Lateral field FBAR

• US 5,233,259 A
• Filed: 02/19/1991
• Issued: 08/03/1993
• Est. Priority Date: 02/19/1991
• Status: Expired due to Term

• Current Assignee: Round Rock Research LLC
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Walker, John M., Adam, John D., Weinert, Robert W., Krishnaswamy, S. Visvanathan
• Primary Examiner(s): Budd, Mark O.
• Assistant Examiner(s): Dougherty, Thomas M.
• Application Number:
  US07/656,657
• Time in Patent Office: 896 Days
• Field of Search: 310/322, 310/324, 310/358, 310/365, 310/366
• US Class Current: 310/324
• CPC Class Codes: H03H 9/17 having a single resonator crystal tuning forks H03H9/21
• CPC Class Codes: H03H 9/172 Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
• CPC Class Codes: H10N 30/853 Ceramic compositions
• CPC Class Codes: H10N 30/8536 Alkaline earth metal based oxides, e.g. barium titanates
• CPC Class Codes: H10N 30/8542 Alkali metal based oxides, e.g. lithium, sodium or potassium niobates

Abstract

This invention is a design for lateral field film bulk acoustic resonators (LF-FBAR). All electrodes in this design are located on one surface of the piezoelectric material, thereby simplifying manufacturing and improving performance. The gap between electrodes is limited to a specified dimension to maximize the efficiency of the device. Single and multi-pole devices are described. Barium magnesium fluoride and lithium niobate are specified as the piezoelectric material for high frequency applications.

Claims

1. A lateral field film bulk acoustic resonator comprising:

piezoelectric means operable to transform electrical energy to acoustic energy, said piezoelectric means having a thickness T_p ;

substrate means operable to support said piezoelectric means, said substrate means having a thickness T_s ;

at least two electrodes disposed on one surface of said piezoelectric means, said electrodes coupled by lateral excitation of said piezoelectric means,

wherein said electrodes are separated by a gap no greater than 3T_p² /(T_p +T_s).

2. A lateral field film bulk acoustic resonator as in claim 1, wherein said piezoelectric means is barium magnesium fluoride.

3. A lateral field film bulk acoustic resonator comprising:

piezoelectric means operable to transform electrical energy to acoustic energy, said piezoelectric means having a thickness T_p ;

substrate means operable to support said piezoelectric means, said substrate means having a thickness T_s ;

an input electrode, an output electrode, and a ground electrode disposed on one surface of said piezoelectric means, said ground electrode being disposed between said input and output electrodes.

4. A lateral field film bulk acoustic resonator as in claim 3, wherein the gaps separating said ground electrode from said input and said output electrodes each have a dimension no greater than 3T_p² /(T_p +T_s).

5. A lateral field film bulk acoustic resonator as in claim 3, wherein said piezoelectric means is barium magnesium fluoride or lithium niobate.

6. A lateral field film bulk acoustic resonator comprising:

a dielectric substrate having a thickness T_s disposed on a layer of semiconductor material and spanning an opening in said semiconductor material;

a piezoelectric layer having a top surface, a bottom surface, and a thickness T_p, said bottom surface disposed on said dielectric substrate opposed said opening in said semiconductor material;

an input electrode and an output electrode disposed on said top surface of said piezoelectric layer,

further comprising said input electrode and said output electrode being coupled by lateral field excitation of said piezoelectric layer.

7. A lateral field film bulk acoustic layer as in claim 6, wherein said input and output electrodes are separated by a gap having a dimension no greater than 3T_p² /(T_s +T_p).

8. A lateral field film bulk acoustic resonator as in claim 6, wherein said piezoelectric layer is barium magnesium fluoride or lithium niobate.

9. A lateral field film bulk acoustic resonator as in claim 6, wherein said dielectric substrate is spinel or sapphire.

10. A lateral field film bulk acoustic resonator comprising:

a dielectric substrate having a thickness T_s disposed on a layer of semiconductor material and spanning an opening in said semiconductor material;

a piezoelectric layer having a top surface, a bottom surface, and a thickness T_p, said bottom surface disposed on said dielectric membrane opposed said opening in said semiconductor material.

an input electrode, an output electrode and a ground electrode disposed on said top surface of said piezoelectric layer, said ground electrode being disposed between said input and output electrodes.

11. A lateral field film bulk acoustic resonator as in claim 10, wherein the gaps separating said ground electrode from said input and said output electrodes each have a dimension no greater than 3T_p² /(T_p +T_s).

12. A lateral field film bulk acoustic resonator as in claim 10, wherein said piezoelectric layer is barium magnesium fluoride or lithium niobate.

13. A lateral field film bulk acoustic resonator as in claim 10, wherein said dielectric substrate is spinel or sapphire.