Filter element, and filter device, duplexer, and high-frequency circuit each including said filter element
View Patent ↗A filter element includes resonators that are arranged in series arms and parallel arms in a circuit. In this filter element, at least one of the series-arm resonators includes a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel.
1. A filter element comprising:
a plurality of resonators that are arranged in series arms and parallel arms in a circuit and have a single piezoelectric thin film common to the plurality of resonators,
at least one of the series-arm resonators including the series-arm resonator at the first stage on the signal input side being composed of a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel,
at least one of the parallel-arm resonators being composed of only one single-terminal pair piezoelectric thin-film resonator.
2. The filter element as claimed in claim 1 , wherein at least one of the parallel-arm resonators including the parallel-arm resonator at the first stage is composed of a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel.
3. The filter element as claimed in claim 2 , wherein the parallel-arm resonator including the plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel has an admittance matched with the admittance of at least one of the other parallel-arm resonators.
4. The filter element as claimed in claim 1 , wherein:
the single-terminal pair piezoelectric thin-film resonators include a substrate that contains at least one of silicon, glass, and ceramics;
the piezoelectric thin film contains at least one of aluminum nitride, zinc oxide, lead zirconate titanate, and lead titanate; and
an upper electrode film and a lower electrode film that are single-layer or multi-layer films containing at least one of aluminum, copper, gold, molybdenum, tungsten, tantalum, chromium, titanium, platinum, and rhodium.
5. The filter element as claimed in claim 1 , wherein the series-arm resonator including the plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel has an admittance matched with the admittance of at least one of the other series-arm resonators.
6. The filter element as claimed in claim 1 , wherein the parallel-arm resonators each includes an upper electrode film having a SiO 2 film formed thereon.
7. The filter element as claimed in claim 1 , wherein the single-terminal pair piezoelectric thin-film resonators connected in parallel have exciting parts that are uniform in size.
8. The filter element as claimed in claim 1 , which has a ladder filter structure.
9. The filter element as claimed in claim 1 , which has a lattice filter structure.
10. A filter element comprising:
a plurality of resonators that are arranged in series arms and parallel arms in a circuit,
only the series-arm and/or parallel-arm resonators at the first stage on the signal input side including a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel.
11. A filter element comprising:
a plurality of resonators that are arranged in series arms and parallel arms in a circuit,
the series-arm resonators at the first stage on the signal input side including more single-terminal pair piezoelectric thin-film resonators connected in parallel than in each of the other series-arm resonators.
12. A filter device comprising:
a filter element; and
a package that houses the filter element,
the filter element including
a plurality of resonators that are arranged in series arms and parallel arms in a circuit and have a single piezoelectric thin film common to the plurality of resonators,
at least one of the series-arm resonators including the series-arm resonator at the first stage on the signal input side being composed of a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel,
at least one of the parallel-arm resonators being composed of only one single-terminal pair piezoelectric thin-film resonator.
13. A duplexer comprising:
a transmission filter element and a reception filter element,
the transmission filter element including a plurality of resonators that are arranged in series arms and parallel arms in a circuit and have a single piezoelectric thin film common to the plurality of resonators,
at least one of the series-arm resonators including the series-arm resonator at the first stage on the signal input side being composed of a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel,
at least one of the parallel-arm resonators being composed of only one single-terminal pair piezoelectric thin-film resonator.
14. A high-frequency circuit that transmits radio signals, comprising:
an amplifier that amplifies transmission signals; and
a filter element that filters the transmission signals,
the filter element including a plurality of resonators that are arranged in series arms and parallel arms in a circuit and have a single piezoelectric thin film common to the plurality of resonators, and
at least one of the series-arm resonators including the series-arm resonator at the first stage on the signal input side being composed of a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel,
at least one of the parallel-arm resonators being composed of only one single-terminal pair piezoelectric thin-film resonator.
15. A high-frequency circuit that transmits and receives radio signals, comprising:
a first amplifier that amplifies transmission signals;
a second amplifier that amplifies reception signals; and
a duplexer that includes a transmission filter element and a reception filter element,
the transmission filter element including a plurality of resonators that are arranged in series arms and parallel arms in a circuit and have a single piezoelectric thin film common to the plurality of resonators, and
at least one of the series-arm resonators including the series-arm resonator at the first stage on the signal input side being composed of a plurality of single-terminal pair piezoelectric thin-film resonators connected in parallel,
at least one of the parallel-arm resonators being composed of only one single-terminal pair piezoelectric thin-film resonator.