RuO₂/Ru electrode on Si₃N₄/Si substrate for microelectromechanical systems devices based on Pb(Zr _1-xTi_x)O₃ film and surface micromachining

RuO₂/Ru conducting films were deposited on low stress Si ₃N₄/Si substrates by reactive r.f. sputtering deposition at a substrate temperature of 400 °C to introduce a new bottom electrode for microelectromechanical system devices based on a Pb(Zr_1-xTi_x)O₃ film and a surface micromachining technique with high temperature processes. X-ray diffraction and scanning electron microscopy measurements after heat treatment at 700 °C were conducted to investigate structural stability of the RuO₂/Ru films, which showed no silicide and silicon oxide formations by the heat treatment. Interfacial structures of the film with the heat treatment were similar to those of the as-deposited films. The surface of the film with the heat treatment consisted of larger grains than those of the as-deposited film. Rutherford backscattering spectrometry and Auger electron spectroscopy showed no interfacial reactions between the RuO₂/Ru and the Si₃N₄. In order to investigate the feasibility of the RuO₂/Ru as a bottom electrode, Pb(Zr_0.53Ti _0.47)O₃ films were deposited by metalorganic decomposition. After deposition of a Pb(Zr_0.53Ti _0.47)O₃ film at 700 °C for 30 min, the interface structure between the RuO₂/Ru and the Pb(Zr _0.53Ti_0.47)O₃ film showed no interface reactions. The electrical properties of the PZT film on the RuO₂/Ru were not changed before and after an HF etching to make an air gap, even though the piezoelectric coefficients on the RuO ₂/Ru were lower than on the Pt/Ti. Therefore, the RuO ₂/Ru conducting film could be used for a bottom electrode on the Si₃N₄/Si for a microelectromechanical system device based on a Pb(Zr_1-xTi _x)O₃ film and a surface micromachining technique with high temperature processes.