Patent Description:
As a material having excellent piezoelectric characteristics and excellent ferroelectricity, there is known a perovskite-type oxide such as lead zirconate titanate (Pb(Zr,Ti)O<NUM>, hereinafter referred to as PZT). A piezoelectric body consisting of a perovskite-type oxide is applied as a piezoelectric film in a piezoelectric element having a lower electrode, a piezoelectric film, and an upper electrode on a substrate. This piezoelectric element has been developed into various devices such as a memory, an inkjet head (an actuator), a micromirror device, an angular velocity sensor, a gyro sensor, a piezoelectric micromachined ultrasonic transducer (PMUT), and an oscillation power generation device.

In a case of applying a piezoelectric element to a device, it is desirable that the piezoelectric element has high piezoelectric characteristics because higher piezoelectric characteristics lead to power saving. So far, for the improvement of the piezoelectric characteristics, methods such as improving the crystallinity of the piezoelectric film and reducing the resistance of the electrode layer have been studied.

As the lower electrode layer of the piezoelectric element, an Ir layer is used in a large number of cases from the viewpoint of the adhesiveness to the piezoelectric film and the reduction of the resistance. It is noted that, for the reduction of the resistance, the Ir layer is generally made to have a thickness of <NUM> or more. Further, although the Ir layer has good adhesiveness to the piezoelectric film, it does not have good adhesiveness to the silicon substrate, and thus in a large number of cases, an intimate attachment layer consisting of a TiW layer or a Ti layer is provided between the Ir layer and the substrate (<CIT> and <CIT>).

<CIT> proposes a laminated structure in which an Ir layer and an Au layer are laminated for more reduction of the resistance of the lower electrode layer. In a case of using Au, which has higher conductivity than Ir, it is possible to realize the reduction of the resistance of the entire lower electrode layer. <CIT> discloses a piezoelectric laminate provided with a lower electrode layer and a piezoelectric film in this order on a substrate, and a region of the lower electrode layer in contact with the piezoelectric film is composed of a metal layer, and the metal layer.

In a case where a piezoelectric film containing a perovskite-type oxide as a main component is formed on an Ir layer, there is a problem that a pyrochlore phase, which is a different phase, is easily formed at the interface between the piezoelectric film and the lower electrode layer. The pyrochlore phase is paraelectric, and thus the deterioration of the piezoelectric characteristics, such as a decrease in the dielectric constant and a decrease in the piezoelectric constant occurs in a case where the pyrochlore phase is formed. Further, in a piezoelectric element including a pyrochlore phase at the interface between the piezoelectric film and the lower electrode layer, peeling or the like occurs easily, and thus the low long-term reliability is low as compared with a piezoelectric element in which the pyrochlore phase is suppressed.

As in <CIT>, in a case where an Au layer is provided in the lower electrode layer, the reduction of the resistance can be realized. On the other hand, it has been found that in a case where an Au layer is provided in the lower electrode layer, the long-term reliability decreases as compared with a case of the laminated structure of the Ir layer and the TiW or Ti intimate attachment layer, which is disclosed in <CIT> and <CIT>. It is conceived that this is because the diffusion of Au occurs due to carrying out the high temperature film formation in a case of forming a piezoelectric film according to a sputter film formation on the lower electrode layer. Due to having a relatively low melting point, it is presumed that Au diffuses into the piezoelectric film at the time of the formation of the piezoelectric film, and thus leaking easily occurs.

The technique of the present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a piezoelectric laminate and a piezoelectric element having improved long-term reliability without decreasing the piezoelectric characteristics as compared with the case of the related art.

Specific means for solving the above problems include the following aspects.

A piezoelectric laminate of the present disclosure is a piezoelectric laminate according to independent device claim <NUM>.

In the piezoelectric laminate of the present disclosure, it is preferable that a first intimate attachment layer that improves adhesiveness between the substrate and the first layer is provided between the substrate and the first layer.

The first intimate attachment layer is preferably a TiW layer.

In the piezoelectric laminate of the present disclosure, it is preferable that a second intimate attachment layer that improves adhesiveness between the first layer and the second layer is provided between the first layer and the second layer.

The second intimate attachment layer is preferably a TiW layer.

In the piezoelectric laminate of the present disclosure, it is preferable that the first layer is a W layer.

In the piezoelectric laminate of the present disclosure, it is preferable that the perovskite-type oxide is a compound represented by General Formula (<NUM>),.

Pb{(ZrxTi<NUM>-x)<NUM>-yB1y}O<NUM>     (<NUM>).

<MAT> and B1 is one or more elements selected from V, Nb, Ta, Sb, Mo, and W.

In the piezoelectric laminate of the present disclosure, it is preferable that the half width at half maximum of the X-ray diffraction peak from the (<NUM>) plane of the Ir of the second layer is <NUM>° or more.

In the piezoelectric laminate of the present disclosure, it is preferable that the second layer is a uniaxial alignment film in which Ir is aligned in a (<NUM>) plane, and the (<NUM>) plane has an inclination of <NUM>° or more with respect to a thickness direction.

In the piezoelectric laminate of the present disclosure, it is preferable that a pyrochlore phase is included at an interface between the lower electrode layer and the piezoelectric film, and a thickness of the pyrochlore phase is <NUM> or less.

The piezoelectric element of the present disclosure has the piezoelectric laminate of the present disclosure and an upper electrode layer provided on the piezoelectric film of the piezoelectric laminate.

According to the piezoelectric laminate and the piezoelectric element of the present disclosure, it is possible to improve long-term reliability without decreasing the piezoelectric characteristics as compared with the case of the related art.

In the drawings below, the layer thickness of each of the layers and the ratio therebetween are appropriately changed and drawn for easy visibility, and thus they do not necessarily reflect the actual layer thickness and ratio.

Piezoelectric laminate <NUM> and piezoelectric element <NUM>, according to first embodimentFig. <NUM> is a cross-sectional view illustrating layer configurations of a piezoelectric laminate <NUM> and a piezoelectric element <NUM> having the piezoelectric laminate <NUM>, according to a first embodiment. As illustrated in <FIG>, the piezoelectric element <NUM> has the piezoelectric laminate <NUM> and an upper electrode layer <NUM>. The piezoelectric laminate <NUM> has a substrate <NUM> and a piezoelectric film <NUM> laminated on the substrate <NUM>, where the piezoelectric film <NUM> includes a lower electrode layer <NUM> and contains a perovskite-type oxide. Here, "lower" and "upper" do not respectively mean top and bottom in the vertical direction. As result, an electrode arranged on the side of the substrate <NUM> with the piezoelectric film <NUM> being interposed is merely referred to as the lower electrode layer <NUM>, and an electrode arranged on the side of the piezoelectric film <NUM> opposite to the substrate <NUM> is merely referred to as the upper electrode layer <NUM>.

In the piezoelectric laminate <NUM> and the piezoelectric element <NUM> according to the present embodiment, the lower electrode layer <NUM> includes a second layer <NUM> arranged in a state of being in contact with the piezoelectric film <NUM> and includes a first layer <NUM> arranged on a side of the second layer <NUM> from the substrate <NUM>. The first layer <NUM> contains one or more of tungsten (W), molybdenum (Mo), niobium (Nb), and tantalum (Ta), as a main component. Here, the "main component" refers to a component that occupies <NUM> wt% or more of the constituent elements. "Contains one or more as a main component" means that only one of W, Mo, Nb, or Ta may be contained as a main component, or two or more thereof may be combinedly contained as a main component. In a case where the first layer <NUM> contains only one of W, Mo, Nb, and Ta, the one thereof occupies <NUM> wt% or more. For example, it means that W occupies <NUM> wt% or more in a case where the first layer <NUM> contains only W in the above group. Further, it means that the total of two or more elements contained occupies <NUM> wt% or more in a case where the first layer <NUM> contains two or more of W, Mo, Nb, and Ta. For example, it means that the total content of W and Mo occupies <NUM> wt% or more in a case where the first layer <NUM> contains W and Mo as main components. It is particularly preferable that the first layer <NUM> is a layer containing W as a main component. All of W, Mo, Nb, and Ta are metals having a high melting point. Here, the metal having a high melting point refers to a metal having a melting point of iron (Fe) of <NUM>,<NUM> or higher.

The second layer <NUM> is a layer containing Ir as a main component, and in the following description, the second layer <NUM> may be referred to as an Ir layer <NUM>. The thickness t2 of the Ir layer <NUM> is <NUM> or less. In addition, the thickness t2 is preferably <NUM> or more. The inventors of the present invention have found that in a case of setting the thickness t2 of the Ir layer <NUM> to <NUM> or less and preferably less than <NUM>, it is possible to suppress the growth of the pyrochlore phase at the initial stage of the formation of the piezoelectric film <NUM> that is formed on the Ir layer <NUM> (see Examples). The inventors of the present invention presume that in a case where the thickness t2 of the Ir layer <NUM> is set to <NUM> or less, the preferential alignment in the Ir (<NUM>) plane does not reach a sufficient alignment level, which enables a state having a low crystallinity, and thus it is possible to suppress the growth of the pyrochlore phase at the time of the formation of the piezoelectric film <NUM>. It is noted that in a case of setting the thickness of the Ir layer <NUM> to <NUM> or more, it is possible to form the Ir layer <NUM> into a uniform film shape, which is preferable.

The thickness of the Ir layer <NUM> is <NUM> or less, which is thin as compared with the Ir layer in the related art, and thus the first layer <NUM> is provided in order to have sufficient conductivity as the lower electrode layer <NUM>.

The thickness t of the entire lower electrode layer <NUM> is preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more.

The thickness t of the lower electrode layer <NUM> and the thickness t2 of the Ir layer <NUM> can be estimated from a scanning electron microscope (SEM) image of a cross section of a piezoelectric element, a transmission electron microscope (TEM) image, or a secondary ion mass spectrometry (SIMS) analysis.

The half width at half maximum of an X-ray diffraction peak (hereinafter, referred to as an Ir (<NUM>) peak) from the (<NUM>) plane in the Ir layer <NUM> is preferably <NUM>° or more. The half width at half maximum of the Ir (<NUM>) peak is more preferably <NUM>° or more. In addition, the half width at half maximum of the Ir (<NUM>) peak is preferably <NUM>° or less and more preferably <NUM>° or less.

Here, the half width at half maximum of the Ir (<NUM>) peak shall be measured as follows. The upper electrode layer <NUM> of the piezoelectric element is removed, and an XRD chart according to the X-ray diffraction (XRD) of a thin film is acquired in a state where the lower electrode layer <NUM> and the piezoelectric film <NUM> are provided on the substrate <NUM>. The Ir (<NUM>) peak in the XRD chart is subjected to fitting with a predetermined function. The Ir (<NUM>) peak appears in the vicinity of 2θ = <NUM>°. The half width at half maximum is determined as an interval between a 2θ value at which the maximum value of a peak is shown and a 2θ value at which the half value of the maximum value is obtained and which is on a side where the peak of the maximum value does not overlap with the other peaks (see <FIG>).

In a case where a film of Ir is formed on a substrate according to sputtering, Ir is preferentially aligned in the (<NUM>) plane to form a natural alignment film. Crystallinity is associated with the half width at half maximum of the Ir (<NUM>) peak in the XRD chart (see <FIG>) that is obtained by the XRD diffraction method. The wider the half width at half maximum of the Ir (<NUM>) peak is, the lower the crystallinity is, and the narrower the half width is, the higher the crystallinity is. In a case where the half width at half maximum is <NUM>° or more, the alignment state of the (<NUM>) plane in the Ir layer <NUM> is disturbed, and thus the crystallinity is slightly low.

Further, in the present embodiment, the (<NUM>) plane in the Ir layer <NUM> has an inclination of <NUM>° or more with respect to the thickness direction.

<FIG> is a view schematically illustrating the Ir layer <NUM> according to the present embodiment, and particles 22a in the figure indicate the Ir element. As illustrated in <FIG>, being inclined by <NUM>° or more with respect to the thickness direction of the (<NUM>) plane means that an inclination α with respect to a thickness direction N, in a direction [<NUM>] perpendicular to the (<NUM>) plane, is <NUM>° or more. Here, the thickness direction N is the thickness direction of the Ir layer, and it is a direction perpendicular to a surface 10a of the substrate <NUM>. The actual Ir layer <NUM> contains a large number of crystals, and the inclination directions of the (<NUM>) planes of the individual crystals are various. In the present specification, the inclination α of the (<NUM>) plane in the Ir layer <NUM> is defined by a value measured by a locking curve measurement by X-ray diffraction. Specifically, the inclination α of the (<NUM>) plane is calculated from the split width of the (<NUM>) diffraction peak in the locking curve measurement data (see Examples).

The (<NUM>) plane is the preferential alignment plane of Ir, and in the related art, an Ir layer, in which Ir is aligned so that the (<NUM>) plane is perpendicular to the thickness direction, that is, the [<NUM>] direction coincides with the thickness direction N as illustrated in <FIG>, has been used as the lower electrode layer. In a case where a piezoelectric film made of a perovskite-type oxide is formed on an Ir layer having high crystallinity as illustrated in <FIG>, a pyrochlore phase is easily formed at the initial stage of film formation. On the other hand, the inventors of the present invention found that in a case of reducing the crystallinity of the Ir layer <NUM>, it is possible to suppress the growth of the pyrochlore phase (see Examples).

The Ir (<NUM>) plane preferably has an inclination α of <NUM>° or more and <NUM>° or less and more preferably has an inclination of <NUM>° or more and <NUM>° or less with respect to the thickness direction N.

It is noted that the larger the inclination α of the (<NUM>) plane in the first layer <NUM> with respect to the thickness direction N is, the higher the effect of suppressing the growth of the pyrochlore phase, which is preferable. On the other hand, in a case of setting the inclination to <NUM>° or less, it is possible to suppress an occurrence that another alignment plane becomes the preferential alignment plane, which is preferable.

The sheet resistance of the lower electrode layer <NUM> is preferably <NUM>Ω/sq or less and more preferably <NUM>Ω/sq or less. The sheet resistance can be measured according to the four-point probe method by using a resistivity meter.

The piezoelectric film <NUM> contains a perovskite-type oxide represented by the general formula ABO<NUM>.

In the general formula, A is an A-site element, which is one of Pb, barium (Ba), lanthanum (La), Sr, bismuth (Bi), lithium (Li), sodium (Na), calcium (Ca), cadmium (Cd), magnesium (Mg), or potassium (K), or a combination of two or more thereof.

In the general formula, B is a B-site element, which is one of Ti, Zr, vanadium (V), Nb (niobium), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), Ru, cobalt (Co), Ir, nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), In, tin, antimony (Sb), or a lanthanide element, or a combination of two or more thereof.

Regarding A:B:O, a reference ratio is <NUM>:<NUM>:<NUM>; however, it suffices that the ratio is in a range in which a perovskite structure is obtained.

It is noted that the perovskite-type oxide preferably occupies <NUM>% by mole or more of the piezoelectric film <NUM>, and the perovskite-type oxide more preferably occupies <NUM>% by mole or more thereof. Further, it is preferable that the piezoelectric film <NUM> is consisting of a perovskite-type oxide (however, it contains unavoidable impurities).

The perovskite-type oxide is preferably a lead zirconate titanate (PZT) type that contains lead (Pb), zirconium (Zr), titanium (Ti), and oxygen (O).

In particular, it is preferable that the perovskite-type oxide is a compound represented by General Formula (<NUM>), which contains an additive B in the B site of PZT.

Pb{(ZrxTi<NUM>-x)<NUM>-yBly}O<NUM>     (<NUM>).

Here, B1 is preferably one or more elements selected from vanadium (V), niobium (Nb), tantalum (Ta), Sb (antimony), molybdenum (Mo), and tungsten (W). It is most preferable that B1 is Nb. Here, <NUM> < x < <NUM> and <NUM> < y < <NUM> are satisfied. It is noted that regarding Pb:{(ZrxTi<NUM>-x)<NUM>-yBly}:O in General Formula (<NUM>), a reference ratio thereof is <NUM>:<NUM>:<NUM>; however, it suffices that the ratio is in a range in which a perovskite structure is obtained.

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

As illustrated in the schematic cross-sectional view of <FIG>, the piezoelectric film <NUM> is preferably a columnar structure film having a columnar structure containing a large number of columnar crystal bodies <NUM>. It is preferable that a large number of columnar crystal bodies <NUM> are uniaxial alignment films that extend non-parallelly with respect to the surface of the substrate <NUM> (see <FIG>) and have the same crystal orientation. In a case of adopting an alignment structure, it is possible to obtain larger piezoelectricity. It is noted that the piezoelectric film <NUM> includes a pyrochlore phase <NUM> at the interface between the piezoelectric film <NUM> and the second layer <NUM> of the lower electrode layer <NUM>. Although details will be described later, the pyrochlore phase <NUM> is in a state of being sufficiently suppressed. The pyrochlore phase <NUM> preferably has a thickness of <NUM> or less. It is noted that the pyrochlore phase <NUM> is not uniformly formed on the surface of the lower electrode layer <NUM> but is partially grown as illustrated in <FIG>. The method of calculating the thickness of the pyrochlore phase <NUM> will be described in Examples.

Further, in the example illustrated in <FIG>, the longitudinal direction of the columnar crystal has an inclination β of <NUM>° or more with respect to the normal line of the substrate (the thickness direction N). This means that the alignment plane of the piezoelectric film <NUM> has an inclination of <NUM>° or more with respect to the surface of the substrate. Here, the alignment plane is a (<NUM>) plane or a (<NUM>) plane. As described above, it is preferable that in the piezoelectric film <NUM>, the (<NUM>) plane or (<NUM>) plane of the columnar crystals is inclined by <NUM>° or more with respect to the surface of the substrate. In this example, the lattice constants of the α-axis and the c-axis in the perovskite structure are almost the same, and the (<NUM>) plane and the (<NUM>) plane cannot be distinguished from each other by the analysis by XRD. However, it can be confirmed by XRD analysis that the alignment film is aligned in at least any one of the planes.

The thickness of the piezoelectric film <NUM> is generally <NUM> or more, and it is, for example, <NUM> to <NUM>. However, it is preferably <NUM> or more.

The substrate <NUM> is not particularly limited, and examples thereof include substrates such as silicon, glass, stainless steel, yttrium-stabilized zirconia, alumina, sapphire, and silicon carbide. As the substrate <NUM>, a laminated substrate having a SiO<NUM> oxide film formed on the surface of the silicon substrate, such as a thermal oxide film-attached silicon substrate, may be used.

The upper electrode layer <NUM> is paired with the lower electrode layer <NUM> and is an electrode for applying a voltage to the piezoelectric film <NUM>. The main component of the upper electrode layer <NUM> is not particularly limited, and examples thereof include, in addition to the electrode material that is generally used in the semiconductor process, a conductive oxide such as indium tin oxide (ITO), LaNiOs, or (SrRuO<NUM> (SRO), and a combination thereof.

The layer thickness of the upper electrode layer <NUM> is not particularly limited, and it is preferably about <NUM> to <NUM> and more preferably <NUM> to <NUM>.

As described above, in the piezoelectric laminate <NUM> and the piezoelectric element <NUM> of the present disclosure, the lower electrode layer <NUM> includes a second layer <NUM> arranged in a state of being in contact with the piezoelectric film <NUM> and includes a first layer <NUM> arranged on a side of the second layer <NUM> from the substrate <NUM>. In addition, the first layer <NUM> contains one or more of W, Mo, Nb, and Ta, as a main component, the second layer <NUM> contains Ir as a main component, and the thickness of the second layer <NUM> is <NUM> or less. As described above, the Ir layer that is formed on the substrate according to sputter film formation is preferentially aligned in the (<NUM>) plane. The aligning properties of this (<NUM>) plane alignment increase as the thickness of the Ir layer <NUM> increases. In the related art, the Ir layer generally has a thickness of about <NUM> or more for the reduction of the resistance of the lower electrode layer, and the crystallinity of the Ir layer in a case of being deposited up to <NUM> is very high. The inventors of the present invention found that in a case of forming a piezoelectric film of a perovskite-type oxide on the Ir layer, the pyrochlore phase easily grows in a case where the crystallinity of the Ir layer is too high, and the growth of the pyrochlore phase can be suppressed by reducing the crystallinity of the Ir layer as compared with the case of the related art. In a case where the thickness of the layer (the Ir layer <NUM>) which is the second layer <NUM> containing Ir as a main component is <NUM> or less, the crystallinity is not yet sufficiently high. As a result, in a case of forming the piezoelectric film <NUM> containing a perovskite-type oxide as a main component on the second layer <NUM> having a thickness of <NUM> or less, it is possible to suppress the growth of the pyrochlore phase. Since the pyrochlore phase can be suppressed, the piezoelectric characteristics can be improved, and the long-term reliability can be improved. Further, in a case where the thickness of the Ir layer <NUM> is set to <NUM> or less, the using amount of Ir can be reduced as compared with the case of the related art, and thus the material cost of the lower electrode layer <NUM> can be suppressed, whereby the manufacturing cost can be suppressed.

In addition, although the reduction of the resistance of the lower electrode layer has been achieved in the related art by setting the thickness of the Ir layer to about <NUM> or more, it has been found that there is a problem that the stress of the Ir layer is large, which is a factor that hinders the improvement of long-term reliability. In the piezoelectric laminate <NUM> and the piezoelectric element <NUM> of the present disclosure, the second layer <NUM> (here, the Ir layer <NUM>) of the lower electrode layer <NUM> has a thickness of <NUM> or less, and thus the stress is small as compared with the case in the related art, where an Ir layer having a thickness of about <NUM> is provided. The first layer <NUM> compensates for the reduced conductivity in a case where the thickness of the second layer <NUM> is set to <NUM> or less. All of W, Mo, Nb, and Ta can realize a lower electrode layer having the same resistivity as in a case of a single layer of the Ir layer. Further, in a case where a film of these metals is formed according to sputter film formation, the stress is small in any case of these metals as compared with Ir. As a result, long-term reliability can be improved.

Further, since all of W, Mo, Nb, and Ta which constitute the first layer <NUM> have a sufficiently high melting point as compared with Au, diffusion hardly occurs even in a case where the film formation temperature of the piezoelectric film <NUM> is set to a high temperature (for example, <NUM>), and thus it is possible to suppress a decrease in long-term reliability as compared with a case where an Au layer is provided as in <CIT>.

It is noted that in a case of setting the thickness of the second layer <NUM> to <NUM> or less, it is possible to further reduce the crystallinity of Ir layer. As a result, the growth of the pyrochlore phase at the time of forming the piezoelectric film <NUM> can be further suppressed, and the piezoelectric characteristics and the long-term reliability can be further improved.

In the piezoelectric laminate <NUM> and the piezoelectric element <NUM> according to the present embodiment, the Ir layer <NUM> which is the second layer <NUM> is a uniaxial alignment film aligned in the Ir (<NUM>) plane, where the half width at half maximum of an X-ray diffraction peak from the (<NUM>) plane of IR is <NUM>° or more. As described above, the description that the half width at half maximum of the X-ray diffraction peak is <NUM>° or more means that the crystallinity of the Ir layer <NUM> is slightly low, and sufficient alignment is not achieved in the (<NUM>) plane which is the preferential alignment plane. Further, in a case where the Ir (<NUM>) plane is disturbed, it is possible to suppress the growth of the pyrochlore phase at the time of the formation of the piezoelectric film <NUM> containing a perovskite-type oxide, where the piezoelectric film <NUM> is provided on the upper layer side. Since it is possible to sufficiently suppress the pyrochlore phase, it is possible to obtain the piezoelectric laminate <NUM> and the piezoelectric element <NUM>, which have the piezoelectric film <NUM> containing a good perovskite-type oxide. Since the piezoelectric film <NUM> in which the pyrochlore phase is suppressed is provided, it is possible to obtain high piezoelectric characteristics, and it is possible to obtain higher drive stability as compared with the case of the related art.

It is noted that in a case where the half width at half maximum of the X-ray diffraction peak from the Ir (<NUM>) plane of the Ir layer <NUM> is <NUM>° or more, the effect of suppressing the growth of the pyrochlore phase can be further enhanced, and as a result, the piezoelectric characteristics and the drive stability can be further enhanced.

Further, in a case where the half width at half maximum of the X-ray diffraction peak from the Ir (<NUM>) plane is <NUM>° or less and preferably <NUM>° or less, the growth of the pyrochlore phase can be suppressed while maintaining the resistance value of the Ir layer <NUM> and the adhesiveness to the piezoelectric film <NUM> at the same level as those of an Ir layer having high crystallinity.

In the piezoelectric laminate <NUM> and the piezoelectric element <NUM> according to the present embodiment, the Ir (<NUM>) plane of the Ir layer <NUM> which is the second layer has an inclination of <NUM>° or more with respect to the thickness direction. This indicates that the aligning properties of the Ir (<NUM>) plane are disturbed and the crystallinity is low, which is similar to the case of the half width at half maximum being <NUM>° or more. In a case where the aligning properties of the Ir (<NUM>) plane are slightly decreased, the effect of suppressing the pyrochlore phase can also be obtained.

The piezoelectric film <NUM> contains a perovskite-type oxide; however, in a case where it contains particularly a perovskite-type oxide containing Pb, the pyrochlore phase is easily formed at the initial stage of film formation since Pb is easily removed. As a result, the effect of suppressing the pyrochlore phase due to the point that the half width at half maximum of the X-ray diffraction peak from the Ir (<NUM>) plane is <NUM>° or more is particularly high. Among the perovskite-type oxides containing Pb, a PZT-based perovskite-type oxide containing Pb, Zr, Ti, and O has high piezoelectric characteristics and thus is particularly preferable. Still higher piezoelectric characteristics can be obtained particularly in a case where the perovskite-type oxide is a compound represented by General Formula (<NUM>),.

where <NUM> < x < <NUM> and <NUM> < y < <NUM> are satisfied, and
B1 is one or more elements selected from V, Nb, Ta, Sb, Mo, and W.

In the above embodiment, the lower electrode layer <NUM> has a two-layer structure of the first layer <NUM> and the second layer <NUM>; however, it may include another layer.

<FIG> illustrate modification examples of the piezoelectric laminate <NUM> and the piezoelectric element <NUM>. In <FIG>, the same reference numerals are respectively assigned to the same constituent elements as those illustrated in <FIG>, and the detailed description thereof will be omitted.

In a piezoelectric laminate 5A and a piezoelectric element 1A of the Modification Example <NUM> illustrated in <FIG>, a lower electrode layer 12A has a first intimate attachment layer <NUM> that improves the adhesiveness between the substrate <NUM> and the first layer <NUM>, between the substrate <NUM> and the first layer <NUM>. The first intimate attachment layer <NUM> is preferably a TiW layer or a Ti layer, and it is particularly preferably a TiW layer.

In a case where the first intimate attachment layer <NUM> is provided between the substrate <NUM> and the first layer <NUM>, interlayer peeling can be suppressed, and long-term reliability can be further improved.

In a piezoelectric laminate 5B and a piezoelectric element 1B of the Modification Example <NUM> illustrated in <FIG>, a lower electrode layer 12B has a first intimate attachment layer <NUM>, similarly to the piezoelectric laminate 5A and the piezoelectric element 1A of Modification Example <NUM>, and further, it has a second intimate attachment layer <NUM> between the first layer <NUM> and the second layer <NUM>. The second intimate attachment layer <NUM> is provided in order to improve the adhesiveness between the first layer <NUM> and the second layer <NUM>. Similar to the first intimate attachment layer <NUM>, the second intimate attachment layer <NUM> is preferably a TiW layer or a Ti layer, and it is particularly preferably a TiW layer.

In a case where the second intimate attachment layer <NUM> is provided between the first layer <NUM> and the second layer <NUM>, interlayer peeling can be suppressed, and long-term reliability can be further improved. In a case where the first intimate attachment layer <NUM> and the second intimate attachment layer <NUM> are provided, it is possible to further improve the long-term reliability as compared with a case where only one of them is provided.

It is noted that as still another modification example of the piezoelectric laminate and the piezoelectric element, a configuration in which the first intimate attachment layer <NUM> is not provided between the substrate <NUM> and the first layer <NUM>, but only the second intimate attachment layer <NUM> is provided between the first layer <NUM> and the second layer <NUM> may be adopted.

It is particularly preferable that the first layer <NUM> of the lower electrode layer <NUM> is W and the first intimate attachment layer <NUM> (and the second intimate attachment layer <NUM>) is TiW. In this case, W of the TiW is less than <NUM> wt%. In a case where the first layer <NUM> is W and the first intimate attachment layer <NUM> (and the second intimate attachment layer <NUM>) is TiW, the adhesiveness is particularly good, and the effect of improving reliability is remarkable.

The piezoelectric element <NUM> or the piezoelectric laminate <NUM> according to each of the above embodiments can be applied to an ultrasonic device, a mirror device, a sensor, a memory, and the like.

Hereinafter, specific examples and comparative examples of the piezoelectric element of the present disclosure will be described. First, a manufacturing method for a piezoelectric element of each example will be described. A radio frequency (RF) sputtering device was used for the film formation of each layer. It is noted that conditions other than the configuration of the lower electrode layer are common in each example. The description of the manufacturing method will be made with reference to the reference numerals of the respective layers of the piezoelectric element 1B illustrated in <FIG>.

As the substrate <NUM>, a thermal oxide film-attached silicon substrate having a size of <NUM> inches was used. The lower electrode layer <NUM> was formed into a film on a thermal oxide film which is the surface of the substrate <NUM>. The layer configuration of the lower electrode layer <NUM> in each example was as shown in Table <NUM>. For example, in the case of Example <NUM>, as the lower electrode layer <NUM>, a TiW layer, which is the first intimate attachment layer <NUM>, was formed into a film of <NUM>, W, which is the first layer <NUM>, was formed into a film of <NUM>, TiW, which is the second intimate attachment layer <NUM>, was formed into a film of <NUM>, and Ir, which is the second layer <NUM>, was further formed into a film of <NUM>.

The sputter conditions for each layer were as follows. It is noted that the conditions of the distance of <NUM> between the target and the substrate and the substrate set temperature of <NUM> were the same.

The substrate <NUM> attached with the lower electrode layer <NUM> was placed in the inside of an RF sputtering device, and an Nb-doped PZT film of <NUM> was formed as the piezoelectric film <NUM>, where the Nb-doping amount to the B site was set to <NUM> at%. The sputter conditions at this time were as follows.

Next, the substrate <NUM> after forming the piezoelectric film <NUM> was placed in a film forming chamber of the RF sputtering device, and by using an indium tin oxide (ITO) target, an ITO layer was formed into a film having a thickness of <NUM> as the upper electrode layer <NUM>. It is noted that before the film formation of the upper electrode layer <NUM>, a lift-off pattern for an evaluation sample was prepared on the piezoelectric film <NUM>, and the upper electrode layer <NUM> was formed on the lift-off pattern. The film forming conditions for the upper electrode layer <NUM> were as follows.

After the formation of the upper electrode layer <NUM>, the upper electrode layer was lifted off along the lift-off pattern according to the lift-off method to carry out the pattering of the upper electrode layer <NUM>.

Through the above steps, the piezoelectric laminated substrate of each example, having the lower electrode layer, the piezoelectric film, and the patterned upper electrode layer on the substrate, was produced.

A strip-shaped portion of <NUM> × <NUM> was cut out from the piezoelectric laminated substrate to prepare a cantilever as an evaluation sample <NUM>.

A portion of <NUM> × <NUM> having, at the center of the surface of the piezoelectric film, an upper electrode layer that had been patterned in a circular shape having a diameter of <NUM>, was cut out from the piezoelectric laminated substrate and used as an evaluation sample <NUM>.

The piezoelectric constant d<NUM> was measured for the evaluation of the piezoelectric characteristics of each of Examples and Comparative Examples.

The piezoelectric element produced as described above was cut into a strip shape of <NUM> × <NUM> to produce a cantilever. Then, according to the method described in I. Sensor and Actuator A <NUM> (<NUM>) <NUM>, the lower electrode layer <NUM> was grounded, and the measurement of the piezoelectric constant d<NUM> was carried out by applying a voltage of sine wave of-<NUM> V ± <NUM> V to the upper electrode layer <NUM>. The results are shown in Table <NUM>.

A time dependent dielectric breakdown (TDDB) test was carried out for the evaluation of the long-term reliability of each of Examples and Comparative Examples. Using the evaluation sample <NUM>, in an environment of <NUM>, the lower electrode layer <NUM> was grounded, a voltage of -<NUM> V was applied to the upper electrode layer <NUM>, and the time (hr) taken from the start of the voltage application to the occurrence of dielectric breakdown was measured, and then the long-term reliability was evaluated with the time taken until dielectric breakdown occurred. The measurement results are shown in Table <NUM>.

The resistivity (the sheet resistance) of the lower electrode layer <NUM> was measured with a dedicated four-point probe by using a low resistivity meter Loresta-AX. For each example, the resistivity was measured at the time when the lower electrode layer <NUM> was formed into a film on the substrate <NUM>.

Regarding each of Examples and Comparative Examples, the half width at half maximum of the Ir (<NUM>) peak was determined by the XRD analysis using RINT-ULTIMA III manufactured by Rigaku Corporation. From the XRD chart obtained from each example, the half width at half maximum of the Ir (<NUM>) peak was determined. The Ir (<NUM>) peak is generated in the vicinity of <NUM>°. <FIG> is a graph in which the vicinity of the Ir (<NUM>) peak of the XRD chart of Example <NUM> is enlarged. The Ir (<NUM>) peak is generated in the vicinity of 2θ = <NUM>°. In Example <NUM> shown in <FIG>, the peak of the TiW layer, which is the first layer of the lower electrode layer, is partially overlapped with the Ir (<NUM>) peak. Fitting was carried out on such peaks using a double Gaussian function. In the fitting curve of the Ir (<NUM>) peak, the half width at half maximum (HWHM) was determined as a width between a 2θ value at which the maximum value lp of the Ir (<NUM>) peak is shown and a 2θ value at which an intensity of <NUM>/<NUM> of the maximum value Ip is shown. The results are shown in Table <NUM>.

Regarding Examples and Comparative Examples, the crystallinity of the first layer was evaluated by XRD using RINT-ULTIMA III manufactured by Rigaku Corporation. Specifically, the inclination of the peak of the Ir (<NUM>) plane was determined, by the locking curve measurement, from the deviation of the position of the peak of the Ir (<NUM>) plane from that of the Ir peak in a case where the (<NUM>) plane was not inclined. <FIG> is the locking curve measurement data of Example <NUM>. The reference position shown in the figure is a position of a peak of the (<NUM>) plane, where the peak appears in a case where the (<NUM>) plane is parallel to the surface of the substrate. The example shown in <FIG> has a first peak P1 and a second peak P2, and the split width therebetween is <NUM>°. The center of the split width between the first peak P1 and the second peak P2 is the reference position, and in this example, it is meant that the (<NUM>) plane of the first layer is inclined by <NUM>° with respect to a state where it is parallel to the substrate. The measured values for each example are shown in Table <NUM>.

Regarding Examples and Comparative Examples, transmission electron microscope (TEM) images were captured, and the thickness of the pyrochlore phase was determined from the TEM images. In the piezoelectric film, the contrast in the TEM image differs between the pyrochlore phase and the perovskite phase, and thus it is possible to specify the region of the pyrochlore phase and calculate the thickness thereof. It is noted that it was observed that columnar crystal bodies of the perovskite-type oxide were formed in the portion of the piezoelectric film other than the pyrochlore phase. The thickness of the pyrochlore phase was calculated as an average thickness since the pyrochlore phase was not uniformly formed on the surface of the lower electrode layer. It is noted that even in the case of the pyrochlore phase that is hardly confirmed on the XRD chart, the pyrochlore phase <NUM> is partially present as illustrated in the schematic view illustrated in <FIG>, and this can be confirmed in the TEM image.

Specifically, the contrast adjustment function of the image processing software is used to binarize the original image at a predetermined threshold value, and the edge extraction function of the image processing software is used to extract the pyrochlore phase. In this case, the threshold value is such that noise is removed as much as possible and only those that can be clearly distinguished from the pyrochlore phase are extracted. In a case where the outline of the pyrochlore-type oxide layer is unclear in the binarized image, the outline is empirically drawn while looking at the binarized image, and the inside thereof is filled. The area of the extracted pyrochlore phase is calculated from the number of pixels obtained from the image processing software and divided by the visual field width of the TEM image to obtain the average layer thickness. As the image processing software, Photoshop (registered trade name) was used here. Table <NUM> shows the thickness of the pyrochlore phase obtained as described above.

As shown in Table <NUM>, the following results were obtained that the piezoelectric constant is large and that the long-term reliability is high in a case where the first layer of the lower electrode layer contains one or more of W, Mo, Nb, and Ta, as a main component, the second layer contains Ir as a main component, and the thickness of the second layer is <NUM> or less, as in Examples <NUM> to <NUM>. In Comparative Example <NUM> in which the lower electrode layer did not have a layer containing one or more of W, Mo, Nb, and Ta, as a main component, and the thickness of the Ir layer was <NUM>, and in Comparative Examples <NUM> and <NUM> in which the first layers of the lower electrode layer were respectively Au and Ir, the long-term reliability was low. Further, even in a case where the Ir layer had a thickness of <NUM>, the piezoelectric constant was low and the resistivity was high in Comparative Example <NUM> in which the lower electrode layer did not have a layer containing one or more of W, Mo, Nb, and Ta, as a main component.

Claim 1:
A piezoelectric laminate (<NUM>, 5A, 5B) comprising, on a substrate (<NUM>) in the following order:
a lower electrode layer (<NUM>); and
a piezoelectric film (<NUM>) containing a perovskite-type oxide,
wherein the lower electrode layer (<NUM>) includes a second layer (<NUM>) arranged in a state of being in contact with the piezoelectric film (<NUM>) and includes a first layer (<NUM>) arranged on a side of the substrate than the second layer (<NUM>) , the second layer (<NUM>) contains Ir as a main component and characterized in that
the first layer (<NUM>) contains one or more of W, Mo, Nb, and Ta, as a main component that occupies <NUM> wt% or more of the constituent elements, and
in that a thickness of the second layer (<NUM>) is <NUM> or less.