Lithium Niobate Filter Layout for Higher Q and Lower Spurious
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Solution Overview
Problem
The transmission characteristics of filters using monocrystalline piezoelectric substances like lithium niobate and lithium tantalate for thickness-shear vibration in high-frequency circuits, such as mobile phones, require improvement.
Innovation Solution
A filter design incorporating a series resonator and a parallel resonator with specific crystal orientations and electrode configurations for the piezoelectric layers, where the electrodes are extracted in directions corresponding to the vibration direction or orthogonal to it, enhancing the Q factor and reducing spurious emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monocrystalline piezoelectric substances are used for thickness-shear vibration in filter resonators, then the filter can operate at high frequencies suitable for wireless terminals, but the transmission characteristics (Q factor, insertion loss, spurious emissions) require improvement
Solution Approach 1:
The patent applies local quality by specifying precise crystal orientation directions for different resonator types within the filter. Series resonators use a first crystal orientation direction while parallel resonators use a second crystal orientation direction, allowing each resonator type to be optimized for its specific function. This directional differentiation improves transmission characteristics by enhancing Q factors and reducing spurious emissions without requiring complete redesign of the entire filter structure.
Solution Approach 2:
The patent changes the crystal orientation parameter as a key variable to improve transmission characteristics. By rotating the crystal orientation by a specific angle (e.g., 45 degrees) between series and parallel resonators, the patent optimizes the piezoelectric coupling and mechanical vibration modes. This parameter change directly affects the Q factor at resonant and antiresonant frequencies, thereby improving insertion loss and reducing spurious emissions.
2Reliability
If electrodes are extracted in directions corresponding to the vibration direction, then the Q factor increases, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-determining the crystal orientation and electrode extraction direction during the design and fabrication process. The piezoelectric layer is deposited with a specified crystal orientation, and electrodes are subsequently formed in predetermined directions relative to this orientation. This preliminary establishment of geometric parameters ensures that the vibration direction aligns with the electrode extraction direction, maximizing the Q factor while providing clear manufacturing guidelines that reduce precision requirements during actual production.
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 design improves the transmission characteristics by increasing the Q factor at resonant and antiresonant frequencies, leading to better insertion loss in the passband and reduced spurious emissions, thus enhancing the overall performance of the filter.
Implementation Method 1
The piezoelectric thin film resonator includes a piezoelectric layer, and a pair of electrodes with the piezoelectric layer interposed therebetween. The region where the pair of electrodes are opposite to each other across the piezoelectric layer is a resonance region where the acoustic wave resonates.
Data Source
AI summary
A filter includes a series resonator including a first piezoelectric layer and first electrodes, and a parallel resonator including a second piezoelectric layer and second electrodes. Each of the first and second piezoelectric layers is a monocrystalline lithium niobate layers, has an X-axis orientation in a planar direction, and has a thickness direction in a direction obtained by a 105° rotation of a +Z-axis orientation toward a +Y-axis orientation. The first electrodes face each other across the first piezoelectric layer to form a first resonance region and are extracted from the first resonance region in a direction substantially parallel to the X-axis orientation of the first piezoelectric layer. The second electrodes face each other across the second piezoelectric layer to form a second resonance region and are extracted from the second resonance region in a direction substantially orthogonal to the X-axis orientation of the second piezoelectric layer.