A MEMS Nanopositioner With Integrated Tip for Scanning Tunneling Microscopy

Abstract

Slow Z-axis dynamics of Scanning Tunneling Microscope (STM) is a key contributing factor to the slow scan speed of this instrument. A great majority of STM systems use piezotube nanopositioners for scanning. The piezotube bulkiness along with the mass of STM tip assembly restrict the overall Z-axis bandwidth of the system to about 1 kHz. This limited bandwidth slows down the STM response to the sample topography changes. In this paper, we report a microfabrication process to build a Microelectromechanical-System (MEMS) nanopositioner for Z-axis positioning in STM with a tenfold bandwidth, and a similar range of motion. The MEMS device features an integrated nanometer-sharp in-plane Si tip, compatible with conventional batch fabrication processes. In addition, a novel electrical isolation technique is developed to electrically isolate the tip from the rest of this device. This enables us to provide a separate routing for tunneling current signal, enabling potential applications in parallelism. The fabricated MEMS device achieves 1.6 μm motion with its first in-plane resonance beyond 10 kHz. The capability of this MEMS nanopositioner to replace the Z-axis of STMs is demonstrated through establishing controlled and stable tunneling current on a graphite sample in ambient conditions. [2020-0345]