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 that lead to raised frame modes and inadequate energy confinement.
Innovation Solution
The BAW device incorporates a piezoelectric layer with a recess outside the active region, surrounded by a frame structure, which includes a raised frame structure to suppress symmetric modes and a recessed frame structure to reduce mass loading, thereby enhancing energy confinement and reducing lateral energy leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a frame structure is added to confine energy, then energy confinement is improved, but device complexity increases
Solution Approach 1:
The patent implements nested frame structures where an outer frame structure and an inner frame structure are positioned at different heights above the piezoelectric layer. The inner frame structure is nested within the region defined by the outer frame structure, creating a hierarchical confinement system that enhances energy confinement while managing device complexity through structured nesting.
Solution Approach 2:
The patent addresses energy confinement by transitioning from a two-dimensional planar confinement approach to a three-dimensional approach with frames positioned at different heights. The outer frame structure and inner frame structure are disposed at different vertical positions, adding a height dimension to the confinement mechanism and improving energy confinement effectiveness.
2Weight of stationary object
If the piezoelectric layer thickness is reduced outside the active region, then mass loading is reduced, but structural strength may be compromised
Solution Approach 1:
The patent applies local quality by creating a recess in the piezoelectric layer specifically in the region outside the active region between the outer and inner frame structures. This localized thinning reduces mass loading in the peripheral area while the active region maintains its full thickness to preserve structural strength and functional performance.
3Reliability
If spurious modes are suppressed through geometric modifications, then quality factor increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent suppresses spurious modes by segmenting the frame structure into distinct outer and inner components positioned at different heights. This segmentation creates discrete acoustic paths and prevents the formation of unwanted symmetric modes, improving quality factor while maintaining manufacturability through modular structure definition.
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 design significantly increases the quality factor (Q) and maintains a stable electromechanical coupling coefficient (kt2), effectively suppressing spurious modes and improving performance in radio frequency applications.
Implementation Method 1
In BAW resonators, acoustic waves propagate in the bulk of a piezoelectric layer
Implementation Method 2
The acoustic reflector can be an air cavity
Data Source
AI summary
Aspects of this disclosure relate to methods of manufacturing a bulk acoustic wave device. Such methods can include forming a piezoelectric layer over a first electrode such that the piezoelectric layer has a recess. A second electrode can be deposited over the piezoelectric layer such that the recess is outside of a region in which the first electrode and the second electrode overlap and are on opposing sides of the piezoelectric layer. Related acoustic wave filters, multiplexers, radio frequency modules, radio frequency systems, wireless communication devices, and methods of filtering are disclosed.