Interactions between superconducting YBa₂Cu₃O _7-x and silicon using different buffer layers

Superconducting YBa₂Cu₃O_7-x (YBCO) thin films were deposited on Si substrates using rf magnetron sputtering from a stoichiometric YBa₂Cu₃O_7-x target. Either metallic RuO₂ or insulating yttria-stabilized zirconia (YSZ) was used as a buffer layer to nucleate the superconducting film, and also to prevent interactions between Si and YBCO. The electrical properties of the Si were studied using deep level transient spectroscopy on a structure of metal/SiO ₂ (∼15 Å)/Si diode after removing YBCO and the buffer layer. The introduction of a new deep level in the Si at E_A = E _v + 0.244 eV after YBCO deposition, where YSZ (∼100 nm) was used as a buffer layer, was attributed to Cu after interaction between YBCO and Si. However, this energy level was not found in the Si if RuO₂ was used as a buffer. The degradation of electrical properties of the Si after YBCO deposition places limitations on the choice of buffer layers in order to realize the integration between superconductor and semiconductor as used in passive or hybrid electronic devices.