Single-Crystal Lamb Wave Resonators With Wide-Tether Energy Confinement
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Solution Overview
Problem
Current acoustic resonator technologies face challenges in achieving high Q and electromechanical coupling coefficients over extreme frequency scaling, particularly in the mm-wave regime, due to limitations in piezoelectric film thickness miniaturization and degradation of performance metrics.
Innovation Solution
A high Q dispersive acoustic waveguide design featuring a substrate with gradual width changes and a single crystal silicon layer, combined with an aluminum nitride film, enables efficient energy localization and anchoring through wide tethers, reducing mechanical energy density and enhancing power-handling and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If piezoelectric film thickness is miniaturized to sub-100 nm range for extreme frequency scaling to mm-wave regime, then frequency scaling is achieved, but electromechanical coupling and energy dissipation coefficients drastically degrade
Solution Approach 1:
The patent changes the fundamental parameter of resonator architecture from thin-film bulk acoustic resonators (FBARs) to membrane-based resonators. This parameter change allows achieving mm-wave frequencies through mechanical tension and geometry control rather than relying solely on extreme thickness miniaturization, thereby maintaining acceptable electromechanical coupling coefficients while achieving the required frequency scaling.
Solution Approach 2:
The patent transitions from a three-dimensional thin-film structure to a two-dimensional membrane structure suspended over a cavity. This dimensional change enables frequency control through in-plane tension and lateral dimensions rather than vertical thickness, avoiding the degradation of electromechanical coupling that occurs with sub-100 nm thickness miniaturization.
2Speed
If piezoelectric film thickness is miniaturized to sub-100 nm range for extreme frequency scaling to mm-wave regime, then frequency scaling is achieved, but energy dissipation coefficients drastically degrade
Solution Approach 1:
The patent changes the fundamental parameter of resonator architecture from thin-film bulk acoustic resonators (FBARs) to membrane-based resonators. This parameter change allows achieving mm-wave frequencies through mechanical tension and geometry control rather than relying solely on extreme thickness miniaturization, thereby maintaining acceptable energy dissipation characteristics while achieving the required frequency scaling.
Solution Approach 2:
The patent transitions from a three-dimensional thin-film structure to a two-dimensional membrane structure suspended over a cavity. This dimensional change enables frequency control through in-plane tension and lateral dimensions rather than vertical thickness, avoiding the degradation of energy dissipation that occurs with sub-100 nm thickness miniaturization.
3Measurement precision
If narrow tethers are used to anchor resonator, then frequency definition is achieved, but mechanical energy density increases and power-handling degrades
Solution Approach 1:
The patent applies local quality by creating a non-uniform tether width profile along the anchor region. The tethers have varying widths that are narrower at certain locations and wider at others, allowing different sections to serve different functions: frequency definition at specific points and power distribution at other sections, thereby resolving the contradiction between frequency precision and power-handling capability.
Solution Approach 2:
The patent introduces dynamic characteristics to the tether anchoring system by using a continuous width variation rather than a fixed uniform width. This allows the tether to adapt its mechanical properties along its length, providing both frequency definition where needed and reduced mechanical energy density in power-critical regions, effectively balancing both requirements.
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 design achieves high Q and kt2 resonators with arbitrary cross-sectional mode shapes and frequencies, improving power-handling and linearity while reducing anchoring energy leakage, enabling integration with transistors and suppressing spurious modes.
Implementation Method 1
a 500 nm aluminum nitride film on the single crystal silicon
Implementation Method 2
Lamb wave resonators enable high Q and kt2 resonators with arbitrary cross-sectional mode shapes and frequencies
Data Source
AI summary
An acoustic waveguide having high-Q resonator characteristics is disclosed and a fabrication method is described. Various waveguide-based test-vehicles, implemented in single crystal silicon and transduced by thin aluminum nitride films, are demonstrated. Silicon resonators with type-I and type-II dispersion characteristics are presented to experimentally justify the analytical mode synthesis technique for realization of high quality-factor silicon Lamb wave resonators. An analytical design procedure is also presented for geometrical engineering of the waveguides to realize high-Q resonators without the need for geometrical suspension through narrow tethers or rigid anchors. The effectiveness of the dispersion engineering methodology is verified through development of experimental test-vehicles in 20 μm-thick single-crystal silicon (SCS) waveguides with 500 nm aluminum nitride transducers.