Q Control of an Active AFM Cantilever with Differential Sensing Configuration

Microcantilevers featuring separate built-in actuation and displacement sensing capabilities allow effective and simple implementation of control methods, opening a pathway to achieving higher scan speeds in tapping-mode atomic force microscopy. Such active cantilevers are a significant milestone to eventually obtain video-rate on-chip atomic force microscopes (AFMs) that can even surpass the functionality and imaging speed of their macroscale counterparts at a significantly lower cost. In this brief, we present an active AFM cantilever with an on-chip actuator and two built-in displacement sensors, designed to be integrated into on-chip AFMs. The common feedthrough problem present in this type of architecture is addressed by a differential sensing configuration, and the revealed dynamics are used for the system identification. A positive position feedback controller is designed to actively tailor the Q factor of the cantilever. The imaging performance of the microcantilever with and without Q control is compared by attenuating the cantilever's Q factor from 177 to 15 using the feedback loop. A common artifact in high-speed scans, the parachuting effect, is mitigated, rendering higher imaging speeds achievable.