A method for fabricating bulk acoustic wave resonator with mass adjustment structure, comprising following steps of: forming a sacrificial structure mesa on a substrate; etching the sacrificial structure mesa such that any two adjacent parts have different heights, a top surface of a highest part of the sacrificial structure mesa is coincident with a mesa top extending plane; forming an insulating layer on the sacrificial structure mesa and the substrate; polishing the insulating layer to form a polished surface; forming a bulk acoustic wave resonance structure including a top electrode, a piezoelectric layer and a bottom electrode on the polished surface; etching the sacrificial structure mesa to form a cavity; the insulating layer between the polished surface and the mesa top extending plane forms a frequency tuning structure, the insulating layer between the mesa top extending plane and the cavity forms a mass adjustment structure.

A method for fabricating bulk acoustic wave resonator with mass adjustment structure, comprising following steps of: forming a sacrificial structure mesa on a substrate; etching the sacrificial structure mesa such that any two adjacent parts have different heights, a top surface of a highest part of the sacrificial structure mesa is coincident with a mesa top extending plane; forming an insulating layer on the sacrificial structure mesa and the substrate; polishing the insulating layer to form a polished surface; forming a bulk acoustic wave resonance structure including a top electrode, a piezoelectric layer and a bottom electrode on the polished surface; etching the sacrificial structure mesa to form a cavity; the insulating layer between the polished surface and the mesa top extending plane forms a frequency tuning structure, the insulating layer between the mesa top extending plane and the cavity forms a mass adjustment structure.

An acoustic resonator includes: a resonating unit including a piezoelectric layer, a first electrode disposed on a lower side of the piezoelectric layer, and a second electrode disposed on an upper side of the piezoelectric layer; a substrate disposed below the resonating unit; a support unit forming a cavity between the substrate and the resonating unit; and a pillar extending through the cavity and connecting the resonating unit to the substrate. The resonating unit further includes a first insertion layer disposed above the pillar.

An acoustic resonator includes: a resonating unit including a piezoelectric layer, a first electrode disposed on a lower side of the piezoelectric layer, and a second electrode disposed on an upper side of the piezoelectric layer; a substrate disposed below the resonating unit; a support unit forming a cavity between the substrate and the resonating unit; and a pillar extending through the cavity and connecting the resonating unit to the substrate. The resonating unit further includes a first insertion layer disposed above the pillar.

An acoustic resonator device is formed that reduces a thermal coefficient of expansion mismatch between a piezoelectric plate and a silicon substrate by bonding the front surface of the silicon substrate having a filled and planarized sacrificial tub to a piezoelectric substrate and thinning the silicon substrate by removing material from a back surface. That back surface is then bonded to a handle wafer having a thermal coefficient of expansion (TCE) closer to a TCE of the piezoelectric substrate than a TCE of the silicon substrate and thinning the piezoelectric substrate to a target piezoelectric membrane thickness to form a piezoelectric plate. A conductor pattern is formed on the thinned piezoelectric plate and the sacrificial tub is removed to form a cavity and release a membrane of the piezoelectric plate using an etchant introduced through holes in the piezoelectric plate.

An acoustic resonator device is formed that reduces a thermal coefficient of expansion mismatch between a piezoelectric plate and a silicon substrate by bonding the front surface of the silicon substrate having a filled and planarized sacrificial tub to a piezoelectric substrate and thinning the silicon substrate by removing material from a back surface. That back surface is then bonded to a handle wafer having a thermal coefficient of expansion (TCE) closer to a TCE of the piezoelectric substrate than a TCE of the silicon substrate and thinning the piezoelectric substrate to a target piezoelectric membrane thickness to form a piezoelectric plate. A conductor pattern is formed on the thinned piezoelectric plate and the sacrificial tub is removed to form a cavity and release a membrane of the piezoelectric plate using an etchant introduced through holes in the piezoelectric plate.

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

A bulk acoustic wave (BAW) resonator includes a substrate defining a cavity, a bottom electrode disposed over the substrate and the cavity, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. The piezoelectric layer includes polycrystalline lithium niobate (LN) material or polycrystalline lithium tantalite (LT) material. The BAW resonator may further include an encapsulant layer formed on side and top surfaces of the piezoelectric layer. The encapsulant layer is configured to protect the LN material or the LT material of the piezoelectric layer from a release solvent previously applied to sacrificial material within the cavity in the substrate.

A bulk acoustic wave (BAW) resonator includes a substrate defining a cavity, a bottom electrode disposed over the substrate and the cavity, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. The piezoelectric layer includes polycrystalline lithium niobate (LN) material or polycrystalline lithium tantalite (LT) material. The BAW resonator may further include an encapsulant layer formed on side and top surfaces of the piezoelectric layer. The encapsulant layer is configured to protect the LN material or the LT material of the piezoelectric layer from a release solvent previously applied to sacrificial material within the cavity in the substrate.