BAW Resonator TFE Package Acoustic Boundary Definition
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Solution Overview
Problem
Existing bulk acoustic wave (BAW) resonators and filters face issues with low-quality resonant areas at the edges due to non-vertical alignment of piezoelectric crystals, leading to unwanted lateral spurious modes, and current solutions require extra masks and separate cap wafer packaging for resonance suppression.
Innovation Solution
A monolithic thin-film encapsulation (TFE) package is used to form a BAW resonator with a defined acoustic boundary condition, suppressing resonances in the low-Q piezoelectric area without additional masks or separate cap wafer packaging, by creating cavities and TFE anchors to define the acoustic boundary condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If air bridge is used over the low-Q region, then resonances are suppressed, but extra mask and etching of sacrificial material are required
Solution Approach 1:
The encapsulation structure is merged with the resonance suppression function. The TFE encapsulation layers (cap layer and seal layer) are formed to extend over and cover the low-Q piezoelectric material areas, combining the protective encapsulation function with the acoustic boundary definition function in a single integrated structure.
Solution Approach 2:
The TFE encapsulation structure serves multiple functions simultaneously: it provides mechanical protection to the resonator, defines acoustic boundary conditions, and suppresses spurious resonances from low-Q areas. This multi-functional design eliminates the need for separate air bridge structures or additional masks.
2Reliability
If slab of conductive or dielectric material is used on upper surface, then resonances are suppressed, but extra mask and fine control of slab dimensions are required
Solution Approach 1:
The encapsulation structure is merged with the resonance suppression function. The TFE encapsulation layers (cap layer and seal layer) are formed to extend over and cover the low-Q piezoelectric material areas, combining the protective encapsulation function with the acoustic boundary definition function in a single integrated structure.
Solution Approach 2:
The TFE encapsulation structure self-defines its boundaries through the anchor regions that extend beyond the resonator electrodes. The cap layer and seal layer naturally form the acoustic boundary conditions through their geometric configuration, eliminating the need for separate dimensional control processes.
3Reliability
If separate cap wafer packaging is used, then boundary condition control is provided, but it is unsuitable to provide required boundary condition control
Solution Approach 1:
The encapsulation structure is merged with the resonance suppression function. The TFE encapsulation layers (cap layer and seal layer) are formed to extend over and cover the low-Q piezoelectric material areas, combining the protective encapsulation function with the acoustic boundary definition function in a single integrated structure.
Solution Approach 2:
The TFE encapsulation structure serves multiple functions simultaneously: it provides mechanical protection to the resonator, defines acoustic boundary conditions, and suppresses spurious resonances from low-Q areas. This multi-functional design eliminates the need for separate air bridge structures or additional masks.
4Reliability
If TFE encapsulation is used to define acoustic BC, then resonances are suppressed and Q factor is improved, but additional TFE layers and anchors are required
Solution Approach 1:
The encapsulation structure is merged with the resonance suppression function. The TFE encapsulation layers (cap layer and seal layer) are formed to extend over and cover the low-Q piezoelectric material areas, combining the protective encapsulation function with the acoustic boundary definition function in a single integrated structure.
Solution Approach 2:
The TFE encapsulation structure serves multiple functions simultaneously: it provides mechanical protection to the resonator, defines acoustic boundary conditions, and suppresses spurious resonances from low-Q areas. This multi-functional design eliminates the need for separate air bridge structures or additional masks.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the Q factor and filter performance by effectively suppressing resonances in the low-Q piezoelectric area, enhancing the quality of BAW resonators and filters without the need for extra masks or separate cap wafer packaging.
Implementation Method 1
a thin-film piezoelectric layer, and a second metal layer... a thin-film piezoelectric layer of the BAW resonator of aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), lithium niobate (LiNbO3), lithium tantalite (LiTaO3), lead zirconate titanate (PZT), or polyvinylidene fluoride (PVDF)
Data Source
AI summary
A BAW resonator/filter with a monolithic TFE package that defines an acoustic BC and suppresses resonances from the low-Q piezoelectric area of the resonator and resulting devices are provided. Embodiments include a BAW resonator over a dielectric layer, the BAW resonator including a first metal layer, a thin-film piezoelectric layer, and a second metal layer; a first cavity in the dielectric layer under the first metal layer and a second cavity over the first cavity on the second metal layer; and a pair of TFE anchors on the second metal layer, each TFE anchor adjacent to and on an opposite side of the second cavity and extending beyond the first metal layer.