In micro-/nanomachined devices and systems, aluminum nitride (AlN) thin films are widely used due to their piezoelectric properties. This work evaluates the potential of modifying the interface between the AlN thin film and the silicon (Si) wafer serving as bottom electrode for optimized crystallographic orientation and, hence, improved electrical and piezoelectric properties. The films were analyzed using temperature-dependant leakage current measurements, transmission electron microscopy, and x-ray diffraction. By preconditioning of the Si substrate surface applying sputter etching prior to film deposition, leakage current levels are substantially decreased and an increased (002) orientation of the AlN grains is observed.
Molybdenum and molybdenum nitride thin films are presented, which are deposited by reactive dc magnetron sputtering. The influence of deposition parameters, especially the amount of nitrogen during film synthesization, to mechanical and electrical properties is investigated. The crystallographic phase and lattice constants are determined by x-ray diffraction analyses. Further information on the microstructure as well as on the biaxial film stress are gained from techniques such as transmission electron microscopy, scanning electron microscopy and the wafer bow. Furthermore, the film resistivity and the temperature coefficient of resistance are measured by the van der Pauw technique starting from room temperature up to 300 °C. Independent of the investigated physical quantity, a dominant dependence on the sputtering gas nitrogen content is observed compared to other deposition parameters such as the plasma power or the sputtering gas pressure in the deposition chamber.
Piezoelectric silicon micro-machined resonators triggered in the two-dimensional roof-tile shaped mode exhibit exceptionally high quality factors even in highly viscous liquids. In combination with an all-electric readout, this enables precise measurements in liquid media with high output signals, if the electrode design and the anchor geometry are tailored to match the selected order of the rooftile shaped mode. This paper provides an overview of this promising class of resonator modes for micro-electromechanical systems (MEMS) and highlights three application scenarios. In the food industry, the MEMS sensor can be used to monitor the fermentation process in wine by tracking the density and hence, the concentration of ethanol. In technical lubricants, the concentration of ferrous particles can be monitored by integrating a magnetic actuator on the resonator. Finally, even in highly viscous bitumen, the MEMS sensor is successfully used to measure the viscosity of this material.
Piezoelektrische AlN-basierte MEMS-Resonatoren für hochgenaue Messungen in Flüssigkeiten.Piezoelektrische, durch Mikrofabrikation hergestellte Siliziumresonatoren, die in 2D-"Wellblech"-Schwingungsmoden angeregt werden, weisen selbst in hochviskosen Flüssigkeiten außergewöhnlich hohe Qualitätsfaktoren auf. In Kombination mit einer vollständig elektrischen Anregung und Auslesung ermöglicht dies präzise Messungen in flüssigen Medien mit hohen Ausgangssignalen, wenn das Elektrodendesign und die Ankergeometrie auf die ausgewählte Ordnung der "Wellblech"-Mode abgestimmt sind. Dieser Artikel bietet einen Überblick über diese vielversprechende Klasse von Resonatormoden für mikroelektromechanische Systeme (MEMS) und zeigt drei Anwendungsszenarien auf. In der Lebensmittelindustrie kann der MEMS-Sensor verwendet werden, um den Fermentationsprozess in Wein durch Verfolgung der Dichte und damit der Ethanolkonzentration zu überwachen. In technischen Schmierstoffen kann die Konzentration von Eisenpartikeln durch Integration eines magnetischen Aktuators auf dem Resonator überwacht werden. Abschließend kann der MEMS-Sensor auch in hochviskosem Bitumen erfolgreich zur Messung der Viskosität dieses Materials eingesetzt werden.
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