U.S. patent application number 09/935959 was filed with the patent office on 2002-04-18 for piezoelectric ceramic composition for surface acoustic wave device and surface a coustic wave device.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Ogiso, Koji.
Application Number | 20020043653 09/935959 |
Document ID | / |
Family ID | 26598937 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020043653 |
Kind Code |
A1 |
Ogiso, Koji |
April 18, 2002 |
Piezoelectric ceramic composition for surface acoustic wave device
and surface a coustic wave device
Abstract
A piezoelectric ceramic composition for a surface acoustic wave
device which can improve the electromechanical coupling coefficient
is provided. The piezoelectric ceramic composition for a surface
acoustic wave device is represented by the formula
Pb.sub.aZr.sub.xTi.sub.y(Ni.sub.mMn.sub.nNb-
.sub.2/3).sub.zO.sub.3, wherein x+y+z=1, 0.93.ltoreq.a.ltoreq.1.02,
0.32.ltoreq.x.ltoreq.0.50, 0.41.ltoreq.y.ltoreq.0.54,
0.03.ltoreq.z.ltoreq.0.21 and 0.24.ltoreq.m+n.ltoreq.0.67.
Inventors: |
Ogiso, Koji; (Moriyama-shi,
JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
|
Family ID: |
26598937 |
Appl. No.: |
09/935959 |
Filed: |
August 23, 2001 |
Current U.S.
Class: |
252/500 ;
252/512 |
Current CPC
Class: |
C04B 35/491 20130101;
H01L 41/1876 20130101 |
Class at
Publication: |
252/500 ;
252/512 |
International
Class: |
H01B 001/00; H01C
001/00; H01B 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2000 |
JP |
2000-262974 |
Jul 10, 2001 |
JP |
2001-209561 |
Claims
What is claimed is:
1. A piezoelectric ceramic composition for a surface acoustic wave
device represented by the formula
A.sub.aZr.sub.xTi.sub.y(Ni.sub.mMn.sub.nNb.sub- .2/3).sub.zO.sub.3,
wherein: x+y+z=1; 0.93.ltoreq.a.ltoreq.1.02;
0.32.ltoreq.x.ltoreq.0.50; 0.41.ltoreq.y.ltoreq.0.54;
0.03.ltoreq.z.ltoreq.0.21; 0.24.ltoreq.m+n.ltoreq.0.67; and wherein
A is Pb or the combination of Pb and at least one member of the
group consisting of Ba, Ca and Sr.
2. A piezoelectric ceramic composition for a surface acoustic wave
device according to claim 1, wherein 0.46.ltoreq.m+n.ltoreq.0.67;
0.01.ltoreq.m.ltoreq.0.66; and 0.01.ltoreq.n.ltoreq.0.66.
3. A piezo electric ceramic composition for a surface acoustic wave
device according to claim 2, wherein A is Pb.
4. A piezoelectric ceramic composition for a surface acoustic wave
device according to claim 2, wherein A is a combination of Pb and
at least one member selected from the group consisting of Ba, Ca,
and Sr.
5. A piezoelectric ceramic composition for a surface acoustic wave
device according to claim 4, wherein said member of the group is
Sr.
6. A piezoelectric ceramic composition for a surface acoustic wave
device according to claim 1, wherein A is Pb.
7. A piezoelectric ceramic composition for a surface acoustic wave
device according to claim 1, wherein A is a combination of Pb and
at least one member selected from the group consisting of Ba, Ca,
and Sr.
8. A piezoelectric ceramic composition for a surface acoustic wave
device according to claim 7, wherein said member of the group is
Sr.
9. A piezoelectric ceramic comprising a sintered piezoelectric
ceramic composition for a surface acoustic wave device according to
claim 1.
10. A piezoelectric ceramic according to claim 9, having a grain
diameter of about 3 .mu.m or less.
11. A piezoelectric ceramic according to claim 10, wherein the size
of pores and defects in the piezoelectric ceramic are about 3 .mu.m
or less.
12. A piezoelectric ceramic according to claim 11, wherein the
absolute value of the change rate of resonant frequency with
respect to temperature is about 100 ppm/.degree. C. or less.
13. A piezoelectric ceramic comprising a sintered piezoelectric
ceramic composition for a surface acoustic wave device according to
claim 2.
14. A piezoelectric ceramic according to claim 13, having a grain
diameter of about 3 .mu.m or less.
15. A surface acoustic wave device comprising a piezoelectric
substrate comprising the piezoelectric ceramic, according to claim
13; and an interdigital transducer on the piezoelectric
substrate.
16. A surface acoustic wave device according to claim 15, wherein
the interdigital transducer is configured to generate a SH type
surface acoustic wave on the piezoelectric substrate.
17. A surface acoustic wave device according to claim 16, wherein
the piezoelectric substrate has a pair of edges defining a surface
on which the interdigital transducer is disposed, and outermost
electrode fingers of the interdigital transducer are flush with
said edges.
18. A surface acoustic wave device comprising a piezoelectric
substrate comprising the piezoelectric ceramic according to claim
9; and an interdigital transducer on the piezoelectric
substrate.
19. A surface acoustic wave device according to claim 18, wherein
the interdigital transducer is configured to generate a SH type
surface acoustic wave on the piezoelectric substrate.
20. A surface acoustic waive device according to claim 19, wherein
the piezoelectric substrate has a pair of edges defining a surface
on which the interdigital transducer is disposed, and outermost
electrode fingers of the interdigital transducer are flush with
said edges.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a piezoelectric ceramic
composition used for a surface acoustic wave device. In particular,
the present invention relates to a piezoelectric ceramic
composition for a surface acoustic wave device which can improve
the impedance ratio and coupling coefficient and such a surface
acoustic wave device.
[0003] 2. Description of the Related Art
[0004] In recent years, accompanying the progress of mobile
communication equipment using high frequencies, components used
therein, for example, resonators and filters, have also been
required for use in higher frequencies and miniaturization. As the
resonators and the filters, surface acoustic wave devices have been
used because of advantages in acceleration of use in higher
frequencies and miniaturization.
[0005] In a surface acoustic wave device, an interdigital
transducer (IDT) composed of at least one pair of interdigital
electrodes is configured on a piezoelectric substrate, and
excitation and reception of the surface acoustic wave are performed
by the IDT. As a piezoelectric substrate material of the surface
acoustic wave device, a piezoelectric single crystal of, for
example, LiTaO.sub.3 and LiNbO.sub.3, or a piezoelectric ceramic
primarily composed of PbTiO.sub.3, Pb(Ti,Zr)O.sub.3, etc., are
used. A laminate in which piezoelectric thin films, such as ZnO
thin films, are laminated on an insulation substrate or a
piezoelectric substrate is also used as the piezoelectric substrate
of the surface acoustic wave device.
[0006] When comparisons are made between the piezoelectric single
crystal and the piezoelectric ceramic, the speed of sound is lower
in the piezoelectric ceramic. Therefore, a piezoelectric substrate
made of piezoelectric ceramic is preferable in order to miniaturize
the surface acoustic wave device.
[0007] Coupling coefficients required of piezoelectric substrate
materials are different depending on the intended purposes,
although regarding the piezoelectric single crystal, the coupling
coefficient is uniquely defined based on the kind and the cut
angle. That is, for a surface acoustic wave device using the
piezoelectric single crystal, the piezoelectric characteristics and
temperature characteristics are uniquely defined based on the kind
of the single crystal and the cut angle, so that flexibility in
design of devices is reduced.
[0008] On the other hand, piezoelectric ceramics, such as
Pb(Ti,Zr)O.sub.3-based ceramics, have piezoelectric characteristics
which can be varied over a wide range by controlling the
composition.
[0009] However, when the piezoelectric ceramics were used as the
piezoelectric substrates of the surface acoustic wave devices in
high frequency regions exceeding 10 MHZ, there was a problem in
that impedance ratios, that is, the ratios of the impedance at an
anti-resonant frequency of Fa to the impedance at a resonant
frequency of Fr, are small.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide a piezoelectric ceramic composition for a surface acoustic
wave device which can achieve a high impedance ratio even in high
frequency regions.
[0011] The piezoelectric ceramic composition for a surface acoustic
wave device is represented by a formula
Pb.sub.aZr.sub.xTi.sub.y(Ni.sub.mMn.su-
b.nNb.sub.2/3).sub.zO.sub.3, where:
[0012] x+y+z=1;
[0013] 0.93.ltoreq.a.ltoreq.1.02;
[0014] 0.32.ltoreq.x.ltoreq.0.50;
[0015] 0.41.ltoreq.y.ltoreq.0.54;
[0016] 0.03.ltoreq.z.ltoreq.0.21; and
[0017] 0.24.ltoreq.m+n.ltoreq.0.67.
[0018] Preferably, m and n fall within the ranges of:
[0019] 0.46.ltoreq.m+n.ltoreq.0.67;
[0020] 0.01.ltoreq.m.ltoreq.0.66; and
[0021] 0.01.ltoreq.n.ltoreq.0.66.
[0022] In the piezoelectric ceramic composition for a surface
acoustic wave device, at least one element selected from the group
consisting of Ba, Ca, and Sr may be substituted for a part of said
Pb.
[0023] By sintering the piezoelectric ceramic composition, a
piezoelectric ceramic suitable for a piezoelectric substrate of a
surface acoustic wave device is obtained. The surface acoustic wave
device preferably utilizes a SH type surface acoustic wave. In the
case, it is preferable that a grain diameter is about 3 .mu.m or
less and the sizes of pores and defects in the piezoelectric
ceramic are about 3 .mu.m or less. Further, it is preferable that
the absolute value of a change rate of resonant frequency with
respect to temperature is about 100 ppm/.degree. C. or less.
[0024] By using the piezoelectric ceramic composition for a surface
acoustic wave device according to the present invention, excellent
impedance ratios can be achieved, higher frequencies can be used
and the piezoelectric characteristics can be controlled over a wide
range.
[0025] Therefore, a surface acoustic wave device which meets use
requirements in higher frequencies and miniaturization can be
provided with ease according to the present invention.
[0026] When m+n is 0.46 or more, but 0.67 or less, m is 0.01 or
more but 0.66 or less, and n is 0.01 or more but 0.66 or less, a
large electromechanical coupling coefficient can be achieved.
[0027] Furthermore, when the crystalline particle diameter is about
3 .mu.m or less, and when sizes of the pores and defects in the
sintered material are about 3 .mu.m or less, the impedance ratio
can be further improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a graph showing changes of the electromechanical
coupling coefficient kBGS with changes of z; and
[0029] FIG. 2 is a perspective view of an end face reflection type
surface acoustic wave device prepared according to an embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The present invention will be explained below in further
detail using specified examples according to the present
invention.
[0031] A piezoelectric ceramic composition for a surface acoustic
wave device, of the present invention is represented by a formula
Pb.sub.aZr.sub.xTi.sub.y(Ni.sub.mMn.sub.nNb.sub.2/3).sub.zO.sub.3,
wherein x+y+z=1, 0.93.ltoreq.a.ltoreq.1.02,
0.32.ltoreq.x.ltoreq.0.50, 0.41.ltoreq.y.ltoreq.0.54,
0.03.ltoreq.z.ltoreq.0.21, and 0.24.ltoreq.m+n.ltoreq.0.67.
[0032] The inventors of the present invention have discovered that
a piezoelectric ceramic composition composed of at least Pb, Ni,
Mn, Nb, Ti, Zr, and O and satisfying the aforementioned formula can
improve the aforementioned impedance ratio could be effectively
improved in a surface acoustic wave device using the aforementioned
piezoelectric ceramic composition as a piezoelectric substrate.
[0033] The piezoelectric ceramic composition according to the
present invention is composed of oxides or carbonates of the
elements, as primary materials, indicated by the aforementioned
formula, although that may be composed of metals, other compounds
or complex oxides thereof as materials. Each material may contain
impurities, although these have little influence as long as the
purity is equivalent to or more than that of first class grade
chemicals. Furthermore, Al.sub.2O.sub.3 and SiO.sub.2 may be
admixed therewith during manufacture, and degradation of
piezoelectric characteristics does not occur by a great degree as
long as the concentrations of these impurities are and 1,000 ppm or
less.
[0034] In the present invention, when a is less than 0.93 or
exceeds 1.02, sinterability is degraded so that a sintered material
having sufficient strength cannot be produced due to inferior
sinterability.
[0035] When x is less than 0.32 or exceeds 0.50, the impedance
ratio and the electromechanical coupling coefficient are reduced.
Likewise, when y is less than 0.41, although the impedance ratio is
high, the heat resistance is remarkably degraded. When y exceeds
0.54, the electromechanical coupling coefficient and the impedance
ratio are reduced. Likewise, when z is less than 0.03, or exceeds
0.21, the impedance ratio and the electromechanical coupling
coefficient are reduced.
[0036] In addition, when m+n is 0.24 or less or exceeds 0.67, the
sinterability is inferior, and many different phases are present,
so that desired sintered material may not be produced.
[0037] In particular, when m+n is 0.46 or more but 0.67 or less, m
is 0.01 to 0.66, and n is 0.01 to 0.66, the electromechanical
coupling coefficient can be effectively improved, so that this case
is preferable.
[0038] The piezoelectric ceramic obtained by sintering the
piezoelectric ceramic composition comprises as a primary component
an oxide having a perovskite structure. At least one element
selected from the group consisting of Ba, Ca and Sr may substitute
for Pb constituting A site of the perovskite structure, and in such
a case, degradation of the piezoelectric characteristics is not
likely to occur. Herein, the rate of substitution of Pb element by
Sr, Ba or Ca in the piezoelectric ceramic composition is preferably
specified to be within the range of about 10% by mol or less of
Pb.
[0039] Preferably, in the piezoelectric ceramic obtained by
sintering the piezoelectric ceramic composition, a grain size is
specified to be about 3 .mu.m or less.
[0040] Furthermore, the sizes of pores and defects formed in the
piezoelectric ceramic are preferably specified to be about 3 .mu.m
or less.
[0041] In a specified piezoelectric ceramic according to of the
present invention, the absolute value of a change rate of resonant
frequency with respect to temperature is preferably specified to be
about 100 ppm/.degree. C. or less.
[0042] The piezoelectric ceramic according to the present invention
is suitably used for a surface acoustic wave device using a SH type
surface acoustic wave. When the SH type surface wave is used, the
surface acoustic wave device can be further miniaturized compared
to a surface acoustic wave device using a Rayleigh wave.
[0043] Hereinafter preferred embodiments of the present invention
will be described in more detail.
[0044] As materials, powders of Pb.sub.3O.sub.4, NiO, MnCO.sub.3,
Nb.sub.2O.sub.3, TiO.sub.2 and ZrO.sub.2 was prepared. These
powders were weighed in order to have each of compositions as shown
in the following Table 1 to Table 5, and after addition of water,
wet mixing was performed with a ball mill so as to produce
slurry.
[0045] The resulting slurry was dehydrated, and the resulting mixed
powder was dried with an oven and was subjected to particle sizing,
thereby obtaining a piezoelectric ceramic composition.
[0046] Subsequently, sized mixed powder was put in a box made of
alumina, and was calcined at a temperature of 800.degree. C. to
1,000.degree. C. so as to produce a calcined material.
[0047] A binder and a dispersing agent were added to the
aforementioned calcined material, and these were wet-mixed with a
ball mill so as to produce a second slurry. The second slurry was
poured into a mold having the plan shape of a square, and cast
molding was performed. The resulting square plate-like molding was
degreased at 300.degree. C. to 600.degree. C., and thereafter, was
baked at 1,000.degree. C. to 1,300.degree. C. in an atmosphere of
oxygen so as to produce a sintered piezoelectric ceramic.
[0048] The surface of the resulting sintered piezoelectric ceramic
was finished by lapping so as to produce a piezoelectric substrate
of 5 cm by 5 cm having a thickness of 0.4 mm to 0.8 mm.
[0049] Polarization electrodes were formed on the piezoelectric
substrate produced as described above, and polarization was
performed at 100.degree. C. in oil with field intensity of 3 kV/mm.
Thereafter, aging was performed at a temperature of 200.degree. C.
for 1 hour.
[0050] A plurality of IDTs were formed on the aged piezoelectric
substrate by photolithography, and each of surface acoustic wave
devices was cut from the resulting piezoelectric substrate. The
surface acoustic wave device produced as described above is shown
in FIG. 2.
[0051] In the surface acoustic wave device 1, an interdigital
transducer (IDTs) 3 is formed on a piezoelectric substrate 2 made
of the aforementioned piezoelectric ceramic composition. The
outermost electrode fingers of IDTs 3 are flush with edges made by
end faces 2a and 2b and the top face of the piezoelectric substrate
2. The surface acoustic wave device 1 is an end face reflection
type surface wave resonator using a BGS wave as a SH type surface
wave. A reflector is not necessary here because of the end face
reflection type. Therefore, miniaturization can be planned.
[0052] In the production of the aforementioned surface acoustic
wave device 1, the compositions of the materials were variously
varied as described above so as to produce surface acoustic wave
devices of Sample Nos. 1 to 78. Subsequently, the electromechanical
coupling coefficients KBGS (%) of BGS wave, impedance ratios ATT
(dB), and change rates of resonant frequency with respect to
temperature (ppm/.degree. C.) were measured. Furthermore, the
particle diameter in each of the piezoelectric substrates was
determined by SEM observation. The results thereof are shown in
FIG. 1 and Table 1 to Table 5. Samples outside the scope of the
invention are indicated by an asterisk (*).
1TABLE 1 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)
(mol) (mol) (mol) (mol) (mol) (%) (dB) (.mu.m) (ppm/.degree. C.) 1
1.000 0.167 0.167 0.500 0.470 0.030 29.6 41.6 3.0 42 2* 1.000 0.167
0.167 0.370 0.600 0.030 17.2 28.6 3.5 -27 3 1.000 0.167 0.167 0.485
0.465 0.050 34.8 52.3 1.5 51 4 1.000 0.167 0.167 0.488 0.463 0.050
40.7 53.3 1.6 -73 5 1.000 0.167 0.167 0.490 0.460 0.050 43.1 58.3
1.4 -122 6 1.000 0.167 0.167 0.410 0.530 0.060 24.8 49.5 1.7 103 7
1.000 0.167 0.167 0.400 0.540 0.060 23.7 47.3 1.5 -32 8* 1.000
0.167 0.167 0.390 0.550 0.060 22.1 39.5 1.7 -29 9 1.000 0.156 0.177
0.482 0.451 0.067 34.2 41.5 2.9 34 10 1.000 0.155 0.178 0.472 0.450
0.078 48.1 48.2 2.5 153 11 1.000 0.167 0.167 0.470 0.450 0.080 43.3
42.5 3.8 170 12 1.000 0.156 0.177 0.467 0.449 0.084 53.3 52.0 2.4
184 13 1.000 0.167 0.167 0.500 0.410 0.090 49.2 52.4 2.0 -100 14
1.000 0.167 0.167 0.440 0.470 0.090 45.9 49.8 2.1 79 15 1.000 0.167
0.167 0.370 0.540 0.090 29.5 43.5 2.2 15 16 1.000 0.156 0.178 0.462
0.448 0.090 54.5 54.3 2.1 98 17 1.000 0.156 0.178 0.463 0.447 0.090
59.3 53.2 2.3 80 18 1.000 0.156 0.178 0.462 0.448 0.090 56.7 56.4
2.2 124
[0053]
2TABLE 2 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)
(mol) (mol) (mol) (mol) (mol) (%) (dB) (.mu.m) (ppm/.degree. C.)
19* 1.000 0.167 0.167 0.500 0.370 0.130 40.2 43.5 2.1 -301 20 1.000
0.167 0.167 0.460 0.410 0.130 55.3 50.8 2.2 -50 21 1.000 0.167
0.167 0.400 0.470 0.130 34.2 48.9 2.0 39 22 1.000 0.167 0.167 0.330
0.540 0.130 27.4 44.3 2.0 -20 23 1.000 0.156 0.178 0.418 0.442
0.140 43.4 51.2 2.0 -19 24 1.000 0.156 0.178 0.380 0.480 0.140 30.0
49.4 2.1 21 25 1.000 0.156 0.177 0.386 0.441 0.173 33.0 46.7 2.4 15
26 1.000 0.156 0.178 0.380 0.440 0.180 32.3 45.9 2.0 22 27 1.000
0.156 0.178 0.370 0.450 0.180 32.7 50.8 2.6 51 28 1.000 0.156 0.178
0.390 0.430 0.180 37.1 51.0 2.2 -91 29 1.000 0.156 0.178 0.360
0.460 0.180 26.4 45.7 2.1 -12 30 1.000 0.156 0.178 0.350 0.450
0.200 27.1 46.5 2.3 -16 31 1.000 0.167 0.167 0.380 0.410 0.210 29.2
45.8 1.9 -31 32 1.000 0.167 0.167 0.320 0.470 0.210 25.0 41.9 2.0
21 33* 1.000 0.156 0.178 0.330 0.450 0.220 23.3 39.4 3.2 -32 34*
1.000 0.167 0.167 0.320 0.410 0.270 20.3 36.3 1.8 -30 35* 1.000
0.167 0.167 0.440 0.540 0.020 11.7 21.5 3.2 81 36 1.000 0.156 0.177
0.500 0.470 0.030 31.6 45.1 2.7 40 37 1.000 0.156 0.177 0.430 0.540
0.030 28.3 43.8 2.6 28 38 1.000 0.167 0.167 0.470 0.450 0.080 44.3
49.1 2.1 127
[0054]
3TABLE 3 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)
(mol) (mol) (mol) (mol) (mol) (%) (dB) (.mu.m) (ppm/.degree. C.) 39
0.980 0.292 0.334 0.488 0.463 0.050 58.1 54.1 1.6 -30 40 1.000
0.292 0.334 0.488 0.463 0.050 60.8 56.7 1.6 -53 41 1.020 0.292
0.334 0.488 0.463 0.050 59.0 55.3 1.5 -81 42 0.960 0.155 0.178
0.472 0.450 0.078 37.5 46.0 2.2 245 43 0.980 0.155 0.178 0.472
0.450 0.078 46.3 48.9 2.7 220 44 1.000 0.155 0.178 0.472 0.450
0.078 48.1 48.2 2.5 153 45 0.980 0.156 0.178 0.463 0.447 0.090 50.1
51.5 2.1 259 46 1.000 0.156 0.178 0.463 0.447 0.090 59.3 53.2 2.3
80 47 1.010 0.156 0.178 0.463 0.447 0.090 54.4 53.3 2.0 79 48 1.020
0.156 0.178 0.463 0.447 0.090 51.5 51.7 2.3 136 49 0.930 0.119
0.119 0.455 0.436 0.109 35.3 45.0 2.4 84 50 0.950 0.119 0.119 0.455
0.436 0.109 41.0 46.6 2.0 64 51 0.969 0.119 0.119 0.455 0.436 0.109
47.5 49.4 2.5 43 52 1.000 0.119 0.119 0.455 0.436 0.109 49.8 51.2
2.6 21 53 0.980 0.156 0.178 0.380 0.440 0.180 37.8 51.3 2.2 18 54
1.000 0.156 0.178 0.380 0.440 0.180 32.3 45.9 2.0 22 55 0.980 0.156
0.178 0.370 0.450 0.180 32.0 49.8 2.3 27 56 1.000 0.156 0.178 0.370
0.450 0.180 32.7 50.8 2.6 51 57 0.980 0.156 0.178 0.360 0.460 0.180
26.1 44.4 2.2 -20 58 1.000 0.156 0.178 0.360 0.460 0.180 26.4 45.7
2.1 -12
[0055]
4TABLE 4 particle a m n x y z kBGS ATT diameter fr-TC No. (mol)
(mol) (mol) (mol) (mol) (mol) (%) (dB) (.mu.m) (ppm/.degree. C.) 59
1.000 0.656 0.010 0.490 0.470 0.040 50.9 58.0 2.2 101 60 1.000
0.500 0.166 0.495 0.465 0.040 52.7 53.6 2.3 -33 61 1.000 0.333
0.333 0.495 0.465 0.040 53.1 58.5 2.3 -40 62 1.000 0.160 0.500
0.495 0.465 0.040 52.0 59.0 2.4 -49 63 1.000 0.010 0.656 0.490
0.470 0.040 49.7 55.9 2.2 42 64 1.000 0.167 0.167 0.490 0.460 0.050
43.1 58.3 1.4 -122 65 1.000 0.292 0.334 0.490 0.460 0.050 63.5 59.3
1.5 -97 66 1.000 0.333 0.333 0.490 0.460 0.050 63.9 59.0 1.7 -60 67
1.000 0.167 0.167 0.488 0.463 0.050 40.7 53.3 1.6 -73 68 1.000
0.230 0.230 0.488 0.463 0.050 51.5 54.1 1.8 -61 69 1.000 0.292
0.334 0.488 0.463 0.050 60.8 56.7 1.6 -53 70 1.000 0.333 0.333
0.488 0.463 0.050 61.2 57.4 1.4 40 71 1.000 0.167 0.167 0.485 0.465
0.050 34.8 52.3 1.5 51 72 1.000 0.292 0.334 0.485 0.465 0.050 54.2
54.7 1.5 96 73 1.000 0.333 0.333 0.485 0.465 0.050 56.1 55.8 1.8
104 74 1.000 0.119 0.119 0.470 0.450 0.080 48.5 48.1 2.2 38 75
1.000 0.139 0.139 0.470 0.450 0.080 52.8 55.2 2.3 65 76* 1.000
0.167 0.167 0.470 0.450 0.080 38.2 38.4 3.8 170
[0056]
5TABLE 5 particle a m n x y z Sr kBGS ATT diameter fr-TC No. (mol)
(mol) (mol) (mol) (mol) (mol) (mol) (%) (dB) (.mu.m) (ppm/.degree.
C.) 77 0.950 0.015 0.017 0.458 0.493 0.050 0.050 51.2 58.2 1.8 -21
78 0.950 0.015 0.024 0.465 0.485 0.050 0.050 44.2 55.3 2.3 36
[0057] Sample Nos. 1 to 38 in Tables 1 and 2 are examples in which
x, y, and z are varied while a=1 and m+n=1/3 in the aforementioned
formula. FIG. 1 shows changes of the electromechanical coupling
coefficient with changes of y and z in the aforementioned
cases.
[0058] As is clear from FIG. 1, the electromechanical coupling
coefficients vary with changes of z, and reach maximum values in
the neighborhood of z=0.1. It is clear that the impedance ratios
(ATT) are sufficiently large, 40 dB or more, in the range of
0.03.ltoreq.z.ltoreq.0.21. On the other hand, in Sample Nos. 33,
34, and 35, which are out of the range of
0.03.ltoreq.z.ltoreq.0.21, sinterability is degraded and the
impedance ratios are reduced.
[0059] When y>0.54, the impedance ratios are reduced, and when
y<0.41, the impedance ratios and the electromechanical coupling
coefficients are large, although heat resistance is degraded.
[0060] Since x satisfies x+y+z=1, if y or z becomes out of the
aforementioned preferable range as a result of selection of x,
characteristics are degraded.
[0061] As is confirmed from the results shown in Tables 1 and 2,
the impedance ratios are excellent when x falls within the range of
0.32.ltoreq.x.ltoreq.0.50.
[0062] In Sample Nos. 39 to 58 as shown in Table 3, the value of a
is varied in the range of 0.93 to 1.02, while x, y and z fall
within the aforementioned preferable ranges. As is clear from Table
3, the impedance ratios and the electromechanical coupling
coefficients are not degraded by a large degree in spite of changes
of a. Therefore, it is clear that excellent piezoelectric
characteristics can be exhibited when a falls within the range of
0.93.ltoreq.a.ltoreq.1.02. When a is out of this range,
sinterability is degraded.
[0063] Table 4 shows examples of Sample Nos. 59 to 76 in which m
and n are varied while x, y, and z fall within the preferable
ranges determined from Tables 1 and 2. It is usually believed that
the perovskite structure is stable when m+n=1/3.
[0064] However, it is clear from the results of Sample Nos. 59 to
76 that the impedance ratios become 40 or more when m +n falls
within the range of 0.24.ltoreq.m+n.ltoreq.0.67, and the impedance
ratios are not degraded compared to that in the case where m+n
=1/3. In particular, it is clear that when m and n fall within the
ranges of 0.46.ltoreq.m+n.ltoreq.0.67, 0.01.ltoreq.m.ltoreq.0.66
and 0.01.ltoreq.n.ltoreq.0.66, the electromechanical coupling
coefficients KBGS preferably become very large, e.g., 50.9% or
more.
[0065] Table 5 shows Sample Nos. 77 and 78 in which Sr was
substituted for part of the Pb in the A site. It is clear that high
impedance ratios and electromechanical coupling coefficients kBGS
can also be achieved in compositions in which Sr is present at the
A site.
[0066] The impedance ratios are reduced for Sample Nos. 3, 13, and
76 in which particle diameters of the sintered materials exceed
about 3 .mu.m. Therefore, the particle diameter of the sintered
material is preferably about 3 .mu.m or less. Regarding defects and
pores in the sintered material, effects similar to those in the
above description are exhibited, so that, as is assumed from the
actions due to the changes of the particle diameter of the sintered
material, the defects and pores are also preferably about 3 .mu.m
or less.
[0067] With the Samples which are within the scope of the present
invention, excellent impedance ratios can be achieved and a wide
range of electromechanical coupling coefficients kBGS of about 30%
to about 50% can be achieved.
[0068] In the aforementioned examples, the case where the present
invention has been applied to the end face reflection type surface
wave device using a SH type surface wave has been explained,
although the piezoelectric ceramic composition for a surface
acoustic wave device according to the present invention can be used
for surface acoustic wave devices using surface waves, such as a
Rayleigh wave, other than SH type.
* * * * *