Acoustic filters, resonators and methods are disclosed. An acoustic filter device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer is formed on the front surface of the piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. At least a portion of a perimeter of the cavity is curved.

Acoustic filters, resonators and methods are disclosed. An acoustic filter device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer is formed on the front surface of the piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. At least a portion of a perimeter of the cavity is curved.

An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having a back surface bonded to the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate and has interleaved fingers on a diaphragm spanning a cavity in the substrate. An etch-stop layer is formed on the front surface of the piezoelectric plate between the interleaved fingers. A portion of the piezoelectric plate and the etch-stop layer form the diaphragm. The etch-stop layer is impervious to the etch process used to form the interleaved fingers. The etch-stop layer may be formed on the piezoelectric plate between but not under the interleaved fingers. In other cases, the etch-stop layer is formed on the piezoelectric plate between and under the interleaved fingers.

An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having a back surface bonded to the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate and has interleaved fingers on a diaphragm spanning a cavity in the substrate. An etch-stop layer is formed on the front surface of the piezoelectric plate between the interleaved fingers. A portion of the piezoelectric plate and the etch-stop layer form the diaphragm. The etch-stop layer is impervious to the etch process used to form the interleaved fingers. The etch-stop layer may be formed on the piezoelectric plate between but not under the interleaved fingers. In other cases, the etch-stop layer is formed on the piezoelectric plate between and under the interleaved fingers.

An acoustic resonator is fabricated by forming a patterned first photoresist mask on a piezoelectric plate at locations of a desired interdigital transducer (IDT) pattern. An etch-stop layer is then deposited on the plate and first photoresist mask. The first photoresist mask is removed to remove parts of the etch-stop and expose the plate. An IDT conductor material is deposited on the etch stop and the exposed plate. A patterned second photoresist mask is then formed on the conductor material at locations of the IDT pattern. The conductor material is then etched over and to the etch-stop to form the IDT pattern which has interleaved fingers on a diaphragm to span a substrate cavity. A portion of the plate and the etch-stop form the diaphragm. The etch-stop and photoresist mask are impervious to this etch. The second photoresist mask is removed to leave the IDT pattern.

An acoustic resonator is fabricated by forming a patterned first photoresist mask on a piezoelectric plate at locations of a desired interdigital transducer (IDT) pattern. An etch-stop layer is then deposited on the plate and first photoresist mask. The first photoresist mask is removed to remove parts of the etch-stop and expose the plate. An IDT conductor material is deposited on the etch stop and the exposed plate. A patterned second photoresist mask is then formed on the conductor material at locations of the IDT pattern. The conductor material is then etched over and to the etch-stop to form the IDT pattern which has interleaved fingers on a diaphragm to span a substrate cavity. A portion of the plate and the etch-stop form the diaphragm. The etch-stop and photoresist mask are impervious to this etch. The second photoresist mask is removed to leave the IDT pattern.

A fine dust concentration sensor includes a bulk acoustic resonator and a cap including an upper portion with holes therein and a lateral portion connected to the upper portion to accommodate the bulk acoustic resonator. An upper surface of the upper portion of the cap is coated with a hydrophobic material.

A fine dust concentration sensor includes a bulk acoustic resonator and a cap including an upper portion with holes therein and a lateral portion connected to the upper portion to accommodate the bulk acoustic resonator. An upper surface of the upper portion of the cap is coated with a hydrophobic material.

A method for forming an aluminum nitride layer (310, 320) comprises the provision of a substrate (100) and the forming of a patterned metal nitride layer (110). A bottom electrode metal layer (210) is formed on the exposed portions (101) of the substrate. An aluminum nitride layer portion (320) grown above the exposed portion (101) of the substrate (100) exhibits piezoelectric properties. An aluminum nitride layer portion (310) grown above the patterned metal nitride layer (110) exhibits no piezoelectric properties (310). Both aluminum nitride layer portions (320, 310) are grown simultaneously.

A method for forming an aluminum nitride layer (310, 320) comprises the provision of a substrate (100) and the forming of a patterned metal nitride layer (110). A bottom electrode metal layer (210) is formed on the exposed portions (101) of the substrate. An aluminum nitride layer portion (320) grown above the exposed portion (101) of the substrate (100) exhibits piezoelectric properties. An aluminum nitride layer portion (310) grown above the patterned metal nitride layer (110) exhibits no piezoelectric properties (310). Both aluminum nitride layer portions (320, 310) are grown simultaneously.