice constant (0.3923 nm) on the (111) plane of Pt and the lattice constant (0.3887) on the (100) plane of PLT. Therefore, as the crystallinity of each layer improves, the stress concentrates on the interface between these layers, the adhesion of the seed layer decreases, and the seed layer peels off. In particular, the piezoelectric actuator is required to improve the piezoelectric constant and to further improve the generated force and driving displacement. However, as the driving displacement is improved, the driving stress is added to the internal stress, and the seed layer Peeling is likely to occur. Therefore, in order to improve the characteristics of the piezoelectric element, it is necessary to ensure adhesion between the layers as well as the piezoelectric displacement.

  This is a problem that can always occur if the atomic spacing (lattice constant) differs between the crystal plane of the electrode and the crystal plane of the seed layer, regardless of the material and orientation direction of the electrode and the material and orientation direction of the seed layer. In some cases, crystal orientation of the electrode is important as a foundation for forming the seed layer or piezoelectric thin film, or ease of processing in the subsequent process may be required. Is different. The same applies to the seed layer, and various materials, crystal structures, and orientations are required for the seed layer depending on the type and orientation of the electrode, the material of the piezoelectric thin film, crystallinity, and other required characteristics. For this reason, it is very important to develop a method for achieving both improvement in adhesion of the seed layer and improvement in piezoelectric characteristics regardless of the type of the electrode and the seed layer.

  The present invention has been made to solve the above-described problems, and its purpose is to reduce the stress generated at the interface between the electrode and the seed layer to improve the adhesion of the seed layer and to improve the piezoelectric characteristics. An object of the present invention is to provide a piezoelectric element that can be improved and a method for manufacturing the same.

  The piezoelectric element of the present invention is a piezoelectric element in which an electrode, a seed layer for controlling crystal orientation of a piezoelectric thin film, and the piezoelectric thin film are formed in this order on a substrate, and the seed layer includes: It includes both a first region that is crystallized and a second region that is made of amorphous. The piezoelectric element manufacturing method of the present invention is a piezoelectric element manufacturing method in which an electrode, a seed layer for controlling crystal orientation of a piezoelectric thin film, and the piezoelectric thin film are formed in this order on a substrate. The seed layer is formed by setting film forming conditions so that the seed layer includes both a first region that is crystallized and a second region that is made of amorphous. Yes.

  According to the above-described configuration and manufacturing method of the piezoelectric element, since a part of the seed layer is amorphous (second region), stress due to the difference in lattice constant does not occur at the interface between the electrode and amorphous. Therefore, as a whole, the stress generated at the interface between the electrode and the seed layer can be reduced. Thereby, the adhesion of the seed layer with respect to the electrode can be improved, and peeling of the seed layer can be reduced.

  Further, since the seed layer includes a crystallized region (first region), that is, a region where the crystal is oriented in a desired direction, the piezoelectric thin film formed on the seed layer seeds the crystal grains in the lower layer. Crystallize as Therefore, the piezoelectric thin film can be formed on the first region with a desired crystal orientation. Further, the second region of the seed layer is amorphous, and the piezoelectric thin film formed on the second region is also amorphous at the initial stage of film formation, but this amorphous region is a piezoelectric film formed thereon. Since the crystallization in the desired orientation direction of the thin film is not hindered, the piezoelectric thin film can be formed with the desired crystal orientation on the second region as the thickness of the piezoelectric thin film is increased. Thus, when the seed layer includes the first region and the second region, most of the piezoelectric thin film can be controlled in a desired orientation direction to improve the piezoelectric characteristics.

  In the above piezoelectric element, it is preferable that a ratio of the first region to the whole seed layer is 5% or more and 90% or less. In the above manufacturing method, it is preferable that the seed layer is formed under a film forming condition in which a ratio of the first region to the whole seed layer is 5% or more and 90% or less.

  If the ratio of the first region to the entire seed layer is below the lower limit, the ratio of the first region is too small, the orientation of the piezoelectric thin film formed on the seed layer is lowered, and the piezoelectric characteristics can be improved. It becomes difficult. On the contrary, if the ratio of the first region to the entire seed layer exceeds the upper limit, the proportion of the second region made of amorphous is too small, the adhesion of the seed layer to the electrode is lowered, and the seed layer is peeled off. It becomes easy. Therefore, when the ratio of the first region to the entire seed layer is within the above range, both the adhesion and orientation of the seed layer can be satisfied.

  In the above piezoelectric element, it is desirable that the ratio of the first region to the whole seed layer is 10% or more and 80% or less. In the above manufacturing method, it is preferable that the seed layer is formed under a film forming condition in which a ratio of the first region to the whole seed layer is 10% or more and 80% or less.

  In this case, both the adhesion and orientation of the seed layer can be satisfied with certainty.

  In the piezoelectric element and the manufacturing method described above, it is desirable that the first region of the seed layer is crystallized with a perovskite structure.

  In this case, since the piezoelectric thin film is crystallized with the same perovskite structure as the lower layer on the first region of the seed layer, the piezoelectric characteristics can be reliably improved.

  In the above piezoelectric element, the electrode may be (111) -oriented platinum, and the first region of the seed layer may be (100) -oriented lead lanthanum titanate. In the above manufacturing method, platinum may be formed with (111) orientation as the electrode, and lead lanthanum titanate with (100) orientation may be formed as the first region of the seed layer.

  On the electrode made of (111) -oriented platinum (Pt), lead lanthanum titanate (PLT) is formed in the (100) orientation as the first region of the seed layer. A thin film can be formed with (100) orientation to improve piezoelectric properties.

  In the piezoelectric element, the piezoelectric thin film may contain lead zirconate titanate as a main component. In the above manufacturing method, the piezoelectric thin film containing lead zirconate titanate as a main component may be formed on the seed layer.

  In this case, a piezoelectric thin film mainly composed of lead zirconate titanate (PZT) can be formed with a (100) orientation to improve the piezoelectric characteristics.

  In the piezoelectric element and the manufacturing method described above, the piezoelectric thin film may include lead lanthanum zirconate titanate in which part of the lead zirconate titanate is replaced with lanthanum.

  When the piezoelectric thin film contains lead lanthanum zirconate titanate (PLZT), the piezoelectric characteristics can be further improved.

  In the above manufacturing method, the seed layer is preferably formed by a sputtering method.

  In the sputtering method, since the seed layer is formed by heating the substrate, thermal stress is likely to be applied to the interface between the electrode and the seed layer. Therefore, the present invention in which a part of the seed layer is formed in an amorphous state to reduce the stress generated at the interface between the electrode and the seed layer is very effective.

  In the above manufacturing method, it is desirable to form the electrode by a sputtering method.

  In this case, the lower electrode and the seed layer can be formed continuously using the same sputtering apparatus.

  Since the seed layer formed on the electrode includes both the crystallized first region and the amorphous second region, the seed generated by reducing the stress generated at the interface between the electrode and the seed layer is reduced. While improving the adhesiveness of a layer, a piezoelectric characteristic can be improved.

It is sectional drawing which shows the schematic structure of the piezoelectric element which concerns on one Embodiment of this invention. It is sectional drawing which expands and shows the principal part of the said piezoelectric element. It is a flowchart which shows the flow of the manufacturing process of the said piezoelectric element. It is sectional drawing which shows the schematic structure of the sputtering device used for manufacture of the said piezoelectric element. It is a graph which shows the result of 2theta / theta measurement of XRD with respect to the seed layer of the said piezoelectric element. It is a graph which shows the result of 2theta / theta measurement of XRD with respect to the piezoelectric thin film of the said piezoelectric element. It is a top view which shows a structure when the said piezoelectric element is applied to a diaphragm. It is A-A 'arrow sectional drawing of FIG. It is explanatory drawing which shows typically the crystal structure of PZT. It is explanatory drawing which shows typically the difference in the piezoelectric effect by the difference in the crystal orientation of a piezoelectric material.

  An embodiment of the present invention will be described below with reference to the drawings.

[1. (Configuration of piezoelectric element)
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a piezoelectric element 10 according to the present embodiment. The piezoelectric element 10 of this embodiment is configured by laminating a thermal oxide film 2, a lower electrode 3, a seed layer 4, a piezoelectric thin film 5 and an upper electrode 6 in this order on a substrate 1.

The substrate 1 is configured by a semiconductor substrate or a SOI (Silicon on Insulator) substrate made of a single crystal Si (silicon) alone having a thickness of, for example, about 300 to 500 μm. The thermal oxide film 2 is made of, for example, SiO ₂ (silicon oxide) having a thickness of about 0.1 μm, and is formed for the purpose of protecting and insulating the substrate 1.

  The lower electrode 3 is formed by laminating a Ti (titanium) layer 3a and a Pt (platinum) layer 3b. The Ti layer 3a is formed to improve the adhesion between the thermal oxide film 2 and the Pt layer 3b. The thickness of the Ti layer 3a is, for example, about 0.02 μm, and the thickness of the Pt layer 3b is, for example, about 0.1 μm.

  The seed layer 4 is a layer for controlling the crystal orientation of the piezoelectric thin film 5 formed thereon, and details thereof will be described later. The thickness of the seed layer 4 is 45 nm, for example.

  The piezoelectric thin film 5 is composed mainly of PZT (lead zirconate titanate) having a perovskite structure. In addition, that PZT is a main component means that the proportion of PZT in the piezoelectric thin film 5 is 80% or more. For example, the piezoelectric thin film 5 may contain lead lanthanum zirconate titanate (PLZT) in which a part of PZT is replaced with lanthanum (La) in addition to PZT. Although the thickness of the piezoelectric thin film 5 varies depending on the application, it is, for example, 1 μm or less for a memory or a sensor, and 3-5 μm for an actuator.

  The upper electrode 6 is formed by laminating a Ti layer 6a and a Pt layer 6b. The Ti layer 6a is formed to improve the adhesion between the piezoelectric thin film 5 and the Pt layer 6b. The thickness of the Ti layer 6a is, for example, about 0.02 μm, and the thickness of the Pt layer 6b is, for example, about 0.2 μm.

  FIG. 2 is an enlarged cross-sectional view showing the main part of the piezoelectric element 10 of the present embodiment. The seed layer 4 includes both a first region 4a that is crystallized in a single crystal or polycrystal state and a second region 4b that is made of amorphous (amorphous). The first region 4a is composed of PLT (lead lanthanum titanate), which is a piezoelectric body having a perovskite structure, and the crystal is oriented so that the direction perpendicular to the substrate 1 is the (100) direction. doing. The second region 4b is formed on the Pt layer 3b, and the first region 4a is located closer to the piezoelectric thin film 5 than the interface between the second region 4b and the Pt layer 3b. That is, the interface between the second region 4 b and the Pt layer 3 b is the interface between the seed layer 4 and the lower electrode 3. The seed layer 4 including both the first region 4a and the second region 4b can be formed by appropriately controlling the PLT film formation conditions (for example, the substrate temperature).

  Here, the first region 4a of the seed layer 4 expands as the film thickness increases, and the second region 4b narrows as the film thickness increases. This is because once the (100) -oriented crystal is formed in the seed layer 4, crystallization with the (100) orientation proceeds in the film thickness direction using the crystal as a base, and the second of the seed layer 4 This is because the region 4b is amorphous and does not hinder crystallization in the (100) orientation, so that crystallization in the (100) orientation proceeds in a direction perpendicular to the film thickness direction.

  As in the present embodiment, since part of the seed layer 4 is an amorphous region (second region 4b), the interface between the Pt layer 3b and the second region 4b is caused by a difference in lattice constant. Since no stress is generated, the stress generated at the interface between the lower electrode 3 and the seed layer 4 can be reduced. Thereby, the adhesiveness of the seed layer 4 with respect to the lower electrode 3 can be improved, and peeling of the seed layer 4 can be reduced.

  In addition, since the seed layer 4 includes the first region 4a in which the crystal is oriented in the (100) direction, the piezoelectric thin film 5 formed on the first region 4a is the first region 4a serving as a base thereof. The crystal grains are crystallized so as to have a (100) orientation as a seed crystal. In FIG. 2, in the piezoelectric thin film 5, a region crystallized with (100) orientation is defined as a region 5a. On the other hand, on the second region 4b, an amorphous region 5b is formed at the initial stage of the formation of the piezoelectric thin film 5 due to the influence of the underlying second region 4b. The amorphous region 5b does not hinder crystallization of the piezoelectric thin film 5 formed thereon in a desired orientation direction. Therefore, as the thickness of the piezoelectric thin film 5 is increased, the amorphous region 5b is also formed on the second region 4b. The piezoelectric thin film 5 can be formed with a desired crystal orientation. That is, as the thickness of the piezoelectric thin film 5 is increased, the region 5a crystallized with the (100) orientation can be expanded. As described above, since the orientation direction of most of the piezoelectric thin film 5 can be controlled to a desired (100) direction, the piezoelectric characteristics can be improved.

  Since the first region 4a of the seed layer 4 is a region where PLT is crystallized with a perovskite structure, the piezoelectric thin film 5 has the same perovskite structure as the lower layer on the first region 4a of the seed layer 4. Crystallize with. Thereby, the perovskite crystallinity of the piezoelectric thin film 5 can be improved, and the piezoelectric characteristics can be reliably improved.

  Further, the electrode (Pt layer 3b) serving as the base of the seed layer 4 is (111) -oriented Pt, and the first region 4a of the seed layer 4 is a (100) -oriented PLT. Even when Pt, which is easy to self-orient in the direction, is used as the lower electrode, the piezoelectric thin film 5 can be formed with the same (100) orientation as PLT to improve the piezoelectric characteristics. In particular, since the piezoelectric thin film 5 has PZT as a main component, PZT can be formed with a (100) orientation to improve the piezoelectric characteristics. Moreover, when the piezoelectric thin film 5 contains PLZT in addition to PZT, the piezoelectric characteristics can be further improved.

[2. Method for manufacturing piezoelectric element]
Next, an example of the method for manufacturing the piezoelectric element 10 of the present embodiment will be described, and a comparative example will also be described. FIG. 3 is a flowchart showing the flow of the manufacturing process of the piezoelectric element 10.

Example 1
First, a single crystal Si wafer having a thickness of about 400 μm is used as the substrate 1, and a thermal oxide film 2 is formed on the substrate 1 with a thickness of about 0.1 μm (S1). The thermal oxide film 2 can be formed by exposing the Si wafer to a high temperature of about 1200 ° C. in an oxygen atmosphere using a wet oxidation furnace.

  Subsequently, Ti and Pt are sequentially formed on the thermal oxide film 2 of the substrate 1 by sputtering to form the lower electrode 3 composed of the Ti layer 3a and the Pt layer 3b (S2, S3). The thickness of the Ti layer 3a is, for example, 6 nm, and the thickness of the Pt layer 3b is, for example, 150 nm. The sputtering conditions for Ti at this time are Ar flow rate: 20 sccm, pressure: 0.7 Pa, substrate temperature: 500 ° C., and RF power applied to the target: 80 W. The sputtering conditions for Pt are Ar flow rate: 20 sccm, pressure: 0.5 Pa, substrate temperature: 500 ° C., and RF power applied to the target: 100 W. Since Pt constituting the Pt layer 3b has self-orientation, it is oriented in the (111) direction with respect to the substrate 1.

Next, PLT is formed on the lower electrode 3 (Pt layer 3b) by sputtering to form a seed layer 4 having a thickness of about 45 nm (S4). The sputtering conditions for PLT are Ar flow rate: 19.5 sccm, O ₂ flow rate: 0.5 sccm, pressure: 0.5 Pa, substrate temperature: 640 ° C., and RF power applied to the target: 150 W.

  The formation of the Ti layer 3a, the Pt layer 3b, and the seed layer 4 is preferably performed using a ternary sputtering apparatus having three targets of Ti, Pt, and PLT in the chamber. In this way, each layer can be formed continuously without taking the substrate out of vacuum in situ (in situ).

FIG. 4 is a cross-sectional view showing a schematic configuration of the sputtering apparatus. In the sputtering apparatus, a target dish 12 on which a target 11 is placed is placed on a magnet 13 and a cover 14 is placed thereon. The magnet 13 and the high-frequency electrode 15 below the magnet 13 are insulated from the vacuum chamber 17 by an insulator 16. The high frequency electrode 15 is connected to a high frequency power source 18. Next, the substrate 1 is placed on the substrate heater 19. Then, the inside of the vacuum chamber 17 is evacuated, and the substrate 1 is heated to a predetermined temperature by the substrate heater 19. After heating, the valves 20 and 21 are opened, and Ar and O ₂ as sputtering gases are introduced into the vacuum chamber 17 from the nozzle 22 at a predetermined ratio, and the degree of vacuum is maintained at a predetermined value. By applying high-frequency power from the high-frequency power source 18 to the target 11 to generate plasma, the target 11 can fly the material molecules of the target 11 to form a desired film.

Next, PZT is formed on the seed layer 4 made of PLT by sputtering to form a piezoelectric thin film 5 having a thickness of about 4 μm (S5). The sputtering conditions for PZT are Ar flow rate: 30 sccm, O ₂ flow rate: 0.3 sccm, pressure: 0.3 Pa, substrate temperature: 650 ° C., and RF power applied to the target: 500 W.

  Subsequently, Ti and Pt are sequentially formed on the piezoelectric thin film 5 by sputtering to form the upper electrode 6 composed of the Ti layer 6a and the Pt layer 6b (S6, S7). Thereby, the piezoelectric element 10 is completed. The film thickness of the Ti layer 6a is, for example, 20 nm, and the film thickness of the Pt layer 6b is, for example, 200 nm. The sputtering conditions for Ti at this time are Ar flow rate: 20 sccm, pressure: 0.7 Pa, substrate temperature: 500 ° C., and RF power applied to the target: 80 W. The sputtering conditions for Pt are Ar flow rate: 20 sccm, pressure: 0.5 Pa, substrate temperature: 500 ° C., and RF power applied to the target: 100 W.

(Example 2)
In the seed layer 4 formation step (S4), the PLT film formation conditions (sputtering conditions) are the same as in Example 1 except that the substrate temperature was changed to 630 ° C.

(Example 3)
In the formation process (S4) of the seed layer 4, it is the same as that of Example 1 except having changed the substrate temperature into 620 degreeC as PLT film-forming conditions (sputtering conditions).

(Comparative Example 1)
In the formation process (S4) of the seed layer 4, it is the same as that of Example 1 except having changed the substrate temperature into 650 degreeC as PLT film-forming conditions (sputtering conditions).

(Comparative Example 2)
In the formation process (S4) of the seed layer 4, it is the same as that of Example 1 except having changed the substrate temperature into 610 degreeC as PLT film-forming conditions (sputtering conditions).

[3. Evaluation of adhesion and orientation)
In each of Examples 1 to 3 and Comparative Examples 1 and 2 described above, XRD (X-ray diffraction) is applied to the PLT constituting the seed layer 4 before the piezoelectric thin film 5 is formed. 2θ / θ measurement was performed to examine the crystal orientation of PLT. FIG. 5 is a graph showing the results of XRD 2θ / θ measurement for the PLTs of Examples 1 to 3 and Comparative Examples 1 and 2. In FIG. 5, for the purpose of simultaneously comparing the graphs of Examples 1 to 3 and Comparative Examples 1 and 2, these graphs are simultaneously shifted in the vertical direction by one scale on the vertical axis. The vertical axis in FIG. 5 indicates the X-ray count rate (cps; count per second) per second. In addition, 1. E + n indicates 1.0 × 10 ⁿ .

  From FIG. 5, it can be seen that the PLTs of Examples 1 to 3 and Comparative Examples 1 and 2 have a (100) single orientation (because other peaks such as (111) do not appear). Incidentally, Table 1 shows values of (100) peak intensity of PLT. Table 1 also shows the results of PLT (100) coverage, PLT adhesion evaluation, and PZT orientation evaluation, which will be described later.

  Next, in each of Examples 1 to 3 and Comparative Examples 1 and 2, the surface shape of the PLT constituting the seed layer 4 was observed using an SEM (Scanning Electron Microscope). Then, the coverage of PLT (100) (the coverage of the first region 4a) was measured. Here, the coverage (%) of PLT (100) is the ratio of the area (total) of (100) -oriented PLT crystal grains to the entire surface area of the seed layer 4 on the piezoelectric thin film 5 side. Point to. Here, simply, the ratio of the area with crystal grains to the total area of the image obtained by SEM was defined as the coverage. From the XRD measurement results shown in FIG. 5, only the peak indicating the (100) orientation was confirmed as the PLT intensity peak, so the crystal grains are considered to be the (100) oriented crystal grains of the PLT. . Therefore, as described above, the ratio of the area with crystal grains to the total area of the SEM image was defined as the PLT (100) coverage. In addition, since the seed layer 4 (PLT) of Examples 1 to 3 and Comparative Examples 1 and 2 is a thin film having a thickness of about 45 nm, the coverage of the PLT (100) is the first for the entire seed layer 4. This substantially corresponds to the ratio of the region 4a.

Subsequently, in each of Examples 1 to 3 and Comparative Examples 1 and 2, evaluation of adhesion of PLT to the Pt layer 3b was performed. Specifically, based on the procedure of the crosscut method stipulated in JIS (Japanese Industrial Standards) K5600-5-6, 5 × 5 pieces of 1 cm square PLT are cut at intervals of 2 mm in the vertical and horizontal directions. Make a grid, apply adhesive tape to the surface, rub it with your fingertips so that it adheres sufficiently, and then visually observe the surface of the PLT when the adhesive tape is peeled off (visually see how much the PLT has been peeled off) Observed). And the adhesiveness of PLT was evaluated based on the following references | standards.
1: There are almost no squares from which PLT has been peeled off, and adhesion is quite good.
2: There are few squares from which PLT peeled off, and adhesiveness is favorable.
3: Many squares from which PLT was peeled off, and adhesion was insufficient.

Next, after forming PZT as the piezoelectric thin film 5 on the seed layer 4 in each of Examples 1 to 3 and Comparative Examples 1 to 2, XRD 2θ / θ measurement was performed on the PZT, and the PZT The crystal orientation was examined. FIG. 6 is a graph showing the results of XRD 2θ / θ measurement for PZT in Examples 1 to 3 and Comparative Examples 1 and 2. Here, the (100) orientation degree of PZT was calculated by calculating the (100) orientation degree of PZT using the peak intensity obtained by performing XRD 2θ / θ measurement on PZT. Specifically, the degree of (100) orientation of PZT is I, the peak intensity indicating the (100) orientation of PZT is I (100), the peak intensity indicating the (110) orientation of PZT is I (110), When the peak intensity indicating the (111) orientation of PZT is I (111), the (100) orientation degree I of PZT is
I (%) = {I (100) / (I (100) + I (110) + I (111))}
× 100
Is required. Evaluation of (100) orientation of PZT was performed based on the following criteria.
A: The (100) orientation degree I of PZT is 99% or more.
X: The (100) orientation degree I of PZT is less than 99%.

  In Table 1, when the coverage of PLT (100) is 100% as in Comparative Example 1, it is considered that there are many PLT (100) -oriented regions (first regions 4a) in the seed layer 4. As a result, the PZT (100) orientation is good. However, the adhesion of PLT is insufficient. This is presumably because the amorphous second region 4b in the seed layer 4 was relatively reduced, and the stress at the interface between the Pt layer 3b and the seed layer 4 could not be reduced.

  Further, as in Comparative Example 2, when the coverage of PLT (100) is 0%, the seed layer 4 has few (100) -oriented regions (first regions 4a) and is an amorphous region. Since there are many (2nd area | regions 4b), although the stress in the interface of Pt layer 3b and the seed layer 4 can be reduced and favorable adhesiveness can be ensured, since there are few 1st area | regions 4a, PZT (100 ) The orientation is not secured. Incidentally, in Comparative Example 2, the degree of PZT (100) orientation I was 96%.

  On the other hand, in Examples 1 to 3, the PLT (100) coverage is 10% or more and 80% or less, and in this range, both PLT adhesion and PZT (100) orientation are good. It turns out that the result is obtained. From Table 1, it is considered that the PZT (100) orientation degree I approaches 99% when the PLT (100) coverage is between 0% (Comparative Example 2) and 10% (Example 3). It is estimated that the PZT (100) orientation can be improved even if the coverage of PLT (100) is 5% between them. Moreover, since it is considered that there is a boundary between PLT (100) coverage of 80% (Example 1) and 100% (Comparative Example 1), the adhesion of PLT is insufficient and good, so PLT If the coverage of (100) is 90% between them, it is estimated that the adhesion of PLT can be improved.

  From the above, if the coverage of PLT (100) is 5% or more and 90% or less, that is, if the ratio of the first region 4a to the whole seed layer 4 is 5% or more and 90% or less, PLT adhesion It can be said that both of the properties and the (100) orientation of PZT can be satisfied.

[4. Electrode, seed layer, piezoelectric thin film materials)
The electrode material constituting the lower electrode 3 is not limited to the above-described Pt, and for example, Au (gold), Ir (iridium), IrO ₂ (iridium oxide), RuO ₂ (ruthenium oxide), Metals or metal oxides such as LaNiO ₃ (lanthanum nickelate), SrRuO ₃ (strontium ruthenate), and combinations thereof are conceivable.

The material constituting the seed layer 4 is not limited to the above-described PLT, and for example, LaNiO ₃ , SrRuO ₃ , MgO (magnesium oxide), PbTiO ₃ (lead titanate), Pb (La, Ti) ) oxides such as O ₃ can be considered.

The material constituting the piezoelectric thin film 5 is not limited to the above-described PZT, and other than that, for example, PZT added with La, Nb (niobium), Sr (strontium), BaTiO ₃ (barium titanate) ), LiTaO ₃ (lithium tantalate), Pb (Mg, Nb) O ₃ , Pb (Ni, Nb) O ₃ , PbTiO _{3 and} other oxides, and combinations thereof are conceivable.

[5. Application example of piezoelectric element)
FIG. 7 is a plan view showing a configuration when the piezoelectric element 10 manufactured in this embodiment is applied to a diaphragm (diaphragm), and FIG. 8 is a cross-sectional view taken along line AA ′ in FIG. . The piezoelectric thin films 5 are arranged in a necessary area of the substrate 1 in a two-dimensional staggered pattern. A region corresponding to the formation region of the piezoelectric thin film 5 in the substrate 1 is a concave portion 1a in which a part in the thickness direction is removed with a circular cross section, and is formed on the upper portion of the concave portion 1a (on the bottom side of the concave portion 1a) Remains a thin plate-like region 1b. The lower electrode 3 and the upper electrode 6 are connected to an external control circuit by wiring not shown.

  Only the predetermined piezoelectric thin film 5 can be driven by applying an electrical signal from the control circuit to the lower electrode 3 and the upper electrode 6 sandwiching the predetermined piezoelectric thin film 5. That is, when a predetermined electric field is applied to the upper and lower electrodes of the piezoelectric thin film 5, the piezoelectric thin film 5 expands and contracts in the left-right direction, and the piezoelectric thin film 5 and the region 1b of the substrate 1 are bent up and down by the bimetal effect. Therefore, when the recess 1a of the substrate 1 is filled with gas or liquid, the piezoelectric element 10 can be used as a pump, which is suitable for an inkjet head, for example.

  Further, the amount of deformation of the piezoelectric thin film 5 can also be detected by detecting the charge amount of the predetermined piezoelectric thin film 5 via the lower electrode 3 and the upper electrode 6. That is, when the piezoelectric thin film 5 is vibrated by sound waves or ultrasonic waves, an electric field is generated between the upper and lower electrodes due to an effect opposite to that described above. By detecting the magnitude of the electric field and the frequency of the detection signal at this time, the piezoelectric film The element 10 can also be used as a sensor (ultrasonic sensor). Furthermore, if the piezoelectric thin film 5 exhibits a pyroelectric effect, the piezoelectric element 10 can be used as a pyroelectric sensor (infrared sensor).

  In addition, by using the piezoelectric effect of the piezoelectric thin film 5, the piezoelectric element 10 can be used as a frequency filter (surface acoustic wave filter). If the piezoelectric thin film 5 is made of a ferroelectric material, the piezoelectric element 10 is nonvolatile. It can also be used as a memory.

  In the present embodiment, the seed layer 4 is formed by sputtering, but the seed layer 4 is formed not only by the sputtering method described above but also by vapor deposition or physical vapor deposition, which is physical vapor deposition. Other methods such as a CVD method as a growth method and a sol-gel method as a liquid phase method can also be used. However, in the sputtering method, since the substrate 1 is heated to form the seed layer 4 as described above, thermal stress is likely to be applied to the interface between the Pt layer 3 b and the seed layer 4. Therefore, in the present invention, a part of the seed layer 4 can be formed of amorphous to reduce the stress generated at the interface between the Pt layer 3b and the seed layer 4 and to reduce the peeling of the seed layer 4. This is very effective when the film is formed by the method. In addition to the sputtering method, the piezoelectric thin film 5 can also be formed by a method such as a vapor deposition method, a CVD method, or a sol-gel method.

  Further, when the seed layer 4 is formed by sputtering, as described above, it is desirable that the lower electrode 3 serving as the underlayer is also formed by sputtering, because it can be continuously formed using a single sputtering apparatus. .

  In the present embodiment, the first region 4a crystallized and the second amorphous region 4b are obtained by appropriately controlling the film formation temperature (substrate temperature) as the film formation condition of the seed layer 4. The seed layer 4 including both is formed, but the film formation conditions other than the film formation temperature (for example, the gas flow rate, the sputtering pressure, the RF power applied to the target) are appropriately controlled to control the first region 4a. Alternatively, the seed layer 4 including the second region 4b may be formed.

  The present invention is applicable to various devices such as an inkjet head, an ultrasonic sensor, an infrared sensor, a frequency filter, and a nonvolatile memory.

1 Substrate 3b Pt layer (electrode)
4 seed layer 4a first region 4b second region 5 piezoelectric thin film 10 piezoelectric element

Claims (18)

A piezoelectric element in which an electrode, a seed layer for controlling crystal orientation of the piezoelectric thin film, and the piezoelectric thin film are formed in this order on a substrate,
The seed layer includes both a first region that is crystallized and a second region that is amorphous ;
The piezoelectric thin film is located on the first region and the second region,
The piezoelectric element according to claim 1, wherein the first region of the seed layer is located closer to the piezoelectric thin film than an interface between the second region and the electrode .   2. The piezoelectric element according to claim 1, wherein a ratio of the first region to the entire seed layer is 5% or more and 90% or less.   3. The piezoelectric element according to claim 1, wherein a ratio of the first region to the entire seed layer is 10% or more and 80% or less.   4. The piezoelectric element according to claim 1, wherein the first region of the seed layer is crystallized with a perovskite structure. 5. The electrode is (111) oriented platinum;
5. The piezoelectric element according to claim 1, wherein the first region of the seed layer is (100) -oriented lead lanthanum titanate.   6. The piezoelectric element according to claim 5, wherein the piezoelectric thin film contains lead zirconate titanate as a main component.   The piezoelectric element according to claim 6, wherein the piezoelectric thin film includes lead lanthanum zirconate titanate in which a part of the lead zirconate titanate is substituted with lanthanum. A method for manufacturing a piezoelectric element, comprising forming an electrode, a seed layer for controlling crystal orientation of a piezoelectric thin film, and the piezoelectric thin film in this order on a substrate,
Forming the seed layer by setting film formation conditions so that the seed layer includes both a first region that is crystallized and a second region that is made of amorphous ;
Forming the piezoelectric thin film on the first region and the second region of the seed layer,
The method for manufacturing a piezoelectric element, wherein the first region of the seed layer is located closer to the piezoelectric thin film than an interface between the second region and the electrode .   9. The method for manufacturing a piezoelectric element according to claim 8, wherein the seed layer is formed under a film forming condition in which a ratio of the first region to the whole seed layer is 5% or more and 90% or less.   10. The method of manufacturing a piezoelectric element according to claim 8, wherein the seed layer is formed under a film forming condition in which a ratio of the first region to the entire seed layer is 10% or more and 80% or less. .   11. The method for manufacturing a piezoelectric element according to claim 8, wherein the first region of the seed layer is crystallized with a perovskite structure. As the electrode, platinum is formed with (111) orientation,
12. The method of manufacturing a piezoelectric element according to claim 8, wherein lead lanthanum titanate is formed in a (100) orientation as the first region of the seed layer.   13. The method of manufacturing a piezoelectric element according to claim 12, wherein the piezoelectric thin film mainly composed of lead zirconate titanate is formed on the seed layer.   14. The method of manufacturing a piezoelectric element according to claim 13, wherein the piezoelectric thin film includes lead lanthanum zirconate titanate in which a part of the lead zirconate titanate is substituted with lanthanum.   The method for manufacturing a piezoelectric element according to claim 8, wherein the seed layer is formed by a sputtering method.   The method of manufacturing a piezoelectric element according to claim 15, wherein the electrode is formed by a sputtering method. 8. The seed layer according to claim 1, wherein the first region is located apart from the electrode through the second region so as not to contact the electrode. 9. The piezoelectric element according to any one of the above. 17. The seed layer according to claim 8, wherein the first region is located apart from the electrode through the second region so as not to contact the electrode. The manufacturing method of the piezoelectric element in any one.

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