Note: Descriptions are shown in the official language in which they were submitted.
" ~ 963~8
01 -- 1 --
02 BACKGROUND OF THE I~VENTION
03 The present invention generally relates
0~ to a piezoelectric resonator and more particularly,
05 to an improved strip type or rectangular type
06 piezoelectric resonator for use, ~or example, in
07 oscillators, electrical filters and the like.
08 With the recent progress in the field of
09 integrated circuits, inexpensive cera~ic resona~ors
have been widely utilized for the actual
11 applicationsl and normally, disc type or rectangular
12 plate type piezoelectric resonators are generally
13 employed for the purpose in a range of resonance
14 frequencies rom 100 KHZ up to 1 MHZ so as -to
utilize the expansion mode of vibration thereof.
16 BRIEF DESCRIPTIO~ OF THE DRAWINGS
17 Objects and features of the present
18 invention will become apparent from the following
19 description taken in conjunction with the preferred
embodiment thereof with reference to the
21 accompanying drawings, in which:
22 Figure 1 is a perspective view showing a
23 construction of a conventional rectangular plate
24 type piezoelectric resonator (already referred to),
Figure 2 is a perspective view showing a
26 construction of a conventional strip type
27 piezoelectric resonator (already referred to),
28 Figure 3 is a perspective view showing a
29 strip type piezoelectric resonator according to one
preferred embodiment of the present invention,
31 Figure 4 is a graph showing a state of
32 resonance for the strip type piezoelectric resonator
33 according to the present invention, and
34 Figure 5 is a graph showing variations
in the characteristics of the strip type
36 piezoelectric resonator according to the present
37 invention when depth of the groove is altered.
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63~3
01 _ ~ _
02 ~s shown in ~igure 1, the known
03 rectangular plate type piezoelectric resonator
04 referred to above includes, for example, a
05 piezoelectric ceramic substrate 1, main electrode
06 faces 2 and 3 ormed on the opposite suraces of
07 said piezoelectric ceramic substrate 1, and lead
08 wires 4 respectively connected to said main
09 electrode faces 2 and 3. However, in the
rectangular plate type piezoelectric resonator as
11 described above or disc type piezoelectric resonator
12 conventionally employed, there have been such
13 disadvantages that -they are generally large in size,
14 and moreover, tend to produce spurious waves due to
thickness mode vibration based on the fundamental
16 wave.
17 Meanwhile, as shown in Figure 2, there
18 has also been conventionally available a strip type
19 piezoelectric resonator utilizing length mode
vibration based on the fundamental wave, and having
21 a construction generally similar to that of the
22 rectangular plate type piezoelectric resonator in
23 Figure 1 as represented by like re~erence
24 numerals. Although advantageous in that the
dimensions are reduced as compared with the
26 rectangular plate type or disc type piezoelectric
27 resonator, the conventional strip type piezoelectric
28 resonator as described above still has disadvantages
29 in that undesirable spurious responses due to width
mode vibration and thicXness mode vibration tend to
31 be produced.
32 SUMMARY OF THE INVENTION
33 Accordingly, an essential object of the
34 present invention is to provide an improved strip
type piezoelectric resonator in which undesirable
36 spurious waves due to width mode vibra~ion and
37 thickness mode vibration are suppressed by formin~ a
,.'.'`,'~
39~
01 _ 3 _
02 groove on one of opposite main electrode faces of
03 the resonator, in a direction parallel to the
04 longitudinal direction thereof, with a depth of said
05 groove being set at 30 to 70~ of a thic~ness of said
06 piezoelectric ceramic substrate so as to
07 substantially eliminate the disadvantages inherent
08 in the conventional piezoelectric resonators of this
09 kind.
Another important object of the present
11 invention is to provide a strip type piezoelectric
12 resonator of the above described type, which is
13 simple in construction and stable in functioning at
14 high reliability, and can be readily manufactured on
a large scale at low cost.
16 In accomplishing these and other
17 objects, according to one preferred embodiment of
18 the present invention, there is provided a strip
19 type piezoelectric resonator utilizing lengthwise
2C mode vibration, which includes a piezoelectric
21 ceramic substrate, and first and second main
22 electrode faces formed on opposite surfaces of the
23 piezoelectric ceramic substrate, and is
24 characterized in that there is -further provided a
groove which is formed in one of said first and
26 second main electrode Eaces so as to extend over an
27 entire length of the piezoelectric ceramic substrate
28 in a direction parallel to the longitudinal
29 direction thereof. The groove is set to have a
depth in the range of 30 to 70% of the thickness of
31 said piezoelectric ceramic substrate.
32 By arrangement according to the present
33 invention as described above, an improved strip type
34 piezoelectric resonator with suppressed spurious
responses has been advantageously presented through
36 simple construction.
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01 - 4
02 DETAILED DESCRIPTIO~ OF THE INVENTIO~
03 Before the description of the present
04 invention proceeds, it is to be noted that like
05 par-ts are designated by like reference numerals
06 throughout the accompanying drawings.
07 Referring now to the drawings, there is
08 shown in Figure 3 a strip type piezoelectric
09 resonator according to one preferred embodiment of
the present invention, which generally includes a
11 piezoelectric ceramic substrate 10, and upper and
12 lower main electrode faces 10A and 10B formed on
13 opposite surfaces of the substrate 10. In one
14 surface of
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~9~;3~B
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the piezoelectric ceramic substrate 10 at the side of the
upper main electrode face 10~, there is formed a groove 11
which extends over an entire length of the substrate 10 in a
direction parallel to the longitudinal direction of said
substrate 10, and is located at a center in a widthwise
direction of said upper main electrode face lOA or said
substrate 10 as illustrated. By the above groove 11, the
upper main electrode face lOA of the substrate 10 is divided
into one region 12 and the other region 13, while the lower
main electrode face lOB is formed on the other entire
surface of the substrate 10 in the similar manner as in the
conventional arrangement of Fiys. 1 or 2.
For the actual use of the piezoelectric resonator
of Fig. 3 as described so far, the rsspective regions 12 and
13 on the upper main electrode ~ace lOA divided by the
groove 11 are short-circuited to each other so as to be
connected to a lead wire 14 for the upper side, while a lead
wire 4 is connected to the lower main electrode face lOB in
the similar manner as in the conventional arrangement of
Fig. 1 or 2, and thus, a two terminal type resonator is
constituted.
More specifically, by way of example, the
piezoelectric ceramic substrate 10 is set in dimensions to
be 4.65 mm in length, 0.8 mm in width, and 0.3 mm in
thickness, and the yroove 11 has a width of 0.15 Inm and a
depth of 0.15 mm, and the oscillation frequency of the strip
3~8
-- 6
type pie~.oelectric resonator o Fig. 3 is ~O0 K~IZ when used
as an oscillator.
Subsequently, in the piezoelectric resonator
havin~ the construction as shown in Fig. 3, on thc
a~sumption that the depth of the groove 11 is represented by
d, and the thickness of the piezoelectric ceramic substrate
10 is denoted by t, measurements were taken on the
characteristics thereof, with the value d/t employed as a
parameter. As shown in Fig. 4, response level was
represented as a level difference between resonant poin~ and
anti-resonant point.
As a result of the above measurements, it has been
found as shown in Fig. 5 that, as the value d/t increases,
the main response gradually decreRses, whereas the spurious
responses due to thickness mode vibration and width mode
vibration based on the fundamental wave, which were
approximat:ely the same magnitude as that of the main
response in the absence of the groove ll, are rapidly
reduced with the increase of the value of d/t. Moreover,
width mode vibration by third harmonics ~first excited
overtone of width mode) is gradually increased, following
tlle increase of the value d/t.
Normally, for the spurious oscillation to be
suppressed, it is necessary that the spurious waves are
reduced to less than half of the main response, and in order
to satisfy the above requirement in the result of
mcasurement in Fig. 5, d/t must be larger than 30%. On the
3~
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other hand, since the strength of the piezoelectric ceramic
substrate 10 tends to b~ reduced due to the increase of d/t,
with a simultaneous reduction of the main response, the
upper limit o, d/t is at 70%.
Accordingly, as is seen from the above
description, the depth oE the groove 11 to be provided
according to the present invention should be in the range of
30 to 70% of the thickness of the piezoelectric ceramic
substrate.
In the arrangement of Fig. 3, although the groove
11 is provided in the upper main electrode face lOA, it is
needless to say that such groove 11 may be so modified as to
be provided in the lower main electrode face lOs to obtain
the same effect.
Furthermore, in the foregoing embodiment, although
the groove 11 is described as formed at ~he center in the
widthwise direction of the upper main electrode surface lOA,
results of measurements generally in the similar trend as
those of Fig. 5 have been obtained even when said groove 11
is deviated in position to either one side of said electrode
surface lOA.
It should be noted here -that, although the
arrangement of the present invention is prepared as a
resonator, it is bes-t suited to applications to an
oscillator.
For manufacturing the strip type piezoelectric
resonator according to the present invention in an efficient
3633~ -
mannerr processings may be effected in such steps as forming
electrode layers over the entire opposite surfaces, i.e.
upper and lower surfaces of a large piezoelectric ceramic
plate having a predetermined thickness, subsequently forming
grooves each having the predetermined depth in one of the
electrode formed surfaces at equal intervals, and finally
cutting off the large piezoelectric ceramic plate thus
processed into dimensions o~ individual piezoelectric
resonators as shown in Fig. 3.
As is clear from the foregoing description,
according to the present invention, since the piezoelectric
resonator is constituted by forming the groove having the
depth at 30 to 70~ of the thickness of the strip type
piezoelectric ceramic substrate in one of the main electrode
faces of the strip type piezoelectric ceramic substrate in a
direction parallel to the longitudinal direction thereof,
spurious waves due to width mode vibration and thickness
mode vibration may be suppressed to less than 40 dB with
respect to the main response of 65 dB, and thus, the
piezoelectric resonator free from generation of spurious
response has been advantageously presented.
Although the present invention has been fully
described by way of example with reference to the
accompanying drawings, it is to be noted here that various
changcs and modifications will be apparent to those skilled
in the art. Therefore, unless otherwise such changes and
modifications depart from the scope of the present
invention, they should be construed as included therein.
