Patent Application
20090128608
The present invention generally relates to a piezoelectric substance element exhibiting preferable characteristics, and more particularly to a piezoelectric substance element suited to a liquid discharge head (an inkjet head) and a MEMS (Micro Electro Mechanical System) element.
With the spread of researches into the MEMS and piezoelectric application, a thin piezoelectric substance film exhibiting a good characteristic is desired as a piezoelectric substance element. The piezoelectric substance element expands and contracts in a way that pinches the piezoelectric substance film with electrodes and applying an electric field thereto, and can be applied to a motor, a supersonic motor, an actuator, etc. PZT-series materials discovered approximately 50 years ago are main materials utilized in the applied field. The PZT material is equal to or higher than 1100° C. in its sintering temperature, and there is seen a progress of material development employing a sol-gel method, a sputtering method, an MBE (Molecular Beam Epitaxial) method, a PLD (Pulsed Laser Deposition) method, a CVD (Chemical Vapor Deposition) method, etc in order to apply the piezoelectric substance element as a thin film element. In the case of its being applied as the thin film, however, a problem is that characteristics as equal as those of the ceramics can not be acquired. For solving this problem, for example, Japanese Patent Application Laid-Open No. H08-116103 discloses a method of controlling crystalline orientation to a (001) mono-crystal. Japanese Patent Application Laid-Open No. 2000-332569 (corresponding to U.S. Pat. No. 6,198,208) proposes employing a 90-degree domain where (100) orientation and (001) orientation taking a tetragonal crystal structure exist in mixture.
Even by the method disclosed in Japanese Patent Application Laid-Open No. H08-116103, the characteristics as equal as those of the ceramics are not exhibited on the side of a high electric field, and the piezoelectric substance element is inferior in terms of a function as the element. Further, the method disclosed in Japanese Patent Application Laid-Open No. 2000-332569 has such problems that an MPB (Morphotropic Phase Boundary) area can not be utilized and that a (100) orientation-to-(001) orientation ratio can not be controlled with high reproducibility. Moreover, a film with an increased ratio of the (100) orientation has a problem of being inferior in terms of film durability as the thin film element.
It is an object of the present invention to solve the problems given above and to provide a piezoelectric substance element exhibiting a high piezoelectric characteristic and preferable durability, a piezoelectric substance film manufacturing method, a liquid discharge head and a liquid discharge apparatus. According to the present invention, an MEMS element etc having excellent displacement controllability and durability can be also provided.
According to a first mode of a piezoelectric substance element of the present invention, there provides a piezoelectric substance element having a piezoelectric substance film and a pair of electrodes connected to the piezoelectric substance film on a substrate, wherein a main component of the piezoelectric substance film is Pb(Zr, Ti)O3, a composition ratio of Zr/(Zr+Ti) is over 0.4 but less than 0.7, the piezoelectric substance film is a film having at last a tetragonal crystal a-domain and a c-domain within a range of ±10° with respect to the surface of the substrate, and a volume rate of the c-domain to the total of the a-domain and the c-domain is equal to or larger than 20% and equal to or smaller than 60%.
According to a second mode of a piezoelectric substance element of the present invention, there provides a piezoelectric substance element having a piezoelectric substance film and a pair of electrodes connected to the piezoelectric substance film on a substrate, wherein a main component of the piezoelectric substance film is Pb(Zr, Ti)O3, a composition ratio of Zr/(Zr+Ti) is over 0.4 but less than 0.7, the piezoelectric substance film is a film having at last a tetragonal crystal a-domain and a c-domain within a range of ±10° with respect to the surface of the substrate, and at least some of the a-domain and the c-domain are in a twinning enantiomorphic relationship where a (N0N) (N is an integer) plane is a twinning crystal plane.
According to a third mode of a piezoelectric substance element of the present invention, there provides a piezoelectric substance element having a piezoelectric substance film and a pair of electrodes connected to the piezoelectric substance film, wherein a main component of the piezoelectric substance film is Pb(Zr, Ti)O3, the piezoelectric substance film is a film having a tetragonal crystal a-domain and a c-domain, and, in a [001] axial length and a [001] axial length that configure the domains, a [001] axial length/[100] axial length ratio is equal to or larger than 1.004 and equal to or smaller than 1.040.
It should be noted that an expression [one unspecified value through another unspecified value] or [one unspecified value−another unspecified value] connotes [being equal to or larger than one unspecified value and being equal to or smaller than another unspecified value] in any case in the specification of the present application.
Over the recent years, there has been made a trial to improve a μμ characteristic of the piezoelectric substance element in a way that controls a crystal structure of the piezoelectric substance film, however, a situation is that the crystal structure exceeding a piezoelectric characteristic as equal as ceramics is not clarified in the piezoelectric substance film having a film thickness equal to or smaller than 25 μm. In this piezoelectric substance film, it is reported that there is an effect due to orientation such as a d33 constant being large in an area where morphotropic phases exist in mixture in a (111) alignment film, however, the clarity is not given to a d31 constant in the case of utilizing the piezoelectric substance element as a unimorph type. This is regarded, the thin film being restricted by a substrate, due to a possibility in which the same relationship between the d33 constant and the d31 constant as that of the ceramics is not established. Therefore, as in Japanese Patent Application Laid-Open No. 2000-332569 given above, it is one of useful means for improving the piezoelectric property to make use of a 90-degree domain where a (100) orientation and a (001) orientation each taking a tetragonal structure exist in mixture. In the case of using the 90-degree domain, however, as described in Japanese Patent Application Laid-Open No. 2000-332569, it is written that the (001) mono-orientation occurs in an MPB area and the piezoelectric property declines. Herein, as to the MPB area, a composition ratio of Zr/(Zr+Ti) is approximately 0.5 or thereabouts in Pb(Zr, Ti)O3. Further, there is a defect in terms of durability such as being unable to follow a high-frequency drive with respect to displacement and being easy to cause a crack in the film in use. The present inventors found out, as a method of solving the problems given above, that the piezoelectric property can be improved even when the composition ratio of Zr/(Zr+Ti) is over 0.4 but less than 0.7 by limiting volume rates of tetragonal crystal a-domain and c-domain of the piezoelectric substance film of the piezoelectric substance element.
Further, even when the composition ratio of Zr/(Zr+Ti) is over 0.4 but less than 0.7, it proves the following points that at least some of the a-domain and the c-domain take a twinning crystal enantiomorphic relationship.
(1) A structure having the a-domain and the c-domain is easy to occur.
(2) It is possible to overcome the defect of the durability such as being easy to cause the crack in the film in use.
(3) The crack gets hard to occur in a patterning film in such an application as to effect fine patterning of the piezoelectric substance film. Moreover, in a range of 1.004-1.040 smaller in ratio given by [001] axial length/[100] axial length that configure the a-domain and the c-domain than in Japanese Patent Application Laid-Open No. 2000-332569, domain switching becomes easy to take place, and it was found out that excellent characteristics both in the piezoelectric property and in the durability are exhibited. Still further, it was discovered that on the occasion of applying an electric field to the piezoelectric substance element, the a-domain changes into the c-domain each time the electric field is applied. Namely, when stopping the application of the electric field, the changed c-domain returns again to the a-domain, and this is repeated, whereby a large piezoelectric characteristic occurs. Further, Japanese Patent Application Laid-Open No. 2000-332569 given above describes that in the MPB area, the (001) mono-orientation occurs, and the piezoelectric property declines. By contrast, according to the present invention, it was discovered that the sufficient a-domain can be made to exist even when the Zr/(Zr+Ti) ratio is over 0.4 but less than 0.7, perhaps depending on a difference in manufacturing method.
Herein, the a-domain of the piezoelectric substance film composed mainly of Pb(Zr, Ti)O3 is a generic term of a domain having a (100) plane within a ±10° range with respect to the substrate surface, i.e., having crystal axes in [100] azimuths within the ±10° range in a film thickness direction. Further, the c-domain of the piezoelectric substance film composed mainly of Pb(Zr, Ti)O3 is a generic term of the following domain. This domain has a (001) plane within the ±10° range with respect to the substrate surface, i.e., having crystal axes in [001] azimuths within the ±10° range in the film-thickness direction.
Moreover, the twinning crystal structure according to the present invention is a structure configured by a domain having the twinning enantiomorphic relationship in which at least some of the a-domain and the c-domain have a (N0N) plane (N is an integer) defined as a twinning plane.
Further, the [001] axial length/[100] axial length ratio according to the present invention, which configure the a-domain and the c-domain, is defined as a ratio given by a c-axis length/a-axis length of the crystal lattices of the tetragonal crystal Pb(Zr, Ti)O3 that configure the a-domain and the c-domain.
In each of modes described above, it is preferable that a volume rate of the c-domain to a total of the a-domain and the c-domain is equal to or larger than 20% and equal to or smaller than 60%. This volume rate is more preferably equal to or larger than 25% and equal to or smaller than 60%. Further, the composition ratio of Zr/(Zr+Ti) is, more preferably, equal to or larger than 0.45 but less than 0.65. Moreover, the piezoelectric substance film can have any one of the tetragonal crystal, a pseudo cubic crystal and a rhombohedral crystal. Namely, the piezoelectric substance film may be structured solely of the tetragonal crystal and may also be structured of a multiphase series crystal (mixed crystal) of the tetragonal crystal and the pseudo cubic crystal or a mixed crystal of the tetragonal crystal and the rhombohedral crystal. Moreover, the piezoelectric substance element is an element, wherein the piezoelectric substance film is an epitaxial mono-crystal film or a single-axis oriented film. Furthermore, a preferable value of [001] axial length/[100] axial length is equal to or larger than 1.005 and equal to or smaller than 1.036, and more preferably equal to or larger than 1.015 and equal to or smaller than 1.029. The PZT film may contain an inorganic element as a dopant. The dopant can be exemplified such as Nb, La, Can, Sr, Sb, Mo, W, Fe, Ni and Co.
A tilt angle of each of the a-domain and the c-domain with respect to the substrate surface will be explained with reference to
Herein, the epitaxial mono-crystal film or the single-axis oriented film according to the present invention indicates a film having a mono-crystalline azimuth in the film thickness direction and an intra film plane direction, or in the film thickness direction by making use of crystallinity of the substrate or a lower-layer film (e.g., a lower electrode film). For example, SRO (ruthenium acid strontium) taking a perovskite type structure and PZT are as close as 4 Å in their lattice constant. Such being the case, after the SRO having the (100) plane with respect to the substrate surface has been formed as the lower electrode film, and the PZT is formed as the piezoelectric substance film, at which time the PZT having, e.g., at least the tetragonal crystal a-domain and c-domain with respect to the substrate surface can be formed depending on the film forming condition. Thus, the film having the mono-crystalline azimuth in the film thickness direction and the intra film plane direction by making use of the crystallinity of the lower-layer film (e.g., the lower electrode film) is the epitaxial mono-crystal film or the single-axis oriented film according to the present invention.
Further, according to the present invention, the definition of the epitaxial mono-crystal film or the single-axis oriented film is in a broad sense applied to a case in which a plurality of morphotropic phases such as the tetragonal crystal, the pseudo cubic crystal and the rhombohedral crystal exists in mixture (multiphase), a case in which the crystals derived from the twinning etc exist in mixture and a case of containing a transition, a defect, etc. This is because the piezoelectric substance film can have at least the tetragonal crystal a-domain and c-domain within the range of ±10° with respect to the substrate surface even in the case where these phases and the twining crystal exist in mixture.
The following are next confirmation methods that will be explained herein. A confirmation method (1) is a method of confirming the a-domain and the c-domain according to the present invention. A confirmation method (2) is a method of confirming the morphotropic phase. A confirmation method (3) is a method of confirming the twinning structure. A confirmation method (4) is a method of confirming the volume rate of the c-domain to the total of the a-domain and the c-domain. A confirmation method (5) is a method of confirming the epitaxial mono-crystal film or the single-axis oriented film. A confirmation method (6) is a method of confirming the composition ratio of Zr/(Zr+Ti).
To start with, the a-domain and the c-domain, the twining structure and the volume rate can be confirmed by an reciprocal space mapping method of X-rays analysis and a pole measurement method over a symmetric plane as illustrated in
Furthermore,
Furthermore, the volume rate according to the present invention can be computed by use of the results of conducting the pole measurement over, for example, the PZT(002) plane and the PZT(200) plane in the X-ray diffraction in
The piezoelectric substance film can be obtained by the method of forming the film over the substrate, wherein a substrate temperature is set equal to or higher than 300° C. and equal to or lower than 550° C. The film is formed, wherein the substrate temperature is set, preferably, equal to or higher than 350° C. and equal to or lower than 490° C. Thereafter, an anneal treatment is effected in oxygen at a temperature that is higher by over 100° C., preferably, over 200° C. than the film forming temperature, and more preferably at a temperature equal to or higher than 450° C. and equal to or lower than 850° C., much more preferably, at a temperature equal to or higher than 520° C. and equal to or lower than 800° C. With such a method adopted, in the case of employing a Si substrate etc as the substrate, the piezoelectric substance film receives a tensile stress, whereby the volume rate of the c-domain to the total of the a-domain and the c-domain can be decreased.
When forming the film at the substrate temperature higher than the temperatures given above, for instance, at a temperature equal to or higher than 600° C., it follows that the film becomes such a type of film that the a-domain is extremely small. In this film, the domain ratio can not be changed even by effecting the anneal treatment after the film formation. Thus, the anneal treatment is executed in the oxygen, however, it is preferable that this anneal treatment is done in a Pb atmosphere when at a temperature as high as over 650° C. A period of treatment time is preferably is equal to or longer than 10 min but less than 3 hours. Formation of the Pb atmosphere can be attained by disposing a compound, i.e., PZT containing Pb in a predetermined position in a heating area. Specific film forming means for the piezoelectric substance film can be exemplified such as a MO-CVD (Metal Organic Chemical Vapor Deposition) method, a sputtering method, a sol-gel method, a hydrothermal synthesis method, an MBE (Molecular Beam Epitaxial) method and a PLD (Pulsed Laser Deposition) method. In these methods, the MO-CVD method is preferable. A preferable method is particularly a method of intermittently supplying a raw gas, which is disclosed in Japanese Patent Application Laid-Open No. 2001-220676. Further, it is preferable that the MO-CVD method involves using a material exhibiting a high soaking property for a nozzle that supplies the raw gas.
The following are materials that are preferably utilized as the raw materials used for the MO-CVD method. Note that a radical of ((CH3)3CCO2)2CH is expressed by thd. The Pb raw material can be exemplified such as Pb(C2H5)4, Pb(thd)2, Pb(thd) (OC2H5)2, (C2H5)3PbOCH2C(H3)3, Pb(C2H5)3(OC4H9-t), Pb(C6H5)4 and PbCl2. A Zr raw material can be exemplified such as Zr(OC4H9-t)4, Zr(i-C3H7)4, Zr(OC2H5)4, Zr(OCH3)4 and Zr(OC5H11-n)4. A Ti raw material can be exemplified such as Ti(OC3H7-i)4, Ti(thd)2(OC3H7-i)2, Ti(OC2H5)4, TiCl4, Ti(OCH3)4 and Ti(OC5H11)4.
Moreover, part of Pb of PZT can be replaced with La etc, however, a raw material in this case involves using La(thd)3, La(C2H3O2)4, LaCl3 and so on. Further, as for the PZT composition, the Zr-to-Ti composition ratio is set as described, however, Pb may be excessive in quantity with respect to a B site element such as Zr and Ti.
As the substrate formed with the piezoelectric substance film, a preferable substrate is a glass substrate or a Si substrate on which a buffer layer and an electrode layer are formed.
A preferable buffer layer is a layer on which a film composed of a perovskite type oxide, e.g., an SRO (100) or SRO(001) film can be formed as the electrode layer. The piezoelectric substance film composed of a PZT perovskite film exhibiting good crystalline controllability can be acquired by through a SrRUO3(SRO) film. The preferable buffer layer can be exemplified by a fluorite oxide film and/or a magnesia spinel film such as a YSZ(100) film or a MgAl2O4(001) film. If, for instance, a MgO(100) mono-crystalline substrate is employed as the substrate, as described above, it follows that the film becomes a film having the large c-domain or a polycrystalline film. According to the present invention, other than the Si substrate and the glass substrate, a SrTiO3 substrate, a sapphire substrate and a KTaO3 substrate may also be employed, however, the glass substrate and the Si substrate are preferable in terms of manufacturing the device. The buffer layer on the substrate can be formed by use of a metal oxide such as YSZ(Y-doped ZrO2), STO(Sr(TiO3), MgO, MgAl2O4 and CeO2, and/or can be also formed by employing a face-centered cubic structure metal, a hexagonal close-packed structure metal and a body-centered cubic structure metal such as Pt, Ir, Ru, Ti and Ta.
The electrode layer can be made from a conductive metal oxide such as SRO(SrRuO3), LNO(LaNiO3), LSCO(LaSrCoO3), CaRuO3, SrCrO3 and LaCuO3. It is preferable that the electrode layer be composed of the perovskite type oxide. One of the upper and lower electrodes of the piezoelectric substance element may involve using the conductive oxide taking the perovskite type structure such as the SRO film, however, in addition to this film, metallic materials such as a metal material having the hexagonal close-packed structure, a metal material having the face-centered cubic structure and a metal material having the body-centered cubic structure, are preferably used. The film thickness of the electrode is 50 nm through 600 nm and, preferably, 100 nm through 300 nm.
The crystalline orientation of each of these layers is (100) or (001) in the case where the electrode layer and the buffer layer are the metal oxide layers and is (111) in the case where the buffer layer is the metal layer. The film thickness of each of the layers described above can be selected from within a range of being equal to or larger than 10 nm and equal to or smaller than 800 nm.
The method of controlling the volume rate of the c-domain to the total of the a-domain and the c-domain adopts the method of controlling the film forming temperature and the anneal temperature described above, and, with the exception of this method, there may be adopted a method of controlling the volume rate with a stress applied on the film by making use of a thermal expansion coefficient of the substrate. To attain this, it is also effective to adjust the film thickness of each of the layers in order to effectively use the thermal expansion coefficients of the buffer layer and the electrode layer.
(Liquid Discharge Head and Liquid Discharge Apparatus)
Given next is an explanation of a liquid discharge head according to the present invention.
The liquid discharge head according to the present invention is a liquid discharge head characterized by including the piezoelectric substance element described above and discharging the liquid by use of the piezoelectric substance element.
To show a specific example of configuration, the liquid discharge head has a discharge port, an individual liquid chamber communicating with the discharge port, a diaphragm configuring part of the individual liquid chamber, and a piezoelectric substance element for giving vibrations to the diaphragm provided outside the individual liquid chamber. In this liquid discharge head, the liquid in the individual liquid chamber is discharged by dint of a change in volume within the individual liquid chamber, which occurs due to the diaphragm. Then, this liquid discharge head is characterized by using the piezoelectric substance element having the configuration described above as the piezoelectric substance element.
It is possible to readily obtain the liquid discharge head capable of exhibiting uniform and high discharge performance by employing the piezoelectric substance film element (piezoelectric substance element) according to the present invention and capable of attaining a discharge pressure generation element hyperfine-structured pattern including the piezoelectric substance film element. The liquid discharge head according to the present invention may be employed for image forming apparatuses such as an inkjet printer, a facsimile, a multi-function machine and a copying machine, or for industrial discharge apparatuses that discharge liquids other than the inks.
The liquid discharge head according to the present invention will be explained with reference to
A thickness of the diaphragm 15 is normally 0.5 μm-10 μm and, preferably, 1.0 μm-6.0 μm. This thickness includes, if the buffer layer 19 is provided, a thickness of the buffer layer. Further, a plurality of layers excluding the buffer layer may also be formed. For example, there may be included an etch stopping layer needed for such a case that the diaphragm and the individual liquid chamber are formed from the same substrate. A width Wa (see
Next, the liquid discharge head manufacturing method according to the present invention will be described. The liquid discharge head manufacturing method according to the present invention has at least the following steps.
To be specific, for example, the following method can be exemplified as a first method of manufacturing the liquid discharge head according to the present invention. Part of the individual liquid chamber and the diaphragm are formed by applying the step (3) on the substrate formed with the piezoelectric substance film element 10 in a way that applies the step (6) given above. The substrate formed with the communication hole and the common liquid chamber is manufactured by applying the steps (2) and (4), and the substrate having the discharge port is manufactured by applying the step (1), separately. Next, the liquid discharge head is manufactured by integrating the substrates with their substrate members in a way that stacks these substrate members.
Further, the following method can be exemplified as a second method of manufacturing the liquid discharge head according to the present invention. To begin with, separately, at least, the substrate member to be formed with the individual liquid chamber or the substrate member formed with the individual liquid chamber is manufactured by applying the step (3). Next, the piezoelectric substance film element or the diaphragm and the piezoelectric substance film element is or are transferred onto this substrate member from the substrate formed with the piezoelectric substance film element by applying the step (6) or from the substrate formed with the diaphragm and the piezoelectric substance film element. Subsequently, the individual liquid chamber is formed by working, in a way that applies the step (2), at least the substrate member portion, on the side opposite to the piezoelectric substance film element etc., of the substrate member onto which the piezoelectric substance film element or the diaphragm and the piezoelectric substance film element is or are transferred. Moreover, in the same way as the first method described above, the substrate member formed with the communication hole and the common liquid chamber and the substrate member formed with the discharge port are manufactured, and the liquid discharge head is manufactured by stacking and thus integrating these substrate members. The first method involves, as shown in
The second method is, for example, as shown in
Moreover, as illustrated in
A joining method at the transferring time may be a method using an inorganic or organic bonding agent, however, metal joining that employs the inorganic material is more preferable. Materials used for the metal joining can be exemplified such as In, Au, Cu, Ni, Pb, Ti, Cr and Pd. When employing these materials, the junction can be attained at a temperature as low as 300° C., the difference in thermal expansion coefficient from the substrate member is decreased, and hence a damage to the piezoelectric substance film element is small as well as avoiding a problem due to a warp etc of the piezoelectric substance film element if elongated.
The communication hole 12 and the common liquid chamber 14 according to the first method and the individual liquid chamber 13, the communication hole 12 and the common liquid chamber 14 according to the second method, can be formed by working, for instance, the formation members (substrate members). This working can involve utilizing a method having a step of patterning the formation members (substrate members) by the lithography and a step of removing some of the members. For example, in the case of the second method, the individual liquid chamber 13, the communication hole 12 and the common liquid chamber 14 are formed by steps shown in
In the second method, It is preferable that another substrate member onto which the piezoelectric substance film element 10 is transferred from the substrate 8 involves using a substrate member set in the state of
Next, the liquid discharge apparatus according to the present invention will be described. The liquid discharge apparatus according to the present invention includes the liquid discharge head of the present invention and the means for mounting the liquid discharge head. A liquid discharge apparatus (an inkjet recording apparatus) illustrated in
In this type of liquid discharge apparatus, the carriage 92 is carried along on the rails by electric signals transmitted from a computer, and the piezoelectric substance (piezoelectric member) gets displaced when a drive voltage is applied to the electrodes pinching the piezoelectric member therebetween. Each piezoelectric chamber is pressurized through the diaphragm 15 by dint of the displacement of this piezoelectric member, and the ink is thereby discharged from the discharge port 11, thus performing the printing.
In the liquid discharge apparatus according to the present invention, the liquid can be uniformly discharged at a high speed, and the apparatus can be downsized.
The example given above is exemplified as the printer, however, the liquid discharge apparatus according to the present invention can be utilized as an industrial liquid discharge apparatus in addition to the inkjet recording apparatus such as the facsimile, the multifunction machine and the copying machine.
Next, the present invention will be explained by giving examples.
Pb(thd)(OC2H5)2, Zr(OC4H9-t)4, Ti(OC5H11)4 and the oxygen gas are used as the raw materials. By the method of intermittently supplying the raw gas, the film was grown up to a thickness of 2.2 μm-2.5 μm on the Si substrate heated at 450° C. in a way that adjusts a supply quantity of the raw gas so that the Zr/(Zr+Ti) ratio becomes 0.50 through 0.53. A diameter of the discharge port of discharging the raw gas was set to 40 Φmm, and there was used a SUS-made nozzle having a wall as thick as 3 mm and exhibiting the high soaking property. The substrate involves employing the Si substrate on which layers of SRO(100)/LaNiO3(100)/CeO2(100)/YSZ(100) are stacked. After the film has been grown, the anneal treatment was conducted for 30 min at 680° C. in a heating furnace wherein a ceramics PZT powder is disposed in a predetermined position in a heating area, thereby acquiring the piezoelectric substance epitaxial film according to the present invention. It proved from the MRD measurement etc that this piezoelectric substance film has the morphotropic phase in which the tetragonal crystal and the rhombohedral crystal exist in mixture, and the domains of the tetragonal crystal are the a-domain and the c-domain. Further, the tilt angles of the c-domain and the a-domain were 0.7° and 0.9°, respectively. Moreover, the volume rate of the c-domain to the total of the a-domain and the c-domain was 43%-45%. Pt/Ti is provided as the upper electrode on this piezoelectric substance film, the constants d31, d33 were measured by employing the unimorph method and the AFM, with the result that both of these constants could be measured as preferable values. Further, the [001] axial length/[100] axial length ratio of this piezoelectric substance film was 1.020.
This piezoelectric substance element was worked in the shape as shown in
The film was grown in the same way as the first example except that the substrate temperature was set at 600° and that the anneal treatment was omitted, and the piezoelectric substance film was acquired. The film had the volume rate of the c-domain to the total of the a-domain and the c-domain, which exceeds 95%, and the piezoelectric substance element was inferior to that in the first example in terms of the displacement amount and the durability.
A PZT piezoelectric substance film with only the tetragonal crystals where the composition ratio of Zr/(Zr+Ti) is 0.5 and 0.39, is grown up to a thickness of 2.0 μm on the substrate having a variety of thermal expansion coefficients. SrRuO3(100) was used as the lower electrode.
It is understood from
SRO(100)/LNO(100) is grown by sputtering as a buffer layer on a quartz glass substrate, wherein Pt(111)/Ti serves as an electrode layer. Further, a PZT single-axis oriented film showing 0.52 as the composition ratio of Zr/(Zr+Ti) was grown thereon up to a thickness of 2.5 μm. This structure is a PZT/SRO/LNO/Pt/Ti quartz glass substrate. Pt is a natural oriented film, however, LNO and SRO are (100) oriented films. The volume rate of the c-domain to the total of the a-domain and the c-domain was 20%, and the [001] axial length/[100] axial length ratio was 1.019. When evaluating an attaching characteristic of Pt as the upper electrode, there was an excellent residual dielectric polarization value (Pr) that is equal to or larger than 55 μC/cm2, and the displacement amount was measured at 0.8% with the electric field intensity of 100 kV/cm. Moreover, though in a state of having a scatter in position, there was a position of exhibiting a large displacement amount exceeding the [001] axial length/[100] axial length ratio.
The electrode layer and the buffer layer were grown with a structure of LSCO(100)/LNO(100)/Ir(111)/Ta on the Si(100) substrate. An oxide film having a thickness of 350 nm was interposed between the Ta/Si substrates so that contraction is restrained till the Si substrate is cooled down to a room temperature from a temperature 490° C. when the film was grown. The PZT single-axis oriented film showing 0.52 as the composition ratio of Zr/(Zr+Ti) was grown thereon up to a thickness of 2.0 μm. The volume rate of the c-domain to the total of the a-domain and the c-domain was 25%, the [001] axial length/[100] axial length ratio was 1.028, and the tilt angle of the a-domain was 1.0°-1.2°. The crystal structure is mainly the tetragonal crystal, however, the film contained the rhombohedral crystal other than the tetragonal crystal. When evaluating the attaching characteristic of Pt as the upper electrode, there was an excellent residual dielectric polarization value (Pr) that is equal to or larger than 60 μC/cm2, and the displacement amount was measured at 1.0% or larger with the electric field intensity of 100 kV/cm.
The PZT film was grown up to the thickness of 2.0 μm in the same way as in the first example so that the composition ratio of Zr/(Zr+Ti) becomes 0.45. It proved from the MRD measurement that this film is the tetragonal crystal, wherein the a-domain and the c-domain exist in mixture. Further, the volume rate of the c-domain to the total of the a-domain and the c-domain was 30%. The tilt angle of the c-domain was 0.2°. A Pt/Ti upper electrode having 100 μmΦ is provided on this film, and, when evaluating the characteristic thereof, there was confirmed a value as large as 280 in the constant d33 characteristic with the electric field intensity of 150 kV/cm.
The PZT film was grown up to the thickness of 2.0 μm in the same way as in the first example so that the composition ratio of Zr/(Zr+Ti) becomes 0.64. It proved from the MRD measurement that this film is a film where the tetragonal crystal and the rhombohedral crystal exist in mixture, and the tetragonal crystal is a film where a-domain and the c-domain exist in mixture. Further, the rhombohedral crystal was (100)-oriented, and the volume rate of the c-domain to the total of the a-domain and the c-domain was 26% through 28%. The [001] axial length/[100] axial length ratio was 1.015. When evaluating the characteristic of this film, there was a value as large as 300 in the constant d33 characteristic with the electric field intensity of 150 kV/cm.
When the PZT film with the composition ratio of Zr/(Zr+Ti) that is 0.75 was grown, it proved from the MRD measurement that the film has only the rhombohedral crystal, and hence none of the existent of the c-domain was observed. The constant d33 characteristic was less than 80 with the electric field intensity of 150 kV/cm.
This application claims priority from Japanese Patent Application Nos. 2005-012131 filed on Jan. 19, 2005 and 2005-034956 filed on Feb. 10, 2005 and 2005-257132 filed on Sep. 5, 2005, which are hereby incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-012131 | Jan 2005 | JP | national |
| 2005-034956 | Feb 2005 | JP | national |
| 2005-257132 | Sep 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/301073 | 1/18/2006 | WO | 00 | 6/3/2008 |
