SAW Resonator SiO2 Opening Layout for Transverse Mode Suppression
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Solution Overview
Problem
Suppression of high-order transverse mode spurious signals and ensuring a satisfactory quality factor (Q) have been challenging in surface acoustic wave (SAW) resonators with heavier electrodes on lower-cut-degree rotated Y-cut LiNbO3 substrates, which are covered with a SiO2 film for temperature compensation.
Innovation Solution
A surface acoustic wave resonator design featuring interdigital transducer electrodes with bus bar, gap, and overlapping regions, where the SiO2 film exposes specific regions to form a phase velocity distribution that confines oscillation energy within the overlapping region, suppressing high-order transverse modes and maintaining a desired Q factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a SiO2 film is provided to cover the IDT electrodes for temperature compensation, then temperature stability is improved, but high-order transverse mode spurious signals are generated
Solution Approach 1:
The patent applies local quality by creating a non-formation region (opening) in the SiO2 film at specific portions in the transverse direction. This selective removal of the dielectric film allows different regions to have different functions: the covered regions provide temperature compensation while the exposed regions suppress high-order transverse mode spurious signals by altering the boundary conditions for acoustic wave propagation.
2Reliability
If heavier electrodes (Mo) are used to ensure high electromechanical coupling, then coupling coefficient is improved, but suppression of high-order transverse modes becomes more difficult
Solution Approach 1:
The patent combines heavier electrodes (Mo) for high electromechanical coupling with selective SiO2 film removal. The heavier electrodes provide strong coupling in the propagation direction, while the opening regions in the SiO2 film create specific boundary conditions that suppress high-order transverse modes, allowing both requirements to be satisfied simultaneously through spatial differentiation.
3Object-generated harmful factors
If the SiO2 film is completely removed to suppress transverse modes, then spurious signal suppression is improved, but temperature compensation is lost
Solution Approach 1:
The patent maintains temperature compensation by keeping the SiO2 film covering the IDT electrodes in most regions, while selectively removing it only in specific portions in the transverse direction. This partial removal strategy allows the film to provide temperature compensation where needed while creating opening regions that suppress high-order transverse mode spurious signals, thus resolving the contradiction between complete removal and complete coverage.
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 effectively suppresses high-order transverse mode spurious signals and ensures a satisfactory quality factor, leading to improved operating characteristics of the SAW resonator.
Implementation Method 1
a silicon dioxide (SiO2) film 12 is disposed on the substrate 11 to cover the IDT electrodes 20
Implementation Method 2
interdigital transducer (IDT) electrodes 20 are disposed on an upper surface of a rotated Y-cut LiNbO3 substrate
Implementation Method 3
heavier electrode including, for example, Mo for ensuring high electromechanical coupling
Data Source
AI summary
Aspects of this disclosure relate to a surface acoustic wave resonator that may include a piezoelectric substrate, interdigital transducer (IDT) electrodes disposed on an upper surface of the piezoelectric substrate, and a dielectric film covering the piezoelectric substrate and the IDT electrode for temperature compensation. The IDT electrodes may include bus bar electrode regions spaced apart from each other in a transverse direction perpendicular to a propagation direction of a surface acoustic wave to be excited, an overlapping region sandwiched between the bus bar regions, and gap regions defined between respective bus bar electrode regions and the overlapping region in the transverse direction. Each of the gap regions may include a dummy electrode in a dummy electrode region extending from the bus bar electrode region in the transverse direction. The dielectric film may include an open region exposing a respective bus bar electrode region and dummy electrode region.