Nanoelectromechanical systems: Potential, progress, & projections

Nanoelectromechanical systems (NEMS) represent the next regime of size reduction beyond the microscale for mechanical devices. In their tiniest, ultimate realization, NEMS will be formed with sub-nanometer scale precision from atomic- and molecular-scale mechanical elements as first envisaged by Feynman (1). Although nanowire and nanotube based NEMS today verge on this domain, their assembly into functional devices remains more of an art than a science, as they are typically fabricated one-by-one by complicated means with low yield. By contrast, the most robust forms of NEMS are currently patterned by top-down methods; in fact their production is now being scaled to enable large-scale integration over 200 mm wafers with minimum feature sizes that are below 50 nm. In this paper I will describe how nanoscale mechanical elements provide benefits beyond the obvious, that is, benefits in addition to the possibility of increased device density. The reduced size of NEMS enables mechanical functionality that completely transcends what is possible at the microscale with MEMS (2). However, size reduction to the nanoscale may not be a panacea for all applications - for some applications larger may still be better

Ultimate and practical limits of fluid-based mass detection with suspended microchannel resonators

Suspended microchannel resonators (SMRs) are an innovative approach to fluid-based microelectromechanical mass sensing that circumvents complete immersion of the sensor. By embedding the fluidics within the device itself, vacuum-based operation of the resonator becomes possible. This enables frequency shift-based mass detection with high quality factors, and hence sensitivity comparable to vacuum-based micromechanical resonators. Here we present a detailed analysis of the sensitivity of these devices, including consideration of fundamental and practical noise limits, and the important role of binding kinetics in sensing.We demonstrate that these devices show significant promise for protein detection. For larger, biologically-important targets such as rare whole virions, the required analysis time to flow sufficient sample through the sensor can become prohibitively long unless large parallel arrays of sensors or preconcentrators are employed

Nanomechanical Analog of a Laser: Amplification of Mechanical Oscillations by Stimulated Zeeman Transitions

We propose a magnetomechanical device that exhibits many properties of a laser. The device is formed by a nanocantilever and dynamically polarized paramagnetic nuclei of a solid sample in a strong external magnetic field. The corresponding quantum oscillator and effective two-level systems are coupled by the magnetostatic dipole-dipole interaction between a permanent magnet on the cantilever tip and the magnetic moments of the spins, so that the entire system is effectively described by the Jaynes-Cummings model. We consider the possibility of observing transient and cw lasing in this system, and show how these processes can be used to improve the sensitivity of magnetic resonance force microscopy.Comment: REVTeX version 4: 4 pages, 2 figures. Submitted to Phys. Rev. Lett. This version incorporates suggestions of John Sidles and PRL referee

Nanoelectromechanical systems

Nanoelectromechanical systems (NEMS) are drawing interest from both technical and scientific communities. These are electromechanical systems, much like microelectromechanical systems, mostly operated in their resonant modes with dimensions in the deep submicron. In this size regime, they come with extremely high fundamental resonance frequencies, diminished active masses,and tolerable force constants; the quality (Q) factors of resonance are in the range Q~10^3–10^5—significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultrafast sensors, actuators, and signal processing components. Experimentally, NEMS are expected to open up investigations of phonon mediated mechanical processes and of the quantum behavior of mesoscopic mechanical systems. However, there still exist fundamental and technological challenges to NEMS optimization. In this review we shall provide a balanced introduction to NEMS by discussing the prospects and challenges in this rapidly developing field and outline an exciting emerging application, nanoelectromechanical mass detection

Fabrication of high frequency nanometer scale mechanical resonators from bulk Si crystals

We report on a method to fabricate nanometer scale mechanical structures from bulk, single-crystal Si substrates. A technique developed previously required more complex fabrication methods and an undercut step using wet chemical processing. Our method does not require low pressure chemical vapor deposition of intermediate masking layers, and the final step in the processing uses a dry etch technique, avoiding the difficulties encountered from surface tension effects when wet processing mechanically delicate or large aspect ratio structures. Using this technique, we demonstrate fabrication of a mechanical resonator with a fundamental resonance frequency of 70.72 MHz and a quality factor of 2 x 10^(4)

Magnetotransport and magnetocrystalline anisotropy in Ga1-xMnxAs epilayers

We present an analysis of the magnetic anisotropy in epitaxial Ga1-xMnxAs thin films through electrical transport measurements on multiterminal microdevices. The film magnetization is manipulated in 3D space by a three-axis vector magnet. Anomalous switching patterns are observed in both longitudinal and transverse resistance data. In transverse geometry in particular we observe strong interplay between the anomalous Hall effect and the giant planar Hall effect. This allows direct electrical characterization of magnetic transitions in the 3D space. These transitions reflect a competition between cubic magnetic anisotropy and an effective out-of-plane uniaxial anisotropy, with a reversal mechanism that is distinct from the in-plane magnetization. The uniaxial anisotropy field is directly calculated with high precision and compared with theoretical predictions

Allan variance of frequency fluctuations due to momentum exchange and thermomechanical noises

We investigate the Allan variance of nanoresonators with random rough surfaces under the simultaneous influence of thermomechanical and momentum exchange noises. Random roughness is observed in various surface engineering processes, and it is characterized by the roughness amplitude w, the lateral correlation length ξ, and the roughness exponent 0<H<1. The roughness influence becomes significant for measurement time τA so that ωoτA~1, with ωo the fundamental resonance frequency. The Allan variance increases significantly with increasing roughness (decreasing H and/or increasing ratio w/ξ) if the quality factor due to gas collisions is smaller than the intrinsic quality factor associated with thermomechanical noise.

Noise processes in nanomechanical resonators

Nanomechanical resonators can be fabricated to achieve high natural resonance frequencies, approaching 1 GHz, with quality factors in excess of 10^(4). These resonators are candidates for use as highly selective rf filters and as precision on-chip clocks. Some fundamental and some nonfundamental noise processes will present limits to the performance of such resonators. These include thermomechanical noise, Nyquist-Johnson noise, and adsorption-desorption noise; other important noise sources include those due to thermal fluctuations and defect motion-induced noise. In this article, we develop a self-contained formalism for treating these noise sources, and use it to estimate the impact that these noise processes will have on the noise of a model nanoscale resonator, consisting of a doubly clamped beam of single-crystal Si with a natural resonance frequency of 1 GHz

Efficient electrothermal actuation of multiple modes of high-frequency nanoelectromechanical resonators

The authors observed resonances from multiple vibrational modes of individual silicon-carbide-based nanomechanical resonators, covering a broad frequency range from several megahertz to over a gigahertz. The devices are actuated thermoelastically in vacuum at room temperature using localized Joule heating in a device-integrated metal loop. Their motion is detected piezoresistively using signal downmixing in a similarly integrated metal piezoresistor. The frequencies and amplitudes of the observed resonant peaks are in good agreement with the results from theoretical modeling and finite-element simulations