Piezoelectric Thin-Film Lamb Wave Structure for Spurious Suppression
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Solution Overview
Problem
Lamb wave devices using piezoelectric thin films face challenges in achieving high bandwidth while suppressing spurious responses, which are often generated in the pass band or attenuation band.
Innovation Solution
A Lamb wave device with a piezoelectric thin film of LiTaO3 or LiNbO3, where the c-axis is aligned perpendicular to the surfaces, and an IDT electrode made of Al or its alloy, with specific thickness ratios between the electrode and film, is used to suppress spurious responses by employing a rotation twin crystal structure, thereby enhancing electromechanical coupling and frequency properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Lamb wave device uses a piezoelectric thin film with an IDT electrode to increase the electromechanical coupling coefficient, then the bandwidth is improved, but spurious responses are generated in the pass band or attenuation band
Solution Approach 1:
The piezoelectric thin film is divided into multiple domains with different polarization directions (180-degree domains and 90-degree domains), creating a segmented structure that suppresses spurious responses while maintaining high electromechanical coupling coefficient for improved bandwidth
Solution Approach 2:
The invention uses a composite structure combining piezoelectric thin film with specific domain patterns and IDT electrodes, creating a multi-domain composite material system that achieves both high coupling coefficient and spurious response suppression
2Reliability
If the piezoelectric thin film thickness is increased to improve frequency properties, then the electromechanical coupling coefficient increases, but the device complexity increases
Solution Approach 1:
The invention optimizes the piezoelectric thin film thickness to a specific range (0.05λ to 0.2λ where λ is the acoustic wavelength) to achieve the optimal balance between electromechanical coupling coefficient and frequency properties, avoiding excessive complexity in manufacturing
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 device achieves superior frequency properties with reduced spurious responses, allowing for a central frequency of 2 GHz to 10 GHz and a fractional band width of 1% to 10%, and provides improved environmental resistance by preventing metal powder adhesion.
Implementation Method 1
devices using various waves excited using a piezoelectric effect have been proposed and used
Implementation Method 2
the Lamb wave is one type of bulk wave, that is, one type of plate wave, and is an elastic wave which propagates in a piezoelectric body while reflecting off two primary surfaces thereof
Data Source
AI summary
A Lamb wave device includes a base substrate, a piezoelectric thin film which is provided on the base substrate and which has a floating portion floating above the base substrate, the floating portion having a first surface facing the base substrate and a second surface opposite to the first surface, and an IDT electrode disposed on at least one of the first and the second surfaces of the piezoelectric thin film. The piezoelectric thin film is made of LiTaO3 or LiNbO3, and the c-axis of the piezoelectric thin film is set in approximately the same direction as that of a line substantially perpendicular to the first and the second surfaces of the piezoelectric thin film, and the crystal structure of the piezoelectric thin film is a rotation twin crystal having the c-axis functioning as the rotation axis.