A Frequency-Tunable Comb Resonator Using Spring Tension and Compression Effects

A 2μm-thick frequency-tunable microresoantor capable of either increasing or decreasing its resonant frequency by a combination of Joule heating and electrostatic force has been successfully demonstrated for the first time. For the heating voltage increase from 0 to 2V under fixed bias voltage of 40V, the resonant frequency changes from 22.2kHz to 16.2kHz, resulting in the 27% reduction in the resonant frequency. For the bias voltage change from 20V to 40V under the heating voltage of 0V, the resonant frequency increase from 19.0kHz to 23.6kHz, resulting in the 24.2% increase in the resonant frequency. As such, this surface-micromachined microactuator could assist complicated frequency tuning for applications of microsensors and microactuators.

Fabrication of Ultra Thick Ferromagnetic Structures in Silicon

A novel fabrication process is presented to create ultra thick ferromagnetic structures in silicon. The structures are fabricated by electroforming NiFe into silicon templates patterned with deep reactive ion etching (DRIE). Thin films are deposited into photoresist molds for characterization of an electroplating cell. Results show that electroplated films with a saturation magnetization above 1.6 tesla and compositions of approximately 50/50 NiFe can be obtained through agitation of the electrolyte. Scanning electron microscopy (SEM) images show that NiFe structures embedded in a 500 μm thick silicon wafer are realized and the roughening of the mold sidewalls during the DRIE aids in adhesion of the NiFe to the silicon.

Design of Micro-Gripper With Topology Optimal Compliant Mechanisms

The objective of this paper describes a new method to design a micro-gripper. In the paper, we use compliant mechanism actuated by micro combined V-shape electrothermal actuator to design a microgripper that the claw can clip the micro object. The compliant mechanism employs flexible to generate movement without any hinge; therefore, it is suitable for MEMS manufacture. The design of micro-gripper is accomplished in compliant mechanism with topology optimum and solved by sequential linear programming (SLP) methods. The design considerations, the analysis method, and the design results are discussed.

Disposable Polydimethylsiloxane/Silicon Hybrid Chips for Protein Detection

This paper presents disposable protein analysis chips with single and multiple chambers - constructed from poly (dimethylsiloxane) (PDMS) and silicon. The chips are composed of a multilayer stack of PDMS layers that sandwich a silicon microchip. This inner silicon chip features an etched array of microcavities hosting agarose beads. The sample is introduced into the fluid network in the top PDMS layer where it is directed to the bead chamber. After reaction of the analyte with the probe beads, signal generated on the beads is captured with a CCD camera, digitally processed, and analyzed. An established bead-based fluorescent assay for C-reactive protein (CRP) was used here to characterize these hybrid chips. The detection limit of the single chamber protein chip was found to be 1ng/mL. Additionally, using the back pressure compensation method, the signals from each of the four-chamber chip were found to be within 10% of each other. Moreover, the fabrication of the multiple-chamber chip may increase throughput and multiplex assay capacity.

Fabrication and Characterization of Vertical Travel Linear Microactuator

This paper describes design, fabrication and characterization of a proof-of-concept vertical travel linear microactuator designed to provide out-of-plane actuation for high precision positioning applications in space. The microactuator is designed to achieve vertical actuation travel by incorporating compliant beam structures within a SOI (Silicon on Insulator) wafer. Device structure except for the piezoelectric actuator is fabricated on the SOI wafer using Deep Reactive Ion Etch (DRIE) process. Incremental travel distance of the piezoelectric actuator is adjustable at nanometer level by controlling voltage. Bistable beam geometry is employed to minimize initial gaps between electrodes. The footprint of an actuator is approximately 2 mm × 4 mm. Actuation is characterized with LabVIEW-based test bed. Actuation voltage sequence is generated by the LabVIEW controlled power relays. Vertical actuation in the range of 500 nm over 10-cycle was observed using WYKO RST Plus Optical Profiler.

Comparison of Thermomechanical and Stress Wave Induced Laser Repair Techniques for Stiction-Failed Microcantilevers

Surface micromachined structures with high aspect ratios are often utilized as sensor platforms in microelectromechanical systems (MEMS) devices. These structures generally fail by stiction or adhesion to the underlying substrate during operation, or related initial processing. Such failures represent a major disadvantage in mass production of MEMS devices with highly compliant structures. Fortunately, most stiction failures can be prevented or repaired in a number of ways. Passive approaches implemented during fabrication or release include: (1) utilizing special low adhesion coatings and (2) processing with low surface energy rinse agents. These methods, however, increase both the processing time and cost and are not entirely effective. Active approaches, such as illuminating stiction-failed microstructures with pulsed laser irradiation, have proven to be very effective for stiction repair [1–5]. A more recent and promising method, introduced by Gupta et al. [6], utilized laser-induced stress waves to repair stiction-failed microstructures. This approach represents a logical extension of the laser spallation technique for debonding thin films from substrates [7–9]. The method transmits stress waves into MEMS structures by laser-irradiating the back side of the substrate opposite the stiction-failed structures. This paper presents an experimental study that compares the stress wave repair method with the thermomechanical repair method on identical arrays of stiction-failed cantilevers.

Numerical Modeling of a Nonlinear MEMS Membrane

A numerical model is developed to understand the behavior of a laminated, piezoelectric, geometrically nonlinear MEMS device. The finite difference method is chosen, along with the Newmark technique to model the static and vibrational behavior. This technique is validated by comparison to empirical data. The developed model is exercised to understand and optimize the device by studying residual stress, layer thicknesses, and electrode sizes with the goal of reduction of fundamental frequency and increase of charge output.

Modelling and Adaptive Control of Tendon-Driven Micromanipulators in the Presence of Van-der-Waals Forces

In this article, the design problem of an adaptive controller for a robotic micromanipulator, including the effects of the applied Van der Waals (VdW) forces is considered. The micro-manipulator’s dynamic model is appropriately modified in order to include the interaction of the attractive VdW-forces. Inhere, every link is decomposed into a series of elementary particles (e.g. spheres), each one interacting with the robot’s neighboring objects during its motion. This interaction induces nonlinear additive terms in the model, attributed to the overall effect of the VdW-forces. The actuation is achieved by a tendon-driven system. At each joint, a pair of tendons is attached and act in an almost passive antagonistic manner. The kinematic and dynamic analysis of the tendon-driven actuation mechanism is offered. Consequently, the microrobot’s model is shown to be linearly parameterizable. Subject to this observation, a globally stabilizable adaptive control scheme is derived, estimating the unknown parameters (masses, generalized VdW-forces) and compensating any variations of those. Simulation studies on a 2-DOF micro-manipulator are offered to highlight the effectiveness of the proposed scheme.

Silicon Microarray Pin With Selective Hydrophobic Coating

We have recently demonstrated the viability of silicon microarray pins, taking advantage of lithographic and batch processing of silicon micromachining in comparison with conventional and serial processing currently used for commercial pins. The reduced spot size (< 50% in diameter, i.e., > 4X in array density), however, made such undesirable needs as preprinting more pronounced. Preprinting, a common practice in microarray printing, drains out the excess liquid formed outside the liquid channel during dipping. In this paper, we describe how surface wettability can be controlled and report its dramatic effect on the printing performance, for the first time. By making the exterior surfaces hydrophobic and the interior surface hydrophilic, the excess liquid outside the liquid channel is eliminated, and the advantages of silicon-micromachined pins are fully exercised.

Experimental Investigation of Dynamic Response of RF-MEMS Switches

Ohmic and capacitive switches constitute an important segment of radio frequency microelectromechanical systems (RF-MEMS) components. The main function of these switches is to provide very rapid opening and closing of electrical contacts. To fulfill this requirement, the structural dynamics and coupled-physics response of candidate switch designs must be thoroughly understood. This paper presents a set of dynamic experimentation of two RF-MEMS ohmic switches with different geometries to determine their natural frequencies, mode shapes, and damping characteristics at pressures spanning from vacuum to atmospheric. The experimental facility used for the tests is also described in detail.