Showing papers in "Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems in 2014"

Erratum to: Design principles and considerations for the `ideal' silicon piezoresistive pressure sensor: a focused review

Abstract: Over the past four decades, the field of silicon piezoresistive pressure sensors has undergone a major revolution in terms of design methodology and fabrication processes. Cutting edge fabrication technologies have resulted in improved precision in key factors like dimensions of diaphragm and placement of piezoresistors. Considering the unique nature of each sensor and the trade-offs in design, it is not feasible to follow a standard design approach. Thus, it is useful to derive the specific design from a number of important factors to arrive at the `ideal' design. In this paper, we critically review and analyze the various design considerations and principles for silicon piezoresistive pressure sensor. We also report the effect of these considerations on the sensor output taking help of various CAD tools. Keeping in view the accuracy of state-of-the-art fabrication tools and the stringent demands of the present day market, it has become important to include many of these design aspects. Modelling using analytical expressions for thin plates has also been looked into as it gives a quick guideline and estimation of critical parameters before detailed finite element method analysis. Wherever possible, fabrication imperfections and their effects have been discussed. Dependency of piezoresistive coefficients on temperature and doping concentration, the effect of clamping condition of diaphragms and fabrication using wet bulk micromachining is also analyzed. Silicon-on-insulator based sensors along with innovative design strategies, and future trends have also been discussed. This paper will serve as a quick and comprehensive guide for pressure sensor developers.

Wide bandgap semiconductor thin films for piezoelectric and piezoresistive MEMS sensors applied at high temperatures: an overview

Abstract: The use of wide bandgap semiconductor thin films as sensing materials for micro-electrical---mechanical systems (MEMS) sensors has been the subject of much discussion in the academic and industrial communities. The motivation is that such materials are recognized as being suitable for extreme environment applications, namely: high temperatures, intense radiation and corrosive atmospheres. Among the wide bandgap semiconductor materials, aluminum nitride (AlN), zinc oxide (ZnO), diamond-like carbon (DLC) and silicon carbide (SiC) are highlighted due to their inherent sensing properties and compatibility with MEMS fabrication processes. Here we show an overview on the development technologies and applications of AlN, ZnO, DLC and SiC thin films in piezoelectric and piezoresistive MEMS sensors. Emphasis is placed on the influence of the temperature on the piezoelectric and piezoresistive properties of these films.

A comprehensive study on RF MEMS switch

Abstract: This paper emphasis on state-of-the-art of the earlier until the current trend and demand, principles, design considerations, key performance and fabrication technology of RF MEMS switch devices developed over the past few years. RF MEMS switch performance and features such as actuation voltage, insertion loss, isolation and ease with cost of fabrication and applications are compared and discussed.

Nonlinear behaviour of membrane type electromagnetic energy harvester under harmonic and random vibrations

Abstract: In this paper, the fabrication and characterization of a vibration-based polydimethylsiloxane (PDMS) membrane type electromagnetic energy harvester (EMEH) is reported. The harvester is suitable for generating electric energy from low level sinusoidal and narrow band random vibrations. Under acceleration levels greater than 0.1 g the behaviour of the EMEH is nonlinear, exhibiting sharp jump and hysteresis phenomena during frequency sweeps. Under sinusoidal excitations (0.1–3 g), the device produces a maximum of 88.8 mV load voltage and 39.4 μW power. At a matching load impedance of 10.1 Ω and when excited at its resonant frequency of 108.4 Hz and 3 g base acceleration, it generates a power of 68.0 μW, which corresponds to a power density of 30.22 μW/cm3. The nonlinear behaviour of the EMEH is exploited to harvest energy under narrow band random excitations. At higher acceleration levels of narrow band (50–150 Hz) random excitations, the device exhibits a broadening of the load voltage spectrum in comparison to the response under relatively low acceleration levels of narrow band (5–150 Hz) random excitations. The results show that the nonlinear behaviour of the PDMS membrane can be utilized to enhance the bandwidth of the harvester under narrow band random excitations and provides a simple alternative to other bandwidth broadening methods such as beam prestress, resonance tuning, or stopper impacts.

Application of quartz tuning forks and extensional microresonators for viscosity and density measurements in oil/fuel mixtures

Abstract: Real time monitoring of the physical properties of liquids is of great concern in the automotive industry. For example, tracking the viscosity of lubricating oils is of great importance because they are exposed to dilution with diesel fuel as result of late-injection processes, which are essential for regenerating diesel particulate filters. Here we describe two in-plane movement based resonators and their capability to assess oil dilution with diesel and biodiesel fuels. One of the resonators is a state-of-the-art micron-sized AlN-based rectangular plate, actuated in the first extensional mode in the MHz range. The second resonator is a commercially available millimeter-sized quartz tuning fork, working at 32.7 kHz. Electrical impedance measurements were performed to characterize the performance of both resonators in various liquid media over a wide range of viscosities. These measurements were compared with the results obtained with low-cost electronic circuits also developed in this work. In order to track density and viscosity of different fluids we have measured two parameters by various techniques: the resonance frequency and the quality factor.

A flexible PDMS capacitive tactile sensor with adjustable measurement range for plantar pressure measurement

Abstract: A flexible capacitive tactile sensor with adjustable characteristics, i.e., measurement range and sensitivity, has been developed. The proposed sensor is designed for large pressure measurement; therefore, polydimethylsiloxane (PDMS) material is selected as the material of the dielectric layer between the parallel plate electrodes of the sensor. Since the elasticity of the PDMS material can be adjusted by the mixing ratio of PDMS pre-polymer and curing agent during formation, sensors in different measurement ranges, i.e., 240–1,000 and 400–3,000 kPa, and corresponding sensitivities, i.e., 2.24 and 0.28 %/MPa, were respectively constructed and demonstrated. These measurement ranges are suitable for most of the biomechanical applications, especially for plantar pressure measurement. Moreover, because the output of the sensor, i.e., capacitance, is highly influenced by the dimension of the sensor structure, each sensor consists of four independent capacitance elements. The output of each sensor is averaged by four capacitances for single force measurement. This could improve the measurement accuracy in practical situation. Also, linearity of the measurement response could be enhanced and it was shown by the R-squared values in two measurement ranges, i.e., 0.9751 and 0.9881, respectively. The proposed sensor is flexible and miniaturized and has the potential to be applied to biomechanical applications.

Magnetic tunnel junction sensors with pTesla sensitivity

Abstract: Ultrasensitive magnetic field sensors at low frequencies are necessary for several biomedical applications. Suitable devices can be achieved by using large area magnetic tunnel junction (MTJ) sensors combined with permanent magnets to stabilize the magnetic configuration of the free layer and improve linearity. However, further increase in sensitivity and consequently detectivity are achieved by incorporating also soft ferromagnetic flux guides (FG). A detailed study of tunnel junction sensors with variable areas and aspect ratios is presented in this work. In addition, the effect in the sensors transfer curve, namely in their coercivity and sensitivity, as a consequence of the incorporation of permanent magnets and FG is also thoroughly discussed. Devices consisting of MgO-based MTJ with magnetoresistance levels of ~200 %, and incorporating thin film permanent magnets (CoCrPt) and CoZrNb flux guides, could reach sensitivities of ~2,000 %/mT at room temperature, in a non-shielded environment. The noise levels of the final device measured at 10 Hz yield 3.9 × 10−17 V2/Hz, leading to the lowest detectable field of ~49 pT/Hz0.5. This value is half of the best value we obtained with MTJ-based devices, and represents a step further towards integration in a biomedical device for magnetocardiography.

Design of novel compact anti-stiction and low insertion loss RF MEMS switch

Abstract: A novel torsional RF MEMS capacitive switch design on silicon substrate is presented. The optimized switch topology such as reduction in up-state capacitance results in insertion loss better than ź0.1 dB till 20 GHz. Off to on state capacitance ratio is also improved by 18 fold and isolation is better than ź43 dB at 9.5 GHz. The achieved on state return loss is ź38 dB as compared to ź21 dB at 9.5 GHz. An optimized reduction in contact area and use of floating metal layer increases the switching speed from 56 to 46 μsec. It also increases the switch reliability by alleviating the stiction.

On the crystallinity of PVA/palm leaf biocomposite using DSC and XRD techniques

Abstract: Biocomposites of polyvinyl alcohol (PVA) and palm leaf powder were prepared using solution casting method. The effect of addition of palm leaf into PVA matrix on thermal behaviour was studied by differential scanning calorimetry and on crystalline properties using X-ray diffraction (XRD) techniques. On the basis of differential scanning calorimetry (DSC) thermograms, the glass transition temperature, melting temperature, melting enthalpy of fusion and crystallinity were determined. It is found that the glass transition temperature initially decreases; however, it increases with further increase in amount of palm leaf powder in the biocomposite. The melting enthalpy of fusion and crystallinity is found to increase for samples with palm leaf up to 15 wt%. The crystallinity is observed to be 37.29 % for biocomposite with 15 wt% of palm leaf as compared to 27.45 % for pure PVA. On the basis of XRD studies, decrease in the interplanar distance and crystallite size is observed while the order of crystallinity is found to increase in similar manner as observed in DSC thermograms. Thus, the addition of palm leaf powder in the poly vinyl alcohol can be developed as a biocomposite with increased thermal stability and crystalline properties.

Evaluation of low-acceleration MEMS piezoelectric energy harvesting devices

Abstract: Microelectromechanical systems-based piezoelectric energy harvesting device research is continuing to increase due to high demands in powering wireless sensor networks. This paper compares three different cantilever structures that have been the most widely used designs in MEMS energy harvesting devices. The cantilever structures consist of a wide beam, narrow beam, and trapezoidal beam structure. Aluminium nitride was used as the piezoelectric material because of its CMOS compatibility. Finite element modelling was used to investigate the theoretical outputs of the devices prior to fabrication. The three different structures were fabricated using standard micro-fabrication techniques on SOI wafers in order to verify the results experimentally. The finite element modelling results agree with the experimental results. The AlN deposited on the experimental wafers had a (002) FWHM rocking curve value of 1.7°. The power density based on the volume of space needed to fabricate the structures was 2.5, 0.78, and 0.65 mW/cm3/g2 at resonant frequency for the wide, trapezoidal, and narrow beam structures respectively. The bandwidth of the devices is also an important parameter when selecting the cantilever structure. An array of the cantilevers over a 4 cm2 area resulted in a bandwidth of was 4.8, 9, and 26.4 Hz for the wide, trapezoidal, and narrow beam structures respectively.

A phase-locked loop frequency tracking system for portable microelectromechanical piezoresistive cantilever mass sensors

Abstract: A closed-loop circuit is developed in this work for tracking the resonant frequency of silicon microcantilever mass sensors. The proposed closed-loop system is mainly based on a phase-locked loop (PLL) circuit. To lock onto the resonant frequency of the resonator, an actuation signal generated from a voltage-controlled oscillator is fed back to the input reference signal of the cantilever sensor. In addition to the PLL circuit, an instrumentation amplifier and an active low-pass filter are connected to the system for gaining the cantilever output signal and transforming a rectangular PLL output signal into a sinusoidal signal used for sensor actuation, respectively. To demonstrate the functionality of the system, a self-sensing silicon cantilever resonator with a built-in piezoresistive Wheatstone bridge is fabricated and integrated with the circuit. A piezoactuator is employed to actuate the cantilever into resonance. From the measurement results, the integrated closed-loop system is successfully employed to characterize a 9.4 kHz cantilever sensor under ambient temperature cross-sensitivity yielding a sensor temperature coefficient of −32.8 ppm/°C. In addition to it, the sensor was also exposed to exhaled human breath condensates and e-cigarette aerosols to test the sensor sensitivity obtained from mass-loading effects. With a high frequency stability (i.e., a frequency deviation as low as 0.02 Hz), this developed system is intended to support the miniaturization of the instrumentation modules for cantilever-based nanoparticle detectors (CANTORs).

PZT length optimization of MEMS piezoelectric energy harvester with a non-traditional cross section: simulation study

Abstract: Cantilevered beams with piezoelectric layers have been used as a MEMS piezoelectric energy harvester for the one decade. The literature includes several structures such as rectangular triangular and trapezoidal geometry. In several literatures the length of cantilever is optimized to enhance the performance. This paper presents enhancing the performance of energy harvester by optimizing the PZT length through simulation using moving mesh analysis in COMSOL Multiphysics. The results show that the MEMS piezoelectric energy harvester with optimized PZT length produces more voltage. Simulation results are compared with other structures having traditional and non-traditional cross section.

A rotary comb-actuated microgripper with a large displacement range

Abstract: This paper reports a novel design for electrostatic microgrippers. The new structure utilizes rotary comb actuators to solve the pull-in problem of microgrippers during large displacement manipulation and therefore avoids the widely used conversion systems which necessitate a high driving voltage. The gripper is fabricated using a SOI process with a 60 μm structural layer. Test results show the gripper obtained a displacement of 94 μm with an applied voltage of 100 V. An animal hair is gripped to demonstrate the applicability of the gripper for micro object manipulations.

Underwater artificial lateral line flow sensors

Abstract: Biomimetics is a promising field of research in which natural processes and structures are transferred to technical applications. The lateral line is a critical component of the fish sensory system and plays an important role in many behaviors by providing hydrodynamic information about the surrounding fluid. It is believed that the artificial lateral line flow sensors (ALLFS) are advantageous for underwater applications. This paper reviews the morphology and biophysics of the lateral line, especially theoretical models of lateral line, including biomechanical model, frequency response and time domain response of lateral line. Also, this paper reviews some efforts to mimic lateral line system in recent years. In order to capture the recent research status, this paper reviews the design and fabrication of ALLFS based on different sensing principles. Further researches to develop ALLFS and their underwater applications are also discussed in this paper.

A biomimetic approach to machine olfaction, featuring a very large-scale chemical sensor array and embedded neuro-bio-inspired computation

Abstract: Biological olfaction outperforms chemical instrumentation in specificity, response time, detection limit, coding capacity, time stability, robustness, size, power consumption, and portability. This biological function provides outstanding performance due, in a large extent, to the unique architecture of the olfactory pathway, which combines a high degree of redundancy and efficient combinatorial coding, with unmatched chemical information processing mechanisms. The last decade has seen important advances in the understanding of the computational primitives underlying the functioning of the olfactory system. The EU-funded Project NEUROCHEM (Bio-ICT-FET- 216916) developed novel computing paradigms and biologically motivated artefacts for chemical sensing, taking its inspiration from the biological olfactory pathway. To demonstrate this approach, a biomimetic demonstrator has been built that features a very large-scale sensor array (65,536 elements) using conducting polymer technology which mimics the olfactory receptor neuron layer. It implements derived computational neuroscience algorithms in an embedded system that interfaces the chemical sensors and processes their signals in real-time. This embedded system integrates abstracted computational models of the main anatomic building blocks in the olfactory pathway: the olfactory bulb, and olfactory cortex in vertebrates (respectively, antennal lobe and mushroom bodies in the insect). For implementation in the embedded processor, an abstraction phase has been carried out in which their processing capabilities are captured by algorithmic solutions implemented in software. Finally, the algorithmic models are tested in mixed chemical plumes with an odour robot having navigation capabilities.

Overview of microneedle system: a third generation transdermal drug delivery approach

Abstract: Transdermal drug delivery has given cardinal contribution to medical practices. First-generation transdermal delivery of small, lipophilic, low-dose drugs and second-generation delivery systems using chemical enhancers, non-cavitational ultrasound and iontophoresis have also resulted in various clinical products provides added functionality. Third-generation delivery systems using microneedles, thermal ablation, microdermabrasion, electroporation and cavitational ultrasound targeting skin's barrier layer of stratum corneum. Microneedles acquire pronounced intrigue in recent days. Currently, microneedles are advancing through clinical trials for delivery of macromolecules and vaccines, such as insulin, parathyroid hormone and influenza vaccine. The review explains about the concept of transdermal drug microneedle system comprising of microreservoir, micropumps, flow sensors, types of microneedles. Various researches carried out on these components of microneedle system is elaborately discussed in this review.

High temperature stability of electrically conductive Pt–Rh/ZrO2 and Pt–Rh/HfO2 nanocomposite thin film electrodes

Abstract: Nanocomposite films made up of either Pt–Rh/ZrO2 or Pt–Rh/HfO2 materials were co-deposited using multiple e-beam evaporation sources onto langasite (La3Ga5SiO14) substrates, both as blanket films and as patterned interdigital transducer electrodes for surface acoustic wave sensor devices. The films and devices were tested after different thermal treatments in a tube furnace up to 1,200 °C. X-ray diffraction and electron microscopy results indicate that Pt–Rh/HfO2 films are stabilized by the formation of monoclinic HfO2 precipitates after high temperature exposure, which act as pinning sites to retard grain growth and prevent agglomeration of the conductive cubic Pt–Rh phase. The Pt–Rh/ZrO2 films were found to be slightly less stable, and contain both tetragonal and monoclinic ZrO2 precipitates that also helps prevent Pt–Rh agglomeration. Film conductivities were measured versus temperature for Pt–Rh/HfO2 films on a variety of substrates, and it was concluded that La and/or Ga diffusion from the langasite substrate into the nanocomposite films is detrimental to film stability. An Al2O3 diffusion barrier grown on langasite using atomic layer deposition was found to be more effective than a SiAlON barrier layer in minimizing interdiffusion between the nanocomposite film and the langasite crystal at temperatures above 1,000 °C.

A microbial fuel cell powering an all-digital piezoresistive wireless sensor system

Abstract: Microbial fuel cells (MFCs) are energy sources, which generate electrical charge thanks to bacteria metabolism. We report on a full custom pressure wireless sensor node especially designed to operate with MFCs, comprising an ultra-low-power Impulse-Radio Ultra-Wide-Band Transmitter operating in the low 0–960 MHz band, a nanostructured piezoresistive pressure sensor connected to a discrete component digital read-out circuit, and an MFC energy supply system. The sensor device comprises an insulating matrix of polydimethylsiloxane and nanostructured multi-branched copper microparticles as conductive filler. Our prototype system comprises two MFCs connected in series to power both the UWB transmitter, which consumes 40 μW, and the read-out circuit. The two MFCs generate an open circuit voltage of 1.2 ± 0.1 V. Each MFC prototype has a total volume of 0.34 L and comprises two circular poly(methyl methacrylate) chambers (anode and cathode) separated by a cation exchange membrane. The paper reports measurements on a fully working prototype that enables the separate transmission of pressure information and MFC voltage level at the same time. The complete sensor node powered by the MFC, thanks to its nature can be located either in harsh environments where there is no connection to energy grids, or in environments where the MFC, hence the complete node, can self-sustain.

Detection principles and development of microfluidic sensors in the last decade

Abstract: Microfluidic sensor converts a physical quantity to useful signal with the help of microfluidic platform. Microfluidic sensors have got a wide attention in the last decade because of the increased demands from the automation and control in microsystems. This review on microfluidic sensors focuses on various types of sensors which have been developed for the microfluidic systems or applications based on the research contributions in the last decade. We start with a detailed comparison on the research developments in the last decade on microfluidic sensors with the help of year and country wise statistical charts on published works in the area. The review continues with the basics of microfluidic sensors and the working principles of microfluidic sensors by classifying various microfluidic sensors based on the parameter to be sensed. This review concludes with the attempt to provide an idea on research gap in the area of microfluidic sensors.

Multi-modal vibration based MEMS energy harvesters for ultra-low power wireless functional nodes

Abstract: In this work we discuss a novel design concept of energy harvester (EH), based on Microsystem (MEMS) technology, meant to convert mechanical energy, available in the form of vibrations scattered in the surrounding environment, into electrical energy by means of the piezoelectric conversion principle. The resonant structure, named four-leaf clover (FLC), is circular and based on four petal-like double mass-spring systems, kept suspended through four straight beams anchored to the surrounding Silicon frame. Differently from standard cantilever-type EHs that typically convert energy uniquely in correspondence with the fundamental vibration frequency, this particular shape is aimed to exploit multiple resonant modes and, thereby, to increase the performance and the operation bandwidth of the MEMS device. A preliminary non-optimized design of the FLC is discussed and physical samples of the sole mechanical resonator, fabricated at the DIMES Technology Center (Delft University of Technology, the Netherlands), are experimentally characterized. Their behaviour is compared against simulations performed in ANSYS Workbench™, confirming good accuracy of the predictive method. Furthermore, the electromechanical multiphysical behaviour of the FLC EH is also analysed in Workbench, by adding a layer with piezoelectric conversion properties in the simulation. The measured and simulated data reported in this paper confirm that the MEMS converter exhibits multiple resonant modes in the frequency range below 1 kHz, where most of the environmental vibration energy is scattered, and extracted power levels of 0.2 μW can be achieved as well, in closed-loop conditions. Further developments of this work are expected to fully prove the high-performance of the FLC concept, and are going to be addressed by the authors of this work in the on-going activities.

Design optimization of micromixer with square-wave microchannel on compact disk microfluidic platform

Abstract: This paper presents a passive micromixer on a compact disk (CD) microfluidic platform that performs plasma mixing function. The driving force of CD microfluidic platform including, the centrifugal force due to the system rotation, the Coriolis force as a function of the rotation angular frequency and velocity of liquid. Numerical simulations are performed to investigate the flow characteristics and mixing performance of three CD microfluidic mixers with square-wave, curved and zig-zag microchannels, respectively. Of the three microchannels, the square-wave microchannel is found to yield the best mixing performance, and is therefore selected for design optimization. Four CD microfluidic micromixers incorporating square-wave PDMS microchannels with different widths in the x- and y-directions are fabricated using conventional photolithography techniques. The mixing performance of the four microchannels is investigated both numerically and experimentally. The results show that given an appropriate specification of the microchannel geometry and a CD rotation speed of 2,000 rpm, a mixing efficiency of more than 93 % can be obtained within 5 s.

Analysis of the correlation between acoustic noise and vibration generated by a multi-layer ceramic capacitor

Abstract: Acoustic noise generated by a multi-layer ceramic capacitor (MLCC) makes users uncomfortable, so the problem must be analyzed to reduce the noise. There is a correlation between the acoustic noise and the vibration of MLCCs and the circuit board. Therefore, the acoustic noise problem must be investigated from a vibration perspective. In this study, the acoustic noise-generating mechanism was investigated, and the relationship between the characteristics of the noise and the dynamic characteristics of the circuit board with MLCC was analyzed. And a correlation criterion was proposed to predict the acoustic noise using the vibration response of the circuit board.

Model-based design and test of vibration energy harvester for aircraft application

Abstract: This paper deals with a development process of a vibration energy harvesting device in aircraft applications. The vibration energy harvester uses ambient energy of mechanical vibration and it provides an autonomous source of energy for wireless sensors or autonomous applications. This application presents a complex engineering problem and the vibration energy harvester consists of precise mechanical part, electro-mechanical converter, electronics and a powered application. It can be perceive as a mechatronic system and a mechatronic approach was used for development of our vibration energy harvester. An essential step of development process is simulation modeling which is based on mechatronic approach. Presented model-based design of vibration energy harvester is very useful during development process and the whole development process of the autonomous energy source is presented in this paper. The main aim of the paper is an introduction of our development methodology and our approach is presented on a sample of the vibration energy harvester for aircraft applications under project ESPOSA.

Modeling the instability of CNT tweezers using a continuum model

Abstract: Carbon nanotube (CNT) tweezers are composed of two parallel cantilever CNTs with a distance in between. In this paper, the static response and instability of CNT-made nano-tweezers is theoretically investigated considering the effects of Coulomb electrostatic force and van der Waals molecular attraction. For this purpose, a nano-scale continuum model is employed to obtain the nonlinear constitutive equation of the nano-tweezers. The Euler–Bernoulli beam theory is applied to model the elastic response of the CNT. The van der Waals attraction is computed from the simplified Lennard-Jones potential. In order to solve the nonlinear constitutive equation of the system, three approaches, e.g. the hemotopy perturbation method (HPM), the Adomian decomposition (AD) and the finite difference method (FDM) are employed. The obtained results are in good agreement with the experimental measurements. As a case study, freestanding CNT tweezers has been investigated and the detachment length and minimum initial gap of the tweezers are determined. Moreover, the effective operation range of the van der Waals attraction that affects the instability behavior of the CNT tweezers is discussed.

Production of vertical nanowire resonators by cryogenic-ICP–DRIE

Abstract: Silicon resonant sensors with large surface area-to-volume ratios provide high weighing sensitivity. This fact implies the possibility for detection of slight mass changes [i.e. by attached nanoparticles (NPs)]. Vertical silicon nanowire (SiNW) resonators are therefore suitable for exposure assessment or airborne NPs. SiNW arrays are top-down fabricated by nanolithography and subsequent inductively coupled plasma reactive ion etching at cryogenic temperature. Nanolithography is performed by conventional UV-lithography and nanoimprint for even smaller structures. Wire diameters are further reduced by multiple thermal oxidations and oxide stripping at times. Parameter effects of cryogenic dry etching are studied for SiNW arrays.

High aspect ratio gold nanopillars on microelectrodes for neural interfaces

Abstract: Microelectrode arrays (MEA) have become an established tool in applied and fundamental research Low impedance at the interface between tissue and conducting electrodes is of utmost importance for the electrical recording or stimulation of electrophysiological active cells such as cardiac myocytes and neurons A common way to improve this interface is to increase the electrochemically active surface area of the electrode In this paper the fabrication of microelectrodes covered with very high aspect ratio (AR > 100) gold nanopillars is presented and electrode biocompatibility is investigated using cell culture experiments The nanopillar electrodes show decreased impedance over the entire scanned frequency range of 1 Hz---100 kHz and an impedance improvement of up to 895 at 1 kHz depending on nanopillar height Neurons adhere well to the substrate and electrodes and signals with amplitudes up to ten times higher than with conventional gold electrodes were recorded in cell culture experiments

Silicon 45° micromirrors fabricated by etching in alkaline solutions with organic additives

Abstract: The fabrication of 45° micromirrors by silicon anisotropic etching in potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) solutions containing organic additives is investigated in this paper. The reflective planes are formed by {110} sidewall planes inclined at 45° towards the Si (100) wafer. Isopropyl alcohol and Triton X-100 surfactant are used as additives, because they are supposed to provide the etch rate ratio R(100)/R(110) > 1, which is necessary for {110} sidewalls development. The fabricated spatial microstructures with 45° sidewalls are examined in terms of the {110} surface roughness and the quality of the {110} sidewall profile. The KOH solution saturated with the alcohol gives the striped {110} surface, though the stripes almost disappear after addition of Triton surfactant to KOH and TMAH etchants. The 45° sidewall profiles fully defined by {110} planes are obtained in KOH as well as TMAH solutions containing additives. The measurements of micromirrors' reflectivity indicate that replacement of the alcohol by Triton surfactant in the KOH solution reduces the optical power loss caused by the reflection. The achieved reflectivity is comparable with the one obtained by etching in the TMAH solution with surfactant.

Finite element modeling and experimental proof of NEMS-based silicon pillar resonators for nanoparticle mass sensing applications

Abstract: The potential use of nanoelectromechanical systems (NEMS) created in silicon nanopillars (SiNPLs) is investigated in this work as a new generation of aerosol nanoparticle (NP)-detecting device. The sensor structures are created and simulated using a finite element modeling (FEM) tool of COMSOL Multiphysics 4.3b to study the resonant characteristics and the sensitivity of the SiNPL for femtogram NP mass detection in 3-D structures. The SiNPL arrays use a piezoelectric stack for resonance excitation. To achieve an optimal structure and to investigate the etching effect on the fabricated resonators, SiNPLs with different designs of meshes, sidewall profiles, heights, and diameters are simulated and analyzed. To validate the FEM results, fabricated SiNPLs with a high aspect ratio of approximately 60 are used and characterized in resonant frequency measurements where their results agree well with those simulated by FEM. Furthermore, the deflection of a SiNPL can be enhanced by increasing the applied piezoactuator voltage. By depositing different NPs [i.e., gold (Au), silver (Ag), titanium dioxide (TiO2), silicon dioxide (SiO2), and carbon black NPs] on the SiNPLs, the decrease of the resonant frequency is clearly shown confirming their potential to be used as airborne NP mass sensor with femtogram resolution level. A coupling concept of the SiNPL arrays with piezoresistive cantilever resonator in terms of the mass loading effect is also studied concerning the possibility of obtaining electrical readout signal from the resonant sensors.

Design, fabrication and testing of a piezoelectric energy microgenerator

Abstract: This article presents the design, fabrication and characterization of a micromachined energy harvester utilizing aluminium nitride (AlN) as a piezoelectric thin film material for energy conversion of random vibrational excitations. The harvester was designed and fabricated using silicon micromachining technology where AlN is sandwiched between two electrodes on top of a silicon cantilever beam which is terminated by a silicon seismic mass. The harvester generates electric power when subjected to mechanical vibrations. The generated electrical response of the device was experimentally evaluated at various acceleration levels. A maximum power of 34.78 μW was obtained for the device with a seismic mass of 5.6 × 5.6 mm2 at an acceleration value of 2 g. Various fabricated devices were tested and evaluated in terms of the generated electrical power as well as the resonant frequency.

Rapid and low cost replication of complex microfluidic structures with PDMS double casting technology

Abstract: In this paper, a new method for fast and precise replication of high-aspect-ratio microfluidic structures is reported. First, SU-8 microfluidic structures on the master mold were replicated into Polydimethylsiloxane (PDMS), which served as an intermediate, negative mold, by a conventional soft lithography process. The PDMS negative mold was then treated by wetting its surface with a diluted aqueous solution of a hydrophilic polymer, hydroxypropylmethylcellulose and rinsed with deionized water. Last, the negative mold was used in yet another PDMS molding process to produce a PDMS replica of the microfluidic structures (the hydrofocusing unit for a micro-cytometer) with the same structures as the master mold. Experimental results showed that microstructures with high-aspect-ratio could be consistently replicated with high fidelity. This technique can not only greatly simplify the design and fabrication of master molds, but also protect the expensive and fragile original master mold. The process does not require sophisticated equipment and is well suited for the replication of precision master structures in bulk quantities at low cost.