Quartz SAW Resonator Structure for High Q and Temperature Stability
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Solution Overview
Problem
Existing surface acoustic wave (SAW) resonators face challenges in achieving sufficient Q factors and improved frequency temperature characteristics, with difficulties in controlling groove depths and limited improvements in first-order temperature coefficients of frequency.
Innovation Solution
A resonator design incorporating a piezoelectric layer made from quartz crystal with specific cut-angles and a high acoustic velocity substrate, along with a low acoustic velocity layer and comb-shaped IDT electrode, to enhance frequency temperature and resonance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grooves are formed in spaces between electrode fingers to improve Q factor, then Q factor is improved, but it is difficult to control groove depth sufficiently
Solution Approach 1:
The patent changes the geometric parameters of the IDT electrode by varying the width of electrode fingers and the spacing between them. This parameter adjustment allows control of acoustic wave confinement and Q factor without requiring precise groove depth control, thus resolving the manufacturing precision issue while maintaining reliability improvement
Solution Approach 2:
The patent extracts the groove structure from the design and replaces it with modified IDT electrode geometry. By removing the problematic groove element that difficult to manufacture, the design achieves Q factor improvement through electrode configuration alone, eliminating the manufacturing precision constraint
2Reliability
If a low acoustic velocity film is provided between support substrate and piezoelectric film to improve Q factor, then Q factor is improved, but device structure becomes more complex
Solution Approach 1:
The patent merges the functions of the low acoustic velocity film and the IDT electrode into a single integrated structure. The IDT electrode itself is designed to provide acoustic confinement, combining the roles of electrode and acoustic waveguide, thus improving Q factor without adding separate layers and reducing device complexity
Solution Approach 2:
The IDT electrode is designed to serve multiple functions simultaneously: electrical transduction and acoustic wave confinement. This multi-functional design eliminates the need for separate low acoustic velocity films, improving Q factor while maintaining simple device structure
3Temperature
If thickness of amorphous silicon oxide layer and piezoelectric layer are set to appropriate values to improve frequency temperature characteristics, then first-order temperature coefficient is improved, but there is room for further improvement
Solution Approach 1:
The patent employs parameter optimization of the piezoelectric layer thickness and acoustic wave propagation characteristics to improve frequency temperature characteristics. By carefully selecting the thickness parameter within specific ranges, the design achieves better frequency stability and reduces the first-order temperature coefficient, thereby improving reliability
Solution Approach 2:
The patent uses rotated Y-cut quartz crystal with specific rotation angles to dynamically adjust the acoustic velocity and temperature characteristics. This dynamic parameter selection allows optimization of frequency stability across temperature ranges, improving both temperature characteristics and overall frequency reliability
4Reliability
If acoustic velocity in high acoustic velocity substrate is made higher than in piezoelectric layer to reduce energy leakage, then resonance characteristics are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the material parameter of the substrate by using high acoustic velocity substrate material. This material selection approach achieves acoustic confinement and reduced energy leakage through inherent material properties rather than precise dimensional control, thus improving resonance characteristics without excessively increasing manufacturing precision requirements
Solution Approach 2:
The patent converts the potential harm of acoustic energy leakage into benefit by using the acoustic velocity difference between layers. The higher acoustic velocity in the substrate creates total internal reflection at the interface, turning what could be energy loss into a confinement mechanism that improves resonance 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 design achieves superior Q factors and frequency temperature characteristics, with improved acoustic velocity, electromechanical coupling coefficients, and reduced leakage of vibrational energy, resulting in enhanced performance compared to conventional SAW resonators.
Implementation Method 1
a piezoelectric layer made from a quartz crystal
Implementation Method 2
an acoustic velocity in the high acoustic velocity substrate is higher than an acoustic velocity in the piezoelectric layer... reduced leakage of vibrational energy
Data Source
AI summary
A resonator is provided that includes a piezoelectric layer having a first and second surfaces that oppose each other, an IDT electrode on the first surface of the piezoelectric layer, and a high acoustic velocity substrate on the second surface of the piezoelectric layer. The piezoelectric layer is made from a quartz crystal having cut-angles obtained by rotating a plane orthogonal to a crystal Y-axis about a crystal X-axis, in a propagation direction at 90°±10° to the crystal X-axis of the piezoelectric layer, an acoustic velocity in the high acoustic velocity substrate is higher than an acoustic velocity in the piezoelectric layer, and the IDT electrode includes a comb-shaped electrode including multiple electrode fingers aligned in the propagation direction.