Dual-Sided Lateral Bulk Wave Resonator for Parasitic Mode Suppression
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Solution Overview
Problem
Existing laterally excited bulk wave resonators suffer from parasitic modes such as S0 and A0 near the A1 mode, leading to cluttered admittance characteristic curves and energy leakage, which significantly affect the quality factor of the device.
Innovation Solution
A laterally excited bulk wave resonator design is proposed, featuring a supporting plate, a piezoelectric base with a cavity, and interdigital transducers on both sides of the piezoelectric base. The transducers have the same polarity, and a metallized through hole connects the bus bars, effectively counteracting parasitic modes by canceling polarization electric fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-sided interdigital transducer configuration is used, then the device structure is simple, but parasitic modes (S0 and A0) cause cluttered admittance curves and energy leakage
Solution Approach 1:
The single interdigital transducer is segmented into two separate transducers positioned on opposite sides of the piezoelectric substrate. Each transducer has interdigital electrodes that can be independently configured, allowing the system to generate and control multiple acoustic wave modes simultaneously. This segmentation enables selective excitation of the desired A1 mode while suppressing parasitic S0 and A0 modes through proper phasing and polarity configuration.
Solution Approach 2:
The patent employs asymmetric positioning of the two interdigital transducers on opposite sides of the substrate, with each transducer having a specific orientation and polarity configuration. The interdigital electrodes are arranged with different polarities on opposite sides, creating an asymmetric electric field distribution that selectively excites the A1 mode while canceling out parasitic modes through destructive interference.
2Reliability
If opposite polarity electrodes are used on both sides, then parasitic modes are suppressed, but the electrical connection complexity increases
Solution Approach 1:
The patent transitions from a planar electrical connection approach to a three-dimensional configuration by routing electrical connections through the thickness of the substrate. metallized through holes provide vertical electrical pathways that connect the interdigital electrodes on opposite sides, enabling complex polarity configurations without increasing lateral connection complexity. This dimensional transition allows independent polarity control of each transducer.
Solution Approach 2:
metallized through holes serve as intermediary elements that facilitate electrical connection between the two interdigital transducers on opposite sides of the substrate. These through holes, filled with conductive material, act as electrical bridges that enable the complex polarity configurations required for parasitic mode suppression while keeping the overall device structure manageable.
3Volume of moving object
If traditional BAW or FBAR technology is used, then the device is compact, but relative bandwidth is limited to less than 8%
Solution Approach 1:
The patent changes the fundamental operating parameters by transitioning from vertical acoustic wave propagation in traditional BAW/FBAR devices to lateral acoustic wave propagation in the piezoelectric substrate. This parameter change enables the use of Love waves or shear horizontal waves that inherently provide broader bandwidth operation while maintaining compact device dimensions. The lateral wave propagation mode allows for greater control over frequency response and bandwidth characteristics.
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 proposed design reduces parasitic clutter on the admittance curve and enhances the quality factor of the resonator, achieving a higher electromechanical coupling coefficient and improved frequency stability.
Implementation Method 1
a piezoelectric base (2)... a lower interdigital transducer (4) provided at a back side of the piezoelectric base (2)... an upper interdigital transducer (5) provided at a front side of the piezoelectric base (2)... such that a laterally excited wave, that is, an A1-mode Lamb wave, may be generated
Implementation Method 2
The A1 mode has high sound speed and a large electromechanical coupling coefficient... A first interdigital electrode of the lower interdigital transducer (4) has a same polarity as a second interdigital electrode of the upper interdigital transducer (5) at a position corresponding to the first interdigital electrode
Data Source
AI summary
A laterally excited bulk wave resonator includes a supporting plate; a piezoelectric base having a back side attached to the supporting plate, in which a cavity is defined on a side of the supporting plate facing toward the piezoelectric base; a lower interdigital transducer provided at a back side of the piezoelectric base and located in the cavity; and an upper interdigital transducer provided at a front side of the piezoelectric base corresponding to the lower interdigital transducer. A first interdigital electrode of the lower interdigital transducer has a same polarity as a second interdigital electrode of the upper interdigital transducer at a position corresponding to the first interdigital electrode.