We report on a novel technique to control the resonance frequency of polymer membranes, without additional external
actuators. An electrostatic force is used to apply compressive stress to a dielectric electroactive polymers membrane,
consisting of a 25 micron thick, 1 to 4 mm diameter, polydimethylsiloxane (PDMS) film bonded onto patterned silicon
or Pyrex wafers. Both sides of the membranes are rendered conductive by low-energy metal ion implantation. Ion
implantation is chosen because it stiffens the membrane much less than sputtering a film of similar thickness [1][2]. The
initial resonance frequency of the membrane is given by its geometry, the Young's modulus and stress of the composite
film. The technique presented here allows tuning the resonance frequency from this initial value down to zero (at the
buckling threshold) by adding compressive stress due to a voltage difference applied to the electrodes on both sides of
the membrane. We have measured a reduction of the first mode resonance frequency of up to 77% (limited by dielectric
breakdown) for ion-implanted membranes [3]. The tuning is repeatable and allows for continuous variation. Excellent
agreement was found between our measurements and an analytical model we developed based on the Rayleigh-Ritz
theory.
The miniaturization of dielectric elastomer actuators requires compliant electrodes that are clean, reliable, and
that can be easily patterned on a mm or μm scale. Carbon-based electrodes, which are commonly used to make large-scale actuators, are not well suited for this application. Metal ion implantation at low energies has, on the other hand, the ability to create compliant and patternable electrode through the creation of nanometer scale clusters in the first tens of nanometers below the elastomer surface. We present the mechanical and electrical properties of metal (Au, Pd, Ti, Cu) implanted electrodes on polydimethylsiloxane, as well as the application of Au-implanted electrode to the fabrication of small-size (∅1.5-3 mm) diaphragm actuators that exhibit vertical displacements up to 25% of their diameter.
This article presents metal ion implantation as an alternative technique to fabricate compliant electrodes for
small-size dielectric elastomer actuators. When reducing the size of these actuators to below 1 cm, the ability
to pattern the electrodes is added to the need for compliance. Metal ion implantation on Polydimethylsiloxane
(PDMS) layers allows the creation of conductive and compliant electrodes, which can be easily defined by
photolithography or with a shadow mask. Mechanical testing show that implantation has a limited impact on
the PDMS' properties, with a Young's modulus increase of 50%-200% depending on the dose. Uniaxial stretching
tests show that conductivity is conserved for strains up to 50% and present no hysteresis. Dielectric breakdown
tests were conducted for Au and Pd implantations, which exhibited high breakdown fields (> 100V/μm), similar
to non-implanted PDMS layers. Other advantages of ion implanted electrodes include transparency and a
negligible mass. Buckling mode diaphragm actuators were fabricated with ion-implanted electrodes and exhibited
out-of-plane displacements up to 7% of their lateral dimensions.
We report on the use of the bulge test method to characterize the mechanical properties of miniaturized buckling-mode dielectric elastomer actuators (DEA). Our actuator consists of a Polydimethylsiloxane (PDMS) membrane bonded to a silicon chip with through holes. Compliant electrodes are fabricated on both sides of the membrane by metal ion implantation. The membrane buckles when a critical voltage is applied to the electrodes. The maximum displacements as well as the efficiency of such actuators strongly depend on the mechanical parameters of the combined electrode-elastomer-electrode layer, mainly effective Young's modulus E and residual stress &sgr;. We report measured E and &sgr; obtained from bulge tests on PDMS membranes for two PDMS brands and for several different curing methods, which allows tuning the residual stress by controlling the rate of solvent evaporation. Bulge test measurements were then used to study the change in membranes' mechanical properties due to titanium ion implantation, compared to the properties obtained from depositing an 8 nm thick gold electrode. At the doses required to create a conductive layer, we find that the Ti ion implantation has a low impact on the membrane's overall rigidity (doubling of the Young's modulus and reducing the tensile stress) compared to the Au film (400% increase in E). The ion implantation method is an excellent candidate for DEAs' electrodes, which need to be compliant in order to achieve large displacements.
The microtribometer fabricated is designed to observe the wear of removable flat silicon test inserts, coated with thin film layers such as DLC and moving in an oscillating manner relatively to each other. For observing the low wear of DLC layers in a reasonable amount of time, high oscillating speed is essential and can be achieved by reducing the mass in motion. The silicon microtribometer reaches oscillating frequencies of 10 Hz while applying a normal force on the test inserts up to 9.6 N, the maximal displacement amplitude being 1.5 mm. The two silicon main parts of the microtribometer guide test inserts along one direction in a back and forth motion while avoiding any side friction, the actuation being done by an external linear motor. For such application crystalline silicon presents, compare to other materials, the advantage of the invariance of its behavior over time.
A high-speed Ta-Si-N gas microvalve has been designed, fabricated and characterized. Ta-Si-N has a unique combination of electrical and mechanical properties suitable for robust high performance MEMS devices. The valve reported here represents the first working MEMS device integrating a sputtered Ta-Si-N layer, for use at differential pressures greater than 2 bar and capable of achieving controlled flow-rates under pulse width modulation (PWM). Previously reported, electrostatically actuated microvalves (3,4,5) were limited to operating pressures less than 200 mbar, and their switching behavior was not studied. The valve is based on a surface micromachined Ta-Si-N membrane that closes a deep reactive ion etched hole. The valve was optimized to achieve a low actuation voltage and fast commutation. This study focuses on the characterization of the switching behavior of the valve membrane and its influence on the flow-rate.
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