XBAR Resonators With Dual Membrane Thickness for Wideband RF Filters
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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 includes bands n77, n79, and millimeter wave frequencies, due to limitations in resonator design and frequency tuning.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with different membrane thicknesses on the same die, utilizing a thin Al2O3 bonding layer to form composite piezoelectric wafers, allowing for tuning of resonators without dielectric frequency setting layers, enabling wideband filter performance across various frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If acoustic wave resonators are used in conventional RF filters, then the filters can operate at current communication frequencies, but they cannot achieve the higher frequencies and wider bandwidths required for future 5G NR bands and millimeter wave applications
Solution Approach 1:
The patent changes the physical parameter of membrane thickness to enable frequency tuning. By providing resonators with different membrane thicknesses on the same die, the filter can operate across wider bandwidths and higher frequencies required for 5G NR bands n77, n79, and millimeter wave applications
Solution Approach 2:
The patent uses composite piezoelectric wafers formed by bonding multiple piezoelectric layers with different thicknesses. This composite structure allows different resonators on the same die to operate at different frequencies, enabling wideband filter performance across multiple 5G communication bands
2Measurement precision
If dielectric frequency setting layers are used to tune resonators, then frequency adjustment is achieved, but admittance performance is significantly affected and spurious modes are generated
Solution Approach 1:
The patent changes the membrane thickness parameter during the wafer bonding process to achieve frequency tuning. This approach avoids the need for dielectric frequency setting layers, thereby maintaining good admittance performance and reducing spurious modes while still achieving the required frequency adjustment for different 5G bands
3Adaptability or versatility
If multiple resonators with different frequencies are integrated on the same die, then wideband filter performance is achieved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent performs preliminary action by providing piezoelectric wafers with different membrane thicknesses before the bonding process. This allows frequency differentiation to be established in advance, simplifying the subsequent integration process on the same die while achieving wideband filter performance across multiple 5G communication bands
Solution Approach 2:
The patent uses composite piezoelectric wafers formed by bonding multiple piezoelectric layers with different thicknesses. This composite structure allows different resonators on the same die to operate at different frequencies, enabling wideband filter performance across multiple 5G communication bands
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 minimally affects admittance performance and maintains high resonator coupling, reducing spurious modes and achieving wide bandwidth filters with improved frequency tuning capabilities, suitable for high-frequency applications like 5G NR bands.
Implementation Method 1
a piezoelectric material, such as lithium niobate, lithium tantalate, or a combination of materials including aluminum nitride, gallium nitride, zinc oxide, or scandium aluminum nitride
Implementation Method 2
acoustic wave resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, film bulk acoustic wave resonators (FBAR)
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.