High-Quality Nanomechanical Resonators with Built-In Piezoelectricity: A Breakthrough for Quantum Sensing Technologies

Jakarta, INTI - Researchers at Chalmers University of Technology in Sweden and the University of Magdeburg in Germany have recently developed an innovative type of nanomechanical resonator that combines two essential features: high mechanical quality and piezoelectricity. This groundbreaking advancement has the potential to pave the way for new possibilities in quantum sensing technologies.

Nanomechanical resonators, devices capable of vibrating at specific frequencies, have been utilized for centuries in various applications. A common example of a resonator is the tuning fork, which oscillates at a specific frequency when struck, producing sound waves that are within the range of human hearing. Over time, with advancements in microfabrication technologies, researchers have managed to reduce the size of mechanical resonators to the micro- and nanometer scale. These miniaturized resonators oscillate at much higher frequencies and exhibit significantly greater sensitivity compared to their macroscopic counterparts.

"The unique properties of nanomechanical resonators make them ideal for precision experiments, such as sensing minuscule forces or detecting small changes in mass. Recently, these resonators have garnered substantial interest from quantum physicists due to their potential applications in quantum technologies. For example, by utilizing quantum states of motion, we could enhance the sensitivity of nanomechanical resonators even further," says Witlef Wieczorek, Professor of Physics at Chalmers University of Technology and project leader of the study.

A key requirement for these applications is that nanomechanical resonators must be able to sustain their oscillations for extended periods without significant energy loss. This ability is quantified by the mechanical quality factor. A high mechanical quality factor implies that the resonator maintains its oscillation with minimal energy dissipation, leading to enhanced sensitivity. Furthermore, it also allows quantum states of motion to persist for longer durations, which is crucial in sensing and quantum technology applications.

The Challenge of Finding High-Quality Materials with Built-In Piezoelectricity

Most of the top-performing nanomechanical resonators are made from tensile-strained silicon nitride, a material renowned for its excellent mechanical quality. However, silicon nitride has its limitations: it does not conduct electricity, nor is it magnetic or piezoelectric. These limitations hinder its use in applications that require the in-situ control or interfacing of nanomechanical resonators with other systems. To overcome this, researchers typically add functional materials to silicon nitride, but this often results in a reduction in the mechanical quality factor, compromising the resonator's performance.

This is where the recent breakthrough at Chalmers University of Technology and the University of Magdeburg comes into play. The researchers demonstrated a nanomechanical resonator made from tensile-strained aluminum nitride, a piezoelectric material that maintains a high mechanical quality factor.

"Piezoelectric materials have the ability to convert mechanical motion into electrical signals and vice versa. This feature allows for direct readout and control of the nanomechanical resonator in sensing applications. Moreover, it enables the interfacing of mechanical and electrical degrees of freedom, which is essential for information transduction, even in the quantum realm," explains Anastasiia Ciers, research specialist in quantum technology at Chalmers and lead author of the study published in Advanced Materials.

The aluminum nitride-based resonator achieved an exceptional quality factor of over 10 million.

"This result suggests that tensile-strained aluminum nitride could become a powerful new material platform for quantum sensors and quantum transducers," says Witlef Wieczorek.

The Path Forward: Improving Quality Factors and Quantum Sensing Applications

Looking ahead, the research team has two major goals: further improving the quality factor of these devices and developing realistic nanomechanical resonator designs that can effectively leverage piezoelectricity for quantum sensing applications.

About Aluminum Nitride-Based Nanomechanical Resonators

To fabricate their nanomechanical resonators, the researchers used a highly stressed 295-nanometer-thick film of aluminum nitride. The film was subjected to a stress of approximately 1 GPa, equivalent to balancing two elephants on a single fingernail. The researchers utilized this high stress in a technique known as "dissipation dilution," which enhances the mechanical quality factor of the resonators.

The aluminum nitride film was epitaxially grown on a silicon substrate, ensuring high crystalline quality that preserves the piezoelectric properties of aluminum nitride. The researchers also designed a novel resonator called the "triangline," a fractal-like structure with a central triangular pad. This resonator design is capable of maintaining a single quantum coherent oscillation at room temperature, an important milestone for its application in quantum technologies.

The development of this new type of nanomechanical resonator is expected to open up new avenues for advancements in quantum sensing and information processing. By combining high mechanical quality with piezoelectric properties, these resonators could play a critical role in the future of quantum technology, making it possible to explore new realms of precision measurement and data transmission.