Mathias Link

Solidly mounted ZnO shear mode film bulk acoustic resonators for sensing applications in liquids

Solidly mounted film bulk acoustic resonators (FBAR) operating at 850 MHz in the shear vibration mode have been fabricated. C-axis inclined zinc oxide (ZnO) thin films realized by modified reactive magnetron sputtering were used. Coupling factors k/sup 2/ of 1.7% and Q-factors of 312 were determined in air. Q-factors of 192 were measured in water, making these devices attractive for sensing applications in liquids, e.g., biosensing.

Investigation of the scaling rules determining the performance of film bulk acoustic resonators operating as mass sensors

Solidly mounted (SMR-type) thin film bulk acoustic resonators operating at 2.2, 4.1, and 8.0 GHz and with lateral extents from 30 to 500 mum were fabricated and their performance as mass sensors was evaluated theoretically as well as experimentally. It was found that increasing the frequency leads to a principally improved performance of these devices. Problems arising for the horizontal as well as the vertical dimension and structure are investigated

Anwendungspotenzial integrierter Dünnschichtresonatoren in flüssigen und gasförmigen Medien (Application Potential of Integrated Thin Film Resonators in Liquid and Gaseous Media)

Integrierte bulk-akustische Dünnschichtresonatoren, sogenannte Film Bulk Acoustic Resonators (FBARs), eignen sich hervorragend für eine Vielzahl von Sensoranwendungen in gasförmigen und unter bestimmten Voraussetzungen auch flüssigen Medien. Analog zur klassischen Quarz-Mikrowaage wird eine Verschiebung der akustischen Resonanz, beispielsweise durch eine Massenanbindung, detektiert. Der entscheidende Vorteil des FBAR liegt in der Realisierbarkeit integrierter Arrays mit einer Vielzahl von Resonatoren, was den Einsatz für komplexe Messaufgaben, beispielsweise in medizinischen Anwendungen, ermöglicht. Neben der gravimetrischen Detektion besteht die Möglichkeit zur Detektion von mechanischen Spannungen und auch zur Messung von Viskositäten des Umgebungsmediums. In diesem Artikel werden Ergebnisse zu Untersuchungen des FBAR für eine Reihe potenzieller Anwendungen vorgestellt und bewertet. Integrated Film Bulk Acoustic Resonators (FBARs) are suitable for various sensor applications in gaseous and under certain circumstances also liquid surroundings. Analogously to the classic quartz crystal microbalance (QCM) a shift of the acoustic resonance frequency, e. g. due to a mass attachment is detected. The distinct advantage of FBARs is based on the feasibility of integrated arrays with numerous resonators which makes it suitable for complex measurement tasks, e. g. in medical applications. Besides the gravimetric detection it is also possible to detect mechanical stress and measure viscosities of the surrounding liquid. In this article results are presented and evaluated concerning investigations of the FBAR with respect to potential applications.

High Frequency Viscosity Sensing with FBARs

Film bulk acoustic resonators operating in thickness shear mode at a frequency of 720 MHz are used to characterize liquids with different viscosities. Their advantage over QCM devices are higher packaging density, CMOS-compatibility as well as lower production costs. Sensor response corresponds with theoretical models in the low viscosity regime but deviates strongly for higher viscosities. This behavior is analyzed as well as an assessment of the FBAR as a viscosity sensor is made