Masao Nakayama

Novel Si Codoped Pb(Zr,Ti,Nb)O3 Thin Film for High-Density Ferroelectric Random Access Memory

We have succeeded in fabricating Pb(Zr,Ti,Nb)O3 (PZTN) thin films with more than 10 at.% Nb at the B site in the ABO3 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)O3 (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 ABO3 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 0.8×0.8 µm2 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.

Ferroelectric Random Access Memory Using Pb(Zr,Ti,Nb)O 3 Films

We have succeeded in fabricating Pb(Zr,Ti,Nb)O3 (PZTN) thin films with 20-atomic% Nb at B site in ABO3 structure, which was suitable for high density and reliable ferroelectric random access memory (FeRAM). A sol-gel spin-coating method was used to prepare the PZTN thin films. 1 mol% Si co-doping was applied to promote the solid-solution of Nb atom into the original Pb(Zr,Ti)O3 films. We suggested that in our PZTN the oxygen vacancies were well suppressed due to Nb substitution comparing with conventional Pb(Zr,Ti)O3 (PZT). We also succeeded in obtaining excellent electric properties in 1times1 mum2 capacitors with PZTN. In addition, we confirmed the no data degradation and the high reliability of our PZTN material has been demonstrated by 64 k-bits FeRAM chip operation.