XBAR Resonator With Half-Lambda Dielectric for High-Frequency RF Filters
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequency communications networks, such as those proposed for future wireless communications, due to limitations in frequency range and performance at higher frequencies.
Innovation Solution
The implementation of a transversely-excited film bulk acoustic resonator (XBAR) with a half-lambda dielectric layer, which enhances the resonator's stiffness, thermal conductivity, and capacitance per unit area, allowing for improved performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing acoustic wave resonators are used, then the filter can operate at lower frequencies, but the performance degrades at higher frequencies
Solution Approach 1:
The patent changes the physical parameters of the resonator by adding a half-lambda dielectric layer, which modifies the acoustic wave propagation characteristics. This enables the resonator to maintain reliable performance at higher frequencies by altering the effective acoustic path length and impedance matching, directly resolving the frequency range limitation of existing resonators
Solution Approach 2:
The invention creates a composite structure by combining the piezoelectric substrate with an additional half-lambda dielectric layer. This composite configuration improves the resonator's ability to operate at higher frequencies by providing better acoustic isolation and enhanced electromechanical coupling, thereby improving reliability in high-frequency applications
2Quantity of substance
If the dielectric layer thickness is increased, then the capacitance per unit area increases, but the thermal management and spurious modes need optimization
Solution Approach 1:
The patent optimizes the dielectric layer thickness to exactly one-half of the acoustic wavelength (half-lambda). This specific parameter value simultaneously achieves high capacitance per unit area while providing optimal thermal management and suppressing spurious acoustic modes, resolving the trade-off between capacitance enhancement and performance reliability
Solution Approach 2:
The invention applies the half-lambda dielectric layer specifically in the region where acoustic waves propagate between the interdigital transducers. This localized optimization provides enhanced capacitance exactly where needed while the specific thickness provides inherent thermal management and spurious mode suppression in the critical acoustic path region
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 XBAR with a half-lambda dielectric layer achieves reduced spurious modes, improved thermal management, and increased capacitance, enabling effective operation in higher frequency bands while maintaining low insertion loss and high rejection.
Implementation Method 1
a piezoelectric plate bonded to a substrate except for a portion of the piezoelectric plate that forms a diaphragm spanning a cavity
Implementation Method 2
where the thickness of the piezoelectric plate is approximately one-half of an acoustic wavelength
Implementation Method 3
A radio frequency (RF) filter is disclosed that incorporates a transversely-excited film bulk acoustic resonator (XBAR) with a half-lambda dielectric layer. The dielectric layer enhances the resonator's stiffness, thermal conductivity, and capacitance per unit area
Data Source
AI summary
Acoustic resonator devices and filters are disclosed. An acoustic resonator includes a substrate having a surface and a single-crystal lithium niobate (LN) plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the LN plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the LN plate such that interleaved fingers of the IDT are disposed on the diaphragm. A half-lambda dielectric layer is formed on one of the front surface and back surface of the diaphragm. Euler angles of the LN plate are [0°, β, 0°], where 20°≤β≤25°.