Microelectromechanical Devices Research Articles

Impact of the Stefan gusting on a bioconvective nanofluid with the various slips over a rotating disc and a substance-responsive species

This paper presents thorough computational and theoretical analyses of steady forced convective flow over a rotating disc submerged in a water-based nanofluid containing microorganisms. It delves into the examination of boundary layer flow characteristics of a viscous nanofluid, considering Stefan blowing effects and multiple slip conditions influenced by a magnetic field. Notably, the study accounts for novel aspects such as thermal radiation and both constructive and destructive chemical reactions. The movement of nanoparticles is elucidated based on thermophoresis and microscopic behaviors, while changes in volume fraction do not affect the thermo-physical properties of the nanofluid. To address the altered nonlinear set of differential equations, an effective numerical approach, the Keller-Box method, is implemented for critical and efficient solutions. These appropriate transformations are defined and applied. When compared to blowing suction, it shows a better enhancement in the rate of heat transfer, mass, and microorganisms. Some of the main observations are there is a decrease in wall skin friction in the directions of radial and tangential as magnetic field strength is increased. The evaluation of thermal boundary layer thickness and temperature is noted for the radiation parameter (Rd) improvement. The present analysis has applications in electromagnetic micro-pumps and nanomechanics. As to the applications in the science and engineering fields, technologies such as micro-electromechanical systems-based microfluidic devices and microfluidic-related technologies will be accepted.

Combustion Efficiency of Carbon-neutral Fuel using Micro-Combustor Designed for Aerospace Applications

Recent advancements in the field of micro combustor research are growing for achieving high-performance systems in micro power generation and microelectromechanical devices. To mitigate the hazardous emissions from carbon fuels, as an alternative, zero-carbon-free fuels ammonia, and hydrogen are being explored in micro combustion processes. The distinctive feature of a micro combustor lies in its significantly higher area to volume ratio in comparison with traditional combustion systems, leading to accelerated combustion reaction rates. However, the small size of micro combustors poses a challenge in achieving efficient mixing of highly reactive fuels like hydrogen and ammonia with oxidizers. The unique properties of micro combustors can lead to differences in the combustion behavior of hydrogen and ammonia compared to larger-scale combustion systems. Hence, examining the performance of carbon-free fuels in micro combustors is crucial for the advancement of clean energy combustion systems. A numerical investigation on a Y-shaped micro-combustor was carried out to identify the aspects of non-premixed combustion of ammonia/air and hydrogen/air. The findings reveal that in the case of hydrogen combustion, stable flames were reached, even at low equivalence ratios. Therefore, the distinct combustion properties of hydrogen and ammonia result in varying NOx emissions, with hydrogen generally leading to higher NOx levels due to its higher flame temperature and increased thermal NOx production.

Integrated silicon electron source for high vacuum microelectromechanical system devices

The article presents the process of developing a silicon electron source designed for high-vacuum microelectromechanical system (HV MEMS) devices, i.e., MEMS electron microscope and MEMS x-ray source. Technological constraints and issues of such an electron source are explained. The transition from emitters made of carbon nanotubes to emitters made of pure silicon is described. Overall, the final electron source consists of a silicon tip emitter and a silicon gate electrode integrated on the same glass substrate. The source generates an electron beam without any carbon nanotube coverage. It generates a high and stable electron current and works after the final bonding process of an HV MEMS device.

Isogeometric analysis of magneto-electro-elastic functionally graded Mindlin microplates

In this study, an accurate numerical method for the static and dynamic response analysis of magneto-electro-elastic functionally graded (MEEFG) microplates with complex geometries is proposed with the application of isogeometric analysis (IGA). Leveraging Hamilton's principle and the extended modified couple stress theory, the weak form of motion equations is derived. By performing convergence analysis, the accuracy of the proposed numerical method is verified. To show the applicability of the new method, the influences of the microstructure effect and gradient index on the static and dynamic behaviors of both the MEEFG square and elliptical microplates with various boundary conditions are discussed in detail. Results illustrate that the microstructure effect dominated by the couple stress effect has an obvious impact on both the mechanical and electromagnetic behavior of structures with microscopic scales which will cause hardening of microstructural stiffness, whereas the macrostructures are minimally affected by the couple stress effect. Besides, microstructures with lower stiffness exhibit a more pronounced microstructure effect and a greater degree of stiffness hardening. The proposed IGA method could serve as a basis for the design and optimization of microelectromechanical devices with complex shapes.

Imaging Ultrafast Dynamics of Pressure-Driven Phase Transitions in Black Phosphorus and Anomalous Coherent Phonon Softening.

Applying high pressure to effectively modulate the electronic and lattice structures of materials could unravel various physical properties associated with phase transitions. In this work, high-pressure-compatible femtosecond pump-probe microscopy was constructed to study the pressure-dependent ultrafast dynamics in black phosphorus (BP) thin films. We observed pressure-driven evolution of the electronic topological transition and three structural phases as the pressure reached ∼22 GPa, which could be clearly differentiated in the transient absorption images containing spatially resolved ultrafast carrier and coherent phonon dynamics. Surprisingly, an anomalous coherent acoustic phonon mode with pressure softening behavior was observed within the range of ∼3-8 GPa, showing distinct laser power and time dependences. Density functional theory calculations show that this mode, identified as the shear mode along the armchair orientation, gains significant electron-phonon coupling strength from out-of-plane compression that leads to decreased phonon frequency. Our results provide insights into the structure evolution of BP with pressure and hold potential for applications in microelectromechanical devices.

Toward Zero Carbon Emissions: Investigating the Combustion Performance of Shaped Microcombustors Using H2/Air and NH3/Air Mixtures

The research effort in the microcombustor field has recently increased due to the demand for high-performance systems in microelectromechanical and micro power generation devices. To address rising concerns about pollutants from fossil sources, zero-carbon fuels such as hydrogen (H2) and ammonia (NH3) have been considered as an alternative in microcombustion processes. In a microcombustor, the surface area-to-volume ratio is much higher compared to conventional combustion systems, resulting in faster heat transfer rates and more intense combustion reactions. However, achieving efficient mixing of fuel and an oxidizer in a microcombustor can be challenging due to its small size, particularly for highly reactive fuels like H2. For NH3, challenges in microcombustion involve a low reactive, high ignition temperature (923 K vs. 793 K of H2) and high concentration of NOx combustion products. Therefore, studying the performance of these fuels in microcombustors is important for developing clean energy technologies. In this paper, to explore features of non-premixed NH3/air and H2/air combustion in micro-scale combustors, an Ansys Fluent numerical investigation was conducted on a Y-shaped microcombustor. Results show that for combustion with H2, stationary flames can be achieved even at lower equivalence ratios. Additionally, the pollutants generated from H2 in the flame are generally twice those of NH3. The overall efficiency of the microcombustor is two times greater for NH3 conditions than for H2 conditions.

Effects of thermal annealing on thermal conductivity of LPCVD silicon carbide thin films

The thermal conductivity (k) of polycrystalline SiC thin films is relevant for thermal management in emerging SiC applications like microelectromechanical and optoelectronic devices. In such films, k can be substantially reduced by microstructure features including grain boundaries, thin film surfaces, and porosity, although these microstructural effects can also be manipulated through thermal annealing. Here, we investigate these effects by using microfabricated suspended devices to measure the thermal conductivities of nine low-pressure chemical vapor deposition SiC films of varying thicknesses (from 120 to 300 nm) and annealing conditions (as-grown and annealed at 950 and 1100 °C for 2 h, and in one case 17 h). Fourier-transform infrared spectroscopy, x-ray diffraction spectra, and density measurements are also used to characterize the effects of annealing on the microstructure of selected samples. Compared to as-deposited films, annealing at 1100 °C typically increases the estimated grain size from 5.5 to 6.6 nm while decreasing the porosity from around 6.5% to practically fully dense. This corresponds to a 34% increase in the measured thin film thermal conductivity near room temperature from 5.8 to 7.8 W/m K. These thermal conductivity measurements show good agreement of better than 3% with fits using a simple theoretical model based on the kinetic theory combined with a Maxwell–Garnett porosity correction. Grain boundary scattering plays the dominant role in reducing the thermal conductivity of these films compared to bulk single-crystal values, while both grain size increase and porosity decrease play important roles in the partial k recovery of the films upon annealing. This work demonstrates the effects of modifying the microstructure and, thus, the thermal conductivity of SiC thin films by thermal annealing.

Towards Systematization of Aurivillius Phases' Formula

Aurivillius structures are a family of layered perovskite that are of great importance due to the many properties they provide (ferroelectricity, dielectric ...) and the applications in which they can be used (thin films, micro-electromechanical devices, etc.); thus, the discovery of such materials can be very useful. Since their appearance, Aurivillius structures have been largely studied, but little work has focused on the systematization of the latter. The main idea of this paper is to systematize the formula of Aurivillius structures [Am-1 B­i2 Bm O3m+3], using combinatorial mathematical techniques to substitute elements in cations A and B, while taking into account the criteria of electronegativity (zero total charge) and structure (tolerance factor). Constraint propagation has been used as a key technique to significantly reduce the number of combinations and thus minimize the execution cost. The results of such a work can present a very large dataset which can be exploited into a research tool that brings a great help to researchers by providing a better visibility on chemical elements forming a potential Aurivillius structure, and thus, bringing a significant asset in the discovery of these materials.

Recent Developments in Low Temperature Wafer Level Metal Bonding for Heterogenous Integration

An overview of various low temperature (<200°C) wafer bonding processes using metal interlayers is presented. Such processes are very attractive for novel applications in 3D heterogenous packaging as the allow for simultaneous formation of electrical interconnects, as well as hermetic encapsulation of various sensors and microelectromechanical systems-based devices. Metal wafer bonding is a generic category of processes consisting of various sub-categories, each one defined by the different principles governing the process. One can differentiate between eutectic wafer bonding (a eutectic alloy is formed as bonding layer during the process by liquid-solid interdiffusion), intermetallic wafer bonding (an intermetallic alloy is formed as bonding layer during the process by solid-liquid interdiffusion, process known also as Solid Liquid Intermetallic Diffusion – SLID or Transient Liquid Phase – TLP), and metal thermo-compression (TC) wafer bonding. Different critical/gating parameters were investigated and their impact for generally reducing processing temperatures for the different metal bonding systems was studied.

Nonlinear Vibration and Stability Analysis of Rotating Functionally Graded Piezoelectric Nanobeams

Presented herein is an investigation for the nonlinear vibration and stability analysis of rotating functionally graded (FG) piezoelectric nanobeams based on the nonlocal strain gradient theory. The present model can be regarded as a simplified version for the rotating nanowire of biomechanical nanogenerators. The Hamilton principle is used to derive nonlinear equations of motion and their related boundary conditions, which are then discretized to form a set of algebraic equations. Accordingly, the nonlinear vibration frequencies and buckling loads of the nanobeams can be determined by an iterative method. A parametric study of rotational velocity, nonlocal parameter, material length parameter, power-law index, and electrostatic voltage on the dynamic stability behavior of such nanobeams is also presented. In the cantilever case, increasing the nonlocal parameter and material length parameter can result in a stiffness-hardening effect that is unaffected by rotational velocity and the material length parameter to nonlocal parameter ratio. Yet, this has not been reported previously. More importantly, incorporating the effect of geometric nonlinearity on the dynamic responses and stability results of the nanobeams is indispensable. In particular, new observations for the coupling effect of vibration amplitude and power-law index on the electric potential effect are useful for the design of rotating microelectromechanical devices.

A Comprehensive Review of Ultrahigh Molecular Weight Polyethylene Fibers for Applications Based on Their Different Preparation Techniques

Ultrahigh molecular weight polyethylene (UHMWPE) fiber is widely recognized for its exceptional properties, including high strength-to-weight ratio, toughness, and chemical resistance, making it a preferred material for reinforcement in various applications. However, its low melting point, surface inertness, and weak adhesion to polymer matrices have limited its potential use in some fields. Researchers have addressed these shortcomings by focusing on surface modifications through physical treatment or chemical coating, thereby enhancing the versatility of materials in numerous UHMWPE fiber composites. By improving the tribological and interfacial properties of UHMWPE, various applications can be explored, including prosthetic joints, energy-absorbing road safety systems, microelectromechanical system devices, and protective materials for defense and personal thermal management. This review provides a comprehensive overview of the remarkable performance of UHMWPE and its composites, providing insights into its wide array of applications.

Built-in Analog Automatic Controls for Small Robots

One of the most promising methods for improving control efficiency is the parallel synthesis of commands by a group of computing devices. However, delays in digital-to-analog conversions and software processing, the need to synchronize calculations, and signal transmission coordination prevent the achievement of maximum performance in distributed systems. Problems can be solved by increasing the power of embedded microprocessors. This leads to an undesirable increase in design complexity, energy consumption, and dimensions of controls. For the miniaturization of embedded control systems, the article proposes to apply the principles of the indivisibility of physical processes in a technical system and the execution of control commands based on the functional combination of aggregates with analog logic devices (agents). A generalized model of changing the states of a technical system is considered, which sets the principles for switching on or off groups of units. The concept of an automaton of ternary logic is introduced, which determines the order of interaction of aggregates in the time domain. The synthesis of the block diagram of the automaton is carried out. In the mathematical model of the automaton, the operations of ternary logic receive a specific physical content in the form of retrospective processing of changes in the states of aggregates. It is shown that ternary logic automata can be combined into open and closed chains, setting hardware control algorithms units robot. The circuits for connecting automata controlled by elements of asynchronous logic are given. When connected in series, the automata control the order of switching on and off the units. Chains of three-valued logic automata can be arbitrarily long, determining the behavior of the system in the process of its operation. Due to the rejection of program control, such automata can operate in real time, limited only by the delay of signals in logic elements. An important advantage of the proposed technical solution is the unification of the automatic control system. The simplicity of the design of devices and the absence of additional add-ons make it possible to integrate such circuits into the controls of microminiature robots, reducing their weight and size parameters. Promising areas of application of analog automata are microelectromechanical and microelectronic devices.

Effects of rolled fibrous microstructure on fatigue properties of extruded Cu-5Al planar micro springs

Planar micro spring is an important elastic component in microelectromechanical system devices, and one of its main failures is fatigue. In this work, a new method to improve the cycles of a planar micro spring by introducing pre-rolled fibrous microstructure was proposed. Cu-5Al alloy billets with a fibrous microstructure rolled at room temperature with a reduction ratio of 70% were obtained. Three types of planar micro springs with fibrous microstructure were prepared through extrusion by varying the angle between the fibrous microstructure direction and the extrusion direction. Fatigue tests were conducted using a customized micro-fatigue test system. The best fatigue performance was obtained by preparing the micro springs with the fibrous microstructure direction perpendicular to the extrusion direction, while the worst fatigue performance was obtained by preparing the planar micro springs with the fibrous microstructure direction parallel to the extrusion direction. The fibrous microstructure direction affected the local strain in the micro springs. The fibrous microstructure slightly affected the location of the crack initiation region but significantly affected the area of crack initiation and steady-state expansion region of the micro spring. The fatigue life cycle of extruded Cu-5Al alloy planar micro spring with the pre-rolled fibrous microstructure improved by 58% more than that of extruded Cu-7Al alloy planar micro spring without the pre-rolled fibrous microstructure. Micro spring fatigue life cycle decreased with increasing strain amplitude. This work provides a new approach for preparing planar micro springs with high fatigue performance.

Ultrathin Pt and Mo films on Al1–xScxN: an interface investigation

Aluminum scandium nitride (Al1–xScxN) with attractive ferroelectric and piezoelectric properties is a promising material for next-generation device applications. However, the understanding of interface properties between integrated ultrathin metal electrodes and Al1-xScxN films is still limited, despite their significant impact on device performance. In the study, we investigated the growth mechanism and interfacial chemistry of ultrathin platinum (Pt) and molybdenum (Mo) films deposited on the high-crystalline Al1-xScxN (x = 0.2) surface. The chemical and electronic structure evolutions of the interface during the deposition process were probed by in-situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The structural properties of the interface were further characterized by cross-sectional transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and atomic force microscopy (AFM). Our results reveal the formation of ionic Pt2+-N bonds at the Pt/Al1-xScxN interface, while Mo does not bond with the substrate. Furthermore, we identified electron transfer induces upward band-bending like effects on the Al1-xScxN surface upon both Pt and Mo interactions. Our work on the chemical and structural research of ultrathin metal electrodes and Al1–xScxN interfaces provides guidance towards designing high-performance micro-electromechanical (MEMS) devices.

On the low temperature limits for cryogenic etching: A quasi in situ XPS study

The cryogenic plasma etching of silicon for nano- and microelectromechanical devices is known to show an optimal operating temperature around –100 °C. The physicochemical mechanisms occurring beyond this limit, however, are not often discussed. Thus, to explore the adsorption of residual gases on the uppermost surface of a Si/SiO2 wafer at –100 ≤T≤ –147 °C, we performed a comprehensive, quasi in situ X-ray photoelectron spectroscopy (XPS) study. Precisely, the cooling down of the sample was performed in a typical plasma-etching reactor at a residual pressure of 10−4 Pa, being afterwards transferred to the XPS chamber at a constant temperature, under high vacuum. We report that water build-up on the surface becomes a major issue for T< –120 °C, as detected in the O 1 s spectra and modelled by QUASES-Generate. The thickness of the H2O layer increases exponentially as the surface temperature decreases, following an anti-Arrhenius behavior. At –147 °C, the overlayer thickness is estimated to ∼125 Å, thus, the silicon is barely probed by XPS. Adsorbed fluorine can also be detected at low temperatures, although less markedly. Finally, the effect of the temperature-dependent Fermi level change on the Si 2p peak binding energy is discussed.

First-Principles Study of Electronic and Optical Properties and Photocatalytic Performance of MS Monolayer under Strain

The study explores the mechanical, optoelectrical and photocatalytic properties of GeS and SnS structures by Density Function Theory (DFT) through Quantum Espresso software. The results show that the GeS and SnS structures are the semiconductor materials at equilibrium with band gaps of 1.75 eV and 1.4 eV, respectively. The band gap of these two structures tends to increase under the tensile strain and decrease under the compressive strain. Especially, at the strain of -10%, the band gap of GeS decreases dramatically and becomes metallic, while the SnS still maintains the semiconductor properties. The absorption coefficient is changed significantly in the ultraviolet region under the biaxial strain. Besides, our calculations also show that the GeS and SnS have photocatalytic properties and can become good candidates for overall water-splitting under the tensile strain. The results obtained from this study are the basis for application in microelectromechanical and optoelectronic devices and cleaning technology.

Machine Learning-Based Modeling and Generic Design Optimization Methodology for Radio-Frequency Microelectromechanical Devices.

RF-MEMS technology has evolved significantly over the years, during which various attempts have been made to tailor such devices for extreme performance by leveraging novel designs and fabrication processes, as well as integrating unique materials; however, their design optimization aspect has remained less explored. In this work, we report a computationally efficient generic design optimization methodology for RF-MEMS passive devices based on multi-objective heuristic optimization techniques, which, to the best of our knowledge, stands out as the first approach offering applicability to different RF-MEMS passives, as opposed to being customized for a single, specific component. In order to comprehensively optimize the design, both electrical and mechanical aspects of RF-MEMS device design are modeled carefully, using coupled finite element analysis (FEA). The proposed approach first generates a dataset, efficiently spanning the entire design space, based on FEA models. By coupling this dataset with machine-learning-based regression tools, we then generate surrogate models describing the output behavior of an RF-MEMS device for a given set of input variables. Finally, the developed surrogate models are subjected to a genetic algorithm-based optimizer, in order to extract the optimized device parameters. The proposed approach is validated for two case studies including RF-MEMS inductors and electrostatic switches, in which the multiple design objectives are optimized simultaneously. Moreover, the degree of conflict among various design objectives of the selected devices is studied, and corresponding sets of optimal trade-offs (pareto fronts) are extracted successfully.

Impedance spectroscopy of electrostatically driven MEMS resonators

The electrical response of vibrating, electrostatically driven microelectromechanical and nanoelectromechanical system (MEMS and NEMS) devices was measured electrically using impedance spectroscopy. A physical model of this structure was elaborated, allowing us to predict the electrical response based on the dimensions and mechanical properties of the structure as well as the measurement conditions. This result was correlated with the results of the electrical equivalent circuit model. The physical model predicted that the magnitude of the electrical response is inversely proportional to the distance between the electrodes to the power of 4. Such a strong dependence was verified experimentally using a vibrating electrostatically driven MEMS operating in vacuum. The verified physical model is suitable for optimization of MEMS structures designed for electrical detection of vibrations.

Influence of Barrier Layers on ZrCoCe Getter Film Performance.

Improving the vacuum degree inside the vacuum device is vital to the performance and lifespan of the vacuum device. The influence of the Ti and ZrCoCe barrier layers on the performance of ZrCoCe getter films, including sorption performance, anti-vibration performance, and binding force between the ZrCoCe getter film and the Ge substrate were investigated. In this study, the Ti and ZrCoCe barrier layers were deposited between the ZrCoCe getter films and Ge substrates. The microtopographies of barrier layers and the ZrCoCe getter film were analyzed using scanning electron microscopes. The sorption performance was evaluated using the constant-pressure method. The surface roughness of the barrier layers and the getter films was analyzed via atomic force microscopy. The binding force was measured using a nanoscratch tester. The anti-vibration performance was examined using a vibration test bench. The characterization results revealed that the Ti barrier layer significantly improved the sorption performance of the ZrCoCe getter film. When the barrier material was changed from ZrCoCe to Ti, the initial sorption speed of the ZrCoCe getter film increased from 141 to 176 cm3·s-1·cm-2, and the sorption quantity increased from 223 to 289 Pa·cm3·cm-2 in 2 h. The binding force between the Ge substrate and the ZrCoCe getter film with the Ti barrier layer was 171 mN, whereas that with the ZrCoCe barrier layer was 154 mN. The results showed that the Ti barrier layer significantly enhanced the sorption performance and binding force between the ZrCoCe getter film and the Ge substrate, which improved the internal vacuum level and the stability of the microelectromechanical system vacuum devices.

An interconnect-free micro-electromechanical 7-bit arithmetic device for multi-operand programmable computing

Computational power density and interconnection between transistors have grown to be the dominant challenges for the continued scaling of complementary metal–oxide–semiconductor (CMOS) technology due to limited integration density and computing power. Herein, we designed a novel, hardware-efficient, interconnect-free microelectromechanical 7:3 compressor using three microbeam resonators. Each resonator is configured with seven equal-weighted inputs and multiple driven frequencies, thus defining the transformation rules for transmitting resonance frequency to binary outputs, performing summation operations, and displaying outputs in compact binary format. The device achieves low power consumption and excellent switching reliability even after 3 × 103 repeated cycles. These performance improvements, including enhanced computational power capacity and hardware efficiency, are paramount for moderately downscaling devices. Finally, our proposed paradigm shift for circuit design provides an attractive alternative to traditional electronic digital computing and paves the way for multioperand programmable computing based on electromechanical systems.