Tunable filter including a surface acoustic wave resonator and a variable capacitor
A tunable filter includes a surface acoustic wave resonator, in which an IDT electrode is defined by an electrode material provided in a recess in an upper surface of a piezoelectric substrate made of LiNbO 3 or LiTaO 3 , and a ZnO film is arranged to cover the upper surface of the piezoelectric substrate, and variable capacitors connected with the surface acoustic wave resonator.
1. A tunable filter, comprising:
a surface acoustic wave resonator including:
a piezoelectric substrate including a recess in an upper surface thereof;
an IDT electrode defined by an electrode material provided in the recess in the upper surface of the piezoelectric substrate;
a ZnO film arranged to cover the upper surface of the piezoelectric substrate; and
a variable capacitor connected with the surface acoustic wave resonator; wherein
the piezoelectric substrate is a LiNbO 3 substrate with Euler angles of (0°, 100°+20°, 0°), and the electrode material defining the IDT electrode is one of Al, Ag, Pt, Au, Ta, W, Mo, Ni, or Cu; and
the IDT electrode of the surface acoustic wave resonator is primarily made of an electrode layer made of Al, and when h is a thickness of the ZnO film and λ is a wavelength determined by a pitch of electrode fingers of the IDT electrode of the surface acoustic wave resonator, a normalized film thickness h/λ of the ZnO film is in a range from about 0.0007 to about 0.006.
2. The tunable filter according to claim 1 further comprising a SiO 2 film provided on the ZnO film.
3. The tunable filter according to claim 1 further comprising a SiO 2 film provided between the upper surface of the piezoelectric substrate and the ZnO film.
4. A tunable filter, comprising:
a surface acoustic wave resonator including:
a piezoelectric substrate including a recess in an upper surface thereof;
an IDT electrode defined by an electrode material provided in the recess in the upper surface of the piezoelectric substrate;
a ZnO film arranged to cover the upper surface of the piezoelectric substrate; and
a variable capacitor connected with the surface acoustic wave resonator; wherein
the piezoelectric substrate is a LiNbO 3 substrate with Euler angles of (0°, 100°+20°, 0°), and the electrode material defining the IDT electrode is one of Al, Ag, Pt, Au, Ta, W, Mo, Ni, or Cu; and
the IDT electrode of the surface acoustic wave resonator is primarily made of an electrode layer that is made of a material selected from Ni, Cu, Mo, and an alloy primarily made of at least one of Ni, Cu, and Mo, and when h is a thickness of the ZnO film and λ is a wavelength determined by a pitch of electrode fingers of the IDT electrode, a normalized film thickness h/λ of the ZnO film is in a range from about 0.004 to about 0.045.
5. The tunable filter according to claim 4 , wherein the IDT electrode includes a laminated body including the electrode layer and a second electrode layer that is made of a metal different from the metal of the electrode layer, and an average density of the laminated body is substantially the same as a density of the metal or an alloy of the electrode layer.
6. The tunable filter according to claim 4 , further comprising a SiO 2 film provided on the ZnO film.
7. The tunable filter according to claim 4 , further comprising a SiO 2 film provided between the upper surface of the piezoelectric substrate and the ZnO film.
8. A tunable filter, comprising:
a surface acoustic wave resonator including:
a piezoelectric substrate including a recess in an upper surface thereof;
an IDT electrode defined by an electrode material provided in the recess in the upper surface of the piezoelectric substrate;
a ZnO film arranged to cover the upper surface of the piezoelectric substrate; and
a variable capacitor connected with the surface acoustic wave resonator; wherein
the piezoelectric substrate is a LiNbO 3 substrate with Euler angles of (0°, 100°+20°, 0°), and the electrode material defining the IDT electrode is one of Al, Ag, Pt, Au, Ta, W, Mo, Ni, or Cu; and
the IDT electrode of the surface acoustic wave resonator is primarily made of an electrode layer that is made of a material selected from Pt, Au, W, Ta, Ag, and an alloy primarily made of at least one of Pt, Au, W, Ta, and Ag, and when h is a thickness of the ZnO film and λ is a wavelength determined by a pitch of electrode fingers of the IDT electrode, a normalized film thickness h/λ of the ZnO film is in a range from about 0.005 to about 0.14.
9. The tunable filter according to claim 8 , further comprising a SiO 2 film provided on the ZnO film.
10. The tunable filter according to claim 8 , further comprising a SiO 2 film provided between the upper surface of the piezoelectric substrate and the ZnO film.