Surface acoustic wave devices based on unpolished nanocrystalline diamond
View Patent ↗Surface Acoustic Wave (SAW) devices with an unpolished or nominally polished nanocrystalline diamond film, metal electrodes and piezoelectric composition coatings are described. The devices are used as radio frequency and microwave filters.
1. A surface acoustic wave (SAW) device which comprises:
(a) a substrate having a surface which has been processed to allow enhanced nucleation of diamond;
(b) a nominally unpolished nanocrystalline diamond film deposited on and adhered to the surface of the substrate and having a diamond grain size distribution between 1 nm and 50 nm wherein the nanocrystalline diamond film is formed in a microwave reactor containing argon, with a concentration of 90% by volume or greater, methane and optionally hydrogen at a pressure between 50 and 300 Torr at a flow rate between about 50 and 600 sccm, and a temperature of the substrate of 600° to 800° C., essentially in the absence of nitrogen or oxygen;
(c) electrodes deposited on the diamond film, or the piezoelectric overlayer, as interdigitated elements; and
(d) a piezoelectric composition coated over the diamond and electrodes, or with electrodes atop the piezoelectric composition, wherein the surface acoustic wave is created on the diamond by electrical waves supplied to the electrodes which strain the piezoelectric composition to produce the surface acoustic wave on the diamond, wherein the SAW device has acoustic wave velocities which have a close correspondence to calculated velocities based upon single crystal diamond values.
2. The device of claim 1 , wherein the substrate has been processed by scratch seeding, by bias-enhanced nucleation, or ion bombardment before deposition of the diamond film.
3. The device of any one of claims 1 or 2 wherein the piezoelectric composition is a polycrystalline metal oxide composition or a polymer composition.
4. The device of any one of claims 1 or 2 wherein the metal electrodes are selected from the group consisting of aluminum, gold, silver, platinum and palladium.
5. The device of any one of claims 1 or 2 wherein the substrate is silicon, wherein the metal electrodes are aluminum and wherein the piezoelectric composition is zinc oxide.
6. The device of claim 1 wherein the piezoelectric composition is deposited by sputtering zinc oxide in an argon and oxygen atmosphere.
7. The device of any one of claims 1 or 2 wherein the surface is roughened or scratched for depositing the diamond.
8. The device of any one of claims 1 or 2 wherein the electrodes are produced on the diamond or the piezoelectric film using photolithography or electron beam lithography.
9. The device of any one of claims 1 or 2 wherein the diamond film is several micrometers thick and the piezoelectric metal oxide coating is between 0.5 and 2.0 micrometers thick.
10. A surface acoustic wave device which comprises unpolished nanocrystalline diamond film with a grain size between 1 nm and 50 nanometers with metal electrodes and a piezoelectric material deposited on the diamond film and electrodes to provide an interdigital transducer for microwaves, wherein the nanocrystalline diamond film is formed in a microwave reactor containing argon, with a concentration of 90% by volume or greater, methane and optionally hydrogen at a pressure between 50 and 300 Torr at a flow rate between about 50 and 600 sccm, and a temperature of the substrate of 600° to 800° C., essentially in the absence of nitrogen or oxygen, and wherein the SAW device has acoustic wave velocities which have a close correspondence to calculated velocities based upon single crystal diamond values.
11. The device of claim 1 or 10 wherein the acoustic wave velocities are over 10,000 meters/sec.