AVS 47th International Symposium
    Magnetic Interfaces and Nanostructures Monday Sessions
       Session MI-MoA

Paper MI-MoA10
Effect of Composition and Microstructure on Temperature Coefficient of Resistance of Polycrystalline La1-xCaxMnO3 Thin Films

Monday, October 2, 2000, 5:00 pm, Room 206

Session: Thin Films and Multilayers
Presenter: C.-H. Lai, National Tsing Hua University, Taiwan, R. O. C.
Authors: C.-H. Lai, National Tsing Hua University, Taiwan, R. O. C.
C.-F. Hsu, National Tsing Hua University, Taiwan, R. O. C.
Y.-C. Chin, Chung-Shan Institute of Science and Technology, Taiwan
C.-T. Jiang, Chung-Shan Institute of Science and Technology, Taiwan
Correspondent: Click to Email
Perovskite La1-xCaxMnO3 has drawn much attention on account of the colossal magnetosistance. Due to the sharp resistivity drop around the insulator-metal transition temperature (Tp), epitaxial La1-xCaxMnO3 thin films have been demonstrated to be a promising candidate for IR detector (bolometric) application. In this work, polycrystalline La1-xCaxMnO3 films were deposited by using rf sputtering on Si/SiO2 substrates, and the dependence of the temperature coefficient of resistance (TCR) on the film composition and the structure was investigated. When the temperature is higher than Curie temperature Tc, the resistivity of our polycrystalline La1-xCaxMnO3 films follow the "small palaron model", that is, the resistivity can be expressed as R=BTexp(Ea/kT). Consequently, increasing the activation energy Ea increases the TCR value. By adjusting the Ar/O2 flux during depositions or changing the atmosphere of post-annealing, oxygen content can be manipulated. Because precise oxygen content is difficult to measure, the lattice constant of the films was used for the indicator of relative oxygen contents. When oxygen content increased, the Ea and TCR decreased accompanied with the increase in Tp. Ea and TCR value also decreased with increasing Ca content. ESCA results showed that the ratio Mn4+/Mn3+ increased with increasing oxygen (or Ca) content. Since the carrier transportation of La1-xCaxMnO3 is mainly by hopping along Mn4+-O-Mn3+, the increase in the ratio Mn4+/Mn3+ may imply that hopping probability increases, resulting in smaller resistance and Ea. The surface roughness can significantly increase the resistance but the TCR value is about the same. The resistance reduced with the grain growth but the TCR value maintained constant. The TCR value can reach 3%/K at room temperature.