Method of making tunable thin film acoustic resonators

• US 6,507,983 B1
• Filed: 11/13/1998
• Issued: 01/21/2003
• Est. Priority Date: 12/21/1993
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Merchant, Paul Philip, Ruby, Richard C.
• Primary Examiner(s): TUGBANG, ANTHONY D
• Application Number:
  US09/192,163
• Time in Patent Office: 1,530 Days
• Field of Search: 29/253.5, 427/100, 310/324, 310/328, 310/331, 310/332
• US Class Current: 29/25.35
• CPC Class Codes: H03H 2009/02181 by application of heat from a heat source
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/02133 of stress
• CPC Class Codes: H03H 9/02236 of surface skimming bulk wave devices
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/583 comprising a plurality of piezoelectric layers acoustically coupled
• CPC Class Codes: H03H 9/588 Membranes
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

An acoustical resonator comprising top and bottom electrodes that sandwich a PZ layer. The resonance frequency of the acoustical resonator may be adjusted after fabrication by utilizing heating elements included in the acoustical resonator and/or by adjusting the thickness of a tuning layer. In the preferred embodiment of the present invention, the electrodes comprise Mo layers. One embodiment of the present invention is constructed on a Si₃N₄ membrane. A second embodiment of the present invention is constructed such that it is suspended over a substrate on metallic columns. In the preferred embodiment, the electrodes are deposited by a method that minimizes the stress in the electrodes.

Claims

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

depositing a layer of Si₃N₄ on the top surface of a silicon substrate having top and bottom surfaces;

depositing a bottom electrode comprising a metallic layer on said Si₃N₄ layer;

depositing a PZ layer on said metallic layer;

depositing a top electrode comprising a metallic layer on said PZ layer;

etching said silicon substrate to remove the portion thereof between said bottom surface and a portion of said Si₃N₄, wherein either said bottom or said top metallic layer comprises a metal chosen from the group consisting of Mo, Ti, and W; and

removing a portion of said silicon substrate from said bottom surface prior to depositing said bottom electrode.

2. A method for fabricating an acoustical resonator comprising the steps of:

depositing a layer of Si₃N₄ on the top surface of a silicon substrate having top and bottom surfaces;

depositing a bottom electrode comprising a metallic layer on said Si₃N₄ layer;

depositing a PZ layer on said metallic layer;

depositing a top electrode comprising a metallic layer on said PZ layer; and

etching said silicon substrate to remove the portion thereof between said bottom surface and a portion of said Si₃N₄, wherein either said bottom of said top metallic layer comprises a metal chosen from the group consisting of Mo, Ti, and W;

wherein the deposition conditions for depositing one of said metallic layers are determined by measuring the deflection of a silicon substrate after a metallic layer is deposited thereon using said deposition conditions.