Surface micromachining is characterized by the fabrication of micromechanical structures from deposited thin films. Originally employed for integrated circuits, films composed of materials such as low-pressure chemical-vapor-deposition polycrystalline silicon, silicon nitride, and silicon dioxides can be sequentially deposited and selectively removed to build or “machine ” three-dimensional structures whose functionality typically requires that they be freed from the planar substrate. Although the process to accomplish this fabrication dates from the 1960’s, its rapid extension over the past few years and its application to batch fabrication of micromechanisms and of monolithic microelectromechanical systems (MEMS) make a thorough review of surface micromachining appropriate at this time. Four central issues of consequence to the MEMS technologist are: i) the understanding and control of the material properties of microstructural films, such as polycrystalline silicon, ii) the release of the microstructure, for example, by wet etching silicon dioxide sacrificial films, followed by its drying and surface passivation, iii) the constraints defined by the combination of micromachining and integrated-circuit technologies when fabricating monolithic sensor devices, and iv) the methods, materials, and practices used when packaging the completed device. Last, recent developments of hinged structures for postrelease assembly, highaspect-ratio fabrication of molded parts from deposited thin films, and the advent of deep anisotropic silicon etching hold promise to extend markedly the capabilities of surface-micromachining technologies.

In order to efficiently design complex microelectromechanical systems (MEMS) having large numbers of multi-domain components, a hierarchically structured design approach that is compatible with standard IC design is needed. A graphical-based schematic, or structural, view is presented as a geometrically intuitive way to represent MEMS as a set of interconnected lumpedparameter elements. An initial library focuses on suspended-MEMS technology from which inertial sensors and other mechanical mechanisms can be designed. The schematic representation has a simulation interface enabling the designer to simulate the design at the component level. Synthesis of MEMS cells for common topologies provides the system designer with rapid, optimized component layout and associated macro-models. A synthesis module is developed for the popular folded-flexure micromechanical resonator topology. The algorithm minimizes a combination of total layout area and voltage applied to the electromechanical actuators. Synthesis results clearly show the design limits of behavioral parameters such as resonant frequency for a fixed process technology.

Fully monolithic, high-Q, micromechanical signal processors are described. A completely monolithic high-Q oscillator, fabricated via a combined CMOS plus surface micromachining technology, is detailed, for which the oscillation frequency is controlled by a polysilicon micromechanical resonator to achieve high stability. The operation and performance of mechanical resonators are modelled, with emphasis on circuit and noise modelling. Micromechanical filter design is described, and a prototype two-resonator bandpass filter is demonstrated. An integrated micro-oven that stabilizes the resonance frequency against temperature variations using only 2 mW of power is reviewed. Brownian motion and mass loading phenomena are shown to have a greater influence on short-term stability and dynamic range in this micro-scale. Scaling strategies are proposed to alleviate potential limitations due to Brownian noise.

design, system simulation, and layout synthesis [8, 9]. Initial success in this area includes the synthesis of 1D resonators [10], optimization-based synthesis of 2D resonators [11], nodal analysis of multiple degree of freedom structures in Saber [12] and inertial sensors [13]. Some of this work has also become commercially available [14]. The success of this approach is critically dependent on the ability to quickly and accurately simulate large numbers of interconnected MEMS devices. In the IC environment, this is done by abstracting the physical world in terms of N-terminal devices. Each device is modeled by ordinary differential equations (ODEs) with coefficients parameterized by device geometry, and material properties derived from measurements or process specifications. Devices are linked together at their terminals, or nodes, and the resulting coupled differential equations can b

Abstract—This paper reports on the design, fabrication, and testing of a low-actuation voltage Microelectromechanical systems (MEMS) switch for high-frequency applications. The mechanical design of low spring-constant folded-suspension beams is presented first, and switches using these beams are demonstrated with measured actuation voltages of as low as 6 V. Furthermore, common nonidealities such as residual in-plane and gradient stress, as well as down-state stiction problems are addressed, and possible solutions are discussed. Finally, both experimental and theoretical data for the dynamic behavior of these devices are presented. The results of this paper clearly underline the need of an integrated design approach for the development of ultra low-voltage RF MEMS switches. Index Terms—Low actuation voltage, microelectromechanical systems (MEMS) switches, residual stress, spring constant, switching speed, top-electrode switches. I.

Two novel designs of micromechanical capacitive switches using serpentine and cantilever springs for low actuation voltage applications are reported. Both designs also incorporate an electrode situated above the switching structure in order to provide system stability. DC measurements indicate pull-in voltages of 14 and 16 V, with RF isolation of better than-30 dB up to 40 GHz. I.

We are developing physical design tools for surfacemicromachined MEMS, such as polysilicon microstructures built using MCNC’s Multi-User MEMS Process service. Our initial efforts include automation of layout synthesis and behavioral simulation from a MEMS schematic representation. As an example, layout synthesis of a folded-flexure electrostatic combdrive microresonator is demonstrated. Lumpedparameter electromechanical models with two mechanical degrees-of-freedom link the physical and behavioral parameters of the microresonator. Simulated annealing is used to generate global optimized layouts of five different resonators from 3 kHz to 300 kHz starting with mixed-domain behavioral specifications and constraints. Development of the synthesis tool enforces codification of all relevant MEMS design variables and constraints. The synthesis approach allows a rapid exploration of MEMS design issues. 1.

Microresonator layouts are synthesized such that their preferred mode of oscillation is well-separated from the higher order in-plane and out-of-plane modes. Building on our previous work, we have incorporated models for four out-of-plane modes. All these modes are modeled as springmass systems. The spring constants and the effective masses of these modes are analytically derived. Synthesis is accomplished by encoding a design quality metric as the design objective while simultaneously constraining the design to meet user specifications. These constraints require that the resonant frequency in the preferred direction is sufficiently lower than (and, hence, dominates over) the resonant frequency of other modes of vibration of the structure. The models are verified by comparison with 3D FEM simulations and also with experimental measurements on fabricated resonators. The usefulness of these models is illustrated by comparing the oscillation modes of layouts synthesized with and without these models. This exercise also shows that such mode-separation can be achieved only if the microresonators have a structural thickness larger than flexure width.

This paper presents some results of our development and test efforts in micromachine design for optical modulation. In this work, we have developed, using a readily available surface micromachine fabrication process (MUMPs), a series of arrayed micromirror elements. These element arrays form phase-mostly spatial light modulators (SLM's), similar to Texas Instruments' flexure beam micromirror device (FBMD) [1]. Characteristics that distinguish our elements from those of TI include: integrated support posts to stabilize the elements at points beyond pull-in potential, non-metallic supporting structures to reduce diffractive noise, bistable drive capabilities without the need for transistor arrays, and greater mirror surface stability. Sections 1 and 2 describe our elements (EmBMP's). Their arrayed operation is covered in Section 3. Optical evaluations in Section 4 measure the feasibility of these devices in the application of optical interconnect, as well as bracket further discussion co...

Transforming software requirements into a software design involves the iterative partition of a solution into software components. The process is human-intensive and does not guarantee that design objectives such as reusability, evolvability, and reliable performance are satisfied. The costly process of designing, building, and modifying high assurance systems motivates the need for precise methods and tools to generate designs whose corresponding implementations are reusable, evolvable, and reliable. This paper demonstrates an analytical approach for partitioning basic elements of a software solution into reusable and evolvable software components. First, we briefly overview the role of partitioning in current design methods and explain why computer-aided design (CAD) tools to automate the design of microelectromechanical systems (MEMS) are high assurance applications. Then we present our approach and apply it to the design of CAD software to layout an optimized design of a MEMS accelerometer to be used in the navigational units of aircraft. Lastly, we discuss the implications of our approach and future research directions. 1.