XBAR Package With Interposer Sealing for >3 GHz RF Filters
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Solution Overview
Problem
Current RF filters using acoustic wave resonators, such as SAW and BAW resonators, are not well-suited for higher frequency communications bands proposed for future wireless networks, particularly those above 3 GHz, as they fail to provide optimal performance in terms of insertion loss, rejection, isolation, power handling, linearity, size, and cost.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) using a thin film conductor pattern on a piezoelectric plate, specifically designed for frequencies above 3 GHz, which includes an interdigital transducer and a cavity structure to enhance acoustic wave propagation, and packaged with an interposer and cap to provide mechanical protection and electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SAW and BAW resonators are used for RF filters, then the filters can operate at traditional frequency bands, but they fail to provide optimal performance at higher frequency bands above 3 GHz
Solution Approach 1:
The patent employs parameter changes by modifying the resonator structure from conventional SAW/BAW to XBAR configuration, changing the excitation mode from longitudinal to transverse, and adjusting the conductor pattern geometry to achieve optimal performance at higher frequency bands above 3 GHz
Solution Approach 2:
The resonator is segmented into distinct functional regions including interdigital transducers (IDTs) with specific finger patterns, reflective gratings, and cavity structures, allowing each segment to be optimized for its specific function in the high-frequency operation
2Loss of energy
If the filter design is optimized for insertion loss, then signal transmission improves, but other performance parameters such as rejection, isolation, and power handling may be compromised
Solution Approach 1:
The XBAR resonator structure serves multiple functions simultaneously: it provides low insertion loss through efficient transverse wave propagation, achieves high rejection through reflective gratings, ensures good isolation through cavity confinement, and maintains power handling capability through the film bulk acoustic wave structure, making it a multi-functional solution for high-frequency filters
3Ease of manufacture
If the resonator structure is simplified for easier manufacturing, then production cost decreases, but performance parameters such as linearity and power handling may deteriorate
Solution Approach 1:
The patent applies local quality by using uniform thin film conductor patterns deposited through standard semiconductor fabrication processes for ease of manufacture, while locally optimizing specific regions such as the IDT finger geometry, reflective grating patterns, and cavity dimensions to maintain high linearity and power handling performance
4Volume of moving object
If the resonator is designed for smaller size, then device compactness improves, but the acoustic wave propagation and filter characteristics may be affected
Solution Approach 1:
The patent transitions from surface acoustic wave propagation in conventional resonators to bulk acoustic wave propagation in the XBAR structure, utilizing the third dimension (vertical film thickness) for wave confinement and resonance, thereby achieving compact device size while maintaining effective acoustic wave propagation and filter characteristics
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 offer improved performance in RF filters for higher frequency bands by reducing transmission loss and enhancing filter characteristics, enabling wider communication channel bandwidths and better suitability for future wireless communication systems.
Implementation Method 1
a piezoelectric plate, upon which is formed a thin film conductor pattern
Implementation Method 2
The conductor pattern includes an interdigital transducer (IDT)
Implementation Method 3
specifically designed for frequencies above 3 GHz, which includes an interdigital transducer and a cavity structure to enhance acoustic wave propagation
Data Source
AI summary
Acoustic resonator devices and filters are disclosed. An acoustic resonator chip includes a piezoelectric plate attached to a substrate, a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. A first conductor pattern formed on a surface of the piezoelectric plate includes interleaved fingers of an interdigital transducer on the diaphragm and a first plurality of contact pads. A second conductor pattern is formed on a surface of an interposer, the second conductor pattern including a second plurality of contact pads. Each pad of the first plurality of contact pads is directly connected to a respective pad of the second plurality of contact pads. A seal is formed between a perimeter of the piezoelectric plate and a perimeter of the interposer.