Novel Si Codoped Pb(Zr,Ti,Nb)O 3 Thin Film for High-Density Ferroelectric Random Access Memory

We have succeeded in fabricating Pb(Zr,Ti,Nb)O 3 (PZTN) thin films with more than 10 at.% Nb at the B site in the A B O 3 structure, which are suitable for application to high-density and reliable ferroelectric random access memory (FeRAM). To prepare the PZTN thin films, we used a sol-gel spin-coating method in which we codoped 1–3 mol% Si to promote the solvation of Nb atoms into the original Pb(Zr,Ti)O 3 (PZT) films as a solid solution. X-ray diffraction (XRD) reciprocal space mapping and Raman scattering revealed that our PZTN film was a single ferroelectric phase of the A B O 3 proposed perovskite-type structure with Nb substituted for B -site atoms. Additionally, we suggested that, through this Nb substitution, the formation of oxygen vacancies in PZTN was effectively suppressed; the number of vacancies was much lower than in conventional PZT. The resultant 150-nm-thick PbZr 0.2 Ti 0.6 Nb 0.2 O 3 film had a very low leakage current and demonstrated excellent imprint and data retention properties. We have also succeeded in obtaining excellent electric properties in 0.8×0.8 µm 2 capacitors fabricated with PZTN. In addition, we confirmed the high reliability and absence of data degradation of our PZTN material during operation as a 1 kbit FeRAM chip. The results of a first-principles calculation indicated that the reduction of the number of oxygen vacancies led to a sufficiently wide band gap to lower the leakage current in our PZTN films.