M. Dadras

Voltage Control of the Resonance Frequency of Dielectric Electroactive Polymer (DEAP) Membranes

We report on the characterization, active tuning, and modeling of the first mode resonance frequency of dielectric electroactive polymer (DEAP) membranes. Unlike other resonance frequency tuning techniques, the tuning procedure presented here requires no external actuators or variable elements. Compliant electrodes were sputtered or implanted on both sides of 20-35-mum-thick and 2-4-mm-diameter polydimethylsiloxane membranes. The electrostatic force from an applied voltage adds compressive stress to the membrane, effectively softening the device and reducing its resonance frequency, in principle to zero at the buckling threshold. A reduction in resonance frequency up to 77% (limited by dielectric breakdown) from the initial value of 1620 Hz was observed at 1800 V for ion-implanted membranes. Excellent agreement was found between our measurements and an analytical model we developed based on the Rayleigh-Ritz theory. This model is more accurate in the tensile domain than the existing model for thick plates applied to DEAPs. By varying the resonance frequency of the membranes (and, hence, their compliance), they can be used as frequency-tunable attenuators. The same technology could also allow the fine-tuning of the resonance frequencies in the megahertz range of devices made from much stiffer polymers.

Generic technological platform for microfabricating silicon nitride micro- and nanopipette arrays

In this paper, the design and the characterization of batch fabricated SixNy micropipette arrays with diameters ranging from 6 µm down to 250 nm are described. The process used to fabricate the micromachined pipettes includes a deep reactive ion etching step, followed by the deposition of two successive layers, a thermal oxide layer and a low stress, low pressure chemical vapor deposited silicon nitride layer, respectively. The diameter of the micropipettes could be modulated simply by choosing the thicknesses of the oxide sacrificial layer and of the nitride walls of the micropipettes. The reactive ion etching of the micropipette top layer in deep cavities and in confined and deconfined configurations is discussed. The mechanical resistance of the micropipette array was qualitatively tested and it was demonstrated that a force of 0.25 mN/micropipette could be applied without rupture of the micropipettes.

Low-temperature thin-film indium bonding for reliable wafer-level hermetic MEMS packaging

This paper reports on low-temperature and hermetic thin-film indium bonding for wafer-level encapsulation and packaging of delicate and temperature sensitive devices. This indium-bonding technology enables bonding of surface materials commonly used in MEMS technology. The temperature is kept below 140 degrees C for all process steps and no surface treatment is applied before and during bonding. This bonding technology allows hermetic sealing at 140 degrees C with a leak rate below 4 x 10(-12) mbar l s(-1) at room temperature. The tensile strength of the bonds up to 25 MPa goes along with a very high yield.

Metal Ion Implanted Compliant Electrodes in Dielectric Electroactive Polymer (EAP) Membranes

One of the key factors to obtain large displacements and high efficiency with dielectric electroactive polymer (DEAPs) actuators is to have compliant electrodes. Attempts to scale DEAPs down to the mm or micrometer range have encountered major difficulties, mostly due to the challenge of micropatterning sufficiently compliant electrodes. Simply evaporating or sputtering thin metallic films on elastomer membranes produces DEAPs whose stiffness is dominated by the metallic film. Low energy metal ion implantation for fabricating compliant electrodes in DEAPs presents several advantages: a) it is clean to work with, b) it does not add thick passive layers, and c) it can be easily patterned. We use this technology to fabricate DEAPs micro-actuators whose relative displacement is the same as for macro-scale DEAPs. With transmission electron microscope (TEM) we observed the formation of metallic clusters within the elastomer (PDMS) matrix, forming a nano-composite. We focus our studies on relating the properties of this nano-composite to the implantation parameters. We identified the optimal implantation parameters for which an implanted electrode presents an exceptional combination of high electrical conductivity and low compliance.