MOCVD PROCESS OF FERROELECTRIC LEAD GERMANATE THIN FILMS AND BOTTOM ELECTRODE EFFECTS

摘要

Pb_5Ge_3O_(11) is a new promising candidate for nonvolatile memory such as one-transistor memory applications because of its moderate polarization and relative low dielectric constant. But this material is a low symmetry ferroelectric material and it is said the spontaneous polarization exists only along the c-axis. Furthermore, in the PbO- GeO_2 system, the stability range for the Pb_5Ge_3O_(11) phase is very limited and that even a relatively small deviation in composition or in growth temperature could lead to the formation of other lead germanate compounds. Many methods have been used to grow Pb_5Ge_3O_(11) film. This is the first time the Pb_5Ge_3O_(11) thin film has been successfully grown by advanced MOCVD technique with a liquid delivery system. This paper will discuss the MOCVD process for growing Pb_5Ge_3O_(11) thin films on different electrodes (Pt, Ir and Pt/Ir). The properties of these electrodes, the microstructures of the Pb_5Ge_3O_(11) thin films on these electrodes and their ferroelectric properties will be discussed. The advanced two-step deposition technique has been used to improve the uniformity of the Pb_5Ge_3O_(11) film. Pure c-axis oriented Pb_5Ge_3O_(11) thin film and polycrystalline Pb_5Ge_3O_(11) thin film with preferred c-axis orientation and some Pb_5Ge_3O_(11) secondary phase have been successfully grown on these electrodes with good ferroelectric properties.