Spin-deposited nanocrystalline lithium ferrite thin films: Fabrication and characterization

Thin films of lithium ferrite (with general composition Li0.5Fe2.5O4) were fabricated at low temperatures (up to 650 8C) by citrate-route using spin-deposition technique. Deposited films consisted of nanometer-sized grains as evidenced by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. XRD patterns for annealed films showed broad peaks exhibiting a spinel phase. Size of nanocrystallites is estimated to be 3–7 nm using Scherrer’s equation. Average grain size 8.5 nm is observed from TEM images of films annealed at 650 8C. Scanning electron micrographs show the formation of spherical aggregates of around 130 nm in diameter. The AFM analysis clearly evidenced the development of nanograins even at low ( 500 8C) annealing temperatures. Significant decrease in complex dielectric permittivity (20 j200) with frequency is observed in the low frequency (100 Hz–1 MHz) as well as in X-band microwave frequency (8–12 GHz) region. 20 is found to be in the range of 15.7–33.9 in low frequency region, whereas in X-band microwave frequency region, it is found to lie between 3.9 and 4.9. Similarly, 200 is found to be 0.16–5.9 in the low frequency region, and 0.002– 0.024 in the X-band microwave frequency region. Room temperature dc resistivity of these films is estimated to lie in the range of 106–108 V cm. These results strongly suggest that citrate-route processed nanocrystalline lithium ferrite thin films are promising candidates for monolithic microwave integrated circuits (MMICs).