BAW Resonator Acoustic Reflector Mass Loading for Frequency Tuning
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Solution Overview
Problem
Conventional BAW resonators face challenges in achieving multiple operating frequencies on a single die due to manufacturing complexities and precision requirements, particularly in thickness variations of deposited layers, which affect frequency tuning and increase costs.
Innovation Solution
The introduction of an acoustic impedance modulation layer (AIML) composed of semiconductor material with varying dopant concentration, embedded in the reflective element, allows for tuning of operating frequencies without precise thickness deposition, enhancing acoustic confinement and reducing manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency tuning is achieved by adjusting the inter-digit transducer (IDT) electrode pattern, then frequency selectivity is improved, but manufacturing complexity and cost increase due to requiring new combs for each frequency
Solution Approach 1:
The patent extracts the frequency tuning function from the IDT electrode pattern and relocates it to the acoustic reflector mass loading elements. This separation allows the IDT to remain fixed while frequency adjustment is achieved by modifying the reflector structure, thereby reducing manufacturing complexity while maintaining frequency selectivity
Solution Approach 2:
The patent changes the physical parameter being adjusted for frequency tuning from the IDT electrode geometry to the mass loading elements in the acoustic reflector. By varying the mass, area, or position of these elements, frequency tuning is achieved through parameter modification rather than structural redesign, simplifying manufacturing
2Measurement precision
If frequency tuning is achieved by adjusting the IDT electrode pattern, then frequency selectivity is improved, but production time and cost increase due to multiple manufacturing steps
Solution Approach 1:
The patent performs preliminary action by pre-configuring the acoustic reflector with mass loading elements that can be adjusted after the main resonator structure is formed. This allows the bulk of manufacturing to be completed once, with frequency tuning achieved through subsequent simpler adjustments, thereby improving production efficiency
Solution Approach 2:
The patent segments the resonator into distinct functional components: the main resonator structure and the adjustable acoustic reflector with mass loading elements. This segmentation allows independent optimization and manufacturing of each component, with the reflector serving as a separate tuning element that can be adjusted without remanufacturing the entire device
3Measurement precision
If frequency tuning is achieved by adjusting the IDT electrode pattern, then frequency selectivity is improved, but device reliability decreases due to more manufacturing steps and potential defects
Solution Approach 1:
The patent extracts the frequency tuning function from the IDT electrode pattern and relocates it to the acoustic reflector mass loading elements. This separation reduces the number of critical manufacturing steps in the IDT, thereby improving device reliability while maintaining frequency selectivity through the reflector adjustments
Solution Approach 2:
The patent changes the tuning mechanism from geometric modifications of the IDT electrode pattern to parameter adjustments of the mass loading elements (mass, area, position). This approach requires fewer precise manufacturing steps and reduces the risk of manufacturing defects, thereby improving reliability while achieving the same frequency selectivity
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 enables efficient generation of multiple frequencies on a single die with reduced manufacturing complexity and cost, improving acoustic confinement and reducing signal interference.
Implementation Method 1
the acoustic reflector 142 may be configured to reflect acoustic waves generated by the inter-digit transducer 122 back toward the inter-digit transducer 122
Implementation Method 2
adjusting a frequency of acoustic waves generated by the inter-digit transducer 122 by adjusting a mass, an area, or a position of one or more mass loading elements 144
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A bulk acoustic wave, BAW, resonator (100) on a substrate (102), comprising a piezoelectric element (104), a bottom electrode (106) on a first face (104A) of the piezoelectric element and a top electrode (108) on a second face (104B) of the piezoelectric element facing away from the first face is provided. The BAW resonator further comprises a reflective element (112) between the bottom electrode and the substrate. The said reflective element comprises at least a first layer (114A,114B) of a first material having a first acoustic impedance and a second layer of a second material having a second acoustic impedance different from the first acoustic impedance. The first or the second layer comprises one or more structures (116A,B,C) of a third material, having a third acoustic impedance different from the first and second impedances. The said structures form an acoustic impedance modulation layer embedded in the first and/or the second layer and allow frequency tuning of the resonator by mass loading. By differently patterning the third structures resonators on the same die may be precisely tuned to different frequencies for ladder or lattice filters without relying on thickness control of particular layers. By asymmetrically arranging the frequency tuning structures (116A,B,C) additionally lateral modes may be suppressed.