Piezoelectric resonator and piezoelectric resonant element

Details Piezoelectric resonator and piezoelectric resonant element Piezoelectric resonator and piezoelectric resonant element

2000-08-26

2002-04-23

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Coupling networks

Electromechanical filter

C333S189000, C310S321000, C310S366000

Reexamination Certificate

active

06377135

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an energy trap-type piezoelectric resonator. More specifically, this invention relates to a piezoelectric resonator having an energy trap-type piezoelectric vibrating section and a capacitor including a pair of mutually opposed capacitor electrodes. Further, the invention also relates to a chip-type piezoelectric resonant element formed by using such piezoelectric resonators.
2. Description of the Related Art
Conventionally, in an intermediate frequency band of a mobile communication device such as an FM receiver and a portable telephone, a piezoelectric filter has generally been used as a frequency band filter.
Japanese Unexamined Patent Application Publication No. 10-284985 discloses one example of the above described piezoelectric filter. In the following, such a kind of a conventional piezoelectric filter will be described in detail with reference to FIG.
7
and FIG.
8
.
As shown in
FIG. 7
, the conventional piezoelectric filter is constructed by using a first piezoelectric substrate plate
71
and a second piezoelectric substrate plate
72
. On the upper surface of the first piezoelectric substrate plate
71
, resonant electrodes
73
a
and
73
b
are provided. Further, on the underside surface of the first piezoelectric substrate plate
71
, another resonant electrode serving as a common electrode is provided in a position opposite the above electrodes
73
a
and
73
b.
By virtue of the resonant electrodes provided on these main surfaces of the substrate plates, an energy trap-type piezoelectric vibrating section is provided which functions in a thickness-extension oscillation mode.
Further, a capacitor electrode
75
a
is connected with the resonant electrode
73
b.
Particularly, the capacitor electrode
75
a
is provided along an edge
71
a
of the piezoelectric substrate plate
71
.
Moreover, a resonant electrode
73
c
serving as a common electrode is provided on the upper surface of the second piezoelectric substrate plate
72
. In addition, the resonant electrode
73
c
is electrically connected with a capacitor electrode
75
b.
Similarly, the capacitor electrode
75
b
is provided along an edge
72
a
of the piezoelectric substrate plate
72
. Here, the piezoelectric substrate plate
71
and the piezoelectric substrate plate
72
have the same structure. Namely, on the bottom surface of the piezoelectric substrate plate
71
an electrode structure is provided which is the same as the electrode structure provided on the upper surface of the piezoelectric substrate plate
72
. In contrast, on the bottom surface of the piezoelectric substrate
72
an electrode structure is provided which is the same at the electrode structure provided on the upper surface of the piezoelectric substrate plate
71
. Therefore, with respect to the same electrodes, the same reference numerals are used to represent similar elements on the two piezoelectric substrate plates
71
and
72
.
With such a piezoelectric filter, the first piezoelectric substrate plate
71
and the second piezoelectric substrate plate
72
are laminated one above the other such that the resonant electrodes
73
c
serving as the common electrodes face each other. Here, spacers
77
to
79
are provided having circular holes
77
a
to
79
a,
respectively, provided such that the oscillation of the piezoelectric oscillating section is not suppressed. Further, sealing substrate plates
80
and
81
are provided.
Moreover, in the above described piezoelectric filter a circuit configuration shown in
FIG. 8
is employed. Namely, the first and second piezoelectric substrate plates
71
and
72
of the piezoelectric filter section are electrically connected by relay capacitors. Such relay capacitors are provided on the piezoelectric substrate plates
71
and
72
by an electrostatic capacitance existing between the capacitor electrodes
75
a
and
75
b.
Furthermore, in the above described piezoelectric filter, the circuit configuration shown in
FIG. 8
has been employed, but the piezoelectric filter section has been divided into first and second piezoelectric filter sections in the first piezoelectric substrate plate
71
and the second piezoelectric substrate plate
72
, respectively. Since the first piezoelectric substrate plate
71
and the second piezoelectric substrate plate
72
are laminated one above the other, the actual mounting area is reduced.
However, to obtain the first piezoelectric substrate plate
71
and the second piezoelectric substrate plate
72
described above, a piezoelectric substrate plate
82
shown in
FIG. 9
must be prepared in the conventional art. By dividing the piezoelectric substrate plate
82
, the first piezoelectric substrate plate
71
and the second piezoelectric substrate plate
72
are obtained.
However, during an actual manufacturing process, in order to ensure improved productivity, a mother piezoelectric substrate plate including several pieces of the piezoelectric substrate plates
82
arranged in parallel with the main surface of each substrate plate has been used.
By dividing the piezoelectric substrate plate
82
along dotted chain lines B—B in
FIG. 9
, the first and the second piezoelectric substrate plates
71
and
72
are obtained. At this time, the capacitor electrodes
75
a
and
75
b
of the piezoelectric substrate plates
71
and
72
are thus formed through such a cutting process.
On the other hand, when the above cutting position deviates from its correct position, the capacitor electrode
75
a
provided on one piezoelectric substrate plate
71
will be different in size from the capacitor electrode
75
b
provided on the other piezoelectric substrate plate
72
in a direction orthogonal to the cutting line.
Therefore, in order to divide the piezoelectric substrate plate
82
into two portions, it is necessary that the piezoelectric substrate plate
82
be very precisely divided.
However, in practice, the cutting of the piezoelectric substrate plate
82
into two portions with high precision is difficult, and often impossible to avoid differences in the size between the two capacitor electrodes
75
a
and
75
b
provided on the piezoelectric substrate plates
71
and
72
.
For the above reason, if a piezoelectric filter is produced having the above described structure, the filter characteristics of one piezoelectric filter will be different from those of another.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide an improved piezoelectric resonator including an energy trap-type piezoelectric vibrating section and a capacitor section provided by two capacitor electrodes arranged to face each other with a piezoelectric plate interposed therebetween. In particular, preferred embodiments of the present invention provide an improved piezoelectric resonator which ensures that the capacitance of a capacitor section does not differ from one piezoelectric resonator to another, so as to produce desired resonance characteristics and desired filter characteristics with high precision. Further, preferred embodiments of the present invention provide a piezoelectric filter.
According to preferred embodiments of the present invention, an energy trap-type piezoelectric resonator is provided which includes a piezoelectric substrate plate having a first main surface and a second main surface, first and second resonant electrodes provided on the first and second main surfaces of the piezoelectric substrate plate, respectively, to form an energy trap-type piezoelectric vibrating section, and first and second capacitor electrodes provided on the first and second main surfaces of the piezoelectric substrate plate, respectively, and arranged one above the other with the piezoelectric substrate plate interposed therebetween. In particular, the first and the second capacitor electrodes extend along the first and the second main surfaces to the edges thereof. Further, the first capacitor electrode is spaced by a desi

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