Fundamental investigations on non-linearity and noise distribution in co-resonantly coupled cantilever sensors with piezoelectric excitation and readout

• Applicant: Professorin Dr.-Ing. Julia Körner
• Subject Area: Microsystems ; Measurement Systems
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413437742

Dynamic-mode cantilever sensors are used as sensitive mass and force sensors for many different applications, e.g. in material characterization and gas sensing. A persisting requirement is the demand for increased sensitivity while maintaining a reliable oscillation detection. To address that challenge, a concept based on co-resonant coupling of a highly sensitive nanocantilever and a microcantilever for detection has been developed. The key aspect of the approach is the eigenfrequency matching between both resonators. Sensor fabrication is one of the main challenges of the concept since (i) the cantilevers are usually very different in their geometric properties and (ii) the eigenfrequency matching requires a precise control of the cantilever dimensions. The development of a batch-fabrication process for monolithic geometrically eigenfrequency matched co-resonant cantilever sensors was the main focus of the current research project. Furthermore, the implications of the co-resonant concept have been studied analytically by a coupled harmonic oscillator model which led to the derivation of effective sensor properties and analytical expression for their estimate. Observations during the theoretical and experimental work conducted in the project raised many new questions with regard to sensor linearity, stability and noise which cannot be answered with the current theoretical knowledge about the complex interplay induced by the co-resonant coupling. However, these are very important considerations for sensor applications. Furthermore, a deeper understanding of the fundamental aspects is not limited to cantilever sensors but can be extended towards basic physical knowledge about coupled harmonic oscillators. Consequently, one focus of the proposed project is on extending the theoretical analysis and modelling, especially with regard to non-linear oscillations, noise and, based on that, consideration for the fundamental limit of detection. The second main aim of the proposed project pertains the expansion of used cases for co-resonant cantilever sensor. So far, they have only be employed in optical detection settings which are rather large and require many additional components. We therefore plan on developing a fabrication process for implementation of a self-sensing/self-actuating co-resonant cantilever sensor by integrating a piezoelectric electrode stack into the microcantilever. This will reduce the microcantilever’s sensitivity as it becomes thicker and stiffer. However, the co-resonant concept offers a unique advantage in that regard, as the overall sensitivity is mainly determined by the nanocantilever’s properties. By combining experimental studies and theoretical modelling, we expect many new fundamental insights into the co-resonant state with regard to (non)linear oscillation behavior and limits of detection for sensing applications, and an evaluation of the suitability of the self-sensing/self-actuation approach for this concept.

• DFG Programme: Research Grants