We have successfully designed, fabricated and characterized a micro-cavity fluidic dye laser with metallic mirrors, which can he integrated with polymer based lab-on-a-chip microsystems without further processing steps. A simple rate-equation model is used to predict the average pumping power threshold for lasing as function of cavity-mirror reflectance, laser dye concentration and cavity length. The laser device is characterized using the laser dye Rhodamine 6G dissolved in ethanol. Lasing is observed, and the inRuence of dye concentration is investigated.

Magnetic bead sensors based on the planar Hall effect in thin films of exchange-biased permalloy have been fabricated and characterized. Typical sensitivities are 3 μV/Oe mA. The sensor response to an applied magnetic field has been measured without and with coatings of commercially available 2 μm and 250 nm magnetic beads used for bioapplications (Micromer-M and Nanomag-D, Micromod, Germany). Detection of both types of beads and single bead detection of 2 μm beads is demonstrated, i.e., the technique is feasible for magnetic biosensors. Single 2 μm beads yield 300 nV signals at 10 mA and 15 Oe applied field.

We present a polymer-based mechanical sensor with an integrated strain sensor element. Conventionally, silicon has been used as a piezoresistive material due to its high gauge factor and thereby high sensitivity to strain changes in the sensor. By using the fact that the polymer SU-8 [1] is much softer than silicon and that a gold resistor is easily incorporated in SU-8, we have proven that a SU-8-based cantilever sensor is almost as sensitive to stress changes as the silicon piezoresistive cantilever. First, the surface stress sensing principle is discussed, from which it can be shown that the SU-8-based sensor is nearly as sensitive as the silicon based mechanical sensor. We hereafter demonstrate the chip fabrication technology of such a sensor, which includes multiple SU-8 and gold layer deposition. The SU-8-based mechanical sensor is finally characterized with respect to sensitivity, noise and device failure. The characterization shows that there is a good agreement between the expected and the obtained performance.

ABSTRACT:Shield currents or common mode currents affect coil tuning, coil-to-coil coupling in phased array coils, image inhomogeneity, and most importantly can cause serious patient burns. Traditionally in MRI, shield currents are reduced by cable traps; they consist of a wound coaxial cable inductor tuned to the desired resonance frequency by a capacitor between end turns of the coaxial cable ground shield. This method increases losses and effects the overall phase distance between the coil and the preamplifiers. We present a cable trap that does not connect or solder to the cable and is completely splitable, allowing easy fitting over any cable without affecting any coil parameters (tuning or phase length). Multiple cables can be placed inside the shield current trap to simultaneously attenuate the shield currents from up to eight cables, as currently designed. The shield current trap reduces shield currents at 64 MHz by ϳ30 dB.

A silicon mold used for structuring polymer microcavities for optical applications is fabricated, using a combination of DRIE (deep reactive ion etching) and anisotropic chemical wet etching with KOH + IPA. For polymer optical microcavities, low surface roughness and vertical sidewalls are often needed. This is achieved by aligning the mold precisely to the [110] direction of a silicon (100) wafer and etching very close to the (110) surfaces using a DRIE Bosch process. The surface roughness of the sidewalls is then removed with a short etch in KOH + IPA. To achieve this, the parameters for DRIE and KOH + IPA etch have been optimized. To reduce stiction between the silicon mold and the polymers used for molding, the mold is coated with a teflon-like material using the DRIE system. Released polymer microstructures characterized with AFM and SEM are also presented.

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Stiction is a serious problem in microelectromechanical systems (MEMS) due to their large surface area-to-volume ratio. Stiction is closely related to surface forces, which greatly depend on the materials used, surface topography and surface treatment process. In this paper, we investigate surface energies and stiction of commonly used MEMS materials by contact angle measurements and atomic force microscopy (AFM). Dispersive and polar components of surface energies are calculated by OwensWendt-Rabel-Kaelble method. Silicon and silicon-related materials have higher polar surface energies than SU-8 and polymethylmethacrylate (PMMA), thereby have larger surface energies and enhanced tendency for stiction. The nano-scale adhesion forces between Si 3 N 4 tip and surfaces obtained by AFM further verified that silicon wafer with native oxide has 3-4 times higher adhesion force than SU-8 and PMMA. It has been shown that the materials with higher surface energy have higher sticton/ adhesion forces. The topography of surface influences the contact angle and stiction, and is also discussed in the paper.

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