Surface acoustic wave filter and duplexer using the same
View Patent ↗A SAW filter includes a piezoelectric body, an IDT electrode on the piezoelectric body, and signal wiring electrically connected to the IDT electrode. The signal wiring has a thickness not less than a skin depth specified based on the frequency of a signal passing through the signal wiring and the electrical conductivity of the signal wiring. As a result, the signal wiring has low propagation loss of the signal passing through it, so that the SAW filter has excellent transmission characteristics.
1. A surface acoustic wave filter comprising:
a piezoelectric body;
an IDT electrode on the piezoelectric body; and
signal wiring electrically connected to the IDT electrode,
wherein the IDT electrode and the signal wiring overlap each other at respective outer edges, and
in the outer edges where the IDT electrode and the signal wiring overlap each other, the IDT electrode and the signal wiring have a total thickness not less than a skin depth “d” (μm), the skin depth “d” being calculated by Formula 1:
d
=
2.0
×
10
-
4
f
×
σ
Formula
1
where “f” represents a frequency (GHz) of a signal passing through the signal wiring, and “σ” represents an electrical conductivity (S/m) of the signal wiring, and
wherein the total thickness is in a range of 1.0 to 1.2 times the skin depth “d”.
2. The surface acoustic wave filter of claim 1 , wherein
the signal wiring has a laminated structure of a plurality of electrode layers, and
in a case where the skin depth “d” is not larger than a thickness of an uppermost electrode layer of the signal wiring, the electrical conductivity “σ” of the signal wiring is equal to an electrical conductivity of the uppermost electrode layer.
3. The surface acoustic wave filter of claim 1 , wherein
the signal wiring has a laminated structure of a plurality of electrode layers, and
in a case where the skin depth “d” is not larger than a thickness of an uppermost electrode layer of the signal wiring, the electrical conductivity “σ” of the signal wiring is equal to an electrical conductivity of the uppermost electrode layer.
4. A duplexer comprising:
a receive filter including a surface acoustic wave filter; and
a transmit filter including a surface acoustic wave filter,
wherein the surface acoustic wave filter of the receive filter has signal wiring larger in thickness than signal wiring of the surface acoustic wave filter of the transmit filter,
wherein each surface acoustic wave filter comprises:
a piezoelectric body;
an IDT electrode on the piezoelectric body; and
signal wiring electrically connected to the IDT electrode, and
wherein the signal wiring has a thickness not less than a skin depth “d” (μm), the skin depth “d” being calculated by Formula 1:
d
=
2.0
×
10
-
4
f
×
σ
Formula
1
where “f” represents a frequency (GHz) of a signal passing through the signal wiring, and “σ” represents an electrical conductivity (S/m) of the signal wiring.
5. A surface acoustic wave filter comprising:
a piezoelectric body;
an IDT electrode on the piezoelectric body; and
signal wiring electrically connected to the IDT electrode,
wherein the signal wiring has a thickness not less than a skin depth “d” (the skin dept “d” being calculated by Formula 1:
d
=
2.0
×
10
-
4
f
×
σ
Formula
1
where “f” represents a frequency (GHz) of a signal passing through the signal wiring, and “σ” represents an electrical conductivity (S/m) of the signal wiring, and
wherein the signal wiring has a laminated structure of a plurality of electrode layers, and
in a case where the skin depth “d” is larger than a thickness of an uppermost electrode layer of the signal wiring, the electrical conductivity “σ” of the signal wiring is equal to an average electrical conductivity of all electrode layers within the skin depth “d” from an upper surface of the signal wiring.
6. A surface acoustic wave filter comprising:
a piezoelectric body;
an IDT electrode on the piezoelectric body; and
signal wiring electrically connected to the IDT electrode,
wherein the IDT electrode and the signal wiring overlap each other at respective outer edges, and
in the outer edges where the IDT electrode and the signal wiring overlap each other, the IDT electrode and the signal wiring have a total thickness not less than a skin depth “d” (μm), the skin depth “d” being calculated by Formula 1:
d
=
2.0
×
10
-
4
f
×
σ
Formula
1
where “f” resents a frequency (GHz) of a signal passing through the signal wiring, and “σ” represents an electrical conductivity (S/m) of the signal wiring, and
wherein the signal wiring has a laminated structure of a plurality of electrode layers, and
in a case where the skin depth “d” is larger than a thickness of an uppermost electrode layer of the signal wiring, the electrical conductivity “σ” of the signal wiring is equal to an average electrical conductivity of all electrode layers within the skin depth “d” from an upper surface of the signal wiring.