Method of mass loading of thin film bulk acoustic resonators (FBAR) for creating resonators of different frequencies and apparatus embodying the method

• US 6,469,597 B2
• Filed: 03/05/2001
• Issued: 10/22/2002
• Est. Priority Date: 03/05/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Ruby, Richard C., Larson, John D. III, Bradley, Paul D.
• Primary Examiner(s): Lee, Benny
• Assistant Examiner(s): Summons, Barbara
• Application Number:
  US09/799,204
• Publication Number:
  US 20020121945A1
• Time in Patent Office: 596 Days
• Field of Search: 333/186-192, 310/312, 29/253.5
• US Class Current: 333/187
• CPC Class Codes: H03H 2003/0428 of an electrode
• CPC Class Codes: H03H 2003/0471 of a plurality of resonators at different frequencies
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/564 implemented with thin-film techniques
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A method for fabricating a resonator, and in particular, a thin film bulk acoustic resonator (FBAR), and a resonator embodying the method are disclosed. An FBAR is fabricated on a substrate by introducing a mass loading electrode to a bottom electrode layer. For a substrate having multiple resonators, mass loading bottom electrode is introduced for only selected resonator to provide resonators having different resonance frequencies on the same substrate.

Claims

1. A method of fabricating resonators on a substrate, the method comprising:

fabricating a bottom loading electrode;

fabricating a first bottom core electrode and a second bottom core electrode, the first bottom core electrode completely bridging a cavity and fabricated over the bottom loading electrode that also completely bridges the cavity, the first bottom core electrode together with the bottom loading electrode defining a first bottom electrode, and the second bottom core electrode defining a second bottom electrode;

fabricating a piezoelectric (PZ) layer;

fabricating a first top electrode such that a first portion of the PZ layer is sandwiched between the first top electrode on one side and the first bottom electrode on the other side, forming a first resonator; and

fabricating a second top electrode such that a second portion of the PZ layer is sandwiched between the second top electrode on one side and the second bottom electrode on the other side, forming a second resonator.

2. The method recited in claim 1 wherein the bottom loading electrode is 100 to 1,000 Angstroms thick.

3. The method recited in claim 1 wherein the bottom loading electrode comprises Molybdenum.

4. The method recited in claim 1 wherein the bottom loading electrode and the first bottom core electrode comprise the same material.

5. The method recited in claim 1 wherein the PZ layer comprises Aluminum Nitride (AlN).

6. The method recited in claim 1 wherein the first resonator has a resonant frequency that is approximately one to six percent lower than resonant frequency of the second resonator.

7. A method of fabricating a resonator on a substrate, the method comprising:

fabricating a bottom loading electrode that completely bridges a cavity;

fabricating a bottom core electrode above the bottom loading electrode, the bottom core electrode also completely bridging the cavity;

fabricating a piezoelectric (PZ) layer; and

fabricating a top electrode above the PZ layer.

8. The method recited in claim 7 wherein the bottom loading electrode and the bottom core electrode comprise the same material.

9. The method recited in claim 7 wherein the bottom loading electrode is approximately 100 to 1,000 Angstroms thick.

10. The method recited in claim 7 wherein the bottom loading electrode comprises Molybdenum.

11. The method recited in claim 7 wherein the PZ layer comprises Aluminum Nitride (AlN).

12. A resonator comprising a bottom a top electrode sandwiching a piezoelectric (PZ) layer, the bottom electrode including a bottom loading electrode that completely bridges a cavity and a bottom core electrode portion that also completely bridges the cavity.

13. The resonator recited in claim 12 wherein the bottom loading electrode and the bottom core electrode comprise the same material.

14. The resonator recited in claim 12 wherein the bottom loading electrode is 100 to 1,000 Angstroms thick.

15. The resonator recited in claim 12 wherein the bottom loading electrode comprises Molybdenum.

16. The resonator recited in claim 12 wherein the PZ layer comprises Aluminum Nitride (AlN).

17. An apparatus comprising:

a first resonator comprising a first bottom and a first top electrode sandwiching a first piezoelectric (PZ) material, the first bottom electrode including a bottom loading electrode that completely bridges a cavity and a bottom core electrode that also completely bridges a cavity; and

a second resonator comprising a second bottom and a second top electrode sandwiching a second PZ material.

18. The apparatus recited in claim 17 wherein the bottom loading electrode and the bottom core electrode comprise the same material.

19. The apparatus recited in claim 17 wherein the bottom loading electrode is 100 to 1,000 Angstroms thick.

20. The apparatus recited in claim 17 wherein the bottom loading electrode comprises Molybdenum.

21. The apparatus recited in claim 17 wherein the PZ layer comprises Aluminum Nitride (AlN).