Surface acoustic wave devices and associated casting methods
Surface acoustic wave devices and methods of forming such devices using CVD techniques are disclosed and described. A mold can be provided which has an interface surface configured to inversely match a configuration intended for the working surface of a diamond layer in a tool. An adynamic diamond mass or layer is then deposited upon the diamond interface surface of the mold, and a support layer is joined to the growth surface of the adynamic diamond layer. At least a portion of the mold is then removed to expose the working surface of the diamond which has received a shape which inversely corresponds to the configuration of the mold's diamond interface surface. Such methods can be used to produce a precursor wafer having multiple partitioned surface acoustic wave devices.
1 . A precursor wafer of multiple partitioned surface acoustic wave devices made in accordance with a method comprising the steps of:
a) providing a mold having an interface surface configured to inversely match a configuration intended for a working surface of the diamond SAW device;
b) defining multiple areas which correspond to individual SAW devices;
c) growing an adynamic diamond layer on the mold using a CVD technique, said adynamic diamond layer having a growth surface opposite the working surface;
d) joining a support layer to the growth surface of the adynamic diamond layer; and
e) removing at least a portion of the mold.
2 . The precursor wafer of claim 1 , wherein the step of defining multiple areas further comprises the step of forming grooves in the mold which define the multiple areas, such that the grooves have a depth which corresponds to a desired piezoelectric layer thickness.
3 . The precursor wafer of claim 2 , wherein the mold is a piezoelectric mold and further comprises the step of removing a portion of the piezoelectric mold which extends beyond the grooves to produce an outer surface of the piezoelectric layer after the step of joining the support layer, such that the working surface of the diamond layer and the outer surface of the mold are parallel and the portion of piezoelectric mold remaining is partitioned along the multiple areas.
4 . The precursor wafer of claim 2 , further comprising the step of filling at least a portion of the grooves with a CVD passive layer prior to growing the adynamic diamond layer on the mold.
5 . The precursor wafer of claim 4 , wherein the CVD passive layer is Cu, Ag, BN, SiO 2 , Al 2 O 3 , graphite, or mixture thereof.
6 . The precursor wafer of claim 1 , wherein the step of defining multiple areas further comprises the step of forming a pattern of CVD passive material on the interface surface of the mold that defines the multiple areas.
7 . The precursor wafer of claim 6 , wherein a thickness of the CVD passive material and size of the multiple areas are chosen to minimize thermal expansion stress.
8 . The precursor wafer of claim 1 , wherein the mold is completely removed and further comprises the step of brazing a semiconductor substrate to the working surface of the diamond layer using a braze alloy subsequent to the removal of the mold.
9 . The precursor wafer of claim 1 , wherein the mold is a ceramic mold made substantially of a material selected from the group consisting of SiO 2 , Al 2 O 3 , LiTaO 3 , LiNbO 3 , ZnO, langaside, lead zirconium titanate, glass, Si 3 N 4 , AlN, BN, TiN, ZrN, and mixtures thereof.
10 . The precursor wafer of claim 1 , wherein the mold comprises a piezoelectric material.
11 . The precursor wafer of claim 10 , wherein the piezoelectric material is AlN or LiNbO 3 .
12 . The precursor wafer of claim 10 , wherein the piezoelectric material is provided from a single crystal ingot.
13 . The precursor wafer of claim 1 , wherein the mold comprises a carbide former.
14 . The precursor wafer of claim 1 , further comprising a thin piezoelectric layer on the working surface of the diamond.
15 . The precursor wafer of claim 14 , further comprising a plurality of interdigital transducers formed on an outside surface of the piezoelectric layer.
16 . The precursor wafer of claim 1 , further comprising a nucleation enhancing layer on the interface surface of the mold.
17 . The precursor wafer of claim 1 , wherein the SAW device is a SAW filter.
18 . The precursor wafer of claim 1 , wherein the working surface of the adynamic diamond layer has a surface roughness (Ra) of less than about 1 micrometer.
19 . The precursor wafer of claim 18 , wherein the surface roughness (Ra) is less than about 1 nanometer.
20 . The precursor wafer of claim 1 , wherein the adynamic diamond layer has a thickness of less than about 30 micrometers.