ICMCTF2001 Session H4-2: Novel Materials and Processes

The polymeric membranes are commercially used for gas separation. The important parameters for their commercial application are good permeabilities and permselectivities. These parameters have a strong dependence on the free volume hole properties of the material.paragrphThe membranes alone are generally not suitable when high product purity and recovery is desired. However, the titanium coated polymeric membranes can effectively solve the problem. Hydrogen molecules when diffuse through metals like titanium and paladium break into atomic form and recombine upon recovery. The binding of the metalic clusters on the polymeric material is improved by heat treatment and swift heavy ion bombardment.

The purity of the permeat gas i.e. hydrogen is estimated by the measurement of decrease in the permeabilties of other gases present in the mixture.

Results of the study of the permeation properties of polycabonate films coated with 50-100Å thick titanium film show increase in the purity of hydrogen.

Cobalt Ferrite thin films have large scale technological applications as catalyst, magnetic recording media, ferrofluids and in microwave devices. All the methods that have been used to sysnthesis of ferrite thin films often require a high degree sophistication and control and substrate heating during and/or after deposition of the films to obtain the desired characteristics properties in thin film form. An alternative method of producing thin film ferrite by a simple technique will be well received. Wet chemical methods such as electroless and/or electrochemical techniques appear to be an attractive method.

This paper reports formation of cobalt ferrite thin films using electrochemcial route. Electrodeposition of CoFe₂ alloy from simple aqueous and nonaqueous sulfate bath was carried out onto various conducting substrates such as tainless steel, brass, copper, titanium and FTO coated glass. The desired thickness was obtained at I1N KOH electryolyte. AAS, XRD, IR absorption and SEM techniques were used for compositional, structural and surface morphological studies. By forming metal-oxide-metal (MOM); cooper-oxide-copper, effect of temperature and frequency on dielectric and conducting properties were studied. The films are nanocrystalline with spinel structure and uniform surface and having low dielectric constant and high electrical resistivity. Thus the feasibility of obtaining cobalt ferrite thin films by electrochemical route is studied.

Formation of Ti/Al₂O₃/Si multilayered nanostructure was developed. A two-chamber ultra-high vacuum technological unit allowed us to fabricate the structure in single cycle. A 4 inch n-type Si wafer with resistivity 0.01 Ωcm was used as a substrate. The first chamber was used for laser evaporation of Al₂O₃ to form 20 nm gate insulator. In the second camber Ti film 8 nm of thick was deposited onto the insulator film.

Conditions (substrate temperature and deposition velocity) were determined on the basis of a volumetric agreement principle. The principle allowed us to form both of Ti/Al₂O₃ and Al₂O₃/Si interfaces with low concentration of surface states.

After formation of the sandwich nanostructure a standard photolitography processing was used to form narrow (1 µm of width)and long (10 µm of lenght)pattern of the Ti film. Al contacts with area of 20x20 µm were formed at the ends of the Ti pattern.

To fabricate channel of a creating field effect transistor we used a technique of SPM tip-induced nanoxidation of the Ti film. Regimes of the nanooxidation were optimized on the basis of a model wich describes the tip-induced oxidation kinetics. Influence of the Ti film thickness and electrical regimes of the oxidation on the resolution, reproducibility and productivity was disscussed. The nanooxidation technique allowed us to form the transistors with TiO₂ channel 8, 10, 20 nm of width and 1 µm of length. The Si substrate with ohmic contact on the back-side was a gate electrode.

Electrical measurements allowed o investigate physical characteristics of the nanoscale transistors. It was shown that developed technological technique is suitable for fabrication of single-electron devices.