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

• US 20020121944A1
• Filed: 03/05/2001
• Published: 09/05/2002
• Est. Priority Date: 03/05/2001
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Ruby, Richard C., Larson, John D. III, Bradley, Paul D.
• Granted Patent: US 6,566,979 B2
• Time in Patent Office: Days
• 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. A resonator is fabricated on a substrate, and its top electrode 56 is oxidized to form a oxide layer 58. For a substrate having multiple resonators, the top electrode 56 of only selected resonator is oxidized to provide resonators having different resonance frequencies on the same substrate.

Claims

1. A method of lowering resonant frequency of a thin film bulk acoustic resonator (FBAR) having a top electrode, the method comprising oxidizing a portion of the top electrode.

2. The method recited in claim 1 wherein the top electrode comprises Molybdenum.

3. The method recited in claim 1 wherein the FBAR comprises a PZ layer comprising Aluminum Nitride (AlN).

4. The method recited in claim 1 wherein the step of oxidizing is performed by heating the FEAR in air.

5. The method recited in claim 1 wherein the top electrode comprises material that progressively oxidizes when exposed to air and heat.

6. The method recited in claim 1 wherein the top electrode comprises Molybdenum, and the FBAR is heated at around 300 degrees Celsius for about an hour to lower the resonant frequency by about 5 MHz.

7. The method recited in claim 1 wherein the oxidation lowers the resonant frequency in the range of about 60 MHz to 100 MHz.

8. A method for fabricating resonators on a substrate, the method comprising:

fabricating a first resonator on the substrate, the first resonator having a first bottom electrode, a first piezoelectric (PZ) layer, and a first top electrode;

fabricating a second resonator on the substrate, the second resonator having a second bottom electrode, a second piezoelectric (PZ) layer, and a second top electrode; and

oxidizing the first top electrode to lower resonant frequency of the first resonator.

9. The method recited in claim 8 further comprising a step of masking the second top electrode to prevent the second top electrode from oxidization.

10. The method recited in claim 9 wherein material used for the masking is silicon dioxide (SiO₂).

11. The method recited in claim 9 further comprising a step of removing the mask.

12. The method recited in claim 8 further comprising the step of monitoring resonant frequency of the first resonator.

13. The method recited in claim 8 wherein the first top electrode comprises Molybdenum.

14. The method recited in claim 8 wherein the first PZ layer comprises Aluminum Nitride (AlN).

15. The method recited in claim 8 wherein the step of oxidizing is performed by heating the resonators in air.

16. The method recited in claim 8 wherein the first top electrode comprises material that progressively oxidizes when exposed to air and heat.

17. The method recited in claim 8 wherein the first top electrode comprises Molybdenum, and the substrate is heated at around 300 degrees Celsius for about an hour to lower the resonant frequency by about 5 MHz.

18. The method recited in claim 8 wherein the oxidation lowers the resonant frequency in the range of about one to six percent compared to that of non-oxidized resonator of same structure.

20. The resonator recited in claim 19 wherein the top electrode comprises Molybdenum.

21. The resonator recited in claim 19 wherein the PZ layer comprises Aluminum Nitride (AlN).

22. The resonator recited in claim 19 wherein the conductor comprises Molybdenum and the oxidized conductor comprises Molybdenum oxide.

23. The resonator recited in claim 19 wherein the top electrode comprises material that progressively oxidizes when exposed to air and heat.

24. The resonator recited in claim 19 wherein the top electrode comprises Molybdenum, and the resonator is heated at around 300 degrees Celsius for about an hour to lower resonant frequency of the resonator by about five MHz.

25. The resonator recited in claim 19 wherein the oxidation lowers the resonant frequency in the range of one to three percent compared to that of the second resonator.

27. The apparatus recited in claim 26 wherein the first top electrode comprises Molybdenum.

28. The apparatus recited in claim 26 wherein the first PZ layer comprises Aluminum Nitride (AlN).

29. The apparatus recited in claim 26 wherein the conductor layer comprises Molybdenum and the oxidized conductor layer comprises Molybdenum oxide.

30. The apparatus recited in claim 26 wherein the first top electrode comprises material that progressively oxidizes when exposed to air and heat.

31. The apparatus recited in claim 26 wherein the apparatus is heated at around 300 degrees Celsius for about an hour to lower resonant frequency of the second resonator by about 5 MHz.

32. The apparatus recited in claim 26 wherein the oxidation lowers the resonant frequency of the first resonator in the range of one to six percent compared to that of the first resonator.

19. A resonator comprising a bottom and a top electrodes sandwiching a piezoelectric (PZ) layer, the top electrode including a conductor portion and an oxidized conductor portion.

26. An apparatus comprising:

a first resonator having a first bottom electrode, a first piezoelectric (PZ) layer, and a first top electrode, the first top electrode comprising a conductor layer and an oxidized conductor layer; and

a second resonator having a second bottom electrode, a second piezoelectric (PZ) layer, and a second top electrode.