Title of Invention

PIEZOELECTRIC DEVICE, PIEZOELECTRIC ACTUATOR, HARD DISK DRIVE, INK JET PRINTER APPARATUS, AND PIEZOELECTRIC SENSOR

Technical Field

[0001] The present invention relates to a piezoelectric device using a piezoelectric material; and a piezoelectric actuator, a hard disk drive, an ink jet printer apparatus and a piezoelectric sensor having the piezoelectric device.

Background Art

[0002] Recently, practical application of piezoelectric devices using thin film piezoelectric materials is spreading, in place of bulk piezoelectric materials. Examples of such application include gyro sensors, shock sensors, microphones, etc. making use of the piezoelectric effect to convert a force exerted on a piezoelectric film to a voltage, or actuators, ink jet heads, speakers, buzzers, resonators, etc. making use of the inverse piezoelectric effect to deform a piezoelectric film with application of voltage thereto.

[0003] Reduction in thickness of the piezoelectric material will enable reduction in scale of the piezoelectric device to expand fields of application. Since a large number of piezoelectric devices can be manufactured together on a substrate, mass productivity must increase. Furthermore, there are many advantages in terms of performance, e.g., improvement in sensitivity when the piezoelectric film is used in a sensor. However, external stress from other films to the piezoelectric film and internal stress of the piezoelectric film itself will bring about more influence on the piezoelectric characteristics than in the case of the bulk materials, and for this reason the piezoelectric thin film requires a stress control technology different from that for the bulk materials. Therefore, a control method of the piezoelectric characteristics with focus on control of thermal stress applied to interfaces of the piezoelectric film becomes an important factor in design of the piezoelectric device.

Citation List

Patent Literature

[0004] Patent Literature 1 : Japanese Patent Application Laid-open No. 2003-176176

Patent Literature 2: Japanese Patent Application Laid-open No. 2006-188414

Patent Literature 3: Japanese Patent Application Laid-open No.

1999-097755

Patent Literature 4: Japanese Patent No. 4142128

Patent Literature 5: Japanese Patent Application Laid-open No.

2009-094449

Non Patent Literature

[0005] Non Patent Literature 1 : R&D Review of Toyota CRDL Vol. 34 No. 1 pp 19-24 (1999)

Summary of Invention

Technical Problem

[0006] One of important factors among the piezoelectric characteristics is the coercive electric field Ec. The coercive electric field Ec is the magnitude of an electric field at reverse points of spontaneous polarization, and the polarization direction starts to reverse when an electric field over this coercive electric field is applied to the piezoelectric material. Fig. 1 shows a hysteresis curve of polarization P-electric field E of a typical piezoelectric device, and positions of coercive electric field Ec. In the case of a device making use of the reverse piezoelectric effect, i.e., deformation of the piezoelectric film with application of voltage, high displacement is achieved in the same direction as the polarization direction.

[0007] Fig. 2 shows a relation of strain x and electric field E of a typical piezoelectric device (which is called a butterfly curve). It is seen from Fig. 2 that the strain direction reverses at points of coercive electric field Ec. This means that even if the electric field E is increased in order to obtain a large strain x, the polarization direction will reverse just over the coercive electric field Ec, so as to result in failure in obtaining the strain x in a desired direction. Therefore, there are desires for a piezoelectric device with a large coercive electric field Ec to obtain a large strain x.

[0008] One of techniques to increase the coercive electric field is to change the composition of the piezoelectric film (Patent Literatures 1 and 2), but even in the case of the piezoelectric material of the same composition, when it is formed as a thin film, as described above, the coercive electric field changes significantly because of the external stress due to the film configuration of the device, the internal stress due to film forming conditions, and factors such as crystallinity and orientation of the piezoelectric film, and the control thereof is difficult. When the coercive electric field is increased by the change in the composition of the piezoelectric film itself, the piezoelectric constants of the piezoelectric film tend to decrease, and it is thus difficult to obtain a desired displacement.

[0009] There is another technique to efficiently drive the piezoelectric film with a small coercive electric field (Patent Literature 3), but it requires preliminary measurement of accurate values of the coercive electric field, which makes a drive circuit complicated and which increases the cost of the device.

[0010] Patent Literature 4 discloses a lamination in which a dielectric film is formed on a silicon substrate and in which an electroconductive intermediate film is laid on the dielectric film to prevent reduction of spontaneous polarization, but the effect of improvement in piezoelectric characteristics is limited just by depositing the intermediate film on only one side of the dielectric film.

[0011] Patent Literature 5 discloses the piezoelectric device in a structure in which an intermediate film to produce stress in compressive directions in the piezoelectric film is provided between an electrode formed on a silicon substrate and the piezoelectric film, though the purpose thereof is different from that of the present invention.

However, there are no restrictions of the linear expansion coefficient and others on the intermediate film, and when the intermediate film is deposited just on only one side of the piezoelectric film, many piezoelectric materials fail to achieve a satisfactory inverse piezoelectric characteristic as a piezoelectric device.

[0012] The present invention has been accomplished in view of the problems of the above-described conventional technologies, and it is an object of the present invention to provide a piezoelectric device capable of readily increasing the coercive electric field of the piezoelectric device.

Solution to Problem

[0013] A piezoelectric device according to the present invention comprises a first electrode film; a first nonmetal electroconductive intermediate film provided on the first electrode film; a piezoelectric film provided on the first nonmetal electroconductive intermediate film; a second nonmetal electroconductive intermediate film provided on the piezoelectric film; and a second electrode film provided on the second nonmetal electroconductive intermediate film. A linear expansion coefficient of the first nonmetal electroconductive intermediate film is larger than a linear expansion coefficient of the first electrode film and a linear expansion coefficient of the piezoelectric film, and a linear expansion coefficient of the second nonmetal electroconductive intermediate film is larger than a linear expansion coefficient of the second electrode film and the linear expansion coefficient of the piezoelectric film.

[0014] According to the present invention, the device comprises the nonmetal electroconductive intermediate films, which facilitates introduction of compressive stress to the piezoelectric film, thereby achieving increase in coercive electric field. The specific resistance (resistivity) of each nonmetal electroconductive intermediate film can be not more than 0.1 Ωαη.

[0015] In the piezoelectric device according to the present invention, the first and second nonmetal electroconductive intermediate films can be in direct contact with the piezoelectric film.

[0016] This configuration makes it easier to further effectively introduce the compressive stress to the piezoelectric film and thus facilitates further increase in coercive electric field of the piezoelectric device.

[0017] The piezoelectric device according to the present invention can be configured as follows: there is no substrate 10 μπι or more thick on a top surface of the second electrode film and there is no substrate 10 μπι or more thick on a bottom surface of the first electrode film, either.

[0018] Without such substrates, there are no restraints on the piezoelectric film from the substrates and thus greater compressive stress can be exerted on the piezoelectric film.

[0019] The first and second nonmetal electroconductive intermediate films can be inorganic oxide films respectively. It is easier to make the inorganic oxide films of materials with a larger linear expansion coefficient than the piezoelectric film, and thus it is easier to exert the compressive stress on the piezoelectric film, by depositing the two inorganic oxide films at high temperature and thereafter cooling them. When the inorganic oxide films are used as the electroconductive intermediate films, it becomes feasible to deposit the electroconductive intermediate film on the piezoelectric film at high temperature or to anneal the electroconductive intermediate films, which enables greater compressive stress to be exerted on the piezoelectric film. This enables introduction of compressive stress to the piezoelectric film by heating and cooling during annealing the electroconductive intermediate films, in addition to thermal expansion of the electroconductive intermediate films, so as to enhance the effect of increase in coercive electric field.

[0020] The two inorganic oxide films can have the same composition. Furthermore, the two electroconductive intermediate films can have respective thicknesses approximately equal to each other. This configuration allows uniform compressive stresses to be exerted on the piezoelectric film from the two sides thereof.

Advantageous Effects of Invention

[0021] The piezoelectric device, etc. of the present invention can have the larger coercive electric field than the conventional piezoelectric devices.

Brief Description of Drawings

[0022] Fig. 1 is a drawing showing a hysteresis curve of polarization P-electric field E of a typical piezoelectric device, and positions of coercive electric field Ec.

Fig. 2 is a drawing showing a relation of strain x and electric field E of a typical piezoelectric device (butterfly curve).

Fig. 3 is a configuration diagram of a piezoelectric device according to the first embodiment of the present invention.

Fig. 4 is a configuration diagram of a piezoelectric device according to the second embodiment of the present invention.

Fig. 5 is a configuration diagram of a piezoelectric device according to the third embodiment of the present invention.

Fig. 6 is a drawing showing a film configuration of a piezoelectric device of Comparative Example 1. Fig. 7 is a configuration view of a head assembly using the piezoelectric device.

Fig. 8 is a configuration view of a hard disk drive on which the head assembly illustrated in Fig. 7 is mounted.

Fig. 9 is a configuration view of an ink jet printer head using the piezoelectric device.

Fig. 10 is a configuration view of a ink jet printer apparatus on which the ink jet printer heads 80 illustrated in Fig. 9 are mounted.

Fig. 11(a) is a configuration view (a plan view) of a gyro sensor using the piezoelectric device and Fig. 11(b) is a cross-sectional view which is taken along a line A- A in Fig. 11(a).

Fig. 12 is a configuration view of a pressure sensor using the piezoelectric device.

Fig. 13 is a configuration view of a pulse wave sensor using the piezoelectric device.

Description of Embodiments

[0023] The preferred embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, identical or equivalent elements will be denoted by the same reference signs. The vertical and horizontal positional relations are as shown in the drawings. The description will be given without redundant description.

[0024] (First Embodiment)

Fig. 3 shows a piezoelectric device 100 according to the first embodiment of the present invention. The piezoelectric device 100 has a substrate 7, a first electrode film 5 laid on the substrate 7, a first electroconductive intermediate film 4 laid on the first electrode film 5, a piezoelectric film 3 laid on the first electroconductive intermediate film 4, a second electroconductive intermediate film 2 formed on the piezoelectric film 3, and a second electrode film 1 formed on the second electroconductive intermediate film 2.

[0025] (Substrate 7)

The substrate 7 is a plate serving as an underlying structure. The substrate 7 to be used herein can be, for example, a silicon substrate having the (100) plane orientation. The substrate 7 can have the thickness, for example, in the range of 10 μιη to 1000 μπι. The substrate 7 to be used herein can also be a silicon substrate having a plane orientation different from the (100) plane, a Silicon-on-Insulator (SOI) substrate, a quartz glass substrate, a compound semiconductor substrate composed of GaAs or the like, a sapphire substrate, a metal substrate composed of stainless steel or the like, a MgO substrate, or a

SrTi0 ₃ substrate. An insulating film may be laid on the substrate 7 when the substrate 7 is an electroconductive material. The insulating film to be used herein can be, for example, a thermally oxidized silicon film (Si0 ₂ ), Si ₃ N ₄ , Zr0 ₂ , Y ₂ 0 ₃ , ZnO, or A1 ₂ 0 ₃ . The thickness of the insulating film can be in the range of 0.001 μηι to 1.0 μπι.

[0026] (First Electrode Film 5)

The first electrode film 5 is an electroconductive film. The first electrode film 5 is made, for example, of platinum (Pt). The first electrode film 5 preferably has the thickness in the range of 0.02 μηι to 1.0 μιη. When the thickness is less than 0.02 μιη, the function as electrode can become insufficient; when the thickness is more than 1.0 μπι, the displacement characteristic of the piezoelectric material can be hindered. The first electrode film 5 to be used herein can also be a metal material such as palladium (Pd), rhodium (Rh), gold (Au), ruthenium (Ru), or iridium (Ir).

[0027] (First Electroconductive Intermediate Film 4)

The first electroconductive intermediate film (first nonmetal electroconductive intermediate film) 4 is a nonmetal film. The linear expansion coefficient of the first electroconductive intermediate film 4 is larger than linear expansion coefficients of the first electrode film 5 and the piezoelectric film 3.

The linear expansion coefficient in the present specification is an average of change rates of length against temperature, per unit length in the range of 20°C to 500°C. It is generally known that the linear expansion coefficient of a thin film is close to or slightly smaller than a value of a bulk material (e.g., cf. Non Patent Literature 1), and if we know types of respective materials forming the piezoelectric device, a magnitude relation of the linear expansion coefficients of the respective thin films can be adequately estimated.

[0028] The linear expansion coefficient of the first electroconductive intermediate film 4 is preferably larger by at least O.l x lO ^-6 (1/K) than the larger value of the linear expansion coefficients of the first electrode film 5 and the piezoelectric film 3.

[0029] The thickness of the first electroconductive intermediate film 4 is preferably in the range of 10 run to 100 nm. If the thickness is less than 10 nm, sufficient compressive stress may be unable to be exerted on the piezoelectric film 3; if the thickness is more than lOOnm, the crystallinity of the piezoelectric film 3 can degrade.

[0030] The first electroconductive intermediate film 4 is preferably an inorganic oxide film. Examples of inorganic oxides are electroconductive metal oxides. In the piezoelectric device 100 of the present embodiment, since a voltage is applied to the piezoelectric film

3 through the first electrode film 5 and the first electroconductive intermediate film 4, the first electroconductive intermediate film with too high specific resistance is not preferred. Therefore, the specific resistance of the first electroconductive intermediate film 4 is preferably not more than 0.1 Qcm. For example, a SrRu0 ₃ film has the specific resistance of about 50-100x l0 ^"6 Ωαη, a SrTi0 ₃ film the specific resistance of about 70-100x l0 ^"6 Ωαη, and a LaNi(D ₃ film the specific resistance of about 300-400x 10 ^"6 Qcm; therefore, they are suitably applicable to the first electroconductive intermediate film 4. Besides, electroconductive metal oxide films such as CaRu0 ₃ , BaRuOs,

(La _x Sri _-x )Co0 ₃ , YBa ₂ Cu ₃ 0 ₇ , and La ₄ BaCu ₅ 0i ₃ also have the specific resistance of not more than 0.1 Qcm, and thus are suitably applicable to the first electroconductive intermediate film 4. For the purpose of decreasing electroconductivity, an alkali metal element such as Li, K, or Na may be added to the first electroconductive intermediate film 4.

Since deposition of the piezoelectric film 3 is carried out at high temperature as described below, metal materials with a low melting point are not suitable for the first electroconductive intermediate film 4.

[0031] (Piezoelectric Film 3)

There are no particular restrictions on a material of the piezoelectric film 3 as long as it exhibits the piezoelectric characteristics; examples of such materials for the piezoelectric film 3 include PZT (lead zirconate titanate), KNN (potassium sodium niobate), BT (barium titanate), LN (lithium niobate), BNT (bismuth sodium titanate), ZnO (zinc oxide), and A1N (aluminum nitride). There are no particular restrictions on the thickness of the piezoelectric film 3, but the thickness can be, for example, in the range of about 0.5 μπι to 5 μπι.

[0032] (Second Electroconductive Intermediate Film (Second Nonmetal Electroconductive Intermediate Film) 2)

The second electroconductive intermediate film 2 is a nonmetal film. The linear expansion coefficient of the second electroconductive intermediate film 2 is larger than those of the second electrode film 1 and the piezoelectric film 3. A material of the second electroconductive intermediate film 2 can be one of the materials listed for the first electroconductive intermediate film 4. The thickness of the second electroconductive intermediate film 2 can also be in the range described for the first electroconductive intermediate film 4.

[0033] The linear expansion coefficient of the second electroconductive intermediate film 2 is preferably larger by at least O. l x lO ^-6 (1/K) than the larger value of the linear expansion coefficients of the second electrode film 1 and the piezoelectric film 3.

[0034] The second electroconductive intermediate film 2 and the first electroconductive intermediate film 4 can have the same composition. The thickness of the second electroconductive intermediate film 2 can be close to that of the first electroconductive intermediate film 4. In this case, it is easy to make the upper and lower stresses on the piezoelectric film 3 approximately equal. If there is a difference between the upper and lower stresses, the device can become warped.

[0035] (Second Electrode Film 1)

The second electrode film 1 is an electroconductive film and can be made, for example, of platinum (Pt). The second electrode film 1 can have the thickness, for example, in the range of 0.02 μπι to 1.0 μπι.

The second electrode film 1 to be used herein is deposited by sputtering and can also be a metal material such as palladium (Pd), rhodium (Rh), gold (Au), ruthenium (Ru), or iridium (Ir). The thickness of the second electrode film 1 can be in the same range as that of the first electrode film 5.

[0036] (Stress on Film)

In the piezoelectric device 100, the first and second electroconductive intermediate films 4, 2 exert the compressive stress in directions along the surfaces of the piezoelectric film 3 in contact with the respective intermediate films 4, 2. As a result, the coercive electric field of the piezoelectric device 100 can be increased. There are no particular restrictions on the magnitude of the compressive stress on the piezoelectric film 3, but it can be, for example, in the range of 10 to 200 MPa. The increase of coercive electric field expands the range of drive voltage and thus provides a larger displacement.

[0037] (Manufacturing Method)

An example of a manufacturing method of the above-described piezoelectric device will be described below.

The first electrode film 5 is formed on the substrate 7, for example, by sputtering. For example, a Pt film is formed by sputtering on the silicon substrate 7 with the (100) plane orientation heated at about 400°C-500°C, whereby the first electrode film 5 is obtained with high (100) orientation. This Pt film is favorable because it can enhance the orientation of the piezoelectric film 3 to be formed thereon thereafter. The first electrode film 5 may be formed by a method other than the foregoing.

[0038] Next, the first electroconductive intermediate film 4 is formed on the first electrode film 5. The first electroconductive intermediate film 4 can be formed by a method such as sputtering. The first electroconductive intermediate film 4 is preferably deposited at a temperature of not less than the Curie point of the piezoelectric film 3 because it affects the crystallinity of the piezoelectric film 3.

[0039] Next, the piezoelectric film 3 is deposited on the first electroconductive intermediate film 4. The piezoelectric film 3 is deposited by a method such as sputtering under a condition that the substrate 7 is heated at about 400°C-600°C.

[0040] Subsequently, the second electroconductive intermediate film 2 is formed on the piezoelectric film 3. The second electroconductive intermediate film 2 is deposited by a method such as sputtering under a condition that the substrate 7 is heated at about 400°C-600°C.

[0041] After the piezoelectric film 3 and the second electroconductive intermediate film 2 are deposited on the first electroconductive intermediate film 4 under the high temperature higher than room temperature in this manner, the first and second electroconductive intermediate films 2, 4 become more contracting than the piezoelectric film 3 according to the difference between their linear expansion coefficients in a process of returning the piezoelectric device to room temperature, so as to exert large compressive stress on the piezoelectric film 3.

[0042] Thereafter, the second electrode film 1 may be formed on the second electroconductive intermediate film 2 by a method such as sputtering. This completes the piezoelectric device 100.

[0043] Furthermore, the piezoelectric device 100 laid on the substrate 7 is then patterned by photolithography, if necessary, and the substrate 7 is further cut, whereby the piezoelectric device 100 can be obtained, for example, with a movable part in the size of 1 mm χ 2 mm.

[0044] (Second Embodiment)

A piezoelectric device 200 according to the second embodiment will be described with reference to Fig. 4. The piezoelectric device 200 of the present embodiment is different from the piezoelectric device 100 in that the substrate 7 as an underlying structure below the first electrode film 5 is removed. Because of this configuration, the top surface of the second electrode film 1 and the bottom surface of the first electrode film 5 are exposed to the outside. Since there are no restraints on expansion and compression by the substrate 7 in the piezoelectric device 200, the piezoelectric film 3 readily has much greater compressive stress. This enhances the effect of increase in coercive electric field. Since the device becomes lighter in weight by the weight of the substrate 7, the device can have a greater displacement. There are no specific restrictions on the magnitude of the compressive stress on the piezoelectric film 3, but it may be, for example, in the range of 20 to 400 MPa.

[0045] The piezoelectric device 200 of this configuration can be obtained, for example, as follows. First, the films 5-1 are deposited on the substrate 7 in the same manner as in the first embodiment. Next, a support substrate 7' preliminarily provided with a metal film 12 is bonded through a resin film 11 to the second electrode film 1. Then the substrate 7 is removed by etching. Thereafter, the films 5-1, 11, and 12 laid on the support substrate T are patterned in a desired shape, e.g., by photolithography. Finally, the support substrate 7', resin film 11 , and metal film 12 are removed by etching.

[0046] (Third Embodiment)

A piezoelectric device 300 according to the third embodiment will be described with reference to Fig. 5. The piezoelectric device 300 of the present embodiment is different from the piezoelectric device 100 in that the substrate 7 as an underlying structure below the first electrode film 5 is removed and in that a resin film 11 is provided on the second electrode film 1 so as to be in contact with the second electrode film 1. The films 1-5 are supported by the resin film 11 with lower rigidity, instead of the substrate 7 with high rigidity, which reduces stress exerted on the films 1-5 by the substrate 7, so as to allow greater compressive stress to be introduced to the piezoelectric film 3 from the first and second electroconductive intermediate films 2, 4, thereby enhancing the effect of increase in coercive electric field. Furthermore, the piezoelectric film 3 becomes less likely to be hindered from displacement by the substrate 7, which results in achieving more adequate displacement. There are no specific restrictions on the magnitude of the compressive stress on the piezoelectric film 3, but it can be, for example, in the range of 20 to 400 MPa. [0047] The resin film 11 can be made, for example of an epoxy resin, a polyimide resin, or the like. A coating thickness of the resin film can be in the range of about 5 μιη to 15 μπι.

[0048] Furthermore, as shown in Fig. 5, the device may have a metal film 12 on the resin film 11. A material of the metal film 12 can be the same as the material of the second electrode film 1 and can be, for example, a metal material such as Pt, Ni, Pd, In, Rh, or Au. The thickness of the metal film 12 can be in the range of 0.02 μπι to 1.0 μπι.

[0049] The piezoelectric device 300 of this configuration can be obtained as follows. First, the films 5-1 are deposited on the substrate

7 in the same manner as in the first embodiment. Next, the support substrate 7' preliminarily provided with the metal film 12 is bonded through the resin film 11 to the second electrode film 1. Then the substrate 7 is removed by etching. Thereafter, the films 5-1, 11 , and 12 laid on the support substrate T are patterned in a desired shape, e.g., by photolithography. Finally, the support substrate T is removed by etching. The metal film 12 may be left without being removed.

[0050] For example, the piezoelectric device of the present invention is suitably applied to the piezoelectric devices making use of the piezoelectric effect, such as gyro sensors, shock sensors, and microphones, or to the piezoelectric devices making use of the inverse piezoelectric effect, such as actuators, ink jet heads, speakers, buzzers, and resonators, and it is particularly suitably applied to the piezoelectric devices making use of the inverse piezoelectric effect.

[0051] (Head Assembly as Piezoelectric Actuator)

Fig. 7 is a configuration view of a head assembly using the piezoelectric device 200. As illustrated in the view, a head assembly 65 includes, as main components, a base plate 29, a load beam 21, a flexure 27, first and second piezoelectric devices 200 which are driving elements, and a slider 29 having a head element 29a.

[0052] Then, the load beam 21 includes a base end section 21b which is fixed to the base plate 29 by using, for example, beam welding or the like, first and second leaf spring sections 21c and 2 Id which are extended from the base end section 21b in a tapered shape, an opening section 21e which is formed between the first and second leaf spring sections 21c and 2 Id, and a beam main section 21f which is extended straightly and in a tapered shape from the first and second leaf spring sections 21c and 2 Id.

[0053] The first and second piezoelectric devices 200 are disposed having a predetermined clearance between them, on a wiring flexible substrate 25 that is a portion of the flexure 27. The slider 29 is fixed to a front end portion of the flexure 27 and is rotated corresponding to expansion and contraction of the first and second piezoelectric devices 200. The first and the second electrode films of the piezoelectric devices are electrically connected to an outer voltage source respectively. The slider 29 can be moved by providing voltage between the first electrode and second electrode of the piezoelectric devices 200 so as to move the front end portion of the flexure 27. The piezoelectric devices 200 can be replaced by the piezoelectric devices 100 or 300.

[0054](Hard Disk Drive)

Fig. 8 is a configuration view of a hard disk drive on which the head assembly illustrated in Fig. 7 is mounted. A hard disk drive 70 includes a hard disk 61 as a recording medium and a head stack assembly 62 which records and reproduces magnetic information on the hard disk 61 inside a housing 67. The hard disk 61 is rotated by a motor (not illustrated).

[0055] The head stack assembly 62 is configured so that a plurality of assemblies, which are configured by an actuator arm 64 rotatably supported around a support shaft by a voice coil motor 63 and a head assembly 65 connected to the actuator arm 64, are stacked in a depth direction of the view. A head slider 29 is attached to a front end portion of the head assembly 65 so as to face the hard disk 61 (see Fig.

7).

[0056] The head assembly 65 employs a form in which the head element 29a (see Fig. 7) is moved in two steps. A relatively large movement of the head element 29a is controlled by entirely driving the head assembly 65 and the actuator arm 64 by using the voice coil motor

63, and a fine movement thereof is controlled by driving the head slider 29 by using the first and/or second piezoelectric devices 200.

[0057](Ink jet Printer Head as Piezoelectric Actuator)

Fig. 9 is a configuration view of the ink jet printer head as another example of the piezoelectric actuator using the piezoelectric device 100.

[0058] A piezoelectric actuator 80 is configured by stacking the piezoelectric device 100 on a substrate 81. The substrate 81 forms a pressure chamber 83 with a nozzle 84.

[0059] When a predetermined ejection signal is not supplied and a voltage is not applied between the first electrode film 5 and the second electrode film 1, deformation does not occur in the piezoelectric film 3. A pressure change does not occur in the pressure chamber 83 to which the piezoelectric film 3, where the ejection signal is not supplied, is provided. In addition, ink droplets are not ejected from a nozzle 84 thereof.

[0060] Meanwhile, when a predetermined ejection signal is supplied and a constant voltage is applied between the first electrode film 5 and the second electrode film 1, deformation occurs in the piezoelectric film 3. The insulation film (substrate) 7 is largely bent in the pressure chamber 83 to which the piezoelectric film 3, where the ejection signal is supplied, is provided. Thus, a pressure inside the pressure chamber 83 is momentarily increased and then ink droplets are ejected from the nozzle 84. The piezoelectric device 100 can be replaced by the piezoelectric device 200 or 300.

[0061](Ink Jet Printer Apparatus)

Fig. 10 is a configuration view of an ink jet printer apparatus 90 on which the ink jet printer heads 80 illustrated in Fig. 9 are mounted.

[0062] An ink jet printer apparatus 90 is configured to mainly include an ink jet printer heads 80, a body 91, a tray 92 and a head driving mechanism 93.

[0063] The ink jet printer apparatus 90 includes ink cartridges Is, Ic, Im and Iy of total four colors of yellow, magenta, cyan and black, and is configured to allow full-color print with the ink jet printer heads 80. In addition, the ink jet printer apparatus 90 includes a dedicated controller board 97 or the like in the inside thereof and controls ink ejection timing of the ink jet printer heads 80 and scanning of the head driving mechanism 93. In addition, the body 91 includes the tray 92 in a rear surface thereof and an auto sheet feeder (an automatic continuous paper feeding mechanism) 96 in the inside thereof as well. The body 91 automatically delivers a recording paper 95 and discharges the recording paper 95 from an outlet 94 in a front face thereof.

[0064] (a Gyro sensor as Piezoelectric Sensor)

Fig. 11(a) is a configuration view (a plan view) of a gyro sensor as an example of the piezoelectric sensor using the piezoelectric device 200 and Fig. 11(b) is a cross-sectional view which is taken along a line A-A in Fig. 11(a).

[0065] A gyro sensor 35 is a tuning fork vibrator type angular velocity detecting element including a base section 32, two arms 33 and 34 connected to one surface of the base section 32. The gyro sensor 35 is obtained by micromachining the piezoelectric device 200 having the first electrode film 5, the first electroconductive intermediate film 4, the piezoelectric film 3, the second electroconductive intermediate film 2, and the second electrode film 1 conforming to a shape of the tuning fork type vibrator.

[0066] A first main surface of one arm 33 has driving electrode film la and lb, and a detection electrode film Id. Similarly, a first main surface of the other arm 34 has the driving electrode films la and lb, and a detection electrode film lc. Each of the electrode films la, lb, lc and Id is obtained by etching the second electrode film 1 into a predetermined electrode shape.

[0067] In addition, the first electrode film 5 formed all over each of second main surfaces (a main surface on a rear side of the first main surface) of the base section 32 and the arms 33 and 34 functions as a ground electrode of the gyro sensor 35.

[0068] Herein, an XYZ orthogonal coordinate system is defined in which a longitudinal direction of each of the arms 33 and 34 is taken as a Z direction and a plane containing the main surfaces of the two arms

33 and 34 is taken as an XZ plane.

[0069] When a driving signal is supplied to the driving electrode films la and lb, the two arms 33 and 34 are excited in an in-plane vibration mode. The in-plane vibration mode refers to a vibration mode in which the two arms 33 and 34 are excited in a direction parallel to the main surfaces of the two arms 33 and 34. For example, when one arm 33 is excited at a velocity VI in a -X direction, the other arm 34 is excited at a velocity V2 in a +X direction.

[0070] In this state, when a rotation of angular velocity ω is applied to the gyro sensor 35 about a Z axis as a rotational axis, Coriolis forces are acted on each of the two arms 33 and 34 in directions orthogonal to velocity directions and the two arms 33 and 34 begin to be excited in an out-of-plane vibration mode. The out-of-plane vibration mode refers to a vibration mode in which the two arms 33 and 34 are excited in a direction orthogonal to the main surfaces of the two arms 33 and 34.

For example, when Coriolis force Fl acted on one arm 33 is in a -Y direction, Coriolis force F2 acted on the other arm 34 is in a +Y direction.

[0071] Since magnitudes of the Coriolis forces Fl and F2 are proportional to the angular velocity ω, mechanical distortions of the arms 33 and 34 by the Coriolis forces Fl and F2 are converted into electrical signals (detection signals) by using the piezoelectric film 3 and the electrical signals are taken out from the detection electrode films lc and Id and then the angular velocity ω can be obtained. The piezoelectric device 200 can be replaced by the piezoelectric device 100 or 300.

[0072] (Pressure Sensor as Piezoelectric Sensor)

Fig. 12 is a configuration view of a pressure sensor as a second example of the piezoelectric sensor using the piezoelectric device 200 described above.

[0073] A pressure sensor 40 has a support body 44 supporting a piezoelectric device 200 and having a cavity 45 to receive a pressure. The electrode films 1 and 5 of the pressure sensor 40 are connected to a current amplifier 46 and a voltage measuring device 47. Herein, when an external force is applied to the support body 44, the piezoelectric device 200 is bent and a voltage is detected in the voltage measuring device 47. The piezoelectric device 200 can be replaced by the piezoelectric device 100 or 300.

[0074](Pulse Wave Sensor as Piezoelectric Sensor)

Fig. 13 is a configuration view of a pulse wave sensor as a third example of the piezoelectric sensor using the piezoelectric device 200.

A pulse wave sensor 50 has a configuration in which a transmission piezoelectric device Tr and a receiving piezoelectric device Re are mounted on a substrate 51. In this example, the piezoelectric devices 200 are used as the transmission Tr and receiving piezoelectric devices Re. Electrodes 56 and an upper surface electrode 57 are formed on the substrate 51. Each of the electrode film 1 and the upper surface electrode 57 are electrically connected to each other via wiring 58. Each of the electrodes 5 and the electrodes 56 are electrically connected to each other.

[0075] In order to detect pulses of a living body, first, a rear surface (a surface on which the piezoelectric device is not mounted) of the substrate of the pulse wave sensor 50 comes into contact with the living body. Then, when the pulse is detected, a specific driving voltage signal is output to both electrode films 1 and 5 of the transmission piezoelectric device Tr. The transmission piezoelectric device Tr is excited and generates ultrasonic wave in response to the driving voltage signal which is input into the both electrode films 1 and 5, and transmits the ultrasonic waves inside the living body. The ultrasonic wave transmitted into the living body is reflected by blood flow and received by the receiving piezoelectric device Re. The receiving piezoelectric device Tr converts the received ultrasonic wave into a voltage signal and outputs the voltage signal from the both electrode films 1 and 5. The piezoelectric device 200 can be replaced by the piezoelectric device 100 or 300.

[0076] The piezoelectric actuators, hard disk drives, ink jet printer apparatuses, and piezoelectric sensors of the present invention can have improved deformation characteristics.

Examples

[0077] The present invention will be described below in more detail on the basis of examples and a comparative example, but it should be noted that the present invention is by no means limited to the examples below.

[0078] (Example 1) The piezoelectric device 100 of Example 1 according to the first embodiment of the present invention as shown in Fig. 3 was manufactured through the steps as described below.

[0079] The silicon substrate 7 with the (100) plane orientation was heated at 400°C and a 200nm Pt film was formed as the first electrode film 5 on the silicon substrate 7 by sputtering. Then the silicon substrate 7 was heated to 550°C and a 15nm SrRu0 ₃ film was formed as the electroconductive intermediate film 4 on the Pt film by sputtering. Next, while the silicon substrate 7 was kept heated at 550°C, a 2000nm potassium sodium niobate (KNN) film was formed as the piezoelectric film 3 on the SrRu0 ₃ film by sputtering. Subsequently, a 15nm BaRu0 ₃ film was formed as the electroconductive intermediate film 2 on the potassium sodium niobate film by sputtering. Next, at room temperature a 200nm Pt film was formed as the second electrode film 1 on the BaRu0 ₃ film by sputtering.

Thereafter, the laminated films on the silicon substrate 7 were patterned by photolithography and singulation was further performed to manufacture the piezoelectric device 100 with the size of movable part of 1 mm x 2 mm.

[0080] Besides the above, potassium sodium niobate (KNN), SrRu0 ₃ ,

BaRu0 ₃ , and Pt films were individually formed under the same conditions as above, on the silicon substrate 7, and the linear expansion coefficients of the respective films were measured by the X-ray reflectivity technique. The resistivity (specific resistance) was also measured for each of the electroconductive intermediate films. The measurement results are provided below. KNN: 8.0 1ο- ⁶ 1/K

SrRu0 ₃ : 10.3 ^χ 10 ^"6 1/K, 5.0 ^χ 10 ^"5 Ωαη

BaRu0 ₃ : 9.8x 10 ^"6 1 K, 8.0 10 ^-5 ΩΟΓΠ

Pt: 8.8x l0 ^-6 1 K

Furthermore, the linear expansion coefficient of the silicon substrate 7 is the value below.

[0081] (Examples 2 to 14)

The piezoelectric devices 100 of Examples 2 to 14 were obtained in the same manner as in Example 1, except that the devices

100 were manufactured using the piezoelectric film 3 and the electroconductive intermediate films 2, 4 made of the materials provided in Tables 2 and 3. The results of measurement of the linear expansion coefficients and resistivities of the respective materials are also provided in Tables 1 to 3.

[0082] (Examples 15 and 16)

The piezoelectric devices 200 of Examples 15 and 16 according to the second embodiment of the present invention as shown in Fig. 4 were manufactured through the steps as described below.

[0083] The films 5-1 were deposited on the silicon substrate 7 by sputtering in the same manner as in Example 1. Thereafter, the support substrate 7' having the metal film 12 was bonded through the resin film 11 of epoxy resin to the second electrode film 1. Then the silicon substrate 7 was removed by an etching process of RIE. The laminated films on the support substrate 7' were patterned by photolithography to obtain the piezoelectric device part with the size of movable part of 1 mm χ 2 mm, and the support substrate 7', resin film 11, and metal film 12 were removed to obtain the rectangular piezoelectric device 200.

[0084] (Comparative Example 1)

A piezoelectric device 400 of Comparative Example 1 was obtained in the same manner as in Example 1, except that the device was constructed without the electroconductive intermediate films 2 and 4 (cf. Fig. 6).

[0085] (Evaluation)

The coercive electric fields were obtained by measuring P-E hysteresis curves by a ferroelectric evaluation system TF-1000 available from Aixacct. Displacements and coercive electric fields with application of voltage to the respective piezoelectric devices were measured using a laser Doppler vibrometer (available from GRAPHTEC corporation).

[0086] The coercive electric fields Ec and Vc were obtained from the P-E hysteresis curves measured by connecting the first electrode film to the positive electrode and the second electrode film to the negative electrode and applying a triangular wave of ±27 kV/cm with the frequency of 120 Hz. Values of displacements were measured similarly by connecting the first electrode film to the positive electrode and the second electrode film to the negative electrode and applying a voltage of a sine wave (±10 V) with the frequency of 120 Hz. The results of these are provided in Table 4.

[0087] It was confirmed that the coercive electric fields Ec+, Vc+ and the coercive electric fields Ec-, Vc- of the piezoelectric devices of Examples 1 to 16 with the first nonmetal electroconductive intermediate film having the linear expansion coefficient larger than those of the first electrode film and the piezoelectric film and with the second nonmetal electroconductive intermediate film having the linear expansion coefficient larger than those of the second electrode film and the piezoelectric film were larger than the coercive electric fields Ec+, Vc+ and the coercive electric fields Ec-, Vc- of Comparative Example 1 without the first and second nonmetal electroconductive intermediate films.

Table 1

Ex: Example; C Ex: Comparative Example; LEC: linear expansion coefficient; T: thickness

Table 2

Ex: Example; C Ex: Comparative Example; LEC: linear expansion coefficient; T: thickness

Table 3

Ex: Example; C Ex: Comparative Example; LEC: linear expansion coefficient; T: thickness

Table 4

Ex: Example; C Ex: Comparative Example; CEF: coercive electric field; D: displacement