MEMS/NEMS

The edge-degree distance of a simple connected graph G is defined as the sum of the terms ( d(e |G ) + d(f |G ) ) d(e, f |G ) over all unordered pairs {e, f } of edges of G, where d(e |G ) and d(e, f |G ) denote the degree of the edge e in G and the distance between the edges e and f in G, respectively. In this paper, we study the behavior of two versions of the edge-degree distance under two graph products called splice and link.

The edge-degree distance of a simple connected graph G is defined as the sum of the terms (d(e|G)+d(f|G))d(e,f|G) over all unordered pairs {e,f} of edges of G, where d(e|G) and d(e,f|G) denote the degree of the edge e in G and the distance between the edges e and f in G, respectively. In this paper, we study the behavior of two versions of the edge-degree distance under two graph products called splice and link.

The miniaturization trend leads to the development of a graphene based nanoelectromechanical (NEM) switch to fulfill the high demand in low power device applications. In this article, we highlight the finite element (FEM) simulation of the graphene-based NEM switches of fixed-fixed ends design with beam structures which are perforated and intact. Pull-in and pull-out characteristics are analyzed by using the FEM approach provided by IntelliSuite software, version 8.8.5.1. The FEM results are consistent with the published experimental data. This analysis shows the possibility of achieving a low pull-in voltage that is below 2 V for a ratio below 15:0.03:0.7 value for the graphene beam length, thickness, and air gap thickness, respectively. The introduction of perforation in the graphene beam-based NEM switch further achieved the pull-in voltage as low as 1.5 V for a 250 nm hole length, 100 nm distance between each hole, and 12-number of hole column. Then, a von Mises stress analysis is conducted to investigate the mechanical stability of the intact and perforated graphene-based NEM switch. This analysis shows that a longer and thinner graphene beam reduced the von Mises stress. The introduction of perforation concept further reduced the von Mises stress at the graphene beam end and the beam center by approximately ~20-35% and ~10-20%, respectively. These theoretical results, performed by FEM simulation, are expected to expedite improvements in the working parameter and dimension for low voltage and better mechanical stability operation of graphene-based NEM switch device fabrication.

Graphene nano-electro-mechanical switches are promising components due to their excellent switching performance such as low pull-in voltage and low contact resistance. Mass fabrication with an appropriate counter electrode remains challenging. In this work, we report the stacking of nanocrystalline graphene (NCG) with a 70-nm dielectric separation layer. The buried NCG layer is contacted through the formation of vias and acts as actuation electrode. After metallization, the top 7.5-nm thin NCG layer is patterned to form double-clamped beams, and the structure is released by hydrofluoric acid etching. By applying a voltage between the top and buried NCG layer, a step-like current increase is observed below 1.5 V, caused by the contact of the movable beam with the buried NCG. No pull-out is observed due to the thin sacrificial layer and high beam length, resulting in low mechanical restoring force. We discuss the possible applications of the NCG stacking approach to realize Nano-Electro-Mechanical (NEM) contact switches and advanced logical components such as a AND logic.

Summary The paper is focused on system level modeling of MEMS using advanced reduced order modeling (ROM) methods based on mode superposition technique and finite element solvers for data extraction. Dynamically accurate behavior representations can be achieved for microstructures with flexible components and their most important interactions with thermal, electrostatic, magnetic and fluid fields. The results are macromodels based on analytical terms which can be transferred to electronic and system simulators for virtual prototyping and device analyses. To demonstrate the theory of the proposed methods and its possibilities, few examples are presented: vibration parameterized electrostatically actuated fixed-fixed beam and SWCNT-based mechanical sensor.

This tutorial deals with the model development of the piezoresistance of Single Walled Carbon Nanotubes (SWCNTs) as components at system level design. The framework VHDL-AMS (virtual hardware description language) is used for implementation and simulation. It is based on compact models to describe the components performing heterogeneous functions. The mechanical and electronical compact submodels of SWCNTs are based on the analytical models and lumped element models. The tutorial presents important aspects in developing these system models and the necessary parameters in creating those models. The developed models can be used for the design of SWCNT based mechanical sensors and for co-simulation with any other system environment or complex electronic circuit.

We report the high-yield fabrication of SiCN doublyclamped nanomechanical resonator arrays for the specific detection of proteins. As a proof of concept, specific detection of Protein A has been demonstrated. The resonant frequencies of the individual resonators were determined using optical interferometry. The bare resonators displayed resonance frequencies of ~ 17 MHz. Immobilization of single domain antibody fragments resulted in frequency downshifts of ~ 341 kHz due to the added mass. Attachment of protein A yielded a further reduction of frequency by ~ 216 kHz. A much smaller frequency reduction of ~ 54 kHz was observed when the resonators are exposed to an identical solution containing no protein A.

Microelectromechanical systems (MEMS) is a multidiscipline area requiring knowledge in various STEM disciplines such as: mechanics, material science, chemistry, physics, and electronics etc.….A graduate course at the University of New Mexico focuses on learning theory of microfabrication and applying this knowledge through a hands-on problem-based learning project. The problem-based learning project focused on developing a MEMS electro-thermal actuator and the challenges associated with microfabrication. The hands-on experience was performed during the lab section of the course in a cleanroom environment. The course was designed to give students theoretical knowledge while giving them hands-on experience as a MEMS process engineer thus giving them experience in MEMS microfabrication. The present work focused on fabricating an aluminum electro-thermal MEMS actuator on a silicon wafer using photoresist as the sacrificial layer and measuring the displacement as a function of the applied voltage, which was performed as laboratory work supplementing the graduate course. Actuators with varying dimensions were developed. Stresses in the aluminum cantilever structure were reduced by controlling sputtering deposition parameters such as thickness and power. Removal of the sacrificial photoresist layer proved to be a limiting factor because a liquid etchant was used, which lead to issues with stiction. Care was taken to optimize the process of the electro-thermal actuators and reduce the amount of stiction and overall intrinsic stress present of the device. The results of this project were working devices and knowledge of process improvements to increase the efficacy of future work in this field.

The paper presents the correlation between the physical model of a dynamic system that is in the steady state dynamic equilibrium and the computer one. The computer model follows the physical model of a dynamic system with one degree of freedom with discretely variable damping. nbsp

This theoretical work corresponds to the hope of extracting, without contradicting EMMY NOETHER's theorem, an energy present throughout the universe: that of the spatial quantum vacuum. This article shows that it should be theoretically possible to maintain a continuous periodic vibration of a piezoelectric structure, which generates current peaks during a fraction of each vibration period. These vibrations are obtained by automatically controlling and in predetermined situations, the action of an attractive Casimir force between two electrodes by a repulsive Coulomb force applied to a third return electrode. The internal electric field of a piezoelectric bridge, deformed by this force of Casimir, attracts from the mass mobile charges of contrary signs. These mobile electric charges of the same sign and blocked on the sources of a MOS transistor as well as on one of the faces of the piezoelectric bridge, suddenly homogenize with a Coulomb electrode located in series. They generate a temporal peak of current as well as an ephemeral and repulsive Coulomb force. Electronics without any power supply, then transform these alternating current signals into a usable direct voltage. To manufacture these different structures, we present an original micro-technology to realize these electronics, and for technologically control and optimize the very weak interfaces between the Casimir electrodes and of the return electrodes.

This theoretical work corresponds to the hope of extracting an energy present everywhere in the universe: that of the quantum vacuum. With the energy of the quantum vacuum as the only source, this article shows that it is theoretically possible, without contradicting EMMY NOETHER's theorem: 1/ to maintain a continuous periodic vibration of a piezoelectric bridge embedded at its two ends, 2/ to extract exploitable electrical power from it. These vibrations of the sensor part of the proposed MEMS have nothing in common with an impossible macroscopic "perpetual motion" because the energy of the quantum vacuum permanently powers the system. They are obtained by automatically controlling the deformation of a piezoelectric bridge. This cyclic deformation is created thanks to the Casimir force FCA, omnipresent, permanent and attractive, between two electrodes. This FCA force is controlled by an automatic Coulomb repulsive force FCO which is applied, thanks to the closure of a switch n°1 on a third electrode called Coulomb. The FCO Coulomb's force derives from the electric charges generated by the deformation of the piezoelectric bridge. The FCO force is in the opposite direction and with a greater intensity than the FCA. The FCO force appears and disappears at predetermined positions z1 and z2, thanks to the very close consecutive activation of two switches which automatically switch by the action of the electric charges appearing on the deformed piezoelectric bridge. The resultant of the applied forces, FCO-FCA, then straightens the bridge and gives it kinetic energy, giving it inertia which will be dissipated by the FCA force. The deformation of the piezoelectric bridge being reduced according to its electric charges, the switch n°1 opens again, immediately after its closure. Very quickly thereafter, the Coulomb electrode is then brought to ground, thanks to the switching-via an R.L.C circuit-of the switch n°2. The FCO force therefore disappears very quickly after its appearance. The kinetic energy acquired by the structure gives it an inertia which allows it to find or slightly exceed the initial position. The Casimir force, still present, then deforms the structure again. The system starts to vibrate. Each time switch n°2 close to ground, a current and voltage peak is generated. These periodic power peaks supply an autonomous electronic circuit (without any power supply) which transforms these signals into a usable DC voltage. In this article we will exclusively present the energy balance of the structure, and we will show that-unless mistaken-this balance is consistent with Miss Emmy Noether's fundamental theorem. For following parts: 1/ Putting into equations the dynamic behavior of the structure 2/ Creation of autonomous electronics for signal shaping 3/ Manufacturing microtechnology [7] [8] [9] See the articles published on Academia at the addresses:

A new design of a micro-mirror device and numerical analysis are presented in this thesis. Thinned beams are used to maximize the deflection angle under low applied voltage, when the electrostatic force is applied. Theoretical model is built to describe the response of the system. FEM is used to simulate the mirror and to analyze stresses and displacements. The maximum deflection angle is 8.82° at 100 V for 1000×1000×8 µm outer mirror plate, and 780×760×8 µm inner mirror plate as well as 750×40×8 µm, and 600×20×8 µm springs dimensions for outer and inner beams respectively. The purpose of micro-mirror devices is to precisely control the reflection of an incident beam. The challenge is to provide a precise control for the tilting angle using minimum power and to maximize the tilting angle of the system. To achieve these requirements, a new mechanism is proposed.

A nanoelectromechanical (NEM) switching device based on carbon nanotube (CNT) was investigated using atomistic simulations. The model schematics for a CNTbased three-terminal NEM switching device fabrication were presented. For the CNT-based three-terminal NEM switch, the interactions between the CNT-lever and the drain electrode or the substrate were very important. When the electrostatic force applied to the CNT-lever was the critical point, the CNT-lever was rapidly bent because of the attractive force between the CNT-lever and the drain; then, the total potential energy of the CNT-lever was rapidly increased and the interatomic potential energy of the CNT-copper was rapidly decreased. The energy curves for the pull-in and the pull-out processes showed the hysteresis loop that was induced by the adhesion of the CNT on the copper, which was the interatomic interaction between the CNT and the copper.

The microassembly of pressure sensor chip with the modernized basic structure for the increase of stability and mechanical strength is presented in this patent. The classical structure of the piezoresistive pressure sensor chip uses the full Wheatstone bridge circuit with 4 piezoresistive resistors. The microassembly structure is necessary for the mechanical decoupling of the chip from any case material with the temperature coefficient of expansion different from silicon. Additionally, the microassembly design contains the structures in the form of stops for the multiple increase of mechanical strength from the overload/burst pressure relative to the nominal pressure. The microassembly design is intended for the measurement of differential pressure, therefore, it has stops on both sides. The certain geometry of the base with the pedestal made of silicon allows to remove the residual mechanical stresses from the case, which cause additional parasitic stresses both at the room temperature, relaxing with time (the influence on the long-term stability), and with the change of temperature (temperature hysteresis and coefficient of output signal). The connection between the chip, the base and the cap is made by frit layer. A certain gap between the front side of the chip, as well as the surfaces of the rigid islands (concentrators) of membrane and the base stop allows the membrane to bend freely within the nominal pressure and to slow down this bending under overload.

The microassembly of pressure sensor chip with an upgraded basic structure for improved long-term stability is presented in this patent. The classic structure of a piezoresistive pressure sensor chip uses a full Wheatstone bridge circuit with 4 piezoresistive resistors. The microassembly structure is necessary for better mechanical decoupling of the chip from any case material with a temperature coefficient of expansion different from silicon. The microassembly design is designed to measure differential pressure. A certain geometry of the base with a pedestal, where smoothed corners are formed (both in the horizontal and vertical planes), made of silicon, allows removing residual mechanical stresses from the case, which cause additional parasitic stresses both at room temperature, relaxing over time (influence on signal stability), and with temperature changes (temperature hysteresis and output signal coefficient). The connection between the chip, the base and the cover is made by a frit layer.

Micro-electroactive polymers have wide applications from industry to healthcare. Artificial muscles, microvalves, microswitches, haptic sensing, blood pressure and pulse monitoring are some potential applications for micro-electroactive polymers. The most advantage of micro-electroactive polymers as sensors and actuators is bio-compatibility and low power threshold for large deformations. In this short review, some applicable fabrication methods of micro-electroactive polymer cantilever are reviewed. Furthermore, a novel method based on standard micro fabrication techniques is designed and discussed in details which presents a conceptual design of a micro-electroactive polymer cantilever on a polymeric anchor located on a silicon substrate for future works.

This work is an experimental study for plasma actuators to get a maximum efficiency at the best operating conditions using several variables such as different electrodes materials, horizontal distances between the effective and ground electrodes, also two type of dielectric materials used like Poly methyl methacrylate (PMMA) and high density polyethylene (HDPE). The discharge plasma was produced by AC power supply source of 8 KHz frequency and applied voltages (3, 5, 7, 9) kV. The results show that, the efficiency have maximum value, up to 0.25, when the dielectric is PMMA, copper electrodes, applied voltage of 7kV, and 1mm dielectric thickness. It's clear there was distinction efficiency up to 0.20 using aluminum electrodes of 2mm thickness for PMMA dielectric and 5kV as applied voltage. Also, most likely the efficiency decrease with the increasing horizontal distance between the two electrodes.

Latent heat thermal energy storage (LHTES) using phase change materials (PCM) is a renewable energy solution that is applicable for implementation in space cooling due to its high energy storage density. A novel thermal energy storage which will encapsulate a PCM layer to absorb the rejected heat from the building during occupied hours and release it to the ambient air during night-time is going to be developed. On the grounds of this development, a selection of seven PCMs are examined. The selected materials comprise the basic classes of PCM, namely: paraffins, fatty acids, and salt hydrates. The objective of this study is to identify experimentally the thermal properties of commercial PCM, renewable based oils, PCM in water emulsions, and PCM polymer blends. The supporting materials used in the polymerization of the PCM are polyethylene glycol diacrylate (PEGDA) and polyvinylpyrrolidone (PVP). The characterization of the thermophysical properties of the PCM is achieved by using differential scanning calorimetry (DSC) in dynamic operation mode. The values of the thermophysical properties for the commercial PCM and the renewable based oils provided by the manufacturers are compared with the experimental results. The long term stability of the thermophysical properties of PCM after 50, 100, 150, and 200 thermal cycles equivalent to a 6-month duty cycle in a real-life application is presented. The cases of the PCM emulsions and the PCM polymer blends are analyzed. The obtained results demonstrate the stability of the PCM under thermal cycling and the supercooling effect during the liquid-solid phase change.

This study presents the developed computational finite element models for transient heat transfer analysis in fabrics enriched by phase change materials along with efforts to provide validation on the basis of obtained experimental results. The environment-friendly butyl stearate is used as a phase change material. Its melting/heating absorption takes place in temperature range from 19 C to 34 C, and the solidification/heat release occurs from 34 C to 19 C. An important aspect in this analysis is the investigation of appropriateness of the material samples dimensions selected for effective heat capacity against temperature measurements. For this purpose, we used the combined experimental and finite element simulation-based analysis. A similar computational procedure enabled us to estimate the effective latent specific heat relationship of the fabric with phase change materials coating. The direct usage of differential scanning calorimetry (DSC) measurement-based specific heat relationships against temperature in the finite element models ensured good compliance of the computed results with the experiment. For validation of the developed computational models the infrared radiation heating-cooling experiments on fabrics with different deposits of a phase change material were performed. The noticeable influence of content of phase change materials for transient thermal behavior during heatingcooling cycles was determined. The experimental results have been compared against the finite element simulation results.

MEPCMs have drawn tremendous attention in TES fields. In this study, eutectic of CA and PA was encapsulated by PVC, and the novel MEPCM for TES applications was developed. Microcapsules were prepared by solvent evaporation method and examined using DSC, SEM, LPSA, FTIR, thermal cycling test and TGA. DSC results demonstrated that the phase change temperature of CA-PA eutectic decreased after microencapsulation. The most satisfied sample was the MEPCM with a shell-core ratio of 1:2, which melted at 17.1 • C with the latent heat of 92.1 J/g, the encapsulation ratio was 57.7%. SEM images and LPSA results showed that the prepared MEPCMs were consisted with micro-sized spheres. FTIR results confirmed that the PCM core was successfully encapsulated by the PVC shell, and no chemical reaction was found among the components. The prepared MEPCM showed an excellent thermal reliability after 500 times of thermal cycling. Microencapsulation enhanced the starting temperature of CA-PA eutectic thermal decomposition, and the novel MEPCM exhibited an excellent thermal stability at working temperature from TGA results. Consequently, MEPCM (1:2) was the optimal composition and had great potential for TES applications.

 Phase change materials (PCMs) are employed for the thermal energy storage owing to their high heat storage ability, narrow temperature difference between storage and retrieval of latent heat energy, and availability in a variety of phase change transition temperatures. Numerous research attempts have been made to develop a broad array of PCMs based on inorganic, organic and polymeric compounds for diverse area of applications. To improve the performance efficiency and proper handling of PCMs, they are often encapsulated or confined within a shape-stabilized supporting material of an inorganic or organic origin. This review emphasizes on the current research status of the polymer-based PCMs developed using the various PCMs-polymer combinations available, material characteristics, encapsulation, and shape-stabilization methods and provides detailed information on the contribution of polymers towards the enhancement of PCM end product properties, in the state of the art of thermal energy storage technology. 

A new concept of using an electrically insulating beam as a constraint is proposed to construct planar spring-like electro-thermal actuators with large displacements. On the basis of this concept, three types of microspring actuators with multi-chevron structures and constraint beams are introduced. The constraint beams in one type (the spring) of these devices are horizontally positioned to restrict the expansion of the active arms in the x-direction, and to produce a displacement in the y-direction only. In the other two types of actuators (the deflector and the contractor), the constraint beams are positioned parallel to the active arms. When the constraint beams are on the inner side of the active arms, the actuator produces an outward deflection in the y-direction. When they are on the outside of the active arms, the actuator produces an inward contraction. Finite-element analysis was used to model the performances. The simulation shows that the displacements of these microspring actuators are all proportional to the number of the chevron sections in series, thus achieving superior displacements to alternative actuators. The displacement of a spring actuator strongly depends on the beam angle, and decreases with increasing the beam angle, the deflector is insensitive to the beam angle, while the displacement of a contractor actuator increases with the beam angle.

The thickness uniformity within a specimen and the cross-sectional profiles of electroplated individual Ni-microstructures have been investigated as a function of the electroplating conditions. It was found that the uniformity and profiles of microstructures could be controlled by varying the process conditions. A uniform thickness distribution and microstructures with flat profiles could be obtained at optimal plating conditions of 8mA/cm 2 and 60°C. Above this optimal plating current density, the microstructure has a rabbit-ears profile and the thickness of a narrow microstructure is thicker than that of wide ones. While below this current density, the microstructure has a cap-like cross-sectional profile, and a narrow structure is thinner than wide ones. Increasing the plating temperature enhances the non-uniformity, whereas other process parameters have insignificant effects on it. The current crowding observed in patterned specimens is responsible for the rabbit-ears profile of individual microstructures, while a combination of the fluidic friction on the sidewall of the photoresist and the electrophoresis of the ions in the solution are believed to be responsible for the abnormal cap-like profile of individual microstructures and the thinning effect on narrow microstructures.

In this paper, we report the finite element method (FEM) simulation of double-clamped graphene nanoelectromechanical (NEM) switches. Pull-in and pull-out characteristics are analyzed for graphene NEM switches with different dimensions and these are consistent with the experimental results. This numerical model is used to study the scaling nature of the graphene NEM switches. We show the possibility of achieving a pull-in voltage as low as 2 V for a 1.5-µm-long and 3-nm-thick nanocrystalline graphene beam NEM switch. In order to study the mechanical reliability of the graphene NEM switches, von Mises stress analysis is carried out. This analysis shows that a thinner graphene beam results in a lower von Mises stress. Moreover, a strong electrostatic force at the beam edges leads to a mechanical deflection at the edges larger than that around the center of the beam, which is consistent with the von Mises stress analysis.

The graphene nano-electro-mechanical switches are promising components due to their outstanding switching performance. However, most of the reported devices suffered from a large actuation voltages, hindering them from the integration in the conventional complementary metal-oxide-semiconductor (CMOS) circuit. In this work, we demonstrated the graphene nano-electro-mechanical switches with the local actuation electrode via conventional nanofabrication techniques. Both cantilever-type and double-clamped beam switches were fabricated. These devices exhibited the sharp switching, reversible operation cycles, high on/off ratio, and a low actuation voltage of below 5 V, which were compatible with the CMOS circuit requirements.

Latent heat storage is one of the most efficient ways of storing thermal energy. There are large numbers of phase change materials that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. In the present paper, Melamine-formaldehyde microcapsules containing eicosane were prepared by in situ polymerization. The characterization of the microcapsules, including the particle size and size distribution, morphology, projection microscopy, thermal properties, was carried out. The prepared microcapsules were added to Indian wool and wool blebded fabrics by a conventional pad-dry-cure process to develop thermo regulating textile materials. The morphology and thermal properties of the treated fabrics were also investigated. The prepared microcapsules were spherical and had a melamine-formaldehyde resin shell containing Hexadecane, Octadecane, Butyl Stearate & Eiscosane. The heat storage capacity increased as the concentration of the microcapsules increased. The thermo regulating fabrics had shown increase in the thermal resistance value

This paper presents an approach to improve the performance of a MicroElectro-Mechanical (MEMS) switch with vertical movement, manufactured using surface micromachining technology. We focused on the investigations of the critical technological dimensions (gap, thickness of the arms) in order to obtain a released, stable mechanical structure and to avoid the stiction effect of the metallic shapes. Technological experiments, Scanning Electron Microscopy (SEM) investigations, CoventorWare and Comsol simulations were performed in order to investigate the electro-thermo-mechanical behaviour of the switch. Key-words: MEMS switch, thermal actuator, microfabrication, sacrificial layer.

An optical fiber with nano-electromechanical functionality is presented. The fiber exhibits a suspended dual-core structure that allows for control of the optical properties via nanometer-range mechanical movements. We investigate electrostatic actuation achieved by applying a voltage to specially designed electrodes integrated in the cladding. Numerical and analytical calculations are preformed to optimize the fiber and electrode design. Based on this geometry an all-fiber optical switch is investigated; we find that optical switching of light between the two cores can be achieved in a 10 cm fiber with an operating voltage of 35 V.

This paper reports the top-down fabrication of CNTs thin film on MEMS structure to develop sensing and actuating micro structures. In particular, this paper review the integration of CNTs film in application of silicon micromirror based on angular vertical comb actuator, development of microstructures with piezoresistive effect and Seebeck effect.

Instrument for Lunar Seismic Activity Studies (ILSA) is a science payload with the objective of studying seismic activities at the landing site of Vikram, the Lander of Chandrayaan-2. ILSA will be deployed to the lunar surface by a specially built mechanism. It is an indigenously developed instrument based on microelectro mechanical systems technology. High sensitivity silicon micro-machined accelerometer is the heart of the instrument that measures ground acceleration due to lunar quakes. The instrument has the capability of resolving acceleration better than 100 nano-g Hz-1/2 up to a range of 0.5 g over bandwidth of 40 Hz. This paper presents the basic concepts in the design, realization, characterization and the performance test results of the space qualified strong motion seismic sensors.

We present a thermoelastic micromotor for driving a rigid plate in an out-of-plane motion. The plate is suspended on spiral thermoelastic bimorph arms, made of a nitride layer coated by gold. Heating of the thermoelastic arms is achieved by driving electric current, either through polysilicon resistors that are embedded in the nitride layer, or through the gold layer itself. Heating generates isotropic internal bending moments in the bimorphs. We show that this bending produces only small deflections of the plate. To improve the performance of the actuator, we use selective stiffeners to convert bending into torsional deformation of the spiral arms. In one orientation of the stiffeners, this conversion may be used to achieve a sevenfold increase of the thermoelastic response of the actuator. In a different orientation of the stiffeners, a complete reversal of the enhanced thermoelastic response is achieved.

Currently a submicron soft reflow process developed in University of Manchester uses silicon nitride (Si 3 N 4) as the hard mask layer to support the T-Gate structure of pHEMTs in order to make it mechanically stable. However, an alternative material known as Spin-on-Glass (SoG) is introduced to replace Si 3 N 4 , offering shorter processing time and consequently, a much simpler and more cost-effective alternative to the e-beam lithography of nanometrescale gate length transistors. The SoG deposition through plasma-enhanced chemical vapour deposition process requires only 30 minutes to complete, as opposed to the one-day process of depositing Si 3 N 4. In this study, the SoG material used is Silicafilm, and the minimum deposition thickness achieved is 138 nm, enabling 150-nm gate length devices to be fabricated. The SoG is also successfully etched at very low power and pressure (20 W and < 25 mTorr respectively), eliminating the detrimental effect of high power plasma etching to the 2DEG carriers. In addition to that, no film cracks observed even by using a single coating and a single baking temperature of 200 o C. All these results indicate the potential of SoG as a suitable hard mask layer alternative to the silicon nitride for the use soft reflow fabrication process.

This paper presents a modeling for a 3DoF electrothermal actuated micro-electro-mechanical (MEMS) mirror used to achieve scanning for optical coherence tomography (OCT) imaging. The device is integrated into an OCT endoscopic probe, it is desired that the optical scanner have small footprint for minimum invasiveness, large and flat optical aperture for large scanning range, low driving voltage and low power consumption for safety reason. With a footprint of 2mm×2mm, the MEMS scanner which is also called as Tip-Tilt-Piston micromirror, can perform two rotations around x and y-axis and a vertical translation along z-axis. This work develops a complete model and experimental characterization. The modeling is divided into two parts: multiphysics characterization of the actuators and parallel kinematics studies of the overall system. With proper experimental procedures, we are able to validate the model via Visual Servoing Platform (ViSP). The results give a detailed overview on the performance of the mirror platform while varying the applied voltage at a stable working frequency. The paper also presents a discussion on the MEMS control system based on several scanning trajectories. 4 4 This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits distribution, and reproduction in any medium, provided the original work is properly cited.

In this paper, we perform an analytic solution of a vibro-impact system including two singledegree-of-freedom vibration systems under random excitations by using the classical Fokker-Planck-Kolmogorov (FPK) method. The numerical solution of the vibro-impact systems is also performed based on the inverse discrete Fourier transform (IDFT) and the Runge-Kutta method. The mean square responses and the mean square responses ratio are calculated to study the deviation between the analytical solution and the numerical solution. Finally, the influence of clearance on the responses of the systems, such as mean square responses, contact ratio and impact force level, is discussed.

This paper presents the design and fabrication of thermally actuated multi-layered microactuator for out of plane actuation application. Multi-layered actuators are fabricated using ammonium persulfate based TMAH (Tetra-Methyl-Ammonium-Hydroxide) etching with metal passivation. Multi-layered [Au/Si 3 N 4 /SiO 2 ] microactuators with straight and cross-heaters are characterized using the I-V measurement tool. Temperature across actuator was similar to simulated results. Gold as an upper layer of a microactuator fully protected during the release process. Fundamental mode or resonant frequency of fabricated multi-layered microactuator measured by laser Doppler vibrometer (LDV) which observed around 20 KHz.

This paper presents the design and fabrication of thermally actuated multi-layered microactuator for out of plane actuation application. Multi-layered actuators are fabricated using ammonium persulfate based TMAH (Tetra-Methyl-Ammonium-Hydroxide) etching with metal passivation. Multi-layered [Au/Si 3 N 4 /SiO 2 ] microactuators with straight and cross-heaters are characterized using the I-V measurement tool. Temperature across actuator was similar to simulated results. Gold as an upper layer of a microactuator fully protected during the release process. Fundamental mode or resonant frequency of fabricated multi-layered microactuator measured by laser Doppler vibrometer (LDV) which observed around 20 KHz.

We present a process flow and characterization for the growth of freestanding carbon nanotubes on a polysihcon microelectromechanical device. Individual or multiple tubes can be directly grown bctween movable posts and electrically connected. The process is characterized to the point where minimum feature sizes of catalytic islands are determined as a function of the catalytic solution concentration. We show scanning electron microscopy pictures that validate the direct growth of nanotubes. The reported technology is batch-fabrication compatible as opposed to discrete fabrication processes and is opening the way to the synthesis and evaluation of mechanical nano-scale transduccrs based on carbon nanotubes. microscope (AFM) to apply a force on a suspended CNT while measuring the electric conductivity [6,7]. We suggest the usage of microsystem technology as a flexible platform for system design to mechanically deform and electrically sense CNTs in various ways (axial & torsional strain, bending, resonance) [8], given that the CNTs can be accurately integrated. Schematically shown in Fig. 1 is a proposed MEMS based test stand. bridgedCNT

Instrument for Lunar Seismic Activity Studies (ILSA) is a science payload with the objective of studying seismic activities at the landing site of Vikram, the Lander of Chandrayaan-2. ILSA will be deployed to the lunar surface by a specially built mechanism. It is an indigenously developed instrument based on microelectro mechanical systems technology. High sensitivity silicon micro-machined accelerometer is the heart of the instrument that measures ground acceleration due to lunar quakes. The instrument has the capability of resolving acceleration better than 100 nano-g Hz-1/2 up to a range of 0.5 g over bandwidth of 40 Hz. This paper presents the basic concepts in the design, realization, characterization and the performance test results of the space qualified strong motion seismic sensors.

In this study, we demonstrate the colloidal synthesis of nearly monodisperse, sub-100-nm phase change material (PCM) nanobeads with an organic n-paraffin core and poly(methylmethacrylate) (PMMA) shell. PCM nanobeads are synthesized via emulsion polymerization using ammonium persulfate as an initiator and sodium dodecylbenzenesulfonate as a surfactant. The highly uniform n-paraffin/PMMA PCM nanobeads are sub-100 nm in size and exhibit superior colloidal stability. Furthermore, the n-paraffin/PMMA PCM nanobeads exhibit reversible phase transition behaviors during the n-paraffin melting and solidification processes. During the solidification process, multiple peaks with relatively reduced phase change temperatures are observed, which are related to the phase transition of n-paraffin in the confined structure of the PMMA nanobeads. The phase change temperatures are further tailored by changing the carbon length of n-paraffin while maintaining the size uniformity of the PCM nanobeads. Su...

A series of on-chip test structures where designed, modeled and fabricated for on-chip fracture characterization of 0.7 µm thick polysilicon film. The first test structure is rotational and actuated by comb- fingers capacitors which develop a force sufficient to load the specimens up to rupture; it allow the determination of Young modulus and rupture strength. The second kind of test structure is actuated in the direction orthogonal to the substrate by means of a system of parallel plate actuators, four specimens placed at the four corners of the device are loaded in bending and torsion; they are conceived in order to estimate the value of the shear elastic modulus of the polysilicon film. The third test structure is again actuated by parallel plate capacitors in the direction orthogonal to the substrate and able to load up to rupture a couple of specimens in bending in the plane orthogonal to the substrate; this device has been built in order to measure the resistance of the polysi...

High-aspect-ratio metallic microstructures have a variety of potential applications in sensing and actuation. However, fabrication remains a challenge. We have fabricated Ni microstructures with over 20:1 aspect ratios by electroplating patterned, carbon-coated, carbon-nanotube forests (CNTs) using a nickel chloride bath. Pulse plating allows nickel ions to diffuse into the interior of the forest during off portions of the cycle. Done properly, this solves the problem of the formation of an external crust which otherwise blocks Ni deposition in the interior of the structures. Thus, densities of 86±3% of bulk Ni for the composite structures are achieved. Cantilever structures do not yield under load but break. Measurements of the material properties of this composite material indicate an elastic modulus of approximately 42 GPa and a strength of 400 MPa. We demonstrate the utility of this method with a simple MEMS magnetic actuator consisting of a proof mass and two flexures. We achieved 7 mN actuation forces.

Usage of thermo-regulative phase change material (PCM) doped polyurethane (PU) foam (PU-PCM) as a building component in cold storage can promote electricity saving in terms of cooling load reduction through utilizing its mutual advantage of insulation as well as thermal energy storage property of PU & PCM respectively. The current review demonstrates the suitable synthesis approaches of PU-PCM that are applicable for perishable food cold storage temperature range (specifically for − 10 • C to 15 • C), optimization of PU-PCM's component in production step, performance evaluation approaches, future research scope. Synthesis of PU-PCM composite by direct method suffers from lower thermal cycling ability, and leakage problem of molten PCM; hence the indirect way of PU-PCM synthesis, i.e., encapsulated-PCM (EPCM) incorporating into PU matrix will be the better option to counteract the deficiency of direct method. Organic-inorganic hybrid shell-based EPCM with the paraffinic core of phase transition range − 10 • C to 15 • C would be suitable for this purpose due to their better thermal reliability and good adhesion to the PU matrix & better balancing of thermal conductivity. Encapsulation methods of PCM core, size of EPCM, EPCM contents in PU matrix directly influence the properties of PU-PCM and the energy performance of cold storage.

This thesis covers the development and characterization of an all polymer micromachining process designed for multiuser applications. This thesis describes the first MEMS process designed to provide multiuser functionality using polymers as structural and sacrificial layers, and offers new fabrication abilities not previously available with silicon micromachining. The structural material for this MEMS process is the negative tone photoresist SU-8, which is excellent for low temperature permanent applications. This work has developed a very reliable method of producing compliant SU-8 microstructures and has characterized it for a new class of structures and actuators. The use of SU-8 offers many advantages with respect to processing, but also introduces many processing challenges that were solved in this work. The polymer MEMS process developed for this work has a multi-thickness structural layer separated from the substrate by a single sacrificial layer. The sacrificial layer includes dimple features to reduce stiction and allow structures in excess of 5000 X 5000 µm 2 to release without problems. The list of working devices fabricated in this process includes low and high aspect ratio compliant mechanisms, micro-optical components, thermal and electrostatic actuators, micro antennas and compliant grippers. The many processing advances introduced through this work include elimination of adhesion failure of polymers during multiple processing steps, alignment of two polymers with similar indices of refraction, development of an anti-stiction substrate with high adhesion anchor areas, characterization of stress gradient in SU-8 with processing conditions, and successful gold wirebonding onto SU-8 devices.

A novel release process without stiction problem is a major concern in surface micromachining technology to fabricate microelectromechanical systems (MEMS) devices. HF vapor-phase etching (VPE) has been focused as a promising dry process to remove sacrificial SiO2 layer, but still has limitation due to water condensation. We have first demonstrated the effectiveness of a new surface modification method using strongly hydrophilic materials (i.e., Ti, Al2O3) in preventing the release-stiction during HF VPE process. The role of hydrophilic surface layer is proposed to suppress the water bridging causing a attractive capillary force between micromechanical and stationary structures.