SH-Wave Acoustic Reflector Layout for Rayleigh Spurious Suppression
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Solution Overview
Problem
Acoustic wave devices using SH waves as a principal mode suffer from spurious responses due to Rayleigh waves, which deteriorate attenuation and reflection characteristics, and existing solutions do not adequately suppress these unwanted responses.
Innovation Solution
The design includes a piezoelectric substrate with a lithium tantalate layer, an IDT electrode, and paired reflectors with electrode fingers of different widths, where the distances between the centers of four consecutive electrode fingers are equal, to reduce or prevent spurious responses by making the Rayleigh wave mode asymmetric.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reflector design with uniform electrode fingers is used, then device structure is simple, but spurious response due to Rayleigh waves occurs deteriorating attenuation and reflection characteristics
Solution Approach 1:
The reflector employs electrode fingers with alternating different widths (first width and second width) rather than uniform widths. This asymmetric design creates a reflector structure that is not periodic in the same way as conventional designs, which suppresses the generation of Rayleigh waves and eliminates spurious responses while maintaining effective acoustic wave reflection.
Solution Approach 2:
Different portions of the reflector (different electrode fingers) have different local properties (different widths). This local variation in electrode finger width creates zones of different acoustic impedance that collectively suppress Rayleigh wave propagation while maintaining the overall reflector function.
2Reliability
If uniform electrode finger widths are used in reflectors, then manufacturing is easier, but spurious responses occur near 0.75 times the resonant frequency
Solution Approach 1:
The alternating width pattern of electrode fingers creates an asymmetric structure that disrupts the periodicity required for Rayleigh wave propagation. This design suppresses spurious responses at frequencies near 0.75 times the resonant frequency while the alternating pattern can be implemented using standard photolithography and etching processes.
Solution Approach 2:
The electrode finger width parameter is varied in an alternating pattern (first width, second width, first width, second width) along the reflector. This parameter change creates the necessary asymmetry to suppress Rayleigh waves while maintaining compatibility with conventional semiconductor manufacturing processes.
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 effectively reduces or prevents spurious responses due to Rayleigh waves, improving the attenuation and reflection characteristics of the acoustic wave devices, band pass filters, duplexers, and multiplexers.
Implementation Method 1
a piezoelectric layer made of lithium tantalate
Implementation Method 2
an IDT electrode on the piezoelectric substrate, and paired reflectors on both sides of the IDT electrode
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate including a piezoelectric layer made of lithium tantalate, an IDT electrode on the piezoelectric substrate, and a pair of reflectors on both sides of the IDT electrode on the piezoelectric substrate in an acoustic wave propagation direction. SH waves are used as a principal mode. The IDT electrode includes electrode fingers and the pair of reflectors each including electrode fingers. When a length along a direction orthogonal to a direction in which the electrode fingers extend is a width, each of the reflectors includes first and second electrode fingers having different widths. Four consecutive electrode fingers, which are any four of the electrode fingers of each of the reflectors, include both of the first and second electrode fingers and distances between centers of the four consecutive electrode fingers are equal or substantially equal.