Method of making an acoustic wave resonator

• US 6,874,212 B2
• Filed: 11/08/2001
• Issued: 04/05/2005
• Est. Priority Date: 08/31/2000
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Larson, John Dwight III
• Primary Examiner(s): TUGBANG, ANTHONY D
• Application Number:
  US10/008,838
• Publication Number:
  US 20020038989A1
• Time in Patent Office: 1,244 Days
• Field of Search: 29/253.5, 295/94, 295/93, 298/31, 298/46, 310/324, 310/346, 310/349, 310/363, 310/315
• US Class Current: 29/25.35
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49128 Assembling formed circuit to base

Abstract

A method of fabricating an acoustic resonator includes forming a ferromagnetic compensator, such as one comprised of a nickel-iron alloy, which at least partially offsets temperature-induced effects introduced by an electrode-piezoelectric stack. The compensator has a positive temperature coefficient of frequency, while the stack has a negative temperature coefficient of frequency. By properly selecting the thickness of the compensator, temperature-induced effects on resonance may be neutralized. Alternatively, the thickness can be selected to provide a target positive or negative composite temperature coefficient of frequency. In order to prevent undue electromagnetic losses in the ferromagnetic compensator, a metallic flashing layer may be added to at least partially enclose the compensator.

Claims

1. A method of fabricating an acoustic resonator comprising the steps of:

providing a substrate; and

forming an electrode-piezoelectric stack on said substrate such that a portion of said electrode-piezoelectric stack is suspended from contact with said substrate by a cavity having a boundary defined by said electrode-piezoelectric stack, said electrode-piezoelectric stack having a negative temperature coefficient of frequency, and

(a) forming a compensator layer, comprised of a ferromagnetic material, in direct contact with said electrode-piezoelectric stack, including selecting a material for said compensator layer having a positive temperature coefficient of frequency.

2. The method of claim 1 wherein said step (a) that includes selecting said material includes selecting a nickel-iron alloy.

3. The method of claim 1 wherein said step (a) includes depositing said material as approximately 35 percent nickel and approximately 65 percent iron.

4. The method of claim 1 wherein said step (a) includes selecting a layer thickness to substantially match a magnitude of temperature-induced effects on resonance by operation of said electrode-piezoelectric stack with a magnitude of temperature-induced effects on said resonance as a consequence of said compensator layer.

5. The method of claim 1 wherein said step of forming said compensator layer further includes (b) forming a metallic flashing layer on a side of said compensator layer opposite to said electrode-piezoelectric stack.

6. The method of claim 5 further comprising using fabrication alignment techniques in said steps (a) and (b) to prevent spurious mode generation resulting from partial coverage of said electrode-piezoelectric stack by said compensator layer.