XBAR RF Filter Tuning With Dual Dielectric Frequency Layers
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications networks, particularly those above 3 GHz, as they struggle to achieve the necessary frequency separation between shunt and series resonators for wide communication channel bandwidths.
Innovation Solution
The use of transversely-excited film bulk acoustic resonators (XBARs) with multiple frequency setting dielectric layers, where the thickness of these layers is varied to adjust the resonance frequencies of both shunt and series resonators, providing enhanced frequency separation and improved performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional acoustic wave resonators are used in RF filters, then the filter structure is simple, but the frequency separation between shunt and series resonators is insufficient for higher frequency communications
Solution Approach 1:
The resonator structure is segmented into distinct shunt and series resonators with different configurations. Each resonator type is optimized independently with specific electrode patterns and cavity structures, allowing precise control over their respective resonance frequencies to achieve the required frequency separation
Solution Approach 2:
Different local structures are implemented for shunt and series resonators. Shunt resonators use specific electrode arrangements and cavity depths optimized for their function, while series resonators have different local characteristics. This local differentiation enables each resonator type to operate at its optimal frequency with the desired separation
2Adaptability or versatility
If the resonator frequency separation is increased for better filter performance, then the bandwidth capabilities improve, but the resonator design complexity increases
Solution Approach 1:
The resonator design incorporates adjustable parameters such as cavity depth, electrode spacing, and finger width that can be dynamically optimized during the design process. This allows the frequency separation and bandwidth to be tuned to specific requirements without fundamentally changing the resonator architecture
Solution Approach 2:
Specific geometric parameters of the resonators are optimized to achieve the desired frequency separation and bandwidth. By carefully controlling parameters such as the thickness of piezoelectric layers, cavity depth, and electrode dimensions, the resonators can be tuned to operate at the required frequencies with adequate separation and bandwidth
3Adaptability or versatility
If conventional resonator designs are used, then the manufacturing process is straightforward, but the filters cannot effectively operate in millimeter wave communication bands above 3 GHz
Solution Approach 1:
The resonator design transitions from two-dimensional surface acoustic wave structures to three-dimensional bulk acoustic wave structures with controlled cavity depths. This dimensional change enables operation at higher frequencies in the millimeter wave band while maintaining manufacturability through standard semiconductor fabrication techniques
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 effective frequency separation and improved filter performance, enabling the use of RF filters in higher frequency communication bands, such as those up to 28 GHz, by precisely tuning the resonance frequencies of XBARs, thereby enhancing communication system capabilities.
Implementation Method 1
a piezoelectric layer formed over a substrate
Implementation Method 2
a first dielectric layer formed over the interdigital transducer fingers and the piezoelectric layer, the first dielectric layer having a first thickness; a second dielectric layer formed over the interdigital transducer fingers and the piezoelectric layer, the second dielectric layer having a second thickness
Data Source
AI summary
Acoustic filters are disclosed. A substrate includes a base and an intermediate layer. A piezoelectric plate is attached to the intermediate layer, portions of the piezoelectric plate forming one or more diaphragms spanning respective cavities in the intermediate layer. A conductor pattern on a front surface of the piezoelectric plate includes interdigital transducers (IDTs) of a plurality of resonators, interleaved fingers of each of the IDTs disposed on a respective diaphragm of the one or more diaphragms. A first frequency setting dielectric layer having a first thickness is disposed over the fingers of the IDTs of a first subset of the plurality of resonators. A second frequency setting dielectric layer having a second thickness greater than the first thickness is disposed over the fingers of the IDTs of a second subset of the plurality of resonators, wherein the first subset and the second subset are not identical.