LiTaO3 Elastic Wave Structure for Higher-Order Mode Suppression
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Solution Overview
Problem
Elastic wave devices using silicon substrates face significant higher-order mode responses due to the crystal orientation and acoustic velocity of the silicon substrate, which affect the performance of high-frequency front-end circuits and communication devices.
Innovation Solution
The elastic wave device incorporates a silicon support substrate with a piezoelectric LiTaO3 film and an interdigital transducer electrode, where the higher-order mode acoustic velocity is set equal to or greater than the acoustic velocity through the silicon substrate, and the film thickness of the LiTaO3 film is optimized within specific ranges to reduce higher-order mode responses, along with the use of a dielectric silicon oxide film to further minimize these modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon substrate is used as the support substrate, then the device can be manufactured with existing semiconductor processes, but higher-order mode responses become significant affecting device performance
Solution Approach 1:
A SiO2 film is introduced as an intermediary layer between the silicon substrate and the LiTaO3 piezoelectric film. This intermediate layer modifies the acoustic wave propagation characteristics, preventing higher-order mode responses while maintaining the benefits of silicon substrate manufacturing. The SiO2 film acts as a mediator that decouples the conflicting requirements of ease of manufacture and device performance.
Solution Approach 2:
The device employs a composite structure combining silicon substrate, SiO2 film, and LiTaO3 piezoelectric film. This multi-material composite approach leverages the manufacturing advantages of silicon while adding layers with specific acoustic properties (SiO2) and piezoelectric properties (LiTaO3) to achieve the desired performance characteristics and suppress higher-order modes.
2Power
If the LiTaO3 film thickness is increased to improve piezoelectric coupling, then the main mode response is enhanced, but higher-order mode responses become more significant
Solution Approach 1:
The patent optimizes the thickness parameter of the LiTaO3 film to a specific range (0.3λ to 1.0λ) where λ is the acoustic wavelength. This parameter optimization achieves a balance between sufficient piezoelectric coupling for main mode response and suppression of higher-order modes. Additionally, the SiO2 film thickness is optimized to further control acoustic wave propagation and eliminate higher-order mode responses.
3Reliability
If the silicon substrate crystal orientation is changed to reduce higher-order modes, then device performance improves, but manufacturing complexity increases
Solution Approach 1:
The SiO2 film serves as an intermediary that compensates for the acoustic coupling between the silicon substrate and LiTaO3 film. This allows the use of standard silicon substrate orientations (such as <100>) without requiring precise crystal orientation control, as the SiO2 layer decouples the acoustic interaction and suppresses higher-order mode responses regardless of the substrate orientation.
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 higher-order mode responses, improves the Q factor of the main mode, and minimizes the absolute temperature coefficient of the resonant frequency, enhancing the performance of high-frequency front-end circuits and communication devices.
Implementation Method 1
a piezoelectric film disposed directly or indirectly on the support substrate
Implementation Method 2
a higher-order mode acoustic velocity of propagation through the piezoelectric film is equal or substantially equal to the acoustic velocity Vsi denoted by formula (1)
Data Source
AI summary
An elastic wave device includes a support substrate made of silicon, a piezoelectric film disposed directly or indirectly on the support substrate, and an interdigital transducer electrode disposed on one surface of the piezoelectric film. A higher-order mode acoustic velocity of propagation through the piezoelectric film is equal or substantially equal to an acoustic velocity Vsi=(V1)1/2 of propagation through silicon or higher than the acoustic velocity Vsi, where Vsi is specified by V1 among solutions V1, V2, and V3 with respect to x derived from Ax3+Bx2+Cx+D=0.