A method for fabricating a film bulk acoustic resonator (FBAR) structure includes: sequentially forming a top electrode material layer, a piezoelectric layer, and a bottom electrode material layer on a substrate; patterning the bottom electrode material layer to form a bottom electrode; forming a sacrificial layer above the bottom electrode; bonding a bottom cap wafer onto the sacrificial layer; removing the substrate; patterning the top electrode material layer to form a top electrode; and removing a portion of the sacrificial layer to form a lower cavity.

A method for fabricating a film bulk acoustic resonator (FBAR) structure includes: obtaining a wafer, at least a portion of the wafer is made of a piezoelectric material; forming a bottom electrode layer on the wafer; patterning the bottom electrode layer to form a bottom electrode; forming a sacrificial island on the bottom electrode; bonding a bottom cap wafer onto the bottom electrode; processing the wafer to form a piezoelectric layer; forming a top electrode layer on the piezoelectric layer; patterning the top electrode layer to form a top electrode; and removing the sacrificial island to form a cavity.

A film bulk acoustic resonator (FBAR) structure includes a bottom cap wafer, a piezoelectric layer disposed on the bottom cap wafer, a bottom electrode disposed below the piezoelectric layer, and a top electrode disposed above the piezoelectric layer. Portions of the bottom electrode, the piezoelectric layer, and the top electrode that overlap with each other constitute a piezoelectric stack. The FBAR structure further includes a lower cavity disposed below the piezoelectric stack. A projection of the piezoelectric stack is located within the lower cavity.

Embodiments disclosed herein include resonators and methods of forming such resonators. In an embodiment a resonator comprises a substrate, where a cavity is disposed into a surface of the substrate, and a piezoelectric film suspended over the cavity. In an embodiment, the piezoelectric film has a first surface and a second surface opposite from the first surface, and the piezoelectric film is single crystalline and has a thickness that is 0.5 μm or less. In an embodiment a first electrode is over the first surface of the piezoelectric film, and a second electrode is over the second surface of the piezoelectric film.

A film bulk acoustic resonator (FBAR) structure includes, a bottom cap wafer, a piezoelectric layer disposed on the bottom cap wafer, the piezoelectric layer including lithium niobate or lithium tantalate, a bottom electrode disposed below the piezoelectric layer, and a top electrode disposed above the piezoelectric layer. Portions of the bottom electrode, the piezoelectric layer, and the top electrode that overlap with each other constitute a piezoelectric stack. The FBAR structure also includes a cavity disposed below the piezoelectric stack. A projection of the piezoelectric stack is located within the cavity.

A bulk acoustic wave resonator and a method of manufacturing the same are provided. The bulk acoustic wave resonator includes: a first carrier substrate; a barrier layer on a main surface of the first carrier substrate and configured to prevent an undesired conductive channel from being generated due to charge accumulation on the main surface; a buffer layer on a side of the barrier layer away from the first carrier substrate; a piezoelectric layer on a side of the buffer layer away from the barrier layer; a first electrode and a second electrode on opposite sides of the piezoelectric layer; a first passivation layer and a second passivation layer, respectively covering sidewalls of the first electrode and the second electrode; a dielectric layer between the first passivation layer and the buffer layer, wherein a first cavity is provided between the first passivation layer and the dielectric layer.

A structure and method for integrating a crystal resonator with a control circuit are disclosed. The resonator is formed by forming a lower cavity (120) in the device wafer (100) containing the control circuit (110) and a piezoelectric vibrator (200) on a front side (100U) of the device wafer (100) and by fabricating a cap layer (420) using planar fabrication processes, which encloses the piezoelectric vibrator (200) within an upper cavity (400). In addition, a semiconductor die (500) may be bonded to a back side (100D) of the device wafer (100), helping in additionally increasing the integration of the crystal resonator and allowing on-chip modulation of the crystal resonator's parameters. In this way, in addition to being able to integrate with other semiconductor components more easily with a higher degree of integration, the crystal resonator is more compact in size and less power-consuming.

The present disclosure provides an integration method and integration structure for a control circuit and a Bulk Acoustic Wave (BAW) filter. The integration method includes: providing a base, the base being provided with a control circuit: forming a first cavity on the base; providing a BAW resonating structure, an input electrode and an output electrode being arranged on a surface of the BAW resonating structure, and the BAW resonating structure including a second cavity; facing the surface of the BAW resonating structure towards the base, such that the BAW resonating structure is bonded to the base and seals the first cavity; and electrically connecting the control circuit to the input electrode and the output electrode. The present disclosure implements the control of the control circuit on the BAW filter by forming the control circuit and the cavity, required by the BAW filter, on the base, and then mounting the existing BAW resonating structure in the cavity, and thus may avoid the problems of the complex electrical connection process, large insertion loss and the like due to a fact that the existing BAW filter is integrated to the Printed Circuit Board (PCB) as a discrete device, has the high level of integration, and reduces the process cost.

In one example, a method of forming a bulk acoustic wave (BAW) resonator comprises: forming an electrode on at least one of a semiconductor substrate, a sacrificial layer, or an acoustic reflector; and forming a piezoelectric layer on the electrode, the piezoelectric layer having a convex surface.

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.