Suspending an Electrode Structure Using a Dielectric
An apparatus is disclosed for suspending an electrode structure using a dielectric. In an example aspect, the apparatus includes a surface-acoustic-wave filter with a piezoelectric layer and an electrode structure. The electrode structure has a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance. The surface-acoustic-wave filter also includes a dielectric disposed on at least one other surface of the electrode structure and configured to extend past a plane defined by the first surface of the electrode structure and toward the piezoelectric layer to define a cavity between at least a portion of the first surface of the electrode structure and the piezoelectric layer.
1 . An apparatus comprising:
a surface-acoustic-wave filter comprising:
a piezoelectric layer;
an electrode structure having a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance; and
a dielectric disposed on at least one other surface of the electrode structure and configured to extend past a plane defined by the first surface of the electrode structure and toward the piezoelectric layer to define a cavity between the first surface of the electrode structure and the piezoelectric layer.
2 . The apparatus of claim 1 , wherein the dielectric is configured to cause at least a portion of the electrode structure to be suspended apart from the piezoelectric layer by the distance.
3 . The apparatus of claim 1 , wherein the dielectric adheres to the at least one other surface of the electrode structure.
4 . The apparatus of claim 1 , wherein portions of the dielectric extend past the plane through different gaps in the electrode structure.
5 . The apparatus of claim 1 , wherein:
the electrode structure comprises multiple gaps; and
at least a portion of the dielectric is present within the multiple gaps and abuts the piezoelectric layer.
6 . The apparatus of claim 1 , wherein the cavity is at least partially filled with a gas.
7 . The apparatus of claim 6 , wherein the gas comprises air.
8 . The apparatus of claim 1 , wherein:
the electrode structure comprises:
a first comb-shaped structure comprising a first busbar and a first set of fingers extending from the first busbar; and
a second comb-shaped structure comprising a second busbar and a second set of fingers extending from the second busbar; and
the cavity is present between the piezoelectric layer and fingers of the first set of fingers and the second set of fingers.
9 . The apparatus of claim 8 , wherein:
the at least one other surface of the electrode structure comprises a second surface that faces at least partially away from the piezoelectric layer; and
the dielectric comprises:
a cap disposed across the second surface of the fingers; and
spacers disposed between the piezoelectric layer and the cap through gaps present between the fingers.
10 . The apparatus of claim 9 , wherein the cap and the spacers comprise a same dielectric material.
11 . The apparatus of claim 9 , wherein a thickness of the cap is between approximately one hundred nanometers and two thousand nanometers.
12 . The apparatus of claim 8 , wherein the cavity extends along lengths of the fingers.
13 . The apparatus of claim 8 , wherein a width of the cavity is greater than individual widths of the fingers.
14 . The apparatus of claim 1 , wherein the dielectric comprises one or more of the following:
a layer of silicon dioxide;
a layer of nitride;
a layer of aluminum oxide;
a layer of polymer;
a layer of titanium dioxide;
a layer of hafnium dioxide;
a layer of yttrium oxide; or
a layer of zirconium dioxide.
15 . The apparatus of claim 1 , wherein a height of the cavity is between approximately one nanometer and fifty nanometers.
16 . The apparatus of claim 1 , wherein the piezoelectric layer is configured to excite one of the following:
a shear mode;
a Rayleigh mode; or
a longitudinal mode.
17 . The apparatus of claim 1 , wherein the surface-acoustic-wave filter comprises at least one of the following:
a first dielectric layer that is disposed between the dielectric and the electrode structure, disposed between the dielectric and the piezoelectric layer, and disposed between the dielectric and the cavity;
a second dielectric layer that is disposed between the first surface of the electrode structure and the cavity; or
a third dielectric layer that is disposed between the piezoelectric layer and the cavity and disposed between the piezoelectric layer and the dielectric.
18 . The apparatus of claim 17 , wherein:
the surface-acoustic-wave filter comprises the first dielectric layer; and
the first dielectric layer has a thickness between approximately one and one hundred nanometers.
19 . The apparatus of claim 17 , wherein:
the surface-acoustic-wave filter comprises the second dielectric layer or the third dielectric layer; and
the second dielectric layer or the third dielectric layer has a thickness between approximately one and five nanometers.
20 . The apparatus of claim 1 , wherein:
the surface-acoustic-wave filter comprises multiple cascaded resonators; and
a resonator of the multiple cascaded resonators comprises the piezoelectric layer and the dielectric.
21 . The apparatus of claim 1 , further comprising:
a wireless transceiver coupled to at least one antenna, the wireless transceiver comprising the surface-acoustic-wave filter and configured to filter, using the surface-acoustic-wave filter, a wireless signal communicated via the at least one antenna.
22 . The apparatus of claim 1 , wherein the surface-acoustic-wave filter comprises a thin-film surface-acoustic-wave filter.
23 . An apparatus comprising:
a surface-acoustic-wave filter configured to generate a filtered signal from a radio-frequency signal, the surface-acoustic-wave filter comprising:
means for converting the radio-frequency signal to an acoustic wave and converting a propagated acoustic wave into the filtered signal;
means for propagating the acoustic wave across a planar surface to produce the propagated acoustic wave; and
means for suspending at least a portion of the means for converting apart from the planar surface.
24 . The apparatus of claim 23 , wherein the means for suspending comprises means for reflecting the acoustic wave.
25 . A method of manufacturing a surface-acoustic-wave filter, the method comprising:
providing a piezoelectric layer;
providing an electrode structure having a first surface facing the piezoelectric layer and separated from the piezoelectric layer by a distance; and
providing a dielectric that suspends at least a portion of the first surface of the electrode structure apart from the piezoelectric layer by the distance.
26 . The method of claim 25 , further comprising:
providing a sacrificial layer on a surface of the piezoelectric layer, the sacrificial layer present between the piezoelectric layer and the portion of the first surface of the electrode structure;
etching through the dielectric to the sacrificial layer; and
removing the sacrificial layer to form a cavity between the portion of the first surface of the electrode structure and the piezoelectric layer.
27 . The method of claim 25 , wherein:
the providing of the piezoelectric layer comprises providing the piezoelectric layer on a first wafer;
the providing of the electrode structure and the providing of the dielectric comprises providing the electrode structure and the dielectric on a second wafer; and
the method further comprises:
bonding the first wafer to the second wafer to form a cavity between the portion of the first surface of the electrode structure and the piezoelectric layer.
28 . A surface-acoustic-wave filter comprising:
a piezoelectric layer having a planar surface;
an electrode structure comprising fingers, the fingers having a first surface facing the planar surface of the piezoelectric layer and a second surface facing at least partially away from the piezoelectric layer; and
a dielectric configured to separate the fingers of the electrode structure from the planar surface of the piezoelectric layer, the dielectric comprising:
a cap disposed across the second surface of the fingers; and
spacers disposed between the piezoelectric layer and the cap through gaps that are present between the fingers.
29 . The surface-acoustic-wave filter of claim 28 , wherein the spacers of the dielectric are configured to extend past a plane defined by the first surface of the fingers toward the planar surface of the piezoelectric layer to define a cavity between the first surface of the fingers and the planar surface of the piezoelectric layer.
30 . The surface-acoustic-wave filter of claim 29 , wherein the cavity extends along lengths of the fingers and extends beyond widths of the fingers.
31 . The surface-acoustic-wave filter of claim 29 , wherein the surface-acoustic-wave filter comprises a dielectric layer that is disposed between the dielectric and the fingers, disposed between the dielectric and the piezoelectric layer, and disposed between the dielectric and the cavity.
32 . The surface-acoustic-wave filter of claim 29 , wherein the surface-acoustic-wave filter comprises a dielectric layer that is disposed between the fingers and the cavity.
33 . The surface-acoustic-wave filter of claim 29 , wherein the surface-acoustic-wave filter comprises a dielectric layer that is disposed between the piezoelectric layer and the cavity and disposed between the piezoelectric layer and the dielectric.
34 . The surface-acoustic-wave filter of claim 28 , wherein the cap and the spacers comprise different dielectric materials.
35 . The surface-acoustic-wave filter of claim 28 , wherein:
the surface-acoustic-wave filter is configured to generate a standing surface acoustic wave across the planar surface of the piezoelectric layer; and
the spacers are positioned at nodes of the standing surface acoustic wave.