BAW Ladder Filter Frame Structure for Spurious Wave Suppression
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Solution Overview
Problem
Acoustic wave devices, particularly bulk acoustic wave (BAW) filters, face challenges in mitigating spurious signals due to transverse acoustic waves generated by the non-zero Poisson's ratio of piezoelectric materials, which degrade frequency response and are undesirable.
Innovation Solution
The design incorporates film bulk acoustic wave resonators with a central active domain and recessed frame regions, along with raised frame regions that contribute to dissipation and scattering of transverse waves, preventing them from entering the main active domain and inducing spurious signals, thereby enhancing the frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If raised frame regions are added to suppress spurious signals, then frequency response is improved, but device complexity increases
Solution Approach 1:
The resonator structure is segmented into distinct functional regions: a central active domain for acoustic wave generation and surrounding raised frame regions for spurious signal suppression. This segmentation allows each region to perform its specific function independently, improving frequency response while maintaining manageable structural complexity through modular design.
Solution Approach 2:
Different regions of the resonator are given different structural properties: the central region has uniform thickness for optimal acoustic wave generation, while the peripheral frame regions have increased thickness to provide mechanical barriers against spurious waves. This local differentiation of structural quality enables targeted suppression of unwanted signals without affecting the main active domain.
2Object-generated harmful factors
If raised frame regions are added to scatter transverse waves, then spurious signals are suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The raised frame regions are pre-configured during manufacturing to create mechanical barriers before spurious signals can propagate. By establishing these structural features in advance during the fabrication process, the design prevents spurious signal generation at the source rather than requiring complex post-manufacturing adjustments or corrections.
Solution Approach 2:
The frame height parameter is specifically increased relative to the central active domain to create an effective mechanical barrier. This parameter change transforms the flat resonator structure into one with elevated peripheral regions that physically block transverse wave propagation, achieving spurious signal suppression through a single key dimensional modification that can be integrated into existing manufacturing processes.
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 configuration effectively suppresses spurious signals, improving the frequency response by creating a barrier that reflects and scatters transverse waves, leading to reduced insertion loss and increased quality factor, especially in ultrawide bandwidth filter implementations.
Implementation Method 1
each of the plurality of series arm film bulk acoustic wave resonators and each of the plurality of shunt film bulk acoustic wave resonators include a piezoelectric film disposed in a central region defining a main active domain in which a main acoustic wave is generated during operation
Implementation Method 2
raised frame regions that contribute to dissipation and scattering of transverse waves, preventing them from entering the main active domain and inducing spurious signals
Implementation Method 3
raised frame regions that contribute to dissipation and scattering of transverse waves
Data Source
AI summary
A ladder filter comprises a plurality of series arm bulk acoustic wave resonators electrically connected in series between an input port and an output port of the ladder filter and a plurality of shunt bulk acoustic wave resonators electrically connected in parallel between adjacent ones of the plurality of series arm bulk acoustic wave resonators and ground, at least one of the plurality of shunt bulk acoustic wave resonators including raised frame regions having a first width, at least one of the plurality of series arm bulk acoustic wave resonators having one of raised frame regions having a second width less than the first width or lacking raised frame regions.