Lamb Wave Device Frequency Stability via Film Thickness Optimization
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Solution Overview
Problem
Lamb wave devices face significant frequency variations due to thickness variations in piezoelectric thin films, which are exacerbated by the dispersibility of sonic velocity with respect to film thickness, leading to unstable resonant frequencies.
Innovation Solution
A lamb wave device is designed with a piezoelectric thin film and an IDT electrode, where the film thickness and electrode pitch are optimized to minimize the change coefficient of sonic velocity with respect to film thickness ratio, and a support structure with a cavity is used to isolate the excitation section, reducing etching rates and further stabilizing the frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the film thickness of the piezoelectric thin film is reduced to increase frequency, then the frequency increases, but the variations in frequency due to processing variations become large
Solution Approach 1:
The patent changes the operating parameters by selecting specific film thickness and wavelength ratios (h/λ) that correspond to minima in the dispersion curve where the change coefficient of sonic velocity is small. This parameter optimization reduces the sensitivity of frequency to film thickness variations, thereby improving frequency stability while maintaining high frequency operation.
2Speed
If the film thickness is reduced to several micrometers to achieve several GHz frequency, then the frequency reaches several GHz, but the variations in film thickness cause large variations in frequency
Solution Approach 1:
The patent optimizes the film thickness to wavelength ratio (h/λ) to specific values that minimize the change coefficient of sonic velocity. By operating at these optimized parameter points, the system achieves several GHz frequency while reducing the impact of manufacturing variations in film thickness on frequency stability.
3Speed
If the sonic velocity has dispersibility with respect to film thickness, then the lamb wave can propagate, but the influence of film thickness variations on resonant frequency becomes significant
Solution Approach 1:
The patent addresses the dispersibility issue by selecting specific operating points where the change coefficient of sonic velocity with respect to h/λ is minimized. This parameter optimization reduces the influence of film thickness variations on resonant frequency while maintaining effective lamb wave propagation.
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 results in reduced frequency variations by minimizing the influence of film thickness on sonic velocity, thereby stabilizing the resonant frequency and improving the device's performance.
Implementation Method 1
a piezoelectric thin film; an IDT electrode which is provided on a main surface of the piezoelectric thin film
Data Source
AI summary
There is provided a lamb wave device with small variations in frequency, the device including: a piezoelectric thin film; an IDT electrode which is provided on a main surface of the piezoelectric thin film; and a support structure which supports a laminate of the IDT electrode and the piezoelectric thin film, and is formed with a cavity that isolates the laminate, wherein a film thickness h of the piezoelectric thin film and a pitch p of a finger of the IDT electrode are selected such that a lamb wave is excited at a target frequency, the lamb wave making dispersibility of a sonic velocity v with respect to the film thickness h of the piezoelectric thin film small.