SM-XBAR Filter Structure With Multiple Plate Thicknesses for RF Tuning
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required by future communications networks, such as the 5G NR standard which includes bands n77 and n79, and WiFi bands at 5 GHz and 6 GHz.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) and solidly-mounted transversely-excited film bulk acoustic resonators (SM-XBARs) with multiple diaphragm thicknesses and advanced fabrication methods, including dielectric layer trimming and piezoelectric plate thickness control, to achieve improved frequency tuning and performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used, then existing filter designs can be maintained, but they cannot achieve the higher frequencies and wider bandwidths required by future communications networks
Solution Approach 1:
The patent changes the physical parameters of the resonator by introducing multiple piezoelectric plate thicknesses (different thicknesses in different regions of the plate) to enable higher frequency operation and wider bandwidth. This parameter modification allows the resonator to achieve the frequency capability and adaptability required for future communication standards while maintaining the basic resonator structure.
2Speed
If multiple piezoelectric plate thicknesses are used, then frequency tuning and performance at higher frequencies are improved, but manufacturing complexity increases
Solution Approach 1:
The piezoelectric plate is segmented into regions with different thicknesses, allowing independent optimization of frequency characteristics in different areas. This segmentation enables frequency tuning and high-frequency performance while the segmented structure can be fabricated using standard semiconductor processing techniques, managing manufacturing complexity.
Solution Approach 2:
Different regions of the piezoelectric plate are given different local qualities (thicknesses) to optimize specific frequency responses. Thinner regions enable higher frequency operation while thicker regions provide structural support and different frequency characteristics, achieving frequency tuning capability without requiring complete redesign of the entire device.
3Measurement precision
If dielectric layer trimming and piezoelectric plate thickness control are implemented, then frequency precision is improved, but manufacturing process complexity increases
Solution Approach 1:
The piezoelectric plate is fabricated with predetermined thickness variations and dielectric layers are deposited with controlled thicknesses before final assembly. This preliminary action establishes the frequency characteristics early in the manufacturing process, allowing precise frequency control to be achieved through standard fabrication techniques rather than complex post-processing.
Solution Approach 2:
The patent replaces mechanical frequency adjustment methods with controlled variations in piezoelectric plate thickness and dielectric layer thickness that are established during fabrication. This substitution of mechanical tuning with fabrication-process-controlled parameters achieves frequency precision while managing manufacturing complexity by integrating frequency control into the standard fabrication flow.
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
These advanced XBAR and SM-XBAR resonators provide high electromechanical coupling and frequency capability, enabling the design of high-performance RF filters that can effectively handle the higher frequencies and wider bandwidths needed for future communication systems, thereby enhancing system performance and capacity.
Implementation Method 1
a single-crystal piezoelectric plate... An interdigital transducer (IDT) formed on a front surface of the piezoelectric plate... All of the IDTs are configured to excite shear acoustic waves in the piezoelectric plate
Implementation Method 2
an acoustic Bragg reflector sandwiched between a surface of the substrate and a back surface of the piezoelectric plate
Implementation Method 3
All of the IDTs are configured to excite shear acoustic waves in the piezoelectric plate
Data Source
AI summary
Filters and methods of making filters are disclosed. A filter device includes a substrate, a piezoelectric plate, and an acoustic Bragg reflector between a surface of the substrate and a back surface of the piezoelectric plate. A first portion of the piezoelectric plate has a first thickness, and a second portion of the piezoelectric plate has a second thickness less than the first thickness. A conductor pattern on front surfaces of the first and second portions of the piezoelectric plate includes a first interdigital transducer (IDT) with interleaved fingers on the first portion, and a second IDT with interleaved fingers on the second portion.