BAW Resonator Leaky Reflector for BO Mode Suppression
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators face challenges in achieving a balance between quality factor and BO mode suppression due to the introduction of undesirable modes by border ring (BO) structures, which can impact filter performance and insertion loss, especially in wide bandwidth and multiplexing applications.
Innovation Solution
The BAW resonator incorporates a border ring (BO) structure with a leaky reflector design, featuring high acoustic impedance layers embedded in a low acoustic impedance region, and a dual-step configuration of the BO structure to suppress BO modes by allowing them to leak into the substrate, thereby maintaining a high quality factor and reducing undesirable modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a border ring (BO) structure is introduced to suppress spurious modes, then filter performance is improved, but BO modes are introduced which degrade quality factor and increase insertion loss
Solution Approach 1:
The reflector is segmented into multiple high acoustic impedance layers (first high acoustic impedance layer and second high acoustic impedance layer) separated by a low acoustic impedance region. This segmentation allows different portions of the reflector to handle different acoustic modes differently, enabling suppression of BO modes while maintaining high quality factor for the fundamental mode.
Solution Approach 2:
The first high acoustic impedance layer is designed with a width smaller than the top electrode structure width, creating a localized high impedance region that specifically targets BO mode suppression without affecting the fundamental mode resonance. This local quality modification allows selective mode control.
2Reliability
If a border ring (BO) structure is introduced to suppress spurious modes, then filter performance is improved, but the quality factor decreases due to BO modes
Solution Approach 1:
The reflector is divided into multiple high acoustic impedance layers with a low acoustic impedance region between them. This segmentation creates a structured acoustic environment that selectively suppresses BO modes while preserving the fundamental mode, thereby maintaining high quality factor.
Solution Approach 2:
The first high acoustic impedance layer is localized with a width smaller than the top electrode structure, creating a targeted intervention that suppresses BO modes without introducing significant losses to the fundamental mode, thus preserving quality factor.
3Reliability
If high acoustic impedance layers are added to suppress BO modes, then device complexity increases, but manufacturing precision requirements are intensified
Solution Approach 1:
The reflector is segmented into discrete high acoustic impedance layers separated by a low acoustic impedance region. This segmentation into distinct manufacturable layers with clear interfaces simplifies the manufacturing process compared to creating a continuously varying impedance profile, while still achieving effective BO mode suppression.
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 effectively suppresses BO modes while maintaining a high quality factor, enhancing the performance of BAW resonators for wide bandwidth filtering and multiplexing applications by balancing quality factor and BO mode suppression.
Implementation Method 1
the leaky reflector with a first high acoustic impedance layer and a second high acoustic impedance layer embedded in a low acoustic impedance region
Implementation Method 2
a piezoelectric layer over the bottom electrode
Data Source
AI summary
The present disclosure relates to a bulk acoustic wave (BAW) resonator that includes a bottom electrode, a top electrode structure with a border ring (BO) structure, a piezoelectric layer sandwiched between the bottom electrode and the top electrode, and a reflector with a high acoustic impedance layer embedded in a low acoustic impedance region. Herein, the BO structure is formed about a periphery of the top electrode structure and defines a BO region of the BAW resonator. The high acoustic impedance layer is vertically underneath the bottom electrode and is separated from the bottom electrode by a first portion of the low acoustic impedance region. A width of the first high acoustic impedance layer is smaller than a width of the top electrode structure, such that the first high acoustic impedance layer does not extend completely through the BO region of the BAW resonator.