BAW filters having different center frequencies on a single substrate and a method for providing same

• US 6,518,860 B2
• Filed: 01/05/2001
• Issued: 02/11/2003
• Est. Priority Date: 01/05/2001
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Ellä, Juha, Pohjonen, Helena
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Summons, Barbara
• Application Number:
  US09/755,007
• Publication Number:
  US 20020089395A1
• Time in Patent Office: 767 Days
• Field of Search: 333/186-192, 333/133, 29/253.5
• US Class Current: 333/189
• CPC Class Codes: H03H 2003/0428 of an electrode
• CPC Class Codes: H03H 2003/0435 of a piezoelectric layer
• 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 9/589 Acoustic mirrors
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A method of fabricating a plurality of bulk acoustic wave (BAW) resonators on a single substrate, and the corresponding product, the BAW resonators having substantially different resonant frequencies, the method including the steps of: providing a substrate having an upper facing surface; depositing an isolation structure on the upper facing surface of the substrate; depositing a first metallic layer on the isolation structure, the first metallic layer serving as a bottom electrode; and depositing piezolayer material on the bottom electrode so as to have thicknesses corresponding to each of the different resonant frequencies, each different thickness located in a location where a resonator having a resonant frequency corresponding to the thickness is to be located. In one of several embodiments, the step of depositing piezolayer material on the bottom electrode itself includes the steps of: depositing piezolayer material to a thickness corresponding to the lowest frequency resonator; providing hard mask material over areas where the lowest frequency resonators are to be located; and removing the piezolayer material down to the thickness of the next higher frequency resonators. In some applications of the method, the isolation structure is an acoustic mirror, and the method further includes the step of providing the acoustic mirror, interposed between the substrate and the bottom electrode, according to a design that imparts to the acoustic mirror a desired reflection coefficient over a predetermined range of frequency including the substantially different resonant frequencies.

Claims

1. A method of fabricating a plurality of bulk acoustic wave (BAW) resonators on a single substrate, the plurality of BAW resonators including BAW resonators from at least two different filters having substantially different resonant center frequencies, the plurality of BAW resonators thus including BAW resonators having substantially different resonant frequencies, the method comprising the steps of:

a) providing a substrate having an upper facing surface;

b) depositing an isolation structure on the upper facing surface of the substrate;

c) depositing a first metallic layer on the isolation structure, the first metallic layer serving as a bottom electrode; and

d) depositing piezolayer material on the bottom electrode so as to have thicknesses corresponding to each of the different resonant frequencies, each different thickness located in a location where a resonator having a resonant frequency corresponding to the thickness is to be located;

wherein the step of depositing piezolayer material on the bottom electrode includes a step of incrementally adjusting the thickness of the piezolayer where at least one electrode is to be located.

2. The method of claim 1, wherein the step of depositing piezolayer material on the bottom electrode comprises the steps of:

a) depositing piezolayer material to a thickness corresponding to the lowest frequency resonator;

b) providing hard mask material over areas where the lowest frequency resonators are to be located; and

c) removing the piezolayer material down to the thickness of the next higher frequency resonators.

3. A plurality of bulk acoustic wave (BAW) resonators on a single substrate fabricated according to the method of claim 2.

4. The method of claim 1, wherein the step of depositing piezolayer material on the bottom electrode comprises the steps of:

a) depositing the piezolayer material to a thickness corresponding to the highest frequency;

b) depositing a lift-off mask where the highest frequency resonators are to be located;

c) depositing additional piezolayer material to a thickness corresponding to the next highest frequency; and

d) removing the lift-off mask.

5. A plurality of bulk acoustic wave (BAW) resonators on a single substrate fabricated according to the method of claim 4.

6. The method of claim 1, wherein the step of depositing piezolayer material on the bottom electrode comprises the steps of:

a) depositing the piezolayer material to a thickness corresponding to the highest frequency;

b) depositing hard mask material where the highest frequency resonators are to be located;

c) depositing additional piezolayer material to a thickness corresponding to the next highest frequency; and

d) depositing hard mask material where the next highest frequency resonators are to be located.

7. The method of claim 1, wherein the isolation structure is an acoustic mirror, and wherein the method further comprises the step of:

providing the acoustic mirror, interposed between the substrate and the bottom electrode, according to a design that imparts to the acoustic mirror a desired reflection coefficient over a predetermined range of frequency including the substantially different resonant frequencies.

8. A plurality of bulk acoustic wave (BAW) resonators on a single substrate fabricated according to the method of claim 1.

9. A multi-resonator chip, in which a plurality of bulk acoustic wave (BAW) resonators are provided on a single substrate, at least two of the BAW resonators for use in different filters having substantially different center resonant frequencies, the plurality of BAW resonators thus including BAW resonators having substantially different resonant frequencies, the multi-resonator chip comprising:

a) a substrate having an upper facing surface;

b) an isolation structure on the upper facing surface of the substrate;

c) a plurality of resonator sections, each resonator section comprising in turn a pair of electrodes in between which a piezolayer is provided at a thickness corresponding to the resonant frequency of the resonator section;

wherein the at least two of the BAW resonators having substantially different resonant frequencies have piezolayers differing substantially in thickness, the different thicknesses corresponding to the substantially different resonant frequencies.

10. The multi-resonator chip of claim 9, wherein the isolation structure is an acoustic mirror provided according to a design that imparts to the acoustic mirror a desired reflection coefficient over a predetermined range of frequency including the substantially different resonant frequencies.