Suspended Lamb Wave Resonator With SiC Membrane for High-Q RF
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Solution Overview
Problem
Current radiofrequency resonators face challenges in achieving high quality factors with narrow bandwidths in the GHz range while maintaining low impedance levels for low loss and RF power transmission, and require MEMS and CMOS compatible fabrication processes.
Innovation Solution
A lateral acoustic wave resonator using a low-damping non-piezoelectric material like silicon carbide (SiC) with a piezoelectric transducer, such as aluminum nitride (AIN), forming a Fabry-Perot cavity with acoustic reflectors to decouple the piezoelectric transducer from the resonator material, allowing for scalable bandwidth and frequency through advanced lithographic processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If piezoelectric materials like PZT are used to increase coupling coefficient, then kt2 improves, but material damping increases causing Q to decrease
Solution Approach 1:
The device is segmented into distinct functional layers: a low-damping resonator material layer (silicon carbide) for high-Q resonance, and separate piezoelectric transducer layers for electrical coupling. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The invention uses a composite structure combining silicon carbide (for low damping and high Q) with piezoelectric materials like aluminum nitride or zinc oxide (for electrical coupling). This composite approach leverages the strengths of each material while mitigating their individual weaknesses.
2Reliability
If thickness-mode BAW resonators are used to achieve high Q, then quality factor improves, but resonant frequency becomes sensitive to film thickness variations
Solution Approach 1:
The invention transitions from thickness-mode resonance (vertical dimension) to lateral acoustic wave resonance (in-plane dimensions). This dimensional change shifts the resonance determination from film thickness to lateral cavity dimensions, which can be more precisely controlled by lithography.
Solution Approach 2:
The invention replaces the mechanical thickness-mode resonance mechanism with a lateral acoustic wave mechanism confined by acoustic reflectors. This substitution allows frequency to be determined by lateral cavity size rather than film thickness, improving manufacturability.
3Ease of operation
If piezoelectric transducer is integrated with resonator material, then transduction is achieved, but anchor losses and material damping limit Q
Solution Approach 1:
Acoustic reflectors serve as intermediaries that couple the piezoelectric transducer to the resonator cavity while isolating the high-Q resonator material from the lossy piezoelectric material. This intermediary structure allows transduction while protecting the resonator quality factor.
Solution Approach 2:
The piezoelectric transducer is extracted from the resonator cavity region and placed outside, coupled through acoustic reflectors. This separation removes the source of material damping and anchor losses from the high-Q resonator material.
4Adaptability or versatility
If conventional resonators are designed for high Q with narrow bandwidth, then selectivity improves, but impedance level increases causing higher losses
Solution Approach 1:
The invention changes the resonator material parameter to use low-damping materials like silicon carbide, which inherently provide high Q with lower impedance. This parameter change allows simultaneous achievement of high selectivity and low energy loss.
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 configuration enables high quality factor resonators with increased scalability and integration capabilities, achieving high Q factors without increasing impedance or insertion loss, and is suitable for CMOS integration.
Implementation Method 1
a piezoelectric transducer disposed on the membrane and adapted to generate a fundamental or overtone mode lateral acoustic wave
Implementation Method 2
A lateral acoustic wave resonator can be suspended from a substrate to reduce damping losses
Data Source
AI summary
A very high-Q, low insertion loss resonator can be achieved by storing many overtone cycles of a lateral acoustic wave (i.e., Lamb wave) in a lithographically defined suspended membrane comprising a low damping resonator material, such as silicon carbide. The high-Q resonator can sets up a Fabry-Perot cavity in a low-damping resonator material using high-reflectivity acoustic end mirrors, which can comprise phononic crystals. The lateral overtone acoustic wave resonator can be electrically transduced by piezoelectric couplers. The resonator Q can be increased without increasing the impedance or insertion loss by storing many cycles or wavelengths in the high-Q resonator material, with much lower damping than the piezoelectric transducer material.