Lead free heterogeneous multilayers with giant magneto electric coupling for microelectronics/microelectromechanical systems applications

Lead free magneto electrics with a strong sub resonant (broad frequency range) magneto electric coupling coefficient (MECC) is the goal of the day which can revolutionise the microelectronics and microelectromechanical systems (MEMS) industry. We report giant resonant MECC in lead free nanograined Barium Titanate–CoFe (Alloy)-Barium Titanate [BTO-CoFe-BTO] sandwiched thin films. The resonant MECC values obtained here are the highest values recorded in thin films/ multilayers. Sub-resonant MECC values are quite comparable to the highest MECC reported in 2-2 layered structures. MECC got enhanced by two orders at a low frequency resonance. The results show the potential of these thin films for transducer, magnetic field assisted energy harvesters, switching devices, and storage applications. Some possible device integration techniques are also discussed

Dynamics deflection analysis of nanoelectromechanical switches based on carbon nanotubes

This paper aims to develop an effective numerical simulation technique for the dynamic deflection analysis of nanotubes-based nanoswitches. The nanoswitch is simplified to a continuum structure, and some key material parameters are extracted from typical molecular dynamics (MD). An advanced local meshless formulation is applied to obtain the discretized dynamic equations for the numerical solution. The developed numerical technique is firstly validated by the static deflection analyses of nanoswitches, and then, the fundamental dynamic properties of nanoswitches are analyzed. A parametric comparison with the results in the literature and from experiments shows that the developed modelling approach is accurate, efficient and effective.

A fundamental numerical and theoretical study for the vibrational properties of nanowires

Based on the molecular dynamics (MD) simulation and the classical Euler-Bernoulli beam theory, a fundamental study of the vibrational performance of the Ag nanowire (NW) is carried out. A comprehensive analysis of the quality (Q)-factor, natural frequency, beat vibration, as well as high vibration mode is presented. Two excitation approaches, i.e., velocity excitation and displacement excitation, have been successfully implemented to achieve the vibration of NWs. Upon these two kinds of excitations, consistent results are obtained, i.e., the increase of the initial excitation amplitude will lead to a decrease to the Q-factor, and moderate plastic deformation could increase the first natural frequency. Meanwhile, the beat vibration driven by a single relatively large excitation or two uniform excitations in both two lateral directions is observed. It is concluded that the nonlinear changing trend of external energy magnitude does not necessarily mean a nonconstant Q-factor. In particular, the first order natural frequency of the Ag NW is observed to decrease with the increase of temperature. Furthermore, comparing with the predictions by Euler- Bernoulli beam theory, the MD simulation provides a larger and smaller first vibration frequencies for the clamped-clamped and clamped-free thin Ag NWs, respectively. Additionally, for thin NWs, the first order natural frequency exhibits a parabolic relationship with the excitation magnitudes. The frequencies of the higher vibration modes tend to be low in comparison to Euler-Bernoulli beam theory predictions. A combined initial excitation is proposed which is capable to drive the NW under a multi-mode vibration and arrows the coexistence of all the following low vibration modes. This work sheds lights on the better understanding of the mechanical properties of NWs and benefits the increasing utilities of NWs in diverse nano-electronic devices.

A practical signal processing approach for condition monitoring of low speed machinery using Peak-Hold-Down-Sample algorithm

A simple and effective down-sample algorithm, Peak-Hold-Down-Sample (PHDS) algorithm is developed in this paper to enable a rapid and efficient data transfer in remote condition monitoring applications. The algorithm is particularly useful for high frequency Condition Monitoring (CM) techniques, and for low speed machine applications since the combination of the high sampling frequency and low rotating speed will generally lead to large unwieldy data size. The effectiveness of the algorithm was evaluated and tested on four sets of data in the study. One set of the data was extracted from the condition monitoring signal of a practical industry application. Another set of data was acquired from a low speed machine test rig in the laboratory. The other two sets of data were computer simulated bearing defect signals having either a single or multiple bearing defects. The results disclose that the PHDS algorithm can substantially reduce the size of data while preserving the critical bearing defect information for all the data sets used in this work even when a large down-sample ratio was used (i.e., 500 times down-sampled). In contrast, the down-sample process using existing normal down-sample technique in signal processing eliminates the useful and critical information such as bearing defect frequencies in a signal when the same down-sample ratio was employed. Noise and artificial frequency components were also induced by the normal down-sample technique, thus limits its usefulness for machine condition monitoring applications.

Tuneable resonance properties of graphene by nitrogen-dopant

Doping as one of the popular methods to manipulate the properties of nanomaterials has received extensive application in deriving different types of graphene derivates, while the understanding of the resonance properties of dopant graphene is still lacking in literature. Based on the large-scale molecular dynamics simulation, reactive empirical bond order potential, as well as the tersoff potential, the resonance properties of N-doped graphene were studied. The studied samples were established according to previous experiments with the N atom’s percentage ranging from 0.43%-2.98%, including three types of N dopant locations, i.e., graphitic N, pyrrolic N and pyridinic N. It is found that different percentages of N-dopant exert different influence to the resonance properties of the graphene, while the amount of N-dopant is not the only factor that determines its impact. For all the considered cases, a relative large percentage of N-dopant (2.98% graphitic N-dopant) is observed to introduce significant influence to the profile of the external energy, and thus lead to an extremely low Q-factor comparing with that of the pristine graphene. The most striking finding is that, the natural frequency of the defective graphene with N-dopant appears uniformly larger than that of the pristine defective graphene. While for the perfect graphene, the N-dopant shows less influence to its natural frequency. This study will enrich the current understanding of the influence of dopants on graphene, which will eventually shed lights on the design of different molecules-doped graphene sheet.

Microelectromechanical torsional varactors with low parasitic capacitances and high dynamic range

This work focuses on the design of torsional microelectromechanical systems (MEMS) varactors to achieve highdynamic range of capacitances. MEMS varactors fabricated through the polyMUMPS process are characterized at low and high frequencies for their capacitance-voltage characteristics and electrical parasitics. The effect of parasitic capacitances on tuning ratio is studied and an equivalent circuit is developed. Two variants of torsional varactors that help to improve the dynamic range of torsional varactors despite the parasitics are proposed and characterized. A tuning ratio of 1:8, which is the highest reported in literature, has been obtained. We also demonstrate through simulations that much higher tuning ratios can be obtained with the designs proposed. The designs and experimental results presented are relevant to CMOS fabrication processes that use low resistivity substrate. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). DOI: 10.1117/1.JMM.11.1.013006]

Mechanics of Adhesion in MEMS-a Review

A review is presented of the mechanics of microscale adhesion in microelectromechanical systems (MEMS). Some governing dimensionless numbers such as Tabor number, adhesion parameter and peel number for microscale elastic adhesion contact are discussed in detail. The peel number is modified for the elastic contact between a rough surface in contact with a smooth plane. Roughness ratio is introduced to characterize the relative importance of surface roughness for microscale adhesion contact, and three kinds of asperity height distributions are discussed: Gaussian, fractal, and exponential distributions. Both Gaussian and exponential distributions are found to be special cases of fractal distribution. Casimir force induced adhesion in MEMS, and adhesion of carbon nanotubes to a substrate are also discussed. Finally, microscale plastic adhesion contact theory is briefly reviewed, and it is found that the dimensionless number, plasticity index of various forms, can be expressed by the roughness ratio.

Stiction and Anti-Stiction in Mems and Nems

Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surface-area-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part.

Enhanced infra-red emission from sub-millimeter microelectromechanical systems micro hotplates via inkjet deposited carbon nanoparticles and fullerenes

In this paper, we demonstrate a micro-inkjet printing technique as a reproducible post-process for the deposition of carbon nanoparticles and fullerene adlayers onto fully CMOS compatible micro-electro-mechanical silicon-on-insulator infrared (IR) light sources to enhance their infrared emission. We show experimentally a significant increase in the infrared emission efficiency of the coated emitters. We numerically validate these findings with models suggesting a dominant performance increase for wavelengths <5.5 μm. Here, the bimodal size distribution in the diameter of the carbon nanoparticles, relative to the fullerenes, is an effective mediator towards topologically enhanced emittance of our miniaturised emitters. A 90% improvement in IR emission power density has been shown which we have rationalised with an increase in the mean thickness of the deposited carbon nanoparticle adlayer. © 2013 AIP Publishing LLC.

Thermo-optical characterization of fluorescent rhodamine B based temperature-sensitive nanosensors using a CMOS MEMS micro-hotplate

A custom designed microelectromechanical systems (MEMS) micro-hotplate, capable of operating at high temperatures (up to 700 C), was used to thermo-optically characterize fluorescent temperature-sensitive nanosensors. The nanosensors, 550 nm in diameter, are composed of temperature-sensitive rhodamine B (RhB) fluorophore which was conjugated to an inert silica sol-gel matrix. Temperature-sensitive nanosensors were dispersed and dried across the surface of the MEMS micro-hotplate, which was mounted in the slide holder of a fluorescence confocal microscope. Through electrical control of the MEMS micro-hotplate, temperature induced changes in fluorescence intensity of the nanosensors was measured over a wide temperature range. The fluorescence response of all nanosensors dispersed across the surface of the MEMS device was found to decrease in an exponential manner by 94%, when the temperature was increased from 25 C to 145 C. The fluorescence response of all dispersed nanosensors across the whole surface of the MEMS device and individual nanosensors, using line profile analysis, were not statistically different (p < 0.05). The MEMS device used for this study could prove to be a reliable, low cost, low power and high temperature micro-hotplate for the thermo-optical characterisation of sub-micron sized particles. The temperature-sensitive nanosensors could find potential application in the measurement of temperature in biological and micro-electrical systems. The Authors. © 2013 Published by Elsevier B.V. All rights reserved.

Doped polycrystalline 3C-SiC films deposited by LPCVD for radio-frequency MEMS applications

Polycrystalline 3C-SiC films are deposited on SiO2 coated Si substrates by low pressure chemical vapour deposition (LPCVD) with C3H8 and SiH4 as precursors. Controlled nitrogen doping is performed by adding NH3 during SiC growth to obtain the low resistivity 3C-SiC films. X-ray diffraction (XRD) patterns indicate that the deposited films are highly textured (111) orientation. The surface morphology and roughness are determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface features are spherulitic texture with average grain size of 100 nm, and the rms roughness is 20nm (AFM 5 x 5 mu m images). Polycrystalline 3C-SiC films with highly orientational texture and good surface morphology deposited on SiO2 coated Si substrates could be used to fabricate rf microelectromechanical systems (MEMS) devices such as SiC based filters.

A MEMS Light Modulator Based on Diffractive Nanohole Gratings

We present the design, fabrication, and testing of a microelectromechanical systems (MEMS) light modulator based on pixels patterned with periodic nanohole arrays. Flexure-suspended silicon pixels are patterned with a two dimensional array of 150 nm diameter nanoholes using nanoimprint lithography. A top glass plate assembled above the pixel array is used to provide a counter electrode for electrostatic actuation. The nanohole pattern is designed so that normally-incident light is coupled into an in-plane grating resonance, resulting in an optical stop-band at a desired wavelength. When the pixel is switched into contact with the top plate, the pixel becomes highly reflective. A 3:1 contrast ratio at the resonant wavelength is demonstrated for gratings patterned on bulk Si substrates. The switching time is 0.08 ms and the switching voltage is less than 15V.