Piezoelectric thin-film filter
A piezoelectric thin-film filter includes a first electrode pair having two or more first electrode fingers disposed on one main surface of a piezoelectric thin film and second electrode fingers disposed on the other main surface of the piezoelectric thin film so as to face the first electrode fingers. A second electrode pair includes two or more third electrode fingers disposed on the main surface such that the third electrode fingers and the first electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface so as to face the third electrode fingers with the piezoelectric thin film therebetween. Insulating films are provided between the first and third electrode fingers. Each of the center-to-center distances Wa+Wm and Wf+Wm between the first and third electrode fingers that are disposed alternately is larger than a value twice the thickness T of the piezoelectric thin film.
1. A piezoelectric thin-film filter comprising:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
a first electrode pair including at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two second electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the first electrode fingers with the piezoelectric thin film therebetween; and
a second electrode pair including at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the third electrode fingers with the piezoelectric thin film therebetween; wherein
a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to each of the second electrode fingers and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to each of the fourth electrode fingers;
the piezoelectric thin-film filter include insulating films provided between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film;
each of center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the portion of the piezoelectric thin film that is acoustically separated from the substrate; and
further comprising a second insulating film provided in at least one of a first area covering the first electrode fingers, the third electrode fingers, and the insulating films; a second area covering the second electrode fingers and the fourth electrode fingers.
2. A piezoelectric thin-film filter comprising:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween; and
a common electrode disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and including portions facing the first electrode fingers and the third electrode fingers with the piezoelectric thin film therebetween; wherein
a first electrode pair is defined by the first electrode fingers and the common electrode;
a second electrode pair is defined by the third electrode fingers and the common electrode;
a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to the common electrode and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to the common electrode;
insulating films provided between the first electrode fingers and the third electrode fingers are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film;
each of the center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the piezoelectric thin film;
the filter element is a unit;
at least two units connected in series to one of input terminals and output terminals are provided; and
at least two of the at least two units are connected in parallel to the other one of the output terminals and the input terminals.
3. A piezoelectric thin-film filter comprising:
at least two filter elements; each of the at least two filter elements comprises:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
a first electrode pair including at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two second electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the first electrode fingers with the piezoelectric thin film therebetween; and
a second electrode pair including at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the third electrode fingers with the piezoelectric thin film therebetween; wherein
the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to each of the second electrode fingers and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to each of the fourth electrode fingers;
the piezoelectric thin-film filter includes insulating films provided between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film; and
each of center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the portion of the piezoelectric thin film that is acoustically separated from the substrate;
the first terminal and the second terminal of each of the filter elements are connected in parallel to one of input terminals and output terminals, and the third terminal and the fourth terminal of each of the filter elements are connected in series between the other one of the input terminals and the output terminals.
4. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the width of all of the electrode fingers is larger than the value twice the thickness of the portion of the piezoelectric thin film that is acoustically separated from the substrate.
5. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the first terminal and the second terminal are connected to unbalanced terminals, and the third terminal and the fourth terminal are connected to balanced terminals.
6. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the piezoelectric thin film is acoustically separated from the substrate with a gap layer or an opening therebetween.
7. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the one main surface of the piezoelectric thin film includes, outside a resonant area in which the first electrode fingers, the third electrode fingers, and the insulating films are disposed, a non-resonant area that continuously extends from the resonant area.
8. A composite filter comprising:
at least one of a ladder filter or a lattice filter that is cascade connected to the piezoelectric thin-film filter according to claim 3 .
9. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the first electrode fingers, the third electrode fingers, and the insulating films are formed using a common resist pattern on the one main surface of the piezoelectric thin film.
10. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the piezoelectric thin film is an epitaxial film.
11. The piezoelectric thin-film filter according to claim 3 , wherein, for each of the at least two filter elements, the total sum of the number of pairs of first electrode fingers and second electrode fingers included in the first electrode pair and the number of pairs of third electrode fingers and fourth electrode fingers included in the second electrode pair is at least twenty.
12. A piezoelectric thin-film filter comprising:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
a first electrode pair including at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two second electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the first electrode fingers with the piezoelectric thin film therebetween; and
a second electrode pair including at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the third electrode fingers with the piezoelectric thin film therebetween; wherein
a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to each of the second electrode fingers and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to each of the fourth electrode fingers;
the piezoelectric thin-film filter include insulating films provided between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film;
each of center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the portion of the piezoelectric thin film that is acoustically separated from the substrate; and
the number of pairs of first electrode fingers and second electrode fingers included in the first electrode pair is different from the number of pairs of third electrode fingers and fourth electrode fingers included in the second electrode pair.
13. A piezoelectric thin-film filter comprising:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween; and
a common electrode disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and including portions facing the first electrode fingers and the third electrode fingers with the piezoelectric thin film therebetween; wherein
a first electrode pair is defined by the first electrode fingers and the common electrode;
a second electrode pair is defined by the third electrode fingers and the common electrode;
a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to the common electrode and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to the common electrode;
insulating films provided between the first electrode fingers and the third electrode fingers are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film;
each of the center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the piezoelectric thin film; and
the number of pairs of first electrode fingers and the common electrode included in the first electrode pair is different from the number of pairs of third electrode fingers and the common electrode included in the second electrode pair.
14. A piezoelectric thin-film filter comprising:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
a first electrode pair including at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two second electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the first electrode fingers with the piezoelectric thin film therebetween; and
a second electrode pair including at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the third electrode fingers with the piezoelectric thin film therebetween; wherein
a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to each of the second electrode fingers and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to each of the fourth electrode fingers;
the piezoelectric thin-film filter include insulating films provided between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film;
each of center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the portion of the piezoelectric thin film that is acoustically separated from the substrate;
the filter element is a unit;
at least two units connected in series to one of input terminals and output terminals are provided; and
at least two of the at least two units are connected in parallel to the other one of the output terminals and the input terminals.
15. The piezoelectric thin-film filter according to claim 14 , wherein the at least two units are disposed adjacent to each other, and the adjacent units are mechanically coupled together.
16. The piezoelectric thin-film filter according to claim 14 , wherein:
the input terminals are connected to unbalanced terminals; and
the output terminals are connected to balanced terminals.
17. The piezoelectric thin-film filter according to claim 14 , wherein, for each of the at least two units, the piezoelectric thin film is acoustically separated from the substrate with a gap or an opening therebetween.
18. The piezoelectric thin-film filter according to claim 14 , wherein
the at least two units comprise first and second units;
the first terminal of each of the units is connected to one of the input terminals;
the second terminal of each of the units is connected to the other one of the input terminals;
the fourth terminal of the first unit is connected to the third terminal of the second unit;
the third terminal of the first unit is connected to one of the output terminals;
the fourth terminal of the second unit is connected to the other one of the output terminals; and
the output terminals are connected to balanced terminals.
19. The piezoelectric thin-film filter according to claim 14 , wherein:
first and second units are provided;
the first terminal of the first unit and the second terminal of the second unit are connected to one of the input terminals;
the second terminal of the first unit and the first terminal of the second unit are connected to the other one of the input terminals;
the fourth terminals of the units are connected to each other;
the third terminal of the first unit and the third terminal of the second unit are connected to the output terminals; and
the output terminals are connected to balanced terminals.
20. The piezoelectric thin-film filter according to claim 14 , wherein:
the at least two units comprise first, second, third, and fourth units are provided;
the first terminal of the first unit and the first terminal of the second unit are connected to one of the input terminals;
the second terminal of the first unit, the second terminal of the second unit, the first terminal of the third unit, and the first terminal of the fourth unit are connected to each other;
the second terminal of the third unit and the second terminal of the fourth unit are connected to the other one of the input terminals;
the third terminal of the first unit is connected to one of the output terminals;
the fourth terminal of the first unit is connected to the third terminal of the second unit;
the fourth terminal of the second unit is connected to the third terminal of the third unit;
the fourth terminal of the third unit is connected to the third terminal of the fourth unit;
the fourth terminal of the fourth unit is connected to the other one of the output terminals; and
the output terminals are connected to balanced terminals.
21. The piezoelectric thin-film filter according to claim 14 , wherein, for each of the at least two units
at least one common electrode is disposed on the portion of the one main surface or the other main surface of the piezoelectric thin film that is acoustically separated from the substrate; and
the first electrode fingers and the third electrode fingers or the second electrode fingers and the fourth electrode fingers of at least one unit is part of the same common electrode.
22. The piezoelectric thin-film filter according to claim 14 , wherein, for each of the at least two units, additional insulating films are provided between adjacent electrode fingers in the portion of at least one of the main surfaces of the piezoelectric thin film that is acoustically separated from the substrate.
23. A piezoelectric thin-film filter comprising:
at least two filter elements; each of the at least two filter elements comprises:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween; and
a common electrode disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and including portions facing the first electrode fingers and the third electrode fingers with the piezoelectric thin film therebetween; wherein
a first electrode pair is defined by the first electrode fingers and the common electrode;
a second electrode pair is defined by the third electrode fingers and the common electrode;
the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to the common electrode and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to the common electrode;
insulating films provided between the first electrode fingers and the third electrode fingers are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film; and
each of the center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the piezoelectric thin film;
the first terminal and the second terminal of each of the filter elements are connected in parallel to one of input terminals and output terminals, and the third terminal and the fourth terminal of each of the filter elements are connected in series between the other one of the input terminals and the output terminals.
24. A piezoelectric thin-film filter comprising:
a substrate;
a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate;
at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween; and
a common electrode disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and including portions facing the first electrode fingers and the third electrode fingers with the piezoelectric thin film therebetween; wherein
a first electrode pair is defined by the first electrode fingers and the common electrode;
a second electrode pair is defined by the third electrode fingers and the common electrode;
a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to the common electrode and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to the common electrode;
insulating films provided between the first electrode fingers and the third electrode fingers are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film;
each of the center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the piezoelectric thin film; and
further comprising a second insulating film provided in at least one of a first area covering the first electrode fingers, the third electrode fingers, and the insulating films, and a second area covering the common electrode.