Etched-Conductor XBAR Resonator for RF Filters Above 3 GHz
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands above 3 GHz, as existing technologies face challenges in achieving optimal performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost for future wireless communication systems.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with an etch-stop layer, which allows for precise control of conductor sidewall angles and improved acoustic mode excitation, enabling the design of high-frequency RF filters using a piezoelectric plate with a thin film conductor pattern and a substrate, suitable for frequencies above 3 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used for RF filters, then existing technologies can be implemented, but they cannot achieve optimal performance for higher frequency communications bands above 3 GHz
Solution Approach 1:
The patent changes the excitation mode parameter from longitudinal to transverse, and modifies the conductor pattern geometry parameters (etched vs. deposited) to achieve optimal performance at higher frequencies above 3 GHz, resolving the limitation of conventional resonators in these frequency bands
2Productivity
If transverse excitation with etched conductor patterns is used, then bandwidth and piezoelectric coupling are improved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces the conventional deposited conductor pattern formation process with an etched conductor pattern approach, substituting the deposition mechanism with an etching mechanism to achieve superior sidewall angles and acoustic mode excitation, thereby improving bandwidth while managing manufacturing complexity
3Reliability
If transverse excitation with etched conductor patterns is used, then piezoelectric coupling is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the conductor pattern formation method from deposition to etching, which fundamentally alters the sidewall angle characteristics and enables superior acoustic mode excitation with enhanced piezoelectric coupling, while the etching process inherently provides better sidewall control
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 provide enhanced performance for RF filters, achieving better bandwidth and higher piezoelectric coupling, enabling the design of microwave and millimeter-wave filters with appreciable bandwidth and improved performance in RF communication systems.
Implementation Method 1
transversely-excited film bulk acoustic resonators (XBARs) ... using a piezoelectric plate with a thin film conductor pattern
Implementation Method 2
film bulk acoustic resonators (FBAR), and other types of acoustic resonators
Data Source
AI summary
An acoustic resonator is fabricated by forming a patterned first photoresist mask on a piezoelectric plate at locations of a desired interdigital transducer (IDT) pattern. An etch-stop layer is then deposited on the plate and first photoresist mask. The first photoresist mask is removed to remove parts of the etch-stop and expose the plate. An IDT conductor material is deposited on the etch stop and the exposed plate. A patterned second photoresist mask is then formed on the conductor material at locations of the IDT pattern. The conductor material is then etched over and to the etch-stop to form the IDT pattern which has interleaved fingers on a diaphragm to span a substrate cavity. A portion of the plate and the etch-stop form the diaphragm. The etch-stop and photoresist mask are impervious to this etch. The second photoresist mask is removed to leave the IDT pattern.