Acoustic resonator filter with reduced electromagnetic influence due to die substrate thickness

• US 6,377,137 B1
• Filed: 09/11/2000
• Issued: 04/23/2002
• Est. Priority Date: 09/11/2000
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Ruby, Richard C.
• Primary Examiner(s): Lee, Benny
• Assistant Examiner(s): Summons, Barbara
• Application Number:
  US09/659,254
• Time in Patent Office: 589 Days
• Field of Search: 333/186-192, 310/321, 310/324, 310/348, 29/253.5, 216/52, 438/959
• US Class Current: 333/189
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48472 the other connecting portion not on the bonding area also being a wedge bond, i.e. wedge-to-wedge
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/16195 Flat cap [not enclosing an internal cavity]
• CPC Class Codes: H03H 2003/021 the resonators or networks being of the air-gap type
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 9/02125 of parasitic elements
• CPC Class Codes: H03H 9/1014 the enclosure being defined by a frame built on a substrate and a cap, the frame having no mechanical contact with the BAW device
• CPC Class Codes: H03H 9/564 implemented with thin-film techniques
• CPC Class Codes: Y10S 438/959 Mechanical polishing of wafer
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A plurality of acoustic resonators are manufactured in a batch process by forming cavities in a substrate and filling the cavities with a sacrificial layer. An FBAR membrane comprising a bottom electrode, a piezoelectric layer, and a top electrode is formed over each cavity and the sacrificial layer. The substrate is then thinned and the substrate is separated into a plurality of dice using a scribe and break process. The sacrificial layer is then removed and the FBAR filter is mounted in a package with thermal vias being thermal communication with underside of the FBAR filter. The production method improves thermal properties by increasing the efficiency of heat dissipation from the FBAR filter. In addition, electromagnetic interference is decreased by reducing the distance between a primary current flowing over the surface of the FBAR filter and an image current flowing in a ground plane beneath the FBAR filter.

Claims

1. A method for batch processing acoustic resonators, comprising:

depositing a first electrode on a top surface of a substrate;

depositing a layer of piezoelectric material on said first electrode;

depositing a second electrode on said layer of piezoelectric material; and

removing material from a bottom surface of said substrate to reduce the thickness of the substrate and to reduce an electromagnetic influence in a resulting filter.

2. The method of claim 1, further comprising:

prior to depositing said first electrode, forming a plurality of depressions in the top surface of said substrate;

depositing a sacrificial material in each of said depressions, wherein said first electrode is deposited on top of said sacrificial material; and

removing said sacrificial material.

3. The method of claim 1, wherein said first and second electrodes are comprised of molybdenum.

4. The method of claim 1, further comprising:

scribing said top surface of said substrate; and

dividing said substrate along said scribe lines to form a plurality of dice.

5. The method of claim 4, further comprising, for each die in said plurality of dice, mounting said die in a die cavity of a package to produce an individual, packaged filter, said die being mounted in said die cavity such that a bottom surface of said die is in thermal communication with a thermal via in said package.

6. The method of claim 5, wherein said step of mounting said die into said die cavity in said package comprises:

depositing a thermally-conductive epoxy in said die cavity in said package; and

mounting said die onto an upper surface of said thermally-conductive epoxy, wherein a lower surface of said thermally-conductive epoxy is in contact with said thermal via.

7. The method of claim 5, wherein the filter has an aspect ratio for a distance between a victim loop and a victimizer loop of the filter to the thickness of said substrate is at least 3:

1.

8. The method of claim 4, further comprising:

prior to dividing said substrate along said scribe lines to form said plurality of dice, depositing a protective layer over said top surface of said substrate.

9. The method of claim 1, wherein said step of removing material from the bottom surface of said substrate comprises thinning said substrate to a thickness of less than 19 mils.

10. The method of claim 1, wherein said step of removing material from the bottom surface of said substrate comprises:

placing the bottom surface of said substrate against a polishing surface; and

polishing the bottom surface to remove material therefrom.

11. A method for batch processing acoustic resonators, comprising:

forming a plurality of depressions in a top surface of a substrate;

depositing a sacrificial material in each of said depressions;

depositing a first electrode on an upper surface of said sacrificial material in each of said depressions;

depositing a layer of piezoelectric material on said first electrode;

depositing a second electrode on said layer of piezoelectric material; and

polishing a bottom surface of said substrate to reduce the thickness of said substrate.

12. The method of claim 11, further comprising removing said sacrificial material after polishing the bottom surface of said substrate.

13. The method of claim 11, wherein the substrate is polished to a thickness of less than 19 mils.

14. The method of claim 11, further comprising:

scribing the top surface of said substrate;

dividing said substrate along said scribe lines to form a plurality of dice; and

for each die in said plurality of dice, mounting said die in a die cavity of a package to produce an individual, packaged filter, said die being mounted in said die cavity such that a bottom surface of said die is in thermal communication with a thermal via in said package.

15. The method of claim 14, wherein the filter has an aspect ratio for a distance between a victim loop and a victimizer loop of the filter to the thickness of said substrate is at least 3:

1.

16. An acoustic filter, comprising:

a die substrate having a thickness of less than 19 mils;

a plurality of acoustic resonators formed on a top surface of the substrate, each acoustic resonator including first and second electrodes and a piezoelectric material disposed in between the first and second electrodes;

a plurality of interconnects providing electrical connections to said plurality of acoustic resonators; and

a package having a die cavity formed therein, said die substrate being mounted in said die cavity such that a primary current flowing along an upper surface of said die substrate creates a primary current magnetic field, and an image current flowing along a ground plane beneath said die substrate creates an image current magnetic field, said primary current magnetic field and said image current magnetic field having opposite polarities.

17. The acoustic filter of claim 16, wherein said die substrate has a thickness in the range of 3 mils to 7 mils.

18. The acoustic filter of claim 16, wherein an aspect ratio for a distance between a victim loop and a victimizer loop of the filter to the thickness of said substrate is at least 3:

1.

19. The acoustic filter of claim 16, wherein the die substrate has a plurality of depressions formed therein, each of the plurality of acoustic resonators being disposed above a respective depression in the die substrate.

20. The acoustic filter of claim 16, wherein said package has at least one thermal via, said die substrate being mounted in said package such that a bottom surface of said die substrate is in thermal communication with said at least one thermal via, said die substrate being affixed to said package using a thermally-conductive epoxy.