Microelectromechanical Systems Devices Research Articles

Construction and Characterization of External Cavity Diode Lasers Based on a Microelectromechanical System Device

Widely tunable external cavity diode lasers (ECDLs) with a narrow linewidth have become a powerful tool for a variety of applications. The difficulty of the present generation of ECDLs is that they are designed as laboratory instruments and are limited due to their size, high costs, and sensitivity to external influences. In this paper, we present our new ECDL design based on a microelectromechanical system (MEMS) device. This design overcomes the previous drawbacks and offers an outstanding improvement of the most important properties. Moreover, it can be adapted to any wavelength of interest and by using MEMS technology, costs can be reduced.

Modelling, design and fabrication of a novel reconfigurable ultra‐wide‐band impedance matching based on RF MEMS technology

This study proposes an adaptive impedance-matching network with tremendously reduced dimensions and presents its fabrication process. The proposed radio-frequency micro-electromechanical system (RF MEMS) device is based on a coplanar waveguide design and relies on suspended bridges for impedance tuning. The tuning is controlled by a variable applied DC voltage to the bridges. Preliminary tests validate the device's operation mechanism, and simulations were performed on both the mechanical aspects of the device (bridge gap manipulation) and tuning capabilities. This device presents the possibility of operating in a wide band of frequencies, namely [1–6] GHz, and for load impedances in the interval of [30–90] Ω for the real part and [−10–30] for the imaginary part. The device's resonant frequency and its bandwidth can be modified easily by changing the bridge gap in the RF MEMS.

The electronic transport characteristics in wide band-gap nitrogen vacancy diamond/Si hetero-structure using Raman spectrum

Abstract The negative charged nitrogen vacancy center in diamond is ideal sensitive detectors for quantum measure applications. Raman active phonon and inelastic light scattering in face-centered cubic diamond/Si(1 0 0) films were primarily studies by Raman spectra in various scattering configurations and NV concentration. The fabricated diamond (1 0 0) thin films were successfully epitaxial grown on Si(1 0 0) substrate using MPCVD. The Raman scattering spectrum of diamond/Si(1 0 0) hetero-structure with different thickness nanostructure is present to investigate spin orbital transport dynamics of phase transition. Diamond hetero-junction experiments were carried out at different conditions such as temperature range of 15–300 K and concentration of NV. The results show a strong peak at 1332 cm−1 of D mode indicates the E2g of diamond, as well as the peak 1550 cm−1 of a broad band F2g symmetry G mode which corresponds to the nano-diamond. The disordered graphitic carbon is formed by disordered SP2 hybridization. The 1132 cm−1 and 1480 cm−1 are corresponding with hydrogen bonding within film grain boundaries. The transfer of diamond sp2 content extracted from C C peak and converted to the sp3 spin related effect. The diamond/Si(1 0 0) PDOS indicated the spin-related couple of SP3, and p and d orbital hybridization. The research leads to a better understanding of the Raman active spectra and inelastic light scattering of diamond/Si(1 0 0) films and offers guidelines for better orbital hybridization material design in deep ultra-violet photo-sensor, gyroscopes, field effect transistors (FET) using diamond hetero-structure and high-k oxide gate structure, magnetometer, thermometer, and optical switching micro-electromechanical system (MEMS) devices.

A two-port electrothermal model for suspended MEMS device structures with multiple inputs

Abstract. Advances in micromachining have led to the development of microelectromechanical systems (MEMS) devices with suspended structures used in a variety of sensors. Of note for this work are sensor types where two elements exist on the suspended membrane, including examples like air flow and differential pressure detectors, gas detection, and differential scanning calorimetry sensors. Intuitively one would argue that some thermal loss exists between the two elements. However, surprisingly little is documented about this electrothermal interaction. The work presented here addresses this shortcoming by defining a new parameter set, a matrix of thermal coupling coefficients. They are used within our novel two-port electrothermal model based on the heat flow equation adapted as a linear system of equations. However, the model is only effective with knowledge of these coefficients. We introduce an approach to extract the coefficients using finite-element method (FEM)-based multiphysics simulation tools and revisit and extend our previous method of non-ideal power coupling, this time to extract the coefficient matrix from measured data. Both specialist simulation tools and device manufacturing are very expensive. However, they are the only choices in the absence of an analytic model. A major contribution of this work is the derivation of a model to predict the coefficients by analytic means from the device dimensions and material properties. The research contribution and paper culminate in a comparison of analytic, simulated, and experimentally extracted values of two different devices to verify and demonstrate the effectiveness of the proposed models. The values compare well and show that the best results achieved are approximately 90 % and 70 % thermal linkage respectively for vacuum and atmospheric pressure conditions.

Low-Density Fan-Out Heterogeneous Integration of MEMS Tunable Capacitor and RF SOI Switch

Abstract Using Low-Density Fan-Out (LDFO) packaging technology, a radio frequency (RF) microelectromechanical systems (MEMS) tunable capacitor array composed of electrostatically actuated beams on 180nm high-voltage CMOS silicon was heterogeneously integrated with a single-pole four-terminal (SP4T) RF switch on 180nm CMOS silicon-on-insulator (SOI). The primary objective of this study was to determine the manufacturability of this System-in-Package (SiP) design, which is proven at time zero through survival of the MEMS device based on acceptable MEMS performance metrics. In addition, the RF SOI switch provides high-voltage electrostatic discharge (ESD) protection for the MEMS device. Capacitive MEMS structures are particularly sensitive to unpredictable electrostatic charging scenarios, such as handling after package assembly and printed circuit board (PCB) surface mount processing. Consequently, resistance to dielectric breakdown by means of robust ESD protection is a very desirable quality. Integrating the RF switch in close proximity with the MEMS device not only enables the ability to withstand charging scenarios in excess of 1kV (human body model), it mitigates the impact of parasitics on RF performance by minimizing interconnect lengths and complexity.

Comparative Study on Modeling Approaches of V-Shaped MEMS Temperature Sensors

Thermal microelectromechanical system (MEMS) devices have gained immensely in popularity due to their good performances, relatively simple fabrication process, and to the availability of modeling tools. In this paper, the modeling results of several models were compared and the ability of each to reliably assess the performances of V-shaped thermal MEMS devices was investigated. The results of several models, in which the governing equations of motion were directly solved, were compared to those obtained from nonlinear large-deflection 3-D finite element analysis that was verified experimentally. The models were modified by including the temperature-dependent properties of the material of the device. In addition, a numerical iterative force control solution scheme was developed and used to predict the performances of V-shaped devices. Important parameters of V-shaped devices, such as apex deflection, stiffness, and output force, were evaluated in terms of the applied temperature and device geometry. In addition, the feasibility of capacitive sensing was demonstrated and high signal-to-noise ratio was calculated. Finally, the influence of microfabrication tolerances and internal stress on the performances of the devices were studied. Therefore, this paper will help future researchers and designers to assess the reliability of models of thermal MEMS devices and better evaluate device performance.

MEMS-Based RF Oscillators Using SiCer Technology: New Integration, Packaging, and Assembly Concepts

In state-of-the-art RF receiver systems, the number of microelectromechanical systems (MEMS)-based devices is rapidly rising [1]. MEMS devices and circuits have become important for tasks formerly performed solely by microelectronic components, such as switches [2], reference oscillators [3], and filters [4]. Furthermore, they deliver small form factors in the submicron range and are compatible with semiconductor processes [5], which is not the case for all types of mechanical components, such as quartz crystals [6]. Modern thin-film microsystem technologies push the usable frequency range of MEMS components into the gigahertz range and improve their electrical properties, resulting in low-noise multiphysical RF subsystems. This makes MEMS suitable even for mobile communication standards with strict requirements in terms of bit error rate and error vector magnitude (EVM) [7], [8].

3D printed micro-mechanical device (MMD) for in situ tensile testing of micro/nanowires

The rise of one-dimensional micro/nanomaterials requires comprehensive understanding on their mechanical properties. Recently, MEMS (micro-electromechanical system)-type devices become an efficient tool for characterizing the mechanical behavior of 1D micro/nanomaterials under high resolution electron microscope or optical microscope. However, existing microfabricated MEMS devices are developed and manufactured based on silicon photolithography processes, which are extremely time consuming and costly. The design, fabrication as well as releasing of such silicon-based devices are also challenging. Here, we proposed to design and manufacture a micro-mechanical device (MMD, based on our earlier design) via projection micro-stereolithography-based 3D printing. The versatility of the high-resolution 3D printing allows the fabrication of a wide range of MMDs with various design and dimensions, facilitating the in situ tensile testing of micro/nanowires with diameters ranging from nanometers to microns. We demonstrated the characterization of tensile behavior of SiC nanowires inside a scanning electron microscope and lead zirconate titanate microwires under an optical microscope by using our 3D printed devices, respectively, suggesting the potential to revolutionize micro/nanomechanical characterization of low-dimensional materials by 3D printing of micro-mechanical or MEMS devices.

Empirical High Cycle Fatigue Assessment Model of MEMS Devices

Abstract Many microelectromechanical systems (MEMS) devices generate large deflections and stresses under some severe loads, and this cumulative stress often causes structural fatigue when applying high cyclic loads. It affects the reliability and quality of the product and can easily damage structures in harsh environments. For example, accelerometers and gyroscopes in motion sensors always combine a movable mass component with a bending or torsion spring, which can severely deform their structure at some large accelerations or angular accelerations. After this high cycle of deformation, the spring structure will be damaged and cause device failure, we call this failure mode high cycle fatigue (HCF). This is very common for MEMS products, but it is difficult for designers to predict it at design stage. To prevent early fatigue problems and reduce product development time, we developed a simulation process and empirical prediction model to help designers predict HCF and improve fatigue strength of moving structures used in MEMS devices. In this study, a bending and a torsion beam are used as test vehicles. A combination of dynamic and electromechanical coupling simulations was developed and applied to analyze the effects of frequency under HCF testing. The test structures were fabricated using silicon-on-insulator (SOI) MEMS technique and these test structures were used to validate empirical life prediction equation developed in this research. The frequency effect of HCF was also to be included in the developed prediction model. Based on the test results, the accuracy of the empirical prediction equation is improved by including frequency effect.

Millipixel image correlation for sub nm measurement of MEMS motion

A 1D digital image correlation algorithm capable of measuring the motion of microelectromechanical systems (MEMS) devices with sub nm resolution is presented. Successive micro photographic images are recorded, then subsets of the images are column averaged and the resulting 1D profiles are cross correlated. Factors that limit the correlation resolution are examined and methods for achieving millipixel level repeatability are discussed. Key to high resolution correlation of MEMS motion were low image noise and high sum of square of subset intensity gradients (SSSIG), a measure of image contrast. Using this correlation algorithm, the motion of MEMS thermal actuators was measured. Sub nm resolution was achieved using a wide range of image subsets, with measured standard deviations as low as 0.10 nm (0.6 millipixels).

Die-Attach Structure of Silicon-on-Glass MEMS Devices Considering Asymmetric Packaging Stress and Thermal Stress.

Die attach is a typical process that induces thermal stress in the fabrication of microelectromechanical system (MEMS) devices. One solution to this problem is attaching a portion of the die to the package. In such partial die bonding, the lack of control over the spreading of the adhesive can cause non-uniform attachment. In this case, asymmetric packaging stress could be generated and transferred to the die. The performance of MEMS devices, which employ the differential outputs of the sensing elements, is directly affected by the asymmetric packaging stress. In this paper, we proposed a die-attach structure with a pillar to reduce the asymmetric packaging stress and the changes in packaging stress due to changes in the device temperature. To verify the proposed structure, we fabricated four types of differential resonant accelerometers (DRA) with the silicon-on-glass process. We confirmed experimentally that the pillar can control the spreading of the adhesive and that the asymmetric packaging stress is considerably reduced. The simulation and experimental results indicated that the DRAs manufactured using glass-on-silicon wafers as handle substrates instead of conventional glass wafers have a structure that compensates for the thermal stress.

Pedestrian Positioning Using a Double-Stacked Particle Filter in Indoor Wireless Networks.

The indoor pedestrian positioning methods are affected by substantial bias and errors because of the use of cheap microelectromechanical systems (MEMS) devices (e.g., gyroscope and accelerometer) and the users’ movements. Moreover, because radio-frequency (RF) signal values are changed drastically due to multipath fading and obstruction, the performance of RF-based localization systems may deteriorate in practice. To deal with this problem, various indoor localization methods that integrate the positional information gained from received signal strength (RSS) fingerprinting scheme and the motion of the user inferred by dead reckoning (DR) approach via Bayes filters have been suggested to accomplish more accurate localization results indoors. Among the Bayes filters, while the particle filter (PF) can offer the most accurate positioning performance, it may require substantial computation time due to use of many samples (particles) for high positioning accuracy. This paper introduces a pedestrian localization scheme performed on a mobile phone that leverages the RSS fingerprint-based method, dead reckoning (DR), and improved PF called a double-stacked particle filter (DSPF) in indoor environments. As a key element of our system, the DSPF algorithm is employed to correct the position of the user by fusing noisy location data gained by the RSS fingerprinting and DR schemes. By estimating the position of the user through the proposal distribution and target distribution obtained from multiple measurements, the DSPF method can offer better localization results compared to the Kalman filtering-based methods, and it can achieve competitive localization accuracy compared with PF while offering higher computational efficiency than PF. Experimental results demonstrate that the DSPF algorithm can achieve accurate and reliable localization with higher efficiency in computational cost compared with PF in indoor environments.

Enhanced electrical and thermal conductivities of 3D-SiC(rGO, Gx) PDCs based on polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO) precursor containing graphene fillers

Lightweight 3D-SiC(rGO, Gx) PDCs were fabricated from polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO) precursor added by different amounts of graphene fillers via direct cold molding and pyrolysis at 1400 °C in an easy manner. Results reveal that SiC(rGO, Gx) PDCs consist of β-SiC nanocrystals homogeneously embedded within amorphous SiOxCy/Cfree, and graphene is well compatible with SiOxCy/Cfree for void-free bonded interface, efficiently delaying decomposition of SiOxCy phase into β-SiC. The nanocomposite structure provides an ingenious strategy for constructing complexes with good integrity, high ceramic yield, excellent thermal stability, high electrical and thermal conductivities. This improvement is primarily attributed to the presence of graphene with considerably increasing electric-charge carriers and wider phonon-channel. Such 3D-SiC(rGO, G20%) PDCs possess satisfying hardness (12.02 GPa), high electrical conductivity (23.82 S cm−1) and thermal conductivity (7.47 W m−1 K−1), which make them attractive candidates for microelectromechanical systems (MEMS) devices, energy storage/conversion systems and high precision components, etc.

Comprehensive Design Considerations and Noise Modeling of Preamplifier for MEMS Electrometry

The purpose of the work is to evaluate various intrinsic noise sources that limit the charge resolution of microelectromechanical systems (MEMS) vibrating-reed (VR) electrometers. We demonstrate a method of reducing total equivalent referred-to-input (RTI) noise voltage per square root hertz for an operational amplifier-based preamplifier (preamp) circuit topology. The proposed circuit’s noise model accurately describes the various noise sources and total RTI noise voltage is experimentally verified. The noise analysis clarifies the path toward a preamp with a noise floor limited by thermal noise due to low-valued shunt resistance at its input. Furthermore, during the charge measurement, a variation of sensitivity occurs by changing the isolation (or dc blocking) capacitor of the preamp. This phenomenon also affects the noise performance of the circuit and the overall charge resolution for the electrometer. RTI noise voltage of 290 nV/ $\surd $ Hz at 5.2 kHz was measured for 50 $\text{M}\Omega $ of shunt resistor and 2 pF of isolation capacitor to implement a prototype of the complete preamp, along with the MEMS device fabricated in silicon-on-glass (SOG) process. Finally, we present a charge resolution model of the proposed SOG-MEMS electrometry system. The model’s underlying design principles reveal low noise preamps accessible to the circuit designers without tangible circuitries and after-the-fact noise measurement.

Dynamic pull-in instability and snap-through buckling of initially curved microbeams under the effect of squeeze-film damping, mechanical shock and axial force

This research investigates the dynamic behavior of microelectromechanical systems (MEMS) containing curved electrodes, under a combined loading of electrostatic force, axial force, mechanical shock loading and squeeze-film damping (SQFD). The dynamic governing equation of a curved microbeam (micro-arch) is solved by utilizing a nonlinear finite element method, while the effect of the fluid film damping on the microbeam is modeled by the nonlinear Reynolds equation. The response of the micro-arch under different loading conditions and the influence of the MEMS device parameters on its behavior are studied and discussed in detail. In particular, the snap-through and pull-in instabilities of the curved microbeam are thoroughly investigated, and the maximum deflections of the micro-arch subjected to different types of loadings are analyzed. Finally, the phase diagram of the curved beam under various loading conditions is presented for guiding the design and analysis of the MEMS in the future.

Direct-Write Dewetting of High Melting Temperature Metals on Flexible Substrates

Microelectromechanical systems (MEMS) are pervasive in modern technology due to their reliability, small foot print, and versatility of function. While many of the manufacturing techniques for MEMS devices stem from integrated circuit (IC) manufacturing, the wide range of designs necessitates more varied processing techniques. Here, new details of a scanning laser based direct-write dewetting technique are presented as an expansion of previous demonstrations. For the first time, the ability to pattern a high melting temperature and high reflectance metallic thin films of Ni and Ag, respectively, on polymer substrates is reported. Novel methods for reducing the power necessary for processing highly reflective films are demonstrated by depositing very thin films of high near-infrared absorbance.

Design, fabrication and experimental validation of a MEMS periodic auxetic structure

Auxetic structures are attracting increasing interest because of their large variety of applications at both the macro and micro scales. In this work, an innovative auxetic unit cell is presented, numerically studied, fabricated at the microscale and experimentally tested. Its versatility in terms of stiffness and Poisson’s ratio and its compatibility with commercial Micro Electro-Mechanical Systems (MEMS) fabrication processes suggest applications such as motion conversion and amplification mechanism in MEMS devices or on-chip biaxial tests. A MEMS auxetic and periodic structure exhibiting an overall equivalent Poisson’s ratio lower than −1 is then proposed. The static and dynamic behaviours are studied both numerically and through a simplified analytical model. Experimental results confirm the simulated behaviour of the structure thus verifying the first MEMS auxetic structure with electrostatic actuation and capacitive readout.

A laminar fluid flow model for study of ventilation systems in micro-electromechanical systems (MEMS) clean room

This paper reports the simulation based analysis results of air flow in a MEMS clean room aimed at predicting the air borne distribution of 0.5 μm particles as per the ISO standard. These particulate contaminants, if not flushed by proper design of the ventilation system of the clean room can get deposited and accumulated on the MEMS devices under fabrication, contributing possibly to the affected functionality of the device, particularly high precision devices such as single cantilever type precision MEMS sensors and actuators. The results of computational fluid dynamics (CFD) based flow analysis done in COMSOL™ estimated for adverse conditions such as a desired ISO-5 cleanliness degrading to ISO-8 cleanliness due to poor maintenance have been presented. Based on the flow conditions, conclusions on the particle accumulation have been drawn.

A Combined Experimental and Numerical Study of the Effect of Surface Roughness on Nanoindentation

Gold and copper thin films are widely used in microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) devices. Nanoindentation has been developed in mechanical characterization of thin films in recent years. Several researchers have examined the effect of surface roughness on nanoindentation results. It is proved that the surface roughness has great importance in nanoindentation of thin films. In this paper, the surface topography of thin films is simulated using the extracted data from the atomic force microscopy (AFM) images. Nanoindentation on a rough surface is simulated using a three-dimensional finite-element model. The results are compared with the results of finite-element analysis on a smooth surface and the experimental results. The results revealed that the surface roughness plays a key role in nanoindentation of thin films, especially at low indentation depths. There was good compatibility between the results of finite-element simulation on the rough surface and those of experiments. It is observed that on rough films, at low indentation depths, the geometry of the location where the nanoindentation is performed is of major importance.

Tuning MEMS cantilever devices using photoresponsive polymers

Microelectromechanical systems (MEMS) energy harvesting devices have had limited commercial success partly due to the frequency mismatch between the device and the vibration source. Tuning the cantilever device is one possible solution but developing a tunable MEMS device is difficult. This paper demonstrates a novel method of tuning a MEMS cantilever device post-fabrication by using light-responsive azobenzene liquid crystal polymers (LCP). Light exposure causes the photoresponsive polymers to change their elastic modulus, thus affecting the resonant frequency of the device. The photoresponsive polymer was integrated with three different MEMS cantilever substrates including LCP, parylene, and silicon. The three cantilever beams all demonstrated changes in resonant frequency when exposed to UV light of 10.4%, 8.13%, and 4.86%, respectively. The change in resonant frequency is dependent on the stiffness of the substrate, the thickness of the azo-LCP, the intensity and duration of the light exposure, and the wavelength of the light. The results in this paper validate that light responsive polymers can be used to reduce the frequency of MEMS cantilevers post-fabrication, which could lead to developing devices that can be precisely tuned for specific applications.