The proper selection of electrical contact materials is one of the critical steps in designing a metal contact microelectromechanical system ͑MEMS͒ switch. Ideally, the contact should have both very low contact resistance and high wear resistance. Unfortunately this combination cannot be easily achieved with the contact materials currently used in macroswitches because the available contact force in microswitches is generally insufficient ͑less than 1 mN͒ to break through nonconductive surface layers. As a step in the materials selection process, three noble metals, platinum ͑Pt͒, rhodium ͑Rh͒, ruthenium ͑Ru͒, and their alloys with gold ͑Au͒ were deposited as thin films on silicon ͑Si͒ substrates. The contact resistances of these materials and their evolution with cycling were measured using a specially developed scanning probe microscope test station. These results were then compared to measurements of material hardness and resistivity. The initial contact resistances of the noble metals alloyed with Au are roughly proportional to their resistivities. Measurements of contact resistance during cycling of different metal films were made under a contact force of 200-250 N in a room air environment. It was found that the contact resistance increases with cycling for alloy films with a low concentration of gold due to the buildup of contamination on the contact. However, for alloy films with a high gold content, the contact resistance increase due to contamination is insignificant up to 10 8 cycles. These observations suggest that Rh, Ru, and Pt and their gold alloys of low gold content are prone to contamination failure as contact materials in MEMS switches.
Single crystal Fe films were grown on Ge (001) substrates by using dc magnetron sputtering. It was found that the microstructures and magnetic properties of Fe films on Ge substrates were strongly dependent upon the substrate temperature during the deposition process. There existed a narrow substrate temperature window of 125±25°C for achieving single crystal Fe film on Ge. Lower substrate temperature led to polycrystalline Fe films due to limited mobility of Fe atoms, while higher substrate temperatures resulted in amorphous Fe–Ge alloy due to severe interdiffusion.
Tremendous progress has been made on boosting the performance of magnetoelecric sensor to detect low frequency magnetic field signal by frequency multiplication based on magnetolectric composites. In this paper, a novel magnetoelectric sensor based on the laminated Metglas/piezoelectric quartz crystal/Metglas composites structure is presented. The Metglas foils are bonded symmetrically on both sides of the X-cut quartz crystal plate with epoxy. Experiments showed that the ME composites sensor was able to achieved a limit of detection of 11 pT for a low frequency magnetic field 1 Hz without any bias field through frequency multiplication method. The noise power spectrum density of the sensor has also been tested to be 3.93·10-6 V/Hz1/2 at 1 Hz. The results indicate that the proposed sensor has favorable features, which provides a cost-effective and high-performance approach for low frequency magnetic field measurement. Keywords: Low frequency, limit of detection, magnetoelectric sensor, piezoelectric quartz crystal.
This article describes the possibility of electrochemical (EC) detection as an alternative to ultraviolet (C!) detection doing peptide mapping. The high sensitivity and selectivity of the electrochemical detection can be applied to determine some digested peptides. This approach demonstrated that peptides containing electroactive amino acids can be determined by EC detection. Furthermore, upon irradiation, noneiectroactive amino acids and peptides can be made electroactive, thereby increasing the sensitivity and selectivity of peptide mapping. A variety of effects are discussed to help in understanding the possibility of this useful approach.
A finite element contact model of a layered hemisphere with a rigid flat, which includes the effect of adhesion, is developed. This configuration has been suggested as a design for a microswitch contact because it has the potential to achieve low adhesion, low contact resistance, and high durability. Elastic-plastic material properties were used for each of the materials comprising the layered hemisphere. Adhesion was modeled based on the Lennard-Jones potential. The effect of the layer thickness on the adhesive contact was investigated. In particular the influence of layer thickness on the pull-off force and maximum contact radius was studied. The results are presented as load vs. interference and contact radius vs. interference for loading and unloading from different values of the maximum interference.
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