Fundamental, longitudinal, thickness mode bulk wave resonator

• US 4,320,365 A
• Filed: 11/03/1980
• Issued: 03/16/1982
• Est. Priority Date: 11/03/1980
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Grudkowski, Thomas W., Black, James F., Norusis, Philip T., Wood, Harry R., Courtney, Richard A.
• Primary Examiner(s): Nussbaum, Marvin L.
• Application Number:
  US06/203,211
• Time in Patent Office: 498 Days
• Field of Search: 333/186-192, 310/311, 310/320-325, 310/328-334, 310/363-366
• US Class Current: 333/187
• CPC Class Codes: H03H 9/564 implemented with thin-film techniques

Abstract

A substrate (10) is thinned to provide a membrane (12) on which are disposed a counter electrode (20), a film of low conductivity piezoelectric material (22) and a top electrode (24) to form a half wavelength, bulk mode resonator employing a longitudinal acoustic wave. A second top electrode (25) provides a second resonator acoustically coupled to the first, to form a filter. Piezoelectric films include zinc oxide, and aluminum nitride; substrates include silicon and aluminum oxide. A buffer layer (18), such as silicon dioxide may assist in preventing surface aberations and providing proper crystallographic orientation.

Claims

1. A longitudinal, fundamental, bulk mode resonator comprising:

a substrate having first and second substantially planar surfaces, a portion of said substrate being thinned to provide a membrane having first and second substantially coplanar surfaces separated by a distance of from about three microns to about fifteen microns;

a metal counter electrode disposed on said substrate with a region of said counter electrode adjacent to said first surface of said membrane;

a film of low conductivity piezoelectric material having a thickness of from about two microns to about ten microns disposed adjacent said region on a side of said counter electrode opposite to said membrane; and

a metal top electrode disposed on said film adjacent said region, said top electrode and said counter electrode providing electroacoustic coupling with said film, the distance between a surface of said top electrode opposite to said film and said second surface of said membrane comprising a half wavelength of a desired longitudinal bulk acoustic wave.

2. A resonator according to claim 1 wherein said film is zinc oxide.

3. A resonator according to claim 1 wherein said film is aluminum nitride.

4. A resonator according to claim 1 wherein said substrate is silicon.

5. A resonator according to claim 1 wherein said substrate is aluminum oxide.

6. A resonator according to claim 1 wherein said first surface of said membrane is coated with an isolation layer, and said counter electrode is disposed on said layer.

7. A resonator according to claim 1 wherein said counter electrode comprises a metal selected from the group consisting of gold, titanium and platinum.

8. A resonator according to claim 1 wherein said film has a second top electrode disposed thereon in close proximity with said first named top electrode, both of said top electrodes being adjacent said region to provide a pair of longitudinal, fundamental, bulk mode resonators acoustically coupled together as a filter.

9. A resonator according to claim 1 wherein the ratio of absolute thickness of said film to said membrane is from about 0.3 to about 1.0.