A Feedback Controlled MEMS Probe Scanner for On-chip AFM

Abstract

Atomic force microscope (AFM) provides a unique possibility in nanoscience research and development for interrogation and manipulation of matter at nanoscale. Miniaturization of AFM significantly reduces the manufacturing cost and breaks the barrier to widespread adoption of this scientific instrument. This paper presents the characterization and control of a novel microelectromechanical system (MEMS)-based AFM. For in-plane motion, the device is equipped with a micro stage with integrated electrostatic actuators and electrothermal sensors. For use in taping-mode AFM imaging, a microcantilever is embedded within the device, featuring a piezoelectric layer for actuation. Positive position feedback (PPF) controller is used to attenuate the highly resonant dynamics of the stage. Scanning performance of device is evaluated by tracking a raster pattern where a 50 Hz triangular signal is applied to the actuators along the X axis. To reduce the tracking error, turnaround points of triangular signal are smoothed by using an optimization method. Moreover, the closed-loop bandwidth is increased with inversion-based feedforward technique. A 50Hz optimal reference signal combined with an inversion-based feedforward technique results in a fivefold decrease in root mean square of tracking error compared with triangular reference signal.