No abstract

Electrowetting on dielectric is demonstrated with a thin spin-coated fluoropolymer over an aluminum electrode. Previous efforts to use thin spin-coated dielectric layers for electrowetting have shown limited success due to defects in the layers. However, when used with a citric acid electrolyte and anodic voltages, repeatable droplet actuation is achieved for 5000 cycles with an actuation of just 10 V. This offers the potential for low voltage electrowetting systems that can be manufactured with a simple low-cost process

Abstract. SiC is a candidate material for micro-and nano-electromechanical systems (MEMS and NEMS). In order to understand the impact that the growth rate has on the residual stress of CVD-grown 3C-SiC hetero-epitaxial films on Si substrates, growth experiments were performed and the resulting stress was evaluated. Film growth was performed using a two-step growth process with propane and silane as the C and Si precursors in hydrogen carrier gas. The film thickness was held constant at ~2.5 µm independent of the growth rate so as to allow for direct films comparison as a function of the growth rate. Supported by profilometry, Raman and XRD analysis, this study shows that the growth rate is a fundamental parameter for low-defect and low-stress hetero-epitaxial growth process of 3C-SiC on Si substrates. XRD (rocking curve analysis) and Raman spectroscopy show that the crystal quality of the films increases with decreasing growth rate.From curvature measurements, the average residual stress within the layer using the modified Stoney's equation was calculated. The results show that the films are under compressive stress and the calculated residual stress also increases with growth rate, from -0.78 GPa to -1.11 GPa for 3C-SiC films grown at 2.45 and 4 µm/h, respectively. IntroductionSilicon Carbide (SiC) has long been recognized as an excellent material for high-power, highfrequency and high-temperature electronics due its outstanding electrical and thermal properties. SiC is now receiving added attention for its potential applications in micro-and nanoelectromechanical systems (MEMS and NEMS) due its exceptional electrical, mechanical and chemical properties as compared with silicon (Si), which is currently the leading material in these technology areas.Among the polytypes of SiC, cubic SiC (i.e., 3C-SiC) possesses unique properties, such as high electron drift velocity, which is more suitable for high-frequency power devices [1]. However the most important property of 3C-SiC is that it can be grown on large diameter Si substrates, which makes it very suitable for many industrial applications. The large area substrates offer the possibility for low-cost batch processing, which makes SiC more attractive for sensor and device applications. The heteroepitaxy of SiC on Si substrates results in the 3C-SiC/Si hetero-system, which is also a very interesting material system by itself [2].Unfortunately, due to high residual stresses (which normally arrise during the growth process) and crystal defects stemming from the large lattice constant mismatch and the thermal expansion coefficient difference between SiC and Si, the use of SiC in Si-based MEMS fabrication techniques has been somewhat limited. The resulting stress relaxation has important implications with regard to processing, epitaxial quality, and the properties of films and coatings that undergo large temperature fluctuations [3]. Therefore, it is necessary to reduce and control the residual stress in 3C-SiC films for the design and performance of MEMS devices.

To understand the impact that the growth rate has on the residual stress of chemical vapor deposition-grown 3C-SiC heteroepitaxial films on Si substrates, growth experiments were performed. The film thickness was held constant at ;2.5 lm independent of the growth rate so as to allow for direct film comparison as a function of the growth rate. Stress analysis performed by profilometer curvature measurement, livqo-Raman shift analysis and micro-machined freestanding structures, show an apparent disagreement about the stress nature. This incongruity between the experimental data can be explained assuming a strong stress field located in the substrate related to defects generated in the silicon during the growth process.

At the millimeter scale, interactions between floating and semi-immersed objects are significant. The local curvature of the interface is modified by the weight/buoyancy forces of floating objects, and by the surface properties of semi-immersed objects. The curvature changes generate attractive (or repulsive) interactions between floating parts, and semi-immersed objects.This work demonstrates how electrowetting can manipulate these interactions in order to position, align, assemble and transport parts attached to the fluid interface. This demonstrates one way in which fluid interfaces can provide an alternative to standard pick and place technology for part positioning/assembly. Typically, the part/rod forces are purely attractive or repulsive, but under some conditions, floating objects reach a stable equilibrium with a finite gap between the floating and semi-immersed bodies. Stable equilibrium positions were measured for rectangular prisms suspended on a water/oil interface and a fixed cylindrical rod. Measurements showed that the equilibrium position depends on the ratio of ∆ where t is the part thickness; w is its width, and  the part/fluid density difference. The stable equilibrium position provides for repeatable positioning without risk of parts sticking to the semi-immersed bodies.