Film bulk acoustic wave device

Embodiments of the present invention provide a small and well-characterized bulk acoustic wave device by fabricating a filter having a wide band width or a resonator having a wide oscillation frequency range together with a semiconductor circuit. In embodiments of the present invention, a bulk acoustic wave device comprises a semiconductor substrate having a dielectric substance layer thereon, the dielectric substance layer has a ground conductor layer thereon, the ground conductor layer has a piezoelectric ceramic thin film thereon and the piezoelectric ceramic thin film has a conductive electrode pattern thereon. The thickness of the piezoelectric ceramic thin film is more than ten times the thickness of the ground conductor layer, and the wave number of acoustic waves that propagate in a direction parallel to a surface of the piezoelectric ceramic thin film multiplied by the thickness of the piezoelectric ceramic thin film is less than 2.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a bulk acoustic wave device using an acoustic 
wave, such as a resonator and a filter, and an electronics device which 
utilizes the bulk acoustic wave device. 
2. Description of Related Arts 
The bulk acoustic wave device operates as the resonator and the filter by 
using the piezoelectric material, which performs transformation between an 
electric signal and the acoustic wave. 
FIG. 54 shows a conventional type of the bulk acoustic wave device 
described in the literatures, for example, the literature "1983 IEEE 
Ultrasonics Symposium, pp.299-310" (hereinafter, referred to as reference 
1), Japanese Unexamined Patent Publication Number sho 63-187713 
(hereinafter, referred to as reference 2), and the literature "IEEE, 41st 
Annual Frequency Control Symposium, pp.371-381, 1987" (hereinafter, 
referred to as reference 3). A semiconductor substrate 1 is, for instance, 
silicon (Si) or gallium arsenide (GaAs). A piezoelectric thin film 2 is 
such as zinc oxide (ZnO) or aluminum nitride (AlN). And, a semiconductor 
circuit 3 is provided. 
As to a device using the piezoelectric thin film 2, there can be two cases. 
One is a case where a surface acoustic wave device as shown in reference 1 
is used and the other is a case where the film bulk acoustic wave device 
as shown in the references 2 and 3 is used. The surface acoustic wave 
device configures an interdigital transducer on the surface of the 
piezoelectric thin film 2. The surface acoustic wave device can realize 
the resonator, the filter, a delay line, a correlator and so on. On the 
other hand, the bulk acoustic wave device can realize a bulk ultrasonic 
resonator, and a bulk acoustic wave filter which consist of the bulk 
acoustic wave resonators. The surface acoustic wave resonator and the bulk 
ultrasonic wave resonator have different structures each other but have 
almost the same electric function. Hereinafter, there is shown a case of 
the bulk acoustic wave device. 
FIGS. 55 and 56 show a conventional type of the bulk acoustic wave 
resonator shown in the references 2 and 3, and the literature "1985 IEEE 
Ultrasonic Symposium, pp.311-318" (hereinafter, referred to as reference 
4), "1990 IEEE Ultrasonics Symposium, pp.529-536" (hereinafter, referred 
to as reference 5), Japanese Unexamined Patent Publication Number hei 
6-350154" (hereinafter, referred to as reference 6) and so on. FIG. 55 
shows an upper-side view of this conventional type of the bulk ultrasonic 
wave resonator. FIG. 56 shows an A--A cross sectional view of the bulk 
ultrasonic wave resonator shown in FIG. 55. In FIG. 56, silicon oxide 
(SiO.sub.2) 4 is provided. A ground conductor 5 is composed of a 
semiconductor in which impurity is doped with high concentration. The 
ground conductor 5 may be one of metals. A top-side electrode 6 is 
composed of one of metals and a via hole 7 is provided. 
The operation will now be described. In FIG. 56, when the voltage is 
applied between the ground conductor 5 and the top-side electrode 6, there 
occurs an electric field in the piezoelectric thin film 2. The 
piezoelectric thin film 2 has a characteristic in that deformation or 
strain is caused when the electric field is generated. Then, when the 
applied voltage oscillates, an acoustic wave is excited in the 
piezoelectric thin film 2 corresponding to the applied voltage. The 
direction of propagation of the excited acoustic wave, the direction of 
displacement of elastic vibration and the excitation efficiency of the 
acoustic wave for the applied voltage is determined by the materials of 
the piezoelectric thin film 2 in use, the shapes of the ground conductor 5 
and the top-side electrode 6, and so on. In the following discussion, it 
is assumed that the direction of propagation of the acoustic wave is in 
the direction of thickness of the piezoelectric thin film 2, this 
direction corresponding to the direction from the ground conductor 5 to 
the top-side electrode 6. And, it is assumed that the direction of 
displacement of elastic vibration is the direction of thickness of the 
piezoelectric thin film 2. 
The acoustic wave is excited in the region between the top-side electrode 6 
and the ground conductor 5 where an electric field exists. Therefore, 
approximately, the acoustic wave is excited in the region between the 
top-side electrode 6 and the ground conductor 5. Since the excited 
acoustic wave is propagated in the direction of the thickness of the 
piezoelectric thin film, it is reflected on the faces touching the air, 
i.e., the surface 6a of the top-side electrode 6 and the bottom side 4a of 
silicon oxide 4. This is because the acoustic impedance of the solid 
medium, like the top-side electrode 6, the piezoelectric thin film 2, the 
ground conductor 5 and silicon oxide 4 is far different from the acoustic 
impedance of the air. The surface 6a and bottom side 4a facing to the air 
can be substantially regarded as the complete reflector. The boundary 
condition on such a surface is disclosed in the literature such as in 
"Supervised by Onoue, The Basics of Solid Oscillation Theory, issued on 
September, 1982, Ohmu-sha, Chapter 5, Wave on Infinite Plate, pp. 77-116" 
(hereinafter, referred to as reference 7). Accordingly, in the bulk 
ultrasonic wave resonator having the configuration as shown in FIG. 56, 
the material of the semiconductor substrate 1 does not directly affect the 
excitation characteristic of the acoustic wave. 
The acoustic wave is contained between the surface 6a of the top-side 
electrode 6 and the bottom side 4a of silicon oxide 4. Resonance occurs 
approximately around the frequency at which the length between the surface 
6a of the top-side electrode 6 and the bottom side 4a of silicon oxide 4 
is an integer multiple of the half wave length of the acoustic wave. 
Namely, the bulk acoustic wave device as shown in FIG. 56 operates as a 
bulk ultrasonic wave resonator. Silicon oxide 4 is thin and its density is 
low in general, compared to the top-side electrode 6, the ground conductor 
5 and the piezoelectric thin film 2. Accordingly, contributions to the 
elastic resonance condition by silicon oxide 4 can be regarded to be low. 
FIG. 57 shows a simplified configuration of the bulk ultrasonic wave 
resonator. The simplified configuration has a triple layer structure 
composed of the top-side electrode 6, piezoelectric thin film 2 and the 
ground conductor 5. The simplified configuration may be used to represent 
the bulk acoustic wave resonator when the triple layer structure 
essentially determines the resonance condition. In the figure, the 
resonance device 8 operates as the resonator. 
In FIG. 57, each of the thicknesses of the top-side electrode 6 and the 
ground conductor 5 is assumed to be d and the thickness of the 
piezoelectric thin film 2 is assumed to be h. When the load effects of the 
top-side electrode 6 and the ground conductor 5 are ignored, the resonant 
frequency f.sub.r is calculated by expression 1. 
expression 1: 
EQU 2f.sub.r =n(h/V.sub.p +d/V.sub.m).sup.-1 
In expression 1, n is an integer, V.sub.p is the propagation velocity of an 
acoustic wave in the piezoelectric thin film 2, V.sub.m is the propagation 
velocity of an acoustic wave of the top-side electrode 6 and the ground 
conductor 5. The propagation velocities V.sub.p and V.sub.m are determined 
by the materials used for the piezoelectric thin film 2, the top-side 
electrode 6 and the ground conductor 5, as well as the direction of 
propagation and the direction of vibration. The actual resonant frequency 
of the resonance device as shown in FIG. 57 is lower than the resonant 
frequency f.sub.r calculated by expression 1 due to the load effects of 
the top-side electrode 6 and the ground conductor 5 which are ignored in 
expression 1. The relationship between the resonant frequency and the load 
effects is described in the literature in "Supervised by Onoue, The Basics 
of Solid Oscillation Theory, issued on September, 1982, Ohmu-sha, Chapter 
9, Wave of Piezoelectric Plate, pp. 189-195" (hereinafter, referred to as 
reference 8). 
As shown in reference 5, the acoustic velocity of the piezoelectric 
material is approximately 6000 m/sec for zinc oxide and approximately 
10000 m/sec for aluminum nitride. The thin film piezoelectric resonator as 
shown in FIG. 57 is configurated by using such piezoelectric material. For 
example, in a case where the resonant frequency of the fundamental wave 
(n=1) is 2 GHz, even when each of the thicknesses d of the top-side 
electrode 6 and the ground conductor 5 is ignored, the thickness h of the 
piezoelectric thin film 2 is calculated as 1.5 .mu.m to 2.5 .mu.m. Namely, 
an extremely thin film thickness is required. Additionally, when each of 
the thicknesses d of the top-side electrode 6 and the ground conductor 5 
is considered, the required film thickness h of the piezoelectric thin 
film 2 is thinner. Piezoelectric thin films used in the conventionally 
well-known piezoelectric resonators and conventionally well-known 
piezoelectric filters for the intermediate frequency (hereinafter, 
referred to as IF) band are produced by planing plate materials. The 
planing method cannot be used to produce a piezoelectric thin film having 
several .mu.m thickness. 
The characteristics of the thin film piezoelectric resonator shown in FIG. 
57 are basically the same as that of conventionally well-known crystal 
oscillators and conventionally well-known ceramic oscillators for the IF 
band using the plate material. The crystal oscillator and the ceramic 
oscillator are described in detail, for example, in the literature in 
"Acoustic wave Device Technology Handbook, edited by the Japan Society for 
the Promotion of Science Acoustic wave Device Technology The 150th 
committee, issued by Ohmu-sha, the 1st edition issued on Nov. 30, 1991, 
volume II, Bulk Wave Device, Chapter 3, Piezoelectric Bulk Wave Device, 
pp. 90 to 143" (hereinafter, referred to as reference 9). 
As described in the reference 9, FIG. 58 shows an equivalent circuit of the 
bulk ultrasonic wave resonator shown in FIG. 57. In the figure, a capacity 
C.sub.0 9 is coupled between the top-side electrode 6 and the ground 
conductor 5. An equivalent inductance L.sub.1 10, an equivalent capacity 
C.sub.1 11 and an equivalent resistance R.sub.1 12 are coupled in series. 
FIG. 59 shows a representative characteristic impedance of the equivalent 
circuit shown in FIG. 58. 
The equivalent circuit in FIG. 58 resonates at frequency F.sub.r. The 
frequency F.sub.r is the frequency which the equivalent inductance L.sub.1 
10 and the equivalent capacity C.sub.1 11 resonate in series. When the 
equivalent resistance R.sub.1 is zero, the impedance comes to be zero. The 
equivalent circuit antiresonates at frequency F.sub.a. The frequency 
F.sub.a is a frequency in which the capacity C.sub.0 9, the series circuit 
of the equivalent inductance L.sub.1 10 and the equivalent capacity 
C.sub.1 11 resonate in parallel. When the equivalent resistance R.sub.1 is 
zero, the impedance comes to be infinite. The characteristic impedance in 
FIG. 59 shows a case where the equivalent resistance R.sub.1 is not zero 
and therefore the impedance at frequency F.sub.a shows a finite value. 
There is a unique relationship among the capacity C.sub.0 9, the equivalent 
inductance L.sub.1 10, the equivalent capacity C.sub.1 11, the resonant 
frequency F.sub.r and the antiresonant frequency F.sub.a. The following 
expressions 2 and 3 are disclosed in reference 9. 
##EQU1## 
Additionally, Q.sub.m, a quality factor of the resonator, is related to the 
circuit constant of the equivalent circuit shown in FIG. 58 and the 
following expression 4 for Q.sub.m is disclosed in reference 9. 
##EQU2## 
The frequency f.sub.r shown in the expression 1 is an approximate value of 
the resonant frequency F.sub.r and the antiresonant frequency F.sub.a. 
Strictly, the value is determined by the materials and physical shapes of 
the top-side electrode 6 and the ground conductor 5, and the material, the 
direction of crystallization and the physical shape of the piezoelectric 
thin film 2. In addition, Q.sub.m and the difference between the resonant 
frequency F.sub.r and the antiresonant frequency F.sub.a are mostly 
determined by the material and the direction of crystallization of the 
piezoelectric thin film 2. The difference between the resonant frequency 
F.sub.r and the antiresonant frequency F.sub.a largely affects the maximum 
frequency adjustment range when an oscillator circuit is configured using 
the bulk ultrasonic wave resonator and affect the maximum passband width 
when a filter is configured with the bulk ultrasonic wave resonators. 
The effective electromechanical coupling factor k.sup.2.sub.eff is 
calculated as the following expression 5 by using the resonant frequency 
F.sub.r and the antiresonant frequency F.sub.a. 
##EQU3## 
The effective electromechanical coupling constant k.sup.2.sub.eff is 
determined based on the materials, the direction eff of crystallization of 
the piezoelectric thin film 2 and the direction of propagation and the 
direction of vibration of the acoustic wave. This is described in the 
literature in "Ultrasonic Wave Technology Handbook, Daily Technical 
Newspaper Publishing Company, the 8th edition issued on Jun. 25, 1991, pp. 
363 to 371" (hereinafter, referred to as reference 10). When the 
electromechanical coupling constant k.sup.2 is assumed as the maximum 
value of the electromechanical coupling constant k.sup.2.sub.eff, the 
frequency difference .DELTA.F between the resonant frequency F.sub.r and 
the antiresonant frequency F.sub.a can be calculated by the following 
expression 6. 
##EQU4## 
FIG. 60 shows an example of the characteristic impedance of a bulk 
ultrasonic wave resonator. In the bulk ultrasonic wave resonator, the 
frequency, at which the impedance varies from the capacitive reactance 
area to the inductive reactance area as the frequency increases and the 
reactance component comes to be zero, is set to be F.sub.r. The frequency, 
at which the impedance varies from the inductive reactance area to the 
capacitive reactance area and the reactance component comes to be zero, is 
set to be F.sub.a. The frequency F.sub.r is the resonant frequency as 
shown in expressions 2 to 5 and the frequency F.sub.a is the antiresonant 
frequency. 
FIG. 61 is a basic portion of the oscillator circuit of a Colpitts type 
which is conventionally well known. In the figure, a transistor 13, 
condensers C.sub.C, C.sub.B 14, and a bulk ultrasonic wave resonator 15 
are provided. 
One of the conditions where the oscillator circuit as shown in FIG. 61 
oscillates is approximately shown in the following expression 7, when it 
is assumed that the affect of the transistor 13 is small. The oscillator 
circuit is described in detail in the literature in "High Frequency, 
Oscillation, Modulation and Demodulation, Tokyo Electric College 
publishing co., the first edition issued on May 10, 1986" (hereinafter, 
referred to as reference 11) on pp. 49 to 91. 
expression 7: 
EQU 1/j.omega.C.sub.C +1/j.omega.C.sub.B +1/Y=0 
In the expression 7, .omega. is the angular frequency and Y is the 
admittance of the bulk ultrasonic wave resonator 15. Admittance Y is 
calculated by the following expression 8 based on the equivalent circuit 
in FIG. 58. 
##EQU5## 
In order to satisfy expression 7, it is necessary that the bulk ultrasonic 
wave resonator 15 have an inductive reactance characteristic. Therefore, 
the possible frequency range of oscillation is limited to the range within 
F.sub.r and F.sub.a. Namely, by using the bulk ultrasonic wave resonator 
15 having the characteristics shown in FIG. 60, the frequency range which 
can be oscillated is smaller than the frequency difference .DELTA.F 
between the resonant frequency F.sub.r and the antiresonant frequency 
F.sub.a. 
In a case where a stable oscillation is required at a specified frequency, 
the resonator with a narrow band width, whose frequency difference 
.DELTA.F between the resonant frequency F.sub.r and the antiresonant 
frequency F.sub.a is small, is appropriate. Conventionally, when stable 
oscillation is required at a specified frequency, as disclosed in the 
reference 9, a quartz resonator has been used widely. Since quartz has an 
extremely small electromechanical coupling constant k.sup.2, the frequency 
difference .DELTA.F between the resonant frequency F.sub.r and the 
antiresonant frequency F.sub.a is extremely small and the temperature 
characteristic is stable. As a result, when an oscillator circuit is 
configured using quartz, the stability of the oscillation frequency is 
extremely large. However, since the piezoelectric thin film 2 is not 
configured using quartz, it is impossible to configure the bulk ultrasonic 
wave resonator using the piezoelectric thin film 2 shown in FIG. 56. In 
addition, since the frequency difference .DELTA.F between the resonant 
frequency F.sub.r and the antiresonant frequency F.sub.a is extremely 
small in case of the quartz, the frequency variable range when the voltage 
control oscillator (VCO) is configured by the quartz is extremely narrow. 
When the high stability, provided by quartz is not required, for example, 
as shown in references 2 and 3, a bulk ultrasonic wave resonator using 
zinc oxide (ZnO) and aluminum nitride (AlN) has been utilized. A bulk 
ultrasonic wave resonator using zinc oxide (ZnO) and aluminum nitride 
(AlN) cannot provide high stability oscillation as a quartz oscillator 
does by itself. Therefore, either the condenser C.sub.B 14 or the 
condenser C.sub.C 14 is replaced by a variable capacitance diode and so 
forth. The capacitance of the variable capacitance diode is varied based 
on the applied voltage to the diode. Accordingly, the bulk ultrasonic wave 
resonator can be used as a VCO with a variable oscillation frequency. In 
this case, the limitation of the frequency range which can be oscillated 
depends on the electromechanical coupling constant k.sup.2. Namely, 
according to the material of the piezoelectric thin film 2, the possible 
oscillation frequency range can be determined. 
FIG. 62 shows an example of one section of a circuit view of the bulk 
ultrasonic wave filter which is conventionally well-known and configurated 
by connecting the bulk ultrasonic wave resonators 15a and 15b in a ladder 
circuit. In the figure, the input terminal 16, an output terminal 17, and 
a ground terminal 18 are provided. FIG. 63 shows a view of the 
characteristic impedance of each of the bulk ultrasonic wave resonators 
15a and 15b which configure the bulk ultrasonic wave filter shown in FIG. 
62. In the figure, the characteristic impedance 19 is the impedance of the 
bulk ultrasonic wave resonator 15a which is a shunt element in FIG. 62, 
and the characteristic impedance 20 is characteristic impedance of the 
bulk ultrasonic wave resonator 15b which is a series element in FIG. 62. 
FIG. 64 shows the frequency responses of the bulk ultrasonic wave filter 
shown in FIG. 62. 
When the filter is configurated by using the ladder shaped connection as 
shown in FIG. 62, as disclosed in the reference 9, the antiresonant 
frequency F.sub.ap of the bulk ultrasonic wave resonator 15a which is the 
shunt element and the resonant frequency F.sub.rs of the bulk ultrasonic 
wave resonator 15b which is the series element are set to be almost the 
same frequency. Around these frequencies F.sub.ap and F.sub.rs, the bulk 
ultrasonic wave resonator 15a (the shunt element) has almost infinite 
impedance. The bulk ultrasonic wave resonator 15b (the series element) has 
an impedance which can be regarded as almost a short-circuit. Then, the 
electric characteristics between the input terminal 16 and the output 
terminal 17 can be regarded as almost a short-circuit and the circuit 
shown in FIG. 62 can be regarded as a transmission line. Namely, the bulk 
ultrasonic wave filter works as a filter which has a passband around 
frequency F.sub.ap and F.sub.rs. On the other hand, around the resonant 
frequency F.sub.rp, the bulk ultrasonic wave resonator 15a (the shunt 
element) has impedance to be regarded as almost short-circuit. Around the 
antiresonant frequency F.sub.as, the bulk ultrasonic wave resonator 15b 
(the series element) has almost infinite impedance. Hence, the electric 
characteristics between the input terminal 16 and the output terminal 17 
can be determined to be opened. The circuit shown in FIG. 62 provides an 
attenuation pole around the frequencies F.sub.rp and F.sub.as. 
Accordingly, the bulk ultrasonic wave filter which is configurated by 
connecting the bulk ultrasonic wave resonators 15a and 15b having the 
characteristic impedance shown in FIG. 63 as shown in FIG. 62 shows the 
passing characteristic as illustrated in FIG. 64. 
When the difference between the resonant frequency F.sub.rp and the 
antiresonant frequency F.sub.ap of the bulk ultrasonic wave resonator 15a 
of the shunt element and the difference between the resonant frequency 
F.sub.rs and the antiresonant frequency F.sub.as of the bulk ultrasonic 
wave resonator 15b are almost the same frequency difference .DELTA.F, the 
passband width based on the frequency responses shown in FIG. 64 cannot 
exceed 2.DELTA.F. The frequency difference, .DELTA.F, as shown in the 
expression 6, depends largely on the electromechanical coupling constant 
k.sup.2 of the piezoelectric thin film 2 and therefore the limiting value 
of the passband width of the bulk ultrasonic wave filter greatly depends 
on the material of the piezoelectric thin film 2. 
By replacing the bulk ultrasonic wave resonators 15a and 15b with the 
equivalent circuit shown in FIG. 58, the insertion loss or the attenuation 
volume at the attenuation pole of the bulk ultrasonic wave filter depends 
on the equivalent resistance of each bulk ultrasonic wave resonators 15a 
and 15b. Therefore, the frequency responses of the bulk ultrasonic wave 
filter such as the insertion loss, the passband width, and the attenuation 
at the attenuation pole depends on the electromechanical coupling constant 
k.sup.2 and Q.sub.m. 
FIGS. 65 and 66 show an example of a bulk ultrasonic wave filter using 
conventionally known multiple mode resonance. FIG. 65 shows an upper-side 
view and FIG. 66 shows a B--B cross sectional view. FIGS. 65 and 66 show a 
double mode filter described in the literature in "Applied Physics 
Letters, Vol.37, No.11, pp.993-995, Dec 1980" (hereinafter, referred to as 
reference 12). In the figure, a semiconductor substrate 1 is composed of 
silicon. A silicon layer 21 is epitaxialized on the semiconductor 
substrate 1. A ground conductor 5 has gold (Au) between titanium (Ti) 
layers. A piezoelectric thin film 2 is composed of zinc oxide (ZnO). A 
top-side electrode 6 is composed of aluminum (Al). A lead electrode on the 
input side 22, a lead electrode on the output side 23 and a via hole 7 are 
provided. 
FIG. 67 shows an example of the equivalent circuit of the bulk ultrasonic 
wave filter shown in FIG. 66. In the figure, equivalent circuit components 
C.sub.s, L.sub.s, R.sub.s in the symmetry mode resonance shown with 
subscript s, and the equivalent circuit components C.sub.a, L.sub.a, 
R.sub.a in asymmetry mode resonance shown with subscript a are coupled by 
a transformer T. The coupling amount or the coupling capacity C.sub.13 of 
the transformer T is determined by materials and thicknesses of the 
piezoelectric thin film 2, the top-side electrode 6 and the ground 
conductor 5, and the shape and the layout of the top-side electrode 6. As 
to the bulk ultrasonic wave filter in FIG. 66, reference 9 discloses the 
equivalent circuit shown in FIG. 67. Reference 9 also discloses that the 
bulk ultrasonic wave filter shown in FIGS. 65 and 66 has characteristics 
corresponding to one section of the bulk ultrasonic wave filter of the 
ladder connection as shown in FIG. 62. Namely, in the case of the bulk 
ultrasonic wave filter shown in FIGS. 65 and 66, the frequency responses 
of the bulk ultrasonic wave filter such as insertion loss, passband with, 
attenuation at the attenuation pole and so forth depend on the 
electromechanical coupling constant k.sup.2 and Q.sub.m of the 
piezoelectric thin film 2. 
As has been described, the characteristics of the bulk acoustic wave 
resonator and the bulk ultrasonic wave filter, are greatly affected by the 
electromechanical coupling constant k.sup.2 and Q.sub.m, which are the 
material characteristics of the piezoelectric thin film 2. The following 
table 1 is a representative value of the material constants of the main 
piezoelectric material shown in reference 9. Generally, the single crystal 
has an extremely large Q.sub.m and a large electromechanical coupling 
constant k.sup.2. But, it is used as a wafer and there is no report of a 
thin film having the characteristic equivalent to that of wafer. Ceramics 
has a feature of having a large electromechanical coupling constant 
k.sup.2 and a large dielectric constant. On the other hand, Q.sub.m is 
small. In ceramics, many various kinds of electromechanical coupling 
constants k.sup.2, Q.sub.m and dielectric constants may be achieved, by 
varying the compound ratio of the composite component and by adding a 
small amount of additions. Usually, the plate material, into which the 
ceramics is burnt, is used in the resonator and the filter to operate in 
the IF band. Reference 6 shows an example of a thin film using lead 
titanate-zirconate (PZT). As to thin films, conventionally, zinc oxide 
(ZnO) and aluminum nitride (AlN) are widely used although only zinc oxide 
is shown in the table 1. These materials have a smaller electromechanical 
coupling constant k.sup.2, compared to the single crystal and the 
ceramics. In addition, Q.sub.m has an intermediate value between the 
single crystal and the ceramics. 
TABLE 1 
______________________________________ 
electro 
speech relative mechanical 
mecha- 
velocity 
dielectric 
coupling 
nical 
classification 
(m/s) constant factor k.sup.2 
Q.sub.m 
______________________________________ 
single crystal 
crytal SiO.sub.2 
5740 4.5 0.11 &gt;100000 
OX 
lithium LiNbO.sub.3 
7360 39 0.49 &gt;100000 
niobate 35Y 
ceramics 
titanate 
PZT-4 4600 1300 0.7 500 
zirconate 
lead PbNb.sub.2 O.sub.6 
3300 300 0.4 (12) 
metaniobate 
lead PbTiO.sub.3 
3980 179 0.4 1240 
titanate 
thin film 
zinc ZnO 6330 8.8 0.28 -- 
oxide 
______________________________________ 
As has been described, various plate materials are used in bulk ultrasonic 
wave resonators for bulk ultrasonic wave filters to be used in the IF 
band, as disclosed in reference 9. However, in the bulk ultrasonic wave 
resonator and the bulk ultrasonic wave filter composing the piezoelectric 
thin film 2 on the semiconductor substrate 1, materials to be used are 
limited. Namely, as actual examples, there are zinc oxide (ZnO) and 
aluminum nitride (AlN) as disclosed in references 1, 2, 3, and 5 or lead 
titanate-zirconate (PZT) as disclosed in reference 6. According to table 1 
and references 3 and 5, the electromechanical coupling constant k.sup.2 of 
zinc oxide has a range of 0.02 to 0.1. The electromechanical coupling 
constant k.sup.2 of aluminum nitride (AlN) is 0.03. When a ratio of the 
frequency difference between the resonant frequency F.sub.r and the 
antiresonant frequency F.sub.a to the resonant frequency 
(.DELTA.F/F.sub.r) is calculated from these values by using expression 6, 
the ratio .DELTA.F/F.sub.r is from 1% to 5% for zinc oxide (ZnO) and about 
1% for aluminum nitride (AlN). Assuming that the electromechanical 
coupling constant k.sup.2 of lead titanate-zirconate (PZT) is 0.5, the 
ratio .DELTA.F/F.sub.r is about 22% for lead titanate-zirconate (PZT). 
When these materials are configured on the semiconductor substrate 1 as the 
piezoelectric thin film 2, the thin film is produced not by planing the 
plate material such as a wafer. The thin film is produced by a plate 
fabrication process such as vacuum evaporation, sputtering and so forth. 
Therefore, it is possible to fabricate the thin film having thickness of 
several microns. Further, it is possible to operate the thin film at a 
higher frequency than the bulk ultrasonic wave resonator and the bulk 
ultrasonic wave filter which operate in the conventional IF band. Since 
the bulk ultrasonic wave resonator and the bulk ultrasonic wave filter can 
be composed on the same substrate with that of the semiconductor circuit, 
it is possible to make a whole circuit small in size and light in weight. 
However, when the bulk ultrasonic wave resonator and the bulk ultrasonic 
wave filter are actually manufactured, manufacturing error surely occurs. 
Especially, it is difficult to control the thicknesses of the 
piezoelectric thin film 2, the top-side electrode 6, and the ground 
conductor, precisely. 
As to this conventional type of bulk ultrasonic wave resonator, in the 
literature in "Manufacture and Application of Piezoelectric Materials, 
issued by CMC, the 2nd edition issued on Aug. 5, 1985" (hereinafter, 
referred to as the reference 13), a method for adjusting the resonant 
frequency and the antiresonant frequency is described. Conventional 
methods include evaporating and adding metals to the top-side electrode 6, 
and trimming the top-side electrode 6 by using, for example, a laser, 
after configuring the bulk ultrasonic wave resonator, is adopted. FIG. 68 
shows the method of adjusting frequency of the conventional type of bulk 
ultrasonic wave resonator. In the figure, the portion 24 is where trimming 
is performed for the top-side electrode 6 by using a laser. 
As has been described, in the bulk ultrasonic wave resonator, approximately 
characterized by expression 1, at the frequency in which the sum of the 
thicknesses of the top-side electrode 6 and the piezoelectric thin film 2 
and the ground conductor 5 is a half wave length, the acoustic wave 
resonates. However, the mass loads of the top-side electrode 6 and the 
ground conductor 5 lower the resonant frequency from that determined using 
expression 1. As shown in FIG. 68, when trimming is performed for a part 
of the top-side electrode 6, the mass load in accordance with the top-side 
electrode 6 is slightly reduced. Therefore, the resonant frequency is 
increased. On the other hand, when metals are added by the means such as 
the vacuum evaporation to the top-side electrode 6, the resonant frequency 
gets lower. Further, when the resonant frequency varies, the antiresonant 
frequency also varies, as it is linked with the resonant frequency. 
Such a method for frequency adjustment can be used for adjusting each bulk 
ultrasonic wave resonator, independently. Therefore, it is necessary to 
know the mass amount for adding or trimming precisely. As a result, the 
adjustment cost becomes higher. Where only the bulk ultrasonic wave 
resonator and only the bulk ultrasonic wave filter, consisting of the bulk 
ultrasonic wave resonators, are manufactured, it is possible to 
manufacture the bulk ultrasonic wave resonator and the bulk ultrasonic 
wave filter in the manufacturing process of the film bulk acoustic wave 
device, and therefore, the above adjustment method can be used. On the 
other hand, where the bulk ultrasonic wave resonator and the bulk 
ultrasonic wave filter are configurated on a semiconductor substrate which 
has the semiconductor circuit thereon, the bulk ultrasonic wave resonator 
and the bulk ultrasonic wave filter are manufactured during the 
manufacturing process of the semiconductor circuit. Since the 
manufacturing process of the semiconductor circuit handles a wafer as a 
manufacturing unit, wherein the wafer includes a plurality of devices, a 
different process from the manufacturing process of the semiconductor 
circuit is required to adjust each device. This additional process 
increases the manufacturing cost. 
When the amount of adjustment achieved by adding or trimming is not enough, 
additional adjustment amount is performed. On the other hand, when the 
amount of adjustment is in excess of that desired, it is not possible to 
perform readjustment by the same adjustment method. For instance, in the 
adjustment method of evaporating and adding metals, when the metal added 
is more than the required mass volume, it is not possible to correct the 
over adjustment by evaporating and adding metals. Similarly, in the 
adjustment method of trimming, when the amount of trimming is more than 
the required mass volume, it is not possible to correct the over 
adjustment by trimming. 
FIGS. 69 and 70 show an example of another conventional method for 
frequency adjustment of a film bulk acoustic wave device. FIG. 69 shows an 
example of connecting a variable condenser C.sub.v 25 to the bulk 
ultrasonic wave resonator in series. FIG. 70 shows an example of 
connecting a variable condenser C.sub.v 25 to the bulk ultrasonic wave 
resonator 15 in parallel. FIG. 71 shows an equivalent circuit of the 
circuit shown in FIG. 69. FIG. 72 shows an equivalent circuit of the 
circuit shown in FIG. 70. 
In FIG. 71, when the equivalent resistance R.sub.1 12 is zero, the 
frequency, at which the impedance between terminals A and B is zero is 
different from the resonant frequency F.sub.r of the bulk ultrasonic wave 
resonator 15 because of the variable condenser C.sub.v 25. This means that 
the resonant frequency of the bulk ultrasonic wave resonator 15 can be 
varied by varying the variable condenser C.sub.v 25. Here, since the 
maximum frequency difference of the resonant frequency and the 
antiresonant frequency is limited by the electromechanical coupling 
constant k.sup.2 of the piezoelectric thin film 2, the frequency range 
which can be adjusted by the variable condenser C.sub.v 25 is limited. 
Namely, it is impossible to perform adjustment in which the resonant 
frequency is beyond the frequency difference .DELTA.F of the resonant 
frequency and the antiresonant frequency. In addition, when there is a 
loss in the variable condenser C.sub.v 25, Q.sub.m of the bulk ultrasonic 
wave resonator 15 is reduced. 
Hence, for example, when zinc oxide (ZnO) is used in the conventional type 
of bulk ultrasonic wave resonator 15, the maximum adjustable frequency 
range is around 1 to 5%. When aluminum nitride (AlN) is used, the maximum 
adjustable frequency range is about 1%. Fluctuation of the antiresonant 
frequency or the resonant frequency of the bulk ultrasonic wave resonator 
15 is mostly caused by the manufacturing errors or fabrication errors that 
cause variations in the thicknesses and composition of the piezoelectric 
thin film 2, thickness of the top-side electrode 6, thickness of the 
ground conductor 5 and so forth. Even when the thickness of the 
piezoelectric thin film 2 is precisely controlled, the manufacturing error 
is in the range of around several percent. When thickness of the 
piezoelectric thin film 2 is not precisely controlled, manufacturing error 
becomes about 10%. The adjustment of frequency in accordance with the 
electrical adjustment wherein the adjustable frequency range is from 1 to 
5% and it is practically impossible to correct for frequency errors of 10% 
with the conventional materials. As to lead titanate-zirconate (PZT), the 
electromechanical coupling constant k.sup.2 of the thin film is not shown 
in the reference 6. When the electromechanical coupling constant k.sup.2 
of lead titanate-zirconate (PZT) is considered to be equivalent to one of 
the ceramics of the bulk material on table 1, the maximum of the 
adjustable frequency range is about 22%. This adjustable frequency range 
is within the fluctuation range of the resonant frequency or the 
antiresonant frequency caused by fabrication error. 
Other factors causing fluctuation of the resonant frequency and the 
antiresonant frequency, is a pattern precision or relative position of the 
top-side electrode 6 and the ground conductor 5 and the dimensional 
tolerances of the top-side electrode and the ground conductor. FIGS. 73 
and 74 will be used to show that the pattern precision affects the 
fluctuation of the resonant frequency and the antiresonant frequency. FIG. 
73 is an upper-side view and FIG. 74 is a C--C sectional view. In the 
figures, a lead electrode 26 is electrically connected to the top-side 
electrode 6. Since a dielectric substance 4 like silicone oxide 
(SiO.sub.2) affects the resonant frequency and the antiresonant frequency 
relatively little, the illustration of the dielectric substance is omitted 
in FIGS. 73 and 74. 
The capacity C.sub.0 between electrodes of the bulk ultrasonic wave 
resonator can be calculated according to expression 9 where a usual 
dielectric substance is positioned between conductors. 
expression 9: 
EQU C.sub.0 =.epsilon..sub.r .epsilon..sub.0 A/h 
Wherein .epsilon..sub.r is a relative dielectric constant of the 
piezoelectric thin film 2. .epsilon..sub.0 is a dielectric constant in a 
vacuum. A is an area of the crossing point where the top-side electrode 6 
and the ground conductor 5 overlap. h is a thickness of the piezoelectric 
thin film 2. As shown in FIG. 65, when the top-side electrode 6 is located 
in the inside of the ground conductor 5, the area A is the area of the 
top-side electrode 6. The area A can be varied as required. The area A can 
be selected such that the impedance of the capacity C.sub.0 between 
electrodes is the characteristic impedance of the circuit in use. In 
general, circuits having an operating frequency of approximately 2 GHz 
have a characteristic impedance of 50 .OMEGA.. The capacity of C.sub.0 
corresponding to an impedance of 50 .OMEGA. at 2 GHz is about 1.6 pF. As 
to the conventional type of bulk ultrasonic wave resonator, shown in the 
reference 6, when the size of the top-side electrode 6 whose capacity 
between electrodes is 1.6 pF is calculated, it is about 19 by 19 .mu.m 
square according to the expression 9, in a case where the thickness of the 
piezoelectric thin film 2 is 2 .mu.m and the relative dielectric constant 
of the piezoelectric thin film 2 is 1000. When the relative dielectric 
constant of the piezoelectric thin film 2 gets larger, the size of the 
top-side electrode 6 gets smaller. For instance, when the relative 
dielectric constant is 2000, the size comes to be about 13 by 13 .mu.m 
square. 
On the other hand, the dimensions of the top-side electrode 6 have a 
tolerance limitation almost corresponding to the thickness of the top-side 
electrode 6. In the conventional type of bulk ultrasonic wave resonator 
shown in reference 6, the thickness of the top-side electrode 6 is 0.2 
.mu.m. When the dimensional tolerances of each edge of the top-side 
electrode 6 are assumed to be +-0.2 .mu.m, the tolerance of the capacity 
C.sub.0 between electrodes is equivalent to the tolerance of the area of 
the top-side electrode. Therefore, when an electrode of 19 by 19 .mu.m 
square is used, the tolerance of the capacity is (19.4/19).sup.2 
.apprxeq.4%. In case of an electrode 13 by 13 .mu.m square, the capacitive 
tolerance is (13.4/13).sup.2 .apprxeq.6%. Namely, the capacity C.sub.0 
between electrodes, determined by the precision of the top-side electrode 
6, contains an error of more than 4 to 6%. This value can be reduced by 
enlarging the size of the top-side electrode 6. However, the capacity 
C.sub.0 between electrodes increases with an increase in size of the 
top-side electrode 6. Considering the relationship with the surrounding 
electric circuits connected to the bulk ultrasonic wave resonator, the 
practically available value of the capacity C.sub.0 between electrodes is 
limited. Consequently, it is impossible to enlarge the size of the 
top-side electrode 6 without limitation. 
Additionally, the capacity C.sub.0 between electrodes is affected by the 
lead electrode 26. When the piezoelectric thin film 2 is zinc oxide (ZnO) 
or aluminum nitride (AlN), the direction of the c axis, which is a crystal 
axis, is oriented in the direction of the thickness of the piezoelectric 
thin film 2. Therefore, the piezoelectric thin film 2 shows 
piezoelectricity by forming only a film. Lead titanate-zirconate (PZT) 
disclosed in reference 6 is a piezoelectric thin film formed with an 
orientation rate of more than 70%. It also shows piezoelectricity by 
forming only a film. That is, the conventional type of piezoelectric thin 
film 2 is a spontaneous polarization film showing piezoelectricity right 
after forming a film. Therefore, the formed piezoelectric thin film 2 
shows piezoelectricity at any point. 
As shown in FIGS. 73 and 74, an overlapping portion 26a where the lead 
electrode 26 and the ground conductor 5 overlap operates electrically in 
exactly the same way as the overlapping area of the top-side electrode 6 
and the ground conductor 5. Namely, the overlapping portion 26a where the 
lead electrode 26 and the ground conductor 5 overlap is a condenser having 
the piezoelectric thin film 2 as a dielectric substance. In addition, an 
acoustic wave is excited from the overlapping portion. A portion 26b of 
the lead electrode 26 does not overlap the ground conductor 5. A 
dielectric constant of the piezoelectric thin film 2 is extremely large 
compared to that of the semiconductor substrate 1. An electric field 
concentratedly occurs between the portion 26b and the ground conductor 5. 
Therefore, the portion 26b of the lead electrode 26 has capacitance even 
though the portion 26b does not overlap the ground conductor 5. An elastic 
wave is excited by the electric field occurring in the portion 26b. Since 
the lead electrode 26 connects the top-side electrode 6 to the surrounding 
electric circuits, there is a case that the lead electrode 26 needs to be 
drawn on other places except for the via hole 7. The acoustic wave excited 
in such place is propagated in the inside of the semiconductor substrate 
1. Therefore, it will cause undesirable resonance points and losses. The 
undesirable resonance points and the losses due to the lead electrode 26 
depend on a ratio of the area of the top-side electrode 6 to the area of 
the lead electrode 26. The line width of the lead electrode 26, is limited 
by the required conductor resistance and the line path impedance. 
Accordingly, when the area of the top-side electrode 6 is not large, an 
affect of the undesirable resonance points and the losses due to the lead 
electrode 26 relatively is relatively large. 
The film bulk acoustic wave device is formed with a semiconductor circuit. 
The film bulk acoustic wave device includes a bulk ultrasonic wave 
resonator and a bulk ultrasonic wave filter. The film bulk acoustic wave 
device is fabricated together with various electric circuits required in 
the electric apparatuses. When the manufacturing cost or fabrication cost 
is high and the problems, such as fluctuation of frequency by the 
manufacturing error or fabrication error, undesirable resonance, and 
increase of loss, cannot be solved, there is no advantage to fabricating 
the bulk ultrasonic wave resonator and the bulk ultrasonic wave filter 
together with various kinds of other electric circuits. As a result, it is 
difficult to provide a small and light bulk acoustic wave device formed 
with many other electric circuits on the same semiconductor substrate. 
Problems to be solved by the Invention 
As has been described, the conventional bulk acoustic wave devices using 
zinc oxide (ZnO) or aluminum nitride (AlN) cannot adjust the fluctuation 
of the resonant frequency and the antiresonant frequency due to 
manufacturing tolerances by electrical adjustment. Accordingly, it is 
necessary to adopt a physical adjustment using either a method of 
sputtering the topside electrode 6 at each device or a method of trimming 
the top-side electrode. This causes the manufacturing cost to be higher. 
Since the conventional type of bulk acoustic wave device using lead 
titanate-zirconate (PZT) has an extremely large dielectric constant, the 
size of the top-side electrode cannot be enlarged because of the 
restriction of the capacity between electrodes. Therefore, the dimensional 
tolerances of the top-side electrode may cause fluctuation of the 
resonance and antiresonant frequency. 
Furthermore, because the conventional type of bulk acoustic wave device is 
a spontaneous polarization film, the acoustic wave is excited in the lead 
electrode and propagated on the semiconductor substrate outside of the via 
hole. Then, undesirable resonance and increase of the loss are caused. 
Since the conventional type of film bulk acoustic wave device cannot solve 
these problems, it cannot be fabricated together with other electric 
circuits on the same semiconductor substrate. 
SUMMARY OF THE INVENTION 
Embodiments of the present invention solve one or more of the problems 
discussed above. It is an object of this invention to provide a film bulk 
acoustic wave device which can adjust characteristics of the film bulk 
acoustic wave device at a low cost. 
It is another object of this invention to provide a well-characterized bulk 
acoustic wave device which decreases undesirable resonance points and 
losses. 
Further, it is another object of this invention to provide a small, light 
and adjustment-free electric apparatus fabricated together with the other 
electric circuits on the same semiconductor substrate. 
According to one aspect of this invention, a film bulk acoustic wave device 
may include: 
a semiconductor substrate; 
a ground conductor layer, having a thickness, mounted on the semiconductor 
substrate; 
a piezoelectric ceramic thin film, having a thickness, mounted on the 
ground conductor layer; and 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; 
wherein the thickness of the piezoelectric ceramic thin film is more than 
10 times the thickness of the ground conductor layer. 
According to another aspect of this invention, film bulk acoustic wave 
device may include: 
a semiconductor substrate; 
a ground conductor layer mounted on the semiconductor substrate; 
a piezoelectric ceramic thin film, having a thickness, mounted on the 
ground conductor layer; and 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; 
wherein the piezoelectric ceramic thin film generates an acoustic wave 
propagated in a direction parallel to a surface of the piezoelectric 
ceramic thin film and a wave number of the acoustic waves is less than 2 
divided by the thickness of the piezoelectric ceramic thin film. 
According to another aspect of this invention, a film bulk acoustic wave 
device may include: 
a ground conductor layer mounted on the semiconductor substrate; 
a piezoelectric ceramic thin film mounted on the ground conductor layer; 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; and 
a semiconductor circuit mounted on the semiconductor substrate; 
wherein the semiconductor circuit is configured by using a part of the 
piezoelectric ceramic thin film. 
According to another aspect of this invention, a film bulk acoustic wave 
device may include: 
a semiconductor substrate; 
a ground conductor layer mounted on the semiconductor substrate; 
a piezoelectric ceramic thin film mounted on the ground conductor layer; 
and, 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; 
wherein the piezoelectric ceramic thin film has a piezoelectric section 
processed by a polarization process and a dielectric section that has not 
been processed by the polarization process. 
According to another aspect of this invention, a film bulk acoustic wave 
device may include: 
a semiconductor substrate; 
a ground conductor layer mounted on the semiconductor substrate; 
a piezoelectric ceramic thin film mounted on the ground conductor layer; 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; 
a semiconductor circuit mounted on the semiconductor substrate; 
a polarization circuit used for a polarization process of the piezoelectric 
ceramic thin film; and 
a protective circuit for protecting the semiconductor circuit from the 
polarization process by the polarization circuit. 
According to another aspect of this invention, a film bulk acoustic wave 
device may include: 
a semiconductor substrate; 
a ground conductor layer mounted on the semiconductor substrate; 
a piezoelectric ceramic thin film mounted on the ground conductor layer; 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; 
a plurality of reactance devices mounted on the semiconductor substrate; 
and 
a means for changing an electrical connection of each of the plurality of 
reactance devices. 
According to another aspect of this invention, a film bulk acoustic wave 
device may include: 
a semiconductor substrate; 
a ground conductor layer mounted on the semiconductor substrate; 
a piezoelectric ceramic thin film mounted on the ground conductor layer; 
a conductive electrode pattern mounted on the piezoelectric ceramic thin 
film; and 
an active device circuit that provides a variable capacitive reactance, 
mounted on the semiconductor substrate. 
According to another aspect of this invention, a method of manufacturing a 
film bulk acoustic wave device may include the steps of: 
(a) forming a ground conductor layer on a semiconductor substrate; 
(b) forming a piezoelectric ceramic thin film of one of lead titanate and 
lead titanate-zirconate (PZT) on the ground conductor layer; and 
(c) forming a conductive electrode pattern on the piezoelectric ceramic 
thin film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
FIGS. 1 and 2 show a bulk ultrasonic wave resonator according to Embodiment 
1 of this invention. FIG. 1 shows an upper-side view and FIG. 2 shows a 
D--D cross sectional view. In the figure, a semiconductor substrate 1 is 
mainly composed of silicon (Si), gallium arsenide (GaAs) or tantalum oxide 
(Ta.sub.2 O.sub.5). A dielectric substance 4 is mainly composed of silicon 
oxide (SiO.sub.2), silicon nitride (SiN) or tantalum oxide (Ta.sub.2 
O.sub.5). A ground conductor 5 is such as platinum (Pt) or gold (Au). A 
top-side electrode 6 is one of metals like platinum (Pt), gold (Au), 
copper (Cu), aluminum (Al), titanium (Ti), tungsten (W) and so forth, The 
top-side electrode 6 may be a semiconductor layer of high conductivity in 
which impurity density is high. The top-side electrode 6 may be one of 
materials of high conductivity like polysilicon. A via hole 7 is provided. 
A piezoelectric ceramic thin film or a piezoelectric thin film 27 is 
mainly composed of lead titanate (PbTiO.sub.3). Hereinafter, a bulk 
ultrasonic wave resonator means a device which generates resonance by 
using an acoustic wave. A bulk ultrasonic wave filter means a device which 
operates as a filter consisting of a plurality of bulk ultrasonic wave 
resonators. A bulk acoustic wave device means a bulk ultrasonic wave 
resonator or a bulk ultrasonic wave filter, and includes the other circuit 
components on the same semiconductor substrate 1. 
In conventional bulk ultrasonic wave resonators, there is a dielectric 
substance 4 on the semiconductor substrate 1, the ground conductor 5 on 
the dielectric substance 4, the piezoelectric thin film 27 on the ground 
conductor 5, a top-side electrode 6 on the piezoelectric thin film 27 and 
a via hole 7 formed in the semiconductor substrate 1 corresponding to a 
place where the top-side electrode 6 located. An area of the via hole 7 is 
bigger than an area of the top-side electrode 6. 
In the bulk ultrasonic wave resonator according to embodiments of the 
present invention, the piezoelectric material mainly composed of lead 
titanate (PbTiO.sub.3) is used for the piezoelectric thin film 27. When a 
thickness of the ground conductor 5 is set to be d, a thickness of the 
piezoelectric thin film is set to be h and a wave number of the acoustic 
waves propagated in the parallel direction of the surface of the 
piezoelectric thin film 27 is assumed to be k, k.times.h is or less than 2 
or d/h is or less than 0.1. The thickness of the top-side electrode 6 can 
be d or the other. 
The bulk ultrasonic wave resonator according to this invention uses lead 
titanate (PbTiO.sub.3) for the piezoelectric thin film 27. Lead titanate 
(PbTiO.sub.3) has an electromechanical coupling constant k.sup.2 of more 
than twice that of zinc oxide (ZnO) and aluminum nitride (AlN) which 
previously have been used in this type of bulk ultrasonic wave resonator. 
The relative dielectric constant of lead titanate (PbTiO.sub.3) is several 
hundred, which is rather small, compared to that of lead 
titanate-zirconate (PZT) which exceeds 1000. 
Since a number of constituent elements of lead titanate is fewer than that 
of lead titanate-zirconate (PZT), the variation of characteristics caused 
by a film formation, are few. 
In the film formation of lead titanate (PbTiO.sub.3), the semiconductor 
substrate 1 needs to be heated with a high temperature of above several 
hundred degrees celsius so as to obtain a well-qualified film. Hence, a 
specific element in the semiconductor substrate 1 is deposited. 
Deterioration of film or inferiority of forming a film are sometimes 
caused. Especially, when gallium arsenide (GaAs) is used for the 
semiconductor substrate 1, there is a danger of depositing arsenic (As). 
To prevent this, it is important to cover the surface of the semiconductor 
substrate 1 with a dielectric substance 4 of silicon oxide (SiO.sub.2), 
silicon nitride (SiN) or tantalum oxide (Ta.sub.2 O.sub.5). 
Especially, silicon nitride (SiN) prevents deposition of arsenic (As) and 
the like. Since lead titanate (PbTiO.sub.3) which is directly layered on 
silicon nitride (SiN) does not show piezoelectricity, it is quite 
effective to utilize silicon nitride (SiN) so as to restrict the resonance 
area only to an area where the ground conductor 5 is formed. 
On the other hand, when lead titanate (PbTiO.sub.3) is directly layered on 
silicon oxide (SiO.sub.2), the film quality of lead titanate (PbTiO.sub.3) 
does not vary at the boundary of silicon oxide (SiO.sub.2). Therefore, 
silicon oxide (SiO.sub.2) is especially appropriate in a case where a 
plurality of bulk ultrasonic wave resonators like filters are closely 
arranged. 
Tantalum oxide (Ta.sub.2 O.sub.5) is mechanically stronger than silicon 
nitride (SiN) and silicon oxide (SiO.sub.2). 
Accordingly, it is appropriate in a case where mechanical strength of 
silicon nitride (SiN) and silicon oxide (SiO.sub.2) is not enough when the 
air-gap like a via hole is composed on the bottom side of the dielectric 
substance 4 and the dielectric substance 4 supports the piezoelectric thin 
film 24. 
The dielectric substance 4 excels in electric insulation. Even when the 
surface of the semiconductor substrate 1 has a relatively high 
conductivity, it is possible to separate the potential of the ground 
conductor 5 due to the existence of the dielectric substance 4. 
Because the piezoelectric thin film 27 contains oxygen, it must be formed 
in an oxygen ambience having high temperature and high chemical 
reactivity. Therefore, when the material of the ground conductor 5 has a 
low melting point or provides a high diffusibility at a high temperature 
or tends to be easily oxidized in an oxygen ambience under a high 
temperature, the ground conductor 5 deteriorates during forming of the 
piezoelectric thin film 27. There is a method of producing a protective 
film partially on the ground conductor 5 and the dielectric substance 4. 
However, the usual protective film deteriorates under conditions used for 
forming the piezoelectric thin film 27. Zinc oxide (ZnO) and aluminum 
nitride (AlN) which have been used in the conventional type of bulk 
ultrasonic wave resonator, need not produce a film under such high 
temperatures as to cause the deterioration of the ground conductor 5 and 
therefore, the above mentioned problems didn't occur. However, the 
piezoelectric thin film 27 of the bulk ultrasonic wave resonator according 
to this invention has a problem of the processing temperature being high. 
In order to solve the problem, platinum (Pt) or gold (Au), which have high 
chemical stability need to be used as the ground conductor 5. Especially, 
platinum (Pt) excels in resisting oxygen reactivity at high temperatures. 
Platinum which is layered on the smooth surface of the dielectric 
substance 4 is oriented towards &lt;111&gt;. Lead titanate (PbTiO.sub.3) is a 
tetragonal crystal and polycrystal. Because the direction of polarization 
of each crystal right after forming a film is in disorder, the 
piezoelectricity is low. By applying the proper direct current voltage at 
above the required temperature to lead titanate (PbTiO.sub.3), the 
disorderly direction of polarization can be arranged and the 
piezoelectricity gets high. 
Metals having a large specific gravity like platinum (Pt) and gold (Au) 
greatly affect the resonant frequency of the piezoelectric thin film 27 
due to the mass load. FIG. 3 shows a view of an equivalent circuit of a 
triple layer structure composed of the ground conductor 5, the 
piezoelectric thin film 27 and the top-side electrode 6. To simplify the 
explanation, it is assumed that both of the ground conductor 5 and the 
top-side electrode 6 are platinum (Pt) and that their thickness is the 
same. In the figure, an equivalent circuit 28 corresponds to the top-side 
electrode 6. An equivalent circuit 29 corresponds to the piezoelectric 
thin film 27. An equivalent circuit 30 corresponds to the ground conductor 
5. An electric terminal 31a corresponds to the top-side electrode 6. An 
electric terminal 31b corresponds to the ground conductor 5. In each 
equivalent circuit, an electric length .theta..sub.m corresponds to the 
thicknesses of the top-side electrode 6 or ground conductor 5 and an 
electric length .theta..sub.p corresponds to the thickness of the 
piezoelectric thin film 27. The boundary condition Z.sub.s1 of the surface 
of the top-side electrode 6, the boundary condition Z.sub.s2 Of the bottom 
side of the ground conductor 5 are treated as short-circuits. The 
equivalent circuit shown in FIG. 3 is disclosed in detail in the 
literature in "Supervised by Onoue, The Basics of Solid Oscillation 
Theory, issued on September, 1982, Ohmu-sha, Chapter 6, Piezoelectric 
Equation and the Application, pp. 115-157" (hereinafter, referred to as 
reference 14). 
FIG. 4 shows an example where the frequency F.sub.a in which the admittance 
estimated at the electric terminals 31a and 31b is zero and the frequency 
F.sub.r in which the impedance estimated at the electric terminals 31a and 
31b is zero are calculated. The frequency F.sub.a corresponds to the 
antiresonant frequency. The frequency F.sub.r corresponds to the resonant 
frequency. In the figure, the horizontal axis is a normalized film 
thickness, which is a ratio of thickness d of the ground conductor 5 to 
thickness h of the piezoelectric thin film 27. The vertical axis on the 
left side is a normalized antiresonant frequency, which is a ratio of 
frequency F.sub.a to frequency f.sub.0 whereat thickness h of the 
piezoelectric thin film 27 is equal to half wave length of the acoustic 
wave. The vertical axis on the right side is a normalized resonant 
frequency difference, which is a ratio of the difference between the 
frequencies F.sub.a and F.sub.r to frequency f.sub.0 whereat the thickness 
h of the piezoelectric thin film 27 is half wave length of the acoustic 
wave. The material constants used in the calculation are as follows: As to 
the lead titanate (PbTiO.sub.3), the density .rho. is 7700(kg/m.sup.3), 
the elastic constant c.sub.33 is 13.2.times.10.sup.10 (N/m.sup.2), the 
piezoelectric constant e.sub.33 is 6.52(C/m.sup.2), the relative 
dielectric constant .epsilon..sub.33 is 190. As to platinum (Pt), the 
density .rho. is 21300 (kg/m.sub.3), the elastic constant c.sub.33 is 
30.9.times.10.sup.10 (N/m.sup.2). The above mentioned material constants 
are the values examined not in the thin film but in the bulk material. 
Therefore, in a case where the thin film is formed, the material constants 
may be different from the above values. The values change according to 
methods and conditions for forming films with lead titanate (PbTiO.sub.3) 
and platinum (Pt). The values change according to the kinds of impurity 
added to lead titanium (PbTiO.sub.3) and the addition ratio. 
When the normalized film thickness is enlarged, both the normalized 
antiresonant frequency and the normalized resonant frequency difference 
are small. This is because the mass load of the top-side electrode 6 and 
the ground conductor 5 increases when the normalized film thickness is 
large. The density of platinum (Pt) or gold (Au) is relatively large, 
compared to that of other metal materials. Therefore, the amount of 
deterioration of the normalized antiresonant frequency and the normalized 
resonant frequency difference is large compared to the normalized film 
thickness. The normalized resonant frequency difference is a value which 
determines a maximum value of the adjustment range of the oscillating 
frequency of an oscillator using a bulk ultrasonic wave resonator. The 
normalized resonant frequency difference is also a value which determines 
the maximum value of the adjustment range of the fluctuation of the 
resonant frequency and the antiresonant frequency of the bulk ultrasonic 
wave resonator or filter caused by manufacturing errors. When the 
normalized film thickness is 0, and the affect of the mass load of the 
top-side electrode 6 and the ground conductor 5 is ignored, the normalized 
resonant frequency difference is about 8%. On the other hand, when the 
normalized film thickness is 0.2, the normalized resonant frequency 
difference is about 4%. This value is similar to that of zinc oxide (ZnO) 
used in conventional bulk acoustic wave devices. Therefore a large value 
of an electromechanical coupling constant of lead titanate (PbTiO.sub.3) 
cannot be used appropriately. Namely, by setting the normalized film 
thickness (d/h) to be less than 0.1, the value of the electromechanical 
coupling constant can be above 5% and it is possible to obtain a larger 
value of the electromechanical coupling constant than the conventional 
type of bulk acoustic wave device. 
FIGS. 5 and 6 show an example of a dispersion characteristic calculated 
result of an acoustic wave which propagates in the lead titanate 
(PbTiO.sub.3) thin film according to Embodiment 1 of this invention. FIGS. 
5 and 6 show a calculated result of the acoustic wave that propagates 
parallel to the surface of the lead titanate (PbTiO.sub.3) thin film and 
contains an amplitude component vertical to the surface of the lead 
titanate (PbTiO.sub.3) thin film and an amplitude component parallel to 
the direction of the thickness. The wave number of the acoustic waves is 
k, the thickness of the lead titanate (PbTiO.sub.3) thin film is h and the 
frequency in which the thickness h of the lead titanate (PbTiO.sub.3) thin 
film is equal to a half wave length is f.sub.0. The horizontal axis is the 
normalized film thickness of the lead titanate (PbTiO.sub.3) thin film 
(kh/2) and the vertical axis is the normalized frequency (f/f.sub.0). The 
right side of the vertical axis is an area where the value of the 
normalized film thickness is a real number. The left side of the vertical 
axis is an area where the value of the normalized film thickness is an 
imaginary number. When the value of the normalized film thickness is a 
real number, the acoustic wave can propagate. On the other hand, when the 
value of the normalized film thickness is an imaginary number, the 
acoustic wave cannot propagate. In FIG. 5, the solid line shows the 
dispersion characteristic in the case there is only one layer of the lead 
titanate (PbTiO.sub.3) thin film and the dashed line shows the dispersion 
characteristic in the case of a triple layer in which the platinum (Pt) 
layers, whose normalized thickness (d/h) is 0.08, are positioned on both 
sides of the lead titanate (PbTiO.sub.3) thin film. In FIG. 6, the solid 
line shows the same dispersion characteristic in the case of a triple 
layer in which the platinum (Pt) layers, whose normalized thickness (d/h) 
is 0.08 are positioned on both sides of the lead titanate (PbTiO.sub.3) as 
shown by the dashed line in FIG. 5. The dashed line shows the dispersion 
characteristic in the case of a triple layer where the platinum (Pt) 
layers whose normalized thickness (d/h) is 0.02 are positioned on both 
sides of the lead titanate (PbTiO.sub.3) thin film. The calculation is 
according to the method described in reference 8. 
In FIGS. 5 and 6, when values on the vertical axis of the acoustic wave are 
proportional to values on the horizontal axis of the acoustic wave, the 
propagation velocity of the acoustic wave is constant. An inclination of 
the above proportional straight line is determined by the propagation 
velocity of the acoustic wave and the thickness h of the lead titanate 
(PbTiO.sub.3) thin film. The calculated values of each dispersion 
characteristic in FIGS. 5 and 6 does not show a straight line. This means 
that the propagation velocity of the acoustic wave varies according to the 
thickness h of the lead titanate (PbTiO.sub.3) thin film and the frequency 
f. 
For example, in the bulk ultrasonic wave resonator shown in FIG. 2, it is 
assumed that the dielectric substance 4 can be substantially ignored for 
elastic vibration. In the case of the triple structure of the top-side 
electrode 6, the piezoelectric thin film 27 and the ground conductor 5, 
the dispersion characteristics as shown in the dashed line of FIG. 5 come 
to be modes of the acoustic wave existable in the triple layer structure. 
In the case of thickness resonance wherein the acoustic wave propagates 
only in the direction of thickness, a crossing point of each mode of the 
acoustic wave and the vertical axis corresponds to the thickness 
resonance. The values at crossing points of the solid and dashed lines in 
FIG. 5 and the vertical axis and at crossing points of the solid and 
dashed lines in FIG. 6 and the vertical axis get small when the 
thicknesses d of the top-side electrode 6 and the ground conductor 5 get 
large. This indicates that the resonant frequency gets lower with 
increases of the thicknesses of the top-side electrode 6 and the ground 
conductor 5. In FIG. 5, the solid line shows a characteristic in a case 
where there are no other components on the surface of the piezoelectric 
thin film 27. When modes shown in the solid line are located in the left 
side of the vertical axis near the normalized frequency (f/f.sub.0), where 
the dashed line crosses the vertical axis, the acoustic wave can propagate 
in the direction parallel to the piezoelectric thin film 27 where the 
top-side electrode 6 and the ground conductor 5 are not located. This 
corresponds to an excitation of an unnecessary acoustic wave for the bulk 
ultrasonic wave resonator shown in FIG. 2 and a quality factor Q of the 
resonator deteriorates. As to modes shown in the dashed line, when modes 
of the acoustic wave to propagate in the direction parallel to the surface 
of the piezoelectric thin film 27 exist near the normalized frequency 
(f/f.sub.0), wherein the dashed line crosses the vertical axis, the 
acoustic wave that propagates parallel to the surface of the piezoelectric 
thin film 27 can exist where the top-side electrode 6 and the ground 
conductor 5 are located. As a result, spurious, which is undesirable to 
the resonator, is caused. 
When the bulk ultrasonic wave filter is composed, the similar situations 
can be predicted. The bulk ultrasonic wave filter which electrically 
connects the bulk ultrasonic wave resonators is affected by the spurious 
of the bulk ultrasonic wave resonator. The bulk ultrasonic wave resonator 
which lays out the bulk ultrasonic wave resonator closely and uses the 
energy trapping resonance of a symmetry mode and an asymmetry mode between 
a plurality of top-side electrodes 6 causes spurious when the acoustic 
wave of a different propagation mode exists near the normalized frequency. 
As a result, characteristics as the bulk ultrasonic wave filter 
deteriorates. In FIGS. 5 and 6, when the normalized film thickness (kh) is 
above 2, there exist various modes at the same normalized frequency 
(f/f.sub.0), which will cause spurious. Therefore, the normalized film 
thickness (kh) needs to be less than 2 in order to realize a 
well-characterized bulk ultrasonic wave resonator and filter. 
FIGS. 7 and 8 show impedance measurement results of the an experimental 
bulk ultrasonic wave resonator configured in accordance with FIGS. 1 and 
2. FIG. 7 is a measurement result before polarization and FIG. 8 is a 
measurement result after polarization. The piezoelectric thin film 27 uses 
lead titanate (PbTiO.sub.3) and the thickness h is about 1 .mu.m. The 
top-side electrode 6 and the ground conductor 5 use platinum (Pt) of about 
0.07 .mu.m thick, which has a titanium ground of about 0.03 .mu.m thick, 
and used an air-bridge as a lead of the top-side electrode 6 and the 
bonding pad. In the bonding pads of the top-side electrode 6 and the 
ground conductor 5, a layer of gold (Au) of about 3 .mu.m thick is 
composed. The dielectric substance 4 is silicon oxide (SiO.sub.2) of about 
0.1 .mu.m thick. During polarization process, a direct current voltage of 
15 Volts is applied for about an hour under the condition that the bulk 
ultrasonic wave resonator is heated at 200 centigrade. 
FIG. 7 shows the piezoelectricity characteristics before polarization. When 
the value of the plate thickness is relatively large, compared to the 
particle size of the piezoelectric ceramics, the direction of polarization 
of each particle is in disorder before polarization and there is little 
indication of piezoelectricity. In the case of the bulk ultrasonic wave 
resonator shown in FIG. 7, the piezoelectric ceramics is thin film. 
Therefore, the direction of polarization of each particle can be arranged 
even before polarization. A comparison of characteristics after 
polarization shown in FIG. 8 with the characteristics before polarization 
shown in FIG. 7, the resonance circle gets larger after polarization and 
the piezoelectricity also increases because of the polarization. The 
resonance occurs in two frequency bands and the frequency indicated by 
marker 1 (shown as .DELTA.1) is about 1.4 GHz and the frequency indicated 
by marker 2 (.DELTA.2) is about 700 MHz. 
The thickness of the lead titanate (PbTiO.sub.3) thin film of the 
experimental bulk ultrasonic wave resonator is about 1 .mu.m and the 
frequency f.sub.0 wherein the thickness is equal to a half wave length of 
the acoustic wave is about 2 GHz. The normalized frequency of marker 1 is 
about 0.7 (=1.4 GHz/2 GHz) and the normalized frequency of marker 2 is 
about 0.4 (=700 MHz/2 GHz). On the other hand, according to the calculated 
result shown in FIG. 5, a dispersion curve shown in the dashed line which 
crosses the vertical axis at point P1 with a little smaller normalized 
frequency than the normalized frequency of 0.8 is a vertical wave that 
propagates in the direction of thickness of the lead titanate 
(PbTiO.sub.3) thin film. This corresponds to the resonance around the 
normalized frequency of about 0.7 denoted by marker 1 in FIGS. 7 and 8. 
The differences between the calculated results and the measured normalized 
frequencies is because the material constant used for the calculation and 
the film thickness differ a little from those of the experimental bulk 
ultrasonic wave resonator. The dispersion curve shown in the dashed line 
crossing the vertical axis at point P2 of FIG. 5 with the normalized 
frequency of about 0.5 corresponds to resonance around the normalized 
frequency of about 0.4 denoted by marker 2. This shows an acoustic wave 
that propagates in a direction parallel to the surface of the lead 
titanate (PbTiO.sub.3) thin film. The frequency of an acoustic wave having 
the same mode shown in the solid line in a case where no metals are 
provided on the surface of the lead titanate (PbTiO.sub.3) thin film is a 
cutoff frequency in the same normalized film thickness (kh/2). Therefore, 
it corresponds to the energy trapping resonance, which resonates between 
both ends of the top-side electrodes 6. The top-side electrode 6 of the 
experimental bulk ultrasonic wave resonator is 100.times.100 .mu.m square 
and the wave length is 200 .mu.m. Accordingly, when the thickness of the 
lead titanate (PbTiO.sub.3) thin film is assumed to be 1 .mu.m, the 
normalized film thickness (kh/2) is as follows. 
expression 10: 
##EQU6## 
The expression shows that resonance occurs at the normalized film thickness 
(kh/2) which is a little to the right of the vertical axis depicted in 
FIG. 5. According to the measurement of the experimental bulk ultrasonic 
wave resonator, there is no unnecessary spurious around the frequency of 
the normalized film thickness and a well-qualified resonance 
characteristic is shown. In addition, the relative dielectric constant is 
about 200 based on the measurements of the experimental bulk ultrasonic 
wave resonator. 
Lead titanate (PbTiO.sub.3) used in the bulk acoustic wave device according 
to this invention shows weak piezoelectricity unless a polarization 
process is performed. In the conventional type of bulk ultrasonic wave 
resonator, a portion of the piezoelectric thin film 27 where the lead 
electrode 26 and the ground conductor do not overlap has almost the same 
piezoelectricity as the portion of the piezoelectric thin film 2 where the 
top-side electrode 6 and the ground conductor 5 overlap. As a result, it 
causes unnecessary spurious. In the piezoelectric thin film 27 of the bulk 
acoustic wave device according to this invention, when a direct electric 
field above a required value is not applied during the polarization 
process, the portion where the lead electrode 26 and the ground conductor 
5 don't overlap does not have as strong piezoelectricity as the 
overlapping portion of the top-side electrode 6 and the ground conductor 
5. Therefore, the portion of piezoelectric thin film 27 in which the lead 
electrode 26 and the ground conductor 5 do not overlap has weak 
piezoelectricity and a large spurious, as in the conventional type of bulk 
ultrasonic wave resonator is not caused. 
The value of the relative dielectric constant of lead titanate 
(PbTiO.sub.3) used in the bulk acoustic wave device of this invention is 
several hundred. The size of the top-side electrode 6 for which the 
capacity C.sub.0 is 50 .OMEGA. around the frequency of 2 GHz, when the 
relative dielectric constant is 200, is about 30.times.30 .mu.m square. 
The error of the capacity of the electrodes according to the error in size 
of the top-side electrode 6 can be 30% more than the equivalent error when 
lead titanate-zirconate (PZT) of about 13.times.13 .mu.m square to 
19.times.19 .mu.m square is used as in conventional bulk acoustic wave 
devices. 
As has been described, the bulk acoustic wave device according to 
Embodiment 1 of this invention has an electromechanical coupling constant 
k.sup.2 above 5% and no spurious, by setting the normalized film thickness 
(kh) to be equal to or less than 2 or the normalized film thickness (dh) 
to be equal to or less than 0.1. Because of the polarization process used 
for the piezoelectric thin film 27, it is possible to restrict the portion 
of the piezoelectric thin film 27 having piezoelectricity. Therefore, it 
is possible to reduce spurious occurring in the portion unrelated to the 
elastic resonance like the portion corresponding to lead electrode 26. 
Because, the electromechanical coupling constant k.sup.2 above 5% 
electrical adjustment can be performed after manufacturing devices having 
the thin film by setting each thin film to have a variation of 
characteristics caused by a film formation of about several %, which is 
within the region of being managed. It means that it is not required that 
the devices are respectively adjusted during the semiconductor 
manufacturing process. Hence, it is possible to manufacture bulk acoustic 
wave devices in mass productivity. Since the steps unsuitable for the 
semiconductor manufacturing process can be avoided, it is further possible 
to manufacture devices together with a large scale integrated 
semiconductor circuit. Furthermore, it is possible to integrate each 
semiconductor device which was conventionally manufactured with divided 
into one semiconductor chip and to downsize the whole electric apparatus. 
Embodiment 2 
FIGS. 9 and 10 show a bulk acoustic wave device according to Embodiment 2 
of this invention. FIG. 9 shows an upper-side view and FIG. 10 shows an 
E--E cross sectional view. In the figure, lead titanate-zirconate (PZT) 
32, a via hole 33, a lead electrode 34 from the ground conductor 5, and a 
bulk ultrasonic wave resonator 35 are provided. 
The structure of the bulk ultrasonic wave resonator 35 shown in FIGS. 9 and 
10 differs from that of the bulk ultrasonic wave resonator according to 
Embodiment 1 shown in FIG. 2. The via hole 33 is formed by using 
anisotropy etching from the side of lead titanate-zirconate (PZT) on the 
semiconductor substrate 1. However, the structure which causes elastic 
resonance as the bulk ultrasonic wave resonator 35 is basically the same 
as that of FIG. 2. The ground conductor 5 is on the dielectric substance 
4. The piezoelectric substance, that is, lead titanate-zirconate (PZT) 32 
is on the ground conductor 5. Top side electrode 6 is on lead 
titanate-zirconate (PZT) 32. The ground conductor 5 is electrically 
connected to a semiconductor circuit 3 through the lead electrode 26. In 
the structure shown in FIG. 10, the dielectric substance 4 supports the 
bulk ultrasonic wave resonator 35. If the dielectric substance is running 
short of mechanical strength, then the lead titanate-zirconate (PZT) 32 
becomes warped and the resonance characteristics of the bulk ultrasonic 
wave resonator deteriorates. In this case, the dielectric substance mainly 
composed of tantalum oxide (Ta.sub.2 O.sub.5) is most suitable. 
Lead titanate-zirconate (PZT) 32 is a polycrystal substance like lead 
titanate oxide (PbTiO.sub.3) of the bulk ultrasonic wave resonator in 
Embodiment 1. After film formation, the direction of polarization of each 
crystal is in disorder and strong piezoelectricity is not shown. The 
disorderly direction is arranged by giving proper direct current voltage 
to lead titanate-zirconate (PZT) 32 at an elevated temperature. As a 
result, a stronger piezoelectricity can be achieved. The electromechanical 
coupling constant k.sup.2, the dielectric constant, and Q of lead 
titanate-zirconate (PZT) 32, vary according to the composition ratio of 
lead zirconate (PbZrO.sub.3) and lead titanate (PbTiO.sub.3). It is 
disclosed in the literature in "Acoustic wave Device Technology Handbook, 
edited by the Japan Society for the Promotion of Science, Acoustic wave 
Device Technology the 150th Committee, issued by Ohmu-sha, the 1st 
edition, issued on Nov. 30, 1991, Volume IV, Acoustic wave Material, 
Chapter 2, Method of Manufacturing Materials and Material Constant, pp. 
280 to 329" (hereinafter, referred to as reference 15). As described in 
reference 15 the usual bulk material, lead titanate-zirconate (PZT) shows 
a phase transition when the compounding ratio of lead zirconate 
(PbZrO.sub.3) to lead titanate (PbTiO.sub.3) is around 52:48. When the 
compounding ratio of lead titanate (PbTiO.sub.3) is smaller, lead 
titanate-zirconate (PZT) becomes a trigonal system. When the compounding 
ratio of lead titanate (PbTiO.sub.3) is larger, it becomes tetragonal 
system and indicates a large electromechanical coupling constant k.sup.2 
around the compounding ratio where the phase transition appears. 
For lead titanate-zirconate (PZT) 32, the processing temperature used when 
forming films is high and the film is formed in an oxide ambience. The 
ground conductor 5 needs to be chemically stable platinum (Pt) or gold 
(Au). Platinum (Pt) excels in chemical stability high temperatures. On the 
other hand, platinum (Pt) and gold (Au) have high density. As shown in a 
calculation example of FIG. 4, when the thickness d of the ground 
conductor 5 is enlarged, the difference between the antiresonant frequency 
F.sub.a and the resonant frequency F.sub.r gets small. Then, the large 
electromechanical coupling constant k.sup.2 of the lead titanate-zirconate 
(PZT) 32 cannot be utilized efficiently. As shown in FIGS. 5 and 6, when 
the value of the product kh of the thickness h of lead titanate-zirconate 
(PZT) by the wave number k of acoustic waves is enlarged, unnecessary 
spurious is caused. Namely, in order to get the bulk ultrasonic wave 
resonator 35 having a required characteristic by using lead 
titanate-zirconate (PZT) 32, the normalized film thickness (kh) should be 
equal to or less than 2 or the normalized film thickness (d/h) should be 
equal to or less than 0.1. 
Embodiment 3 
FIG. 11 shows a thin film piezoelectric oscillator according to Embodiment 
3 of this invention. A bulk ultrasonic wave resonator 35 using lead 
titanate (PbTiO.sub.3) is shown with a simplified form of the bulk 
ultrasonic wave resonator 35 shown in FIG. 9. A transistor 13 is an active 
device. The transistor 13 can be an electric field effect transistor even 
though the form of the bipolar transistor is shown as the transistor 13 in 
FIG. 11. Resistances 36 are composed in the semiconductor circuit 3 and 
condensers 14 are composed in the semiconductor circuit 3. An output 
terminal 37, a power supply terminal 38 and a ground terminal 39 are 
provided. 
An oscillator circuit shown in FIG. 11 oscillates a wave having a frequency 
.omega., in which admittance Y, condenser C.sub.B 14 and condenser C.sub.C 
14 of the bulk ultrasonic wave resonator 35 satisfy expression 7. Hence, 
the bulk ultrasonic wave resonator 35 can oscillate within the frequency 
range which shows inductive reactance. The maximum value within the range 
of oscillation is between the antiresonant frequency and the resonant 
frequency. By using lead titanate (PbTiO.sub.3) and setting the normalized 
film thickness (d/h) to be equal or less than 0.1, it is possible to set 
the difference of the antiresonant frequency and the resonant frequency to 
be more than 5% of frequency f.sub.0 of which the film thickness h of lead 
titanate (PbTiO.sub.3) is a half wave length. Further, it is possible to 
configure a well-characterized oscillator circuit which has no spurious. 
Furthermore, since lead titanate (PbTiO.sub.3) is chemically stable, the 
oscillator circuit does not deteriorate through the manufacturing process 
of the semiconductor circuit 3 and the oscillator circuit is fabricated 
together with the semiconductor circuit 3 without deteriorating a yield 
rate. 
Embodiment 4 
FIGS. 12 and 13 show a thin film piezoelectric amplifier according to 
Embodiment 4 of this invention. FIGS. 12 and 13 show the same thin film 
piezoelectric amplifier. FIG. 12 shows the structure. FIG. 13 shows the 
circuit configuration. In the figure, a top-side electrode 40, and a bulk 
ultrasonic wave filter 41 are provided. A semiconductor amplifier 42 is 
configured in the semiconductor circuit 3 and composed of an active 
circuit device like a transistor and a passive circuit device like a 
condenser, a resistance, an inductor, a transmission line or a stub. 
Further, an input terminal is provided. 
The top-side electrode 6 is connected to the semiconductor amplifier 42 by 
a lead electrode 26. An elastic resonance occurs between the top-side 
electrode 40 and the top-side electrode 6 which has no connecting path 
with the external circuit directly. By setting each resonant frequency of 
a symmetry mode and an asymmetry mode appropriately, the bulk ultrasonic 
wave filter 41 operates as a band pass filter. The maximum value of the 
available band width is between the antiresonant frequency and the 
resonant frequency. Therefore, the bulk ultrasonic wave filter 41 using 
lead titanate-zirconate (PZT) 32 can expand the maximum value of the 
relative band {(F.sub.a -F.sub.r)/f.sub.0 } by more than 20% in comparison 
with conventional filters previously discussed. The bulk ultrasonic wave 
filter 41 according to this invention uses platinum (Pt) or gold (Au) as 
the ground conductor. When forming films of lead titanate-zirconate (PZT) 
32, the ground conductor is chemically stable. In addition, since the 
normalized film thickness (kh) is equal to or less than 2 or the 
normalized film thickness (d/h) is equal to or less than 0.1, it is 
possible to obtain the well-characterized thin film piezoelectric 
amplifier which has no spurious. Since lead titanate-zirconate (PZT) 32 is 
chemically stable, the bulk ultrasonic wave filter 41 is not deteriorated 
by the manufacturing process of the semiconductor circuit 3, and the bulk 
ultrasonic wave filter 41 is fabricated together with the semiconductor 
circuit 3 without deteriorating a yield rate. 
Embodiment 5 
FIG. 14 shows a thin film piezoelectric filter according to Embodiment 5 of 
this invention. In the figure, a condenser 14, an inductor 44 are 
configurated as parts of the semiconductor circuit 3 on the semiconductor 
substrate 1. A bulk ultrasonic wave filter 41, as shown in FIG. 12, is 
configured on lead titanate (PbTiO.sub.3). 
It is appreciated that the bulk ultrasonic wave filter 41 is configurated 
to cohere with the characteristic impedance of the connected external 
circuit. However, considering the error in size of the top-side electrode 
6 during manufacturing, coherency with the characteristic impedance is not 
always achieved. Also, because of design limitations, the bulk ultrasonic 
wave filter 41, configurated on lead titanate (PbTiO.sub.3), does not show 
enough coherency with the characteristic impedance. In this case, in order 
to provide coherence with the characteristic impedance of the external 
circuit, the inductor 44, the condenser 14 and a coherent circuit using a 
passive circuit device like a transmission line or a stub need to be 
connected to the front and rear side of the bulk ultrasonic wave filter 
41. By configuring the coherent circuit on the same semiconductor 
substrate 1 with the bulk ultrasonic wave filter 41, it is possible to 
configure a small and light filter which excels in the mass productivity. 
The bulk ultrasonic wave filter 41 uses lead titanate (PbTiO.sub.3). Since 
the normalized film thickness (hk) is equal to or less than 2 or the 
normalized film thickness (d/h) is equal to or less than 0.1, it is 
possible to obtain a filter having a characteristic of wide band width in 
which there occurs no spurious. 
Embodiment 6 
FIG. 15 shows a thin film piezoelectric device according to Embodiment 6 of 
this invention. FIG. 15 shows an example of an amplifier circuit using a 
transistor 13 and having an output terminal 37. A bias circuit and a 
coherent circuit on the side of the input terminal 43 are omitted in the 
figure. 
In the amplifier, in general, the input and output impedance of the 
transistor 13 is different from the characteristic impedance of the 
external circuit. Therefore, each of the input and output terminals of the 
transistor 13 needs a coherent or matching circuit. Since the transistor 
has capacitive admittance in many cases, a coherent circuit having the 
inductive admittance can be used. An inductor, a transmission line or a 
stub may be used in the coherent circuit. The size of a transmission line 
and a stub used in a coherent circuit depends on the wave length of an 
electromagnetic wave having an expected frequency excited in the 
semiconductor substrate where the semiconductor circuit is configured. 
When the frequency is relatively low, the region required for a 
transmission line and a stub gets large and the area of the semiconductor 
chip required to configure the amplifier gets large. As a result, there is 
a problem that the cost for manufacturing the semiconductor chip rises and 
the semiconductor cannot be configured in the actual chip area. In many 
cases, in the frequency band where the frequency is less than around 1 to 
2 GHz, an inductor is used as a device to provide inductive admittance. 
However, in the inductor, compared to the transistor 13 and the condenser 
14, a relatively larger area in the semiconductor circuit is needed. 
Further, when the line width is made narrow and the line density is raised 
in order to make the area of the inductor small, the resistance component 
of the inductor becomes large and the loss of the inductor increases. 
Accordingly, it is difficult to downsize the inductor and, consequently, 
the area of the semiconductor chip becomes large and the cost for 
manufacturing the semiconductor chip rises. 
On the other hand, the bulk ultrasonic wave resonator 35 using the 
piezoelectric ceramics such as lead titanate (PbTiO.sub.3) and lead 
titanate-zirconate (PZT) can be configured on the same semiconductor 
substance with the semiconductor circuit parts such as a transistor 13, a 
condenser 14 and a resistance 36. In addition, the occupying area is less 
than several hundreds .mu.m square, which is relatively small in 
comparison with the area of an inductor. Further, since lead titanate and 
lead titanate-zirconate (PZT) have a relatively large electromechanical 
coupling constant in comparison with that of zinc oxide (ZnO) and aluminum 
nitride (AlN), it is possible to exhibit inductive reactance over a wide 
frequency band. Then, it is possible to use lead titanate (PbTiO.sub.3) 
and lead titanate-zirconate (PZT) as an inductance in all the band 
required by the usual semiconductor circuit. As a result, it is possible 
to make the area of the whole semiconductor circuit including the bulk 
ultrasonic wave resonator 35 small and reduce the manufacturing cost. 
Embodiment 7 
FIG. 16 shows a thin film piezoelectric oscillator according to Embodiment 
7 of this invention. The circuit shown in FIG. 16 is similar to the 
circuit of FIG. 11. In the circuit device shown in FIG. 11, the condensers 
C.sub.O and C.sub.E which require a large capacitance use lead titanate 
(PbTiO.sub.3), that is used in the bulk ultrasonic wave resonator 35, as 
the dielectric substance. FIGS. 17 and 18 show an example of the 
configuration of the condenser 45 of FIG. 16 which uses lead titanate 
(PbTiO.sub.3), that is used in the bulk ultrasonic wave resonator 35, as 
the dielectric substance. FIG. 17 shows an upper-side view and FIG. 18 
shows an F--F cross sectional view. FIGS. 19 and 20 show another example 
of the configuration of the condenser 45 using lead titanate 
(PbTiO.sub.3), that is used in the bulk ultrasonic wave resonator 35, as 
the dielectric substance. FIG. 19 shows an upper-side view and FIG. 20 
shows a G--G cross sectional view. In the figures, air-bridges 46 and lead 
terminals 47 are provided. 
The capacitance of the condenser is determined by the dielectric constant, 
the thickness and the electrode area of the dielectric substance to be 
used. In the condenser used in the semiconductor circuit, there is a 
condenser which is utilized for cut off of the direct current, and there 
is a condenser which can be treated as a short circuit in a frequency 
band. The condenser 45 needs a large capacitance. Depending on the 
dielectric substance material used, the realistic dielectric substance 
thickness and the realistic dielectric substance area each have 
limitations. Further, it is better to make the chip area as small as 
possible in view of the cost for manufacturing the semiconductor circuit. 
Therefore, the dielectric substance is required to have a large dielectric 
constant. Lead titanate (PbTiO.sub.3) has a relative dielectric constant 
of about 200 in the GHz band. It has more than ten times the dielectric 
constant of silicon oxide (SiO.sub.2). This means that the area to realize 
the same capacitance can be one tenth of that required for silicon oxide. 
The use of a dielectric substance like lead titanate (PbTiO.sub.3) reduces 
the chip area of the semiconductor circuit and reduces the manufacturing 
cost. Furthermore, since an additional dielectric substance material is 
not required and it is possible to compose the condenser 45 simultaneously 
when the bulk ultrasonic wave resonator 35 is composed, it has the 
advantage of preventing an increase of manufacturing process caused by 
forming the condenser 45 having a different dielectric substance material. 
As to the structure of the condenser 45, there is a case where it is 
located between the ground conductor 5 and the top-side electrode 6 in the 
direction of thickness of lead titanate (PbTiO.sub.3) as shown in FIGS. 17 
and 18. And, there is a case where the surface of lead titanate 
(PbTiO.sub.3) has an interdigital structure by inserting the electrodes of 
two top-side electrodes 6 within each other as shown in FIGS. 19 and 20. 
In either case, in contrast with the bulk ultrasonic wave resonator 35, 
the polarization process is not performed and the via hole on the bottom 
side is not required for the condenser. 
Embodiment 8 
FIG. 21 shows a bulk ultrasonic wave resonator according to Embodiment 8 of 
this invention. In the figure, terminals 48a and 48b are for applying the 
direct current voltage for polarization. A condenser 49 and a direct 
current power source 50 are provided. 
In a case where a piezoelectric ceramic like lead titanate (PbTiO.sub.3) is 
used, when the proper direct current voltage is not applied to lead 
titanate (PbTiO.sub.3) for more than the defined time under the required 
temperature, a large piezoelectricity cannot be obtained. The polarization 
process is not required for zinc oxide (ZnO) and aluminum nitride (AlN) 
and other conventional piezoelectric ceramics which has a spontaneous 
polarization. In the polarization process, for example, the direct current 
voltage is applied between the top-side electrode 6 and the ground 
conductor 5 of the bulk ultrasonic wave resonator 35. When the bulk 
ultrasonic wave resonator 35 is fabricated together with the semiconductor 
circuit 3, the direct current voltage is applied to the semiconductor 
circuit 3 connected to the bulk ultrasonic wave resonator 35 and there 
occurs a problem that the direct current voltage for this polarization 
will cause damage to the semiconductor circuit 3 especially for active 
devices like the transistor 13. In order to prevent this, the condenser 49 
is inserted in series between the semiconductor circuit 3 and the terminal 
48a to which the direct current voltage of the bulk ultrasonic wave 
resonator 35 is applied. It is possible to block the direct current 
voltage at the time of polarization on the side of the semiconductor 
circuit 3 by inserting the condenser 49. At the operation frequency of the 
bulk ultrasonic wave resonator 35, the capacitance of the inserted 
condenser 49 should be such a large value whereby the impedance of the 
condenser 49 is possible to ignore substantially. Or the capacitance of 
the inserted condenser 49 should have a value which is possible to be used 
as the external additional capacitance of the bulk ultrasonic wave 
resonator 35. For safety, it is desirable to ground all the other 
terminals 37, 38 and 39 except for the terminal 48a to which the direct 
electric voltage is applied, during the polarization process. According to 
such methods, it is possible to prevent the damage of the semiconductor 
circuit 3 during the polarization process. 
Embodiment 9 
FIG. 22 shows a bulk ultrasonic wave oscillator according to Embodiment 9 
of this invention. In the figure, a terminal 51a of the bulk ultrasonic 
wave resonator 35 and a terminal 51b of the semiconductor circuit 3 are 
provided. 
In the polarization process, the terminal 51a and the terminal 51b are 
electrically separated. The terminal 48a is electrically connected to the 
transistor 13 in the semiconductor circuit 3. When the direct current 
voltage at the time of polarization is applied, the terminal 48a is 
grounded. By adopting such method, it is possible to prevent from applying 
the direct current voltage for the polarization process to the 
semiconductor circuit 3. When the polarization process ends and the 
operation as the bulk ultrasonic wave resonator starts, the terminal 51a 
and the terminal 51b should be bonded or connected according to a pattern 
of the circuit. The two terminals 48b and 51a in FIG. 22 can be combined 
and can be one terminal. 
Embodiment 10 
FIG. 23 shows a bulk ultrasonic wave oscillator according to Embodiment 10 
of this invention. In the figure, resistance 52 has a resistance value 
larger than the resistance 36 in the semiconductor circuit 3 in the direct 
current path from the terminal 48a with the direct current power source 50 
to the ground potential. 
During the polarization process, the direct current voltage is applied 
across the bulk ultrasonic wave resonator but there is no substantial 
direct current through the bulk ultrasonic wave resonator 35. Therefore, 
when the resistance 52 is inserted in series between the bulk ultrasonic 
wave resonator 35 and the direct current power source 50, the polarization 
process will not be affected. Hence, by arranging the resistance 52 which 
has a larger resistance value than the resistance 36 in the semiconductor 
circuit 3 located in the direct current path from the terminal 48a of the 
direct current power source 50 to the ground potential, it is possible to 
prevent the transistor 13 or active devices like the semiconductor circuit 
3 in the electric circuit from being destroyed due to an inappropriate 
applying method of direct current. Even though the applying method of 
direct current is proper, according to the transient response in a case 
where the direct current power source 50 is connected, the transient 
electric current flows. In this case, the resistance 52 is possible to 
prevent the active device from being destroyed. Further, when the 
semiconductor circuit 3 or the electric circuit actually operate, since a 
larger resistance value than the other resistance 36 is provided, the 
resistance 52 can be substantially ignored. Then, in the frequency band 
where the electric circuit operates, it is possible to prevent the 
operation of the electric circuit from being damaged. Here, when the 
resistance 36 exists to be connected in series with the resistance 52 on 
the path from the terminal 48a to the ground potential, the direct 
potential applied to the bulk ultrasonic wave resonator 35 is determined 
by the voltage dividing rate of the resistance 52 and the resistance 36 
located between the resistance 52 and the ground potential. Accordingly, 
there is a case that the polarization is not performed properly. The 
polarization process according to Embodiment 10 limits the type of the 
applicable semiconductor circuit 3 and the electric circuit. 
Embodiment 11 
FIG. 24 shows a view of the bulk acoustic wave device according to 
Embodiment 11 of this invention. The bulk ultrasonic wave resonator 35 of 
FIG. 22 is illustrated in FIG. 24 not in the circuit view but in the 
configuration view similar to FIG. 1. In the figure, a bulk ultrasonic 
wave oscillator chip 53 is provided. A semiconductor circuit 54 forms a 
pattern for applying the voltage at the time of polarization and is 
configurated on the same semiconductor 1 of the bulk ultrasonic wave 
oscillator chip 53. A pattern 55 is for applying the voltage at the time 
of polarization. When one of the patterns crosses over, multiple layer 
wiring is used. 
A plurality of bulk ultrasonic wave oscillator chips 53 are usually formed 
on a single semiconductor wafer at one time. The polarization process is 
preferentially performed before division into each of the bulk ultrasonic 
wave oscillator chips 53 to reduce the process cost required for 
polarization. As shown in FIG. 24, the bulk ultrasonic wave resonators 35 
in a number of bulk ultrasonic wave oscillator chips 53 on the wafer are 
grouped together and connected by the pattern 55 for polarization. After 
polarization, the semiconductor substrate that forms the pattern 55 for 
polarization is removed from the bulk ultrasonic wave oscillator chips 53. 
According to this procedure, the undesirable pattern 55 for the oscillator 
does not remain in each of the bulk ultrasonic wave oscillator chips 53. 
Therefore, it is possible to make the mount area of the chip smaller when 
the bulk ultrasonic wave oscillator chips 53 are mounted on a printed 
circuit board, a package or the other chips. 
In the polarization process, when all the bulk ultrasonic wave resonators 
35 on the same semiconductor wafer are connected by the pattern 55 for 
polarization, if there is even one inferior bulk ultrasonic wave resonator 
35 on the semiconductor wafer having a high direct current leakage between 
the top-side electrode 6 and the ground conductor 5, the polarization 
process of the other normal bulk ultrasonic wave resonator 35 on the 
semiconductor wafer will not be performed properly. Therefore, when the 
bulk ultrasonic wave resonators 35 on the semiconductor wafer are divided 
into multiple groups and the polarization process is performed by 
connecting each group by the pattern 55 for polarization, it is possible 
to reduce the effects of a bulk ultrasonic wave resonator 35 having 
excessive leakage current. 
Embodiment 12 
FIG. 25 shows a bulk acoustic wave device according to Embodiment 12 of 
this invention. In the figure, a pattern 56 directly connects a plurality 
of top-side electrodes 6. 
FIG. 25 shows an example of a bulk ultrasonic wave filter configured using 
a plurality of bulk ultrasonic wave resonators in close proximity to each 
other. In such a bulk ultrasonic wave filter, a plurality of bulk 
ultrasonic wave resonators are included in a single filter. It is 
necessary to perform the polarization process of the plurality of bulk 
ultrasonic wave resonators under the same conditions so that each of the 
plurality of bulk ultrasonic wave resonators has the same 
piezoelectricity. As shown in FIG. 25, when the plurality of bulk 
ultrasonic wave resonators are connected by the pattern 56 and a direct 
current voltage is applied to each in the same way, the polarization 
process can be performed for the plurality of bulk ultrasonic wave 
resonators under exactly the same conditions. Therefore, it is possible to 
reduce the processing cost for the polarization and to have the same 
piezoelectricity of the bulk ultrasonic wave resonator. Accordingly, the 
well characterized bulk ultrasonic wave filter can be processed at a low 
price. 
Additionally, by configuring the pattern 56 to have a characteristic 
impedance greater than 50 .OMEGA., in the neighborhood frequency of the 
operational frequency of the bulk ultrasonic wave filter, the impedance of 
the pattern 56 is regarded to be almost opened. Therefore, even when the 
pattern 56 remains after the polarization process, it does not affect the 
operation of the bulk ultrasonic wave filter. Hence, the step of cutting 
the pattern 56 after the polarization process can be omitted. 
When the pattern 56 has a resistance greater than 50 .OMEGA., the 
polarization process is not be affected. In the neighborhood frequency of 
the operational frequency of the bulk ultrasonic wave filter, the pattern 
56 has an impedance which is essentially an open circuit. Therefore, even 
when the pattern 56 remains after the polarization process, it is possible 
not to affect the operation of the bulk ultrasonic wave filter. Hence, the 
step of cutting the pattern 56 after the polarization process can be 
omitted. 
When the pattern 56 is composed of the resistance line wherein the 
characteristic impedance is above 50 .OMEGA., and the resistance is above 
50 .OMEGA., the polarization process is not affected. In the neighborhood 
frequency of the operational frequency of the bulk ultrasonic wave filter, 
the pattern 56 has an impedance which is essentially an open circuit. 
Therefore, even when the pattern 56 remains after the polarization 
process, it does not affect the operation of the bulk ultrasonic wave 
filter. Hence, the step of cutting the pattern 56 after the polarization 
process can be omitted. 
Embodiment 13 
FIG. 26 shows a bulk acoustic wave device according to Embodiment 13 of 
this invention. In the figure, a pattern 56 connects a plurality of ground 
conductors 5 directly. 
FIG. 26 shows an example of configuring the bulk ultrasonic wave filter by 
laying out a plurality of bulk ultrasonic wave resonators closely. In such 
a bulk ultrasonic wave filter, there exists a plurality of bulk ultrasonic 
wave resonators in a single filter. Therefore, it is necessary to perform 
the polarization process under the same conditions so that each of the 
plurality of bulk ultrasonic wave resonators has the same 
piezoelectricity. As shown in FIG. 26, when the plurality of bulk 
ultrasonic wave resonators is connected by the pattern 56 and the direct 
current voltage is applied, the polarization process can be performed for 
the plurality of bulk ultrasonic wave resonators under exactly the same 
conditions. Therefore, it is possible to reduce the processing cost for 
the polarization and to have same piezoelectricity for each of the bulk 
ultrasonic wave resonators. Accordingly, the well characterized bulk 
ultrasonic wave filter can be processed at a low price. 
Additionally, by using the line path, wherein the characteristic impedance 
is above 50 .OMEGA., as the pattern 56, in the neighborhood frequency of 
the operational frequency of the bulk ultrasonic wave filter, the pattern 
56 operates with an impedance which is regarded to be almost opened. 
Therefore, when the pattern 56 remains after the polarization process, it 
does not affect the operation of the bulk ultrasonic wave filter. Hence, 
the step of cutting the pattern 56 after the polarization process can be 
omitted. 
When the pattern 56 is composed of the resistance line, wherein the 
characteristic impedance is above 50 .OMEGA. and the resistance is above 
50 .OMEGA., the polarization process is not affected. In the neighborhood 
frequency of the operational frequency of the bulk ultrasonic wave filter, 
the pattern 56 operates with an impedance which can be regarded to be 
almost an open circuit. Therefore, even when the pattern 56 remains after 
the polarization process, it does not affect the operation of the bulk 
ultrasonic wave filter. Hence, the step of cutting the pattern 56 after 
the polarization process can be omitted. 
Embodiment 14 
FIG. 27 shows a bulk acoustic wave device according to Embodiment 14 of 
this invention. In the figure, a dielectric substance 57, a ground 
electrode 58 and a top-side electrode 59 and a wire 60 are provided. 
The dielectric substance 57 between the ground electrode 58 and the 
top-side electrode 59 operates as a condenser. The dielectric substance 
material can be an unpolarized dielectric substance like lead titanate 
(PbTiO.sub.3) configurated on the same semiconductor substrate 1. The 
dielectric substance material can be a general insulating material like 
silicone oxide (SiO.sub.2). A plurality of condensers is connected in 
series for the top-side electrode 6 of the bulk ultrasonic wave resonator. 
Some of the plurality of condensers are connected by the wire 60 to the 
lead electrode 47. Since the capacitive reactance is directly connected to 
the bulk ultrasonic wave resonator, it is possible to adjust the resonant 
frequency of the bulk ultrasonic wave resonator by varying the total 
capacitive reactance. The area of the top-side electrode 59 of each 
condenser is set to be different from each other. Based on the difference 
from the expected resonant frequency of the bulk ultrasonic wave 
resonator, the condenser to be connected by the wire 60 is appropriately 
selected and connected. In this case, since, each condenser is connected 
in parallel according to the wire 60, the capacitive reactance component, 
inserted in series in the bulk ultrasonic wave resonator, gets large when 
the condenser is connected. There is little deterioration due to age when 
the condensers are connected using the wires 60. When an appropriate 
material, selected based on age deterioration, is used for the capacitance 
of the condenser, the bulk ultrasonic wave resonator in which the resonant 
frequency is adjusted according to the above connecting demonstrates 
stable resonance characteristics. The above connecting method is also 
applicable to the impedance adjustment of the resonator. 
Embodiment 15 
FIG. 28 shows a bulk acoustic wave device according to Embodiment 15 of 
this invention. The ground conductor 5 of the bulk ultrasonic wave 
resonator serves as the ground electrode of each condenser. Each condenser 
is connected in parallel to the bulk ultrasonic wave resonator and it is 
possible to adjust the resonant frequency of the bulk ultrasonic wave 
resonator by varying the total capacitance of these condensers. The area 
of the top-side electrode 59 of each condenser is set to be different from 
each other. Based on a difference from the expected resonant frequency of 
the bulk ultrasonic wave resonator, the condenser to be connected by the 
wire 60 is appropriately selected and connected. In this case, since each 
condenser is connected in parallel by the wire 60, when the condenser is 
connected, the capacitive reactance component inserted in parallel to the 
bulk ultrasonic wave resonator gets large. 
Embodiment 16 
FIG. 29 shows a bulk acoustic wave device according to Embodiment 16 of 
this invention. In the figure, a pad 61 is provided. Each condenser is 
connected in series with each other and the condensers connected in series 
are connected to the bulk ultrasonic wave resonator in series. By varying 
the total capacitance of these condensers, it is possible to adjust the 
resonant frequency of the bulk ultrasonic wave resonator. In this case, 
the area of the top-side electrode 59 of each condenser is set to be 
different from each other. Based on the difference from the expected 
resonant frequency of the bulk ultrasonic wave resonator, the condenser is 
appropriately selected. Based on the selected condenser, each pad 61 is 
connected by the wire 60 forming a short circuit. In this case, each 
condenser is connected by the wire 60. When each pad 61 is selectively 
connected by forming a short-circuit, the capacitive reactance component 
inserted in series to the bulk ultrasonic wave resonator becomes large. 
Embodiment 17 
FIG. 30 shows a bulk acoustic wave device according to Embodiment 17 of 
this invention. Each condenser is connected in series with each other and 
further each of the condensers connected in series are connected in 
parallel to the bulk ultrasonic wave resonator. By varying the total 
capacitance of these condensers, it is possible to adjust the resonant 
frequency of the bulk ultrasonic wave resonator. The area of the top-side 
electrode 59 of each condenser is set to be different from each other. 
Based on the difference from the expected resonant frequency of the bulk 
ultrasonic wave resonator, the condenser to be connected by the wire 60 is 
appropriately selected and each pad 61 can be connected to form a short 
circuit. In this case, when each condenser is selectively connected by 
forming a short circuit, the capacitive reactance component inserted in 
parallel to the bulk ultrasonic wave resonator becomes large. 
Embodiment 18 
FIG. 31 shows a bulk acoustic wave device according to Embodiment 18 of 
this invention. The dielectric substance 57 between the ground electrode 
58 and the top-side electrode 59 operates as a condenser. The dielectric 
substance material can be an unpolarized piezoelectric substance like lead 
titanate (PbTiO.sub.3) composed on the same semiconductor substance 1 or a 
general insulating material like silicon oxide (SiO.sub.2). A plurality of 
condensers is connected in series to the top-side electrode 6 of the bulk 
ultrasonic wave resonators. The plurality of condensers are connected to 
the lead electrode 47 via the line patterns 62. Since the capacitive 
reactance is connected in series to the bulk ultrasonic wave resonator, it 
is possible to adjust the resonant frequency of the bulk ultrasonic wave 
resonator by varying the total capacitive reactance. Here, the area of the 
top-side electrodes 59 are set to be different from each other. Based on 
the difference from the expected resonant frequency of the bulk ultrasonic 
wave resonator, the condensers to be connected by the line patterns 62 are 
appropriately selected and connected. Because each condenser is connected 
in parallel via the line pattern 62, when the condenser is connected, the 
capacitive reactance component inserted in series to the bulk ultrasonic 
wave resonator becomes large. There is little deterioration due to age 
when the condensers are connected via the line patterns 62. When an 
appropriate material based on age deterioration is used for the 
capacitance of the condenser, the bulk ultrasonic wave resonator in which 
the resonant frequency is adjusted by the above connecting method can show 
a stable resonance characteristic. The above connecting method using the 
line pattern 62 is not suitable for adjusting each of the bulk ultrasonic 
wave resonators independently. However, when the variation of frequency at 
each lot is within a definite range, it is acceptable to perform 
adjustment lot by lot. The above connecting method has the advantage of 
adjusting the bulk ultrasonic wave resonators fabricated on one wafer 
together. 
Embodiment 19 
FIG. 32 shows a bulk acoustic wave device according to Embodiment 19 of 
this invention. The ground conductor 5 of the bulk ultrasonic wave 
resonator serves as the ground electrode of each condenser. Each condenser 
is connected in parallel to the bulk ultrasonic wave resonator. It is 
possible to adjust the resonant frequency of the bulk ultrasonic wave 
resonator by varying the total capacitance of these condensers. In this 
case, the area of the top-side electrode 59 of each condenser is set to be 
different from each other. Based upon a difference from the expected 
resonant frequency of the bulk ultrasonic wave resonator, the condensers 
to be connected by the line pattern 62 are appropriately selected and 
connected. Since each condenser is connected in parallel using the line 
pattern 62, when the condenser is connected, the capacitive reactance 
component inserted in parallel to the bulk ultrasonic wave resonator 
becomes large. 
Embodiment 20 
FIG. 33 shows a bulk acoustic wave device according to Embodiment 20 of 
this invention. Each condenser is connected in series with each other. The 
condensers connected in series are connected to the bulk ultrasonic wave 
resonator in series. It is possible to adjust the resonant frequency of 
the bulk ultrasonic wave resonator by varying the total capacitance of 
these condensers. The area of the top-side electrode 59 of each condenser 
is set to be different from each other. Based on the difference from the 
expected resonant frequency of the bulk ultrasonic wave resonator, the 
condensers to be connected by the line pattern 62 are appropriately 
selected and each pad 61 is connected to form a short circuit. Because 
each condenser is connected by forming the short-circuit using the line 
pattern 62, the capacitive reactance component inserted in series to the 
bulk ultrasonic wave resonator becomes large. 
Embodiment 21 
FIG. 34 shows a bulk acoustic wave device according to Embodiment 21 of 
this invention. Each condenser is connected in series with each other. The 
condensers connected in series are connected in parallel to the bulk 
ultrasonic wave resonator. It is possible to adjust the resonant frequency 
of the bulk ultrasonic wave resonator by varying the total capacitance of 
the condensers. The area of the top-side electrode 59 of each condenser is 
set to be different from each other. Based on a difference from the 
expected resonant frequency of the bulk ultrasonic wave resonator, the 
condensers to be connected by the line pattern 62 are appropriately 
selected and each pad 61 can be connected to form a short-circuit. Because 
each condenser is connected by forming the short-circuit using the line 
pattern 62, the capacitive reactance component inserted in parallel to the 
bulk ultrasonic wave resonator becomes large. 
Embodiment 22 
FIG. 35 shows a bulk acoustic wave device according to Embodiment 22 of 
this invention. The portion 63 is a cut off portion of the line pattern 62 
where the line pattern is cut off by using, for example, a laser. The 
dielectric substance 57 between the ground electrode 58 and the top-side 
electrode 59 operates as a condenser. The dielectric substance material 
can be an unpolarized dielectric substance like lead titanate 
(PbTiO.sub.3) composed on the same semiconductor substrate 1 or a general 
insulating material like silicon oxide (SiO.sub.2). plurality of 
condensers are connected in series to the top-side electrode 6 of the bulk 
ultrasonic wave resonator and the plurality of condensers are connected to 
the lead electrode 47 by the line pattern 62. Because the capacitive 
reactance is connected in series to the bulk ultrasonic wave resonator, it 
is possible to adjust the resonant frequency of the bulk ultrasonic wave 
resonator by varying the total capacitive reactance. The area of the 
top-side electrodes 59 of each condenser is set to be different from each 
other. By cutting the line pattern 62 using a laser, based on a difference 
from the expected resonant frequency of the bulk ultrasonic wave 
resonator, the condensers are selected appropriately or electrically 
separated. Since each condenser is separated from the parallel connection 
by the cut off, the capacitive reactance component inserted in series to 
the bulk ultrasonic wave resonator gets small. There is little 
deterioration due to age when the condensers are connected via the line 
patterns 62. When an appropriate material based upon the age deterioration 
is used for the capacitance of the condenser, the bulk ultrasonic wave 
resonator in which the resonant frequency is adjusted by the above 
connecting method shows a stable resonance characteristic. This connecting 
method can determine the portion 63 to be cut at each lot. This connecting 
method can change the portion to be cut independently based on each bulk 
ultrasonic wave resonator. Therefore, this connecting method has an 
advantage of being applicable in many cases, such as a case where the 
range to be adjusted is relatively wide and a case where the each bulk 
ultrasonic wave resonator is strictly adjusted one by one. 
Embodiment 23 
FIG. 36 shows a bulk acoustic wave device according to Embodiment 23 of 
this invention. The ground conductor 5 of the bulk ultrasonic wave 
resonator serves as the ground electrode of each condenser. Each condenser 
is connected in parallel to the bulk ultrasonic wave resonator. It is 
possible to adjust the resonant frequency of the bulk ultrasonic wave 
resonator by varying the total capacitance of these condensers. The area 
of the top-side electrodes 59 is set to be different from each other. 
Based on the difference from the expected resonant frequency of the bulk 
ultrasonic wave resonator, the line patterns 62 to be cut are determined 
and the condensers are appropriately selected or separated. In this case, 
because the condenser to be separated from the parallel connection are 
cut, the capacitive reactance inserted in parallel to the bulk ultrasonic 
wave resonator becomes small. 
Embodiment 24 
FIG. 37 shows a bulk acoustic wave device according to Embodiment 24 of 
this invention. Each condenser is connected in series with each other. The 
condensers connected in series are connected in series to the bulk 
ultrasonic wave resonator. In addition, each condenser is shorted in 
advance by the line pattern 62. By varying the total capacitance of these 
condensers, it is possible to adjust the resonant frequency of the bulk 
ultrasonic wave resonator. The area of the top-side electrodes 59 of each 
condenser are set to be different from each other. The condensers are 
selected by cutting the line patterns 62 based on the difference from the 
expected resonant frequency of the bulk ultrasonic wave resonator. In this 
case, because each condenser is connected in series by being cut, the 
capacitive reactance component inserted in series to the bulk ultrasonic 
wave resonator gets small. 
Embodiment 25 
FIG. 38 shows a bulk acoustic wave device according to Embodiment 25 of 
this invention. Each condenser is connected in series with each other. The 
condensers connected in series are connected to the bulk ultrasonic wave 
resonator in parallel. In advance, each condenser is shorted by the line 
patterns 62. By varying the total capacitance of these condensers, it is 
possible to adjust the resonant frequency of the bulk ultrasonic wave 
resonator. The area of the top-side electrodes 59 of each condenser are 
set to be different from each other. The condensers are selected by 
cutting the line pattern 62 based on the difference from the expected 
resonant frequency of the bulk ultrasonic wave resonator. In this case, 
because each condenser is connected in series by being cut, the capacitive 
reactance inserted in parallel to the bulk ultrasonic wave resonator 
becomes large. 
Embodiment 26 
FIG. 39 shows a bulk acoustic wave device according to Embodiment 26 of 
this invention. In the figure, a power source 64 and a diode 65 with 
variable capacity are provided. 
The diode 65 with variable capacitance can change the capacitance based on 
the voltage applied from the power source 64. When the diode 65 with 
variable capacitance and the bulk ultrasonic wave resonator 35 are 
connected in parallel, as shown in FIG. 39, or in series, the applied 
voltage from the power source 64 is controlled to vary the value of the 
capacitive reactance connected in parallel or in series to the bulk 
ultrasonic wave resonator 35. In this manner, the resonant frequency of 
the bulk ultrasonic wave resonator 35 is adjusted. Since the bulk 
ultrasonic wave resonator 35 according to this invention is capable of 
being fabricated together with the semiconductor circuit, the power source 
64 can be manufactured on the same semiconductor substrate 1 with the bulk 
ultrasonic wave resonator by using a transistor and the like easily. 
Embodiment 27 
FIG. 40 shows a bulk acoustic wave device according to Embodiment 27 of 
this invention. In the figure, resistances 66 and a terminal 67 are 
provided. 
In the film bulk acoustic wave device shown in FIG. 40, the applied voltage 
to the diode 65 with variable capacitance is selected based on the voltage 
ratio of the resistances 66. Each resistance 66, having a terminal 67, has 
a different resistance value from the other resistances 66. The terminal 
67 which can provide the proper amount of adjustment is selected using, 
for example, a wire. Accordingly, the applied voltage to the diode 65 with 
variable capacitance is determined. As a result, the resonant frequency of 
the bulk ultrasonic wave resonator can be adjusted easily. 
Embodiment 28 
FIG. 41 shows a bulk acoustic wave device according to Embodiment 28 of 
this invention. The bulk acoustic wave device shown in FIG. 41 determines 
the applied voltage to the diode 65 with variable capacitance based on the 
voltage ratio of the resistances 66. Each resistance 66, having a terminal 
67, has different resistance values from the other resistances 66. For 
instance, in case of connection with another power source 64 or connection 
with power source 64 on the same semiconductor substrate 1 with the bulk 
acoustic wave device, the terminal 67 of one of the resistances 66 and the 
lead electrode 47 are connected to provide the proper amount of 
adjustment. Such method excels in lot by lot adjustment. 
Embodiment 29 
FIG. 42 shows a bulk acoustic wave device according to Embodiment 29 of 
this invention. The bulk acoustic wave device shown in FIG. 42 determines 
the applied voltage to the diode 65 with variable capacitance based on the 
voltage ratio of the resistances 66. The terminal 67 of each resistance 
66, which have different resistance values respectively, is connected in 
advance to the lead electrode 47 using to the line pattern 62. In order to 
provide the proper amount of adjustment, the connection between the 
terminal 67 and the lead electrode 47 is cut off by using, for example, a 
laser. Such method has the advantage of being applicable in case of 
adjustment at each lot and in case of adjusting each of the bulk acoustic 
wave devices respectively. 
Embodiment 30 
FIG. 43 shows a bulk acoustic wave device according to Embodiment 30 of 
this invention. The bulk acoustic wave device shown in FIG. 43 determines 
the applied voltage to the diode 65 with variable capacitance based on the 
voltage ratio of the resistance 66. Each resistance 66, having a terminal 
67, has a different resistance value than the other resistances 66. By 
selecting the terminal 67 which can provide the proper amount of 
adjustment by using such as the wire 60 and shorting the resistance 66, 
the applied voltage to the diode 65 with variable capacitance is 
determined. As a result, it is possible to adjust the resonant frequency 
of the bulk ultrasonic wave resonator 35 easily. 
Embodiment 31 
FIG. 44 shows a bulk acoustic wave device according to Embodiment 31 of 
this invention. The bulk acoustic wave device shown in FIG. 44 determines 
the applied electric voltage to the diode 65 with variable capacitance 
according to the voltage ratio of the resistance 66. Each resistance 66, 
having a terminal 67, has a different resistance value than the other 
resistances 66. By selecting the terminal 67 to provide the proper amount 
of adjustment, the applied electric voltage to the diode 65 with variable 
capacitance is determined. As a result, the resonant frequency of the bulk 
ultrasonic wave resonator 35 can be adjusted easily. Such method excels in 
lot by lot adjustment. 
Embodiment 32 
FIG. 45 shows a bulk acoustic wave device according to Embodiment 32 of 
this invention. The bulk acoustic wave device shown in FIG. 45 determines 
the applied voltage to the diode 65 with variable capacitance according to 
the voltage ratio of the resistance 66. Each resistance 66 has a different 
resistance value than the other resistances 66. Each resistance 66 is 
shorted in advance using the line pattern 62. The connection of the line 
pattern 62 between the terminals 67 is cut off by using, for example, a 
laser to provide the proper amount of adjustment. Such method has the 
advantage of being applicable in case of lot by lot adjustment and in case 
of adjusting each of the bulk acoustic wave devices respectively. 
As has been described, FIGS. 1 and 2 show an example of using lead titanate 
(PbTiO.sub.3) as the piezoelectric substance. In this invention, lead 
titanate-zirconate (PZT) 32 can be used instead of the lead titanate 
(PbTiO.sub.3) as the piezoelectric substance. Similarly, in FIGS. 9, 10, 
lead titanate (PbTiO.sub.3) can be used as the piezoelectric substance. In 
addition, FIGS. 1, 2, 9 and 10 illustrate only the bulk ultrasonic wave 
resonator. But in the figures, the bulk ultrasonic wave filter and other 
semiconductor circuits 3 can be on the same semiconductor substrate 1. The 
structure of the via holes 7 and 33 on the bottom side of the ground 
conductor 5 shown in FIGS. 1, 2, 9 and 10 can be one of structures shown 
in FIGS. 46 to 53 in which the via holes 7, 33 or the air gap 88 are 
provided on the bottom side of the ground conductor 5 or the dielectric 
substance 4. 
As has been described, FIGS. 11, 16, 21, 22, 23 and 24 show an example of 
the bulk ultrasonic wave oscillator using the bulk ultrasonic wave 
resonator. In this invention, it is also useful to configure it on the 
same semiconductor substrate 1 with other generally used semiconductor 
circuits such as the bulk ultrasonic wave filter, a semiconductor 
amplifier, a semiconductor mixer, an analog to digital convertor, a 
digital to analog convertor, a Central Processing Unit (CPU), a Digital 
Signal Processor (DSP), a memory and so on. As stated, since it is 
possible to fabricate the bulk ultrasonic wave resonator together with 
many sorts of semiconductor circuits on the same semiconductor substrate 
1, it is possible to apply it to the whole electric circuit or whole 
electronics circuit using the bulk acoustic wave device without limiting 
to a specific device. 
As has been described, FIG. 15 shows an example in which the bulk 
ultrasonic wave resonator 35 is inserted as an inductor between the 
transistor 13 and the output terminal 37. In this invention, it is 
possible to insert the bulk ultrasonic wave resonator into an arbitrary 
position in the semiconductor circuit. 
As has been described, FIG. 16 shows an example in which the dielectric 
substance of the condenser C.sub.0 45 and the condenser C.sub.E 45 uses 
the piezoelectric substance that is used in the bulk ultrasonic wave 
resonator 35. However, this invention is applicable to the arbitrary 
condenser 45 in the semiconductor circuit 3. 
As has been described, FIGS. 17, 18, 19 and 20 show only condensers in 
which the piezoelectric substance uses lead titanate (PbTiO.sub.3). In 
this invention, it is possible to use the bulk ultrasonic wave resonator 
and the bulk ultrasonic wave filter, and arbitrary semiconductor circuits 
3 in addition to the condenser. In case of connection with the lead 
electrode 47, the other connecting methods, except for the air bridge 46, 
are also effective. 
As has been described, FIGS. 21, 22 and 23 show polarization methods. The 
combination of these methods is more effective. In FIG. 24, the bulk 
ultrasonic wave oscillator is shown as an example of processing a 
plurality of chips 53. It is also applicable to other circuits like bulk 
ultrasonic wave filters and semiconductor circuits. Further, the shape of 
polarization patterns and the shape of the semiconductor forming the 
polarization pattern are not necessarily the same as those shown in FIG. 
24 and an arbitrary shape can be used. The structure in each chip 53 of 
FIG. 24 shows a case of employing the polarization process shown in FIG. 
22. The structure shown in FIGS. 21 and 23 also can be used for FIG. 24. 
As has been described, FIGS. 25 and 26 show examples of the bulk ultrasonic 
wave filter composed of two electrodes. This invention is also applicable 
to the connection of the bulk ultrasonic wave filter having more than two 
electrodes. This invention is also applicable to the connection of the 
bulk ultrasonic wave resonator and the bulk ultrasonic wave filter formed 
in a plurality of chips. 
As has been described, FIGS. 27 to 38 show a case of the bulk ultrasonic 
wave resonator. In this invention, the bulk ultrasonic wave filter is also 
available. Further, the condenser need not always have a structure as 
shown in FIGS. 27 to 38. 
As has been described, FIGS. 39 to 45 show an example using the diode 65 
with variable capacitance. A transistor can also be used as well as the 
diode 65 with variable capacitance. Further, there is shown a case where 
the diode 65 with variable capacitance is connected in parallel to the 
bulk ultrasonic wave resonator 35. Instead, the diode 65 can be connected 
in series. 
As has been described, according to this invention, the piezoelectric 
substance uses piezoelectric ceramics which is mainly composed of lead 
titanate (PbTiO.sub.3) or lead titanate-zirconate (PZT). When the 
thickness of the piezoelectric ceramics is h, the thickness of platinum 
(Pt) or gold (Au) as the ground conductor is d and the wave number of 
acoustic waves to propagate in the direction parallel to the surface of 
the piezoelectric ceramics is k, kh is less than 2 or d/h is less than 
0.1. Accordingly, there causes no spurious and a large electromechanical 
coupling constant can be realized. As a result, it is possible to obtain a 
well characterized film bulk acoustic wave device. 
Since the piezoelectric ceramics have a large electromechanical coupling 
constant, it is possible to adjust the resonant frequency by using an 
electrical adjusting method. Even when the piezoelectric ceramics are 
fabricated together with the semiconductor circuit, it is possible to 
select one of the adjustment methods which can be used with the 
manufacturing process of the semiconductor circuit. Consequently, the 
manufacturing cost can be reduced. 
Furthermore, according to this invention, since the piezoelectric ceramics 
can show an inductive reactance characteristic in a wide frequency band, 
it can be used as the inductor in the semiconductor circuit. Consequently, 
it is possible to make the area of the semiconductor circuit small and to 
reduce the manufacturing cost of the semiconductor circuit. 
Furthermore, according to this invention, the piezoelectric ceramics whose 
piezoelectricity is strengthened by the polarization process is used. By 
using a part of the piezoelectric ceramics as a high dielectric substance, 
the area of the condenser is made small. The other parts can be used as 
the bulk acoustic wave device by using the polarization process. 
Therefore, by controlling the manufacturing process of the bulk acoustic 
wave device, it is possible to downsize the condenser and to reduce the 
manufacturing cost. 
Furthermore, according to this invention, it is possible to prevent the 
damage of devices in the semiconductor circuit caused by the polarization 
process. It is possible to perform the polarization process of many bulk 
ultrasonic wave resonators and the filters at the same time. Therefore, 
the processing cost for polarization process can be reduced and the 
effective polarization process can be realized. 
Furthermore, according to this invention, since it is electrically possible 
to adjust the variation of the resonant frequency caused by manufacturing 
errors of the piezoelectric thin film thickness, the well-qualified film 
bulk acoustic wave device can be obtained. 
Having thus described several particular embodiments of the invention, 
various alterations, modifications, and improvements will readily occur to 
those skilled in the art. Such alterations, modifications, and 
improvements are intended to be part of this disclosure, and are intended 
to be within the spirit and scope of the invention. Accordingly, the 
foregoing description is by way of example only, and not intended to be 
limiting. The invention is limited only as defined in the following claims 
and the equivalents thereto.