Microresonator electrode design
A microresonator with an input electrode and an output electrode patterned thereon is described. The input electrode includes a series of stubs that are configured to isolate acoustic waves, such that the waves are not reflected into the microresonator. Such design results in reduction of spurious modes corresponding to the microresonator.
1. An acoustic width-extensional microresonator having at least one operating frequency f, comprising:
a first layer composed of a metal;
a second layer composed of the metal; and
a third layer composed of a piezoelectric film, wherein the third layer is disposed between the first layer and the second layer, the first layer formed to comprise an input electrode and an output electrode, wherein the input electrode comprises:
a first interconnect bus;
a first plurality of fingers that extend orthogonally from the first interconnect bus, each finger in the first plurality of fingers having a first length; and
a first plurality of stubs that extend orthogonally from the first interconnect bus, each stub in the first plurality of stubs having a second length, the second length being less than the first length, wherein the acoustic microresonator has a size of less than 500 μm in length, 150 μm in width, and 10 μm in thickness;
and wherein the output electrode comprises:
a second interconnect bus in parallel with the first interconnect bus, wherein the first plurality of fingers extend from the first interconnect bus toward the second interconnect bus;
a second plurality of fingers that extend orthogonally from the second interconnect bus toward the first interconnect bus, each finger in the second plurality of fingers having the first length; and
a second plurality of stubs that extend orthogonally from the second interconnect bus toward the first interconnect bus, each stub in the second plurality of stubs having the second length, the first and second plurality of stubs and the first and second plurality of fingers being arranged such that each finger of the first plurality of fingers opposes a respective stub of the second plurality of stubs across a first gap and each finger of the second plurality of fingers opposes a respective stub of the first plurality of stubs across a second gap.
2. A chip comprising a plurality of acoustic microresonators, in which the width-extensional acoustic microresonator of claim 1 is included in the plurality of acoustic microresonators.
3. A frequency filter comprising the width-extensional acoustic microresonator of claim 1 .
4. The width-extensional acoustic microresonator of claim 1 , wherein the metal is aluminum.
5. The width-extensional acoustic microresonator of claim 1 , wherein the piezoelectric film is composed of aluminum nitride.
6. The width-extensional acoustic microresonator of claim 1 , wherein the gaps between the first and second plurality of fingers and their respective first and second plurality of stubs have a length equal to the second length.
7. The width-extensional acoustic microresonator of claim 1 , wherein the operating frequency f corresponds to an acoustic wavelength and wherein the second length lies in the range from 0.75 to 1.25 times the acoustic wavelength at the operating frequency.
8. The width-extensional acoustic microresonator of claim 1 , wherein the first plurality of fingers consists of four fingers, and wherein the first plurality of stubs consists of four stubs.
9. A mobile communications device comprising the width-extensional acoustic microresonator of claim 1 .
10. The mobile communications device of claim 9 , being a mobile telephone.