XBAR Piezoelectric Trimming to Suppress Substrate-Coupled Modes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and bandwidths required in future communications networks, particularly for 5G NR standards, leading to increased insertion loss and suboptimal performance in filters for bands n77, n79, and millimeter wave frequencies.
Innovation Solution
The development of improved Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with excess piezoelectric material removed between conductors to avoid exciting acoustic modes that couple to the substrate, reducing insertion loss and enhancing frequency capabilities by optimizing the resonator design and fabrication techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If acoustic wave resonators are used in current RF filter designs, then the filters can operate at existing frequency bands, but they exhibit increased insertion loss and suboptimal performance at higher frequencies required for 5G NR standards
Solution Approach 1:
The patent changes the resonator design parameters by removing excess piezoelectric material between conductors, optimizing the resonator geometry for higher frequency operation. This parameter change reduces unwanted acoustic mode coupling and lowers insertion loss at 5G NR frequency bands while maintaining reliable filter performance
Solution Approach 2:
The patent extracts or removes the excess piezoelectric material between conductors from the resonator structure. This extraction eliminates the source of unwanted acoustic mode coupling that causes insertion loss, thereby improving energy efficiency and performance at higher frequencies without compromising reliability
2Loss of energy
If excess piezoelectric material is removed between conductors, then insertion loss is reduced and frequency performance is improved, but the device complexity and manufacturing process become more complex
Solution Approach 1:
The patent applies preliminary action by removing excess piezoelectric material between conductors during the fabrication process before final assembly. This preliminary removal prevents unwanted acoustic mode coupling from the outset, reducing insertion loss while integrating the complexity into the existing manufacturing workflow rather than adding post-processing steps
3Power
If acoustic modes are excited in the piezoelectric material between conductors, then the material utilizes the piezoelectric effect for signal transmission, but these modes couple to the substrate and increase insertion loss
Solution Approach 1:
The patent extracts the problematic piezoelectric material between conductors that generates unwanted acoustic modes. By removing this material, the source of mode coupling to the substrate is eliminated, preventing energy loss while preserving the necessary piezoelectric effect in the resonator structures for signal transmission
Solution Approach 2:
The patent applies local quality by differentiating the treatment of piezoelectric material in different locations: the material within resonator structures is preserved to maintain signal transmission capability, while the material between conductors is removed to eliminate harmful acoustic mode coupling. This selective approach optimizes both power transmission and reduces insertion loss
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
The solution effectively reduces insertion loss and improves the frequency performance of RF filters, enabling them to handle higher frequencies and wider bandwidths, thus enhancing the performance of communication systems by providing better isolation and power handling.
Implementation Method 1
An XBAR resonator comprises an interdigital transducer (IDT) formed on a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
High performance RF filters for present communication systems commonly incorporate acoustic wave resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, film bulk acoustic wave resonators (FBAR), and other types of acoustic resonators.
Data Source
AI summary
A filter device has a substrate with a first cavity and a second cavity on a single die; and a bonding layer formed on the substrate but not spanning the first cavity or the second cavity. A piezoelectric plate is bonded to the bonding layer and spans the first and the second cavity. However, excess portions of piezoelectric plate are removed that extend a certain length past the perimeter of the first cavity and of the second cavity. Excess portions may be piezoelectric material that extends in the length and width direction past the perimeter of a cavity by more than between 2 and 25 percent of the cavity perimeter. An interdigital transducer (IDT) is on a front surface of the piezoelectric plate and having interleaved fingers over the first cavity.