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

• Published in: Applied surface science 2007-09, Vol.253 (22), p.9039-9045
• Main Authors: Gupta, Nutan, Kashyap, Subhash C., Dube, D.C.
• Format: Article
• Language: English
• Subjects: AFM; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Dielectric behavior; Electrical properties of specific thin films; Electrical properties of specific thin films and layer structures (multilayers, superlattices, quantum wells, wires, and dots); Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Lithium ferrite; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Microwave behavior; Nanocrystalline; Physics; Spin-deposition; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Thin films
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2007.05.038

Thin films of lithium ferrite (with general composition Li 0.5Fe 2.5O 4) were fabricated at low temperatures (up to 650 °C) 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 °C. 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 °C) annealing temperatures. Significant decrease in complex dielectric permittivity ( ∈′ − j ∈″) with frequency is observed in the low frequency (100 Hz–1 MHz) as well as in X-band microwave frequency (8–12 GHz) region. ∈′ 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, ∈″ 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 10 6–10 8 Ω cm. These results strongly suggest that citrate-route processed nanocrystalline lithium ferrite thin films are promising candidates for monolithic microwave integrated circuits (MMICs).