Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2002-06-20
2004-05-18
Wamsley, Patrick (Department: 2819)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C029S025350
Reexamination Certificate
active
06737940
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric resonator, a method of manufacturing the piezoelectric resonator, a piezoelectric filter, a method of manufacturing the piezoelectric filter, a duplexer, and an electronic communication device. More particularly, the piezoelectric resonator is used in filters, oscillators, and other suitable devices, thickness longitudinal vibrations are generated in the VHF, UHF, and higher frequency bands, and vibrating portions are provided on a diaphragm.
2. Description of the Related Art
The construction of a related piezoelectric resonator of this type includes a thin-film diaphragm that is provided on a substrate having a uniform thickness so as to cover an opening formed in the substrate. A laminated body, in which a piezoelectric thin film is sandwiched by upper and lower electrodes, is mounted on the upper surface of the diaphragm. When a voltage signal is applied between the electrodes, the laminated body as a vibrating portion resonates on the diaphragm. It becomes possible for such a piezoelectric resonator to resonate in higher frequency bands when the piezoelectric film is made thinner.
In the piezoelectric resonator of this type, the vibrating portion is spaced a fixed distance from the diaphragm fixing ends so that the vibrating portion may perform required vibrations.
Furthermore, in the case of a piezoelectric resonator in which a plurality of vibrating portions are provided on a diaphragm, the vibrating portions are located a fixed distance away from each other on the diaphragm so that the resonance characteristics of each of the vibrating portions may not be influenced by the other vibrating portions.
Then, in such a piezoelectric resonator, to make the resonator smaller, it is considered that the vibrating portions are provided so as to be close to the diaphragm fixing ends and the other vibrating portions. In this case, if the vibrating portions are too close to the diaphragm fixing ends and the other vibrating portions, etc., the size of the piezoelectric resonator can be achieved. But, they influence the vibration characteristics. To the contrary, if the vibrating portions are too far from the diaphragm fixing ends and the other vibrating portions, etc., their influence on the vibration characteristics diminishes or disappears. But, the size becomes larger. Thus, when the vibrating portions are disposed on a diaphragm, it is very difficult to achieve a highly precise position of the vibrating portions. Therefore, the performance of the piezoelectric resonator, and other devices including such a piezoelectric resonator, is degraded or its productivity becomes lower.
Such disadvantages can be also seen in the filtering characteristics of a filter in which a plurality of these piezoelectric resonators is combined.
In a dual mode filter and ladder filter, the resonators must be separated by a predetermined distance from each other so that the vibration of the adjacent resonators does not influence the other. In case of the dual mode filter, even if the resonators are separated too far from each other, the characteristics do not deteriorate. However, in the case of a ladder filter, the upper electrode or lower electrode of one resonator and the upper electrode or lower electrode of another adjacent resonator are integrally formed and they are required to be electrically connected. Therefore, if a distance between the resonators is greater than 3&lgr; in order to prevent vibrational interference, the wiring between the resonators is lengthened, and the resistance of the wiring and an inductance due to the wiring are generated between the resonators. As a result, the characteristics are deteriorated. In particular, if the wiring resistance is generated between the resonators connected in series, insertion loss is increased.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention minimize the influence of one of the vibration portions on the resonance characteristics of the other and also minimize the total dimensions of the device.
According to a preferred embodiment of the present invention, a piezoelectric resonator includes a substrate and a plurality of vibrating portions constructed such that a thin film portion having a piezoelectric thin film of one or more layers disposed on the substrate is sandwiched between at least a pair of upper electrodes and a lower electrode, opposed to each other, on the upper and lower surfaces of the thin film portion, the vibrating portions are separated by at least about &lgr;/2 (&lgr; represents the vibration wavelength) from elements affecting the vibration characteristics.
According to this preferred embodiment of the present invention, since the vibrating portions are separated by at least about &lgr;/2 from elements affecting the vibration characteristics, for example, the opening end portions or the other vibrating portions, the vibration characteristics are not improperly influenced by the elements such as the opening end portions and other portions, as in the case when the vibrating portions are located too close to the opening end portions or other portions. In addition, the piezoelectric resonator has a significantly reduced size and excellent vibration characteristics.
In the above-described piezoelectric resonator of the present invention, the substrate preferably includes an opening portion or concave portion and the vibrating portions are preferably disposed in the opening portion or concave portion. The periphery of the opening portion or concave portion and the vibrating portions constitute the elements affecting vibration characteristics.
In the piezoelectric resonator of the preferred embodiments of the present invention, the vibrating portions preferably include an insulation film below the lower electrode and a beam on the lower surface of the insulation film to increase the mechanical strength of the vibrating portions and the vibrating portions are separated by at least about &lgr;/2 from the beam which is an element affecting the vibration characteristics. In this way, even if the vibrating portions are separated by at least about &lgr;/2 from the beam, a piezoelectric resonator having such a construction can be made smaller while the performance of the piezoelectric resonator or a device including such a piezoelectric resonator is maintained at a sufficiently high quality.
Preferably, in a piezoelectric resonator of preferred embodiments of the present invention, the vibrating portions are preferably separated by about 3&lgr; or less from the elements.
More preferably, in a piezoelectric resonator of preferred embodiments of the present invention, the piezoelectric thin film preferably includes zinc oxide or aluminum nitride as a main component.
In a method of manufacturing a piezoelectric resonator according to another preferred embodiment of the present invention, the piezoelectric resonator including a substrate having an opening portion or concave portion and a plurality of vibrating portions constructed such that a thin film portion having a piezoelectric thin film of one or more layers, which is disposed in the opening portion or concave portion, is sandwiched between at least a pair of upper electrodes and a lower electrode, opposed to each other, on the upper and lower surfaces of the thin film portion, the method includes the step of forming the vibrating portions to be separated by at least about &lgr;/2 (&lgr; represents the vibration wavelength) from elements affecting the vibrating characteristics and formed in the opening portion or concave portion.
According to preferred embodiments of the present invention, since the vibrating portions are separated by at least about &lgr;/2 from elements affecting the vibration characteristics, from the opening end portions or the other vibrating portions, undesired influence of the elements such as the opening end portions and other vibrating portions, on the vibration characteristics as in the
Goto Yoshihiko
Nomura Tadashi
Takeuchi Masaki
Yamada Hajime
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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