Fabrication and characterization of dual AFM probe with narrow-gapped silicon tips and switchable cantilevers with magneto-strictive FePd film actuator

Abstract

This paper presents fabrication and characterization of a dual probe for atomic force microscopic (AFM) in-situ imaging and mechanical operation for cutting of bio-molecules. The dual AFM probe has narrow-gapped twin sharp silicon tips and cantilevers on which Fe60Pd40 magneto-strictive film actuators are stacked for cantilever switching. The two cantilevers were orthogonally located to each other. A 600nm-gapped dual silicon tip was fabricated in a device layer of a silicon-on-insulator (SOI) wafer through a self-aligning etching process based on narrow silicon trench etching, refilling, polish-back, and silicon crystalline anisotropic etching. After the dual silicon tip was formed, a Fe60Pd40 (1μm)/Si (2μm) dual cantilever was successfully formed from the same silicon device layer of the SOI wafer. By applying a static magnetic flux density of 300G along a cantilever, it was successfully deflected to 1μm or larger in the direction of film extension by magneto-striction of the Fe60Pd40 film. In particular, the other cantilever orthogonal to the magnetic flax shows no deflection, resulting in sufficient individual actuation of the dual cantilever for switching. The Fe60Pd40 film was able to generate large magneto-striction above 250ppm even though it was a thin film with a thickness of 1μm.