STRUCTURAL AND ELECTRICAL PROPERTIES OF CaCu3Ti4O12 THIN FILMS AND THEIR APPLICATIONS

Abstract

In this research, the effects of Fe-doping on structural and gas-sensing properties of CaCu3Ti4O12 (CCTO) thin film prepared by a sol–gel methodwere systematically studied. Sol–gel-derived CCTO thin films with different concentrations of Fe-doping were deposited on alumina substrates by spin-coating technique and Au/Cr interdigitated electrodes were patterned onto the films by photolithography, sputtering and lift-off processes. Characterizations by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, X-ray photoemission spectroscopy (XPS) confirmed the perovskite CCTO phase with TiO2 and CuO secondary phases and suggested the substitution of Fe3+ ions at Ti4+ sites of CCTO structure. From gas-sensing measurements, Fe dopants greatly enhance H2S response, response time and H2S selectivity against NH3, CO, C2H2, CH4, ethanol and NO2. In particular, 9 wt% (∼3 at%) Fe-doped CCTO sensor exhibited the highest response of ∼126 to 10 ppm H2S, which was more than one order of magnitude higher than that of the undoped CCTO sensor at a low optimum operating temperature of 250 oC. The roles of Fe-dopant on gas-sensing mechanisms of CCTO sensor were proposed. Furthermore, highly-oriented CaCu3Ti4O12 (CCTO) thin films have been deposited successfully on LaAlO3(100), NdGaO3(100) and NdGaO3(110) substrates using a sol-gel method. These substrates were chosen in terms of small lattice mismatch between CCTO and the substrate. The X-ray diffraction patterns showed that the CCTO film layers grow with the c-axis perpendicular to the substrate surface. The plane view and cross sectional FE-SEM images showed a smooth and crack-free surface throughout the film with large grains and dense packing. The interface between the CCTO film and the single crystal substrate was sharp. In this experiment, it was shown that the preferred orientation of CCTO thin films can be manipulated by growing on various types of substrates and different substrate orientations without any conducting buffer layers. The correlation between the preferred orientations of the films and their dielectric properties were also reported.