A Vision of Structured CAD for MEMS

Computer-aided design tools tailored for microelectromechanical systems (MEMS) are needed to enable design of complex systems with multiple energy domains. In an analogy to the VLSI design methodology, physical, structural, and behavioral views of MEMS can be formed and coupled together in an integrated toolset. Of key importance is the formation of parameterized MEMS component libraries to support these views. Fast coupled-domain numerical (physical) simulation and behavioral simulation are required to move freely between the views

Integrated MEMS in Conventional CMOS

This paper provides an overview of fabrication and design of CMOS-based microelectromechanical systems with emphasis on inertial sensor and data storage applications. High-aspect-ratio (4.4:1) microstructures can be fabricated using conventional CMOS processing followed by a sequence of maskless dry-etching steps. The CMOS dielectric and metallization layers, normally used for electrical interconnect, serve a dual function as a composite metal/dielectric structural material. Reactive-ion etching produces near vertical sidewalls, enabling micromechanical beam widths and gap spacings down to 1.2 μm. The process is tailored for design of lateral electrostatic actuators as well as capacitive position and motion sensors. Tight integration of the microstructures with CMOS provides an opportunity to make low-noise sensor interface circuitry, and to include the signal processing needed to manage arrayed sensor-and-actuator systems-on-a-chip. Novel actuator and sensor topologies can be designed by embedding multiple isolated conductors into the microstructures. An additional post-CMOS processing sequence produces platinum tips on the movable microstructures. These tips are being explored for use in probe-based data storage and tunneling sensor applications

Structured Design Of Microelectromechanical Systems

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 technolog

Design Methodology for Mixed-Domain Systems-on-a-Chip

Digital design tools such as logic synthesis, semicustom layout and behavioral simulation have drastically changed the digital IC design process, enabling design of complex “systems on a chip”. The usefulness of such chips are limited in a world dominated by information that is not represented by 0s and 1s. Overcoming these limitations has led to mixed-signal, and mixed-domain technologies. We focus on design methodologies and tools to aid the design of complex microelectromechanical systems (MEMS) having large numbers of mixed-domain components. We propose a hierarchically structured design approach that is compatible with standard IC design involving a schematic approach to MEMS design, a layout synthesis strategy for cell-level design automation, and a feature-recognition based device extractor for layout verification. We present emerging results on our design methodology and tools

Modeling and Simulation of Microresonators with Meander Suspensions

Surface-micromachined comb-drive resonators suspended by meander springs are modeled and simulated. General analytic expressions for lateral spring constants and effective mass of meander springs are derived and verified by finite-element simulations. The spring constant equations are accurate to within 1% over a wide range of geometries. Analytic, simulated, and measured resonant frequency values agree to within 0.3% for each of ten different microresonator designs

A CMOS-MEMS lateral-axis gyroscope

This paper reports on the experimental results from the first design of a CMOS lateral-axis vibratory gyroscope that utilizes comb fingers for both actuation and sensing. The fabrication is compatible with standard CMOS processes and the design has an integrated, fully-differential capacitive interface circuit. This gyroscope design uses integrated comb drives for out-of-plane actuation, and is motivated by the desire to integrate three-axis gyroscopes on a single chip. The packaged gyroscope operates at atmospheric pressure with a sensitivity of 0.12 mV/deg/s and the resonant frequency of the drive mode is thermomechanically tuned between 4.2-5.1 kHz. Resonant frequency matching between the drive and sense modes is realized by integrating a polysilicon heater inside the spring beam

A Comparison of Induction-Detection NMR and Force- Detection NMR on Micro-NMR Device Design

Nuclear Magnetic Resonance (NMR) is widely used in medical diagnostics and chemical analysis. Due to rapid growing of the NMR applications, the conventional NMR systems may not fulfill the need of all applications. The development of a micro-NMR device would not only benefit the original NMR applications but could also open a door for new NMR applications. Two approaches for building a NMR system, Induction-Detection Nuclear Magnetic Resonance (IDNMR) and Force-Detection Nuclear Magnetic Resonance (FDNMR) are explored and compared in this paper. The comparison result shows that the FDNMR approach outperforms the IDNMR approach in signal-to-noise ratio when the sample radius is below 410 mm for protons and 1900 mm for chlorides. This suggests that the FDNMR approach is more appropriate for making the micro-NMR device

Suspended, Porous Cellulose Acetate Membranes For Microdialysis Use

Porous cellulose acetate membranes were suspended over 75 micron wide silicon microchannels. The microchannels are formed when a viscous polymer lacquer is directly spin cast onto etched silicon cavities (Fig. 1). Standard fabrication processes are used to create the channel, preventing the need for adhesives, substrate bonding, or other complex assembly procedures. These microchannels can allow the isolation and concentration of specific biological molecules

A 1 mG lateral CMOS-MEMS accelerometer

This paper reports a lateral CMOS-MEMS accelerometer with a measured noise floor of 1 mG/√(Hz) and a dynamic range larger than 13 G. The accelerometer is fully compatible with conventional CMOS processes enabling the integration of most of the conditioning circuits. It is fabricated in a three metal layer 0.5 μm CMOS process followed by a two-step dry etch release. An improved curl matching technique is utilized to solve the out-of-plane curl problem. A new differential amplifier is used for the capacitive sensing interface. The CMOS micromachining process used in this project is described. The design of accelerometer, system schematic applying force-balance feedback and experimental test results are presente

Multi-mode Sensitive Layout Synthesis of Microresonators

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