Elastic Wave Filter IDT Tilt Angle Optimization
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Solution Overview
Problem
Elastic wave filter devices with tilted interdigital transducers (IDTs) face challenges in achieving sufficient steepness of filter characteristics, as they often generate transverse mode ripples and fail to effectively reduce or prevent these ripples.
Innovation Solution
The elastic wave filter device incorporates a piezoelectric film made of a piezoelectric single crystal laminated on a high acoustic velocity member, with IDT electrodes having tilt angles that differ between serial and parallel arm resonators, specifically with smaller tilt angles for serial arm resonators to improve lower frequency side steepness and larger tilt angles for parallel arm resonators to enhance higher frequency side steepness, effectively reducing transverse mode ripples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a tilted IDT is used in the elastic wave device having a lamination structure, then transverse modes are reduced or prevented, but sufficient steepness of the filter characteristics cannot be obtained
Solution Approach 1:
The patent applies different tilt angles to different groups of IDT electrodes: serial arm resonators use a first tilt angle while parallel arm resonators use a second tilt angle. This local differentiation allows each resonator type to be optimized for its specific function, with the serial arm resonators controlling transverse modes and the parallel arm resonators providing the necessary filter steepness.
Solution Approach 2:
The filter is segmented into multiple resonators with different IDT configurations. By dividing the filter into serial arm resonators and parallel arm resonators with distinct tilt angles, the patent achieves both transverse mode suppression and adequate filter steepness through the combined response of the segmented components.
2Object-affected harmful factors
If the tilt angle is increased to reduce transverse mode ripples, then transverse modes are suppressed, but the Q-value decreases and filter steepness deteriorates
Solution Approach 1:
Different tilt angles are assigned to different resonator groups based on their functional requirements. Serial arm resonators use a larger tilt angle for transverse mode suppression, while parallel arm resonators use a smaller tilt angle to maintain high Q-values and ensure filter steepness.
Solution Approach 2:
The patent changes the tilt angle parameter across different resonator groups rather than using a uniform value. This parameter variation allows optimization of both transverse mode suppression and Q-value maintenance by selecting appropriate tilt angles for each resonator type.
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 configuration improves the steepness of filter characteristics on both lower and higher frequency sides by optimizing the Q-value and reducing transverse mode ripples, thereby enhancing the performance of the elastic wave filter device.
Implementation Method 1
an elastic wave filter device using a piezoelectric film
Implementation Method 2
a plurality of IDT electrodes provided to be in contact with the piezoelectric film
Implementation Method 3
a high acoustic velocity member in which an acoustic velocity of a propagating bulk wave is larger than an acoustic velocity of a main mode elastic wave propagating in the piezoelectric film
Data Source
AI summary
An elastic wave filter device includes a piezoelectric film, a high acoustic velocity support substrate in which an acoustic velocity of a propagating bulk wave is larger than an acoustic velocity of a main mode elastic wave propagating in the piezoelectric film, and IDT electrodes in contact with the piezoelectric film. A serial arm resonator and a parallel arm resonator are defined by the IDT electrodes such that, a direction in which tips of first and second electrode fingers are connected defines a tilt angle with respect to a propagation direction of elastic waves excited by the IDT electrodes. A tilt angle of the serial arm resonator is different from a tilt angle of the parallel arm resonator.