Abstract: Ultra-fine oxidized titanium (TiOx) lines are formed on the surface of a titanium (Ti) layer by an atomic force microscope (AFM) tip acting as a selective anodization electrode.The Ti layers are about 3nm thick on the GaAs substrates and are formed by magnetron sputtering.The Ti-TiOx-Ti construction forms a metal-insulator-metal tunneling junction,which is the basic structure of the ultra-fast photoconductive switch.The TiOx works as an energy barrier for the electrons.In order to illustrate the effect of the TiOx line width on the tunneling and to determine the narrowest TiOx line as well as the conditions under which it can be formed without leading to the breakdown of the tunneling junction,TiOx lines with widths of 15.6,34.2,and 46.9nm are fabricated by changing the ambient humidity while keeping the scanning speed,oxygen concentration,and applied voltage fixed.The I-V characteristics of tunneling junctions with different widths are measured.The results indicate that the narrowest TiOx line with a width of about 10nm, can be fabricated between the two electrodes of the ultra-fast photoconductive switch when the voltage between the two electrodes is 6V without leading to the breakdown of the tunneling junction.

Key words: FM tip induced anodic oxidation, Ti oxidation wires, tunneling junction, ambient humidity, ultra fast photoconductive switch