An acoustic device includes a foundation structure and a transducer provided over the foundation structure. The foundation structure includes a piezoelectric layer between a top electrode and a bottom electrode. The piezoelectric layer has an active portion within an active region of the transducer, and a bi-polar border portion within a border region of the transducer. The piezoelectric material in the active portion has a first polarization. The bi-polar border portion has a first sub-portion and a second sub-portion, which resides either above or below the first sub-portion. The piezoelectric material in the first sub-portion has the first polarization, and the piezoelectric material in the second sub-portion has a second polarization, which is opposite the first polarization.

Embodiments of this disclosure relate to bulk acoustic wave resonators on a substrate. The bulk acoustic wave resonators include a first bulk acoustic wave resonator, a second bulk acoustic wave resonator, a conductor electrically connecting the first bulk acoustic wave resonator to the second bulk acoustic wave resonator, and an air gap positioned between the conductor and a surface of the substrate.

Embodiments of this disclosure relate to acoustic wave filters configured to filter radio frequency signals. An acoustic wave filter includes a first bulk acoustic wave resonator on a substrate, a second bulk acoustic wave resonator on the substrate, a conductor electrically connecting the first bulk acoustic wave resonator in anti-series with the second bulk acoustic wave resonator, and an air gap positioned between the conductor and a surface of the substrate. The air gap can reduce parasitic capacitance associated with the conductor. Acoustic wave filters disclosed herein can suppress a second harmonic.

Bulk acoustic wave (BAW) resonators, and particularly shaped border (BO) rings for BAW resonators are disclosed. Top electrode arrangements are disclosed that include a BO ring arranged about a periphery of a top electrode, where the BO ring forms a top surface having a shape that is sloped or graded in comparison to planar surfaces of the top electrode. The top surface of the BO ring may be arranged such that a height of the top surface is graded in a descending manner toward a central region of the BAW resonator. BAW resonators as disclosed herein are provided with high quality factors and suppression of spurious modes while also providing reduced acoustic leakage and mode conversion.

An acoustic resonator includes: an upper electrode including a first active region disposed on an upper portion of a piezoelectric layer, and a first extended region extended from the first active region; a lower electrode including a second active region disposed on a lower portion of the piezoelectric layer, and a second extended region extended from the second active region; a first metal layer including a first resistance reduction region disposed on the first extended region; and a second metal layer including a second resistance reduction region disposed on the second extended region. The first metal layer includes a first conductive link region extended from the first resistance reduction region. The second metal layer includes a second conductive link region extended from the second resistance reduction region. The first and second conductive link regions correspond to respective portions of a side boundary of the first and second active regions.

Techniques are disclosed for forming high frequency film bulk acoustic resonator (FBAR) devices having multiple resonator thicknesses on a common substrate. A piezoelectric stack is formed in an STI trench and overgrown onto the STI material. In some cases, the piezoelectric stack can include epitaxially grown AlN. In some cases, the piezoelectric stack can include single crystal (epitaxial) AlN in combination with polycrystalline (e.g., sputtered) AlN. The piezoelectric stack thus forms a central portion having a first resonator thickness and end wings extending from the central portion having a different resonator thickness. Each wing may also have different thicknesses. Thus, multiple resonator thicknesses can be achieved on a common substrate, and hence, multiple resonant frequencies on that same substrate. The end wings can have metal electrodes formed thereon, and the central portion can have a plurality of IDT electrodes patterned thereon.

A bulk-acoustic wave resonator includes: a membrane layer disposed on a substrate and forming a cavity; a lower electrode disposed on the membrane layer; a piezoelectric layer disposed on the lower electrode; an upper electrode disposed on the piezoelectric layer, and including a frame part disposed at an edge of an active area and having a thickness greater than that of a portion of the upper electrode disposed in a central portion of the active area; and a frequency adjusting layer disposed on the piezoelectric layer and the upper electrode. The frequency adjusting layer is excluded from an inclined surface of the frame part, or a thickness of a portion of the frequency adjusting layer on the inclined surface is less than that of other portions of the frequency adjusting layer. The frequency adjusting layer is disposed on a portion of the piezoelectric layer protruding from the upper electrode.

An acoustic resonator includes: an upper electrode including a first active region disposed on an upper portion of a piezoelectric layer, and a first extended region extended from the first active region; a lower electrode including a second active region disposed on a lower portion of the piezoelectric layer, and a second extended region extended from the second active region; a first metal layer including a first resistance reduction region disposed on the first extended region; and a second metal layer including a second resistance reduction region disposed on the second extended region. The first metal layer includes a first conductive link region extended from the first resistance reduction region. The second metal layer includes a second conductive link region extended from the second resistance reduction region. The first and second conductive link regions correspond to respective portions of a side boundary of the first and second active regions.

Techniques are disclosed for forming high frequency film bulk acoustic resonator (FBAR) devices having multiple resonator thicknesses on a common substrate. A piezoelectric stack is formed in an STI trench and overgrown onto the STI material. In some cases, the piezoelectric stack can include epitaxially grown AlN. In some cases, the piezoelectric stack can include single crystal (epitaxial) AlN in combination with polycrystalline (e.g., sputtered) AlN. The piezoelectric stack thus forms a central portion having a first resonator thickness and end wings extending from the central portion having a different resonator thickness. Each wing may also have different thicknesses. Thus, multiple resonator thicknesses can be achieved on a common substrate, and hence, multiple resonant frequencies on that same substrate. The end wings can have metal electrodes formed thereon, and the central portion can have a plurality of IDT electrodes patterned thereon.

Embodiments of a tunable bandpass microelectromechanical (MEMS) filter are described. In one embodiment, such a filter includes a pair of arch beam microresonators, and a pair of voltage sources electrically coupled to apply a pair of adjustable voltage biases across respective ones of the pair of arch beam microresonators. The pair of voltage sources offer independent tuning of the bandwidth of the filter. Based on the structure and arrangement of the filter, it can be tunable by 125% or more by adjustment of the adjustable voltage bias. The filter also has a relatively low bandwidth distortion, can exhibit less than 2.5 dB passband ripple, and can exhibit sideband rejection in the range of at least 26 dB.