Structural and electrical properties of MnO films grown by pulsed laser deposition

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Structural and electrical properties of MnO films grown by pulsed laser deposition


Author: Sin, Wai-lun
Title: Structural and electrical properties of MnO films grown by pulsed laser deposition
Degree: M.Phil.
Year: 2004
Subject: Hong Kong Polytechnic University -- Dissertations
Manganese compounds
Pulsed laser deposition
Thin films -- Surfaces -- Magnetic properties
Thin films, Multilayered -- Magnetic properties
Department: Dept. of Applied Physics
Pages: xviii, 136 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Manganese monoxide (MnO) thin films of pure rock salt structure were prepared on single crystal MgO(001) and TiN buffered silicon(001) substrates by pulsed laser deposition method using dense ceramic Mn3O4 targets. In general, single phase MnO films were obtained at low ambient oxygen pressure of <10-4 Torr. Structural characterization by X-ray diffraction (XRD) showed that the MnO films started to crystallize at growth temperature as low as 200C. Progressively improved crystalline structure and orientation were seen at higher deposition temperatures. XRD 360o-phi scans revealed epitaxial relationships of (001)MnO||(001)TiN||(00l)Si and (001)MnO||(00l)MgO for MnO films grown at low substrate temperature of 300 C. MnO films of excellent structural quality were obtained at 600C and under a base pressure of 2xl0-5 Torr. In the case of MnO/TiN/Si, higher deposition temperature, however, caused structural deterioration in the MnO films due to chemical interdiffusion across the interface and oxidation of the TiN sub-layer. The electrical properties of the epitaxial MnO films integrated with Si were examined by depositing platinum spot electrodes to form a Pt/MnO/TiN/Si capacitor structure. MnO films grown at optimum condition yielded a room temperature dielectric constant of 17.4 with a dissipation factor as small as 0.049 at 10 MHz. They exhibited dielectric constant similar to that of bulk MnO single crystal. The correlation between leakage current and film thickness was also investigated. With an E-field of 1x105 V cm-1 applied across the MnO film, the leakage current decreased from 78.6 to 1.17x10-8 A cm-2 for a film thickness change from 37 nm to 450 nm. Resistivity versus temperature measurements revealed that the MnO films had a semiconducting transport behavior. Films deposited on MgO substrate exhibited a hopping energy of 0.51 eV and a thermal coefficient of resistivity that varied from -5.5 to -2.4 % K-1 for different deposition pressure. Electrical measurements thus showed possible applications of MnO films as negative temperature coefficient (NTC) thermistor. Heteroepitaxial structures of Au/MnO/TiNIMgO(111) were also prepared. Electrical measurements on these heterostructures at temperature from 80 K to 310 K showed no obvious dielectric anomaly as those observed in bulk samples. This deviation was partially attributed to the stress and asymmetric interface nature of the thin film. Mixed-metal monoxides of composition of MnxCo1-xO were fabricated too. Structural and electrical conduction of epitaxial films with 0<x<1 were studied. The lattice parameters of these films were tuned from 0.426 nm to 0.441 nm according to Vegard's law based on the mole ratio (x). The structural measurement showed possible applications as template for strain layer growth.

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