Nanoimprinted strain-controlled elastomeric gratings for optical wavelength tuning

We demonstrate strain-controlled gratings made of an organic elastomer, polydimethylsiloxane (PDMS), which can achieve optical wavelength tuning by varying their spatial periods. The whole device structure presented in this work incorporates a nanoimprinted PDMS grating integrated with electrostatic microelectromechanical systems actuators on a silicon chip. The fabrication of the device combines polymer soft lithography, nanoimprint lithography, and silicon micromachining across multiscale dimensions ranging from a few hundred nanometers to a few millimeters. The fine tuning capability with fast dynamic response of our PDMS/silicon hybrid optical grating device makes it attractive for use in various micro-optical instruments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87849/2/161113_1.pd

Anisotropic Thermal Properties of Solid Polymers

This paper discusses the thermal conduction anisotropy in polymers by reviewing currently available theories and experimental methods for studying oriented polymers. The anisotropic thermal conductivity and diffusivity of oriented polymers originate from the difference between the thermal energy transport mechanisms parallel and perpendicular to their molecules. Recent progress in the development of experimental techniques for studying the thermal conduction anisotropy of polymer films with thicknesses near 1 μm is discussed in connection with modern microelectronics applications. The data obtained from these techniques are expected to serve for developing sophisticated thermal conduction theories that account for the polymer anisotropy and for performing precise thermal design of organic electronic devices that incorporate highly oriented polymer structures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44567/1/10765_2004_Article_293684.pd

Transition from multiple to single microcontact conduction during hot switching of microelectromechanical switches with ball-shaped dimples

Previous studies of electron transport within direct contact microelectromechanical switches have found that conduction occurs via nanoscale contact asperities. It has been claimed that reduced contact resistance can be achieved by using multiple contact switches; however, the ability of these switches to enhance power handling or lifetime remains a question. To study the contact mechanism, single-input-multiple-output switches with ball-shaped dimples were specially designed and tested. At all voltage levels of hot-switching operation, uneven current sharing among the outputs was observed. Furthermore, at softening voltage, an irreversible multiple to single conduction transition occurs and is found to alternate among different outputs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87795/2/133501_1.pd

Comparison of Semi-Analytical Formulations and Gaussian Quadrature Rules for Quasi-Static Double Surface Potential Integrals

This paper presents a comparison of a new semi-analytical expression with Gaussian-quadrature formulas for the quasi-static double-surface potential integrals arising in the boundary integral (BI) models of micron-size objects, such as RF-MEMS switches. The integrals considered are the quasi-static Green's functions for the scalar and vector potentials, with constant or linear basis functions over triangular subdomains. The examples given illustrate that the new semi-analytical formulations can achieve significantly higher solution accuracy and are more efficient when compared to the Gaussian-quadrature formulas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87252/4/Saitou47.pd

Fully Integrated Electrothermal Multi-Domain Modeling of RF MEMS Switches

RF MEMS switches have demonstrated excellent performance. However, before such switches can be fully implemented, they must demonstrate high reliability and robust power-handling capability. Numerical simulation is a vital part of design to meet these goals. This paper demonstrates a fully integrated electrothermal model of an RF MEMS switch which solves for RF current and switch temperature. The results show that the beam temperature increases with either higher input power or increased frequency. The simulation data are used to predict switch failure due to temperature-related creep and self pull-in over a wide range of operating frequency (0.1-40 GHz) and power input (0-10 W). Self pull-in is found to be the dominant failure mechanism for an example geometry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87264/4/Saitou33.pd

Low-force contact heating and softening using micromechanical switches in diffusive-ballistic electron-transport transition

We demonstrate softening of the gold-to-gold contact in surface micromachined microelectromechanical switches under electrostatic force near 30 μN30μN, which results from the heating of contact asperities sustaining electron transport. A bias potential that causes the switch contacts to soften is measured for initial contact resistance varying between 0.5 and 300 Ω300Ω. The asperity sizes in this range are comparable to the electron mean-free path at room temperature. We show that contact spots smaller than the mean-free path require larger bias for softening. Our results can be explained using a model accounting for ballistic electron transport in the contact.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87858/2/023507_1.pd

Lifetime Extension of RF MEMS Direct Contact Switches in Hot-Switching Operations by Ball-Grid-Array (BGA) Dimple Design

Direct contact RF microelectromechanical systems switches have demonstrated excellent ultrawideband performance from dc to 100 GHz. However, they are prone to failures due to contact adhesion and arcing, particularly for pure-gold/pure-gold contacts. In this letter, we present a new contact design employing ball grid array (BGA) dimples that limit the effective contact area to a few tens of nanometers in diameter. We experimentally show the performance of the BGA dimple with pure-gold/pure-gold contacts and demonstrate RF power handling greater than 1 W during hot switching in excess of 100 million cycles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87268/4/Saitou10.pd

Fabrication of beam structures with micro-scale cross-sections and meso-scale spans

To allow testing of micro-scale aerodynamics, a process was created to manufacture beam structures that combine spans of 1 cm with a cross-section of 5 µm by 100 µm. The structural considerations limiting the fabrication of a structure combining macro-scale spans with a micro-scale cross-section are analyzed. Limiting considerations include forces during operation, fluid forces during release, vibrational limitations and beam buckling. Based on these results, a fabrication process for creating a beam structure for large spans without support structures is devised, incorporating the use of back-side etches and extra handling wafers to avoid stiction. This process is used to successfully fabricate the desired structure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58143/2/jmm7_12_018.pd

Adhesion effects on contact opening dynamics in micromachined switches

We propose a technique to measure the opening time for micromachined switches and present substantial experimental data for switches with gold–gold contacts. The data demonstrate that contact opening time increases dramatically as apparent contact area increases or as pull-apart force or contact resistance decreases. A model of opening time is also presented with model parameters that fit the experimental data. Moreover, we show that transient mechanical vibrations can play an important role in reducing switch opening time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87500/2/103535_1.pd

Analysis of RF-MEMS Switches Using Finite Element-Boundary Integration with Moment Method

This paper presents a new hybrid methodology for modeling RF-MEMS switches. This method combines the usual finite element-boundary integration (FE-BI) method for the fixed section of the switch, and the method of moments for the movable beam. This approach is intended to address the large 100:1 scale variation within a single computational domain, which also spans a very small fraction of a wavelength.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87249/4/Saitou98.pd