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Micromachines, Volume 6, Issue 2 (February 2015) , Pages 163-290

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Open AccessArticle Researching the Aluminum Nitride Etching Process for Application in MEMS Resonators
Micromachines 2015, 6(2), 281-290; https://doi.org/10.3390/mi6020281
Received: 12 October 2014 / Accepted: 6 February 2015 / Published: 16 February 2015
Cited by 6 | Viewed by 2397 | PDF Full-text (2123 KB) | HTML Full-text | XML Full-text
Abstract
We investigated the aluminum nitride etching process for MEMS resonators. The process is based on Cl2/BCl3/Ar gas chemistry in inductively coupled plasma system. The hard mask of SiO2 is used. The etching rate, selectivity, sidewall angle, bottom surface [...] Read more.
We investigated the aluminum nitride etching process for MEMS resonators. The process is based on Cl2/BCl3/Ar gas chemistry in inductively coupled plasma system. The hard mask of SiO2 is used. The etching rate, selectivity, sidewall angle, bottom surface roughness and microtrench are studied as a function of the gas flow rate, bias power and chamber pressure. The relations among those parameters are reported and theoretical analyses are given. By optimizing the etching parameters, the bottom surface roughness of 1.98 nm and the sidewall angle of 83° were achieved. This etching process can meet the manufacturing requirements of aluminum nitride MEMS resonator. Full article
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Open AccessArticle Noise Reduction of MEMS Gyroscope Based on Direct Modeling for an Angular Rate Signal
Micromachines 2015, 6(2), 266-280; https://doi.org/10.3390/mi6020266
Received: 24 December 2014 / Revised: 7 February 2015 / Accepted: 10 February 2015 / Published: 16 February 2015
Cited by 11 | Viewed by 2758 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel approach for processing the outputs signal of the microelectromechanical systems (MEMS) gyroscopes was presented to reduce the bias drift and noise. The principle for the noise reduction was presented, and an optimal Kalman filter (KF) was designed by [...] Read more.
In this paper, a novel approach for processing the outputs signal of the microelectromechanical systems (MEMS) gyroscopes was presented to reduce the bias drift and noise. The principle for the noise reduction was presented, and an optimal Kalman filter (KF) was designed by a steady-state filter gain obtained from the analysis of KF observability. In particular, the true angular rate signal was directly modeled to obtain an optimal estimate and make a self-compensation for the gyroscope without needing other sensor’s information, whether in static or dynamic condition. A linear fit equation that describes the relationship between the KF bandwidth and modeling parameter of true angular rate was derived from the analysis of KF frequency response. The test results indicated that the MEMS gyroscope having an ARW noise of 4.87°/h0.5 and a bias instability of 44.41°/h were reduced to 0.4°/h0.5 and 4.13°/h by the KF under a given bandwidth (10 Hz), respectively. The 1σ estimated error was reduced from 1.9°/s to 0.14°/s and 1.7°/s to 0.5°/s in the constant rate test and swing rate test, respectively. It also showed that the filtered angular rate signal could well reflect the dynamic characteristic of the input rate signal in dynamic conditions. The presented algorithm is proved to be effective at improving the measurement precision of the MEMS gyroscope. Full article
(This article belongs to the Special Issue Next Generation MEMS-Based Navigation—Systems and Applications)
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Open AccessArticle Performance of SU-8 Membrane Suitable for Deep X-Ray Grayscale Lithography
Micromachines 2015, 6(2), 252-265; https://doi.org/10.3390/mi6020252
Received: 8 December 2014 / Accepted: 4 February 2015 / Published: 9 February 2015
Cited by 6 | Viewed by 2965 | PDF Full-text (3745 KB) | HTML Full-text | XML Full-text
Abstract
In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of [...] Read more.
In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Microfluidic Vortex Enhancement for on-Chip Sample Preparation
Micromachines 2015, 6(2), 239-251; https://doi.org/10.3390/mi6020239
Received: 2 December 2014 / Accepted: 30 January 2015 / Published: 6 February 2015
Cited by 14 | Viewed by 2891 | PDF Full-text (953 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In the past decade a large amount of analysis techniques have been scaled down to the microfluidic level. However, in many cases the necessary sample preparation, such as separation, mixing and concentration, remains to be performed off-chip. This represents a major hurdle for [...] Read more.
In the past decade a large amount of analysis techniques have been scaled down to the microfluidic level. However, in many cases the necessary sample preparation, such as separation, mixing and concentration, remains to be performed off-chip. This represents a major hurdle for the introduction of miniaturized sample-in/answer-out systems, preventing the exploitation of microfluidic’s potential for small, rapid and accurate diagnostic products. New flow engineering methods are required to address this hitherto insufficiently studied aspect. One microfluidic tool that can be used to miniaturize and integrate sample preparation procedures are microvortices. They have been successfully applied as microcentrifuges, mixers, particle separators, to name but a few. In this work, we utilize a novel corner structure at a sudden channel expansion of a microfluidic chip to enhance the formation of a microvortex. For a maximum area of the microvortex, both chip geometry and corner structure were optimized with a computational fluid dynamic (CFD) model. Fluorescent particle trace measurements with the optimized design prove that the corner structure increases the size of the vortex. Furthermore, vortices are induced by the corner structure at low flow rates while no recirculation is observed without a corner structure. Finally, successful separation of plasma from human blood was accomplished, demonstrating a potential application for clinical sample preparation. The extracted plasma was characterized by a flow cytometer and compared to plasma obtained from a standard benchtop centrifuge and from chips without a corner structure. Full article
(This article belongs to the Special Issue Biomedical Microdevices)
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Open AccessArticle Structure Design and Implementation of the Passive μ-DMFC
Micromachines 2015, 6(2), 230-238; https://doi.org/10.3390/mi6020230
Received: 5 November 2014 / Revised: 20 January 2015 / Accepted: 29 January 2015 / Published: 4 February 2015
Viewed by 2018 | PDF Full-text (1896 KB) | HTML Full-text | XML Full-text
Abstract
A dual-chamber anode structure is proposed in order to solve two performance problems of the conventional passive micro direct methanol fuel cell (μ-DMFC). One of the problems is the unstable performance during long time discharge. The second problem is the short operating time. [...] Read more.
A dual-chamber anode structure is proposed in order to solve two performance problems of the conventional passive micro direct methanol fuel cell (μ-DMFC). One of the problems is the unstable performance during long time discharge. The second problem is the short operating time. In this structure, low concentration chamber is filled with methanol solution with appropriate concentration for the μ-DMFC. Pure methanol in high concentration chamber diffuses to the low concentration chamber to keep the concentration of methanol solution suitable for long-term discharge of μ-DMFC. In this study, a Nafion-Polytetrafluoroethylene (PTFE) composite membrane is inserted between the two chambers to conduct pure methanol. The experimental results during long-term discharge show that the stable operating time of passive μ-DMFC increases by nearly 2.3 times compared to a conventional one with the same volume. These results could be applied to real products. Full article
(This article belongs to the Special Issue Power MEMS)
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Open AccessArticle Deformation Analysis of a Pneumatically-Activated Polydimethylsiloxane (PDMS) Membrane and Potential Micro-Pump Applications
Micromachines 2015, 6(2), 216-229; https://doi.org/10.3390/mi6020216
Received: 10 November 2014 / Accepted: 21 January 2015 / Published: 29 January 2015
Cited by 10 | Viewed by 2948 | PDF Full-text (3666 KB) | HTML Full-text | XML Full-text
Abstract
This study presents a double-side diaphragm peristaltic pump for efficient medium transport without the unwanted backflow and the lagging effect of a diaphragm. A theoretical model was derived to predict the important parameter of the micropump, i.e., the motion of the valves [...] Read more.
This study presents a double-side diaphragm peristaltic pump for efficient medium transport without the unwanted backflow and the lagging effect of a diaphragm. A theoretical model was derived to predict the important parameter of the micropump, i.e., the motion of the valves at large deformations, for a variety of air pressures. Accordingly, we proposed an easy and robust design to fabricate a Polydimethylsiloxane (PDMS)-based micropump. The theoretical model agrees with a numerical model and experimental data for the deformations of the PDMS membrane. Furthermore, variations of the generated flow rate, including pneumatic frequencies, actuated air pressures, and operation modes were evaluated experimentally for the proposed micropumps. In future, the theoretical equation could provide the optimal parameters for the scientists working on the fabrication of the diaphragm peristaltic pump for applications of cell-culture. Full article
(This article belongs to the Special Issue Biomedical Microdevices)
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Open AccessArticle Adaptive Covariance Estimation Method for LiDAR-Aided Multi-Sensor Integrated Navigation Systems
Micromachines 2015, 6(2), 196-215; https://doi.org/10.3390/mi6020196
Received: 24 November 2014 / Accepted: 20 January 2015 / Published: 28 January 2015
Cited by 4 | Viewed by 2569 | PDF Full-text (1145 KB) | HTML Full-text | XML Full-text
Abstract
The accurate estimation of measurements covariance is a fundamental problem in sensors fusion algorithms and is crucial for the proper operation of filtering algorithms. This paper provides an innovative solution for this problem and realizes the proposed solution on a 2D indoor navigation [...] Read more.
The accurate estimation of measurements covariance is a fundamental problem in sensors fusion algorithms and is crucial for the proper operation of filtering algorithms. This paper provides an innovative solution for this problem and realizes the proposed solution on a 2D indoor navigation system for unmanned ground vehicles (UGVs) that fuses measurements from a MEMS-grade gyroscope, speed measurements and a light detection and ranging (LiDAR) sensor. A computationally efficient weighted line extraction method is introduced, where the LiDAR intensity measurements are used, such that the random range errors and systematic errors due to surface reflectivity in LiDAR measurements are considered. The vehicle pose change is obtained from LiDAR line feature matching, and the corresponding pose change covariance is also estimated by a weighted least squares-based technique. The estimated LiDAR-based pose changes are applied as periodic updates to the Inertial Navigation System (INS) in an innovative extended Kalman filter (EKF) design. Besides, the influences of the environment geometry layout and line estimation error are discussed. Real experiments in indoor environment are performed to evaluate the proposed algorithm. The results showed the great consistency between the LiDAR-estimated pose change covariance and the true accuracy. Therefore, this leads to a significant improvement in the vehicle’s integrated navigation accuracy. Full article
(This article belongs to the Special Issue Next Generation MEMS-Based Navigation—Systems and Applications)
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Open AccessArticle Infrared Optical Switch Using a Movable Liquid Droplet
Micromachines 2015, 6(2), 186-195; https://doi.org/10.3390/mi6020186
Received: 8 November 2014 / Revised: 8 January 2015 / Accepted: 21 January 2015 / Published: 27 January 2015
Cited by 5 | Viewed by 2254 | PDF Full-text (801 KB) | HTML Full-text | XML Full-text
Abstract
We report an infrared (IR) optical switch using a wedge-like cell. A glycerol droplet is placed in the cell and its surrounding is filled with silicone oil. The droplet has minimal surface area to volume (SA/V) ratio in the [...] Read more.
We report an infrared (IR) optical switch using a wedge-like cell. A glycerol droplet is placed in the cell and its surrounding is filled with silicone oil. The droplet has minimal surface area to volume (SA/V) ratio in the relaxing state. By applying a voltage, the generated dielectric force pulls the droplet to move toward the region with thinner cell gap. As a result, the droplet is deformed by the substrates, causing the SA/V of the droplet to increase. When the voltage is removed, the droplet can return to its original place in order to minimize the surface energy. Owing to the absorption of glycerol at 1.55 μm, the shifted droplet can be used to attenuate an IR beam with the advantage of polarization independent. Fluidic devices based on this operation mechanism have potential applications in optical fiber switches, IR shutter, and variable optical attenuations. Full article
(This article belongs to the Special Issue Optical Microsystems)
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Open AccessArticle Programmable Electrowetting with Channels and Droplets
Micromachines 2015, 6(2), 172-185; https://doi.org/10.3390/mi6020172
Received: 1 December 2014 / Accepted: 8 January 2015 / Published: 22 January 2015
Cited by 11 | Viewed by 2806 | PDF Full-text (2838 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, we demonstrate continuous and discrete functions in a digital microfluidic platform in a programmed manner. Digital microfluidics is gaining popularity in biological and biomedical applications due to its ability to manipulate discrete droplet volumes (nL–pL), which significantly reduces the need [...] Read more.
In this work, we demonstrate continuous and discrete functions in a digital microfluidic platform in a programmed manner. Digital microfluidics is gaining popularity in biological and biomedical applications due to its ability to manipulate discrete droplet volumes (nL–pL), which significantly reduces the need for a costly and precious biological and physiological sample volume and, thus, diagnostic time. Despite the importance of discrete droplet volume handling, the ability of continuous microfluidics to process larger sample volumes at a higher throughput cannot be easily reproduced by merely using droplets. To bridge this gap, in this work, parallel channels are formed and programmed to split into multiple droplets, while droplets are programmed to be split from one channel, transferred and merged into another channel. This programmable handling of channels and droplets combines the continuous and digital paradigms of microfluidics, showing the potential for a wider range of microfluidic functions to enable applications ranging from clinical diagnostics in resource-limited environments, to rapid system prototyping, to high throughput pharmaceutical applications. Full article
(This article belongs to the Special Issue Biomedical Microdevices)
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Open AccessArticle Classification of Cells with Membrane Staining and/or Fixation Based on Cellular Specific Membrane Capacitance and Cytoplasm Conductivity
Micromachines 2015, 6(2), 163-171; https://doi.org/10.3390/mi6020163
Received: 10 December 2014 / Accepted: 8 January 2015 / Published: 22 January 2015
Cited by 7 | Viewed by 2593 | PDF Full-text (1584 KB) | HTML Full-text | XML Full-text
Abstract
Single-cell electrical properties (e.g., specific membrane capacitance (Cspecific membrane) and cytoplasm conductivity (σcytoplasm)) have been regarded as potential label-free biophysical markers for the evaluation of cellular status. However, whether there exist correlations between these biophysical markers and cellular [...] Read more.
Single-cell electrical properties (e.g., specific membrane capacitance (Cspecific membrane) and cytoplasm conductivity (σcytoplasm)) have been regarded as potential label-free biophysical markers for the evaluation of cellular status. However, whether there exist correlations between these biophysical markers and cellular status (e.g., membrane-associate protein expression) is still unknown. To further validate the utility of single-cell electrical properties in cell type classification, Cspecific membrane and σcytoplasm of single PC-3 cells with membrane staining and/or fixation were analyzed and compared in this study. Four subtypes of PC-3 cells were prepared: untreated PC-3 cells, PC-3 cells with anti-EpCAM staining, PC-3 cells with fixation, and fixed PC-3 cells with anti-EpCAM staining. In experiments, suspended single cells were aspirated through microfluidic constriction channels with raw impedance data quantified and translated to Cspecific membrane and σcytoplasm. As to experimental results, significant differences in Cspecific membrane were observed for both live and fixed PC-3 cells with and without membrane staining, indicating that membrane staining proteins can contribute to electrical properties of cellular membranes. In addition, a significant decrease in σcytoplasm was located for PC-3 cells with and without fixation, suggesting that cytoplasm protein crosslinking during the fixation process can alter the cytoplasm conductivity. Overall, we have demonstrated how to classify single cells based on cellular electrical properties. Full article
(This article belongs to the Special Issue Biomedical Microdevices)
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