Developments of Low-Temperature Solution Processing for Nanostructured Titania Dielectric Films

We explored two low-temperature processing pathways, namely, (1) thermohydrolytic chemical bath deposition (CBD) and (2) cathodic electrodeposition (ED), to deposit dielectric thin films of titania on Si, fluorine-doped tin oxide (FTO)-coated glass and copper substrates. In CBD technique, films were grown from aqueous solution bath of titanium tetrachloride at 70 degrees C, whereas ED films were deposited from peroxotitanium mixed solvent electrolyte at near 0 degrees C by application of an electrochemical potential. In particular, the latter process has been developed to deposit the dielectric films on metallic substrates. Nanocrystalline films with distinctly different micro-/nanostructures and phases (e.g., anatase and rutile) at various precursor supersaturations were obtained in CBD processes. In contrast, microstructures consisting of mostly amorphous films embedded with nanocrystallites of a rutile phase were obtained from ED processes at different durations of deposition time. Further, Fourier transform infrared (FTIR) spectra show the presence of peroxo bonds in ED films in addition to Ti-O and Ti-OH bonds that appear in CBD films. Dielectric constants ranging from 22 to 35 for CBD films and from 12 to 20 for ED films at 100 kHz were achieved without any post-deposition annealing treatments. This result indicates the potential for using these low-temperature solution processes in fabricating the capacitor structure in embedded passive and flexible electronics technologies that have a strict requirement for low process temperature and low manufacturing cost.