Modern RF front end filters feature acoustic resonators in a film bulk acoustic resonator (FBAR) structure. An acoustic filter is a circuit that includes at least (and typically significantly more) two resonators. The acoustic resonator structure comprises a substrate including sidewalls and a vertical cavity between the sidewalls and two or more resonators deposited in the vertical cavity.

A process for fabricating a micro-electro-mechanical system, includes the following steps: production of a stack on the surface of a temporary substrate so as to produce a first assembly, comprising: at least depositing a piezoelectric material or a ferroelectric material to produce a layer of piezoelectric material or of ferroelectric material; producing a first bonding layer; production of a second assembly comprising at least producing a second bonding layer on the surface of a host substrate; production of at least one acoustic isolation structure in at least one of the two assemblies; production of at least one electrode level containing one or more electrodes in at least one of the two assemblies; bonding the two assemblies via the two bonding layers, before or after the production of the at least one electrode level in at least one of the two assemblies; removing the temporary substrate.

A process for fabricating a micro-electro-mechanical system, includes the following steps: production of a stack on the surface of a temporary substrate so as to produce a first assembly, comprising: at least depositing a piezoelectric material or a ferroelectric material to produce a layer of piezoelectric material or of ferroelectric material; producing a first bonding layer; production of a second assembly comprising at least producing a second bonding layer on the surface of a host substrate; production of at least one acoustic isolation structure in at least one of the two assemblies; production of at least one electrode level containing one or more electrodes in at least one of the two assemblies; bonding the two assemblies via the two bonding layers, before or after the production of the at least one electrode level in at least one of the two assemblies; removing the temporary substrate.

Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a front surface and a cavity, a perimeter of the cavity defined by a lateral etch-stop comprising etch-stop material. A back surface of a single-crystal piezoelectric plate is attached to the front surface of the substrate except for a portion of the piezoelectric plate that forms a diaphragm that spans the cavity. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm.

Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a front surface and a cavity, a perimeter of the cavity defined by a lateral etch-stop comprising etch-stop material. A back surface of a single-crystal piezoelectric plate is attached to the front surface of the substrate except for a portion of the piezoelectric plate that forms a diaphragm that spans the cavity. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm.

A method for manufacturing a vibrator device includes a first dry etching step of dry-etching a quartz crystal substrate having a first surface and a second surface from the side facing the first surface to form first grooves and part of the outer shapes of a first vibrating arm and a second vibrating arm, a second dry etching step of dry-etching the quartz crystal substrate from the side facing the second surface to form second grooves and part of the outer shapes of the first vibrating arm and the second vibrating arm, and thereafter, a wet etching step of wet-etching the side surfaces of the first vibrating arm and the second vibrating arm.

An acoustic filter device includes first and second series resonators and at least one shunt resonator, each shunt resonator electrically coupled to the first series resonator or the second series resonator. Each of the first and second series resonators includes respective first and second sub-resonators electrically connected in series, The first sub-resonators of the first and second series resonators are acoustically coupled along a first shared acoustic track. The second sub-resonators of the first and second series resonators are acoustically coupled along a second shared acoustic track.

An acoustic filter device includes first and second series resonators and at least one shunt resonator, each shunt resonator electrically coupled to the first series resonator or the second series resonator. Each of the first and second series resonators includes respective first and second sub-resonators electrically connected in series, The first sub-resonators of the first and second series resonators are acoustically coupled along a first shared acoustic track. The second sub-resonators of the first and second series resonators are acoustically coupled along a second shared acoustic track.

A crystal oscillator includes an oscillating substrate, a hollow frame, a first electrode, and a second electrode. The oscillating substrate includes a main oscillating region and a thinned region that has a thickness smaller than that of the main oscillating region. The first and second electrodes are disposed on a first surface of the oscillating substrate and a second surface opposite to the first surface, respectively. The hollow frame is disposed on the second surface. The second electrode includes a second electrode portion that has at least one opening in positional correspondence with the thinned region. A method for making the crystal oscillator is also provided herein.

Acoustic resonator devices, filters, and methods are disclosed. An acoustic resonator includes a substrate and a piezoelectric plate having front and back surfaces, the back surface attached to a 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 (IDT) is formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The IDT is configured to excite a primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT. At least one finger of the IDT is disposed in a groove in the diaphragm. A depth of the groove is less than a thickness of the at least one finger of the IDT.