Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2003-05-09
2004-08-31
Le, Dinh T. (Department: 2816)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S191000, C333S186000, C310S361000
Reexamination Certificate
active
06784763
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric bulk wave filters for use as, for example, a band-pass filter. More particularly, the present invention relates to a longitudinally coupled multi-mode piezoelectric bulk wave filter using the piezoelectric longitudinal effect and using coupling between modes having different orders, and relates to an electronic component including such a piezoelectric bulk wave filter.
2. Description of the Related Art
Various piezoelectric bulk wave filters have been used as a band-pass filter. For frequency ranges of several megahertz to several tens of megahertz bands, double-mode piezoelectric bulk wave filters are primarily used because they are easily miniaturized and inexpensive.
This type of double-mode piezoelectric bulk wave filter is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 5-327401.
FIG. 15
shows the cross sectional view of a known double-mode piezoelectric bulk wave filter using the thickness longitudinal vibration mode.
A piezoelectric bulk wave filter
201
includes a piezoelectric plate
202
undergoing a polarizing process in the thickness direction. On the top surface of the piezoelectric plate
202
, a pair of excitation electrodes
203
and
204
is provided. On the bottom surface, a common excitation electrode (ground electrode)
205
is disposed so as to face the excitation electrodes
203
and
204
with the excitation plate
202
sandwiched therebetween.
To operate the piezoelectric bulk wave filter
201
, an input signal is applied between the excitation electrodes
203
and
205
on the top surface. This causes the piezoelectric plate
202
to produce the symmetric mode shown in FIG.
16
A and the anti-symmetric mode shown in FIG.
16
B. These modes are combined to define a filter passband. The output is obtained from between the excitation electrode
204
and the ground electrode
205
.
In place of the thickness longitudinal vibration mode, there is also known a double-mode piezoelectric bulk wave filter using the thickness shear mode obtained by applying the polarizing process to the piezoelectric plate
202
in the direction parallel to the top surface of the piezoelectric plate
202
.
In the known piezoelectric bulk wave filter
201
, the strength of the coupling between the symmetric mode and the anti-symmetric mode depends on the distance between the excitation electrodes
203
and
204
. The distance determines the frequency difference between the frequency of the symmetric mode and the frequency of the anti-symmetric mode. This determines the passband.
Therefore, in order to obtain a broadband filter, the distance between the excitation electrodes
203
and
204
must be narrowed to increase the degree of coupling between both modes and to increase the frequency difference between the frequencies of both modes.
The excitation electrodes
203
and
204
are normally generated by applying conductive paste by a screen-printing method. There is a limit to how narrow the distance between the excitation electrodes
203
and
204
can be using the screen-printing method. Photolithography enables the distance between the excitation electrodes
203
and
204
to be even more narrowed. Applying photolithography is, however, expensive.
Furthermore, even though the distance between the excitation electrodes
203
and
204
can be narrowed, the capacitance between the input and output is increased and the attenuation is decreased.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a longitudinally coupled multi-mode piezoelectric bulk wave filter which achieves widening of the passband, increasing out-of-band attenuation, and being manufactured inexpensively.
According to a first preferred embodiment of the present invention, a longitudinally coupled multi-mode piezoelectric bulk wave filter using the piezoelectric longitudinal effect includes at least one laminated piezoelectric body having at least four excitation electrodes disposed substantially parallel and spaced from one another at a distance D, and a plurality of piezoelectric layers, each disposed between two adjacent electrodes of the excitation electrodes, the plurality of piezoelectric layers being polarized in a direction that is substantially perpendicular or substantially parallel to the excitation electrodes, wherein the cross section of the at least one laminated piezoelectric body in the direction substantially perpendicular to the laminated direction of the at least one laminated piezoelectric body is a rectangle having a thickness T, a piezoelectric portion having a thickness that is greater than the thickness dimension T and aligned with the at least one laminated piezoelectric body, an input electrode, an output electrode, a ground electrode, the excitation electrodes including a first group of excitation electrodes electrically connected to the input electrode, a second group of excitation electrodes electrically connected to the output electrode, and a third group of excitation electrodes electrically connected to the ground electrode, the first group and the third group being alternately disposed in the laminated direction, and the second group and the third group being alternately disposed in the laminated direction. In the longitudinally coupled multi-mode piezoelectric bulk wave filter, when an input signal is applied between the input electrode and the ground electrode, mode vibrations having different orders are generated and combined into an output signal between the output electrode and the ground electrode, and the ratio of the thickness T to the distance D is equal to or less than about 0.9.
In the longitudinally coupled multi-mode piezoelectric bulk wave filter, the input electrode, the output electrode, and the ground electrode may be disposed on the piezoelectric portion. This enables the piezoelectric portion aligned with the laminated piezoelectric body to have the input electrode, the output electrode, and the ground electrode easily formed and to be easily electrically connected to the outside even though the laminated piezoelectric body is small.
The longitudinally coupled multi-mode piezoelectric bulk wave filter may further include a piezoelectric substrate for providing the at least one laminated piezoelectric element and piezoelectric portion thereon. In the longitudinally coupled multi-mode piezoelectric bulk wave filter, a plurality of grooves are disposed on one side of the piezoelectric substrate, and a portion of the piezoelectric substrate between each pair of adjacent grooves of the plurality of grooves defines the laminated piezoelectric element and a remaining piezoelectric substrate portion defines the piezoelectric element. In this case, after the piezoelectric substrate is prepared, a plurality of grooves is formed on one surface of the piezoelectric substrate. This achieves easy formation of the laminated piezoelectric body and the piezoelectric portion.
According to another preferred embodiment of the present invention, a groove is disposed on one surface of a piezoelectric substrate for providing the at least one laminated piezoelectric element and the piezoelectric portion thereon, a portion between the bottom of the groove and the other principal surface of the piezoelectric substrate defines the laminated piezoelectric element, and a piezoelectric substrate portion on both sides of the groove defines the piezoelectric portion.
According to another preferred embodiment of the present invention, a plurality of laminated piezoelectric elements are provided on the piezoelectric substrate.
According to another preferred embodiment of the present invention, the mode vibrations having different orders are harmonics waves in the longitudinal vibration mode using the piezoelectric longitudinal effect.
According to another preferred embodiment of the present invention, the mode vibrations having different orders are harmonics waves in the thickness l
Inoue Jiro
Kaida Hiroaki
Nishimura Toshio
Keating & Bennett LLP
Le Dinh T.
Murata Manufacturing Co. Ltd.
LandOfFree
Longitudinally coupled multi-mode piezoelectric bulk wave... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Longitudinally coupled multi-mode piezoelectric bulk wave..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Longitudinally coupled multi-mode piezoelectric bulk wave... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3308498