Roughness characterisation of gas phase micromachining process suitable for fabricating silicon based microsystems

Chapter 5 - Micro-Electro-Mechanical Systems (MEMS) for Optical-Fiber Communications

For the last two decades, the majority of research and development at LLNL in microtechnology has focused on photonics devices and bulk micromachining, including miccroelectro-mechanical systems and associated areas. For the last ten years, we have used these capabilities to address our analytical instrumentation needs. Just as the miniature photonics have enable the fabrication of analytical instruments that are either higher performance, smaller, more portable, or are combinations of these. Examples of these are our portable thermal cyclers for DNA analysis, our hand-held gas chromatograph, our flow-stream-waveguide-based flow cytometer, and our etched-microchannel electrophoresis systems. This presentation will describe these and related developments.

With recent development in wireless communication and Micro Electro Mechanical Systems (MEMS) technology, it becomes easier to monitor rotating machinery conditions by mounting compact wireless MEMS accelerometers directly on the rotor. This has the potential to provide more accurate dynamic characteristics of the rotating machine and hence achieving high monitoring performance. In this paper, a tiny MEMS accelerometer together with a battery powered microcontroller is mounted on the flywheel to acquire the on-rotor accelerations of a two-stage reciprocating compressor. The measured acceleration data is streamed to a host computer wirelessly via Bluetooth Low Energy (BLE) module. The true tangential acceleration is reconstructed by combining two orthogonal outputs of the sensor, which contain gravitational accelerations. To evaluate the performance of the wireless sensor, three different fault conditions including intercooler leakage, second stage discharge valve leakage and asymmetric stator winding of the motor driver are simulated individually on the compressor test rig. To confirm the wireless sensor performance, an incremental optical encoder was installed on the compressor flywheel to acquire the Instantaneous Angular Speed (IAS) signal for comparison with signals from the wireless sensor. The experimental results show that the running status of the compressor can be remotely monitored, allowing different leakages and motor faults to be diagnosed based on the tangential acceleration reconstructed from a wireless on-rotor MEMS accelerometer.

Recent process developments have permitted the highly anisotropic bulk micromachining of titanium microelectromechanical systems (MEMS). By using the metal anisotropic reactive ion etching with oxidation (MARIO) process, arbitrarily high-aspect-ratio structures with straight sidewalls and micrometre-scale features have been bulk micromachined into titanium substrates of various thicknesses, ranging from 0.5-mm sheet down to 10-microm free-standing titanium foils. Bulk micromachined structures are generally free of residual stresses and are preferred when large, rigid, flat and/or high-force actuators are desired. However, so far there has been a limited ability to select materials on the basis of specific application in bulk micromachining, primarily because of the predominance of MEMS processes dedicated to single-crystal silicon, such as silicon deep reactive ion etching. The MARIO process permits the creation of bulk titanium MEMS, which offers potential for the use of a set of material properties beyond those provided by traditional semiconductor-based MEMS. Consequently, the MARIO process enables the fabrication of novel devices that capitalize on these assets to yield enhanced functionalities that would not be possible with traditional micromechanical material systems.

In this research we proposed, designed, fabricated, and measured a novel micro electro mechanical system (MEMS) based vertical probe tips which differs from conventional cantilever probe tips. The main idea of the vertical probe design was how to distribute the total forces vertically concentrated on the probe tip in measuring semiconductor devices. To solve the problem, we designed the vertical probe tip with meander structure which could provide enough displacements so that the vertical probe tips could distribute the forces acting on the tips. The structural analyses of the probe tip were accomplished using finite element method (FEM) and compared with actual measurement values. The primary fabrication processes were surface micromachining, wafer bonding technology, and electroplating. The material of the electro-plated probe tip was an Ni-Co alloy. In this study, we demonstrated the potential of the vertical probe tip that could apply to a small area with the over drive (O.D.) of 10~40 mum and the contact force of 1~8 gf. The measured contact resistance was less than 2 Omega and little noise was observed.

In this research, a CO micro gas sensor was fabricated based on a micro-heater by using a tin oxide nano-powder for effective gas detection and a monitoring system with low power consumption and high sensitivity. Tin-oxide-based nano-powders were fabricated using a conventional method and their structural properties were examined by using the scanning electron microscope, X-ray diffractor, etc. Membrane type micro-heater based on Si substrate was fabricated by using complementary metal-oxide semiconductor (CMOS) compatible micro electro mechanical systems (MEMS) process by using bulk micromachining. The gas sensing properties for slurry-dropped tin oxide thick film device were measured for CO gas. The micro gas sensors showed high sensitivity and low power consumption, about 15 mW power consumption, 2 ppm CO could be detected.

This paper presents pedagogical issues and experience in teaching the introduction to MEMS (Micro Electro-Mechanical System) course to a group of engineering students, primarily Mechanical Engineering students. The paper draws upon the author’s experience in teaching the MEMS course. Since MEMS is highly inter-disciplinary, the presentation of various relevant topics in MEMS, which may or may not be familiar to a mechanical engineering student, is of critical importance. These topics vary from physics, electrochemistry, materials, and electronic engineering, to various areas in mechanical engineering. An integrated approach for the presentation of subjects, especially in design and fabrication, was found to be very helpful. Moreover, the paradigm shift from the macro world, that most students are familiar and comfortable with, to the micro world is significant and needs to be emphasized. The author found the concept of scaling law, when shifting to the micro world, to be essential in the presentation of MEMS to engineering students in order for them to comprehend the size factor in MEMS. In addition, understanding and appreciation of the strengths and limitations of MEMS are also critical in learning MEMS. Finally, a good textbook will facilitate the learning process of such vast subject. A bibliography of useful textbooks and reference books used by the author will be listed at the end of this paper.

Micro electro mechanical systems (MEMS) have experienced an explosive growth over the past few years driven mainly by its physical properties and its promising technological applications in many different fields, particularly in space and Radio Frequency (RF) systems. MEMS technology exhibits greater advantages over the existing semiconductor switches. In this paper, electro-thermal performances of a two hot arms actuator MEMS switch have been investigated. The switch is designed using CST Microwave Studio. Some mathematical equations have been developed to see the temperature distribution of the hot arms as voltage applied on it. Based on this thermal distribution, the linear thermal expansion of the hot arms and the air gap used in this switch is expressed mathematically. The developed equations have been solved and analyzed using the MATLAB software. This analysis shows that this MEMS switch has a wider range of linear operation and has extremely higher breakdown voltage.

Diversity of application fields and properties of new materials generate new failure mechanisms in Micro electro Mechanical Systems (MEMS). Now if we take into account the lessons from the past in microelectronics, we note that failure analysis played a major rule not only in development time reduction but also in qualification and reliability evaluation Most of the researches which have been done in MEMS reliability are about new material properties and fabrication technologies. Only a few fault detection methods have been introduced for fault detection in MEMS. Some of these methods can be used only for special MEMS. Additionally most of them need a precise model of system. In this paper a new intelligent method is proposed for fault detection in MEMS. In addition some parts of proposed neural network are changed in order to implement it as a BIST mechanism.

MEMS (Micro Electro Mechanical Systems) technology is becoming a crucial enabling technology for optical and RF telecommunication applications due to the performance, cost and integration advantages. All-optical switches and silicon optical benches for optical network systems and RF MEMS components such as RF MEMS switches, tunable capacitors, high Q inductors, and thin film bulk acoustic resonators for miniaturized single chip RF transceivers are discussed. Despite all the promising aspects, practical problems to be addressed for successful commercialization are not trivial. By reviewing optical and RF MEMS research activities and some of the implementation examples, key success factors of MEMS components for the commercialization are discussed.

In this paper, we report monolithic integration of MEMS (micro electro mechanical systems) actuators and high-voltage driver circuits into a silicon chip. Driver circuits of up to 40 V were prepared on an 8-/spl mu/m-thick SOI (silicon-on-insulator) wafer by the DMOS (double-diffused metal oxide semiconductor) processes, after which MEMS electrostatic actuators were integrated into an identical SOI layer by post-processing using DRIE (deep reactive ion etching). This technique opens up a new way of high-voltage ASIC (application specific integrated circuit) for MEMS designer. As a prototype application model, we have developed microlens optical scanners and other elementary MEMS electrostatic actuators with multi-channel driver circuits.

Inertial Measurement Units (IMUs) using MEMS (Micro Electro Mechanical Systems) sensors, to detect rotation and acceleration, are extremely sensitive to vibration and shock. Because these IMUs are used in aircraft, missiles, and even in gun launched projectiles, the vibration and shock levels can be extremely high. We have been successful in designing isolation systems that protect the MEMS sensors from these harsh environments. These isolation systems attenuate the shock and vibration in frequency ranges that would otherwise degrade IMU performance and even damage the sensors. In designing an isolation system, for an IMU with MEMS devices, the designer must first acquire a good definition of the shock and vibration environment to which the IMU will be exposed. Then the designer must determine the frequencies and levels to which the MEMS devices are sensitive. Finally the designer must have knowledge of IMU properties such as resonant frequencies, mass properties, clock frequencies, etc. By knowing all of this information, and how it affects IMU performance, the designer can determine the proper parameters for the isolation system. A well designed isolation system using these parameters will be capable of protecting the MEMS devices while maintaining IMU performance through out all specified environments.

In this paper, rectification methods for micro-energy harvesting systems are proposed and estimated. We present introduce two methods. The first is a mechanical rectification. The second is semiconducting rectification which is fabricated through MEMS technology. Vibration-driven micro-energy harvesting by micro electro mechanical systems (MEMS) technology is needed because the electrical power consumption of our society is increasing. But most of the vibration-driven generators supply alternating-current and intermittent electro energy. For using, it is necessary to construct the micro energy system supplying direct current. Therefore, we present the micro energy system that is composed of vibration-driven micro-energy harvesting, rectification and energy storage. In particular, we consider the rectification in this paper. In designing, we consider that vibration-driven micro-energy harvestings are developed through MEMS technology. Compatibility between semiconductor process and MEMS process is hard to achieve in materials, temperature, contamination and so on.

Micro electro mechanical systems (MEMS) technology has developed considerably in recent years and many sensors utilizing this technology are available in the market. MEMS technology enables miniaturization, mass production, and cost reduction of many sensors. In particular, MEMS inertial sensors that include an acceleration sensor and an angular velocity sensor (gyroscope, or simply ldquogyrordquo) are the most popular devices. Applications of inertial sensors have now extended into the field of networked sensing systems. In this presentation, we will describe current MEMS inertial sensors and their applications.

Etching of silicon with molecular fluorine for the micromachining of micro electro mechanical systems (MEMS) has been evaluated. The etching process is carried out in a continuous flow etching system that uses a 25 vol% mixture of F2 in N2 and operates at room temperature and atmospheric pressure. Fluorine etches silicon isotropically at a rate of 0.2 µm min−1 and is a viable etchant for bulk silicon micromachining. The F2 etch results in the formation of pits about 10–50 µm in size within the silicon features and roughness in the micrometer and sub-micrometer length scales. SiO2, Pt, Ni, Al and Ta do not etch or roughen after several hours of F2 exposure. In addition, F2 does not etch low-stress silicon nitride; a solid layer forms on the silicon nitride surface upon exposure to F2 that protects the underlying silicon nitride from further attack. In contrast, a commercial XeF2 etching system etches low-stress silicon nitride with a silicon nitride:silicon selectivity of approximately 1:200. The F2 etching system is used to release tubes of a MEMS fuel processor that have 2 µm thick low-stress silicon nitride walls.