U.S. patent application number 10/206192 was filed with the patent office on 2003-01-09 for piezoelectric ceramic, method for producing piezoelectric ceramic, and piezoelectric oscillator.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Kida, Masataka, Kohno, Yoshiaki, Okuda, Akihito, Takamura, Akinobu.
Application Number | 20030006677 10/206192 |
Document ID | / |
Family ID | 15483774 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030006677 |
Kind Code |
A1 |
Okuda, Akihito ; et
al. |
January 9, 2003 |
Piezoelectric ceramic, method for producing piezoelectric ceramic,
and piezoelectric oscillator
Abstract
A piezoelectric ceramic comprising lead titanate as a primary
component, wherein the primary component contains a titanium oxide
crystalline phase. Methods for producing the ceramic, and
piezoelectric oscillators making use of the ceramic are also
disclosed.
Inventors: |
Okuda, Akihito; (Hikone-shi,
JP) ; Takamura, Akinobu; (Yokaichi-shi, JP) ;
Kida, Masataka; (Omihachiman-shi, JP) ; Kohno,
Yoshiaki; (Moriyama-shi, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY, LLP
1177 Avenue of the Americas
New York
NY
10036
US
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
|
Family ID: |
15483774 |
Appl. No.: |
10/206192 |
Filed: |
July 29, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10206192 |
Jul 29, 2002 |
|
|
|
09321243 |
May 27, 1999 |
|
|
|
Current U.S.
Class: |
310/328 |
Current CPC
Class: |
H03H 9/0207 20130101;
H01L 41/187 20130101; H03H 9/178 20130101 |
Class at
Publication: |
310/328 |
International
Class: |
H01L 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 1998 |
JP |
10-149838 |
Claims
What is claimed is:
1. A method for producing a piezoelectric ceramic comprising firing
a lead titanate piezoelectric ceramic at 1230-1245.degree. C.
2. The method of claim 1 wherein the ceramic in the form of a
compact is fired.
3. A method according to claim 2 further comprising providing an
electrode on a surface of the compact.
4. A method for producing a piezoelectric ceramic comprising: (a)
providing a piezoelectric ceramic material mixture comprising lead
oxide and titanium oxide; (b) firing the mixture to thereby produce
a calcined product; (c) crushing the calcined product and adding
titanium oxide powder and a binder to the crushed product to
thereby produce a binder-containing mixture; (d) molding the
binder-containing mixture to thereby produce a compact; and (e)
firing the compact.
5. A method according to claim 4 wherein the compact is fired at
about 1230-1295.degree. C.
6. The method of claim 5 wherein the ceramic in the form of a
compact is fired.
7. A method according to claim 6 further comprising providing an
electrode on a surface of the compact.
8. The method of claim 4 wherein the ceramic in the form of a
compact is fired.
9. A method according to claim 8 further comprising providing an
electrode on a surface of the compact.
Description
[0001] This is a division of application Ser. No. 09/321,243, filed
May 17, 1999.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a piezoelectric ceramic,
and more particularly to a piezoelectric ceramic which is useful in
a high frequency range of 10 MHz or more. The invention also
relates to a piezoelectric oscillator using the piezoelectric
ceramic and to a method for producing the piezoelectric
ceramic.
[0004] 2. Background Art
[0005] A piezoelectric ceramic including lead titanate as a main
component has been often employed for a piezoelectric oscillator
which has a vibration frequency of 10 MHz or more.
[0006] In such type of oscillator, the third order vibration mode
of longitudinal vibration in the oscillator is utilized. The use of
this mode is preferable especially in the high frequency region to
achieve good response to an input signal. A method for enhancing
the response of third order vibration of a piezoelectric ceramic in
which pores of the ceramic are reduced so as to densify the ceramic
is known. However, in addition to improving the response of third
order vibration, densification of a piezoelectric ceramic also
enhances the response of fifth order vibration, which is
unnecessary when a third order vibration mode is used. Thus, such a
piezoelectric oscillator generating fifth order vibration needs
improvements in its characteristics.
[0007] There is a method for suppressing the response of fifth
order vibration by forming pores dispersed in a piezoelectric
ceramic. However, in this case, porosity of the ceramic increases
to disadvantageously deteriorate the mechanical strength and
reliability of the piezoelectric ceramic.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing, the present invention provides a
piezoelectric ceramic suppressing the response of fifth order
vibration without deteriorating the mechanical strength and
reliability thereof. In accordance with another aspect of the
present invention, a method for producing the piezoelectric ceramic
is provided. Still further, the present invention provides a
piezoelectric oscillator using the piezoelectric ceramic.
[0009] Accordingly, in a first aspect of the present invention,
there is provided a piezoelectric ceramic comprising lead titanate
as a primary component, wherein the primary component contains a
titanium oxide crystalline phase. By employment of such a
constitution, the response of fifth order vibration decreases to
thereby suppress unnecessary vibration without deteriorating the
mechanical strength and reliability of the piezoelectric
ceramic.
[0010] Preferably, the grain size of the titanium oxide crystalline
phase is about 4 to 28 im.
[0011] In a second aspect of the present invention, there is
provided a method for producing a piezoelectric ceramic comprising
a step of firing a compact formed of a piezoelectric ceramic
predominantly containing lead titanate at about 1230 to 1245EC. By
employment of such a temperature range, the response of fifth order
vibration can be suppressed without substantial suppression of that
of third order vibration.
[0012] In a third aspect of the present invention, there is
provided a method for producing a piezoelectric ceramic comprising
the following steps (1) to (5):
[0013] (1) mixing a piezoelectric ceramic material containing lead
oxide and titanium oxide to thereby produce a mixture;
[0014] (2) firing the mixture to thereby produce a calcined
product;
[0015] (3) crushing the calcined product and adding titanium oxide
powder and a binder to the crushed product to thereby produce a
binder-containing mixture;
[0016] (4) molding the binder-containing mixture to thereby produce
a compact; and
[0017] (5) firing the compact.
[0018] By employment of such steps, dispersion of a titanium oxide
crystalline phase into lead titanate serving as a primary component
is ensured.
[0019] In a fourth aspect of the present invention, there is
provided a piezoelectric oscillator comprising an insulating
substrate, a piezoelectric ceramic element, lead terminals and an
outer resin covering for the piezoelectric ceramic element,
wherein
[0020] the insulating substrate has patterned electrodes
thereon;
[0021] the piezoelectric ceramic element comprises the
piezoelectric ceramic and electrodes formed on main surfaces of the
ceramic and electrically connected with the patterned electrodes;
and
[0022] the lead terminals are electrically connected to the
patterned electrodes.
[0023] In a fifth aspect of the present invention, there is
provided a piezoelectric oscillator comprising a piezoelectric
ceramic element, upper and lower substrates sandwiching the
piezoelectric ceramic element, and external electrodes, wherein
[0024] the piezoelectric ceramic element comprises the
piezoelectric ceramic and internal electrodes formed on main
surfaces thereof, and
[0025] the external electrodes are electrically connected to the
internal electrodes and formed on sides faces of the piezoelectric
ceramic element and side faces of the upper and lower
substrates.
[0026] By employment of such a constitution, there is provided a
piezoelectric oscillator in which the response of an unnecessary
fifth order vibration is suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Various other objects, features, and many of the attendant
advantages of the present invention will be readily appreciated as
the same becomes better understood with reference to the following
detailed description of the preferred embodiments when considered
in connection with accompanying drawings, in which:
[0028] FIG. 1 is a schematic perspective view of a piezoelectric
oscillator according to the present invention;
[0029] FIG. 2 is a perspective view of a partially cut-away
piezoelectric oscillator according to one embodiment of the present
invention; and
[0030] FIG. 3 is a perspective view of a partially cut-away
piezoelectric oscillator according to another embodiment of the
present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0031] The piezoelectric ceramic according to the present invention
comprises lead titanate as a primary component and a titanium oxide
crystalline phase.
[0032] The piezoelectric ceramic may further contain a variety of
secondary components such as La.sub.2O.sub.3 and MnO in accordance
with need.
[0033] The titanium oxide crystalline phase of the present
invention refers to a secondary phase comprising titanium oxide,
and the form thereof is not particularly limited.
[0034] The titanium oxide crystalline phase may be generated by
segregating titanium oxide in lead titanate during firing or by
separately adding a titanium oxide powder to lead titanate,
followed by crystallization.
[0035] The firing temperature of the piezoelectric ceramic
according to the present invention must be a temperature at which a
titanium oxide crystalline phase is formed. The higher the firing
temperature, the greater the ratio of the titanium oxide
crystalline phase to the primary component and the greater the
grain size of the titanium oxide crystalline phase.
EXAMPLES
[0036] The methods for producing piezoelectric ceramic and
piezoelectric oscillator will next be described in detail by way of
examples and with reference to FIGS. 1 to 3. FIG. 1 is a schematic
perspective view of a piezoelectric oscillator according to the
present invention. The chained double-dashed line in FIG. 1
represents the location of a protective cap and molding resin.
Example 1
[0037] Powders of PbO, TiO.sub.2, La.sub.2O.sub.3, and MnCO.sub.3
were provided as starting materials. The powders were weighed so as
to attain predetermined proportions and wet-mixed by use of a ball
mill to thereby obtain a mixture. The mixture was dehydrated,
granulated, and calcined at 980EC for 1 hour to thereby obtain a
calcined product. The calcined product was crushed and a binder was
added thereto to thereby obtain a binder-containing mixture. The
binder-containing mixture was compression-molded into a flat plate
under a pressure of 4 ton/cm.sup.2 to thereby obtain a compact. The
compact was fired at 1220-1260EC, so as to induce precipitation of
a TiO.sub.2 crystalline phase in the primary component to thereby
obtain a piezoelectric ceramic. Electrodes were formed on the two
main surfaces of the piezoelectric ceramic obtain a piezoelectric
ceramic element.
[0038] The thus-obtained piezoelectric ceramic was mirror-polished
and subjected to SEM photography so as to measure the average grain
size of the TiO.sub.2 crystalline phase in the primary component of
the ceramic. Responses of third order vibration (3max) and fifth
order vibration (5max) of the piezoelectric ceramic element were
determined by use of an impedance gain phase analyzer. The results
are shown in Table 1. A sample having no TiO.sub.2 crystalline
phase served as a comparative sample (Comparative Example). Samples
in Table 1 marked with * fall outside certain limited scopes of the
present invention.
1TABLE 1 Average grain Firing size of the TiO.sub.2 temperature
crystalline phase 3 max 5 max Sample No. (.sup.EC) (m) (deg) (deg)
*1 1220 3.0 82.6 54.1 2 1230 4.0 81.3 49.2 3 1235 4.5 80.5 41.8 4
1240 5.0 80.5 41.0 5 1245 28.0 78.7 32.3 *6 1250 52.5 64.1 -21.3 *7
1260 100.0 59.7 -25.4 Comparative 1180 -- 81.6 54.5 Example
[0039] As is apparent from Table 1, the fifth order vibration
response (5max) of samples having a TiO.sub.2 crystalline phase is
suppressed as compared with samples having no TiO.sub.2 crystalline
phase.
[0040] The average grain size of a TiO.sub.2 crystalline phase
preferably falls within the range of about 4-28 im. This is because
when the average grain size is less than about 4 im as in the case
of Sample No. 1, effect of suppressing a fifth order vibration
response (5max) is disadvantageously small, whereas in the case in
which the average grain size of the TiO.sub.2 crystalline phase is
more than about 28 im as in the case of Sample No. 6 or 7, the
third order vibration response (3max) is also suppressed, which is
disadvantageous.
[0041] The firing temperature of piezoelectric ceramic material is
preferably about 1230-1245EC. This is because when the firing
temperature is lower than about 1230EC as in the case of Sample No.
1, the effect of suppressing a fifth order vibration response
(5max) is disadvantageously small, whereas when firing the
temperature is higher than about 1245EC as in the case of Sample
No. 6 or 7, the third order vibration response (3max) is also
suppressed, which is disadvantageous.
Example 2
[0042] In a manner similar to that described in Example 1, a
calcined PbTiO.sub.3 product was produced. The calcined PbTiO.sub.3
was crushed and TiO.sub.2 powder was added thereto and mixed
therewith. A binder was added to and mixed with the resultant
crushed product to thereby obtain a binder-containing mixture. The
binder-containing mixture was compression-molded into a flat plate
under a pressure of 4 ton/cm.sup.2 so as to obtain a compact. The
compact was fired at 1180EC to thereby obtain the piezoelectric
ceramic of the present invention. Electrodes were formed on the two
main surfaces of the piezoelectric ceramic to thereby obtain a
piezoelectric ceramic element.
[0043] The resultant piezoelectric ceramic was subjected to
measurement as described in Example 1 to thereby confirm that the
TiO.sub.2 crystalline phase was present in PbTiO.sub.3 serving as
the primary component of the piezoelectric ceramic and that the
fifth order vibration response (5max) of the piezoelectric ceramic
was suppressed.
Example 3
[0044] A resin-molding-type piezoelectric oscillator will next be
described. However, the piezoelectric oscillator of the present
invention is not limited only to this type of resonator.
[0045] As illustrated in FIG. 1, electrodes 3b were formed on the
two main surfaces of a piezoelectric ceramic 3a obtained from
Example 1 or 2 to thereby obtain a piezoelectric ceramic element 3.
Subsequently, an insulating substrate 5 printed with three
patterned electrodes 7 was provided, and the piezoelectric ceramic
element 3 was mounted on the insulating substrate 5 by use of a
conductive adhesive (not illustrated) such that the electrodes on
the lower side of the piezoelectric ceramic element 3 were
connected directly to two of the patterned electrodes 7. The
electrode on the upper side of the piezoelectric ceramic element 3
was connected to the remaining patterned electrode 7 by use of a
wire 15. Lead terminals 9 were soldered onto the patterned
electrodes 7, and thereafter, the entirety of the insulating
substrate was covered with an outer resin by way of molding to
thereby obtain a piezoelectric oscillator 1. A vibration region of
the piezoelectric ceramic 3a was formed in such a manner that a wax
was applied to the corresponding portion in advance followed by
evaporation during curing of the outer resin 13 to thereby obtain a
cavity.
Example 4
[0046] A surface mounted type piezoelectric oscillator will next be
described. However, the piezoelectric oscillator of the present
invention is not limited only to this type of resonator.
[0047] As illustrated in FIG. 2, internal electrodes 4b were formed
on the main surfaces of a piezoelectric ceramic 4a obtained from
Example 1 or 2, to thereby obtain a piezoelectric ceramic element
4. Subsequently, upper and lower substrates 6a and 6b formed of an
insulation material were respectively fixed to the upper and lower
main surfaces of the piezoelectric ceramic element 4 by use of
epoxy-based adhesive 8 for holding the piezoelectric ceramic
element 4 therebetween. External electrodes 10 were formed on outer
surfaces of the piezoelectric ceramic element 4 to which internal
electrodes 4b extended to thereby obtain a piezoelectric oscillator
2.
[0048] As illustrated in FIG. 3, when the upper substrate is formed
of a dielectric substrate and an external electrode 10 is
additionally provided at the center of the upper surface of the
piezoelectric oscillator 2, there can be obtained a piezoelectric
oscillator 2 having the function of a capacitor. In order to serve
as a vibration region, each of the upper and lower substrates 6a
and 6b is provided with a concave portion for forming a cavity.
* * * * *