Q Control of an AFM Microcantilever With Double-Stack AlN Sensors and Actuators

Active Atomic Force Microscope (AFM) cantilevers with integrated actuator/sensor pairs display larger feedthrough than conventional base excited cantilevers operating in conjunction with optical displacement sensors. To control the Q factor of a cantilever, this feedthrough needs to be canceled or significantly reduced. We use an AFM microcantilever with a double-stack sensor/actuator pair to address the feedthrough cancellation problem. Our device provides two sensor signals: one used for displacement sensing and the other for velocity measurement, with the latter being used for feedback. A readout circuit is designed to sense the displacement signal and to implement the velocity feedback controller. With this method, we were able to reduce the Q factor from 390 to 30.