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The consideration of compliant mechanisms as Microelectromechanical Systems (MEMS) is the focus of this research endeavor. MEMS are micron to millimeter devices that combine electrical, mechanical, and information processing capabilities on the same device. These MEMS need some mechanical motion or parts that move relative to each other. This relative motion, using multiple parts, is not desired because of the assembly requirement and the friction introduced. Compliant devices limits or eliminates friction and the need for multi-component assembly. Compliant devices improve designs by creating single piece mechanisms. The purpose of this research is to validate surface micromachining as a viable fabrication process for compliant MEMS designs. Specifically, this research has sought to fabricate a micro-compliant gripper and a micro-compliant clamp to illustrate the process. While other researchers have created compliant MEMS, most have used comb-drive actuation methods and bulk micromachining processes. This research focuses on fully compliant devices that use device flexibility for motion and actuation. Validation of these compliant MEMS is achieved by structural optimization of device design and functional performance testing. This research contributes to the ongoing research in MEMS by evaluating the potential of using surface micromachining as a process for fabricating compliant freestanding micro-mechanisms.
MEMS technology and applications have grown at a tremendous pace, while structural dimensions have grown smaller and smaller, reaching down even to the molecular level. With this movement have come new types of applications and rapid advances in the technologies and techniques needed to fabricate the increasingly miniature devices that are literally changing our world. A bestseller in its first edition, Fundamentals of Microfabrication, Second Edition reflects the many developments in methods, materials, and applications that have emerged recently. Renowned author Marc Madou has added exercise sets to each chapter, thus answering the need for a textbook in this field. Fundamentals of Microfabrication, Second Edition offers unique, in-depth coverage of the science of miniaturization, its methods, and materials. From the fundamentals of lithography through bonding and packaging to quantum structures and molecular engineering, it provides the background, tools, and directions you need to confidently choose fabrication methods and materials for a particular miniaturization problem. New in the Second Edition Revised chapters that reflect the many recent advances in the field Updated and enhanced discussions of topics including DNA arrays, microfluidics, micromolding techniques, and nanotechnology In-depth coverage of bio-MEMs, RF-MEMs, high-temperature, and optical MEMs. Many more links to the Web Problem sets in each chapter
This paper describes the design and design issues associated with silicon surface micromachined device design Some of the tools described are adaptations of macro analysis tools. Design issues in the microdomain differ greatly from design issues encountered in the macrodomain. Microdomain forces caused by electrostatic attraction, surface tension, Van der Walls forces, and others can be more significant than inertia, friction, or gravity. Design and analysis tools developed for macrodomain devices are inadequate in most cases for microdomain devices. Microdomain specific design and analysis tools are being developed, but are still immature and lack adequate functionality. The fundamental design process for surface micromachined devices is significantly different than the design process employed in the design of macro-sized devices. In this paper, MEMS design will be discussed as well as the tools used to develop the designs and the issues relating fabrication processes to design. Design and analysis of MEMS devices is directly coupled to the silicon micromachining processes used to fabricate the devices. These processes introduce significant design limitations and must be well understood before designs can be successfully developed. In addition, some silicon micromachining fabrication processes facilitate the integration of silicon micromachines with microelectronics on-chip. For devices requiring on-chip electronics, the fabrication processes introduce additional design constraints that must be taken into account during design and analysis.
The silicon age that led the computer revolution has significantly changed the world. The next 30 years will see the incorporation of new types of functionality onto the chip-structures that will enable the chip to reason, to sense, to act and to communicate. Micromachining technologies offer a wide range of possibilities for active and passive devices. Recent developments have produced sensors, actuators and optical systems. Many of these technologies are based on surface micromachining, which has evolved from silicon integrated circuit technology. This book is written by experts in the field. It contains useful details in design and processing and can be utilized as a reference book or as a textbook.
Surface micromachining generally offers more design freedom than related technologies, and it is the technology of choice for most microelectromechanical applications that require multi-level structures. However, the design flexibility that surface micromachining offers is not without limitations. In addition to determining how to fabricate devices in a planar world, the designer also needs to consider issues such as film quality, thickness, residual stress, topography propagation, stringers, processing limitations, and concerns about surface adhesion [1]. Only a few years ago, these were the types of issues that limited design complexity. As the technology improved, the number of mechanical layers available to the designer became the dominant constraint on system functionality. In response, we developed a 5-level polysilicon fabrication technology [2] that offers an unprecedented level of microelectromechanical complexity with simultaneous increases in system yield and robustness. This paper outlines the application that was the driving force behind this work and describes the first devices specifically designed for and fabricated in this technology. The 5-level fabrication technology developed to support this program is known as SUMMiT-V. Four mechanical layers of polysilicon referred to as polyl, poly2, poly3, and poly4 are fabricated above a polyO electrical interconnect and ground plane layer [2,4]. PolyO is 0.3 pm thick, polyl is 1.0 pm, poly 2 is 1.5 pm, and both poly3 and poly4 are 2.25 pm. All films except polyl and poly2 are separated by 2-pm thick depositions of sacrificial oxide. A 0.5-m sacrificial oxide between polyl and poly2 typically defines the clearance between close mating parts such as hubs and hinges. This entire stack is built on a single crystal substrate with a dielectric foundation of 0.8 pm of nitride over 0.63 m of oxide. Seventeen drawing layer are combined to generate the 14 photolithographic masks used to pattern these films during a 240-step fabrication sequence. Mirror Operation To become operational, both mirrors must be driven up to a 45 degree angle. In this position, optical energy entering through an opening in the substrate beneath one mirror [5] is redirected to the second mirror, then down through another substrate opening and onto the target receiver. Each mirror is actuated through a chain of gears driven by a mirror control engine. This chain incorporates a series of gear reduction units that significantly increase drive torque and positional resolution. Also included in this chain are two gears that are not coupled to each other (see figure 3). This prevents the mirror control engine from driving the rack that actuates the mirror. To complete the drive train, two additional gears must be inserted between the interrupted gear pair [4]. The coupling gears that perform this function are shown in figure 4. Both of these gears are fabricated on a plate that moves towards the interrupted pair of gears as the discrimination sequence The plate onto which the coupling gears are fabricated is attached to the left end of the maze rack, so it moves as the rack moves. If the wrong path is taken at any of the 24 decision points in the maze, the coupling gears will not move far enough to complete the mirror gear chain, and the mirror can never be operated. Thus, this is a single attempt device with more than 16 million possible code sequences.
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