LiNbO3 SH Plate Wave Resonator Layout for Wider Filter Bandwidth
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Solution Overview
Problem
Existing elastic wave devices using SH plate waves in LiNbO3 substrates face limitations in achieving a sufficiently large electromechanical coupling coefficient k2 and fractional bandwidth.
Innovation Solution
The elastic wave device incorporates a LiNbO3 substrate with Euler angles ranging from 92° to 138° and thickness between 0.05λ and 0.25λ, along with IDT electrodes made of specific metals and having a duty ratio within specified ranges, to enhance the electromechanical coupling coefficient and fractional bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiNbO3 substrate with Euler angles (0°, 80° to 160°, 0°) is used, then piezoelectric effect is large, but electromechanical coupling coefficient k2 is not sufficiently large
Solution Approach 1:
The patent changes the Euler angle parameter from the conventional (0°, 80° to 160°, 0°) range to a specific optimized range of (0°, 100° to 120°, 0°), and adjusts the substrate thickness parameter to 0.03λ to 0.06λ. This parameter optimization resolves the contradiction by achieving both large piezoelectric effect and sufficiently large electromechanical coupling coefficient k2 of 0.15 or more.
2Reliability
If LiNbO3 substrate thickness is reduced to enhance SH plate wave, then electromechanical coupling coefficient improves, but fractional bandwidth is limited
Solution Approach 1:
The patent optimizes the substrate thickness parameter to a specific range of 0.03λ to 0.06λ, which balances the electromechanical coupling coefficient and fractional bandwidth. This parameter change enables achieving both k2≥0.15 and fractional bandwidth≥25%, resolving the contradiction between coupling strength and bandwidth.
3Speed
If IDT electrode pitch is adjusted to change wavelength, then operating frequency changes, but electromechanical coupling coefficient and fractional bandwidth are compromised
Solution Approach 1:
The patent establishes the substrate thickness as a fixed proportion of the wavelength (0.03λ to 0.06λ), where λ is determined by the IDT electrode pitch. This proportional relationship ensures that when the pitch and operating frequency are adjusted, the coupling coefficient and bandwidth are maintained within optimal ranges, resolving the contradiction between frequency adjustment and performance maintenance.
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 increases the electromechanical coupling coefficient and fractional bandwidth, enabling the creation of resonators and filters with a larger bandwidth ratio.
Implementation Method 1
a major component of elastic vibration is an SH wave and a piezoelectric effect is large
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4~5
AI summary
Provided is an elastic wave device which makes use of an SH plate wave propagating in LiNbO3 substrates, which can effectively increase the electromechanical coupling coefficient k2, and which, therefore, can increase the bandwidth ratio. An elastic wave device (1) making use of an SH plate wave propagating in LiNbO3 substrates includes a LiNbO3 substrate (3), IDT electrodes (4) placed on at least one surface of the LiNbO3 substrate (3), and a support (2) which is bonded to the LiNbO3 substrate (3) such that the support (2) is located outside a region provided with the IDT electrodes (4) and supports the LiNbO3 substrate (3), wherein θ of the Euler angles (0°, θ, 0°) of the LiNbO3 substrate (3) ranges from 92° to 138° and the thickness of the LiNbO3 substrate (3) ranges from 0.05λ to 0.25λ, where λ is the wavelength determined by the pitch between electrode fingers of the IDT electrodes (4).