Bulk acoustic resonator perimeter reflection system
First Claim
1. An acoustic resonator comprising:
- a substrate having a depression formed in a top surface thereof;
a first electrode disposed on the top surface of the substrate and over the depression, the first electrode extending beyond a plurality of edges of the depression by a first distance to define a first region therebetween;
a piezoelectric material disposed on the top surface of the substrate and over the first electrode; and
a second electrode disposed on the piezoelectric material and including a portion located above the depression, the portion located above the depression having at least one edge that is offset from a corresponding edge of the depression by a second distance to define a second region therebetween, the second region having an impedance that differs from an impedance of the first region, wherein an overlap of the first electrode, the piezoelectric material and the second electrode forms an acoustic cavity of the resonator, and the first and second distances are chosen such that reflections from the edges of the first and second regions will constructively interfere.
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Abstract
A bulk acoustic resonator having a high quality factor is formed on a substrate having a depression formed in a top surface of the substrate. The resonator includes a first electrode, a piezoelectric material and a second electrode. The first electrode is disposed on the top surface of the substrate and extends beyond the edges of the depression by a first distance to define a first region therebetween. The piezoelectric material is disposed on the top surface of the substrate and over the first electrode, and the second electrode is disposed on the piezoelectric material. The second electrode includes a portion that is located above the depression. The portion of the second electrode that is located over the depression has at least one edge that is offset from a corresponding edge of the depression by a second distance to define a second region therebetween. The first and second regions have different impedances, as a result of the different materials located in the two regions. In addition, the first and second distances are approximately equal to a quarter-wavelength of a sound wave travelling laterally across the respective region, such that reflections off of the edges of the regions constructively interfere to maximize the reflectivity of the resonator.
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Citations
20 Claims
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1. An acoustic resonator comprising:
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a substrate having a depression formed in a top surface thereof;
a first electrode disposed on the top surface of the substrate and over the depression, the first electrode extending beyond a plurality of edges of the depression by a first distance to define a first region therebetween;
a piezoelectric material disposed on the top surface of the substrate and over the first electrode; and
a second electrode disposed on the piezoelectric material and including a portion located above the depression, the portion located above the depression having at least one edge that is offset from a corresponding edge of the depression by a second distance to define a second region therebetween, the second region having an impedance that differs from an impedance of the first region, wherein an overlap of the first electrode, the piezoelectric material and the second electrode forms an acoustic cavity of the resonator, and the first and second distances are chosen such that reflections from the edges of the first and second regions will constructively interfere. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An acoustic resonator comprising:
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a substrate having a depression formed in a top surface thereof, the depression having a plurality of edges;
a first electrode disposed on the top surface of the substrate and over the depression, the first electrode having a plurality of edges and extending beyond the edges of the depression by a first distance to define a first region therebetween;
a piezoelectric material formed on the top surface of the substrate and the first electrode; and
a second electrode disposed on the piezoelectric material, the second electrode including a portion located above the depression, a plurality of edges of the portion located above the depression being offset from corresponding edges of the depression by a second distance to define a second region therebetween, the second region having a second impedance that differs from a first impedance of the first region, wherein an overlap of the first electrode, the piezoelectric material and the second electrode forms an acoustic cavity of the resonator, and wherein the first and second regions form Bragg reflectors that reflect sound waves back to the acoustic cavity of the resonator. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A method of making an acoustic resonator, the method comprising:
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providing a substrate having a depression formed in a top surface thereof and a first electrode disposed on the top surface, the first electrode being located above the depression and extending beyond a plurality of edges of the depression by a first distance to define a first region therebetween;
depositing a piezoelectric material on the top surface of the substrate and over the first electrode; and
depositing a second electrode on the piezoelectric material, the second electrode including a portion located above the depression, the portion located above the depression having at least one edge that is offset from a corresponding edge of the depression by a second distance to define a second region therebetween, wherein an overlap of the first electrode, the piezoelectric material and the second electrode forms an acoustic cavity of the resonator, and the first and second distances are chosen such that reflections from the edges of the first and second regions will constructively interfere. - View Dependent Claims (18, 19, 20)
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Specification