Method of manufacture of acoustic wave device with trench portions for transverse mode suppression
A method of manufacturing an acoustic wave device is provided. The method of manufacturing the acoustic wave device comprises providing a layer of piezoelectric material, disposing a pair of interdigital transducer electrodes on an upper surface of the layer of piezoelectric material, each interdigital transducer electrode including a bus bar and a plurality of electrode fingers extending from the bus bar towards an edge region of the interdigital transducer electrode at the distal ends of the electrode fingers, and etching trench portions into the upper surface of the layer of piezoelectric material, the trench portions overlapping with the edge regions of the interdigital transducer electrodes. The formation of the trench portions through etching results in an easier fabrication, that is less likely to damage the interdigital transducer electrodes.
1 . A method of manufacturing an acoustic wave device, the method comprising:
providing a layer of piezoelectric material;
disposing a pair of interdigital transducer electrodes on an upper surface of the layer of piezoelectric material, each interdigital transducer electrode including a bus bar and a plurality of electrode fingers extending from the bus bar towards an edge region of the interdigital transducer electrode at distal ends of the electrode fingers; and
etching trench portions into the upper surface of the layer of piezoelectric material, the trench portions extending into the layer of piezoelectric material but not through the layer of piezoelectric material, the trench portions overlapping with the edge regions of the interdigital transducer electrodes.
2 . The method of manufacturing of claim 1 further comprising, before the etching, positioning an etch resistant mask to cover the pair of interdigital transducer electrodes and the upper surface of the layer of piezoelectric material other than in the edge regions.
3 . The method of manufacturing of claim 1 wherein the etching includes etching the trench portions in areas of the upper surface of the layer of piezoelectric material that are overlapped by the edge regions of the interdigital transducer electrodes and that are not covered by the interdigital transducer electrodes.
4 . The method of manufacturing of claim 1 wherein the disposing the pair of interdigital transducer electrodes on the upper surface of the layer of piezoelectric material includes forming each interdigital transducer electrode from a single layer of etch resistant material.
5 . The method of manufacturing of claim 4 wherein the etch resistant material is selected from the group consisting of copper, platinum, tungsten, molybdenum, ruthenium, iridium, gold, and silver.
6 . The method of manufacturing of claim 1 wherein disposing the pair of interdigital transducer electrodes on the upper surface of the layer of piezoelectric material includes forming each interdigital transducer electrode from one or more lower layers of material and an upper layer of etch resistant material selected from the group consisting of copper, platinum, tungsten, molybdenum, ruthenium, iridium, gold, and silver.
7 . The method of manufacturing of claim 6 wherein disposing the pair of interdigital transducer electrodes on the upper surface of the layer of piezoelectric material includes forming upper layers of the plurality of electrode fingers with a lesser maximum width than the one or more lower layers of the plurality of electrode fingers.
8 . The method of manufacturing of claim 6 wherein disposing the pair of interdigital transducer electrodes on the upper surface of the layer of piezoelectric material includes forming upper layers of the plurality of electrode fingers with trapezoidal cross-sections.
9 . The method of manufacturing of claim 1 further comprising, before the etching, applying a mask layer onto the upper surfaces of each of the pair of interdigital transducer electrodes.
10 . The method of manufacturing of claim 9 wherein the mask layer is a layer of chromium.
11 . The method of manufacturing of claim 1 further comprising, after the etching, disposing a protective layer over the upper surfaces of the pair of interdigital transducer electrodes and the layer of piezoelectric material.
12 . The method of manufacturing of claim 11 wherein the protective layer is formed from one or more of the group consisting of silicon nitride, silicon oxynitride, and silicon dioxide.
13 . The method of manufacturing of claim 1 wherein the electrode fingers of each interdigital transducer electrode disposed on the upper surface of the layer of piezoelectric material interleave with one another in an active region of the pair of interdigital transducer electrodes, and form gap regions between the ends of the fingers of one of the interdigital transducer electrodes and the bus bar of the other interdigital transducer electrode.
14 . The method of manufacturing of claim 13 wherein the trench portions etched into the upper surface of the layer of piezoelectric material also overlap with at least part of the gap regions.
15 . The method of manufacturing of claim 14 further comprising, before the etching, positioning an etch resistant mask to cover the pair of interdigital transducer electrodes and the upper surface of the layer of piezoelectric material other than in the edge regions and the at least part of the gap regions.
16 . The method of manufacturing of claim 13 wherein disposing the pair of interdigital transducer electrodes on the upper surface of the layer of piezoelectric material includes disposing a second bus bar within the gap region.
17 . The method of manufacturing of claim 16 wherein disposing the pair of interdigital transducer electrodes on the upper surface of the layer of piezoelectric material includes forming dummy electrodes extending from the second bus bar partially through the gap region toward an adjacent edge region.
18 . The method of manufacturing of claim 13 wherein the active region includes a central region and the edge regions of the interdigital transducer electrodes, each edge region extending from tips of the plurality of electrode fingers of one of the interdigital transducer electrodes towards a center of the central region.
19 . The method of manufacturing of claim 18 wherein each of the plurality of electrode fingers of the interdigital transducer electrodes disposed on the upper surface of the layer of piezoelectric material has a width in a direction perpendicular to an extension of the electrode fingers that is smaller in the edge regions than in the central regions.
20 . The method of manufacturing of claim 1 wherein the etching includes etching using at least one of chemical etching, laser etching, dry etching, vapor phase etching, wet etching, and/or plasma etching.