BAW Piezoelectric Recess Structure for Spurious Mode Suppression
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Solution Overview
Problem
Existing bulk acoustic wave (BAW) devices face challenges in achieving high quality factor (Q) and suppressing spurious modes while maintaining electromechanical coupling coefficient (kt2), particularly due to issues with frame geometries leading to raised frame modes and inadequate energy confinement.
Innovation Solution
Incorporating a recess in the piezoelectric layer outside the active region of the BAW device, combined with a frame structure that is positioned outside the active region, to suppress asymmetric and symmetric modes, and enhance energy confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a frame structure is added to confine energy in the active region, then energy confinement is improved, but raised frame modes are generated
Solution Approach 1:
The harmful frame modes are extracted and removed by positioning the frame structure outside the active region, separating the energy confinement function from the spurious mode generation zone. The frame structure is strategically placed in the inactive region where it confines energy without being excited into harmful resonant modes.
Solution Approach 2:
Different regions of the device are given different structural qualities: the active region maintains uniform piezoelectric layer thickness for optimal acoustic wave generation, while the inactive region incorporates the frame structure for energy confinement. This local differentiation allows each region to perform its specific function without interfering with the other.
2Object-generated harmful factors
If the piezoelectric layer thickness is reduced outside the active region to suppress asymmetric modes, then asymmetric mode suppression is improved, but device complexity increases
Solution Approach 1:
The piezoelectric layer is segmented into different thickness zones: a first thickness in the active region for optimal acoustic performance, and a second reduced thickness in the inactive region for asymmetric mode suppression. This segmentation allows targeted control of acoustic modes in different spatial zones.
Solution Approach 2:
The solution moves from a two-dimensional planar structure to a three-dimensional stepped structure by creating different thickness levels of the piezoelectric layer. This dimensional change enables asymmetric mode suppression through the thickness variation while maintaining the active region functionality.
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
The solution significantly increases the quality factor (Q) and maintains a stable electromechanical coupling coefficient (kt2), effectively decoupling Q and spurious mode strength, thereby improving BAW device performance.
Implementation Method 1
In BAW resonators, acoustic waves propagate in the bulk of a piezoelectric layer
Implementation Method 2
The piezoelectric layer can be thinner outside of the active region from an edge of the active region to an edge of the acoustic reflector
Data Source
AI summary
Aspects of this disclosure relate to bulk acoustic wave devices that include a first electrode, a second electrode, and a piezoelectric layer having a recess outside of the active region of the bulk acoustic wave device. The first electrode and the second electrode overlap and are on opposing sides of the piezoelectric layer throughout the active region. Related acoustic wave filters, multiplexers, radio frequency modules, radio frequency systems, wireless communication devices, methods of manufacture, and methods of filtering are disclosed.