COMPOSITE COUPLED-MODE FILTER

• US 3,582,839 A
• Filed: 06/06/1968
• Issued: 06/01/1971
• Est. Priority Date: 06/06/1968
• Status: Expired due to Term

• Current Assignee: Don A. Berlincourt, Kendall A. Pim
• Original Assignee: Don A. Berlincourt, Kendall A. Pim
• Inventors: Pim, Kendall A., Berlincourt, Don A.
• Application Number:
  US04/734,911
• Time in Patent Office: 1,090 Days
• US Class Current: 333/191
• CPC Class Codes: H03H 9/56 Monolithic crystal filters

Abstract

An essentially two-dimensional electric-wave filter is formed by depositing a film of piezoelectric material upon a substrate and by applying input and output electrode pairs to different portions of the film. Each electrode pair together with the film and substrate form a composite resonator. The two composite resonators are located for a desired mechanical coupling between the two composite resonators. The filter may also consist of an array of n coupled composite-resonators having a common film and a common substrate and having the electrode pairs of two resonators of the array serving as input and output electrodes.

Claims

1. A composite coupled-mode filter comprising in combination a substrate, a film of piezoelectric material on said substrate and substantially thinner than said substrate and a plurality of spaced electrodes each covering different portions of the surfaces of the piezoelectric film to form input and output electrode means and to form composite resonant structures in the substrate-film electrode combination under and immediately surrounding the electrodes, the electrodes being substantially thinner than the piezoelectric film, the resonant structures so formed being spaced such that, with suitable filter termination, substantially critical mechanical coupling determines the bandpass characteristics of the filter.

2. A composite coupled-mode filter as described in claim 1, wherein a plurality of portions of the surface having piezoelectric film are electroded, a pair of electrodes at opposite surfaces of a portion of the film forming input electrode means and a pair of electrodes at opposite surfaces of another portion of the film serving as output electrode means, other portions of the film spaced from each other and from the portions at which said pairs of electrodes are located serving to form in combination an array of a plurality of composite resonators on a common substrate with a plurality of distinct modes of vibration.

3. A composite coupled-mode filter as described in claim 1 wherein a pair of electrodes on opposite surfaces of a portion of the piezoelectric film serve as input electrode means, a pair of electrodes on opposite surfaces of a different portion of the piezoelectric film serve as output electrode means and intermediate portions of the film between the input and output electrode means are mass loaded to form a plurality of resonators.

4. A composite coupled-mode filter comprising in combination a substrate, a film of piezoelectric material on a substrate and a plurality of spaced electrodes each covering different portions of the surfaces of the pIezoelectric film to form input and output electrode means and to form resonant structures under portions of the film covered by electrodes, the resonant structures so formed being spaced such that, with suitable filter termination, substantially critical mechanical coupling between said resonant structures determines the band-pass characteristics of the filter, the thickness of the piezoelectric film being of the order of one-tenth the thickness of the substrate and the thickness of the electrodes being of the order of one-tenth the thickness of the piezoelectric film.

5. A composite coupled-mode filter as described in claim 1 wherein the piezoelectric film comprises vapor deposited piezoelectric materials selected from the group consisting of cadmium sulfide, cadmium selenide, zinc oxide, beryllium oxide, wurtzite zinc sulfide, wurtzite aluminum nitride, lithium niobate, lithium tantalate and solid solutions thereof.

6. A composite coupled-mode filter as described in claim 1, wherein the spaced electrodes are of restricted dimensions and the film is in direct contact with the substrate except where an electrode intervenes, at which portions the film is in direct contact with the electrode and the electrode is in turn, in direct contact with the substrate.

7. A composite coupled-mode filter as described in claim 1 with characteristic frequencies chosen to provide critical interelectrode coupling.

8. A composite coupled-mode filter as described in claim 1 with characteristic frequencies chosen to provide an interelectrode coupling within the range of slight undercoupling and slight overcoupling with suitable filter termination.