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, a method such as improving the crystallinity of the piezoelectric film or reducing the resistance of the electrode layer has 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.

On the other hand, 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 decrease in the dielectric constant and the deterioration of the piezoelectric characteristics occur 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.

<CIT> proposes providing an alignment control layer (a seed layer) on the lower electrode layer as a method of suppressing the formation of the pyrochlore phase and improving the crystallinity of the piezoelectric film. <CIT> discloses a semiconductor device, comprising: a capacitor having a titanium nitride film as a part of a lower electrode, wherein: the titanium nitride film is a film in which a titanium film formed after applying a PLA (plasma annealing) process is nitrided. <CIT> discloses a dielectric element comprising a lower electrode layer, dielectric layer and upper electrode layer in this order on a substrate, wherein at least one of the lower and upper electrode layers comprises a first electrode layer mainly composed of a metal and second electrode layer mainly composed of an oxide, each of the first electrode layer, second electrode layer and dielectric layer has a preferentially or uniaxially oriented crystal structure, and the first electrode layer, second electrode layer and dielectric layer satisfy the relationship represented by the general formula (<NUM>): f3 > f2 > f1 ≥ <NUM>°.

The lower electrode materials (specifically, Ir and, Ti or TiW) disclosed in <CIT>, <CIT>, and the like and currently widely used in actual devices are materials that have been narrowed down based on the past achievements. The lower electrode materials that have been used in the related art have a good interfacial reaction with piezoelectric materials and are excellent in long-term durability (stability) as compared with other materials, and thus there is a strong demand to avoid changing these lower electrode materials. On the other hand, further improvement in the long-term reliability of the piezoelectric element is also desired.

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. <CIT> discloses an exemplary <NUM>% Nb-doped PZT piezoelectric film formed by sputtering on a lower electrode comprising a <NUM> thick (<NUM>)Ir film on a <NUM> thick Ti film. XRD shows an Ir film peak with a FWHM of about <NUM>°.

<CIT> improves the crystallinity of the piezoelectric film by providing an alignment control layer to achieve piezoelectric characteristics and long-term stability. However, since a novel layer called an alignment control layer is introduced separately from the piezoelectric film and the electrode, there is a problem that the load in the manufacturing process is large.

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 piezoelectric characteristics and drive stability without increasing the process load.

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

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

In the piezoelectric laminate of the present disclosure, it is preferable that in the second layer, the (<NUM>) plane of Ir 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 the thickness of the second layer is <NUM> or less.

In the piezoelectric laminate of the present disclosure, it is preferable that the thickness of the lower electrode layer is <NUM> or more.

In the piezoelectric laminate of the present disclosure, it is preferable that a sheet resistance of the lower electrode layer is preferably <NUM> Q/sq or less.

In the piezoelectric laminate of the present disclosure, it is preferable that a height difference of a surface unevenness of the piezoelectric film is <NUM> or less.

In the piezoelectric laminate of the present disclosure, it is preferable that the perovskite-type oxide contains Pb, Zr, Ti, and O.

In the piezoelectric laminate of the present disclosure, it is preferable that the piezoelectric film has a columnar structure consisting of a large number of columnar crystals.

In the piezoelectric laminate of the present disclosure, it is preferable that a (<NUM>) or (<NUM>) plane of the columnar crystals has an inclination of <NUM>° or more with respect to a surface of the substrate.

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 piezoelectric characteristics and the drive stability without increasing the process load.

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.

<FIG> 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 first layer <NUM> arranged in a state of being in contact with the substrate <NUM> and includes a second layer <NUM> arranged in a state of being in contact with the piezoelectric film <NUM>. The first layer <NUM> is a layer containing titanium (Ti) or a titanium-tungsten alloy (TiW) as a main component. In the present specification, "the main component" refers to a component that occupies <NUM> at% or more of the constituent elements. In a case where TiW is contained as the main component, the total of the Ti content and the W content may be <NUM> at% or more.

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 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 <NUM>° or more. The half width at half maximum of the Ir (<NUM>) peak is <NUM> to <NUM>. The wider half width at half maximum of the Ir (<NUM>) peak means that the lower the crystallinity is, and the wider the half width is, the more the pyrochlore phase tends to be suppressed. On the other hand, in order to further reduce the crystallinity of the Ir layer <NUM>, it is required to carry out a treatment such as the addition of an impurity element, and thus there is a concern that the adhesiveness to the piezoelectric film or the like may be reduced due to the addition of the impurity element or the like. At present, the half width of the Ir (<NUM>) peak is <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.

Regarding the second layer <NUM>, that is, the Ir layer <NUM>, the thickness t2 is preferably <NUM> or less. The thickness t2 is more preferably less than <NUM> and still more preferably <NUM> or less. Further, from the viewpoint that it can be formed into a uniform film shape, the thickness t2 is preferably <NUM> or more.

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

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

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 a lead zirconate titanate (PZT) type that contains lead (Pb), zirconium (Zr), titanium (Ti), and oxygen (O).

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>-yB1y}O<NUM>     (<NUM>).

Here, B1 is 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>-yBy}: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 a-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 height difference of the surface unevenness of the piezoelectric film <NUM> is preferably <NUM> or less. The method of measuring the surface unevenness will be described in Examples described later: however, the height difference of the surface unevenness shall be the peak to valley (the PV value), which is the maximum unevenness difference. Here, the cycle of the surface unevenness is not a fine cycle such as in several tens of nm to several hundred nm, but a cycle having an order in terms of µm.

In a case where the PV value of the surface unevenness of the piezoelectric film <NUM> is <NUM> or less, the effect of improving the pressure resistance of the piezoelectric element and the effect of improving the drive stability can be enhanced. The PV value of the surface unevenness of the piezoelectric film <NUM> is more preferably <NUM> or less.

The height difference of the surface unevenness can be measured in a dynamic force mode (DFM) using a scanning probe microscope (SPM). In a case where the upper electrode layer <NUM> having a pattern formed on the piezoelectric film <NUM> is formed, the height difference of the surface unevenness can be measured on the surface of the piezoelectric film <NUM> where the upper electrode layer <NUM> is not formed and is exposed. Alternatively, the measurement can be carried out on the surface of the piezoelectric film <NUM> before the formation of the upper electrode layer <NUM>.

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>.

In the piezoelectric laminate <NUM> and the piezoelectric element <NUM> according to the present embodiment, the lower electrode layer <NUM> includes a first layer <NUM> arranged in a state of being in contact with the substrate <NUM> and includes a second layer <NUM> arranged in a state of being in contact with the piezoelectric film <NUM>, where the first layer <NUM> contains Ti or TiW as a main component, and the second layer <NUM> contains Ir as a main component. Ti and TiW have good adhesiveness to the substrate <NUM>, and Ir has good adhesiveness to the piezoelectric film <NUM>. As a result, interlayer peeling is suppressed, and long-term reliability is high. The lower electrode layer <NUM> may include another metal layer between the first layer <NUM> and the second layer <NUM>. However, since Ir and TiW, or Ir and Ti have high adhesiveness, it is most preferable that the lower electrode layer <NUM> has a two-layer structure of the first layer <NUM> and the second layer <NUM>.

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>° to <NUM> 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.

Further, since the piezoelectric laminate <NUM> and the piezoelectric element <NUM> according to the present embodiment are obtained by directly laminating a piezoelectric film on the Ir layer <NUM> without providing a layer such as an alignment control layer, they can be manufactured without increasing the process load as in the case in the related art, where an alignment control layer is provided. As a result, it is possible to suppress an increase in manufacturing cost.

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.

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, the half width at half maximum is <NUM>° or more, and the crystallinity is also low. 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.

In the piezoelectric laminate and the piezoelectric element <NUM> according to the present embodiment, it is preferable that the thickness t2 of the second layer <NUM> of the lower electrode layer <NUM>, that is, that of the Ir layer <NUM> is <NUM> or less. In a case where the thickness t2 of the Ir layer <NUM> is set to <NUM> or less, the aligning properties of the Ir (<NUM>) plane can be decreased. The inventors of the present invention found that in a case where the thickness t2 of the Ir layer <NUM> is set to <NUM> or less, the half width at half maximum of the Ir (<NUM>) peak can be made to be <NUM>° or more, and in a case where the thickness t2 of the Ir layer <NUM> is set to <NUM> or less, which is thin as compared with a case in the related art, the half width at half maximum of the Ir (<NUM>) peak can be made to be <NUM>° or more. It is noted that the method of making the half width at half maximum of the Ir (<NUM>) peak <NUM>° or more is not limited to a method of forming the Ir layer <NUM> to be thin as compared with a case in the related art, and it is also possible to use another method such as reducing the crystallinity of the first layer <NUM> which is the underlying layer of the Ir layer <NUM>. 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 suppression of the manufacturing cost can be achieved.

In a case where the thickness t of the lower electrode layer <NUM> is <NUM> or more, sufficient conductivity as the lower electrode layer <NUM> can be obtained. Further, in a case where the thickness t of the lower electrode layer <NUM> is <NUM> or more, it is possible to obtain still better conductivity. Although the Ir layer <NUM> is made thin as compared with a case in the related art, the sheet resistance can be decreased in a case where the first layer <NUM> is made to be thick to some extent and the thickness of the entire lower electrode layer <NUM> is made to be <NUM> or more.

It is noted that in a case where the sheet resistance of the lower electrode layer <NUM> is Q/sq or less, it is suitable for applying a voltage to the piezoelectric film <NUM> by being paired with the upper electrode layer <NUM>.

The piezoelectric film <NUM> contains 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. A PZT-based perovskite-type oxide containing Pb, Zr, Ti, and O has high piezoelectric characteristics. High piezoelectric characteristics are obtained where the perovskite-type oxide is a compound represented by General Formula (<NUM>),.

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 <NUM> illustrated in <FIG>.

As the substrate <NUM>, a thermal oxide film-attached silicon substrate having a size of <NUM> (<NUM> inches) was used. The lower electrode layer <NUM> was formed into a film on the substrate <NUM> by radio-frequency (RF) sputtering. Specifically, as the lower electrode layer <NUM>, the TiW layer <NUM> as the first layer <NUM>, and the Ir layer <NUM> as the second layer <NUM> were laminated in this order on the substrate <NUM>. The thicknesses of the TiW layer <NUM> and the Ir layer <NUM> differ depending on each example and are as shown in Table <NUM>. In addition, the sputter conditions for each layer were as follows.

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. The measurement results are shown in Table <NUM>. It is noted that the TDDB test was carried out for <NUM>,<NUM> hours, and those in which dielectric breakdown did not occur up to <NUM>,<NUM> hours are described as <NUM>,<NUM> 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>.

The crystallinity of the piezoelectric film (the PZT film) and the crystallinity of the Ir layer of the lower electrode layer of the piezoelectric laminate of each example were evaluated by the XRD analysis using RINT-ULTIMA III manufactured by Rigaku Corporation.

<FIG> shows an XRD chart from Comparative Example <NUM>, and <FIG> shows an XRD chart from Example <NUM>. The evaluation of crystallinity was carried out using the piezoelectric laminate before the film formation of the upper electrode layer.

From the XRD chart obtained from each example, the intensity of the pyrochlore phase (<NUM>), which is a different phase, was determined. The region where the pyrochlore phase (<NUM>) was detected was in the vicinity of <NUM>°, and the peak intensity derived from the pyrochlore phase (<NUM>) was adopted as a peak intensity obtained by removing the noise derived from the background, from the obtained XRD diffraction intensity (counts).

Further, from the XRD chart, py (<NUM>)/{pr (<NUM>) + pr (<NUM>) + pr (<NUM>)} × <NUM>% was calculated as the pyrochlore rate.

The intensity from each plane was determined as follows.

The average value of the number of counts in a case where 2θ is <NUM>° to <NUM>° is defined as the noise N derived from the background.

The intensity of py (<NUM>) was defined as the value obtained by eliminating N from the maximum number of counts in a range in which 2θ was <NUM>° to <NUM>°.

The intensity of pr (<NUM>) was defined as the value obtained by eliminating N from the maximum number of counts in a range in which 2θ was <NUM>° to <NUM>°.

In <FIG> and <FIG>, the peak values of the perovskite phase (<NUM>) are the same. On the other hand, there is a difference in the pyrochlore phase (<NUM>). As shown in <FIG>, in Comparative Example <NUM>, there is a clear peak of the pyrochlore phase (<NUM>) in the vicinity of <NUM>°. In Example <NUM> shown in <FIG>, the peak value of the pyrochlore phase (<NUM>) is decreased as compared with the case of Comparative Example <NUM>. As shown in <FIG>, in Example <NUM>, a PZT film uniaxially aligned at (<NUM>) has been obtained. It is noted that in any one of Examples <NUM> to <NUM>, a PZT film uniaxially aligned in the same manner as in Example <NUM> (<NUM>) has been obtained.

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 Comparative Example <NUM> is enlarged, and <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 adjacent, and thus peaks are partially overlapped with each other. It is noted that in Comparative Example <NUM>, the peak of the TiW layer was hardly observed. Fitting was carried out on 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 sample before forming the upper electrode layer was used to evaluate the crystallinity of the first layer 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.

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.

Surface unevenness was measured in a dynamic force mode (DFM) using an S-image type scanning probe microscope (SPM) manufactured by Hitachi High-Tech Science Corporation. The surface unevenness was measured within a range of <NUM><NUM> on the surface of the piezoelectric film <NUM> where the circular upper electrode layer <NUM> was not formed and was exposed. The peak to valley (the PV value), which is the maximum unevenness difference on the surface, was about <NUM>, and there was substantially no difference in all of Comparative Examples and Examples.

Claim 1:
A piezoelectric laminate (<NUM>) comprising, on a substrate 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 first layer (<NUM>) arranged in a state of being in contact with the substrate (<NUM>) and includes a second layer (<NUM>) arranged in a state of being in contact with the piezoelectric film (<NUM>),
the first layer (<NUM>) contains Ti or TiW as a main component,
and
the second layer (<NUM>) is a uniaxial alignment film which contains Ir as a main component and in which the Ir is aligned in a (<NUM>) plane, and
characterised in that a half width at half maximum of an X-ray diffraction peak from the (<NUM>) plane of the second layer is <NUM>° to <NUM>°;
and
the perovskite-type oxide is a compound represented by General Formula (<NUM>),

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

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