Note: Descriptions are shown in the official language in which they were submitted.
~2~l55~
~he present invention relates to a piezoelectric
resonator and/ more particularly, relates to a
piezoelectric resonator having an improved structure and
characteristic.
In the accompanying drawings:-
Figs. lA and lB show a front surface and a rear
surface of a substrate of a conventional piezoelectric
ceramic resonator of TE vibration mode with two-stage
structure, respectively;
Fig. 2 is a cross-sectional view of the piezoelectric
resonator shown in Figs. 1~ and lB,
~ig. 3 shows a frequency characteristic of the
piezoelectric resonator shown in Figs. lA and lB
Fig. 4 is a frequency spectrum diagram of a
television signal after video signal detection;
Fig~ 5 shows an SIF filter using a conventional
piezoelectric resonator employed in a television;
Figs. 6A and 6B show a front surface and a rear
surface of a substrate of a conventional piezoelectric
resonator of TS vibration mode with two-stage structure,
respectively;
Fig. 7 shows a frequency characteristic of the TS
vibration mode piezoelectric resonator shown in Figs. 6A
and 6B;
Fi~s. 8A and 8B show a front cross-sectional view and
a side view~ respectively, of a piezoelectric resonator of
a single-stage structure which is a preferred embodiment
o the present invention,
Fi~. 9 is a perspective view showing a process step
for forming a piezoelectric resonator of a preferred
embodiment of the present invention;
Fig. 10 is a perspective view showing a piezoelectric
resonator of a preferred embodiment oE the present
invention~ which is formed through the step shown in Fig. 9;
and
Figs. 11 and 12 show a frequency plot of a piezoelectric
~L2~78S~
resonator of a preferred embodiment of the present
invention.
A piezoelectric resonator has been being employed
widely in the prior art, for example, as a filter in a
sound signal detecting circuit of a television and as a
reactance element or a phase shifting element in an FM
demodulating circuit, utilizing a characteristic operating
as an impedance transducer element to a frequency. A
piezoelectric resonator utilizing a substrate thickness
expansion vibration (TE vibration3 mode and a piezoelectric
resonator utilizing a substrate thickness shear vibration
(TS vibration) mode have been d~veloped as a piezoelectric
resonator in a frequency zone of mainly 1 to 50 MHzo These
two piezoelectric resonators are generally structured as
an energy trapping type dual mode piezoelectric resonator.
Figs. lA and lB show a typical example of a
conventional piezoelectric ceramic resonator substrate
(two-stage structure) utili~ing a TE vibration mode,
wherein Fig. lA shows a front surface of the substrate and
Fig. lB shows a rear surface thereof. In these ~igures,
the hatched portion shows an electrode film formed on the
surface of the resonator substrate.
The piezoelectric resonator having such an electrode
structure exhi~its a distribution of electric field as
shown in Fig. ~. Fig. 2 shows a cross-sectional view o~
the sub~trate of a piezoelectric ceramic resonator shown
in Figs. lA and lB, wherein a verti~al electric field Ez
i5 an electric field necessarily needed in this mode and a
hori~ontal or parallel electric field Ey i3 an electric
field generated between an input electrode and an output
electrode, which electric field is not necessary. The
horizontal electric field ~y localIy causes a TS vibration
and as a result, a spurious appears due to the TS
vibration mode. Since the speed of the TS vibration
propagating through the substrate is a half of that of the
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TE vibration, the spurious appears in the neighborhood of
about a half of the necessary frequency.
Fig. 3 shows a frequency characteristic when a
piezoelectric ceramic resonator as shown in Figs. lA
and lB is used as a filter. In Fig. 3 r the abscissa axis
indicates frequency in MHz and the ordinate axis indicates
attenuation in decibels (dB). As can be seen from Fig. 3,
a signal having a frequency of ~.50 MHz passes through
this filter and the spurious appears in the neighborhood
of 1.8 MHz which is about a half of the frequency.
Fig. 4 is a frequency spectrum diagram of a
television signal after ~ideo detection. The abscissa
axis indicates a fre~uency and the ordinate axis indicates
a spectrum. As can be seen in Fig. 4~ a vid~o signal Y is
distributed in a frequency region of 0 to fv and a sound
signal S i9 superimposed in the frequency region the
middle of which is a frequency fs, and a color signal C is
superimposed in a frequency region the middle of which is
a frequency fc-
Now, it is assumed that the piezoelectric resonator
of a conventional TE vibration mode ha~ing the above
described characteristic of Fig. 3 is used as an SIF
filter which makes only the particular frequency fs pass
therethrough. Then, a video signal having a fre~uency in
the neighborhood of a half of the frequency fs is made to
pass due to a spurious vibration of the filter and appears
as a sound buzz of a television.
Accordingly, in case where such a piezoelectric
resonator is conventionally used as an SIF filter, the
original function as the SIF filter has been able to be
achieved by using as assistant a separate high-pass filter
52 connected in series to the piezoelectric filter 51 as
shown in Fig. 5.
Figs. 6~ and 6B show a typical example of a
conventional piezoelectric ceramic resonator substrate
. , .
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(two-stage structure) utilizing a TS vibration mode,
wherein Fig. 6A shows a front surface and Fig. 6B shows a
rear surface. In these figuresr the hatched portion
indicates an electrode film formed on the filter surface.
Fig. 7 indicates a fre~uency characteristic when a
piezoelectric ceramic resonator of a TS vibration mode
shown in Figs. 6A and 6B is used as a filter. In Fig. 7,
the abscissa axis indicates a frequency in MHz and the
ordinate a~is indicates attenuation in decibels (diB).
It can be understood through a cGmparison of Fig. 7 with
Fig. 3 that the spurious attenuation in the fre~uency
region of 0 to 4O0 MHz in the TS vibxation mod~
piezoelectric resonator is very superior to a
piezoelectric resonator of the TE vibration mode~ However,
even in the piezoelectric resonators of the TS vibration
~ode, the attenuation of 50 to 55 ~ which is practically
needed as an SIF filter of a television signal can never
be obtained.
Thus, only a circuit as shown in Fig. 5 can be
prac-tically employed in the case where the conventional
piezoelectric resonator of the TS vibration mGde is used as
an SIF ilter as well as in case where the conventional
pie~oelectric resonator of the TE vibration mode is used
as an SIF filter.
In additionr the thickness of the substrate of the
piezoelectric resonator of the TS vibration mode must be
made to about one half the thickness of the substrate of
the piezoelectric resonator of the TE vibration mode. The
reason for this is that, due to different vibratlon manners
in these modes, the same resonating frequency can be
obtained, in the TS vibration mode, by usinq a substrate
having the thickness which is a half o the thickness in
case of theT~ vibration mode. As typically shown in Figs. 6A
and 6B, a structure of the piezoelectric resonator of the TS
vibration mode with two-stage structure should be in the
t_~ ?
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form of U-shape in view o~ the nature of the vibration
mode. For this reason, the yield of good products and
relia~ility become poor in terms of mechanical strength.
Furthermore, a siæe or dimension of a substrate is
determined so as to obtain a predetermined electrical
characteristic. In this connection, for example, as shown
in Figs. lA and 6A, the~size or dimension of the substrate
for the conventional TE vibration mode piezoelectric
resonator and a conventional TS vibration mode piezoelectric
resonator is relatively larger and he~ce there is a defect
that there is a limitation for making smaller parts or
components u~ilizing such piezoelectric resonators.
The present invention is directed to a piezoelectric
resonator having an improved structure and characteristic.
lS Accordingly, an object of the present invention is to
provide a piezoelectric resonator ~hich may be made smaller
and may have an improved frequency characteristic and
enhanced mechanical strength.
The invention provides a piezoelectric resonator
comprising a first resonating single mode thickness
expansion vibration unit including a first substrate
comprised of a piezoelectric material and having two major
surfaces, a first common electrode disposed on one major
surface of the first substrate, and a first electrode
disposed on the other major surface of the ~irst substrate,
the first electrode being at least partially opposed to the
first common electrode through the first substrate, a
second single mode thickness expansion vibration resonating
unit including a secon~ substrate comprised of a piezo-
electric material and havi~g two major surfaces, a secondcommon electrode disposed on one major surface of the
second substrate, and a secon~ electrode disposed on the
oth~r major surface of the second substrate, the second
~lectrode being at least partiall~ opposed to the second
common electrode through the second substrate, and
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arraying means for arraying and ~ixing the ~irst and
second resonating units so that the first and second
common electrodes are opposed to each other and the first
ana second common electrodes are electrically connected
at at least one portion thereof so that a third electrode
is formed whereby the piezoelectric resonator resonates
in a dual mode thickness expansion vibration.
The present invention will become more readily
apparent from the followin~ detailed description of an
embodiment of the present invention when taken in
conjunction with the accompanying drawinqs.
Referring to Figs. 8A and 8B, a piezoelectric
resonator embodying the invention comprises a ~irst
resonating unit 81 and a second resonating unit 82. Each
of the resonating units 81 and 82 has the same shape and
structure. The resonating unit 81 has a substrate 811
comprised of piezoelectric material, preferably, ceramic.
On one major surface of the pie~oelectric ceramic substrate
811 is formed an electrode film 812 in a longitudinal
direction thereof from the one end to about three fifths,
for example. Similarly, a common electrode film 813 is
formed on the other major surface in a longitudinal
direction thereof from the other end to about three fifths,
for example. These electrode ilms 812 and 813 are
partially opposed to each other in the middle portion of
the piezoelectric ceramic substrate 811 therethrough.
Another resonating unit 82 is of the same structure as that
of the resonatinq unit 81.
Two resonating units 81 and 82 are combined such that
the common electrode films 813 and 823 are opposed ~o each
other and affixed by a stronq and insulating adhesive 84
while leaving a connecting portion 83 of common electrodes.
The common electrodes 813 and 823 affixed in an opposed
manner are electrically connected at the connectinq portion
83 so that a single electrode is formed. A common lead 86
3Si4
is connected to the common electrode connecting portion 83
by a solder or an electrically conductive adhesive 85.
An input lead 87 and an output lead 88 are connected to the
electrodes 812 and 822, respec-tively, near the end portion
thereoE by means of a solder 85 or an electrically
conductive adhesive.
Fig. 8B is a side view of the piezoelectric resonator
explained in the foregoing and shown in Fig. 8A, wherein
the solder or electricaIly conductive adhesive 85 and the
leads 86 and 87 are omitted.
A preferred method of manufacturing a piezoelec~ric
resonator according to a preEerred embodiment of the present
invention as shown inFigs. 8A and 8B will now be described
with reference to Figs. 9 and 10. Fig. 9 is a perspective
view showing one manufacturing step for a piezoelectric
resonator. First of all, resonating unit source substrates
91 and 92 comprised of a piezoelectric material, preferably,
a ceramic, are prepared. The polarization axes of the
resonating unit source substrates 91 and 92 are in the
direction indicated in arrow P which is along the major
surfaces thereof. Electrode films 912, 913, 922 and 923
coverinq about three fifths of the major surEaces are
~ormed on the respective major sur~aces of the source
substrates 91 and 92. The electrode films 912 and 913 are
partially opposed in the nei~hbo~hood of a middle portion
and in a longitudinal dire~ion of the source substrate 91
and the electrode films 922 and 923 are partially opposed
in the neighborhood oE a middle portion and the longitudinal
direction of the source substrate 92. These electrode films
may ~e of electrically conductive paint, for example, and
are formed by means of painting~ vapor deposition or the like.
Source substrates 91 and 92 for t~o resonating units
are brought together with the electrode ~ilms 913 and 922
thereof opposed to ~ach other. An insulating adhesive 840
(Fig. 10) is -Eirstly painted extremely thinly on the major
surface 92a on which the electroae film 922 of the resonating
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.. ~ . . . . .. .. .
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source substrate 92 is formed. The -two resonating units
source substrat~s 91 and 92 are affixed together in this
way.
An electrically conductive adhesive 830 (Fig. 10) is
painted on one end surface of the combined resonating units,
in the middle portion of which the electrode films 91~ and
922 are disposed. The electrically conductive adhesive 830
soaks between the electrode films 913 and 922, whieh are
opposed, so that an electrode eonnecting portion ~30a is
formed, and hence the electrode films 91~ and 922 are
electrically connected.
The thus affixed resonating unit source substrates
are cut along line 1 indicated by arrows 95 in Fig. 9. As
a result, a plurality of piezoeleetrie resonators, one of
which is shown in Fig. 10, are obtained. It will be readily
understood that the piezoelectric resonator as shown in
Fig. 10 has substantially the same strueture as the
piezoelectric resonator shown in Figs. 8A and 8B. In
Fig. 10, the same portions as in Fig. 9 are indieated by
correspondin~ primed reference numerals.
In the above-described embodiment, two resonating unit
source substrates are affixed by using an inæulating
adhesive. However, instead ~hereof, an electrically
eonduetive adhesive may be employ~d. In sueh a ~ase, only
the portion of the eleetrode films 91~ and 922 are affixed
to each other. The electric conductive adhesive is
painted thinly only on the surfaee 922a of the eleetrode
film 922 and, thereafter, the two resonating unit source
sub~trates 91 and 92 are combined. Aecordingly, the
electrode films 913 and 922 are affixed so that substantially
a single electrode is formed.
In the piezoelectrie resonator shown in FigO 10, the
T~ vibration is excited in each of the resonating units 11
and 12. For example, in the resonating unit 12, the TS
vi~ration is exeited in the opposed portion o the
electrodes 922' and 923' shown by the reference charaeter
~r ~
~ 2~
L in figure and the energy i5 trapped in the longitudinal
direction of the substrate 92'. Accordinglyr if and when
the length of the substrate 9Z' is made extremely large,
for example, more than twenty times as compared with the
thic]~ness thereof, neither of the end surfaces o~ -the
substrate 92' vibrates. The same applies to the substrate
91'. Hence, it is possible to provide input and output
leads in the end portions of electrodes 912' and 923l and a
common lead in the common electrode portion 830 by means
of solder~ electrically conductive adhesive, or the like so
that the element as shown in Fig. 8A is obtained.
In the above-described embodiment, in order to obtain
a desired elect~ical characteristic, the shape or
configuration of the resonating unit source substrates 91
and 92 and the arrangement of the electrode films on the
source substrates may be adequately changed.
Figs. 11 and 12 show electrical characteristics of the
piezoelectric resonator of a preferred embodiment ~f the
present invention as shown in Figs. 8A, 8B and 10.
Fig. 11 is a plot of admi~tance versus frequency
20 wherein the abscissa axis indicates a fre~uency in ~Hz
and the ordina-~e axis indicates a~mittance. In thi.s
igure, an S mode curve shows variation of an admittance
between a connecting lead (no~ shown) provided for
connecting an input lead 87 and an output lead 88 to
each other and a common lead 86 in Fig. 8A when an
a]ternating current of high frequency of 3 to 6 MHz is
applied therebetween. An A mode indicates variation of an
a~littance between the input lead 87 and the output lead
8~ when nothing is connected to the common lead 86 and an
alternating current of high frequency of 3 to 6 M~z is
applied therebetween. As seen fr~m Fig. 11, by chanqing
the connecting manner of three terminals of the piezoelectric
resonator in Fig. 8A two vibration responses can be obtained.
The two resonating frequencies in these vibration responses
are slightly offset. Accordingly, it can be understood that
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the piezoelectric resonator ~orms a dual mod~ piezoelectric
resonator as a conventional energy trapping type dual mode
piezoelectric resonator stated above.
Fiq. 12 shows a characteristic of attenuation with
respect to a frequency when a piezoelectric resonator
shown in Fig. 8A is used as a filter. In Fig. 12, the
abscissa axis indicates frequency (MHz) and the ordinate
axis represents an attenuation (dB). As readily understood
~rom Fig. 12, the spurious response in the frequency reqion
13 o~ 0 to 10 MHz of the piezoelectric resonator is about
37 or 38 dB. This corresponds to the ~requency
characteristic of the conventional TS vibration mode
piezoelectric resonator with a two-stage structure as
described in the oregoing. Thus, a single structure
piezoelectric resonator in accordance with the present
invention has per~ormance corresponding to a conventional
two-stage structured piezoelectric resonator. Accordingly,
an insertion loss of the present piezoelectric resonator
is about a half of that o~ a conventional piezoelectric
resonator, which means a great improvement.
The dimensions of the piezoelectric resonator shown
in Fiqs~ 8A and 8B are such that the width is 0.8 mm, the
height is 5.0 ~m and the thickness is 0.5 mm. Accordingly,
the sur~ace area thereo~ is 4.0 ~Tl2~ On the other hand, the
size of a conventional TE vibration mode piezoelectric
resonator as shown in Figs. lA and 2 and having the same
resonating frequencyas the resonator of the invention is
such that the width is 9.0 mm, the height is 6.0 mm and
the thickness 0.5 mm and hence the surface area is 54.0 mm2,
In addition, the size o~ the conventional TS vibration mode
piezoelectric resonat~x hauing the same resonating ~requency
is such that the width is 3.0 ~mJ the height is 6.5 mm and
the thickness is 0.23 mm and hence the sur~ace area is 19.5
mm . Thus, the piezoelectric resonator in accordance with
the present invention can be made substantially smaller in
size.
, . . . ... .. . . . .... . . . . . . . . . . . . .
7~
In addition, since the piezoelectric resonator
embodying the present invention is of such structure -that
two resonating substrates are affixed to each other, the
~hickness is thick as cornpared with a conventional
piezoelectric resonator, particularly, a piezoelectric
resonator of a TS vibration mode, and thus, the mechanical
strength is enhanced and the mechanical reliability can
be improved.
An electric characteristic of a piezoelectric
resonator shown in Fig. 10 can be properly changed by
properly selecting the opposed width L of the electrode ~ilms
and a cut width W of a substrate. The opposed width L of
the electrode Eilms can be easily changed by changing a
printing pattern in forming the electrode films and the cut
width W can be simply changed by initial adjustment of ~he
cutting when the affixed resonating unit source substrate is
cut. Accordingly, as compared with a con~entional
piezoelectric resonator, the design of the piezoelectric
resonator embodying the present invention can be easily
changed so that desired electrical characteristicsJ such as
passband width, maximum attenuation and insertion loss,
are obtained. Particularly, it is easy to change the passband
width.
Fi~. 13 shows c~nother preEerred embodiment of the
piezoelectric resonator embodying the present invention.
The significant feature of the piezoelectric resona-tor
shown in Fig. 13 resides in that the above described
piezoelectric resonator is made to be a two-stage structured
piezoelectric resonator. A gap 133 is formed in the two-
stage structured piezoelectric resonator so that a firstresonating element 131 and a second resonating element 132
can independently operate. The gap 133 can be easily
formed by using a stripe of conductive adhesive 134 having
an appropriate width and thickness and extending perpendicular
to the paper so as to adhere the first resonating element 131
to the second resonating element 13Z.
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In manufacturing the piezoelectric xesonator 13 as
shown in Fig. 13, many produc-ts can be simply made by
fixing together the resonating unit source substrates
and thereafter cuttinq them, which is similar to the
manufacturing method explained in the foregoing referring
to Figs. 9 and 10.
Since the Fig. 13 piezoelectric resonator is of a
two-stage structure, the insertion loss thereof is the
same as the above described conventional two-stage
structured piezoelectric resonator. However, the spurious
characteristic in the frequencY region of 0 to 10 MHz is
greatly improved. Accordingly, such Fig. 13 piezoelectric
resonator can be used solely as an SIF filter of a
television signal.
lS Furthermore, the piezoelectric resonator in accordance
with the present invention has the followiny advantages.
More particularly, conventionally, a piezoelectric resonator
for an FM detection circuit is generally of a single-stage
structure and a piezoelectric resonator for a filter is of
a two-stage structure. Thus different size of piezoelectric
resonator has been used for various usage in the past and,
therefore, standardization of devices has never been
achieved and an easy assembly has not been made by an
automatlc assembly machine. As described above, the
~5 piezoelectric resonator of a single-stage in accordance
with the present invention has the same characteristic as a
conventional two-stage struc~ured piezoelectric resonator.
Therefore, it becomes possible to use the same size of
piezoelectric resonator for various kinds of usage and
standardi~ation of devices can be achieved. As a result,
an easy assembly is made possible by means of an automatic
assembly ma~hine, with a consequent decrease in the cost of
manufacturing.
Although the present invention has been described and
illustrated in detail, it is to be understood that the
same is by way of illustration and example only and is not
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to be taken by way of limitation, the spirit and scope of
the present invention being limited only by the terms of
the appended claims.
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