Gap-Shorted Electro Acoustic Resonator for Transversal Gap Modes
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Solution Overview
Problem
Electro acoustic resonators face challenges in suppressing transversal gap mode excitations and reducing transversal modes, which disrupt filter performance and transition steepness between passband and stopband, especially in material systems like TFSAW, where conventional piston mode approaches are insufficient.
Innovation Solution
The introduction of a gap short structure with conductor strips that electrically shorts the transversal gaps, reducing electrical fields and modifying the acoustic velocity profile to suppress transversal gap mode excitations, while maintaining the same manufacturing steps as the electrode structure, thereby improving resonator performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transversal gap with higher wave velocity is used to reduce leakage of acoustic waves, then acoustic wave leakage is reduced, but wave diffraction excites transversal modes that show up as peaks in admittance curves and dips in filter passband
Solution Approach 1:
The patent modifies the electrical field distribution parameter in the transversal gap region by introducing conductor strips that create a non-uniform field. This changes the boundary conditions for acoustic wave propagation, suppressing the excitation of transversal modes while maintaining the beneficial higher wave velocity effect for reducing acoustic leakage.
Solution Approach 2:
Conductor strips are introduced as intermediary elements within the transversal gaps. These strips act as mediators that modify the electrical field distribution, thereby controlling the acoustic wave behavior and suppressing unwanted transversal mode excitations without eliminating the transversal gap structure itself.
2Ease of manufacture
If conventional piston mode approach is used in TFSAW material systems, then basic resonator function is achieved, but transversal gap modes are not sufficiently suppressed and filter performance is significantly disturbed
Solution Approach 1:
The patent applies local quality modification by introducing conductor strips specifically in the transversal gap regions where transversal modes are excited. The electrode structure has non-uniform properties: the conductor strips are placed locally in the gaps between electrode fingers, creating localized field modification exactly where needed to suppress transversal modes, while the rest of the structure maintains conventional piston mode characteristics.
3Reliability
If additional structures are introduced to suppress transversal gap modes, then filter performance is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The conductor strips forming the gap short structure are merged with the existing electrode structure layers. The same metal layers that form the electrode fingers are also used to create the conductor strips in the transversal gaps, combining multiple functions into a single integrated structure. This eliminates the need for separate additional structures and reduces manufacturing complexity.
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 solution effectively reduces or eliminates transversal gap modes, enhancing filter performance by improving passband ripple reduction, skirt steepness, and insertion attenuation, particularly at frequencies where conventional methods struggle, such as 1963 MHz, 1980 MHz, and 1998 MHz, with over 20 dB suppression of transversal gap modes.
Implementation Method 1
Due to the piezoelectric effect an electro acoustic resonator converts between electromagnetic RF signals and acoustic RF signals
Implementation Method 2
The gap short structure with conductor strips that electrically shorts the transversal gaps, reducing electrical fields and modifying the acoustic velocity profile to suppress transversal gap mode excitations
Data Source
AI summary
An electro acoustic resonator is provided. The resonator has a gap short structure (GSS) to electrically short at least an area of the transversal gap to suppress transversal gap mode excitations. The gap short structure may be provided by a conductive stripe in the gap and parallel to or inclined with respect to the bus bar (BB) shorting adjacent IDT fingers. Additional connectors between the stripe and the bus bar may be provided. The connectors may have different pitch or metallization ratio with respect to the ID fingers. The connectors may be offset from the position of the fingers and my be inclined with respect to the bus bars. Multiple parallel stripes in the gap may provide a transversal reflector. By using a gap short structure a further improved transversal mode suppression of piston mode designs can be achieved.