Multi-port filter using transversely-excited film bulk acoustic resonators

Patent metadata

Field	Value
Publication number	US-11888463-B2
Application number	US-202017094569-A
Country	US
Kind code	B2
Filing date	Nov 10, 2020
Priority date	Jun 15, 2018
Publication date	Jan 30, 2024
Grant date	Jan 30, 2024

Abstract

Filter devices and methods are disclosed. A single-crystal piezoelectric plate is attached to substrate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate. A conductor pattern formed on the piezoelectric plate defines a low band filter including low band shunt resonators and low band series resonators and a high band filter including high band shunt resonators and high band series resonators. Interleaved fingers of interdigital transducers (IDTs) of the low band shunt resonators are disposed on respective diaphragms having a first thickness, interleaved fingers of IDTs of the high band series resonators are disposed on respective diaphragms having a second thickness less than the first thickness, and interleaved fingers of IDTs of the low band series resonators and the high band shunt resonators are disposed on respective diaphragms having thicknesses intermediate the first thickness and the second thickness.

First claim

It is claimed:

1. A filter device, comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate, portions of the single-crystal piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate; and
a conductor pattern formed on the front surface, the conductor pattern defining a low band filter including one or more low band shunt resonators and one or more low band series resonators and a high band filter including one or more high band shunt resonators and one or more high band series resonators, wherein
interleaved fingers of interdigital transducers (IDTs) of the one or more low band shunt resonators are disposed on respective diaphragms having a first thickness ts 1 ,
interleaved fingers of IDTs of the one or more high band series resonators are disposed on respective diaphragms having a second thickness ts 2 less than ts 1 , and
interleaved fingers of IDTs of the one or more low band series resonators and the one or more high band shunt resonators are disposed on respective diaphragms having other thicknesses intermediate ts 1 and ts 2 .

2. The filter device of claim 1 , wherein
interleaved fingers of IDTs of the one or more low band series resonators and the one or more high band shunt resonators are disposed on respective diaphragms having a third thickness ts 3 intermediate ts 1 and ts 2 .

3. The filter device of claim 1 , wherein the single-crystal piezoelectric plate and all of the IDTs are configured such that a respective radio frequency signal applied to each IDT excites a respective shear primary acoustic mode within the respective diaphragm.

4. The filter device of claim 3 , wherein a direction of acoustic energy flow of all of the shear primary acoustic modes is substantially orthogonal to the front and back surfaces of the respective diaphragms.

5. The filter device of claim 3 , wherein the single-crystal piezoelectric plate is one of lithium niobate and lithium tantalate.

6. The filter device of claim 1 , the conductor pattern further defining one or more mid band filters including one or more mid band shunt resonators and one or more mid band series resonators, wherein
interleaved fingers of IDTs of the one or more mid band series resonators and the one or more mid band shunt resonators are disposed on respective diaphragms having other thicknesses intermediate ts 1 and ts 2 .

7. The filter device of claim 1 , the conductor pattern further defining a mid band filter including one or more mid band shunt resonators and one or more mid band series resonators, wherein
interleaved fingers of IDTs of the one or more low band series resonators and the one or more mid band shunt resonators are disposed on respective diaphragms having a third thickness ts 3 ,
interleaved fingers of the IDTs of the one or more mid band series resonators and the one or more high band shunt resonators are disposed on respective diaphragms having a fourth thickness ts 4 , and
ts 1 >ts 3 >ts 4 >ts 2 .

8. The filter device of claim 1 , wherein
the low band filter is a band n77 bandpass filter, and
the high band filter is a band n79 bandpass filter.

9. A method of fabricating a filter device, comprising:
attaching a back surface of a piezoelectric plate having opposing front and back surfaces and a first thickness ts 1 to a surface of a substrate;
selectively thinning portions of the piezoelectric plate from the first thickness ts 1 to a second thickness ts 2 less than the first thickness;
selectively thinning additional portions of the piezoelectric plate from the first thickness to one or more additional thicknesses intermediate ts 1 and ts 2 ;
forming cavities in the substrate such that portions of the single-crystal piezoelectric plate form a plurality of diaphragms spanning respective cavities; and
forming a conductor pattern on the front surface, the conductor pattern defining a low band filter including one or more low band shunt resonators and one or more low band series resonators and a high band filter including one or more high band shunt resonators and one or more high band series resonators, wherein
interleaved fingers of interdigital transducers (IDTs) of the one or more low band shunt resonators are disposed on respective diaphragms having the first thickness ts 1 ,
interleaved fingers of IDTs of the one or more high band series resonators are disposed on respective diaphragms having the second thickness ts 2 , and
interleaved fingers of IDTs of the one or more low band series resonators and the one or more high band shunt resonators are disposed on respective diaphragms having one of the one or more additional thicknesses intermediate ts 1 and ts 2 .

10. The method of claim 9 , wherein
the one or more additional thicknesses consists of a third thickness intermediate ts 1 and ts 2 , and
interleaved fingers of IDTs of the one or more low band series resonators and the one or more high band shunt resonators are disposed on respective diaphragms having the third thickness.

11. The method of claim 9 , wherein the single-crystal piezoelectric plate and all of the IDTs are configured such that a respective radio frequency signal applied to each IDT excites a respective shear primary acoustic mode within the respective diaphragm.

12. The method of claim 11 , wherein a direction of acoustic energy flow of all of the shear primary acoustic modes is substantially orthogonal to the front and back surfaces of the respective diaphragms.

13. The method of claim 11 , wherein the single-crystal piezoelectric plate is one of lithium niobate and lithium tantalate.

14. The method of claim 9 , the conductor pattern further defining one or more mid band filters including one or more mid band shunt resonators and one or more mid band series resonators, wherein
interleaved fingers of IDTs of the one or more mid band series resonators and the one or more mid band shunt resonators are disposed on respective diaphragms having other thicknesses intermediate ts 1 and ts 2 .

15. The method of claim 9 , the conductor pattern further defining a mid band filter including one or more mid band shunt resonators and one or more mid band series resonators, wherein
interleaved fingers of IDTs of the one or more low band series resonators and the one or more mid band shunt resonators are disposed on respective diaphragms having a third thickness ts 3 ,
interleaved fingers of the IDTs of the one or more mid band series resonators and the one or more high band shunt resonators are disposed on respective diaphragms having a fourth thickness ts 4 , and
ts 1 >ts 3 >ts 4 >ts 2 .

16. The method of claim 9 , wherein
the low band filter is a band n77 bandpass filter, and
the high band filter is a band n79 bandpass filter.

Assignees

• Murata Manufacturing Co

Inventors

• Guyette Andrew
• Fenzi Neal
• Turner Patrick

Classifications

• H03H9/132 Primary

  characterized by a particular shape · CPC title

• H03H3/02 Primary

  for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence) · CPC title

• H03H9/02031

  consisting of ceramic · CPC title

• H03H9/02228

  Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer · CPC title

• H03H9/174

  Membranes · CPC title