High-aspect-ratio mechanical resonators are pivotal in precision sensing, from macroscopic gravitational wave detectors to nanoscale acoustics. However, fabrication challenges and high computational costs have limited the length-to-thickness ratio of these devices, leaving a largely unexplored regime in nano-engineering. We present nanomechanical resonators that extend centimeters in length yet retain nanometer thickness. We explore this expanded design space using an optimization approach which judiciously employs fast millimeter-scale simulations to steer the more computationally intensive centimeter-scale design optimization. By employing delicate nanofabrication techniques, our approach ensures high-yield realization, experimentally confirming room-temperature quality factors close to theoretical predictions. The synergy between nanofabrication, design optimization guided by machine learning, and precision engineering opens a solid-state path to room-temperature quality factors approaching 10 billion at kilohertz mechanical frequencies – comparable to the performance of leading cryogenic resonators and levitated nanospheres, even under significantly less stringent temperature and vacuum conditions.

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Nanomechanical resonators have become integral to technological advancements and scientific progress in modern society. Not only do they enable exquisite precision in sensing applications, but they also allow for exploring quantum mechanics and the development of quantum technologies. These applications require resonators with high quality factors capable of isolating them from environmental noise, specifically crucial at room temperature. The focus of this thesis is on investigating the limits of quality factors in nanomechanical resonators operating at room temperature. The study revolves around four main facets, addressing limitations in fabrication techniques, and design strategies, exploring the impact of aspect ratio on quality factor enhancement, and investigating the potential for temperature sensing. Firstly, we address the limits imposed by current fabrication techniques to realize high aspect ratio resonators, such as stiction and collapse due to interfacial forces like capillary. To overcome these challenges, we develop and characterize an SF6 plasma etching technique which enables a quick and controllable release of nanomechanical resonators. The high fidelity achieved through this approach allows the use of advanced optimization strategies to design resonators with exceptional quality factors. In doing so, we tackle the limits of design strategies, which have primarily relied on human intuition until now. By harnessing the power of Bayesian Optimization and inspired by nature, we discover a strategy to increase the quality factor at low order mode via a torsional soft-clamping mechanism. The experimental validation of the resulting spiderweb resonators confirms quality factors surpassing 1 billion at room temperature in the kHz frequency range. Notably, these resonators contain no features smaller than 1 micrometer, ensuring a fast and cost-effective fabrication. Expanding on these findings, the thesis explores the limits of aspect ratio in quality factor enhancement. By bridging nanomechanics and macromechanics, we create nanomechanical resonators with centimeter-scale lateral sizes. Utilizing multi-fidelity Bayesian Optimization alongside stiction-free fabrication techniques, our strategy allows to reduce the computational cost and to suspend the fragile structures with a fabrication yield approaching 100%, leading to a quality factor above 6 billion. Finally, the thesis investigates the potential of high quality factor nanomechanical resonators for temperature sensing. We develop a primary noise thermometer to detect temperature across a wide range. The elevated quality factor enables the detection of the effect of the Brownian motion on the resonator’s motion. However, it also poses limitations on the measurement scheme due to the narrow linewidth of the resonators. Combining all these aspects, this thesis explores and pushes the boundaries of quality factors in nanomechanical resonators at room temperature. It presents novel fabrication techniques, advanced design strategies, and sensing capabilities of high quality factor resonators. The findings offer valuable insights and open up new possibilities for applications in precision sensing, quantum mechanics, and beyond.@en

Mechanical frequency combs are poised to bring the applications and utility of optical frequency combs into the mechanical domain. So far, their main challenge has been strict requirements on drive frequencies and power, which complicate operation. We demonstrate a straightforward mechanism to create a frequency comb consisting of mechanical overtones (integer multiples) of a single eigenfrequency, by monolithically integrating a suspended dielectric membrane with a counter-propagating optical trap. The periodic optical field modulates the dielectrophoretic force on the membrane at the overtones of a membrane’s motion. These overtones share a fixed frequency and phase relation, and constitute a mechanical frequency comb. The periodic optical field also creates an optothermal parametric drive that requires no additional power or external frequency reference. This combination of effects results in an easy-to-use mechanical frequency comb platform that requires no precise alignment, no additional feedback or control electronics, and only uses a single, mW continuous wave laser beam. This highlights the overtone frequency comb as the straightforward future for applications in sensing, metrology and quantum acoustics.

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For decades, mechanical resonators with high sensitivity have been realized using thin-film materials under high tensile loads. Although there are remarkable strides in achieving low-dissipation mechanical sensors by utilizing high tensile stress, the performance of even the best strategy is limited by the tensile fracture strength of the resonator materials. In this study, a wafer-scale amorphous thin film is uncovered, which has the highest ultimate tensile strength ever measured for a nanostructured amorphous material. This silicon carbide (SiC) material exhibits an ultimate tensile strength of over 10 GPa, reaching the regime reserved for strong crystalline materials and approaching levels experimentally shown in graphene nanoribbons. Amorphous SiC strings with high aspect ratios are fabricated, with mechanical modes exceeding quality factors 10⁸ at room temperature, the highest value achieves among SiC resonators. These performances are demonstrated faithfully after characterizing the mechanical properties of the thin film using the resonance behaviors of free-standing resonators. This robust thin-film material has significant potential for applications in nanomechanical sensors, solar cells, biological applications, space exploration, and other areas requiring strength and stability in dynamic environments. The findings of this study open up new possibilities for the use of amorphous thin-film materials in high-performance applications.

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Mechanical resonators that possess coupled modes with harmonic frequency relations have recently sparked interest due to their suitability for controllable energy transfer and non-Hermitian dynamics. Here we show coupling between high-𝑄-factor (greater than 104) resonances with a nearly 1:1 frequency relation in spatially symmetric microresonators. We develop and demonstrate a method to analyze their dynamical behavior based on the simultaneous and resonant detection of both spectral peaks, and validate this with experimental results. The frequency difference between the peaks modulates their ringdown, and creates a beat pattern in the linear decay. This method applies to both the externally driven regime and the Brownian-motion (thermal) regime, and allows characterization of both linear and nonlinear parameters. The mechanism behind this method renders it broadly applicable to both optical and electrical readout, as well as to different mechanical systems. This will aid studies using near-degenerate mechanical modes, for example, optomechanical energy transfer, synchronization, and gyroscopic sensors.@en

State-of-the-art nanomechanical resonators are heralded as a central component for next-generation clocks, filters, resonant sensors, and quantum technologies. To practically build these technologies will require monolithic integration of microchips, resonators, and readout systems. While it is widely seen that mounting microchip substrates into a system can greatly impact the performance of high-Q resonators, a systematic study has remained elusive, owing to the variety of physical processes and factors that influence the dissipation. Here, we analytically analyze a mechanism by which substrates couple to resonators manufactured on them and experimentally demonstrate that this coupling can increase the mechanical dissipation of nanomechanical resonators when resonance frequencies of resonator and substrate coincide. More generally, we then show that a similar coupling mechanism can exist between two adjacent resonators. Since the substrate–mode coupling mechanism strongly depends on both the resonator position on the substrate and the mounting of the substrate, this work provides key design guidelines for high-precision nanomechanical technologies.@en

From ultrasensitive detectors of fundamental forces to quantum networks and sensors, mechanical resonators are enabling next-generation technologies to operate in room-temperature environments. Currently, silicon nitride nanoresonators stand as a leading microchip platform in these advances by allowing for mechanical resonators whose motion is remarkably isolated from ambient thermal noise. However, to date, human intuition has remained the driving force behind design processes. Here, inspired by nature and guided by machine learning, a spiderweb nanomechanical resonator is developed that exhibits vibration modes, which are isolated from ambient thermal environments via a novel “torsional soft-clamping” mechanism discovered by the data-driven optimization algorithm. This bioinspired resonator is then fabricated, experimentally confirming a new paradigm in mechanics with quality factors above 1 billion in room-temperature environments. In contrast to other state-of-the-art resonators, this milestone is achieved with a compact design that does not require sub-micrometer lithographic features or complex phononic bandgaps, making it significantly easier and cheaper to manufacture at large scales. These results demonstrate the ability of machine learning to work in tandem with human intuition to augment creative possibilities and uncover new strategies in computing and nanotechnology.

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