WO2000076007A1 - Sheet-shaped piezoelectric device, method for making same, and piezoelectric vibrator and piezoelectric sound generator using same - Google Patents

Sheet-shaped piezoelectric device, method for making same, and piezoelectric vibrator and piezoelectric sound generator using same Download PDF

Info

Publication number
WO2000076007A1
WO2000076007A1 PCT/JP2000/003686 JP0003686W WO0076007A1 WO 2000076007 A1 WO2000076007 A1 WO 2000076007A1 JP 0003686 W JP0003686 W JP 0003686W WO 0076007 A1 WO0076007 A1 WO 0076007A1
Authority
WO
WIPO (PCT)
Prior art keywords
sheet
piezoelectric
electrode
over
deposition
Prior art date
Application number
PCT/JP2000/003686
Other languages
French (fr)
Inventor
Atsushi Omote
Jun Kuwata
Futoshi Takeshi
Original Assignee
Matsushita Electric Industrial Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Matsushita Electric Industrial Co., Ltd. filed Critical Matsushita Electric Industrial Co., Ltd.
Priority to AU52454/00A priority Critical patent/AU5245400A/en
Publication of WO2000076007A1 publication Critical patent/WO2000076007A1/en

Links

Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/853—Ceramic compositions
    • H10N30/8548—Lead based oxides
    • H10N30/8554—Lead zirconium titanate based
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/06—Forming electrodes or interconnections, e.g. leads or terminals
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/09—Forming piezoelectric or electrostrictive materials
    • H10N30/093—Forming inorganic materials
    • H10N30/097—Forming inorganic materials by sintering
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/85—Piezoelectric or electrostrictive active materials
    • H10N30/853—Ceramic compositions
    • H10N30/8548—Lead based oxides
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/80—Constructional details
    • H10N30/87—Electrodes or interconnections, e.g. leads or terminals
    • H10N30/877—Conductive materials

Definitions

  • This invention relates to a sheet-shaped piezoelectric device, and more particularly, to an improved sheet-shaped piezoelectric device which is in the form of a thin sheet and is adapted for use as a sound generating source such as of a portable telephone, a computer and the like, or also as a piezoelectric vibrator.
  • the invention also relates to a method for making such an improved piezoelectric device.
  • the invention further relates to a sound generator and a piezoelectric vibrator comprising the piezoelectric device.
  • the baked silver electrode of a silver paste which has been employed in a conventional piezoelectric device, adversely influences the device characteristics.
  • the baked electrode contains a glass component whose dielectric constant is 10 or below.
  • the piezoelectric device is shaped in the form of 200 ⁇ m or below, the influence of the low dielectric constant of the glass component in the electrode is not negligible.
  • high- piezoelectric materials have a dielectric constant as high as 4000 or over, and thus, suffer the influence of the glass component in the electrode to a greater extent than known counterparts. It has now been confirmed that when the dielectric constant inherent to a piezoelectric material is compared with that determined after formation as a piezoelectric device, the dielectric constant is lowered by 10% or over.
  • the metal electrode formed by sputtering or vacuum deposition In this case, the bonding force of the metal electrode is very low in comparison with that of the silver electrode. Hence, the metal electrode has never been applied to the device in view of its reliability when taking into account the bonding strength as experienced in a thermal shock test and a drop test.
  • a sheet-shaped piezoelectric device which comprises a sheet of a ferroelectric composite oxide having piezoelectric properties and a dielectric constant of 4000 or over, and a pair of electrodes directly formed on opposite sides of the sheet, each electrode being made of a metal and being free of a glass component.
  • the electrode has a double-layered structure including an underlying layer, which is in contact with the sheet and contains at least one of chromium, titanium and nickel, and an upper layer made of Ag, Au, Cu or the like.
  • a method for making a sheet-shaped piezoelectric device comprises a pair of electrodes and a sheet of a piezoelectric material composition comprising a ferroelectric composite oxide having a dielectric constant of 4000 or over and provided between the pair of electrodes, the method comprising providing the sheet, and forming a pair of electrodes made of a metal on opposite sides of the sheet wherein the pair of electrodes are free of a glass component.
  • the formation of the paired electrodes is preferably carried out by sputtering, vacuum deposition or CVD method.
  • the underlying layer is first deposited on opposite sides of the sheet, followed by further deposition of the upper layer.
  • the piezoelectric device is appropriately used as a sheet-shaped piezoelectric vibrator when attached to a vibration sheet. Moreover, when the piezoelectric vibrator is placed in a resonance box having an opening at one side thereof, from which a sound is emitted, in a state wherein the vibration sheet is able to be vibrated in correspondence with the movement of the piezoelectric device.
  • Fig. la is a sectional view showing a sheet-shaped piezoelectric device according to the invention
  • Fig. lb is a sectional view showing a double-layered structure of an electrode of the device;
  • Figs. 2a is a sectional view illustrating a piezoelectric sound generator and Fig. 2b is a schematic perspective view showing a resonance box of the sound generator.
  • Fig. la there is shown a thin sheet-shaped piezoelectric device D.
  • the device D includes a piezoelectric element 1 in the form of a layer and a pair of electrodes 2, 3 formed on opposite sides of the element 1 as shown.
  • the piezoelectric element 1 should have a dielectric constant of 4000 or over.
  • the dielectric constant is determined in the following manner.
  • the device D is subjected to measurement of a capacitance C by use of an impedance analyzer, and the dielectric constant is calculated according to the following equation.
  • the piezoelectric element 1 is made of a ferroelectric composite oxide including, for example, xPbTiO 3 -yPbZrO 3 -(l-x-y)Pb(Mg 1 /3 Nb 2/3 )O 3 wherein x and y are, respectively, defined hereinlater. This material is described, for example, in Journal of American Ceramic Society, Vol . 48, No. 12 , pp .
  • the element 1 should have a dielectric constant of 4000 or over, for which x and y in the above formula are, respectively, range from 0.3 to 0.5 and 0. 1 to 0.3 although these values may vary depending on the manner of preparation of the composite oxide.
  • the values of x and y are optimally in the ranges of 0.35 to 0.45 and 0.1 to 0.2 , respectively, within which both x and y are mutually changed to provide an optimum combination of x and y.
  • the element 1 is not limited to the composite oxide set out above, and any piezoelectric materials exhibiting the above- defined piezoelectric constant may also be used without limitation.
  • piezoelectric materials include composite oxides such as xPbTiO 3 -yPbZr ⁇ 3 -Pb(Ni 1/3 Nb 2/3 ) ⁇ 3 , xPbTiO 3 -yPbZrO 3 - Pb(Zn 1/2 Nb 1/2 )O 3 , and the like wherein x and y are , respectively, as defined above. These compounds also have a dielectric constant as defined above.
  • the element 2 in the form of a thin layer should have a thickness of 30 ⁇ m or below, preferably from 0.1 to 10 ⁇ m, and may have any desired form such as a disc, a square or the like.
  • the piezoelectric device D of the invention also has a pair of electrodes, each of which is made of a metal which is fully free of any glass component therein. Examples of such a metal include silver, gold, copper and the like, of which silver is preferred because gold is more expensive and copper is more likely to corrode.
  • the metal electrode, which is free of any glass component therein, can be formed, for example, by a sputtering, vacuum deposition or CVD technique.
  • Each electrode generally has a thickness of 0.1 to 20 ⁇ m, preferably 0.1 to lO ⁇ m.
  • the thickness of the electrode should preferably be at 1/5 or below of the thickness of the piezoelectric element 1.
  • the total thickness of the piezoelectric device of the invention is 200 ⁇ m or below, within which the thicknesses of the piezoelectric element 1 and the electrodes are preferably determined, respectively.
  • the electrodes 2, 3 stated above have a single layer structure, respectively.
  • Each electrode may have a multi-layered structure, particularly, a double-layered structure as shown in Fig. lb .
  • the double-layered structure of the electrode 2 has a lower or underlying layer 2b in contact with the dielectric material layer 1 and an upper layer 2a formed on the underlying layer 2b when illustrated only for the electrode 2. This is true of the electrode 3.
  • the upper layer 2a is preferably made of silver for the reason set out above although other metals, such as Au, Cu or the like, may also be used.
  • the upper layer should preferably have a thickness of 0.1 to 20 ⁇ m.
  • the thickness of the lower layer is usually 100 nm or below.
  • the lower layer 2b is made of a metal that is more likely to be bonded to the piezoelectric material layer 1 than silver. More particularly, the metal for the lower layer 2b should have better affinity for the piezoelectric element 1 than silver. Examples of such a metal include chromium, nickel, titanium, or the like.
  • the electrodes 2, 3 have such a double-layered structure as mentioned above, they are significantly improved in the property of bonding to the piezoelectric element 1. Thus, the device is eventually more improved in reliability when undergoing an abrupt temperature change.
  • starting metal oxides such as PbO , TiO 2 , ZrO 2 , MgO, Nb 2 O 5
  • PbO , TiO 2 , ZrO 2 , MgO, Nb 2 O 5 are, respectively, provided in the form of particles having a size, for example, of 0.1 to 2 ⁇ m and weighed to make predetermined mixing ratios by weight.
  • These powders lare mixed, for example, in a ball mill and calcined under conditions of a temperature of 800 to 900°C for 2 to 10 hours. The thus calcined product was broken into pieces having a size of 0.1 to 2.
  • the mixing ratios should be so determined that a finally sintered product has a dielectric constant of 4000 or over in the vicinity of the triple point discussed before.
  • the pieces are mixed with a binder resin and a dispersant in a solvent and mixed, for example, in a ball mill or the like milling means.
  • binder resin used for this purpose include polyvinyl butyral, polyvinyl alcohol and the like.
  • the binder resin is usually present in an amount of 5 to 10 wt% based on the piezoelectric pieces.
  • dispersant include ordinarily employed ones such as dibutyl phthalate .
  • the dispersant is generally used in an amount of 30 to 50 wt% based on the piezoelectric pieces.
  • the solvent for the binder resin may be ones which are ordinarily employed for this purpose, and include, for example, ethyl acetate, butyl acetate, ethyl cellosolve (ethylene glycol monoethyl ether) , butyl cellosolve (ethylene glycol monobutyl ether) , and mixtures thereof.
  • the solvent is used in an appropriate amount permitting the mixture to be milled without difficulty.
  • the mixture is milled for 24 to 120 hours to make a uniform slip .
  • the slip is sub sequently applied onto an appropriate sub strate, such as a glass plate, in a dry thickness of 200 ⁇ m or below by any known coating technique such as doctor blade coating, and dried to obtain a green sheet.
  • the green sheet is punched into a desired form such as a square, a disk or the like form.
  • the thus punched sheet is sintered under conditions of a temperature of 1100 to 1300 °C for a time of 30 minutes or over, preferably 60 to 120 minutes, thereby providing a sintered piezoelectric element made of an intended piezoelectric material.
  • This element is subsequently deposited directly with a metal by a sputtering, vacuum deposition or CVD technique as is well known in the art, thereby forming a metal electrode on opposite sides of the element.
  • the metal is preferably silver.
  • the sputtering, vacuum deposition or CVD technique of a metal is well known in the art and is not described in detail. In this way , the single-layered metal electrode is formed or deposited directly on opposite sides of the piezoelectric element in the thickness defined before.
  • the electrode is formed while heating the piezoelectric element at a temperature not lower than 200°C, preferably from 200 to 300°C.
  • a temperature not lower than 200°C preferably from 200 to 300°C.
  • the piezoelectric device is thermally treated immediately after the formation of the electrode on opposite sides of the element. More particularly, the piezoelectric device is thermally treated at a temperature of 200°C or over, preferably 200 to 300°C for a time of at least 30 minutes in air. This thermal treatment is effective in improving the bonding strength between each electrode and the piezoelectric element.
  • the bonding strength is further improved than in the case where the thermal treatment is effected in air.
  • the device reliability is further improved as well.
  • an underlying layer When silver is used as an electrode material, it is preferred to form an underlying layer in order to improve the bonding strength between the electrode and the piezoelectric element.
  • a metal such as chromium, titanium or nickel is first deposited on the piezoelectric element on opposite sides thereof by a sputtering, vacuum dep osition or CVD technique in a thickness of 100 nm or below. Thereafter, silver is likewise deposited on the underlying layer in a manner as stated hereinbefore . In this case, the silver layer is formed in a thickness of 0.1 to 20 ⁇ m.
  • the underlying layer is formed while heating the piezoelectric element under such conditions as defined before .
  • the heating of the device after the formation of the electrodes having a double-layered structure under such conditions as defined before is also effective in the improvement.
  • the piezoelectric device made in this manner is thin and has such a high dielectric constant of 4000 or over because of the use of a metal electrode.
  • the bonding strength between the metal electrode and the piezoelectric element is improved, so that the piezoelectric element and device are improved in reliability when exp osed to an abrupt change of temperature.
  • the device of the invention has wide utility in various fields of a piezoelectric vibrator, a sound generator using the vibrator, and electronic parts, which are required to be scaled down and be made thin. For instance, a device for acceleration detection or for ceramic filter makes use of plural piezoelectric devices being built up .
  • the thin sheet- shaped piezoelectric device of the invention can be appropriately applied to the fabrication of such a device mentioned above.
  • a sound generator S including a piezoelectric vibrator V.
  • the vibrator V including the piezoelectric device D and a vibrating sheet or member 4 bonded to the device D at one side thereof through a bonding agent 5 such as an optically or thermally curable resin, e. g. an acrylic resin, an epoxy resin or the like.
  • the vibrating member 4 is made of a metal or alloy such as Fe/Ni, Al, brass or the like.
  • the member 4 is as thin as 20 to 100 ⁇ m.
  • the vibrating member 4 is vibrated in a horizontal direction when an appropriate AC voltage of about 1 V is applied to the electrodes 2, 3 of the device D from a power source (not shown) through leads (not shown) attached to the electrodes 2, 3, respectively.
  • the vibrating member is arranged to extend from the device D at opposite sides thereof so that when the vibrator V is set in position of a sound generator S, the vibrator V is fixed, for example, by means of a silicone bonding agent at the peripheral extended ends thereof as shown in Fig. 2a.
  • the sound generator S includes a resonance box 6 having an opening 7 at one side of the resonance box 6 as shown in Figs. 2a and 2b .
  • the arrangement of such a sound generator S is known in the art, and the use of the piezoelectric device of the invention ensures a prolonged life of the piezoelectric vibrator V and the piezoelectric sound generator S and results in improved reliability of these devices when undergoing an abrupt change of temperature.
  • Material B A green sheet was obtained in the same manner as set forth above using the composite oxide for comparison.
  • the green sheets made of Materials A and B were, respectively, punched so that a thin sheet-shaped disk element having a diameter of 10 mm and a thickness of 70 ⁇ m after sintering at a temperature of 1250°C for 2 hours.
  • a baked silver electrode of a silver paste (Shouei Chem. Co. , Ltd.) was applied onto opposite sides of each disk element and baked at 650°C for 10 minutes in a thickness of 2 ⁇ m after baking.
  • Kp indicates an electromechanical coupling coefficient
  • ⁇ indicates a dielectric constant
  • the device including the sputtered silver electrodes is better in the piezoelectric constants than that including the baked silver electrodes. This constants are much better when using Material A having a dielectric constant of 4000.
  • cap acitance C of the device using sputtered silver electrodes is expressed according to the following equation
  • ⁇ A is a dielectric constant of a piezoelectric material
  • S is the total area of the electrodes
  • d is a distance between the electrodes
  • ⁇ 0 is a dielectric constant of vacuum
  • the above devices were used to make piezoelectric vibrators by bonding a 70 ⁇ m thick vibrating member made of Fe/Ni to one side of each device. Each vibrator was set in a resonance box as is particularly shown in Fig. 2a to obtain a piezoelectric sound generator.
  • the thus obtained sound generators were compared with one another with respect to the sound pressure characteristic, revealing that with Material A, the device using the sputtered silver electrodes was improved in sound pressure by 5 dB or over at 100 Hz than the device using the baked silver electrodes when 1 V was inputted thereto.
  • the sound pressure was measured by the method described in "RC 8104" of the standards of Electronic Industries Association of Japan (EIAJ) .
  • the electrodes were formed by sputtering, and similar results were obtained when using vacuum deposition and a CVD technique.
  • Example 2
  • the green sheet of Material A made in Example 1 was used, from which a number of disk elements of a sheet thickness of 40 ⁇ m and a diameter of 10 mm were punched and sintered. Sputtered silver electrodes having different thicknesses of 100 nm to 15 ⁇ m were deposited on the disk elements to make piezoelectric devices, respectively. These devices were poled and evaluated with respect to the dielectric constant and Kp. The results are shown in Table 2 below. Table 2
  • the electromechanical coupling coefficient Kp along the radial direction depends on the electrode thickness.
  • the electrode thickness is changed, the piezoelectric constant is changed, and when the electrode thickness exceeds a certain level, the characteristic properties are lowered.
  • the electrode thickness is at 40 ⁇ m and the electrode thickness is at 8 ⁇ m or over, the influence of the electrode is not negligible, resulting in the lowering of the piezoelectric characteristic. More particularly, good piezoelectric characteristics were obtained when the electrode thickness was at 1/5 or below of the thickness of the piezoelectric layer.
  • the electrodes were formed by sputtering, and similar results were obtained when using a vacuum deposition or CVD technique .
  • a thin sheet- shaped piezoelectric device was made in the same manner as in Example 2. Prior to the poling and evaluation, the device was thermally treated at 300°C for 30 minutes. After the thermal treatment, the device was poled, to which a vibrating member was bonded. The resultant piezoelectric vibrator was set in a resonance box as shown in Fig. 2a to make a piezoelectric sound generator. Like the thermally treated device, a non-treated device was use d to make a sound generator. The thermally treated and non-treated devices were, respectively, subj ected to measurement of a sound pressure at 1 kHz prior to and after a thermal shock test.
  • the thermal shock test was conducted in the following manner: the device was subj ected to 100 thermal shock cycles, each cycle including cooling down to — 40°C, standing at the temperature for 30 minutes, heating to 85°C in 10 minutes, standing at the temperature for 30 minutes, and again cooling down to -40°C in 10 minutes.
  • the results of five measurements are shown in Table 3 below.
  • the electrodes were formed by sputtering, and similar results were obtained when using a vacuum deposition of CVD method.
  • Material A was used and sintered to make piezoelectric disk elements in the same manner as in Example 2. Subsequently, different types of electrodes, one being a 1 ⁇ m thick silver electrode and the other being an electrode, which had a built-up structure including a 30 nm chromium underlying layer and a 900 nm thick silver upper layer, were, respectively, formed on opposite sides of each disk element by sputtering.
  • Each piezoelectric device was poled, after which a vibrating member was bonded to the device at one side thereof by use of an epoxy resin bonding agent and cured to obtain a piezoelectric vibrator. This vibrator was set in a resonance box to provide a piezoelectric sound generator. The generator was subjected to the thermal shock test in the same manner as in Example 3. The results of a sound pressure at 1 kHz prior to and after the thermal shock test are shown in Table 4 below. Table 4
  • electrodes having different chromium film thicknesses were formed so that the thickness of one electrode having the double-layered structure was set at 1 ⁇ m, from which it was found that when the chromium electrode film had a thickness of 100 nm or over, the value of Kp became worsened.
  • the reason for this is considered as follows: chromium has an elastic constant larger than silver and is harder, so that when a thick chromium film is formed, the vibrations of the resultant piezoelectric device are impeded.
  • the film thickness of the chromium underlying layer should be 100 nm or below in order to obtain good device characteristics .
  • Example 5 Material A was used to make piezoelectric disk elements in the same manner as in Example 2. Thereafter, a 1 ⁇ m thick silver electrode was formed on opposite sides of each disk element by vacuum deposition. When the electrodes were formed, the disk element was heated at 250°C . The resultant thin sheet- shaped piezoelectric devices were polarized and each attached with a vibrating member to provide a piezoelectric vibrator. The vibrator was placed in a resonance box to obtain a piezoelectric sound generator. The generators obtained in this way were subjected to a thermal shock test in the same manner as set out hereinbefore, along with the generator wherein the disk element was not heated when the electrodes were formed.
  • the green sheet containing the above composite oxide was punched so that a thin sheet-shaped disk element having a diameter of 10 mm and a thickness of 50 ⁇ m after sintering at a temperature of 1250°C for 2 hours.
  • These devices were each bonded to a vibrating sheet having a thickness of 70 ⁇ m and made of Fe/Ni by means of an epoxy resin bonding agent.
  • the resultant piezoelectric vibrator was placed in a resonance box having an opening in a manner as is particularly shown in Fig. 2a, thereby making a piezoelectric sound generator.
  • the vibrator was fixed at the opposite sides thereof to the box wall by means of a silicone resin bonding agent.
  • the initial sound pressure of the piezoelectric sound generator was measured. Thereafter, the generator was subjected to a thermal shock test in the same manner as in Example 1 , followed by measurement of a sound pressure by applying an AC voltage of IV to the paired electrodes at 1 kHz after the test.
  • a thin sheet-shaped piezoelectric device was made in the same manner as set forth above, and was subsequently thermally treated in air under conditions of 300°C and 0.5 hours prior to polarization. After completion of the thermal treatment, the device was poled.
  • a piezoelectric vibrator was made using the device in the same manner as stated above, and was used to make a piezoelectric sound generator. This generator was subjected to a reliability test according to the thermal shock test in the same manner as described before. Further, a thin sheet- shaped piezoelectric device was likewise made and subsequently thermally treated in an atmosphere of nitrogen under conditions of 300°C and 0.5 hours.
  • the device After completion of the thermal treatment, the device was poled. Thereafter, a piezoelectric vibrator was made using the device in the same manner as stated above, and was used to make a piezoelectric sound generator in a like manner. This generator was subjected to a reliability test according to the thermal shock test in the same manner as set out above.
  • the piezoelectric sound generator using the electrodes whose color was changed by oxidation tends to undergo characteristic degradation after the thermal shock test.
  • the analyses of the degraded sound generator reveal that the degradation is ascribed to the partial separation between the piezoelectric device D and the vibrating member 24 in Fig. 2a, not to the degradation of the piezoelectric characteristic of the device. More particularly, the oxidized metal electrode 22 in contact with the vibrating member 24 via a bonding layer becomes poor in bonding strength. Thus, partial separation took place between the oxidized metal electrode and the vibrating member when subjected to the thermal shock test.
  • the electrodes were formed by sputtering, and similar results were obtained using a vacuum deposition or CVD method.

Abstract

A sheet-shaped piezoelectric device comprises a sheet of a ferroelectric composite oxide having piezoelectric properties and a dielectric constant of 4000 or over, and a pair of electrodes directly formed on opposite sides of the sheet. Each electrode is made of a metal and is free of a glass component. A method for making such a device is also described along with a piezoelectric vibrator and a piezoelectric sound generator.

Description

DESCRIPTION
SHEET-SHAPED PIEZOELECTRIC DEVICE, METHOD FOR
MAKING SAME, AND PIEZOELECTRIC VIBRATOR AND
PIEZOELECTRIC SOUND GENERATOR USING SAME
BACKGROUND OF THE INVENTION Field of The Invention This invention relates to a sheet-shaped piezoelectric device, and more particularly, to an improved sheet-shaped piezoelectric device which is in the form of a thin sheet and is adapted for use as a sound generating source such as of a portable telephone, a computer and the like, or also as a piezoelectric vibrator. The invention also relates to a method for making such an improved piezoelectric device. The invention further relates to a sound generator and a piezoelectric vibrator comprising the piezoelectric device.
Description of the Prior Art In recent years, attention has been paid to piezoelectric speakers, receivers or microphones using piezoelectric materials because of the discovery of new merits in the field of portable telephones, computes and voice inputting and outputting devices. Especially, there is a great demand for a piezoelectric vibrator, which is made small in size and is highly sensitized for portable purposes. To this end, it is required that the piezoelectric vibrator have 1) good piezoelectric characteristics and 2) high reliability. To meet the requirements, a great number of studies have been made on novel materials, which are based on ceramics of ferroelectric oxides having a perovskite structure, and also on improvements by addition of additives thereto. For the purpose of increasing the displacement of a piezoelectric device, an attempt has been made to shorten the distance between the electrodes, between which a piezoelectric material is sandwiched. More particularly, there has been developed a technique of improving the performance of the device by forming a piezoelectric material in a thin layer. For instance, developments have been made including a method of sintering a sheet-shaped device having a thickness of 100 μm or below and a method of controlling the grain size of the piezoelectric material used to make a sheet-shaped device.
In case where the above-mentioned development of a high piezoelectric material is compatible with the formation of the device in a thin sheet, the baked silver electrode of a silver paste, which has been employed in a conventional piezoelectric device, adversely influences the device characteristics. The baked electrode contains a glass component whose dielectric constant is 10 or below. When the piezoelectric device is shaped in the form of 200 μm or below, the influence of the low dielectric constant of the glass component in the electrode is not negligible. Moreover, recently developed, high- piezoelectric materials have a dielectric constant as high as 4000 or over, and thus, suffer the influence of the glass component in the electrode to a greater extent than known counterparts. It has now been confirmed that when the dielectric constant inherent to a piezoelectric material is compared with that determined after formation as a piezoelectric device, the dielectric constant is lowered by 10% or over.
For the assessment of piezoelectric characteristics of a piezoelectric material, there has been sometimes used the metal electrode formed by sputtering or vacuum deposition. In this case, the bonding force of the metal electrode is very low in comparison with that of the silver electrode. Hence, the metal electrode has never been applied to the device in view of its reliability when taking into account the bonding strength as experienced in a thermal shock test and a drop test.
In the studies of improving the characteristics of a piezoelectric device and making a thin piezoelectric material sheet for the purpose of the scale-down and high sensitization of the device, the demand for both high sensitization and high reliability of the piezoelectric device has not been met at present.
The improvement in piezoelectric characteristic of articles comprising a piezoelectric device has been strongly demanded, for which the performance of piezoelectric material has to be brought out to a satisfactory extent. Moreover, there is also a demand not only for the characteristic improvement, but also for high reliability equal to or better than in conventional ones.
SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a sheet- shaped piezoelectric device, which comprises metal electrodes whereby the characteristic properties of a piezoelectric material can be brought out to a substantially full extent.
It is another object of the invention to provide a method for making a sheet-shaped piezoelectric device which solves the problem on the reliability of the device as will be otherwise encountered due to the shortage in bonding force of the electrode.
It is a further obj ect of the invention to provide a sound generator or piezoelectric vibrator comprising the sheet-shaped piezoelectric device of the type mentioned above.
According to one embodiment of the invention, there is provided a sheet-shaped piezoelectric device which comprises a sheet of a ferroelectric composite oxide having piezoelectric properties and a dielectric constant of 4000 or over, and a pair of electrodes directly formed on opposite sides of the sheet, each electrode being made of a metal and being free of a glass component.
Preferably, the electrode has a double-layered structure including an underlying layer, which is in contact with the sheet and contains at least one of chromium, titanium and nickel, and an upper layer made of Ag, Au, Cu or the like.
According to another embodiment of the invention, there is also provided a method for making a sheet-shaped piezoelectric device comprises a pair of electrodes and a sheet of a piezoelectric material composition comprising a ferroelectric composite oxide having a dielectric constant of 4000 or over and provided between the pair of electrodes, the method comprising providing the sheet, and forming a pair of electrodes made of a metal on opposite sides of the sheet wherein the pair of electrodes are free of a glass component. The formation of the paired electrodes is preferably carried out by sputtering, vacuum deposition or CVD method.
When individual electrodes have such a double-layered structure as mentioned above, the underlying layer is first deposited on opposite sides of the sheet, followed by further deposition of the upper layer.
The piezoelectric device is appropriately used as a sheet-shaped piezoelectric vibrator when attached to a vibration sheet. Moreover, when the piezoelectric vibrator is placed in a resonance box having an opening at one side thereof, from which a sound is emitted, in a state wherein the vibration sheet is able to be vibrated in correspondence with the movement of the piezoelectric device. BREIF DESCRIPTION OF THE DRAWINGS Fig. la is a sectional view showing a sheet-shaped piezoelectric device according to the invention, and Fig. lb is a sectional view showing a double-layered structure of an electrode of the device; and
Figs. 2a is a sectional view illustrating a piezoelectric sound generator and Fig. 2b is a schematic perspective view showing a resonance box of the sound generator.
EMBODIMENTS OF THE INVENTION Reference is now made to the accompanying drawings and particularly, to Figs, la and lb. In Fig. la, there is shown a thin sheet-shaped piezoelectric device D. The device D includes a piezoelectric element 1 in the form of a layer and a pair of electrodes 2, 3 formed on opposite sides of the element 1 as shown.
The piezoelectric element 1 should have a dielectric constant of 4000 or over. The dielectric constant is determined in the following manner. The device D is subjected to measurement of a capacitance C by use of an impedance analyzer, and the dielectric constant is calculated according to the following equation.
C = ε0ε(S/d) wherein ε0 is a dielectric constant of vacuum, ε is a dielectric constant of a piezoelectric material sheet, S is an area of electrodes, and d is a distance between the electrodes. In order to meet the requirement for the dielectric constant, the piezoelectric element 1 is made of a ferroelectric composite oxide including, for example, xPbTiO3-yPbZrO3-(l-x-y)Pb(Mg1 /3Nb2/3)O3 wherein x and y are, respectively, defined hereinlater. This material is described, for example, in Journal of American Ceramic Society, Vol . 48, No. 12 , pp . 630- 635. In the above formula, when 1 -x-y is taken as z, this material exhibits a great piezoelectric characteristic in the vicinity of the triple point expressed by (x, y, z) = (0.4375, 0.125, 0.4375) . When the values of x, y and z are appropriately changed, there can be obtained piezoelectric materials having different characteristic properties. In the practice of the invention, the element 1 should have a dielectric constant of 4000 or over, for which x and y in the above formula are, respectively, range from 0.3 to 0.5 and 0. 1 to 0.3 although these values may vary depending on the manner of preparation of the composite oxide. The values of x and y are optimally in the ranges of 0.35 to 0.45 and 0.1 to 0.2 , respectively, within which both x and y are mutually changed to provide an optimum combination of x and y. The optimum combination includes, for example, x = 0.37 and y = 0.13, and x = 0.40 and y = 0.15.
As a matter of course, the element 1 is not limited to the composite oxide set out above, and any piezoelectric materials exhibiting the above- defined piezoelectric constant may also be used without limitation. Examples of such materials include composite oxides such as xPbTiO3-yPbZrθ3-Pb(Ni1/3Nb2/3) θ3, xPbTiO3-yPbZrO3- Pb(Zn1/2Nb1/2)O3, and the like wherein x and y are , respectively, as defined above. These compounds also have a dielectric constant as defined above. In order to realize a thin sheet- shaped piezoelectric device, the element 2 in the form of a thin layer should have a thickness of 30 μm or below, preferably from 0.1 to 10 μm, and may have any desired form such as a disc, a square or the like. The piezoelectric device D of the invention also has a pair of electrodes, each of which is made of a metal which is fully free of any glass component therein. Examples of such a metal include silver, gold, copper and the like, of which silver is preferred because gold is more expensive and copper is more likely to corrode. The metal electrode, which is free of any glass component therein, can be formed, for example, by a sputtering, vacuum deposition or CVD technique. Each electrode generally has a thickness of 0.1 to 20 μm, preferably 0.1 to lOμm. The thickness of the electrode should preferably be at 1/5 or below of the thickness of the piezoelectric element 1. In this connection, it is preferred that the total thickness of the piezoelectric device of the invention is 200μm or below, within which the thicknesses of the piezoelectric element 1 and the electrodes are preferably determined, respectively. The electrodes 2, 3 stated above have a single layer structure, respectively. Each electrode may have a multi-layered structure, particularly, a double-layered structure as shown in Fig. lb . The double-layered structure of the electrode 2 has a lower or underlying layer 2b in contact with the dielectric material layer 1 and an upper layer 2a formed on the underlying layer 2b when illustrated only for the electrode 2. This is true of the electrode 3.
The upper layer 2a is preferably made of silver for the reason set out above although other metals, such as Au, Cu or the like, may also be used. The upper layer should preferably have a thickness of 0.1 to 20 μm. The thickness of the lower layer is usually 100 nm or below.
Where the upper layer is made of silver, the lower layer 2b is made of a metal that is more likely to be bonded to the piezoelectric material layer 1 than silver. More particularly, the metal for the lower layer 2b should have better affinity for the piezoelectric element 1 than silver. Examples of such a metal include chromium, nickel, titanium, or the like. When the electrodes 2, 3 have such a double-layered structure as mentioned above, they are significantly improved in the property of bonding to the piezoelectric element 1. Thus, the device is eventually more improved in reliability when undergoing an abrupt temperature change.
Next, the method of making the piezoelectric device according to the invention is described.
For the preparation of the xPbTiO3-yPbZrO3-(l -x- y)Pb(Mg1/3Nb2/3)O3-type ferroelectric composite oxide, starting metal oxides, such as PbO , TiO2, ZrO2, MgO, Nb2O5, are, respectively, provided in the form of particles having a size, for example, of 0.1 to 2 μm and weighed to make predetermined mixing ratios by weight. These powders lare mixed, for example, in a ball mill and calcined under conditions of a temperature of 800 to 900°C for 2 to 10 hours. The thus calcined product was broken into pieces having a size of 0.1 to 2. The mixing ratios should be so determined that a finally sintered product has a dielectric constant of 4000 or over in the vicinity of the triple point discussed before.
The pieces are mixed with a binder resin and a dispersant in a solvent and mixed, for example, in a ball mill or the like milling means. Examples of the binder resin used for this purpose include polyvinyl butyral, polyvinyl alcohol and the like. The binder resin is usually present in an amount of 5 to 10 wt% based on the piezoelectric pieces. Examples of the dispersant include ordinarily employed ones such as dibutyl phthalate . The dispersant is generally used in an amount of 30 to 50 wt% based on the piezoelectric pieces. The solvent for the binder resin may be ones which are ordinarily employed for this purpose, and include, for example, ethyl acetate, butyl acetate, ethyl cellosolve (ethylene glycol monoethyl ether) , butyl cellosolve (ethylene glycol monobutyl ether) , and mixtures thereof. The solvent is used in an appropriate amount permitting the mixture to be milled without difficulty.
Usually, the mixture is milled for 24 to 120 hours to make a uniform slip . The slip is sub sequently applied onto an appropriate sub strate, such as a glass plate, in a dry thickness of 200 μm or below by any known coating technique such as doctor blade coating, and dried to obtain a green sheet.
Thereafter, the green sheet is punched into a desired form such as a square, a disk or the like form. The thus punched sheet is sintered under conditions of a temperature of 1100 to 1300 °C for a time of 30 minutes or over, preferably 60 to 120 minutes, thereby providing a sintered piezoelectric element made of an intended piezoelectric material.
This element is subsequently deposited directly with a metal by a sputtering, vacuum deposition or CVD technique as is well known in the art, thereby forming a metal electrode on opposite sides of the element. As set forth before, the metal is preferably silver. The sputtering, vacuum deposition or CVD technique of a metal is well known in the art and is not described in detail. In this way , the single-layered metal electrode is formed or deposited directly on opposite sides of the piezoelectric element in the thickness defined before.
In order to improve the bonding strength between the metal electrode and the piezoelectric element, the electrode is formed while heating the piezoelectric element at a temperature not lower than 200°C, preferably from 200 to 300°C. When the formation or deposition of the electrode is carried out while heating the element, the piezoelectric characteristics of the resultant device are improved along with improved bonding strength. This leads to an improvement in reliability of the device especially when the device undergoes an abrupt temperature change. The improvement in the piezoelectric characteristics and the reliability are considered to result from the improvement in the bonding strength.
Similar results as set out above are obtained when the piezoelectric device is thermally treated immediately after the formation of the electrode on opposite sides of the element. More particularly, the piezoelectric device is thermally treated at a temperature of 200°C or over, preferably 200 to 300°C for a time of at least 30 minutes in air. This thermal treatment is effective in improving the bonding strength between each electrode and the piezoelectric element.
If the atmosphere is replaced from air to nitrogen gas, the color change of the electrode through oxidation thereof can be effectively prevented, and thus, the bonding strength is further improved than in the case where the thermal treatment is effected in air. The device reliability is further improved as well.
This is true of the case where the thermal treatment is effected in vacuum.
When silver is used as an electrode material, it is preferred to form an underlying layer in order to improve the bonding strength between the electrode and the piezoelectric element. For the formation of the underlying layer, a metal such as chromium, titanium or nickel is first deposited on the piezoelectric element on opposite sides thereof by a sputtering, vacuum dep osition or CVD technique in a thickness of 100 nm or below. Thereafter, silver is likewise deposited on the underlying layer in a manner as stated hereinbefore . In this case, the silver layer is formed in a thickness of 0.1 to 20 μm.
For the improvement of the bonding strength , the underlying layer is formed while heating the piezoelectric element under such conditions as defined before . Likewise, the heating of the device after the formation of the electrodes having a double-layered structure under such conditions as defined before is also effective in the improvement.
The piezoelectric device made in this manner is thin and has such a high dielectric constant of 4000 or over because of the use of a metal electrode. The bonding strength between the metal electrode and the piezoelectric element is improved, so that the piezoelectric element and device are improved in reliability when exp osed to an abrupt change of temperature. The device of the invention has wide utility in various fields of a piezoelectric vibrator, a sound generator using the vibrator, and electronic parts, which are required to be scaled down and be made thin. For instance, a device for acceleration detection or for ceramic filter makes use of plural piezoelectric devices being built up . In this case, if it is required that the piezoelectric element of the device have a dielectric constant of 4000 or over and a thickness of 200 μm or below for one element, the thin sheet- shaped piezoelectric device of the invention can be appropriately applied to the fabrication of such a device mentioned above.
The application of the piezoelectric device of the invention to a piezoelectric vibrator and also to a sound generator is described .
Reference is now made to Figs. 2a and 2b . In Fig. 2a, there is shown a sound generator S including a piezoelectric vibrator V.
The vibrator V including the piezoelectric device D and a vibrating sheet or member 4 bonded to the device D at one side thereof through a bonding agent 5 such as an optically or thermally curable resin, e. g. an acrylic resin, an epoxy resin or the like. The vibrating member 4 is made of a metal or alloy such as Fe/Ni, Al, brass or the like. The member 4 is as thin as 20 to 100 μm. The vibrating member 4 is vibrated in a horizontal direction when an appropriate AC voltage of about 1 V is applied to the electrodes 2, 3 of the device D from a power source (not shown) through leads (not shown) attached to the electrodes 2, 3, respectively. The vibrating member is arranged to extend from the device D at opposite sides thereof so that when the vibrator V is set in position of a sound generator S, the vibrator V is fixed, for example, by means of a silicone bonding agent at the peripheral extended ends thereof as shown in Fig. 2a.
The sound generator S includes a resonance box 6 having an opening 7 at one side of the resonance box 6 as shown in Figs. 2a and 2b . The arrangement of such a sound generator S is known in the art, and the use of the piezoelectric device of the invention ensures a prolonged life of the piezoelectric vibrator V and the piezoelectric sound generator S and results in improved reliability of these devices when undergoing an abrupt change of temperature.
The invention is more particularly described by way of examples, which should not be construed as limiting the invention thereto . Example 1
A calcined powder of an composite oxide of the formula, xPbTiO3-yPbZrO3- ( l -x-y) Pb (Mg1/3Nb /3) O3, wherein x = 0.435 and y = 0.125, which had a dielectric constant of 4000 in the vicinity of the triple point indicated before (i. e. (x, y, z) = (0.4375, 0.125 , 0.4375) , was prepared, as a piezoelectric material, by mixing 70.1 wt% of PbO , 10.9 wt% of TiO2, 4.8 wt% of ZrO2, 1.9 wt% of MgO and 12.3 wt% of Nb2O5 and calcining the mixture at a temperature of 850 ° C for 3 hours. This powder material is hereinafter referred to as Material A.
100 g of the calcined powder, 7 g of polyvinyl butyral, 3 g of dibutyl phthalate were charged into a mixed solvent of 40 g of butyl acetate and 10 g of butyl cellosolve (ethylene glycol monobutyl ether) , followed by mixing in a ball mill for 48 hours to obtain a slip. This slip was used to form a green sheet by a doctor blade coating technique .
For comparison, a calcined powder of a composite oxide of the formula xPbTiO3-yPbZrO3- (l -x-y)Pb(Mg1/3Nb2/3) O3 wherein x = 0.390 and y = 0.290 having a dielectric constant of 2000 was prepared in the same manner as set out above, but changing the amounts of the respective starting oxides so as to obtain the composite oxide of the above formula (hereinafter referred to as Material B) . A green sheet was obtained in the same manner as set forth above using the composite oxide for comparison.
The green sheets made of Materials A and B were, respectively, punched so that a thin sheet-shaped disk element having a diameter of 10 mm and a thickness of 70 μm after sintering at a temperature of 1250°C for 2 hours.
Next, silver was sputtered on opposite sides of each disk element in a thickness of 2 μm to form a pair of sputtered silver electrodes.
For comparison, a baked silver electrode of a silver paste (Shouei Chem. Co. , Ltd.) was applied onto opposite sides of each disk element and baked at 650°C for 10 minutes in a thickness of 2 μm after baking.
Four piezoelectric devices thus obtained were poled and evaluated with respect to the dielectric constant and the electromechanical coupling coefficient Kp. The dielectric constant was measured in a manner similar to that stated hereinbefore by use of an impedance analyzer 4194A (made by Hewlett Packard Co.) to determine a capacitance C at lKHz, from which the dielectric constant ε was calculated. Likewise, the electromechanical coupling coefficient along the radial direction was calculated from a resonance frequency and an antiresonance frequency obtained by use of the impedance analyzer 4194A. The results of the evaluation are shown in Table 1 below. Table 1
Figure imgf000016_0001
In Table 1 , Kp indicates an electromechanical coupling coefficient, and ε indicates a dielectric constant.
From the above table, it will be seen that the device including the sputtered silver electrodes is better in the piezoelectric constants than that including the baked silver electrodes. This constants are much better when using Material A having a dielectric constant of 4000.
It is assumed that these results are ascribed to the glass frit contained in the baked silver(paste. For instance, the cap acitance C of the device using sputtered silver electrodes is expressed according to the following equation
C = εA - ε0 - S/d wherein εA is a dielectric constant of a piezoelectric material, S is the total area of the electrodes, d is a distance between the electrodes and ε0 is a dielectric constant of vacuum.
Where baked silver electrodes are used, capacitance C of the device is expressed according to the following equ ations because the cap acitance of a glass component on the surface of the device is added to an apparent capacitance of the electrode C = 1/( 1/C + 1/Cβl„.)
= l/{l/εA - ε0 - S/d} + l/(εglass - ε0 - S/d)}
= εA - ε0 - S/d/{l + εA/εgla s • { dglass/d} = C/{ 1 + (εA/εfl„1) - (dβl„./d)} wherein εglass represents a dielectric constant of glass and dgla ss represents a film thickness of the glass component.
In the above equation, εA of a material with a high piezoelectric characteristic is 4000 or over, and εgla5S is usually at 3 to 4. Thus, it may be established that εA/εgJu 6S, ^ 100. When the value of dglass/d is adequately small, the influence of the glass component is negligible. In this connection, however, when the distance d between the electrodes becomes small, the app arent dielectric constant of the electrode including the glass component film becomes worsened. From the above equations, it will be apparent that with Material B which is small in εA, like ordinary materials, the influence of the glass is so small that no problem is involved when using a baked silver electrode . The above devices were used to make piezoelectric vibrators by bonding a 70 μm thick vibrating member made of Fe/Ni to one side of each device. Each vibrator was set in a resonance box as is particularly shown in Fig. 2a to obtain a piezoelectric sound generator. The thus obtained sound generators were compared with one another with respect to the sound pressure characteristic, revealing that with Material A, the device using the sputtered silver electrodes was improved in sound pressure by 5 dB or over at 100 Hz than the device using the baked silver electrodes when 1 V was inputted thereto. The sound pressure was measured by the method described in "RC 8104" of the standards of Electronic Industries Association of Japan (EIAJ) .
In this example, the electrodes were formed by sputtering, and similar results were obtained when using vacuum deposition and a CVD technique. Example 2
The green sheet of Material A made in Example 1 was used, from which a number of disk elements of a sheet thickness of 40 μm and a diameter of 10 mm were punched and sintered. Sputtered silver electrodes having different thicknesses of 100 nm to 15 μm were deposited on the disk elements to make piezoelectric devices, respectively. These devices were poled and evaluated with respect to the dielectric constant and Kp. The results are shown in Table 2 below. Table 2
Figure imgf000019_0001
From Table 2, it will be seen that when sputtered silver electrodes are used, the electromechanical coupling coefficient Kp along the radial direction depends on the electrode thickness. When the electrode thickness is changed, the piezoelectric constant is changed, and when the electrode thickness exceeds a certain level, the characteristic properties are lowered. It will be seen that when the electrode becomes thick, the electrode thickness and weight cannot be neglected relative to the device thickness, thus leading to a poorer piezoelectric constant. When the device thickness is at 40 μm and the electrode thickness is at 8 μm or over, the influence of the electrode is not negligible, resulting in the lowering of the piezoelectric characteristic. More particularly, good piezoelectric characteristics were obtained when the electrode thickness was at 1/5 or below of the thickness of the piezoelectric layer.
In this example, the electrodes were formed by sputtering, and similar results were obtained when using a vacuum deposition or CVD technique . Example 3
Using Material A, a thin sheet- shaped piezoelectric device was made in the same manner as in Example 2. Prior to the poling and evaluation, the device was thermally treated at 300°C for 30 minutes. After the thermal treatment, the device was poled, to which a vibrating member was bonded. The resultant piezoelectric vibrator was set in a resonance box as shown in Fig. 2a to make a piezoelectric sound generator. Like the thermally treated device, a non-treated device was use d to make a sound generator. The thermally treated and non-treated devices were, respectively, subj ected to measurement of a sound pressure at 1 kHz prior to and after a thermal shock test. The thermal shock test was conducted in the following manner: the device was subj ected to 100 thermal shock cycles, each cycle including cooling down to — 40°C, standing at the temperature for 30 minutes, heating to 85°C in 10 minutes, standing at the temperature for 30 minutes, and again cooling down to -40°C in 10 minutes. The results of five measurements are shown in Table 3 below.
Table 3
Figure imgf000020_0001
From Table 3, it will be seen that desired bonding strength can be readily obtained when the device is thermally treated, so that the degradation of the characteristic can be prevented prior to and after the thermal shock test.
Similar tests were conducted at different thermal treating temperatures, revealing that the thermal treatment at temperatures of 200°C or over was effective.
In this example, the electrodes were formed by sputtering, and similar results were obtained when using a vacuum deposition of CVD method. Example 4
Material A was used and sintered to make piezoelectric disk elements in the same manner as in Example 2. Subsequently, different types of electrodes, one being a 1 μm thick silver electrode and the other being an electrode, which had a built-up structure including a 30 nm chromium underlying layer and a 900 nm thick silver upper layer, were, respectively, formed on opposite sides of each disk element by sputtering. Each piezoelectric device was poled, after which a vibrating member was bonded to the device at one side thereof by use of an epoxy resin bonding agent and cured to obtain a piezoelectric vibrator. This vibrator was set in a resonance box to provide a piezoelectric sound generator. The generator was subjected to the thermal shock test in the same manner as in Example 3. The results of a sound pressure at 1 kHz prior to and after the thermal shock test are shown in Table 4 below. Table 4
Figure imgf000022_0001
The results of Table 4 reveal that the provision of the Cr underlying electrode enables one to obtain desired bonding strength, and the degradation of the characteristic after the thermal shock test in comparison with the characteristic prior to the thermal shock test can be prevented.
Further, electrodes having different chromium film thicknesses were formed so that the thickness of one electrode having the double-layered structure was set at 1 μm, from which it was found that when the chromium electrode film had a thickness of 100 nm or over, the value of Kp became worsened. The reason for this is considered as follows: chromium has an elastic constant larger than silver and is harder, so that when a thick chromium film is formed, the vibrations of the resultant piezoelectric device are impeded. Although the use of chromium ensures a ready improvement of the bonding strength, the film thickness of the chromium underlying layer should be 100 nm or below in order to obtain good device characteristics . A similar improvement in bonding strength was confirmed when using titanium or nickel in place of chromium. In this example , the electrodes were formed by spu ttering, and similar results were obtained when using a vacuum dep osition or CVD technique . Example 5 Material A was used to make piezoelectric disk elements in the same manner as in Example 2. Thereafter, a 1 μm thick silver electrode was formed on opposite sides of each disk element by vacuum deposition. When the electrodes were formed, the disk element was heated at 250°C . The resultant thin sheet- shaped piezoelectric devices were polarized and each attached with a vibrating member to provide a piezoelectric vibrator. The vibrator was placed in a resonance box to obtain a piezoelectric sound generator. The generators obtained in this way were subjected to a thermal shock test in the same manner as set out hereinbefore, along with the generator wherein the disk element was not heated when the electrodes were formed.
The device having the electrode attached while heating the disk element had substantially no degradation after having subj ected to the thermal shock test. This reveals that when the disk element was heated at the time of the formation of the electrodes, similar results are obtained as in the thermal treatment after the formation of the electrodes in Example 3. Example 6
A calcined powder of an composite oxide of the formula, xPbTiO3-yPbZrO3- (l -x-y)Pb(Mg1/3Nb2/3) O3, wherein x = 0.37 and y = 0.17, which had a dielectric constant of 4000 in the vicinity of the triple point indicated before (i. e . (x, y, z) = (0.4375, 0.125 , 0.4375) , was prepared in the same manner as in Example 1. 100 g of the calcined powder, 7 g of polyvinyl butyral, 3 g of dibutyl phthalate were charged into a mixed solvent of 40 g of butyl acetate and 10 g of butyl cellosolve (ethylene glycol monobutyl ether) , followed by agitation in a ball mill for 48 hours to obtain a slip. This slip was used to form a green sheet by a doctor blade coating technique .
The green sheet containing the above composite oxide was punched so that a thin sheet-shaped disk element having a diameter of 10 mm and a thickness of 50 μm after sintering at a temperature of 1250°C for 2 hours.
Next, silver was sputtered on opposite sides of the disk element in a thickness of 2 μm to form a pair of sputtered silver electrodes. In this way, several thin sheet-shaped piezoelectric devices were made, and each device was polarized and subjected to evaluation of characteristics including Kp and dielectric constant.
These devices were each bonded to a vibrating sheet having a thickness of 70 μm and made of Fe/Ni by means of an epoxy resin bonding agent.
The resultant piezoelectric vibrator was placed in a resonance box having an opening in a manner as is particularly shown in Fig. 2a, thereby making a piezoelectric sound generator. The vibrator was fixed at the opposite sides thereof to the box wall by means of a silicone resin bonding agent.
The initial sound pressure of the piezoelectric sound generator was measured. Thereafter, the generator was subjected to a thermal shock test in the same manner as in Example 1 , followed by measurement of a sound pressure by applying an AC voltage of IV to the paired electrodes at 1 kHz after the test. Next, a thin sheet-shaped piezoelectric device was made in the same manner as set forth above, and was subsequently thermally treated in air under conditions of 300°C and 0.5 hours prior to polarization. After completion of the thermal treatment, the device was poled. A piezoelectric vibrator was made using the device in the same manner as stated above, and was used to make a piezoelectric sound generator. This generator was subjected to a reliability test according to the thermal shock test in the same manner as described before. Further, a thin sheet- shaped piezoelectric device was likewise made and subsequently thermally treated in an atmosphere of nitrogen under conditions of 300°C and 0.5 hours.
After completion of the thermal treatment, the device was poled. Thereafter, a piezoelectric vibrator was made using the device in the same manner as stated above, and was used to make a piezoelectric sound generator in a like manner. This generator was subjected to a reliability test according to the thermal shock test in the same manner as set out above.
The above procedure was repeated wherein the thermal treatment was effected in vacuum at 300°C for 0.5 hours prior to the poling and evaluation, thereby obtaining a piezoelectric sound generator. The generator was subjected to the reliability test in a like manner.
The results of five measurements in each case are shown in Table 5 below. Table 5
Figure imgf000026_0001
Evaluation of color change
O : No change
Δ : Partially changed
X : Fully changed
The results of Table 5 reveal that when the metal electrodes are thermally treated, the characteristic degradation prior to and after the thermal shock test can be conveniently prevented. Thus, the thermal treatment is preferred .
Moreover, when the thermal treatment is effected in a reducing atmosphere, the color change of the metal oxide via oxidation can be readily prevented.
The piezoelectric sound generator using the electrodes whose color was changed by oxidation tends to undergo characteristic degradation after the thermal shock test. The analyses of the degraded sound generator reveal that the degradation is ascribed to the partial separation between the piezoelectric device D and the vibrating member 24 in Fig. 2a, not to the degradation of the piezoelectric characteristic of the device. More particularly, the oxidized metal electrode 22 in contact with the vibrating member 24 via a bonding layer becomes poor in bonding strength. Thus, partial separation took place between the oxidized metal electrode and the vibrating member when subjected to the thermal shock test.
As will be apparent from Table 5, when the thermal treatment is carried our in a reducing atmosphere such as an atmosphere of nitrogen, or in vacuum, not only the color change of the electrode can be prevented, but also high bonding strength is maintained after fabrication of the sound generator, thus ensuring the high reliability of the generator.
Similar tests were repeated except that the thermal treatment was carried out at different temperatures by use of different types of atmospheric gases, thereby obtaining similar results when the temperature was at 200°C or over. In addition, hydrogen gas or argon gas was likewise effective.
In this example, the electrodes were formed by sputtering, and similar results were obtained using a vacuum deposition or CVD method.

Claims

CLAIMS :
1. A sheet-shaped piezoelectric device which comprises a sheet of a ferroelectric composite oxide having piezoelectric properties and a dielectric constant of 4000 or over, and a pair of electrodes directly deposited on opposite sides of the sheet, each electrode being made of a metal and being free of a glass component.
2. A sheet-shaped piezoelectric device according to Claim 1 , wherein said device has a thickness of 200 μm or below.
3. A sheet-shaped piezoelectric device according to Claim 1 , wherein said composite oxide is of the following formula
XPbTiO3-yPbZrO3-(l-x-y)Pb(Mg1 /3Nb2/3)O3 wherein x is a value ranging from 0.3 to 0.5, and y is a value ranging from 0.1 to 0.3.
4. A sheet-shaped piezoelectric device according to Claim 1 , wherein said electrode has a thickness, which is 1/5 of the thickness of said sheet.
5. A sheet-shaped piezoelectric device according to Claim 1 , wherein said electrode has a double-layered structure including an underlying layer in contact with said sheet and an upper layer formed on said underlying layer.
6. A sheet-shaped piezoelectric device according to Claim 5, wherein said underlying layer is made of a metal selected from the group consisting of Ni, Ti and Cr and has a thickness of 10 nm or below.
7. A piezoelectric vibrator comprising the sheet-shaped piezoelectric device defined in Claim 1 and a vibrating member bonded to said device on one side thereof.
8. A piezoelectric vibrator according to Claim 7, wherein said vibrating member is made of a metal or an alloy.
9. A piezoelectric sound generator comprising the piezoelectric vibrator defined in Claim 7, and a resonance box having said piezoelectric vibrator in position.
10. A method for making a sheet-shaped piezoelectric device, the method comprising providing a piezoelectric powder having a dielectric constant of 4000 or over, forming a green sheet comprising the piezoelectric powder, sintering said green sheet after shaping in a desired form, depositing a metal electrode on opposite sides of the sintered sheet wherein said metal electrode is free of a glass component.
11. A method according to Claim 10, wherein the deposition is carried out by a sputtering, vacuum deposition or CVD method.
12. A method according to Claim 10, wherein the deposition is carried out while heating the sintered sheet at a temperature of 1100 to 1300°C for a time of 30 minutes or over.
13. A method according to Claim 10, wherein after the deposition, the resultant device is thermally treated in air at a temperature of 200°C or over for a time of 30 minutes or over.
14. A method according to Claim 10, wherein after the deposition, the resultant device is thermally treated in an atmosphere of nitrogen at a temperature of 200°C or over for a time of 30 minutes or over.
15. A method according to Claim 10, wherein after the deposition, the resultant device is thermally treated in vacuum at a temperature of 200°C or over for a time of 30 minutes or over.
16. A method according to Claim 10, wherein the deposition is carried out such that an underlying layer made of Ni, Ti or Cr is first formed on said sintered sheet and then, an upper layer made of silver is further formed on said underlying layer.
17. A method according to Claim 16, wherein the underlying layer is formed while heating the sintered sheet.
18. A method according to Claim 16, wherein the device after the deposition is thermally treated in air, in an atmosphere of nitrogen gas or in vacuum.
PCT/JP2000/003686 1999-06-08 2000-06-07 Sheet-shaped piezoelectric device, method for making same, and piezoelectric vibrator and piezoelectric sound generator using same WO2000076007A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU52454/00A AU5245400A (en) 1999-06-08 2000-06-07 Sheet-shaped piezoelectric device, method for making same, and piezoelectric vibrator and piezoelectric sound generator using same

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP16051099 1999-06-08
JP11/160510 1999-06-08
JP11232937A JP2001057449A (en) 1999-06-08 1999-08-19 Thin plate piezoelectric element, piezoelectric oscillator and voice generator utilizing it
JP11/232937 1999-08-19

Publications (1)

Publication Number Publication Date
WO2000076007A1 true WO2000076007A1 (en) 2000-12-14

Family

ID=26486993

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2000/003686 WO2000076007A1 (en) 1999-06-08 2000-06-07 Sheet-shaped piezoelectric device, method for making same, and piezoelectric vibrator and piezoelectric sound generator using same

Country Status (3)

Country Link
JP (1) JP2001057449A (en)
AU (1) AU5245400A (en)
WO (1) WO2000076007A1 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2003283705A1 (en) * 2002-12-13 2004-07-09 Koninklijke Philips Electronics N.V. Electro-acoustic resonator
JP4665155B2 (en) * 2004-10-22 2011-04-06 株式会社昭和真空 Thin film forming apparatus and method

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0344000A2 (en) * 1988-05-27 1989-11-29 Mitsui Petrochemical Industries, Ltd. Ferroelectric ceramic material
EP0344978A2 (en) * 1988-05-27 1989-12-06 Mitsui Petrochemical Industries, Ltd. Ferroelectric ceramic material
EP0736915A1 (en) * 1995-04-03 1996-10-09 Seiko Epson Corporation Piezoelectric thin film, method for producing the same, and ink jet recording head using the thin film
EP0747976A1 (en) * 1994-12-27 1996-12-11 Seiko Epson Corporation Thin-film piezoelectric element, process for preparing the same, and ink jet recording head made by using said element

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0344000A2 (en) * 1988-05-27 1989-11-29 Mitsui Petrochemical Industries, Ltd. Ferroelectric ceramic material
EP0344978A2 (en) * 1988-05-27 1989-12-06 Mitsui Petrochemical Industries, Ltd. Ferroelectric ceramic material
EP0747976A1 (en) * 1994-12-27 1996-12-11 Seiko Epson Corporation Thin-film piezoelectric element, process for preparing the same, and ink jet recording head made by using said element
EP0736915A1 (en) * 1995-04-03 1996-10-09 Seiko Epson Corporation Piezoelectric thin film, method for producing the same, and ink jet recording head using the thin film

Also Published As

Publication number Publication date
AU5245400A (en) 2000-12-28
JP2001057449A (en) 2001-02-27

Similar Documents

Publication Publication Date Title
CA2248801C (en) Improved piezoelectric ceramic-polymer composites
US6217979B1 (en) Piezoelectric/electrostrictive film element
JP5641668B2 (en) Ferroelectric ceramic materials with low sintering temperature
EP1387417A2 (en) Manufacturing method for monolithic piezoelectric part, and monolithic piezoelectric part
JP4859593B2 (en) Multilayer ceramic capacitor and manufacturing method thereof
EP1710911A2 (en) Resonator
WO2003104163A1 (en) Piezoelectric porcelain composition, laminated piezoelectric device therefrom and process for producing the same
KR100869093B1 (en) Method of producing piezoelectric ceramic device
JP2011159993A (en) Piezoelectric component
JP5931127B2 (en) Piezoelectric ceramics, method for manufacturing the same, and piezoelectric ceramic speaker having the same
WO2000076007A1 (en) Sheet-shaped piezoelectric device, method for making same, and piezoelectric vibrator and piezoelectric sound generator using same
CN103958439A (en) Piezoelectric device and piezoelectric ceramic composition
JP2884635B2 (en) Piezoelectric ceramics and method of manufacturing the same
JP3207315B2 (en) Piezoelectric / electrostrictive film type element
JPH09312234A (en) Laminated ceramic electronic device
JP4927419B2 (en) Piezoelectric ceramic composition and piezoelectric element using the same
JP2957002B2 (en) Piezoelectric porcelain composition
JP4231653B2 (en) Manufacturing method of laminated piezoelectric actuator
Seveyrat et al. Processing and characterization of piezoelectric thick films screen-printed on silicon and glass-ceramic substrates
JP2926827B2 (en) Dielectric porcelain composition
JPH10167821A (en) Piezoelectric ceramic composition
JP2000281434A (en) Dielectric porcelain
Terada Actuator characteristic and electrode of multilayer piezoelectric ceramics
JPH08143359A (en) Piezoelectric ceramic composition
SU1217852A1 (en) Piezoelectric ceramic material

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY CA CH CN CR CU CZ DE DK DM DZ EE ES FI GB GD GE GH GM HR HU ID IL IN IS KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX NO NZ PL PT RO RU SD SE SG SI SK SL TJ TM TR TT TZ UA UG US UZ VN YU ZA ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE BF BJ CF CG CI CM GA GN GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
REG Reference to national code

Ref country code: DE

Ref legal event code: 8642

122 Ep: pct application non-entry in european phase