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We present some of the design, modeling, and simulation features of a computer-aided engineering tool for microelectromechanical systems (MEMS) called SUGAR. The features include a flexible SPICE-like netlist language for MEMS design, a simple modeling framework for computationally efficient lumped models, an extensible architecture to which users can add features, and the ability to display 3-D circuits together with deflected electromechanical structures. Since SUGAR is programmed in MATLAB, many MATLAB functions and toolboxes may be used with SUGAR. Such attributes facilitate the exploration of design spaces and feature modifications. In this paper, we describe SUGAR's extensible architecture, flexible design methodology, modeling framework, and reduced-order modeling technique. We do not present the many other advances made for SUGAR by other developers. For a test case, we choose an advanced microdevice that is difficult to simulate with conventional MEMS software. We show that the relative errors of our lumped models are less than 3% of the finite-element analysis (FEA), that the computational costs are less than 1% of the FEA, and that simulation of the test case fairly agrees with the experiment. [2006-0268] Index Terms--Design methodology, finite-element methods, modeling, simulation software, SPICE, system analysis and design.

MEMS scanning micromirrors have been proposed to steer a modulated laser beam in order to establish secure optical links between rapidly moving platforms. An SOI/SOI wafer-bonding process has been developed to fabricate scanning micromirrors using lateral actuation. The process is an extension of established SOI technology and can be used to fabricate stacked high-aspect-ratio structures with well-controlled thicknesses. Fabricated one-axis micromirrors scan up to 21.8[degrees] optically under a dc actuation voltage of 75.0 V, and have a resonant frequency of 3.6 kHz. Fabricated two-axis micromirrors scan up to 15.9[degrees] optically on the inner axis at 71.8 V and 13.2[degrees] on the outer axis at 71.2 V. The micromirrors are observed to be quite durable and resistant to shocks. Torsional beams with T-shaped cross sections are introduced to replace rectangular torsional beams in two-axis MEMS micromirrors, in order to reduce the cross-coupling between the two axial rotations. Fabricated bidirectional two-axis micromirrors scan up to [+ or -] 7[degrees] on the outer-axis and from -3[degrees] to 7[degrees] on the inner-axis under dc actuation. [1524] Index Terms--Electrostatic actuation, MEMS, micromirror, silicon on insulator technology, wafer bonding.

We have fabricated sub-millimeter-sized quad corner-cube retroreflectors (CCRs) for free-space optical communication. Each quad CCR structure comprises three mirrors micromachined from silicon-on-insulator wafers, and is designed to facilitate manual assembly with accurate angular alignment. Assembled CCRs exhibit mirror nonflatness less than 50 nm, mirror roughness less than 2 nm, and mirror misalignment less than 1 mrad, leading to near-ideal optical performance. The quad CCR incorporates a gap-closing actuator to deflect a base mirror common to the four CCRs, allowing their reflectivity to be modulated up to 7 kb/s by a drive voltage less than 5 V. We have demonstrated a 180-m free-space optical communication link using a CCR as a passive optical transmitter. Quad CCRs have been integrated into miniature, autonomous nodes that constitute a distributed wireless sensor network. We present an analysis of the signal-to-noise ratio of CCR-based links, considering the impact of CCR dimensions, ambient light noise, and other factors. [907] Index Terms--Assembly, corner-cube retroreflector, free-space communication, microelectromechanical systems (MEMS).

We have demonstrated a family of large force and large displacement electrostatic linear inchworm motors that operate with moderate to high voltages. The inchworm motor design decouples actuator force from total travel and allows the use of electrostatic gap-closing actuators to achieve large force and large displacement while consuming low power. A typical inchworm motor measures 3 mm x 1 mm x 50 [micro]m and can lift over 130 times its own weight. One motor has achieved a travel of 80 [micro]m and a calculated force of 260 [micro]N at 33 V. The force density of that motor was 87 [micro]N/[mm.sup.2] at 33 V and the energy efficiency was estimated at 8%. Another motor displaced the shuttle at an average velocity of almost 4 mm/s and achieved an estimated power density of 190 W/[m.sup.3]. Motors were cycled 23.6 million times for over 13.5 h without stiction. This family of motors is fabricated in silicon-on-insulator (SOI) wafers using a single mask. [663] Index Terms--Actuators, electrostatics, gap closing, inchworm motors, microrobots.

A lateral switching relay structure has been developed which provides a double gold contact with as low as 70-m[Omega] measured contact resistance, 0.45-A current-carrying ability at MEMS compatible force levels, TTL compatible actuation, and air gap isolation when open. The die area used for the relay mechanism itself (distinct from the actuation) is approximately 75 [[micro]meter] by 100 [[micro]meter] and was designed to allow fabrication of the relays in the MCNC MUMP's dual polysilicon foundry process with no assembly. Design analysis shows that substantial characterization is needed to design optimal microrelays. Temperature softening and failure modes have been characterized by current voltage techniques. Polysilicon vernier structures were used to develop force/current/conductance curves. Relays using thermal actuators have been built. Index Terms - Contact physics, microrelay, plastic deformation, relay, tribology.

A class of articulated micromanipulator robots with multiple degrees of freedom, workspaces on the order of a cubic millimeter, and payloads on the order of a milligram are proposed. Rigid links, mechanical couplings, and large-force, large-displacement micromotors have been created. Hollow triangular beams made from rotated microhinged polysilicon plates with polysilicon locks can withstand axial loads of up to 2.6 gm. Mechanical couplings with sliding mechanisms are used to rotate hinged structures off the substrate. The typical frictional force observed is approximately 2 [micro]N. Linear electrostatic stepper motors with an estimated force of 6.5 [micro]N at 35 V and a travel of 40 [[micro]meter] have also been demonstrated.

A microelectromechanical systems (MEMS) force transducer system, with a volume less than 1 [mm.sup.3] millimeter, has been developed to measure forces generated by living heart muscle cells. Cell attachment and measurement of contractile forces have been demonstrated with a commercially fabricated surface-micromachined hinged polysilicon device. Two freestanding polysilicon clamps, each suspended by a pair of microbeams, hold each end of a heart cell. When the cell contracts, the beams bend and force is determined from the measured deflection and the spring constant in the beams. The average maximal force over seven contractile experiments using a calcium solution stimulus was [F.sub.max] = 12.6 [+ or -] 4.66 [micro]N. Normalizing to a cross-sectional area, [F.sub.max]/area was 23.7 [+ or -] 8.6 mN/[mm.sup.2]. These force data were also correlated to optically imaged striation pattern periodicity. Intermediate forces were also measured in response to a calcium solution gradient and showed similar behavior to those measured in other laboratories. This MEMS force transducer demonstrates the feasibility of higher fidelity measurements from muscle cells and, thus, an improved understanding of the mechanisms of muscle contraction. [389] Index Terms--Force transducer, heart cell, hinged microstructures, MEMS, micromechanical, surface micromachining.