Properties of evaporated titanium thin films and their possible application in single electron devices

The influence of the deposition rate of titanium thin films on their microscopic structure has been investigated by transmission electron microscopy, X-ray diffraction analyses and atomic force microscopy. Furthermore, the resistivity of the films has been characterized by van der Pauw measurements in a temperature range of 5-300 K. Titanium films with a thickness of 10 nm evaporated with a rate of 1 Å/s showed the typical and well known temperature dependency of the resistivity (i.e. decreasing resistivity with falling temperature). In contrast, the resistivity of thin films deposited with a rate of 0.2 Å/s rises with decreasing temperature. Additionally, the resistivity of the films evaporated with the lower rate rises significantly when reducing their film thickness down to 3 nm. Due to this increase of the resistivity we are able to present an alternative and relatively simple approach for the fabrication of single electron transistors (SETs). The presented SET design is based on the evaporated thin titanium films with a deposition rate of 0.2 Å/s onto well defined trenches previously etched into a dielectric layer of thermally grown silicon dioxide. The tunnel junctions originate from a local increase of the resistance of the metallic wire at the edges of the trenches. The devices fabricated in this manner with lateral dimensions in the 50-100 nm range show clear SET features at an operating temperature of up to 77 K. Additionally, the influence of background charges on the Coulomb oscillations in this devices are demonstrated and discussed in comparison with simulated data.