Multi-Pitch XBAR IDT Layout for Spurious Mode Suppression
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Solution Overview
Problem
Existing RF filters are not well-suited for high frequency and wide bandwidth applications required by future communications networks, particularly in 5G NR and WiFi bands, due to limitations in spurious mode suppression and power handling.
Innovation Solution
The use of a transversely-excited film bulk acoustic resonator (XBAR) with a multi-pitch interdigital transducer (IDT) design, which modulates the pitch along the length of the IDT to effectively suppress spurious modes and enhance frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional uniform-pitch IDT is used in an XBAR resonator, then the device structure is simple and easy to manufacture, but spurious modes are not suppressed effectively and frequency response is degraded
Solution Approach 1:
The IDT is designed with non-uniform pitch distribution where different sections have different pitch values. The pitch varies along the length of the IDT, with first, second, and third pitch values in different sections, allowing local optimization to suppress spurious modes at specific frequency locations while maintaining overall device performance
Solution Approach 2:
The pitch parameter of the IDT fingers is deliberately varied across different sections rather than maintaining a constant value. This parameter change strategy allows the resonator to suppress spurious modes by creating destructive interference at unwanted frequencies while preserving the fundamental resonance characteristics
2Speed
If existing acoustic wave resonators are used, then the devices are well-established and easy to manufacture, but they are not suitable for high frequency and wide bandwidth applications required by future communications networks
Solution Approach 1:
The XBAR resonator employs an IDT with spatially varying pitch characteristics, where different regions of the IDT have optimized pitch values tailored to suppress specific spurious modes. This local optimization approach enables the resonator to achieve both high frequency capability and effective spurious mode suppression, meeting the requirements for 5G and WiFi applications
Solution Approach 2:
The IDT is divided into multiple sections with distinct pitch characteristics. This segmentation allows each section to be optimized for different frequency ranges, enabling the resonator to handle wide bandwidth applications while maintaining reliability through targeted suppression of spurious modes in each frequency band
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 multi-pitch IDT design significantly reduces spurious modes by up to 8 dB, improving the frequency response and power handling capabilities of RF filters for high-frequency applications.
Implementation Method 1
a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
Transversely-Excited Film Bulk Acoustic Resonator (XBAR) is an acoustic resonator structure for use in microwave filters. The XBAR comprises an interdigital transducer (IDT) formed on a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Data Source
AI summary
A filter device is provided that includes a plurality of resonators that each include a piezoelectric layer attached to a surface of a substrate; and a conductor pattern comprising an IDT having interleaved fingers. Each IDT is a multi-pitch IDT and is divided along a length of the respective IDT into at least three sections, with one pair of interleaved fingers from each section having a pitch that is different from respective pitches of other sections of the at least three sections. Moreover, a change in the pitch between the sections has a smaller effect on a primary shear acoustic mode of all of the at least three sections in comparison to an effect that the change in pitch has on a spurious acoustic mode other than the primary shear acoustic mode of the three sections.