The invention provides a planarization method, which can make the local flatness of the product to be processed more uniform. The product has a cavity filled with oxide and includes a first electrode layer, a piezoelectric layer and a second electrode layer superposed on the cavity. The first electrode layer covers the cavity and includes a first inclined face around the first electrode layer, and the piezoelectric layer covers the first electrode layer and is arranged on the first electrode layer. The planarization method includes: depositing a passivation layer on the second electrode layer and etching the passivation layer completely until the thickness of the passivation layer is reduced to the required thickness.

A formation method of a filter device includes: forming a first layer by providing a first substrate and forming a resonance device preprocessing layer with a first side and a second side opposite to the first side, wherein the first substrate is located on the first side; forming a second layer by providing a second substrate and forming a first passive device with a third side and a fourth side opposite to the third side, wherein the second substrate is located on the third side; connecting the first layer located on the fourth side and the second layer located on the second side; removing the first substrate; and forming at least one first resonance device based on the resonance device preprocessing layer. The resonance device and the passive device are integrated in one die to form a filter device, which requires less space in an RF front-end chip.

A film bulk acoustic wave resonator includes a piezoelectric film disposed over a cavity. The cavity is shaped as partial ellipse including first, second, and third vertices. The film bulk acoustic wave resonator further includes three release ports in positions that minimize etch time to remove all sacrificial material from within the cavity.

Disclosed are a bulk acoustic wave resonator and a fabrication method for the bulk acoustic wave resonator. The fabrication method includes: preparing a cavity with a top opening on a first silicon wafer; preparing an insulating layer on an upper surface of a second silicon wafer, and preparing a resonant piezoelectric stack on an upper surface of the insulating layer; preparing a first silicon dioxide layer on an upper surface of the resonant piezoelectric stack; bonding a surface where the top opening of the cavity is located with an upper surface of the first silicon dioxide layer; and preparing a lead out pad of the first electrode and the second electrode.

A bulk acoustic wave filter comprises a substrate, an insulating layer disposed on the substrate and having a first cavity and a second cavity formed therein, a first bulk-acoustic-wave-resonance-structure disposed on the first cavity and a second bulk-acoustic-wave-resonance-structure disposed on the second cavity. The first bulk-acoustic-wave-resonance-structure comprises a first bottom electrode disposed on the first cavity, a first top electrode disposed on the first bottom electrode, a first piezoelectric layer portion sandwiched between the first top electrode and the first bottom electrode, and a first frequency tuning structure disposed between the first cavity and the first bottom electrode. The second bulk-acoustic-wave-resonance-structure comprises a second bottom electrode disposed on the second cavity, a second top electrode disposed on the second bottom electrode, a second piezoelectric layer portion sandwiched between the second top electrode and the second bottom electrode.

The RF filters used in conventional mobile devices often include resonator structures, which often require free-standing air-gap structure to prevent mechanical vibrations of the resonator from being damped by a bulk material. A method for fabricating a resonator structure comprises depositing a non-conformal thin-film to the resonator structure to seal air gap cavities in the resonator structure.

A piezoelectric thin film resonator includes: a substrate; a piezoelectric film located on the substrate and including a penetration hole penetrating therethrough; a lower electrode and an upper electrode facing each other across at least a part of the piezoelectric film; and a protective film covering an upper surface of the piezoelectric film, a side surface of the piezoelectric film, and an inner surface of the penetration hole.

A method for forming cavity of bulk acoustic wave resonator comprising following steps of: forming a sacrificial epitaxial structure mesa on a compound semiconductor substrate; forming an insulating layer on the sacrificial epitaxial structure mesa and the compound semiconductor substrate; polishing the insulating layer by a chemical-mechanical planarization process to form a polished surface; forming a bulk acoustic wave resonance structure on the polished surface, which comprises following steps of: forming a bottom electrode layer on the polished surface; forming a piezoelectric layer on the bottom electrode layer; and forming a top electrode layer on the piezoelectric layer, wherein the bulk acoustic wave resonance structure is located above the sacrificial epitaxial structure mesa; and etching the sacrificial epitaxial structure mesa to form a cavity, wherein the cavity is located under the bulk acoustic wave resonance structure.

A seed layer (210) of a noble metal is formed by electrochemical deposition on a metal electrode (111) disposed on a dielectric layer (110,310). The noble metal seed layer allows the deposition of a highly textured piezoelectric layer (320) on the metal electrode.

A method and structure for a transfer process for an acoustic resonator device. In an example, a bulk acoustic wave resonator (BAWR) with an air reflection cavity is formed. A piezoelectric thin film is grown on a crystalline substrate. A first patterned electrode is deposited on the surface of the piezoelectric film. An etched sacrificial layer is deposited over the first electrode and a planarized support layer is deposited over the sacrificial layer, which is then bonded to a substrate wafer. The crystalline substrate is removed and a second patterned electrode is deposited over a second surface of the film. The sacrificial layer is etched to release the air reflection cavity. Also, a cavity can instead be etched into the support layer prior to bonding with the substrate wafer. Alternatively, a reflector structure can be deposited on the first electrode, replacing the cavity.