Novel probe structures for high-speed atomic force microscopy

Abstract

Atomic Force Microscopy (AFM) has become an indispensable metrology tool for nanoscale surface characterization. Today, research and industry demand faster and more accurate metrology and these demands must be met expediently. Traditional AFM cantilevers and associated actuators (i.e. piezoelectric) are limited in regards to actuation speed and resonance frequency presenting the user with an undesired trade-off of speed versus resolution. Based on a pre-existing technology known as the FIRAT (Force Sensing Integrated Readout and Active Tip) AFM probe, this work aims to remedy actuation and response issues by implementing a cantilever-on-cantilever probe as well as a novel seesaw probe. Both cases implement electrostatic actuation, eliminating the need for piezoelectrics while demonstrating large - micron scale - actuation and sensitive displacement detection. These new probe designs can potentially demonstrate a wide bandwidth frequency response (e.g. 100 kHz) ideal for high-speed video-rate imaging. Unlike traditional AFM cantilevers, this is realized by mechanically coupling two physically separate structures to provide a soft resonator sensor atop a stiff actuator structure. Common surface-micromachining techniques are utilized to solve the logistical challenge of fabricating these stacked structures. By manipulating the viscous damping and mechanical mode coupling it becomes feasible to attain the aforementioned desired dynamic characteristics.