Method of providing differential frequency adjusts in a thin film bulk acoustic resonator (FBAR) filter and apparatus embodying the method

• US 20020121840A1
• Filed: 03/05/2001
• Published: 09/05/2002
• 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.
• Granted Patent: US 6,483,229 B2
• Time in Patent Office: Days
• US Class Current: 310/312
• 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

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 mass loading piezoelectric (PZ) layer between two electrodes. For a substrate having multiple resonators, only selected resonator is mass loaded to provide resonators having different resonance frequencies on the same substrate.

Claims

1. A method for fabricating resonators, the method comprising:

fabricating a first bottom electrode and a second bottom electrode on a substrate;

fabricating a core piezoelectric (PZ) layer above the first and the second bottom electrodes, the core PZ layer having a first portion above the first bottom electrode and a second portion above the second bottom electrode;

fabricating an additional PZ layer above the first portion; and

fabricating a first top electrode above the additional PZ layer and a second top electrode above the second portion of the PZ layer.

2. The method recited in claim 1 wherein the step of fabricating the additional PZ layer comprises:

masking over the core PZ layer but not above the first portion;

depositing PZ material above the mask and the first portion;

removing the mask thereby removing all PZ material above the mask and leaving the PZ material over the first portion.

3. The method recited in claim 2 wherein the mask is Silicon dioxide (SiO₂).

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

5. The method recited in claim 1 wherein the first bottom electrode comprises Molybdenum.

6. The method recited in claim 1 further comprising fabricating a cavity within the substrate, the first bottom electrode bridging the cavity.

7. The method recited in claim 1 wherein the first bottom electrode, the first portion of the PZ layer, the additional PZ layer, and the first top electrode form a first resonator having a first resonant frequency, the second bottom electrode, the second portion of the PZ layer, and the second top electrode form a second resonator having a second resonant frequency, the first resonant frequency being lower than the second resonant frequency.

8. The method recited in claim 7 wherein the first resonant frequency is approximately three percent lower than the first resonant frequency.

9. The method recited in claim 7 wherein resonant frequency of the first resonator is one to eight percent lower than resonant frequency of the second resonator.

10. The method recited in claim 1 wherein the core PZ layer and the additional PZ layer comprises the same material.

11. The method recited in claim 1 wherein thickness of the additional PZ layer is an order of magnitude smaller than that of the core PZ layer.

12. The method recited in claim 1 wherein thickness of the additional PZ layer is in a range from one percent to eight percent of thickness of the core PZ layer.

14. The apparatus recited in claim 13 wherein the first PZ material comprises Aluminum Nitride (AlN).

15. The apparatus recited in claim 13 wherein the first bottom electrode comprises Molybdenum.

16. The apparatus recited in claim 13 wherein the first resonator bridges a first cavity.

17. The apparatus recited in claim 13 wherein the first resonator has a resonant frequency approximately three percent lower compared to that of the second resonator.

18. The apparatus recited in claim 13 wherein the core PZ layer and the additional PZ layer comprises the same material.

19. The apparatus recited in claim 13 wherein thickness of the additional PZ layer is an order of magnitude smaller than that of the core PZ layer.

20. The apparatus recited in claim 13 wherein thickness of the additional PZ layer is in a range from one to eight percent of thickness of the core PZ layer.

21. The apparatus recited in claim 13 wherein resonant frequency of the first resonator is one to eight percent lower than resonant frequency of the second resonator.

13. An apparatus comprising:

a substrate;

a first resonator fabricated on the substrate, the first resonator comprising a first bottom electrode;

a first top electrode;

a first piezoelectric (PZ) material sandwiched between the first bottom electrode and the first top electrode, the first PZ material comprising a core PZ layer and an additional PZ layer; and

a second resonator fabricated on the substrate, the second resonator comprising a second bottom electrode;

a second top electrode;

a second PZ material sandwiched between the second bottom electrode and the second top electrode.