XBAR Resonator Package With Diaphragm Cavity for 3 GHz RF Filtering
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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, such as those proposed for future wireless communication systems, due to limitations in design and performance parameters like insertion loss, rejection, and size.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with 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 filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators (SAW, BAW, FBAR) are used, then filter performance is adequate for current frequency bands, but they cannot achieve required performance for higher frequency bands above 3 GHz
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic wave propagation to bulk acoustic wave propagation through transverse excitation. This parameter change enables the resonator to achieve stable performance at higher frequency bands above 3 GHz where conventional resonators fail, while maintaining adequate performance in lower bands through proper design optimization.
2Ease of manufacture
If conventional acoustic wave resonators are used, then device structure is well-established, but insertion loss and rejection parameters deteriorate at higher frequencies
Solution Approach 1:
The patent substitutes the mechanical wave propagation mechanism by replacing surface acoustic wave (SAW) propagation with bulk acoustic wave (BAW) propagation through transverse excitation. This substitution fundamentally changes how acoustic energy travels through the resonator structure, enabling lower insertion loss at high frequencies by confining acoustic energy within the bulk material rather than allowing it to propagate along the surface where losses increase with frequency.
3Ease of manufacture
If conventional acoustic wave resonators are used, then manufacturing processes are mature, but rejection and isolation performance worsen at frequencies above 3 GHz
Solution Approach 1:
The patent introduces a new dimensional aspect to acoustic wave propagation by using transverse excitation that generates bulk waves traveling through the thickness dimension of the resonator substrate, rather than surface waves propagating in the planar dimension. This dimensional change enables better rejection performance at high frequencies by utilizing the third dimension for acoustic energy confinement and by creating resonant modes that are less susceptible to frequency-dependent losses.
4Volume of moving object
If filter size is reduced for compact devices, then integration density improves, but performance parameters like insertion loss and rejection deteriorate
Solution Approach 1:
The patent exploits the thickness dimension of the resonator substrate to achieve compact filter design. By using bulk acoustic waves that propagate through the thickness of the substrate rather than surface waves that require large planar dimensions, the resonator achieves high-frequency performance in a much smaller volume, resolving the contradiction between size reduction and performance maintenance.
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 improved filter performance for higher frequency bands, enabling wider communication channel bandwidths and better meeting the requirements of future wireless communication systems by optimizing insertion loss, rejection, and size.
Implementation Method 1
transversely-excited film bulk acoustic resonators (XBARs) with a thin film conductor pattern on a piezoelectric plate
Implementation Method 2
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. A piezoelectric plate is attached to a substrate, a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. A first conductor pattern is formed on a surface of the piezoelectric plate. The first conductor pattern includes interleaved fingers of an interdigital transducer disposed on the diaphragm, and a first plurality of contact pads. A second conductor pattern is formed on a surface of a base, the second conductor pattern including a second plurality of contact pads. Each pad of the first plurality of contact pads is directly bonded to a respective pad of the second plurality of contact pads. A ring-shaped seal is form between a perimeter of the piezoelectric plate and a perimeter of the base.