Nanodevices that operate with fundamental frequencies in the previously inaccessible microwave range (greater than 1 gigahertz) have been constructed. Two advances have been crucial to breaking the 1-GHz barrier in nanoelectromechanical systems (NEMS): the use of 3C- silicon carbide epilayers, and the development of balanced, high frequency displacement transducers. This achievement represents a significant advance in the quest for extremely high frequency nanoelectromechanical systems.However, silicon carbide nanomechanical resonators with fundamental frequencies in the ultrahigh frequency and microwave range have exhibited deteriorating quality factors compared to devices at lower frequencies, which could significantly restrict the application of this developing technology. Our experiments have established a strong correlation between silicon carbide surface roughness and deteriorating quality factor. Also, dissipation in such devices increases as the aspect ratio of the doubly clamped beams is reduced. Based on such observations, we have then demonstrated that the SiC free-free beam nanomechanical resonators offer significant improvement in quality factor compared to doubly clamped beam design operating at similar frequencies.Apart from 3C-SiC epilayers on silicon, polished 6H-SiC bulk material based NEMSare also made possible by our invention. A tilted Electron Cyclotron Resonance (ECR) etching technique has been developed to fabricate suspended nanomechanical structures from bulk 6H-SiC wafers. A suspended nanoscale, doubly clamped beam resonator has been made as an initial demonstration of this new fabrication method. Fundamental flexural mode mechanical resonance is detected at 171.2 MHz, with a quality factor of about 3000. The ability to fabricate 3-D suspended nanostructures from 6H-SiC is an important breakthrough in NEMS not only because it enables electronic integration, but also because it provides a unique platform for exploring the effects of crystal and surface quality on resonator performance at microwave frequencies.Magnetomotive transduction has been used extensively in the above achievements, where eddy current damping is usually negligible. However, it was realized that such damping phenomena may turn out to be crucial for doubly clamped beam nanotube mechanical resonators. This concept has been experimentally demonstrated. Silicon carbide material is used to create a dummy nanotube, and in turn being used to investigate the role of eddy current damping phenomena in the context of studying nanotube mechanical motion.Another nanotube-based novel device structure, using a nanotube carrying a single domain nanomagnet paddle, forming a torsional mechanical resonator, has been designed and analyzed. This device design appears capable of force sensing in zeptoNewton/Hz1/2 range at room temperature.As we cool down GHz nanomechanical resonators to low temperatures, the devices approach their quantum regime of operation. A structure designed to enable observation of quantum jumps in nanomechanical devices is described. A prototype device demonstrating a frequency shift transduction scheme is fabricated and tested in the classical domain. The coupling mechanism involved is analogous to Kerr nonlinearity in quantum optics. This nanomechanical approach should allow quantum nondemolition (QND) measurements if the experimental technique is extended into the quantum regime. Based on quantum simulations and experimental analysis, we argue that single quanta sensitivity can be achieved in next-generation devices of this kind.
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Ultrahigh and microwave frequency nanomechanical systems
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