Vanadium pentoxide is one these promising materials for microelectronic, electrochemical and optoelectronic devices [1]. It is a low mobility semiconductor with a predominantly n-type conductivity.
V2O5 polycrystalline films exhibit multicoloured electrochromism, photochromism and have high potential for the use in electrochromic display devices, colour filters, and other optical devices. V2O5 is a potential candidate for application in thin-film microbatteries and gas sensor. The possibility to reduce V2O5 to lower oxides such as, e.g., VO2 exhibiting a metal-insulator transition (MIT) makes this material even more interesting. Therefore, the working out of lithography methods for V2O5 is of a topical problem.
Amorphous V2O5 films (100-300 nm) were obtained by vacuum thermal evaporation of V2O5 powder onto room temperature substrates (Si and Si/SiO2 plates). UV (402 nm wavelength) modification was performed through a mask in a standard stepper. The irradiation dose was ~20 J/cm2. Development of the modified films was accomplished in the methanol-water (10:1) solution, where the process of development occurred like in a case of a negative resist. Also, development was accomplished in a formic acid-acetone-formalin (15:10:1) solution, where it occurred like in a case of a positive resist. Resolution of the V2O5 resist was determined by the granular structure of the films, which, in turn, depends on the type of the substrate and its temperature. The lines of V2O5 with the width of 8 ìm were obtained and then reduced to VO2 with the conductivity jump of 3 orders of magnitude at the MIT. After deposition of metal contacts onto these lines, devices with electrical switching (S-shaped I-V characteristics) were fabricated.
Thus, in this work the possibility of the use of V2O5 films as UV resists with the following patterning was demonstrated. Also, it was shown that these structures can be transformed into the VO2 phase with the MIT after development.
This work was supported by Svenska Institutet (Dnr:01370/2006), US CRDF grant (award No. RUX0-000013-PZ-06) and by Ministry of Education of Russian Federation.[1] Imada M., Fujimori A., Tokura Y. "Metal-Insulator Transitions" Rev. Mod. Phys.1998, v.70, n.4, p.1059-1263.
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