Dielectric-Cover XBAR Packaging for Reduced Capacitive Coupling
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators, such as SAW and BAW resonators, are not well-suited for the higher frequencies and bandwidths required by future communications networks, particularly in 5G NR bands n77, n79, and WiFi bands at 5 GHz and 6 GHz, due to issues like increased insertion loss and capacitive coupling.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with wafer-level packaging (WLP) employing a dielectric cover, such as glass or quartz, to reduce capacitive coupling and insertion loss, thereby improving RF performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional SAW or BAW resonators are used for high-frequency applications, then device complexity is reduced, but insertion loss increases and capacitive coupling worsens
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic waves (SAW) or bulk acoustic waves (BAW) to transverse electric (TE) mode resonators. This parameter change enables operation at higher frequencies (3.3-5.0 GHz) with reduced insertion loss and capacitive coupling, as the TE mode resonance mechanism fundamentally differs from conventional approaches
Solution Approach 2:
The patent employs a composite structure consisting of a piezoelectric material layer (such as aluminum nitride or zinc oxide) deposited on a dielectric substrate. This composite material approach enables the resonator to achieve both mechanical stability and reduced capacitive coupling, while maintaining high-frequency performance and low insertion loss
2Productivity
If the frequency range is extended to 3.3-5.0 GHz for wider bandwidth, then communication bandwidth increases, but capacitive coupling increases causing performance degradation
Solution Approach 1:
The patent changes the resonance mode parameter from longitudinal or surface acoustic waves to transverse electric (TE) mode, which fundamentally alters the electromagnetic field distribution. This parameter change reduces capacitive coupling effects while enabling operation in the 3.3-5.0 GHz frequency range, thus achieving wider communication bandwidth without the harmful capacitive coupling that plagues conventional designs
Solution Approach 2:
The patent replaces the conventional mechanical acoustic wave resonance (SAW/BAW) with an electromagnetic resonance mechanism in TE mode. This substitution reduces the harmful capacitive coupling that is inherent in mechanically-coupled acoustic resonators, while maintaining the desired wide bandwidth performance for modern communication standards
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
XBARs with dielectric covers enhance RF performance by reducing distortion and loss, enabling better bandwidth and gain, making them suitable for high-frequency applications.
Implementation Method 1
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with wafer-level packaging (WLP) employing a dielectric cover, such as glass or quartz, to reduce capacitive coupling and insertion loss
Implementation Method 3
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm, such that the acoustic energy flows substantially normal to the surfaces of the layer
Data Source
AI summary
An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate bonded to the substrate surface. A portion of the piezoelectric plate forms a diaphragm that spans a cavity. A conductor pattern including an interdigital transducer (IDT) formed on a surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. A dielectric cover is disposed over the IDT and the plate, and the dielectric cover forms an air gap above the IDT and the plate.