Researchers have created an innovative type of nanomechanical resonator that features both excellent mechanical quality and piezoelectric properties. This advancement is expected to pave the way for exciting new applications in quantum sensing technologies.
Scientists from Chalmers University of Technology in Sweden and the University of Magdeburg in Germany have developed a cutting-edge nanomechanical resonator that integrates two essential characteristics: high mechanical quality and piezoelectricity. This breakthrough could lead to significant advancements in quantum sensing technologies.
Mechanical resonators have served diverse purposes for centuries. A fundamental characteristic of these devices is their capacity to vibrate at designated frequencies. A classic example is a tuning fork, which, when struck, vibrates at its specific resonance frequency, generating sound waves that we can hear. Thanks to improvements in microfabrication methods, researchers have successfully miniaturized mechanical resonators to the micro and nanometer scales. At these minuscule dimensions, resonators oscillate at much higher frequencies and demonstrate increased sensitivity compared to larger versions.
“These traits render them valuable in precision experiments, such as detecting tiny forces or changes in mass. Recently, nanomechanical resonators have garnered notable interest among quantum physicists for their potential applications in quantum technologies. Utilizing quantum states of motion could further enhance the sensitivity of nanomechanical resonators,” explains Witlef Wieczorek, a Physics Professor at Chalmers University and project leader of the study.
A primary requirement for these applications is that nanomechanical resonators must maintain their oscillation for extended periods without significant energy loss. This capability is measured by the mechanical quality factor. A higher mechanical quality factor not only indicates better sensitivity but also allows quantum states of motion to persist longer. Such qualities are highly desirable in sensing and quantum technology applications.
In the search for a material that offers a high-quality factor and intrinsic piezoelectricity
Many of the top-performing nanomechanical resonators are constructed from tensile-strained silicon nitride, a material recognized for its excellent mechanical quality. However, silicon nitride has limitations: it is non-conductive, not magnetic, and lacks piezoelectric properties. This has posed challenges in applications needing in-situ control or integration with other systems. To fulfill these requirements, researchers typically add a functional material on top of silicon nitride, but this often lowers the mechanical quality factor, restricting the resonator’s effectiveness.
Recently, researchers from Chalmers University of Technology and the University of Magdeburg made significant progress by demonstrating a nanomechanical resonator made from tensile-strained aluminum nitride, a piezoelectric material that retains a high mechanical quality factor.
“Piezoelectric materials can transform mechanical movement into electrical signals and vice versa. This functionality is advantageous for directly reading and controlling nanomechanical resonators in sensing tasks. It also facilitates the connection between mechanical aspects and electrical ones, which is crucial for information transduction, even in quantum applications,” remarks Anastasiia Ciers, a quantum technology research specialist at Chalmers and lead author of the research published in Advanced Materials.
The aluminum nitride resonator achieved an impressive quality factor exceeding 10 million.
“This indicates that tensile-strained aluminum nitride has the potential to serve as a robust new material platform for quantum sensors or transducers,” states Witlef Wieczorek.
The researchers have set two primary objectives: to further enhance the quality factor of their devices and to develop practical designs for nanomechanical resonators that leverage piezoelectricity in quantum sensing applications.
About the aluminum nitride-based nanomechanical resonators
The research team utilized a highly stressed 295-nanometer-thick film of aluminum nitride to fabricate their nanomechanical resonators. The stress was around 1 GPa, comparable to balancing two elephants on a fingernail. This high stress was employed in a method known as dissipation dilution, which increases the mechanical quality factor. The aluminum nitride film was epitaxially grown on a silicon substrate to ensure high crystalline quality, preserving the piezoelectric characteristics of aluminum nitride. They designed an innovative resonator, named “triangline,” resembling a fractal structure with a central triangular pad. This triangline resonator can sustain a single quantum coherent oscillation at room temperature, marking a crucial milestone for its use in quantum technology.
