Candidate
Geoffrey Lee
Title
Design, Fabrication and Validation of a CMOS-MEMS Kelvin Probe Force Microscope
Supervisor
Abstract
The Kelvin Probe Force Microscope (KPFM) is a type of scanning probe instrument that is used to discern the different work functions of a sample. A sharp probe at the end of a cantilever is lowered onto a substrate where electrostatic forces, caused by the difference in work function cause the cantilever to oscillate at the modulated frequency. Using this instrument, high resolution images can be obtained, mapping the surface electronic characteristics. However, developments of this instrument have generally been limited to obtaining higher resolution images as well as reducing noise in the output, limiting the widespread appeal of this expensive instrument. There exist many applications where extremely cheap, low footprint and easy-to-use KPFMs would be beneficial.
In this work, a microelectromechanical system (MEMS) based KPFM is designed, fabricated and validated using a CMOS-MEMS process. Designed following similar characteristics of a generic KPFM cantilever, the stiffness, length, resonant frequency and tip characteristics can be mimicked closely. Piezoresistive strain gauges are used to replace the optical sensing system, and bimorph actuators are used to create a fine adjusting stage. Tip modification methods such as electroless plating can be applied in order to increase hardness, and decrease the rate of oxidation.
The CMOS-MEMS KPFM is validated through testing. The characteristics obtained from the scans closely resemble that of the generic KPFM; the work functions of differing materials can be relatively traced. The advent of this device allows for the miniaturization of the KPFM into a simpler and cheaper instrument.