Microelectromechanical Systems Technology Research Articles

A MEMS-Based Quad-Wavelength Hybrid Plasmonic-Pyroelectric Infrared Detector.

Spectrally selective detection is of crucial importance for diverse modern spectroscopic applications such as multi-wavelength pyrometry, non-dispersive infrared gas sensing, biomedical analysis, flame detection, and thermal imaging. This paper reports a quad-wavelength hybrid plasmonic–pyroelectric detector that exhibited spectrally selective infrared detection at four wavelengths—3.3, 3.7, 4.1, and 4.5 μm. The narrowband detection was achieved by coupling the incident infrared light to the resonant modes of the four different plasmonic perfect absorbers based on Al-disk-array placed on a Al2O3–Al bilayer. These absorbers were directly integrated on top of a zinc oxide thin film functioning as a pyroelectric transducer. The device was fabricated using micro-electromechanical system (MEMS) technology to optimize the spectral responsivity. The proposed detector operated at room temperature and exhibited a responsivity of approximately 100–140 mV/W with a full width at half maximum of about 0.9–1.2 μm. The wavelength tunability, high spectral resolution, compactness and robust MEMS-based platform of the hybrid device demonstrated a great advantage over conventional photodetectors with bandpass filters, and exhibited impressive possibilities for miniature multi-wavelength spectroscopic devices.

Reconfigurable RF-MEMS-based impedance matching networks for a hybrid RF-MEMS/CMOS class-E power amplifier

Microelectromechanical-systems technology (MEMS) applied to radio frequency (RF) and microwave systems (i.e. RF-MEMS) has recently started to exhibit its market potential in applications centred on telecommunications and consumer segments. As evolution towards the 5G (5th generation of mobile communications) and the Internet of things (IoT) is progressing, more agile, reconfigurable and multi-functional RF passive components and networks will be necessary. In this work, an entirely RF-MEMS-based impedance matching network (IMN) is reported and discussed, taking the global system for mobile communications (GSM) protocol as testing scenario. The mentioned RF-MEMS IMN was designed in order to perform proper impedance conversion between a CMOS class-E power amplifier (PA) and the transmitting/receiving antenna of a GSM system. In the following pages, the RF-MEMS IMN will be discussed in details against its design solution, working principles, as well as electromechanical and RF simulated and measured characteristics.

Design and characterization of solid articulated four axes microrobot for microfactory applications

In this paper, we present the design and experimental evaluation of a 3-dimensional microrobot called Solid Articulated Four Axes Microrobot (sAFAM). The sAFAM is fabricated using Microelectromechanical System (MEMS) technology, then assembled to achieve out-of-plane motion and perform micro and nano manipulation tasks relevant to future microfactories such as pick and place and applying controlled forces onto the environment. The paper discusses the design, fabrication and assembly processes for constructing sAFAM. Four in-plane electrothermal actuators drive the end-effector through a complaint mechanical coupling. The microrobot structure was simulated by finite element analysis (FEA), predicting a 13 μm × 47 μm × 115 μm workspace and verifying appropriate concentration of stresses during actuation. The resolution, repeatability, and workspace of the microrobot were then measured experimentally via optical microscopy and laser ranging, indicating a 16 μm × 20 μm × 118 μm dimension workspace. Experiments also indicate that the motion resolution and repeatability of the microrobot varies depending on the location of the end-effector in space, but generally range between 20 nm (minimum) and 150 nm (maximum). With FEA simulation result, the force output of sAFAM falls in the range of tens of micro Newtons. Thus, sAFAM has the potential for future use as an assist micro/nano manipulation tool in the scanning electron microscope (SEM) or in conjunction with an atomic force microscope (AFM).

Advanced microelectromechanical systems-based nanomechanical testing: Beyond stress and strain measurements

Abstract

MEMS-based non-contact voltage sensor with multi-mode resonance shutter

Miniature non-contact voltage sensor has significant benefit for condition monitoring of power systems in terms of ease of installation and a minimum disturbance to an existing design. The electrostatic field sensor miniaturized by MEMS (Micro Electro Mechanical Systems) technology is a promising method to realize low cost and small sensors. However, the behavior of micro-sized mechanical shutter under an intense electric field and performance as a voltage sensor are barely studied. Here, we design the SOI (Silicon on Insulator) based shutter which has multiple vibration modes, evaluate the performance under an intense electric field (˜1.4 MV/m). The vibration spectrum obtained by sensor output shows a resonance frequency shift and a non-linearity of sensitivity. These results are explained by a numerical model which consider a vertical displacement of shutter due to the tensile force from an electric field. Finally, practical demonstrations are carried such as a calibration for linear response using multiple linear regression analysis of sensor outputs with various resonance mode and evaluation of sensor bandwidth with a synthesized sinusoidal and rapid change of an electric field for a quantitative comparison with past studies.

Modeling of Packaged MEMS Thermal Wind Sensor Operating on CP Mode

Modeling of the packaged wind sensor operating on constant power (CP) mode is proposed in this paper. The proposed model is based on the theory of heat conduction and forced convection. The presented model indicates that the total output dc voltage is proportional to the square root of the wind speed, and ${V}_{x}$ , as well as ${V}_{y}$ , varies with the wind direction based on cosine function. The wind sensor is fabricated by microelectromechanical systems (MEMS) technology and packaged with the glue. The test is performed in the wind tunnel and the measured results indicate an agreement with the presented model. The relative error of voltage for the wind speed is less than 14% up to 30 m/s, while that for the wind direction is no more than 10.7% from 0° to 360°.

A Plasma Switch Induced by Electroexplosion of p-n Junction for Mini Exploding Foil Initiator

In this paper, a possible conduction model of a kind of plasma switch induced by electroexplosion of the p-n junction was established to better understand the underlying mechanism. The model showed that the resistance of the plasma switch is considerable before switching and a constant during closing, which was validated by complementary experiments. Additionally, several parameters were defined to evaluate the performance of this type of plasma switch. Finally, a highly integrated microchip exploding foil initiator (McEFI) was designed and fabricated using the microelectromechanical system (MEMS) technology. Electrical characterizations, ignition test, and initiation test were conducted to demonstrate the capability of the McEFI, as well as the plasma switch, and the results indicated that the minimum firing voltage is 1150 V/ $0.15~\mu \text{F}$ , providing new ideas for the development of not only McEFI but also low-energy EFI (LEEFI).

Generation of Linear Traveling Waves in Piezoelectric Plates in Air and Liquid.

A micro- to milli-sized linear traveling wave (TW) actuator fabricated with microelectromechanical systems (MEMS) technology is demonstrated. The device is a silicon cantilever actuated by piezoelectric aluminum nitride. Specifically designed top electrodes allow the generation of TWs at different frequencies, in air and liquid, by combining two neighboring resonant modes. This approach was supported by analytical calculations, and different TWs were measured on the same plate by laser Doppler vibrometry. Numerical simulations were also carried out and compared with the measurements in air, validating the wave features. A standing wave ratio as low as 1.45 was achieved in air, with a phase velocity of 652 m/s and a peak horizontal velocity on the device surface of 124 μm/s for a driving signal of 1 V at 921.9 kHz. The results show the potential of this kind of actuator for locomotion applications in contact with surfaces or under immersion in liquid.

Optimization of a Piezoelectric Energy Harvester and Design of a Charge Pump Converter for CMOS-MEMS Monolithic Integration.

The increasing interest in the Internet of Things (IoT) has led to the rapid development of low-power sensors and wireless networks. However, there are still several barriers that make a global deployment of the IoT difficult. One of these issues is the energy dependence, normally limited by the capacitance of the batteries. A promising solution to provide energy autonomy to the IoT nodes is to harvest residual energy from ambient sources, such as motion, vibrations, light, or heat. Mechanical energy can be converted into electrical energy by using piezoelectric transducers. The piezoelectric generators provide an alternating electrical signal that must be rectified and, therefore, needs a power management circuit to adapt the output to the operating voltage of the IoT devices. The bonding and packaging of the different components constitute a large part of the cost of the manufacturing process of microelectromechanical systems (MEMS) and integrated circuits. This could be reduced by using a monolithic integration of the generator together with the circuitry in a single chip. In this work, we report the optimization, fabrication, and characterization of a vibration-driven piezoelectric MEMS energy harvester, and the design and simulation of a charge-pump converter based on a standard complementary metal–oxide–semiconductor (CMOS) technology. Finally, we propose combining MEMS and CMOS technologies to obtain a fully integrated system that includes the piezoelectric generator device and the charge-pump converter circuit without the need of external components. This solution opens new doors to the development of low-cost autonomous smart dust devices.

Mode Localization and Sensitivity in Weakly Coupled Resonators

Localization of normal modes is used in recent microelectromechanical systems (MEMS) technologies with orders of magnitude improvements in sensitivity. A pair of eigenvalues veer, or avoid crossing each other, as a single parameter of a vibrating system is varied. While it is well-known that the sensitivity ($s$) of modal amplitude ratio varies with strength of coupling ($\kappa$) as $s \propto\kappa^{-1} $ in the case of two identical coupled oscillators, recently, we showed that asymmetry $\alpha$ will also influence sensitivity according to $s \propto (\alpha \kappa)^{-1}$. Here, we show that further enhancements in sensitivity is possible in higher degrees of freedom ($n$) systems using energy analysis. In the case of $n-2$ uniformly coupled oscillators embedded between two oscillators, we show that $s \propto \alpha^{-1}\kappa^{1-n}$, if the blocked resonance spectra of the embedded oscillators and the end oscillators are well-separated. We also show that asymmetric coupled oscillators also enhance linear range in addition to sensitivity when compared to their symmetric counterparts. We do not use a perturbation approach in our energy analysis; hence the sensitivity and linear range expressions derived have a wider range of accuracy.

Fabrication and Characteristics of a SOI Three-Axis Acceleration Sensor Based on MEMS Technology.

A silicon-on-insulator (SOI) piezoresistive three-axis acceleration sensor, consisting of four L-shaped beams, two intermediate double beams, two masses, and twelve piezoresistors, was presented in this work. To detect the acceleration vector (ax, ay, and az) along three directions, twelve piezoresistors were designed on four L-shaped beams and two intermediate beams to form three detecting Wheatstone bridges. A sensitive element simulation model was built using ANSYS finite element simulation software to investigate the cross-interference of sensitivity for the proposed sensor. Based on that, the sensor chip was fabricated on a SOI wafer by using microelectromechanical system (MEMS) technology and packaged on a printed circuit board (PCB). At room temperature and VDD = 5.0 V, the sensitivities of the sensor along x-axis, y-axis, and z-axis were 0.255 mV/g, 0.131 mV/g, and 0.404 mV/g, respectively. The experimental results show that the proposed sensor can realize the detection of acceleration along three directions.

Fabrication and Characterization of the Li-Doped ZnO Thin Films Piezoelectric Energy Harvester with Multi-Resonant Frequencies.

A novel piezoelectric energy harvester with multi-resonant frequencies based on Li-doped ZnO (LZO) thin films is proposed in this paper, consisting of an elastic element with three (or more) different length cantilever beam arrays and a piezoelectric structure (Al/Li-doped ZnO/Pt/Ti). The LZO thin films of piezoelectric structure were prepared on Pt/Ti/SiO2/Si by using a radio frequency (RF) magnetron sputtering method under certain process conditions. When the LZO thin films were deposited with an LZO target concentration of 5 wt%, the piezoelectric coefficient d33 was 9.86 pm/V. Based on this, the energy harvester chips were fabricated on a <100> silicon substrate using micro-electromechanical systems (MEMS) technology, and its performance can be measured by fixing it to a printed circuit board (PCB) test substrate. The experimental results show that, when exerting an external vibration acceleration of 2.2 g and a vibration frequency of 999 Hz, the energy harvester can achieve a big load voltage of 1.02 V at a load resistance of 600 kΩ, and a high load power of 2.3 µW at a load resistance of 200 kΩ.

An integrated magnetic microfluidic chip for rapid immunodetection of the prostate specific antigen using immunomagnetic beads.

The authors describe an integrated microfluidic chip for immunodetection of the prostate specific antigen (PSA) by using giant magnetoimpedance (GMI) sensor. This chip contains an immunoreaction platform and a biomarker detection system. The immunoreaction platform contains anincubation chamber anda reactive chamber to implement immunological reaction in microfluidics. The system can detect PSA rapidly with ultra-high sensitivity. Both are fabricated by MEMS technology. Immunomagnetic beads (If PSA binds to its antibody (that islabeled with immunomagnetic beads; IMBs)it will be trapped on the surface of self-assembled film. Trapped IMBs generatea stray magnetic field under the magnetization of the external applied magnetic field and can be detected by theGMI sensor. The chip can detect PSA with a detection limit as low as 0.1ng ∙ mL-1 and works in the 0.1ng ∙ mL-1 to 20ng ∙ mL-1concentration range. Compared to established GMI biosensors, the magnetic microfluidic chip reduces assay time, and lends itself to fast detection. It also avoids complex handling steps, enhances reaction efficiency and decreases experimental errors. Graphical abstract An integrated magnetic microfluidic chip which contains immunoreaction platform and biomarker detection system was designed and microfabricated by micro-electromechanical systems (MEMS) technology to detect prostate specific antigen (PSA) rapidly, and has promise in Point-of-care (PoC) diagnostic applications.

Study on a high-temperature optical fiber F–P acceleration sensing system based on MEMS

Vibration measurement at high temperature is of great significance to monitoring the operation of major projects and mechanical equipment. As the temperature resistance of electrical vibration sensors is usually below 600 °C, it cannot meet the requirements of some high-temperature measuring conditions. This paper studies a high-temperature Fabry–Perot (F–P) acceleration sensing system with general single-mode fiber. A high-temperature sensitive diaphragm is machined based on micro-electromechanical system (MEMS) technology and it is combined with the fiber microstructure to enable the sensing probe to be packaged under high temperatures. According to the temperature characteristic of the length of the F–P cavity, a signal demodulation system was proposed based on the rapid automatic tracking of the quiescent operation point. The complete optical fiber F–P acceleration sensing system conducted real-time vibration detection of high temperature casting in the foundry factory. The experimental result indicates that the optical fiber high-temperature acceleration sensor showed a better vibration response in the working frequency of 100–1000 Hz and the relative error of the frequency measurement is less than 1.56% under normal temperatures and a high temperature of 800 °C.

Analytical design of MEMS variable capacitors based on shaped-finger comb-drives

A variable capacitor is one of the widely used components in radio frequency (RF) circuits. Variable capacitors can benefit from the microelectromechanical systems (MEMS) technology, to be equipped with attractive characteristics such as high quality factor and wide tuning range. One of the design goals for MEMS varactors has been to realize linear capacitance–voltage (C–V) characteristics, for which a design method is proposed in this paper, based on shaped-finger comb-drive actuators. The shaped-finger design method, originally developed for a tunable optical filter application by the author, is redeveloped in this work for a linear C–V varactor. Moreover, the conformal mapping method is employed in calculation of capacitances, making the whole design process more time-efficient, being almost all-analytical with the minimum usage of numerical analysis methods. Effects of sense capacitor finger shapes to the optimized drive capacitor finger shapes and the corresponding C–V characteristics are investigated as well. Variable capacitors with the shaped-finger design show linearity factor (LF)—defined as the maximum deviation from the perfect linear relationship—as good as 0.4%, enormously improved from that of the conventional constant-finger-gap devices (LF: 49.9%). Further probed by 3-D numerical analysis, the C–V characteristics of the designed variable capacitor show LF better than 2.62% in the case of constant-gap sense capacitors, and as good as 0.77% in the case of shaped-finger sense capacitors. Versatility of the design method is further demonstrated by presenting a varactor for linear resonant frequency–voltage (f–V) characteristics in voltage-controlled oscillator (VCO) applications. Finally, effects of etch bias, one of common fabrication imperfections, to the linearity of C–V characteristics are studied. The developed analytical design method with shaped fingers can find a wide range of applications where comb-drive actuators are used.

A semi-packed micro GC column for separation of the NAFLD exhaled breath VOCs

The separation and detection of human breath play a significant role in early and non-invasive disease diagnosis. Various volatile organic compound (VOC) gases are considered as the biomarkers of a nonalcoholic fatty liver disease (NAFLD) patient. In this paper, a micro gas chromatography (GC) column used for VOCs separation of the NAFLD breath sample was presented, from its design, fabrication and separation performance testing. The serpentine column made using microelectromechanical system (MEMS) technology was chosen for its relatively small band broadening. The micro pillar configuration was simulated and optimized. The 3 m and 1 m long column with a cross-section of 200 μm × 240 μm was fabricated by deep-reactive-ion-etching (DRIE) method and sealed with anodic bonding. The stationary phase was coated to the inner wall of the column by static coating. The column was installed into the conventional gas chromatography to test separation performance of the GC. The nonpolar alkane mixture containing the NAFLD biomarker gas pentane was separated and the experimental factors such as the temperature and the carrier gas flow rate were studied. The results indicated that the micro GC column can effectively separate alkanes from C5-C12 within 5 min. This could help the micro detector of micro GC system to quickly identify the contents or concentrations of characteristic alkanes. The micro GC column can meet the requirements of the micro GC system for the breath analysis of the NAFLD or other metabolic liver diseases. The micro column assembled with micro gas detector and preconcentrator can be hopefully developed into a portable breath analysis device.

Extended-gate field-effect transistor-based pesticide microsensor for the detection of organophosphorus and carbamate

Using microelectromechanical systems technology, a high-performance extended-gate field-effect transistor (EGFET)-based pesticide microsensor for organophosphorus and carbamate (CM) detection is developed. To minimize the whole pesticide-sensing system, we also integrated a planar Ti/Ag/AgCl/KCl-gel microreference electrode into the same silicon chip. The total dimensions of the proposed pesticide-sensing system are only 0.92 × 0.95 × 0.1 cm3. This EGFET-based microsensor for organophosphorus and CMs demonstrates extremely high sensitivity (194 and 268.1 mV/dec, respectively) and sensing linearity (0.993 and 0.974, respectively) and extremely low response time (120 and 300 s, respectively). The microsensor detection limit for both pesticides is 0.001 ppm.

Towards an Ultra-Sensitive Temperature Sensor for Uncooled Infrared Sensing in CMOS⁻MEMS Technology.

Microbolometers and photon detectors are two main technologies to address the needs in Infrared Sensing applications. While the microbolometers in both complementary metal-oxide semiconductor (CMOS) and Micro-Electro-Mechanical Systems (MEMS) technology offer many advantages over photon detectors, they still suffer from nonlinearity and relatively low temperature sensitivity. This paper not only offers a reliable solution to solve the nonlinearity problem but also demonstrate a noticeable potential to build ultra-sensitive CMOS–MEMS temperature sensor for infrared (IR) sensing applications. The possibility of a 31× improvement in the total absolute frequency shift with respect to ambient temperature change is verified via both COMSOL (multiphysics solver) and theory. Nonlinearity problem is resolved by an operating temperature sensor around the beam bending point. The effect of both pull-in force and dimensional change is analyzed in depth, and a drastic increase in performance is achieved when the applied pull-in force between adjacent beams is kept as small as possible. The optimum structure is derived with a length of 57 µm and a thickness of 1 µm while avoiding critical temperature and, consequently, device failure. Moreover, a good match between theory and COMSOL is demonstrated, and this can be used as a guidance to build state-of-the-art designs.

Investigation of Broadband Characteristics of Multi-Frequency Piezoelectric Micromachined Ultrasonic Transducer (MF-pMUT)

Multi-frequency ultrasonic transducers are highly promising devices in biomedical applications for providing both good imaging resolution and large detection depth. However, most conventional multi-frequency ultrasonic transducers are designed through integrating multiple single-frequency transducers, with complicated fabrication process, imperfect beam profiles, and limited bandwidths. In this paper, a single-element multi-frequency piezoelectric micromachined ultrasonic transducer (MF-pMUT) is proposed and investigated in terms of broadband property. Three rectangular-diaphragm MF-pMUTs with different length-to-width aspect ratios are fabricated with the microelectromechanical system (MEMS) technology and characterized both in air and underwater. All MF-pMUT samples exhibit at least two broad bands. After optimization of the aspect ratio, two smooth bands with comparable sound pressure level are achieved, providing -6 dB bandwidths of 112%/38% and corresponding central frequencies of 0.615 MHz/1.63 MHz. Benefited from such broadened multi-frequency property and simple structure design, the proposed MF-pMUT shows a great potential in ultrasonic detection, diagnosis, and imaging applications as well as wireless acoustic energy transmission.

A Terahertz Tunable Waveguide Bandpass Filter Based on Bimorph Microactuators

Terahertz (THz) tunable filter plays a significant role for miniaturization and multifunction in application systems. The frequency of existing schemes for tunable waveguide filter can only reach up to the $W$ -band. The selection of tuning and assembly solution for THz band is significant and challenging. In this letter, we investigate the design of bimorph microactuator which uses microelectromechanical system (MEMS) technology. Based on this microactuator, we propose a THz tunable waveguide bandpass filter, whose center frequency can be tuned from 247 to 260 GHz. It is the first time to extend the center frequency of tunable waveguide bandpass filter to over 220 GHz while using MEMS bimorph microactuators to tune. The tuning ratio of the filter is 5.26%, and the measured insertion loss is better than 6 dB in the passband.