Low temperature amorphous growth of semiconducting Y-Ba-Cu-O oxide thin films in view of infrared bolometric detection

YBa2Cu3O6+x (YBCO) compounds are well known to exhibit superconducting properties for x>0.5 and semiconducting properties for lower oxygen content. In this work, YBCO oxide thin films of the semiconducting phase were deposited by direct-current (DC) hollow cathode sputtering at low temperature in the 100 to 400 degrees C range. Structural, electrical and optical properties are investigated and discussed in relation with the envisaged bolometric detection application. Structural characterizations show that films are amorphous, with a granular structure of low roughness (3 nm rms). DC electrical measurements both reveal that films grown at 100 degrees C exhibit a high temperature coefficient of resistance (TCR similar to -3%K-1 to e-4%K-1 at 300 K) and an optimized low resistivity value of 345 Omega.cm at 300 K. Consequently, this material is suitable for uncooled infrared bolometer application and can be deposited at 100 degrees C in a complementary metal-oxide-semiconductor compatible technological process for co-integration with readout circuitry. In addition, optical measurements performed in the 0.5 to 2.2 mu m wavelength range on films grown at 100 degrees C highlight optical conductivity values in line with those expected for YBCO material, as well as the presence of two optical band gaps that are discussed with respect to the film nanostructure. (C) 2011 Elsevier B.V. All rights reserved.