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 ABO(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 ABO(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 PbZr0.2Ti0.6Nb0.2O3 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 X 0.8 mum(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 I 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.