Incremental tuning process for electrical resonators based on mechanical motion
View Patent ↗The present invention is a method for adjusting the resonant frequency of a mechanical resonator whose frequency is dependent on the overall resonator thickness. Alternating selective etching is used to remove distinct adjustment layers from a top electrode. One of the electrodes is structured with a plurality of stacked adjustment layers, each of which has distinct etching properties from any adjacent adjustment layers. Also as part of the same invention is a resonator structure in which at least one electrode has a plurality of stacked layers of a material having different etching properties from any adjacent adjustment layers, and each layer has a thickness corresponding to a calculated frequency increment in the resonant frequency of the resonator.
1. A method of manufacturing a resonator having a resonant frequency, the method comprising:
(a) forming a resonator having a transducer layer between first and second electrode layers;
(b) forming a plurality of stacked adjustment layers over the resonator, wherein at least one adjustment layer has an etching property different from an etching property of an adjacent underlying layer;
(c) measuring the resonant frequency of the resonator with the plurality of stacked adjustment layers; and
(d) then sequentially removing one or more of the adjustment layers to adjust the resonant frequency of the resonator based on the measured resonant frequency.
2. The method according to claim 1 , wherein the resonator is a mechanical resonator.
3. The method according to claim 1 , wherein step (a) comprises forming the resonator on a substrate.
4. The method according to claim 3 , wherein step (a) comprises:
(a1) forming an acoustic mirror on the substrate; and
(a2) forming the resonator over the acoustic mirror.
5. The method according to claim 1 , wherein step (d) comprises sequentially removing the one or more adjustment layers to adjust the resonant frequency of the resonator to achieve a desired resonant frequency.
6. The method according to claim 5 , wherein step (b) further comprises selecting a number of layers for the plurality of stacked adjustment layers such that the resonant frequency of the resonator with the plurality of stacked adjustment layers is lower than the desired resonant frequency.
7. The method according to claim 1 , wherein step (d) further comprises calculating a number of the adjustment layers to be removed based on (1) the measured resonant frequency of the resonator with the plurality of stacked adjustment layers and (2) resonant frequency adjustment increments corresponding to the adjustment layers.
8. The method according to claim 7 , wherein at least two of the adjustment layers correspond to different resonant frequency adjustment increments.
9. The method according to claim 7 , wherein all of the adjustment layers correspond to substantially a single resonant frequency adjustment increment.
10. The method according to claim 1 , wherein step (b) further comprises:
(b1) selecting at least one desired resonant frequency adjustment increment; and
(b2) designing at least one of the adjustment layers to correspond to the at least one specified desired resonant frequency adjustment increment.
11. The method according to claim 1 , wherein step (d) comprises removing the at least one adjustment layer by etching.
12. The method according to claim 11 , wherein the at least one adjustment layer is removed by wet etching.
13. The method according to claim 11 , wherein the etching removes the at least one adjustment layer and substantially none of the adjacent underlying layer.
14. The method according to claim 1 , wherein:
steps (a)-(c) are implemented to form at least first and second resonators on a single substrate, each resonator with a corresponding plurality of stacked adjustment layers; and
step (d) is implemented to remove different sets of adjustment layers from the first and second resonators.
15. The method according to claim 14 , wherein the first and second resonators with their corresponding pluralities of stacked adjustment layers have different measured resonant frequencies.
16. The method according to claim 14 , wherein different numbers of adjustment layers are removed from the first and second resonators to achieve different desired resonant frequencies.
17. The method according to claim 14 , wherein:
the plurality of stacked adjustment layers for the first resonator comprise a first pair of layer materials; and
the plurality of stacked adjustment layers for the second resonator comprise a second pair of layer materials different from the first pair of layer materials.
18. The method according to claim 17 , wherein the etching properties of the first pair of layer materials are different from the etching properties of the second pair of layer materials, such that the one or more adjustment layers of the first resonator are removed substantially independently of the removal of the one or more adjustment layers of the second resonator.