MEMS-based Micro Research Articles

Methanol Sensing Behavior Analysis of Pt-Sn/C Based Micro DMFC

A MEMS-based micro DMFC structure of 1cm2, fabricated using 3D printing technology. Pt-Sn/C is offering good power density which was identified as the novel catalyst in DMFC. The synthesized nanoparticles of Pt-Sn/C was characterized and the MEA of the same was fabricated with Nafion membrane was and the cathode catalyst of pure Pt. Physically attached MEA with the DMFC cell was tested for the methanol of different concentrations and different operating temperature of the cell. The polarization curves were plotted for the redox reaction. The performance of the cell was increased with the increment of the temperature. At the same time, the considerable amount of current was observed while the cell was operated at low temperature The produced current was amplified and the sensor’s minimal detection ability of methanol was tested and results are presented.

Challenges and Opportunities of Chemiresistors Based on Microelectromechanical Systems for Chemical Olfaction.

Microelectromechanical-system (MEMS)-based semiconductor gas sensors are considered one of the fastest-growing, interdisciplinary high technologies during the post-Moore era. Modern advancements within this arena include wearable electronics, Internet of Things, and artificial brain-inspired intelligence, among other modalities, thus bringing opportunities to drive MEMS-based gas sensors with higher performance, lower costs, and wider applicability. However, the high demand for miniature and micropower sensors with unified processes on a single chip imposes great challenges. This review focuses on recent developments and pitfalls in MEMS-based micro- and nanoscale gas sensors and details future trends. We also cover the background of the topic, seminal efforts, current applications and challenges, and opportunities for next-generation systems.

MEMS-Based Micro Sensors for Measuring the Tiny Forces Acting on Insects.

Small insects perform agile locomotion, such as running, jumping, and flying. Recently, many robots, inspired by such insect performance, have been developed and are expected to be smaller and more maneuverable than conventional robots. For the development of insect-inspired robots, understanding the mechanical dynamics of the target insect is important. However, evaluating the dynamics via conventional commercialized force sensors is difficult because the exerted force and insect itself are tiny in strength and size. Here, we review force sensor devices, especially fabricated for measuring the tiny forces acting on insects during locomotion. As the force sensor, micro-force plates for measuring the ground reaction force and micro-force probes for measuring the flying force have mainly been developed. In addition, many such sensors have been fabricated via a microelectromechanical system (MEMS) process, due to the process precision and high sensitivity. In this review, we focus on the sensing principle, design guide, fabrication process, and measurement method of each sensor, as well as the technical challenges in each method. Finally, the common process flow of the development of specialized MEMS sensors is briefly discussed.

Performance of MEMS-Based Monopropellant Microthruster With Insulating Effect

Excessive heat loss in micro scale has been a long-lasting issue, affecting catalyst reactivity particularly for monopropellant thrusters and causing insufficient propellant decomposition. Various MEMS fabrication substrates and technologies were utilized for micro propulsion, but few studies on MEMS-based propulsion have reported their propulsion performance, due to not only insufficient propellant decomposition, but also difficulties of measuring high temperature and pressure in a micro scale chamber. In this work, a microthruster was fabricated using high insulation material (glass) in an optical lithography process of photosensitive glass to suppress heat loss. Chamber temperature and pressure sensing tips were integrated in a MEMS fabrication process, which were essential to evaluating propulsion performance and gaining an understanding of the insulating effects of the material on micro propulsion performance. Experimental test results showed successful propellant decomposition with 78% temperature efficiency, which is one of the highest temperature efficiencies in MEMS-based micro propulsion studies reported. The use of glass as a MEMS fabrication substrate was evaluated favorably through numerical analysis as well, in terms of suppression of thermal energy loss and superior propulsion performance.[2022-0014]

Continuously Adjustable Micro Valve Based on a Piezoelectric Actuator for High-Precision Flow Rate Control

A MEMS-based micro valve fitted with a piezoelectric actuator is presented in order to achieve a continuously adjustable flow rate control. The micro valve is realized using a cost-effective fabrication scheme with simple polyimide (PI) bonding, which has an average shear strength of up to 39.8 MPa, indicating a relatively high reliability. The simulation results based on the finite element method (FEM) show that the valve membrane is able to seal the inlet and cut off the flow successfully with a piezoelectric force of 3N when the differential pressure is 200 kPa. The measurement of the flow rate through the outlets shows that the micro valve can control the flow rate effectively in a large range under different actuation voltages and differential pressures. When the actuation voltage is 140 V, the measured leak flow of the closed micro valve is smaller than 0.5 sccm with a differential pressure of 200 kPa.

Research of Low-Power MEMS-Based Micro Hotplates Gas Sensor: A Review

In this paper, the research status of low power micro hot plate gas sensor is reviewed. This type of sensor is characterized by the combination of MEMS technology and related insulation measures. Compared with the traditional ceramic tubular sensor, the power consumption of the sensor is greatly reduced, which provides the possibility of remote sensor arrangement and long term stable operation. This paper firstly collects the current sensor-related heat conduction, heat convection and heat radiation theories, and summarizes the calculation model of heat loss in different regions of the micro hot plate gas sensor. Then, the application examples of the finite element method in the analysis of thermal characteristics of the sensor and the common preparation process of the substrate and gas sensitive layer of the micro hot plate are listed. Finally, the main test methods of the stability and gas sensitivity of the micro hot plate gas sensor are summarized.

A micro electromagnetic actuator with high force density

In this paper, we propose a planar type micro electromagnetic actuator with high force density. The actuator is composed of a mover (8 mm*8 mm*0.5 mm) and a stator (14mm*10mm*0.2 mm). As the mover, a thick NdFeB permanent magnet film (300 μm) with a chessboard pattern (unit size is 0.8 mm*0.8 mm) is attached with a ferromagnetic back yoke to provide enhanced magnetic flux density. In the stator, 3D mesh type micro coil with multi-turn configuration is designed accordingly. The micro coil has a novel connection between adjacent mesh units, which enables easy fabrication. The thick film magnet with chessboard pattern as well as the multi-turn micro coil with novel connection constitute the originality of this actuator. The mover and the stator can be produced by batch fabrication. The magnetic flux density (B) generated by the magnet are simulated and experimentally measured. The magnitude of B at vertical direction attains around 40 m T at 770 μm plane above the surface. Due to delicate design, the MEMS-based micro coil can withstand as high as 0.4A constant current input for over 60 min on a thermal isolated ceramic plate. The long-time duration experiment testifies the practicality of this micro actuator. Both repulsive and attractive electromagnetic force can be generated on the mover by altering the current direction in the stator. The measured force is around 4.3 mN at 20 μm gap with 0.1A stable current input in the stator and the force density attains as high as 0.96 mN/A/mm3.

Concept and proof for an all-silicon MEMS micro speaker utilizing air chambers

MEMS-based micro speakers are attractive candidates as sound transducers for smart devices, particularly wearables and hearables. For such devices, high sound pressure levels, low harmonic distortion and low power consumption are required for industrial, consumer and medical applications. The ability to integrate with microelectronic circuitry, as well as scalable batch production to enable low unit costs, are the key factors benchmarking a technology. The Nanoscopic Electrostatic Drive based, novel micro speaker concept presented in this work essentially comprises in-plane, electrostatic bending actuators, and uses the chip volume rather than the its surface for sound generation. We describe the principle, design, fabrication, and first characterization results. Various design options and governing equations are given and discussed. In a standard acoustical test setup (ear simulator), a MEMS micro speaker generated a sound pressure level of 69 dB at 500 Hz with a total harmonic distortion of 4.4%, thus proving the concept. Further potential on sound pressure as well as linearity improvement is outlined. We expect that the described methods can be used to enhance and design other MEMS devices and foster modeling and simulation approaches.

Electro Thermal Effects of Geometrically Modified MEMS-Based Micro Heater for Gas Sensing Applications

Micro heaters play a major role in gas sensing applications owing to their accuracy, selectivity and low power consumption. The proposed micro heater employs a window type polysilicon micro-hotplate structure, which is a square cell of side 500 μm, designed using COMSOL Multiphysics. It is highly imperative that an evenly distributed temperature is necessary over the broad area of the heater in order to improve its gas sensitivity and selectivity. In this paper, we have explained the design and analysis of a novel window-type micro heater made of polysilicon. The main aim of the work is to achieve temperature uniformity and low power consumption. By optimizing the geometry of the micro heater, we can obtain both temperature uniformity and low power consumption. This geometrical optimization also improves the sensitivity and response time of the sensor. To support them, we have carried out simulations using COMSOL Multiphysics. The proposed structure has obtained a uniform temperature of 1134.1 K and an average temperature of 1130.39 K. Such high and uniform temperatures finds applications in gas sensors. This work also analyzes the proper choice and placement of electrodes across the geometry of the heater.

Start-up characteristics of MEMS-based micro oscillating heat pipe with and without bubble nucleation

The startup characteristics of micro oscillating heat pipe (micro-OHP) have been experimentally investigated using a high-speed CCD camera in conjunction with the temperature measurement. The micro-OHP was fabricated on a silicon wafer by the MEMS technology, having trapezoidal channels with a hydraulic diameter of 357 μm. HFE-7100 was used as the working fluid with volumetric filling ratios ranging from 31% to 72%. The effects of filling ratio and heating power input on the start-up process were presented. Two different start-up behaviors, so-called start-up with and without bubble nucleation (STWBN/STWOBN), subject to different heat input levels were observed, and the underlying mechanisms were elaborately analyzed. The occurrence of STWBN or STWOBN depends mostly upon the spatial distribution of slugs/plugs in the micro-OHP. For the STWOBN mode, the fluid movement could be triggered by intense liquid film evaporation without nucleation with evaporator temperature less than 80 °C. However, the STWBN mode is sometimes indispensable to excite the two-phase oscillations in the micro-OHP due to the non-desirable slug/plug distribution, leading to much higher evaporator temperatures even greater than 140 °C to initiate the bubble generation. To predict the startup temperature at the STWBN mode, a theoretical model to describe the wall superheat required for incipient bubble nucleation in microchannels was propounded and largely agreed with the present experimental data. Micro-OHPs worked at the STWBN mode may greatly hinder their applications in electronics cooling, and artificial cavities fabricated or embedded on silicon channel wall surfaces are proposed to facilitate bubble nucleation and then the startup at low temperatures.

Operational characteristics of an MEMS-based micro oscillating heat pipe

The flow characteristics and thermal performance of an MEMS-based micro oscillating heat pipe (micro-OHP) were experimentally investigated using dielectric liquid HFE-7100 as working fluid. The micro-OHP was integrated on a silicon wafer with trapezoidal channels having a hydraulic diameter of 357μm. The gravity action on the micro-OHP performance functioned greatly and could not be ignored. High-speed visual observation demonstrated the annular/semi-annular flow, injection/slug flow, and bubbly flow in the micro-OHP. The alternate “small-amplitude oscillation phase (SAOP)—large-amplitude oscillation phase (LAOP)” was verified in this micro-OHP at the quasi-steady oscillation state, and its performance improvement was attributable to the extended time ratio of LAOP. In addition, the ephemeral circulation flow and bubble nucleation were observed intermittently. The occurrence of dry-out mainly appeared at lower filling ratios and higher power inputs.

Flow Analysis of MEMS-based Micro Pump

Flow Analysis of MEMS-based Micro Pump

Development of MEMS-based micro capacitive tactile probe

In this paper, a micro capacitive sensor with nanometer resolution is presented for ultra-precision measurement of micro components, which is fabricated by the MEMS (micro electromechanical systems) non-silicon technique. Based on the sensor, a micro capacitive tactile probe is constructed by stylus assembly and packaging design for dimension metrology on micro/nano scale, in which a data acquiring system is developed with AD7747. Some measurements of the micro capacitive tactile probe are performed on a nano positioning and measuring machine (NMM). The measurement results show good linearity and hysteresis with a range of 11.6 μm and resolution of better than 5 nm. Hence, the micro capacitive tactile probe can be integrated on NMM to realize measurement of micro structures with nanometer accuracy.

Fabrication of MEMS-based Micro Direct Methanol Fuel Cell Using Porous Silicon as Catalysts Substrates

In order to further miniaturize the silicon-based micro direct methanol fuel cell (μDMFC), a novel method of fabricating MEMS-based single is μDMFC introduced. Using the silicon micromachining techniques, including thermal oxidation, optical lithography, wet etching, silicon anodization, physical vapor deposition, electroless plating, laser beams cauterization, and anodic bonding, we have successfully made single μDMFC as small as 10 mm×8 mm×3 mm. First a porous silicon (PS) layer used as single cells substrate is formed by anodic etching in a HF-ethanol solution which is considered an effective and cheap fabrication method. Differs from other researchers, the electrocatalysts layer is deposited by electroless plating platinum or platinum and ruthenium (Pt-Ru) co-deposition over PS substrates. Catalyst being deposited over PS brings three-dimensional features, and the non-planar interfaces for the catalytic electrodes will increase the active surface area within a stated volume. Additionally, as high as 95% the utilization ratio of noble metal in electroless plating solution leads economizing platinum and ruthenium. SEM, EDX are employed to analysis the PS and catalyst layer. Moreover, using the MEMS technology makes the batch fabrication of μDMFC much easier and can reduce the usage of rare metals.

MEMS-Based Micro Sensor Detecting the Nitrogen Oxide Gases

Abstract In this study, a micro gas sensor for NO x was fabricated using a microelectromechanical system (MEMS)technology and sol-gel process. The membrane and micro heater of the sensor platform were fabricated by a standard MEMSand CMOS technology with minor changes. The sensing electrode and micro heater were designed to have a co-planar structurewith a Pt thin film layer. The size of the gas sensor device was about 2 mm × 2 mm. Indium oxide as a sensing material forthe NO x gas was synthesized by a sol-gel process. The particle size of synthesized In 2 O 3 was identified as about 50 nm byfield emission scanning electron microscopy (FE-SEM). The maximum gas sensitivity of indium oxide, as measured in termsof the relative resistance (R s =R gas /R air ), occurred at 300 o C with a value of 8.0 at 1 ppm NO 2 gas. The response and recoverytimes were within 60 seconds and 2 min, respectively. The sensing properties of the NO 2 gas showed good linear behavior withan increase of gas concentration. This study confirms that a MEMS-based gas sensor is a potential candidate as an automobilegas sensor with many advantages: small dimension, high sensitivity, short response time and low power consumption.Key wordsgas sensor, indium oxide, nitrogen oxides, sol-gel process, MEMS.

Hydrodynamic Characteristics of Crossflow over MEMS-Based Pillars

A parametric study was performed to reveal the hydrodynamic processes controlling crossflow over MEMS-based micro pin fin devices. Pressure drop experiments were conducted and used to obtain friction factors on a wide range of micro pin fin devices for various flow conditions and geometrical configurations, including pin fin height-to-diameter aspect ratios, spacings, and shapes. The acquired data suggests that the device geometry is the key parameter dictating friction factor trends and magnitude along with the Reynolds number. Additionally, friction factor data has shown that correlations based on experimental results performed on conventional scale tube bundles do not accurately predict the trends under working conditions pertaining to microfluidic systems.

G100063 MEMS技術によるECFマイクロレートジャイロの開発([G10006]機械力学・計測制御部門一般セッション(6):新技術)

G100063 MEMS技術によるECFマイクロレートジャイロの開発([G10006]機械力学・計測制御部門一般セッション(6):新技術)

Study on the MEMS-type gas sensor for detecting a nitrogen oxide gas

In this study, MEMS-based micro gas sensors were prepared by adopting MEMS technology and using sol–gel process. These sensors can be used for application of the air quality system monitoring the automobile indoor atmosphere. An array of MEMS-based gas sensors was designed to achieve low power consumption and high efficiency; this was done by adjusting the heater pattern and line width of the microheater. The thermal efficiency and the temperature distribution for a given microheater were estimated using the finite element method (FEM). In order to prepare the material for NO x sensing, W-sol was mixed with Sn-sol, which was prepared separately, and then 1–7 wt.% WO 3 was added to the mixture; this mixture was then deposited on the MEMS platform, and the platform was heated to a temperature between 350 and 700 °C. The topography of the sensing film was studied using an FE-SEM, and it was observed that the particle sizes were approximately 10–20 nm and that they decreased with an increase in the WO 3 content. The XRD patterns showed that SnO 2–WO 3 crystallization occurred above 500 °C. The response of the gas sensor to NO 2 gas was examined at various operating temperatures and gas concentrations. The maximum response of the gas sensor, as measured in terms of the relative resistance (R gas/R air), was 37 at 300 °C for 3-ppm NO 2, and it increased almost linearly with the gas concentration. The results of this study suggest that in the future, MEMS-based gas sensors can be used as automotive-exhaust-gas sensors.

Cyclic operation of a MEMS-based resonant micro heat engine: Experiment and model

The operation of a MEMS-based micro heat engine at resonant and off-resonant conditions is presented. Both model and experiment are used to investigate resonant and off-resonant operation of the engine. In this work, we look at the pressure-volume (PV) diagrams of an engine operated at resonance and off-resonance. Model predictions of the PV diagram are in favorable agreement with measured data. The results show that resonant operation is beneficial. At resonance, the pressure and volume in the engine cavity are decoupled and more mechanical work is observed. The PV diagram describes an elliptical shape. However, for an off-resonant operation the pressure and volume become more coupled and less mechanical work is observed. The PV diagram is described by a sigmoidal shape.

Design of MEMS-based micro direct methanol fuel cell stack

This paper presents two kinds of direct methanol fuel cell (μDMFC) stack in planar array. The silicon-based DMFC stack is designed in a flip-flop configuration using MEMS technology, and the stainless steel stack is fabricated using stamping technology. Compared to stainless steel stack, the flip-flop silicon-based stack may reduce the connection space and lower the contact resistance between the membrane electrode assembly and the plates. Experimental results show that these two kinds of stacks have similar output 6.75mW and 6.77mW at same operation conditions. The performance of the MEMS-based DMFC stack is rather good for application in portable electronic products.