XBAR IDT Layout for Spurious Mode Suppression in Wideband RF Filters
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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 those defined in the 5G NR standard, particularly in bands n77, n79, and WiFi bands at 5 GHz and 6 GHz, due to limitations in handling transmit power and bandwidth.
Innovation Solution
The use of a Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with multi-mark and multi-pitch interdigital transducers (IDTs) to enhance RF filters, where the IDT fingers have varying mark and pitch along their length to suppress spurious modes and improve frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic wave resonators are used, then existing filter designs can be maintained, but they cannot handle higher frequencies and wider bandwidths required by future communications networks
Solution Approach 1:
The patent changes the fundamental operating parameters of the resonator by transitioning from longitudinal to transverse excitation mode, enabling operation at higher frequencies (above 3 GHz) and wider bandwidths while maintaining power handling capability. The XBAR structure with transverse excitation allows the resonator to operate in a different regime that supports both high frequency and high power requirements for 5G bands n77 and n79
Solution Approach 2:
The patent employs composite material structures in the XBAR resonator design, combining piezoelectric materials with specific crystal orientations and layered configurations that enable simultaneous achievement of high frequency operation and high power handling. The composite structure includes piezoelectric layers, electrode patterns, and substrate materials configured to optimize both frequency response and power capacity
2Manufacturing precision
If single-mark, single-pitch IDTs are used, then manufacturing is simpler, but spurious modes are not suppressed and frequency response is degraded
Solution Approach 1:
The patent applies local quality by varying the IDT finger marks and pitches at different locations along the IDT length. Instead of uniform dimensions, the finger width and spacing are locally adjusted to suppress spurious modes at specific frequency locations. This local variation in geometry creates destructive interference for unwanted modes while preserving the fundamental resonance, achieving superior frequency response without requiring complete redesign of the entire IDT structure
Solution Approach 2:
The IDT is segmented into multiple sections with different mark and pitch characteristics. Each section is optimized for specific frequency ranges or mode suppression requirements. By dividing the IDT into segments with varying parameters, the design achieves comprehensive suppression of multiple spurious modes across the operating bandwidth while maintaining a systematic manufacturing approach
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 XBAR with multi-mark and multi-pitch IDTs achieves reduced spurious modes and negligible impact on primary resonance frequencies, resulting in improved filter performance for higher frequencies and wider bandwidths, with reduced loss and enhanced power handling.
Implementation Method 1
a radio frequency or microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm
Implementation Method 2
XBAR resonators provide very high electromechanical coupling and high frequency capability
Data Source
AI summary
Acoustic resonator devices and acoustic filter devices. An acoustic resonator includes a piezoelectric plate having front and back surfaces. The back surface is attached to a surface of a substrate. The piezoelectric plate comprises a diaphragm spanning a cavity. A conductor pattern is formed on the front surface. The conductor pattern includes a multi-mark multi-pitch interdigital transducer (IDT), wherein fingers of the IDT are on the diaphragm.