XBAR Resonator Membrane Thickness Tuning on a Composite Piezoelectric Die
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Solution Overview
Problem
Current RF filters, particularly those using acoustic wave resonators, are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which necessitates the development of more advanced filter technologies capable of handling higher frequency ranges like 3300 MHz to 40 GHz.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with different membrane thicknesses on the same die, employing a thin Al2O3 bonding layer to form composite piezoelectric wafers, allowing for the creation of resonators that can tune resonance frequencies without relying on dielectric frequency setting layers, thereby enabling wideband filters with improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional acoustic wave resonators are used, then existing filter technologies can be maintained, but they cannot handle higher frequency bands and wider bandwidths required for future communication networks
Solution Approach 1:
The patent changes the physical parameters of the resonator by varying the membrane thickness to achieve different resonance frequencies. This allows the same resonator structure to be adapted for different frequency bands, enabling the filter to handle higher frequency ranges while maintaining reliable performance through optimized thickness parameters
Solution Approach 2:
The patent employs composite piezoelectric wafers with different membrane thicknesses bonded together to create resonators that can operate at different frequencies. This composite structure enables the filter to simultaneously support multiple frequency bands and wider bandwidths while maintaining the reliability needed for future communication networks
2Adaptability or versatility
If different membrane thicknesses are used on the same die, then frequency tuning capabilities are enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent segments the piezoelectric wafer into multiple layers with different thicknesses, where each layer contributes to the overall resonance characteristics. This segmentation allows independent optimization of each layer's thickness to achieve desired frequency tuning while using standardized bonding processes
Solution Approach 2:
The patent creates a universal bonding process that can accommodate different membrane thicknesses on the same die. The thin Al2O3 bonding layer serves multiple functions: bonding different thickness membranes, providing mechanical support, and enabling frequency tuning, thereby simplifying the overall manufacturing approach despite the varied thickness requirements
3Adaptability or versatility
If thin Al2O3 bonding layer is used to form composite piezoelectric wafers, then resonators can be created with different membrane thicknesses on the same die, but the bonding process precision requirements increase
Solution Approach 1:
The patent uses a thin Al2O3 bonding layer that is flexible enough to accommodate different membrane thicknesses while maintaining sufficient mechanical strength. This thin film approach allows for precise thickness control through advanced deposition techniques, enabling the bonding of composite piezoelectric wafers with varying membrane thicknesses on the same die
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 allows for the creation of RF filters with enhanced frequency tuning capabilities and minimal impact on admittance performance, maintaining high-Q resonances and reducing spurious modes, thus addressing the limitations of existing filters in handling higher frequency bands.
Implementation Method 1
A resonator includes an interdigital transducer (IDT) over a piezoelectric membrane
Implementation Method 2
The range of frequencies passed by a filter is referred to as the 'pass-band' of the filter. The range of frequencies stopped by such a filter is referred to as the 'stop-band' of the filter
Data Source
AI summary
An acoustic resonator is fabricated by bonding a first piezoelectric plate to a substrate and spans locations for a first and second cavity in the substrate. A top surface of the first piezoelectric plate is planarized to a first thickness. A bonding layer is formed on the first piezoelectric plate and spans the first and second cavity locations. A second piezoelectric plate is bonded to the bonding layer and spans the first and second cavity locations. A portion of the second piezoelectric plate spanning the second cavity location is etched away to form a first membrane over the first cavity location and a second membrane over the second cavity location. Interdigital transducers are formed on the first and second membranes over the first and second cavity location to form a first and second resonator on the same die.