XBAR Filter Openings to Cut Substrate-Coupled Insertion Loss
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Solution Overview
Problem
Existing RF filters, including XBAR resonators, face challenges in handling higher frequencies and bandwidths required for future communications networks, particularly in 5G NR bands n77, n79, and WiFi bands at 5 GHz and 6 GHz, due to increased insertion loss from acoustic modes coupling to the substrate.
Innovation Solution
The removal of excess piezoelectric material between conductors in XBAR resonators prevents acoustic energy loss by eliminating unwanted acoustic modes, thereby reducing insertion loss and improving filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If excess piezoelectric material is retained between conductors in XBAR resonators, then the structural integrity and manufacturing simplicity are maintained, but acoustic energy loss increases due to unwanted acoustic modes coupling to the substrate
Solution Approach 1:
The patent extracts and removes the excess piezoelectric material between conductors from the XBAR resonator structure. This extraction eliminates the source of unwanted acoustic modes that couple to the substrate, thereby reducing insertion loss. The removal is performed selectively to retain only the piezoelectric material necessary for resonator operation while eliminating the harmful excess material.
2Loss of energy
If excess piezoelectric material is removed between conductors, then insertion loss is reduced by eliminating acoustic mode coupling, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by removing excess piezoelectric material between conductors before final device assembly and testing. This preliminary removal prevents acoustic mode coupling issues from developing, making the manufacturing process more efficient overall despite the additional step. The early elimination of problematic material avoids downstream rework and ensures optimal device performance from the outset.
3Reliability
If excess piezoelectric material is removed between conductors, then capacitance is minimized improving filter performance, but device complexity increases
Solution Approach 1:
The patent extracts excess piezoelectric material that creates parasitic capacitance between conductors. By removing this excess material, the unwanted capacitive coupling is eliminated, improving filter performance and signal integrity. The extraction process is designed to remove only the harmful excess material while preserving the functional piezoelectric structures necessary for resonator operation.
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 approach enhances the performance of RF filters by minimizing insertion loss and capacitance, enabling them to handle higher frequencies and wider bandwidths effectively.
Implementation Method 1
A radio frequency electric field between the conductors induces a shear acoustic mode in the piezoelectric layer
Implementation Method 2
A radio frequency electric field between the conductors induces a shear acoustic mode in the piezoelectric layer
Implementation Method 3
XBAR resonators provide very high electromechanical coupling and high frequency capability
Data Source
AI summary
Filter devices and fabrication methods are disclosed. A filter device includes a piezoelectric plate and a conductor pattern on a front surface of the piezoelectric plate. The conductor pattern includes interdigital transducers (IDTs) of a plurality of transversely-excited film bulk acoustic resonators (XBARs) and a plurality of conductors connecting the plurality of XBARs in a ladder filter circuit architecture. The plurality of conductors includes a first conductor adjacent to a second conductor. An opening is provided through the piezoelectric plate between the first conductor and the second conductor.