Transversely-excited film bulk acoustic filters with symmetric layout
There are disclosed acoustic resonators and radio frequency filter devices. An acoustic resonator includes a piezoelectric plate having a front surface. A conductor pattern is formed on the front surface, the conductor pattern including interdigital transducers (IDTs) of one or more pairs of sub-resonators, each pair consisting of two sub-resonators. The two sub-resonators of each pair of sub-resonators are positioned symmetrically about a central axis.
1. An acoustic resonator, comprising:
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of a substrate except for portions of the piezoelectric plate forming a plurality of diaphragms, each of which spans a respective cavity in the substrate; and
a conductor pattern formed on the front surface, the conductor pattern comprising interdigital transducers (IDTs) of one or more pairs of sub-resonators, wherein
the IDT of each sub-resonator comprises interleaved fingers disposed over a respective diaphragm,
the two sub-resonators of each pair of sub-resonators are positioned symmetrically about a central axis, and
the IDTs of all of the sub-resonators have a common pitch.
2. The acoustic resonator of claim 1 , wherein
the conductor pattern comprises two or more pairs of sub-resonators, and
all of the sub-resonators of the two or more pairs of sub-resonators are electrically connected in parallel.
3. The acoustic resonator of claim 1 , wherein all of the sub-resonators have a common length, a common aperture, and a common IDT finger width.
4. An acoustic resonator, comprising:
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of a substrate except for portions of the piezoelectric plate forming a plurality of diaphragms, each of which spans a respective cavity in the substrate; and
a conductor pattern formed on the front surface, the conductor pattern comprising interdigital transducers (IDTs) of one or more pairs of sub-resonators, wherein
the IDT of each sub-resonator comprises interleaved fingers disposed over a respective diaphragm,
the two sub-resonators of each pair of sub-resonators are positioned symmetrically about a central axis, and
the IDTs of all of the sub-resonators have a common pitch.
5. A radio frequency 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 except for portions of the piezoelectric plate forming a plurality of diaphragms, each of which spans a respective cavity in the substrate; and
a conductor pattern formed on the front surface, the conductor pattern defining a ladder filter circuit including a plurality of acoustic resonators, one or more resonators from the plurality of acoustic resonators divided respectively into one or more pairs of sub-resonators, wherein
each sub-resonator comprises an interdigital transducer (IDT) with interleaved fingers disposed over a diaphragm from the plurality of diaphragms, and the two sub-resonators of each pair of sub-resonators are arranged in symmetrical positions with respect to a central axis of the filter device.
6. The radio frequency filter device of claim 5 , wherein,
for each of the plurality of acoustic resonators, the IDTs of all of the respective sub-resonators have a common pitch.
7. The radio frequency filter device of claim 6 , wherein,
for each of the plurality of acoustic resonators, all of the respective sub-resonators have a common length, a common aperture, and a common IDT finger width.
8. The radio frequency filter device of claim 6 , wherein
a resonator of the one or more resonators comprises a first pair of sub-resonators and a second pair of sub-resonators, the two sub-resonators of the first pair of sub-resonators are electrically connected in parallel, the two sub-resonators of the second pair of sub-resonators are electrically connected in parallel, and
the first pair of sub-resonators and the second pair of sub-resonators are electrically connected in series.
9. The radio frequency filter device of claim 6 , wherein
the plurality of resonators further comprises one or more undivided resonators, and each of the undivided resonators is disposed along the central axis of the device.
10. The radio frequency filter device of claim 9 wherein
each of the one or more undivided resonators is approximately bisected by the central axis of the device.
11. The radio frequency filter device of claim 5 , wherein
the plurality of acoustic resonators includes two or more series resonators and two or more shunt resonators.
12. The radio frequency filter device of claim 11 , wherein
the two or more series resonators and the two or more shunt resonators are disposed alternately along the central axis of the device.
13. The radio frequency filter device of claim 11 , wherein
the two or more series resonators are disposed in sequence along the central axis of the device and the two or more shunt resonators are disposed outboard of the series resonators.
14. The radio frequency filter device of claim 13 , wherein IDT fingers of a sub-resonator of one of the shunt resonators and IDT fingers of a sub-resonator of one of the series resonators are disposed on the same diaphragm.
15. The radio frequency filter device of claim 6 , wherein
a resonator of the one or more resonators is divided into two or more pairs of sub-resonators, and
all of the sub-resonators of the two or more pairs of sub-resonators are electrically connected in parallel.