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Piezoelectric filter, duplexer, composite piezoelectric resonator, communication device and method for adjusting frequency of piezoelectric filter

  • US 7,019,604 B2
  • Filed: 07/18/2003
  • Issued: 03/28/2006
  • Est. Priority Date: 07/23/2002
  • Status: Active Grant
First Claim
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1. A piezoelectric filter comprising:

  • a plurality of piezoelectric resonators including a substrate and a vibration portion provided on the substrate, the vibration portion having a structure in which top and bottom surfaces of a thin film portion including at least one piezoelectric thin film are sandwiched between at least a pair of an upper electrode and a lower electrode facing each other; and

    an additional film provided on the upper electrode of at least one of the plurality of piezoelectric resonators;

    wherein the additional film has susceptibility to physical etching that is lower than that of materials used for the upper electrodes of the others of the plurality of piezoelectric resonators.

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