Preparation and characterization of reactively sputtered conducting Rh oxide thin films

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Rh oxide thin films were prepared by reactively sputtering a Rh metal target in Ar and O_2 mixed gas atmosphere. Influences of sputtering parameters and post-deposition annealing on crystal structure, chemical bonding state and electrical properties of the deposited thin films were studied by X-ray diffraction, X-ray photoelectron spectroscopy and four-point probe method.Conducting RhO_2 thin films were deposited at low substrate temperatures below 100℃, low sputtering power and low sputtering gas pressure using pure O_2 gas. The as-deposited RhO_2 thin films were poorly crystallized and resistivity of about 300 μΩcm was obtained. In order to improve the crystallinity of the films and reduce resistivity, the as-deposited RhO_2 thin films were annealed in oxygen atmosphere. It was found that the crystal grain size of the RhO_2 thin films increased and the resistivity decreased with increasing annealing temperature. The minimum resistivity of 80 μΩcm and positive temperature coefficient of resistivity (TCR), which indicate metallic conduction characteristics, were obtained for the RhO_2 thin films after annealing at 600-700℃ for 1 hour. The minimum resistivity obtained in this study is almost the same with that reported for bulk RhO_2. The RhO_2 thin films were stable up to 700℃ and thermally decomposed to Rh_2O_3 above 750℃. The resistivity of the Rh_2O_3 thin films was larger than 1mΩcm and negative TCR was observed, which indicate semiconducting characteristics of Rh_2O_3.Low resistivity conducting oxides of platinum group metals, such as RuO_2 and IrO_2, are considered to be promising material for capacitor electrodes of dynamic random access memory (DRAM) and ferroelectric RAM (FeRAM). RhO_2 is thought to be applicable to the electronic devices because thin films of RhO_2 with low resistivity (80 μΩcm) were prepared.