Miniature Microelectromechanical Systems Research Articles

Signal detection and imaging methods for MEMS electron microscope

In the paper, new detection methods that can be used to detect signals in a miniature MEMS (Micro-Electro-Mechanical System) electron microscope were presented. The methods were designed to fit the structure of the developed MEMS microscope, equipped with an electron-optical microcolumn and a scanning system based on an octupole deflector. In the experiments carried out, imaging was performed using a system of three silicon detectors placed above, below, and at the sample level and integrated with the octupole deflection system. Measurements were carried out under different pressure conditions (vacuum and atmospheric pressure) and for different detector bias voltage and electron beam energy. Good quality images were obtained using all three detectors, both in vacuum and in air. The results presented indicate that in the final implementation of the MEMS electron microscope, all three detection systems can be successfully incorporated.

On overtravel and skate in cantilever-based probes for on-wafer measurements

Due to the deformability of a microcantilever-based probe, there is an interesting and subtle interplay between the probe overtravel, the tip skate on the surface, and the ultimate tangency of the tip of the probe with the wafer surface. The relationship between these parameters is described here. The scalable model is tested using a macroscopic cantilever and found to be accurate in its predictions. In addition, to avoid potential skate-induced damage to metallisation, the idea of zero-skate using a cantilever-based probe has been introduced; minimal skate is demonstrated using a macroscopic cantilever—the skate can be reduced by a factor of 0.176. As the model is scalable, this information could be of use to the designer of emerging miniature microelectromechanical systems (MEMS) microcantilever-based surface contact probes destined for on-wafer electrical measurements or the test engineer concerned with on-wafer probe contacting—where skate and overtravel are important practical concerns having repercussions in electrical contact quality. Some predictions of the modelling for microcantilever-based probes are provided.

Recent advances in MEMS mass spectrometers

In the past two decades, miniature mass spectrometers have developed rapidly as the requirements of on-site detection have been growing continuously. At present, it seems that further miniaturization of mass spectrometers meets its bottleneck, since the traditionally used processing technologies have been approaching to their limitations. MEMS (micro-electro mechanical systems) is a widely used microfabrication technology which provides new solutions for the next generation of miniature mass spectrometers or MEMS mass spectrometers. Over the past three decades, a large number of key components of mass spectrometers, e.g., ion sources, mass analyzers, ion detectors, vacuum pumps and gauges, monolithic integrated mass spectrometer chips and so on, have all been microfabricated successfully. The development of MEMS mass spectrometers is ready for more rapid growth. In the article, the latest progress of MEMS mass spectrometers, potential applications, existing problems and challenges as well as future trends were reviewed.

A Miniature Optical Force Dual-Axis Accelerometer Based on Laser Diodes and Small Particles Cavities.

In recent years, the optical accelerometer based on the optical trapping force effect has gradually attracted the attention of researchers for its high sensitivity and high measurement accuracy. However, due to its large size and the complexity of optical path adjustment, the optical force accelerometers reported are only suitable for the laboratory environment up to now. In this paper, a miniature optical force dual-axis accelerometer based on the miniature optical system and a particles cavity which is prepared by Micro-Electro-Mechanical Systems (MEMS) technology is proposed. The overall system of the miniature optical levitation including the miniature optical system and MEMS particles cavity is a cylindrical structure with a diameter of about 10 mm and a height of 33 mm (Φ 10 mm × 33 mm). Moreover, the size of this accelerometer is 200 mm × 100 mm × 100 mm. Due to the selected light source being a laser diode light source with elliptical distribution, it is sensitive to the external acceleration in both the long axis and the short axis. This accelerometer achieves a measurement range of ±0.17 g–±0.26 g and measurement resolution of 0.49 mg and 1.88 mg. The result shows that the short-term zero-bias stability of the two orthogonal axes of the optical force accelerometer is 4.4 mg and 9.2 mg, respectively. The main conclusion that can be drawn is that this optical force accelerometer could provide an effective solution for measuring acceleration with an optical force effect for compact engineering devices.

Model improvement of the miniature switched capacitor for high‐speed applications

In this work, it is shown that the spring constant model for rectangular fixed–fixed beam used in the literature for high-speed applications is not correct and the model is improved for all fixed–fixed beams with a desired symmetrical shape. The new model is used to calculate the resonance frequency of the fabricated high-speed-specific 3D bridge named boat-like shape beam existing in the literature. The comparison shows that the model result is in good agreement with the simulation and measurement results. Also, the concept of the miniature microelectromechanical systems switched capacitors will be explained and it is shown that the rectangular beam with a simple fabrication process can be designed to achieve high speed about 150 ns like a boat-like shape beam which needs to two specific lithography processes that are so involved.

Recent Progress of Miniature MEMS Pressure Sensors.

Miniature Microelectromechanical Systems (MEMS) pressure sensors possess various merits, such as low power consumption, being lightweight, having a small volume, accurate measurement in a space-limited region, low cost, little influence on the objects being detected. Accurate blood pressure has been frequently required for medical diagnosis. Miniature pressure sensors could directly measure the blood pressure and fluctuation in blood vessels with an inner diameter from 200 to 1000 μm. Glaucoma is a group of eye diseases usually resulting from abnormal intraocular pressure. The implantable pressure sensor for real-time inspection would keep the disease from worsening; meanwhile, these small devices could alleviate the discomfort of patients. In addition to medical applications, miniature pressure sensors have also been used in the aerospace, industrial, and consumer electronics fields. To clearly illustrate the “miniature size”, this paper focuses on miniature pressure sensors with an overall size of less than 2 mm × 2 mm or a pressure sensitive diaphragm area of less than 1 mm × 1 mm. In this paper, firstly, the working principles of several types of pressure sensors are briefly introduced. Secondly, the miniaturization with the development of the semiconductor processing technology is discussed. Thirdly, the sizes, performances, manufacturing processes, structures, and materials of small pressure sensors used in the different fields are explained in detail, especially in the medical field. Fourthly, problems encountered in the miniaturization of miniature pressure sensors are analyzed and possible solutions proposed. Finally, the probable development directions of miniature pressure sensors in the future are discussed.

Glow-discharge ion source for MEMS mass spectrometer

This work describes construction, technology, working principle and properties of an ion source dedicated to a miniature MEMS (Micro-Electro-Mechanical System) mass spectrometer. Conditions allowing efficient ionization of a gas sample, and obtaininga properly directed ion beam were determined. An influence of parameters such as shape, dimension and distance between the electrodes, as well as applied magnetic and electric field and pressure level, on the operation of this device were investigated. The experiment allowed choosing the optimal parameters, thus it may be concluded that the ion source will satisfy all the requirements necessary for the MEMS mass spectrometer.

A Micro Oven-Control System for Inertial Sensors

This paper presents a modular and generic micromachined oven-control system for use with miniature micro-electro-mechanical system (MEMS) transducers. The micro-oven-controlled off-the-shelf commercial six-axis MEMS inertial measurement unit (IMU), Invensense MPU-6050, provides the lowest reported temperature-induced root of sum of squares bias errors of 62.71°/h and 1.920 mg from -40°C to 85°C for three-axis gyroscopes and three-axis accelerometers, respectively. The micro-oven control system provides thermal isolation from the surrounding environment using a micro-machined isolation platform, vacuum-sealing, and a metal package. In addition, a CMOS temperature sensor, a proportional-integral-derivative-based temperature control scheme, and least mean square and random forest compensation algorithms are utilized to reduce temperature-induced bias drifts of IMUs. The most stable axes achieve peak-to-peak bias drifts of 12.78°/h and 665.2 ug during a thermal-cycle test for gyroscopes and accelerometers, respectively. The oven's heater power consumption is <;125mW at the lowest temperature, -40°C. This oven-control system can be applied to a wide range of MEMS sensors to reduce performance degradation due to temperature variation.

Performance Improvement of an INS by using a Magnetometer with Pedestrian Dynamic Constraints

This paper proposes to improve the performance of a strap down inertial navigation system using a foot-mounted low-cost inertial measurement unit/magnetometer by configuring an attitude and heading reference system. To track position accurately and for attitude estimations, considering different dynamic constraints, magnetic measurement and a zero velocity update technique is used. A conventional strap down method based on integrating angular rate to determine attitude will inevitably induce long-term drift, while magnetometers are subject to shortterm orientation errors. To eliminate this accumulative error, and thus, use the navigation system for a long-duration mission, a hybrid configuration by integrating a miniature micro electromechanical system (MEMS)-based attitude and heading detector with the conventional navigation system is proposed in this paper. The attitude and heading detector is composed of three-axis MEMS accelerometers and three-axis MEMS magnetometers. With an absolute algorithm based on gravity and Earth’s magnetic field, rather than an integral algorithm, the attitude detector can obtain an absolute attitude and heading estimation without drift errors, so it can be used to adjust the attitude and orientation of the strap down system. Finally, we verify (by both formula analysis and from test results) that the accumulative errors are effectively eliminated via this hybrid scheme.

Automatic jump detection in skiing/snowboarding using head-mounted MEMS inertial and pressure sensors

With advancing technology in the miniature microelectromechanical systems (MEMS) sensors, wearable devices are becoming increasingly popular, facilitating convenient activity detection. One particular application is in sports performance monitoring. This article presents a novel real-time jump detection algorithm in skiing and snowboarding using a microelectromechanical systems–based inertial measurement unit, which is integrated with a barometric pressure sensor. The key performance variables of the jump can be extracted and evaluated for training and/or entertainment purposes. In contrast to the existing jump detection algorithms based on acceleration signals, the proposed algorithm uses vertical velocity and air time in addition to acceleration in the vertical direction. The experimental results show that by incorporating the velocity and air time into the detection algorithm, the sensitivity and specificity increase dramatically to 92% and 93%, respectively.

Design, fabrication and characterization of miniature RF MEMS switched capacitor based phase shifter

This paper aims to present in detail the design, fabrication and the various characterization techniques adopted in realizing a novel miniature-size switched capacitor based phase shifter. The work strives to provide an all-round development of a DMTL (Distributed MEMS Transmission Line) based phase shifting unit yielding an overall phase shift of 15° at a frequency of 15GHz. The RF MEMS (Radio Frequency Micro Electro Mechanical Systems) Switched Capacitor based phase shifter has highly miniaturized dimensions, and is capable of solving many limitations to which the conventional Switched Capacitors are mostly susceptible. This miniature RF MEMS switched capacitor actuates at a low actuation voltage of 12V, exhibits a fundamental frequency of vibration as high as 1.468MHz and a switching time of 1.4µs which is an improvement over the other reported designs. Various characterization results seem to validate the simulations.

Miniature MEMS Switches for RF Applications

This paper presents a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers. A single 25 × 25 μm switch is first demonstrated with a Au-to-Ru contact, Cu = 5 fF and Ron = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To reduce the effective switch resistance, 10-20 miniature RF MEMS switches have been placed in parallel and result in equal current division between the switches, an up-state capacitance of 30-65 fF and a down-state resistance of 1.4-1.5 Ω. Furthermore, 10-20 element back-to-back switch arrays are developed and result in a marked improvement in the reliability of the overall switching device. A series-shunt design is also demonstrated with greatly improved isolation. The device has a figure-of-merit of fc = 1/(2πRonCu) = 3.8 THz (RonCu = 42 fs).

Vortex Anemometer Using MEMS Cantilever Sensor

This paper presents construction and performance of a novel hybrid microelectromechanical system (MEMS) vortex flowmeter. A miniature cantilever MEMS displacement sensor was used to detect frequency of vortices development. 3-mm-long silicon cantilever, protruding directly out of a trailing edge of a trapezoidal glass-epoxy composite bluff body was put into oscillatory motion by vortices shed alternately from side surfaces of the obstacle. Verified linear measurement range of the device extended from 5 to 22 m/s; however, it could be broadened in absence of external 50-Hz mains electrical interfering signal which required bandpass frequency-domain digital sensor signal processing. The MEMS vortex sensor proved its effectiveness in detection of semilaminar airflow velocity distribution in a 40-mm-diameter tubular pipe.

Biomimetic Soft Multifunctional Miniature Aquabots

Engineered locomotive systems are widespread on the macro scale (e.g., planes, trains, automobiles), yet miniaturized mobile systems are largely limited to the research lab. In particular, integration of specific functions such as sensing or drug delivery into a small robot is a great challenge. The ability to miniaturize parts affecting motion, such as MEMS-based components and electroactive polymers, while widely demonstrated has not led to practical advances in miniature multifunctional mobile robots. Rather complex construction, limits in the use of diverse materials, and cost (in case of the MEMS-based bot) all hinder the production of these robots. The small (micro-/millimeter scale) system within aqueous environments is particularly challenging, yet there are important potential applications for robots in such environments. To date, engineers have explored soft materials for creating components at the micro-/millimeter scales; for example, actuators such as ionic polymer metal composites, conducting polymers, and carbon nanotube actuators, and engineered devices housing hydrogel valves, filters, and lenses, as well as other soft material actuators that mimic natural movement (earthworm, myriapod, etc.). Still, the creation of miniature multifunctional robots that operate in aqueous environments has been elusive. Nature provides numerous examples of small, multifunctional and autonomous ‘‘robots’’ in the insect and marine worlds after which we aimed to model miniature polymeric aquabots. Here we present mini (microto millimeter) soft aquabots that combine multiple functionalities to perform multifunctional operations in aqueous environments, effectively simulating their natural counterparts. Despite extensive research on macroscale robotics and miniature micro-electromechanical systems, relatively little attention has been paid to the creation of miniature soft robots with diverse shapes, actuation mechanisms, and integrated functionalities. As a fabrication method, we describe a technique that takes advantage of the small volume required by amicrofluidic chamber; this will be used for photopolymerizing multifunctional minibots that possess several ‘‘organs,’’ allowing for movement, sensing/signaling, and capture/transport/release. A diverse group of aquabots mimicking three kinds of living organisms – octopus, sperm, and myriapod, each representing a different mode of locomotion – has been developed. These aquabots have the following key features: 1) diverse shape and small size (sub-millimeter feature sizes); 2) a variety of functions (e.g., actuation, sensing) integrated in a single robot; and 3) rapid, scalable fabrication both in dimension and quantity. The aquabots were fabricated out of soft materials, due to the ease of polymerization, as well as the ability to tailor the material composition towards achieving certain functionality (e.g., responsiveness to pH, temperature, or electric/ magnetic field). Sequential in situ photopolymerization within a microfluidic device allowed for precise fabrication of different components (arms, legs, body; see detailed procedure for photopolymerization in Experimental section). The bodies were constructed using a relatively inert polyethylene glycol (PEG) material, whereas ionic electroactive polymers (electroactive hydrogels) were chosen from a large number of available soft materials to serve as the actuators, thus facilitating controlled movement. Depending on the application, some aquabots contained temperature-, pH-, or chemical-sensitive polymers in addition to their electroactive hydrogel and PEG components. The gel network of polymerized actuator material was anionic, causing positively charged surfactant molecules to bind to its surface; this surfactant binding leads to an osmotic pressure difference between the gel interior and the external solution, thus inducing the contraction and curvature of the gel strip. Four parameters control electroactive hydrogelbased actuators: 1)magnitude of the applied potential; 2) angle of the applied potential; and both 3) width and 4) length of the actuator. Figure 1A illustrates the behavior of a rectangular gel actuator under changing parameters (width of post and applied voltage; see Supporting Information Fig. S1 for more complete parameter characterization). In situ photopolymerization facilitates the control of the geometric parameters and is amenable to the use of laser or multiphoton polymerization methods for improved resolution (e.g., further reduce actuator width to achieve faster and larger motion). To date, diverse electroactive hydrogels have been broadly applied to creating polymeric microactuators (see the detailed behavior of electric-sensitive hydrogel in Supporting Information). Here, we demonstrate the use of electroactive hydrogel for fabricating octopus-, sperm-, and myriapod-like aquabots that retain respective characteristic movement (Fig. 2; movies are available for octopus-like aquabot and sperm-like aquabots in Supporting Information – Videos 1 and 2, respectively). The repeated bending test under aquatic conditions was carried out to investigate the durability of the electroactive hydrogel strips (see Supporting Information for a detailed durability test conditions). The operation of the communications

High-Reliability Miniature RF-MEMS Switched Capacitors

This paper presents a radical departure from the standard RF microelectromechanical systems (MEMS) devices and introduces novel miniature MEMS switched capacitors for RF to millimeter-wave applications, which are around 150 times smaller in lateral dimensions than standard MEMS designs. The measured capacitance of a single device (l,w,t of 20, 9.5, 0.37 mum), suspended 0.25 mum above the pull-down electrode, is 3.9 and 11.7-12.1 iF (Cr = 3.0-3.1) in the up- and down-state positions, respectively. The measured capacitance ratio of a 4 X 4 array fabricated on quartz substrates and in a coplanar waveguide (CPW) configuration is 3.0 with an electrical Q > 90 at 20 GHz. The miniature MEMS spring constant is very high, and is much less sensitive to residual stress or temperature variations than standard MEMS devices. Dielectric charging simulations show that these devices can withstand a charge density 6.25 times higher than the standard MEMS devices. The mechanical resonant frequency for a gold device is 2.6 MHz and results in a switching time of 200 ns under a 32-V actuation voltage. Preliminary reliability tests at 13 GHz using bipolar actuation (plusmn30 V) and hot power switching have been performed on five 4 times 4 devices at 100 mW for 20 billion cycles, and at 500 mW for 5 billion cycles with no failures. A 4 times 4 array has also been used in the design of a tunable CPW resonator at 19.3 GHz with a 21% tuning range and 1.6-dB insertion loss. The authors believe that miniature MEMS devices will be very useful in the future for high-reliability MEMS and reconfigurable networks.

Organic "Wafer-Scale" packaged miniature 4-bit RF MEMS phase shifter

This paper presents for the first time a 4-bit microelectromechanical systems (MEMS) phase shifter fabricated on, integrated, and packaged into an organic flexible low-permittivity material. A microstrip switched-line phase shifter has been optimized at 14 GHz for small size and excellent performance. In addition, the MEMS phase shifter was packaged in an all-organic flexible low-permittivity liquid-crystal polymer (LCP) package. The improved geometry of the reduced size phase shifter is 2.8 times smaller than a traditional switched-line phase shifter and is much less lossy. For the 4-bit phase shifter, the worst case return loss is greater than 19.7 dB and the average insertion loss is less than 0.96 dB (0.24 dB/bit or 280/spl deg//dB). The average phase error is only 3.96/spl deg/. It has been demonstrated that the addition of the LCP package has a negligible effect on the phase-shifter performance, but will enable the device to remain flexible and protected against various environmental conditions.

GPS/INS uses low-cost MEMS IMU

A description of the design, operation, and test results of a miniature, low-cost, integrated GPS/inertial navigation system that uses commercial off-the-shelf micro-electro-mechanical system (MEMS) accelerometers and gyroscopes. The MEMS inertial measurement unit (EMU) is packaged in a small size and provides the raw EMU data through a serial interface to a processor board where the inertial navigation solution and integrated GPS/inertial Kalman filter is generated. The GPS/inertial software integration is performed using NAVSYS' modular InterNav software product. This allows integration with different low-cost GPS chip sets or receivers and also allows the integrated GPS/inertial navigation solution to be embedded as an application on a customer's host computer. This modular object-oriented architecture facilitates integration of the miniature MEMS GPS/INS navigation system for embedded navigation applications and is designed to handle the large errors characteristic of a low-grade MEMS IMU. Test results are presented showing the performance of the integrated MEMS GPS/inertial navigation system. Data is provided showing the position, velocity, and attitude accuracy when operating with GPS aiding and also for periods where GPS dropouts occur and alternative navigation update sources are used to bound the MEMS inertial navigation error growth.