Microelectromechanical Systems Technology Research Articles

Low-Cost MEMS-Based NARX Model for GPS-Denied Areas

Autonomous vehicle navigation has witnessed a huge revolutionary revision regarding development in Micro-Electro Mechanical System (MEMS) technology. Most recently, Strapdown Inertial Navigation System (SDINS) has successfully been integrated with Global Positioning System (GPS). However, different grades of MEMS inertial sensors are available and choosing the convenient grade is quite important. Noises in inertial sensor are mostly treated through de-noising the additive errors to improve the precision of SDINS output. Unfortunately, integration in SDINS mechanization causes a growing in SDINS error output which considered the main challenge in integrating MEMS inertial sensors with GPS. This paper aims to promote the long-term performance of the MEMS-SDINS/GPS integrated system. A new integrated structure is proposed to model the nonlinearities that exist in SDINS dynamics in addition to the error uncertainty in the inertial sensors’ measurements. A robust Nonlinear AutoRegressive models with eXogenous inputs (NARX) based algorithm are designed for data fusion in the proposed GPS/INS integrated system. Validation for the proposed integrated system has been carried out using different field tests data in order to assess the accuracy of the system during GPS denied environment. The results obtained demonstrate that the proposed NARX model is applicative and satisfactory which shows a desired prediction performance.

Preparation and Test of NH3 Gas Sensor Based on Single-Layer Graphene Film.

The ammonia sensing properties of single-layer graphene synthesized by chemical vapor deposition (CVD) were studied. The Au interdigitated electrode (IDE) was prepared by microelectromechanical systems (MEMS) technology, and then, the single-layer graphene was transferred to the IDE by wet transfer technology. Raman spectroscopy was used to monitor the quality of graphene films transferred to SiO2/Si substrates. Moreover, the theory of graphene’s adsorption of gases is explained. The results show that gas sensing characteristics such as response/recovery time and response are related to the target gas, gas concentration, test temperature, and so on. In the stability test, the difference between the maximum resistance and the minimum resistance of the device is 1 ohm without ammonia, the change is less than 1% of its initial resistance, and the repeatability is up to 98.58%. Therefore, the sensor prepared with high quality single-layer graphene has good repeatability and stability for ammonia detection.

Rapid detection of fuel adulteration using microfabricated gas chromatography

Rapid and accurate quality control for fuel adulteration is a major economic and health concern. Current technology lacks capability to provide speedy and accurate point of sale (POS) solutions. Most of the work done on portable solutions rely on absorbance spectroscopy, which provide a qualitative solution with a trade-off between speed and accuracy. This paper demonstrates a technique based on micro gas chromatography (μGC) for portable, fast, and accurate analysis of diesel fuels adulterated with kerosene. The separation columns are fabricated using microelectromechanical systems (MEMS) technology. The columns are 1 m-long and consist of an embedded array of pillars. Two different stationary phase coating were examined to explore the efficacy of the proposed technique. The analysis relies on aggressive pressure and temperature programming of the chip to obtain partially separated chromatograms. When analyzed with well-established chemometrics methods such as Principal Component Analysis and Partial least Squares Regression a linear relationship between the chromatograms and diesel purity was determined. The separation column could discriminate as little as 5% added kerosene to diesel fuel with only four seconds of chromatogram analysis.

MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications.

Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI was hindered by the challenges of manufacturing and assembling miniature imaging components. Over the last decade, microelectromechanical systems (MEMS) technology has greatly facilitated the development of photoacoustic endoscopes and extended the realm of applicability of the PAI. As the key component of photoacoustic endoscopes, micromachined ultrasound transducers (MUTs), including piezoelectric MUTs (pMUTs) and capacitive MUTs (cMUTs), have been developed and explored for endoscopic PAI applications. In this article, the recent progress of pMUTs (thickness extension mode and flexural vibration mode) and cMUTs are reviewed and discussed with their applications in endoscopic PAI. Current PAI endoscopes based on pMUTs and cMUTs are also introduced and compared. Finally, the remaining challenges and future directions of MEMS ultrasound transducers for endoscopic PAI applications are given.

Determination of Thermal Conductivities for Thin-Film Materials in CMOS MEMS Process

The determination of thermal conductivities for complementary metal-oxide-semiconductor (CMOS) thin-film materials is very important as the operation and failure of integrated circuits (ICs) and CMOS microelectromechanical systems (MEMS) devices are most likely limited by thermal issues, that is, heat transfer. In this article, we present four micro thermal conductivity measurement (μTCM) devices for silicon oxide, polysilicon, and aluminum thin films using CMOS MEMS technology. To determine the thermal conductivities of those thin-film materials from the μTCM devices, a linear thermal resistance model was proposed and validated by the computational fluid dynamics (CFD) study, which showed an error of less than 5.5%. The thermal conductivities of thin-film materials were then measured over a temperature range of 210-362 K, while the measured results for silicon oxide, polysilicon, and aluminum at room temperature were 1.32, 21.22, and 70.2 W/mK, respectively. Those measured thermal conductivities were significantly smaller than the available bulk values. The discrepancies between the thin film and bulk materials are consistent with the reported data and trends, which reveals the importance of determining the thermal conductivities for thin-film materials in the CMOS MEMS process.

UV LED Assisted Printing Platform for Fabrication of Micro-Scale Polymer Pillars

Ultraviolet (UV) assisted printing has emerged as a promising additive manufacturing (AM) technology, which puts UV light sources with focused emission in high demand. Unfortunately, current ultraviolet light-emitting diodes (UV LEDs) are not able to provide adequately focused UV emission required for printing. Thus, a UV LED package with focused UV emission was proposed and fabricated using microelectromechanical system (MEMS) technology in this study. An optical model of the UV LED package with focused UV emission was developed. Based on the designed model, a silicon reflector stacked on another was achieved. By assembling the stacked silicon reflector and hemispherical quartz lenses, the UV LED package with focused UV emission was successfully achieved. A narrow beam with a beam angle of 16° between half maximum intensity was achieved, while the intensity at 0° was greater than 1000 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the focal point. The UV LED curing system using two focused UV LED packages was successfully developed based on the optical simulation results. Polymer pillars were fabricated by instantaneous UV curing process with synchronized UV curable polymer jetting process in one shot, and micro-scale polymer pillars with a diameter of 20 μm were achieved. Thanks to the high intensity and focused UV emission, polymer pillars can be formed in as little as 100 ms. 13600 polymer pillars were printed on a silicon wafer with uniform diameter and geometry in a single dispensing cycle. The UV LED assisted printing platform was successfully demonstrated for fabrication of micro-scale 3D structures in a fast speed with smooth printing process.

Dynamic Analysis of Viscoelastic Circular Diaphragm of a MEMS Capacitive Pressure Sensor using Modified Differential Transformation Method

In this paper, a dynamic analysis of the viscoelastic circular diaphragm of a Micro-Electro-Mechanical System (MEMS) capacitive pressure sensor using the Modified Differential Transformation Method (MDTM) is presented. The MEMS technology has been increasingly used to fabricate sensors and actuators and the MEMS capacitive pressure sensor is emerging in many high-performance applications. The deflection of these sensors diaphragm (plate) depends largely on the material of the diaphragm. In this study, a circular diaphragm of viscoelastic material is modeled using the classical plate theory. The governing differential equation is solved using Modified Differential Transformation Method (MDTM) and the result is validated with Finite Difference Method (FDM). The result shows excellent agreement with the numerical method. The effects of amplitudes, frequency, viscoelastic parameter, and time of applied pressure on deflection of the viscoelastic circular diaphragm are investigated. It is established from the results that the deflection of the sensor increases with an increase in the amplitude, frequency and time of the applied pressure. In addition, an increase in the viscoelastic parameters resulted in an increase the deflection of the diaphragm which consequently increases the capacitance and sensitivity of the sensor. Hence, the viscoelastic circular diaphragm of the MEMS capacitive pressure sensor exhibits better sensitivity performance when compared with that of elastic material. Finally, the Modified Differential Transformation Method applied in obtaining the solution of the developed model is effective in predicting sensor characteristics. The study will enhance the design of MEMS capacitive pressure sensor with viscoelastic circular diaphragm.

Enhancement of Mechanical and Thermal Properties of SU-8 Photoresist with Multilayer Woven Glass Fabric Based on Micromachining Technology

SU-8 photoresist has been more and more widely used as a structural material in micro electromechanical system (MEMS) because of its low cost and excellent biocompatibility. However, the inferior mechanical and thermal performances immensely impinge the reliability of the MEMS device based SU-8 and accordingly restrict its application. Here we report the mechanical and thermal performance of SU-8 reinforced by the multilayer glass fabric with the MEMS technology. The finite element simulation and specific experiment are conducted, which confirm that the reinforced SU-8 composites have a 281% increase in Young's modulus and a 64% decrease in coefficient of thermal expansion (CTE) compared with pure SU-8. Additionally, the improved mechanism has also been analyzed, including the excellent interface bonding between the SU-8 and glass fabric, and the high-bond energy of Si–O-Si chain structures in glass fabric. Furthermore, the glass fabric reinforced SU-8 could still possess a high light transmittance to maintain the ability of lithography patterning. Therefore, it is believed that the strategy proposed here may satisfy higher requirements of MEMS devices, which guarantees its practical applications in the functional microstructures.

AZ4620 Photoresist as an Alternative Sacrificial Layer for Surface Micromachining

The mechanical actuation of suspended structures in microelectromechanical system (MEMS) switches plays an important role in obtaining an open or short circuit in radio-frequency (RF) transmission lines. These micromachined switches have moving parts which are realized by a sacrificial layer. Several sacrificial materials have been utilized in the fabrication of MEMS structures. The traditional method of using metal such as copper or nickel as a sacrificial layer is difficult due to metal etchant compatibility issues. A photoresist is the best choice for this process. Generally, the HiPR photoresist has been found to be suitable␣for the role of sacrificial layer. However, the HiPR is no longer available in the commercial market. As an alternative to the HiPR, the AZ4620 photoresist can be used. In this paper, a unit process optimization technique is described featuring an AZ4620 photoresist as a sacrificial layer for the microfabrication of a suspended structure. The AZ4620 meets all the requirements for the development of RF MEMS switches. Hence, the recipe and fabrication technique are optimized according to the required thickness. Preliminary measurements of the fabricated switch beam indicate that the required gap has been achieved. This optimized process is compatible with standard MEMS technology.

Dissipation Analysis Methods and Q-Enhancement Strategies in Piezoelectric MEMS Laterally Vibrating Resonators: A Review.

Over the last two decades, piezoelectric resonant sensors based on micro-electromechanical systems (MEMS) technologies have been extensively studied as such sensors offer several unique benefits, such as small form factor, high sensitivity, low noise performance and fabrication compatibility with mainstream integrated circuit technologies. One key challenge for piezoelectric MEMS resonant sensors is enhancing their quality factors (Qs) to improve the resolution of these resonant sensors. Apart from sensing applications, large values of Qs are also demanded when using piezoelectric MEMS resonators to build high-frequency oscillators and radio frequency (RF) filters due to the fact that high-Q MEMS resonators favor lowering close-to-carrier phase noise in oscillators and sharpening roll-off characteristics in RF filters. Pursuant to boosting Q, it is essential to elucidate the dominant dissipation mechanisms that set the Q of the resonator. Based upon these insights on dissipation, Q-enhancement strategies can then be designed to target and suppress the identified dominant losses. This paper provides a comprehensive review of the substantial progress that has been made during the last two decades for dissipation analysis methods and Q-enhancement strategies of piezoelectric MEMS laterally vibrating resonators.

Displacement Analysis of the MEMS Device

In this study, the displacement analysis of the microelectromechanical system (MEMS) device was performed. The current passing through the microdevice radiates heat energy as it pushes the device to the desired distance through thermal expansion. The amount of expansion varies depending on the current flowing through the device. With the designed model, the amount of current required for the displacement of the MEMS device is determined. In addition, the displacements produced in the microdevice for different metallic materials (silver and gold) and input potentials (0.4 V, 0.8 V, and 1.2 V) were calculated. These types of materials are frequently preferred in MEMS technology due to their high conductivity. Increasing the voltage value as a result of the analysis studies increased the displacement of the materials. When 1.2 V voltage is applied, the highest displacement values for silver and gold are; 6.45 μm, 4.32 μm, respectively. According to the results, the silver material showed a significant displacement compared to gold material.

On-Chip Fully Integrated Field Emission Arrays for High-Voltage MEMS Applications

Vacuum-sealed fully integrated diode and triode field emission arrays based on Ti Spindt-type field emitters have been developed in a scalable, CMOS-compatible process directly on Si. Diode characterization in air demonstrates effective vacuum sealing and field emission conduction, with current drivability that scales with array size. Triode characterization in vacuum demonstrates gate-modulated field emission of the output current and highlights new effects observed in a fully integrated geometry with closely spaced electrodes. Demonstrating up to 200-V blocking voltage and similar magnitude punchthrough voltages, the arrays can be utilized as high-voltage devices in CMOS applications or with microelectromechanical systems (MEMS) technologies using post-CMOS MEMS integration techniques. Low-temperature measurements reveal areas of improvement for electrode isolation; combined with the use of improved cathode materials, these devices have the potential to be used in high-power applications.

Road Tests of the Positioning Accuracy of INS/GNSS Systems Based on MEMS Technology for Navigating Railway Vehicles

Thanks to the support of Inertial Navigation Systems (INS), Global Navigation Satellite Systems (GNSS) provide a navigation positioning solution that, in the absence of satellite signals (in tunnels, forest and urban areas), allows the continuous positioning of a moving object (air, land and sea). Passenger and freight trains must, for safety reasons, comply with several formal navigation requirements, particularly those that concern the minimum acceptable accuracy for determining their position. Depending on the type of task performed by the train (positioning a vehicle on a route, stopping at a turnout, stopping at a platform, monitoring the movement of rolling stock, etc.), the train must have positioning systems that can determine its position with sufficient accuracy (1–10 m, p = 0.95) to perform the tasks in question. A wide range of INS/GNSS equipment is currently available, ranging from very costly to simple solutions based on Micro-Electro-Mechanical Systems (MEMS), which, in addition to an inertial unit, use one or two GNSS receivers. The paper presents an assessment of the accuracy of both types of solutions by testing them simultaneously in dynamic measurements. The research, due to the costs and logistics complexity, was made using a passenger car. The surveys were carried out in a complex way, because the measurement route was travelled three times at four different speeds: 40 km/h, 80 km/h, 100 km/h and 120 km/h on seven representative test sections with diverse land development. In order to determine the positioning accuracy of INS devices, two precise GNSS geodetic receivers (2 cm accuracy, p = 0.95) were used as a reference positioning system. The measurements demonstrated that only INS/GNSS systems based on two receivers can meet the requirements of most railway applications related to rail navigation, and since a solution with a single GNSS receiver has a much lower positioning accuracy, it is not suitable for many railway applications. It is noted that considerable differences between the standards defining the navigation requirements for railway applications. For example, INS/GNSS systems based on two receivers meet the vast majority of the expectations specified in the Report on Rail User Needs and Requirements. However, according to the Federal Radionavigation Plan (FRP), it cannot be used in any railway application.

A low-cost integrated MEMS-based INS/GPS vehicle navigation system with challenging conditions based on an optimized IT2FNN in occluded environments

Integration of both global positioning system (GPS) and inertial navigation system (INS) assures a continuous and accurate navigation system. In low-cost low-precision micro-electromechanical system (MEMS)-based INS/GPS integration navigation systems, one of the major concerns is high-level stochastic noise and uncertainties existing in INS sensors and complex model of real noisy data. In such uncertainty-oriented environments, an intelligence structure with extra degrees of freedom which can handle and model a high-level of uncertainties in INS sensors, and an efficient denoising technique as a precursor to the intelligence structure can be efficient solutions. Our approach to these problems is taken in different steps. First, a denoising technique based on empirical mode decomposition (EMD) is used to provide more accurate INS sensor outputs and better generalization ability. Second, an optimized interval type-2 fuzzy neural network is used to model and handle a high-level of uncertainties efficiently and estimate the positioning error of INS sensors when GPS signals are blocked, and still meet both accuracy maximization and complexity minimization. Fast learning and convergence of the algorithm and less computational complexity can be achieved by using an extended Kalman filter in the learning of algorithm and an accurate and simple type-reduction, respectively, which can be utilized in real-time applications with significant performance. The results of EMD-based denoising technique, as a preprocessing phase, verify superior performance in comparison with the discrete wavelet transform denoising method in the signal-to-noise ratio improvement for raw and noisy signals of INS sensors. To verify the effectiveness of our proposed model, we applied challenging conditions consisting of low-cost low-precision inertial sensors based on MEMS technology, long-term outages of GPS satellites, a high-speed experimental test vehicle and noisy real-world data in the real-time flight experiments. The achieved experimental accuracies are compared with the results that we have achieved in other methods, and our proposed method verifies significant improvements.

Ultrasensitive detection of cadmium ions using a microcantilever-based piezoresistive sensor for groundwater.

This paper proposes the selective and ultrasensitive detection of Cd(II) ions using a cysteamine-functionalized microcantilever-based sensor with cross-linked ᴅʟ-glyceraldehyde (DL-GC). The detection time for various laboratory-based techniques is generally 12–24 hours. The experiments were performed to create self-assembled monolayers (SAMs) of cysteamine cross-linked with ᴅʟ-glyceraldehyde on the microcantilever surface to selectively capture the targeted Cd(II). The proposed portable microfluidic platform is able to achieve the detection in 20–23 min with a limit of detection (LOD) of 0.56 ng (2.78 pM), which perfectly describes its excellent performance over other reported techniques. Many researchers used nanoparticle-based sensors for the detection of heavy metal ions, but daily increasing usage and commercialization of nanoparticles are rapidly expanding their deleterious effect on human health and the environment. The proposed technique uses a blend of thin-film and microcantilever (micro-electromechanical systems) technology, which mitigate the disadvantages of the nanoparticle approaches, for the selective detection of Cd(II) with a LOD below the WHO limit of 3 μg/L.

100\u2009pT/cm single-point MEMS magnetic gradiometer from a commercial accelerometer

Magnetic sensing is present in our everyday interactions with consumer electronics and demonstrates the potential for the measurement of extremely weak biomagnetic fields, such as those of the heart and brain. In this work, we leverage the many benefits of microelectromechanical system (MEMS) devices to fabricate a small, low-power, and inexpensive sensor whose resolution is in the range of biomagnetic fields. At present, biomagnetic fields are measured only by expensive mechanisms such as optical pumping and superconducting quantum interference devices (SQUIDs), suggesting a large opportunity for MEMS technology in this work. The prototype fabrication is achieved by assembling micro-objects, including a permanent micromagnet, onto a postrelease commercial MEMS accelerometer using a pick-and-place technique. With this system, we demonstrate a room-temperature MEMS magnetic gradiometer. In air, the sensor’s response is linear, with a resolution of 1.1 nT cm−1, spans over 3 decades of dynamic range to 4.6 µT cm−1, and is capable of off-resonance measurements at low frequencies. In a 1 mTorr vacuum with 20 dB magnetic shielding, the sensor achieves a 100 pT cm−1 resolution at resonance. This resolution represents a 30-fold improvement compared with that of MEMS magnetometer technology and a 1000-fold improvement compared with that of MEMS gradiometer technology. The sensor is capable of a small spatial resolution with a magnetic sensing element of 0.25 mm along its sensitive axis, a >4-fold improvement compared with that of MEMS gradiometer technology. The calculated noise floor of this platform is 110 fT cm−1 Hz−1/2, and thus, these devices hold promise for both magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

Fabrication of piezoelectric thick-film stator using electrohydrodynamic jet printing for micro rotary ultrasonic motors

This paper proposes a lead zirconate titanate (PZT) thick-film piezoelectric microstator based on a high-performance PZT thick film fabricated by electrohydrodynamic jet (E-jet) printing. The PZT thick film element was printed directly on the elastic body from a PZT composite slurry to form the piezoelectric microstator. This fabrication process does not require conventional machining techniques such as thinning, bonding, and etching, and can be compatible with microelectromechanical systems (MEMS) technology. The printed PZT thick-film element exhibited compact and uniform features. The thick-film microstator produced a travelling wave with an amplitude of 345 nm, and the mechanical quality factor was found to be 736. The combination of E-jet printing and PZT thick-film technology simplified the manufacturing process and enhanced the performance of the piezoelectric stator, enabling the fabrication of a unique MEMS rotary ultrasonic motor device.

Analysis of current and future technologies of capsule endoscopy: A mini review

Many existing methods of endoscopy can be very uncomfortable and potentially even painful for a patient. Using a conventional endoscope is also limited in its usable range, unable to access a majority of the small bowel. Recent advancements in LEDs, optical design, and MEMS (microelectromechanical systems) technologies have provided the ability to create a wireless endoscope. Since its inception, the capsule endoscope has seen advancements in existing technology as well as the introduction of new components. As the capsule endoscope continues to advance, more application possibilities will grow as well.

A high-resolution area-change-based capacitive MEMS tilt sensor

Tilt sensors have been widely used in many applications, such as instrumentation leveling, oil drilling and structural health monitoring. With the rapid development of the micro-electromechanical system (MEMS) technology, MEMS accelerometer-based high-performance tilt sensors are capable of replacing conventional tilt sensors in most of application fields. High-sensitivity MEMS resonant accelerometers (MRAs) are fully qualified for tilt sensing. However, MRA chips have to be vacuum packaged and require complex circuits; therefore, they are difficult to be miniaturized and commercialized. In this case, this paper introduces a commercial-oriented capacitive MEMS accelerometer for tilt sensing with both high-resolution and compact size. The proposed MEMS sensor utilizes simplified fabrication processes, the area-change-based capacitive displacement transducer and the capacitance-to-voltage conversion application specific integrated circuit (ASIC) for low-cost, high-sensitivity, low power consumption and miniaturization. The developed MEMS sensor has a package dimension of 14 mm × 14 mm × 3.6 mm with a single +5 V power supply and analog voltage output. Several evaluation experiments have been conducted with the results showing that the developed MEMS tilt sensor has a full measurement range of ±180°, a linear measurement range of ±30° with a nonlinearity of ±2.8%, a sensitivity of 33.6 mV/°, a noise floor of 2 × 10−4°/√Hz, a bandwidth of 100 Hz and an angle resolution of 7 × 10−4° with an integral time of 0.5 s. Compared with other commercial MEMS tilt sensors, the proposed sensor has a better resolution, a lower noise floor, a larger bandwidth, a lower power consumption and a smaller package. The simplified fabrication process and high performance suggest the developed MEMS tilt sensor is promising to be competitive in the market.

RETRACTED ARTICLE: A new structure and modeling of a three-axis MEMS capacitive accelerometer with high dynamic range and sensitivity

In this paper, a three-axis capacitor accelerator has been analyzed, modeled and optimized using micro-electromechanical systems technology. In the proposed structure, acceleration measurements are carried out on all three axes simultaneously using a mass and spring system, which makes it possible to achieve a high sensitivity at a low occupancy level without losing other accelerator factors. In this structure, it is shown that each axis acceleration has a very low impact on the acceleration of the other two axes. If any external factor (e.g., electromagnetic waves) changes the value of a single capacitor, the original output of the capacitor does not change for detecting acceleration. In this paper, first the model is extracted for the proposed accelerometer structure and then to prove the validity of the model, the proposed structure is simulated using Intellisuite software. Moreover, a multi-objective genetic optimization algorithm which is made of NSGA2 and SPEA algorithms has been used to determine the dimensions of the constituents of the spring and the weight. This algorithm is implemented in MATLAB software. This study covers a dynamic range up to 1000 g and an operating frequency up to 20 kHz. The accelerometer sensitivity is 4fF/g in the z axis direction while it is 9fF/g in the x and y axes directions.