Microfabricated bulk wave acoustic bandgap device
A microfabricated bulk wave acoustic bandgap device comprises a periodic two-dimensional array of scatterers embedded within the matrix material membrane, wherein the scatterer material has a density and/or elastic constant that is different than the matrix material and wherein the periodicity of the array causes destructive interference of the acoustic wave within an acoustic bandgap. The membrane can be suspended above a substrate by an air or vacuum gap to provide acoustic isolation from the substrate. The device can be fabricated using microelectromechanical systems (MEMS) technologies. Such microfabricated bulk wave phononic bandgap devices are useful for acoustic isolation in the ultrasonic, VHF, or UHF regime (i.e., frequencies of order 1 MHz to 10 GHz and higher, and lattice constants of order 100 μm or less).
1. A method for fabricating a bulk wave acoustic bandgap device, comprising:
providing a substrate;
forming a release layer on the substrate;
forming a matrix layer comprising a matrix material on the release layer;
forming a two-dimensional periodic array of scatterers within the matrix material, wherein the periodic array comprises a cermet topology and wherein the scatterer material has a higher acoustic impedance than the matrix material; and
removing the release layer to release a membrane comprising the matrix material and the periodic array of scatterers within the matrix material, wherein the periodicity of the array causes destructive interference within an acoustic bandgap of a longitudinal acoustic wave that propagates in the plane of the membrane.
2. The method of claim 1 , wherein the substrate comprises silicon, semiconductor, glass, ceramic, or metal.
3. The method of claim 1 , wherein the scatterer material has a higher density than the matrix material.
4. The method of claim 1 , wherein the scatterer material has higher elastic constant than the matrix material.
5. The method of claim 1 , wherein the matrix material comprises silicon dioxide, silicon, or polymer.
6. The method of claim 1 , wherein the scatterer material comprises tungsten, tungsten carbide, platinum, polycrystalline diamond, or molybdenum.
7. The method of claim 1 , wherein the frequency of the acoustic wave is greater than 1 MHz.
8. The method of claim 1 , wherein the periodicity of the periodic array is less than 100 microns.
9. The method of claim 1 , further comprising forming an etch-stop layer on the substrate prior to forming the release layer.
10. The method of claim 1 , wherein the etch-stop layer comprises silicon oxide.
11. The method of claim 1 , further comprising forming at least one defect within the periodic array of scatterers.