Interposer-Cavity XBAR Packaging for High-Bandwidth RF Filtering
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Solution Overview
Problem
Current RF filters are not well-suited for higher frequency bands proposed for future communications networks, particularly those above 3 GHz, as they lack the necessary bandwidth and performance to support increased data rates and wider communication channel bandwidths required for 5G and millimeter wave communications.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) using a thin film conductor pattern on a piezoelectric plate, which excites a primary acoustic mode through an interdigital transducer, allowing for better performance at higher frequencies by utilizing a shear-mode acoustic resonance and a packaging method that provides mechanical protection, sealing, and electrical connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RF filters are used for higher frequency bands, then existing filter structures can be maintained, but bandwidth and performance are insufficient for 5G and millimeter wave communications
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal acoustic wave modes to transverse shear-horizontal modes. This parameter change enables the filter to operate effectively at higher frequencies (5G and millimeter wave bands) while achieving the required bandwidth performance that conventional filters cannot provide
2Adaptability or versatility
If transverse excitation mode is used to increase bandwidth, then higher frequency performance is improved, but device complexity increases
Solution Approach 1:
The resonator structure is segmented into distinct functional layers: piezoelectric substrate, piezoelectric film, and conductor pattern layers. This segmentation allows each layer to be optimized independently for its specific function while maintaining overall system performance, managing the complexity through modular design
Solution Approach 2:
The patent transitions from traditional longitudinal acoustic wave propagation to transverse shear-horizontal modes, effectively changing the dimension of acoustic wave propagation. This dimensional change enables higher frequency operation and increased bandwidth while maintaining a planar device structure suitable for integration
3Speed
If thin film conductor pattern is used to excite acoustic mode, then higher frequency operation is enabled, but manufacturing precision requirements increase
Solution Approach 1:
The piezoelectric film acts as an intermediary layer between the conductor pattern and the piezoelectric substrate. This intermediary enables the conversion of electrical signals to acoustic waves with enhanced coupling efficiency, allowing higher frequency operation while providing a buffer that tolerates moderate variations in conductor pattern fabrication
Solution Approach 2:
The resonator employs a composite structure combining piezoelectric substrate, piezoelectric film, and conductor materials. This composite approach leverages the advantageous properties of each material to achieve high-frequency performance while managing manufacturing tolerances through material property optimization
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 achieve improved performance and bandwidth, enabling efficient operation in higher frequency bands, such as 5G and millimeter wave communications, with reduced insertion loss and increased bandwidth, addressing the limitations of existing RF filters.
Implementation Method 1
a thin film conductor pattern on a piezoelectric plate, which excites a primary acoustic mode through an interdigital transducer
Implementation Method 2
allowing for better performance at higher frequencies by utilizing a shear-mode acoustic resonance
Data Source
AI summary
Acoustic resonator devices and filters; and methods of their fabrication are disclosed. A piezoelectric plate is bonded to a substrate, a portion of the piezoelectric plate forming a diaphragm spanning a cavity that is formed in the substrate. A first conductor pattern is formed on a surface of the piezoelectric plate. The first conductor pattern includes interleaved fingers of an interdigital transducer on the diaphragm, and first contact pads. Walls of an interposer back surface are formed onto the resonator front surface and surround the diaphragm. An interposer cover layer is formed on the walls, spans the walls and creates an enclosed interposer cavity over the diaphragm. A second conductor pattern is formed on the walls and cover layer that includes second contact pads on the interposer back surface; and connections that electrically connect the first contact pads to respective ones of the second contact pads.