Electrical properties of Pt/Bi 3.25 La 0.75 Ti 3 O 12 /Pt thin film capacitors tailored by cerium doping
- PDF / 218,500 Bytes
- 7 Pages / 585 x 783 pts Page_size
- 80 Downloads / 194 Views
Cerium-doped Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated by depositing sol-gel solutions on Pt/Ti/SiO2/Si 〈100〉 substrates. The Ce-doping in BLT up to 6.7% of Ti atoms did not affect the single-phase bismuth-layered structure but small modification was observed in structural orientation, which influenced the microstructure and ferroelectric properties of BLT films. As we did not observe any structural distortion in x-ray diffraction data, it was suggested that doped Ce4+ was converted to Ce3+ during the annealing at 750 °C, and cerium ions might be substituted at Bi-site in BLT films. The small amount of Ce doping (1% of Ti atoms) enhanced the remanent polarization and reduced the coercive field by about 17% in BLT films, and these films showed fatigue-free response up to 1010 switching cycles at 300 kV/cm applied fields. Moderately Ce-doped films (1.7% of Ti atoms) also showed fatigue-free response up to 1010 switching cycles in 200 kV/cm applied field, but the polarization was found to increase with switching cycles when applied field was higher than 200 kV/cm. After Ce doping, the oxygen vacancy concentration may decrease in BLT films, and consequently, one can expect less domain pinning and higher fatigue resistance. Under the high cycling field, the high probability of field-assisted unpinning may be the main cause for the increased polarization.
I. INTRODUCTION
Bismuth layered perovskite compounds such as SrBi2Ta2O9 (SBT) and La-substituted Bi4Ti3O12 (BTO) are considered to be candidates for memory applications, such as non-volatile ferroelectric random-access memory (NvFeRAM) because of their high fatigue endurance limit and lead-free chemical composition compared with simple perovskite Pb(Zr1−xTix)O3 (PZT).1,2 SBT (n ⳱ 2) and BTO (n ⳱ 3) belong to the class of Aurivillius phases with layered intergrowth structures, which consist of n layers of perovskite-like blocks sandwiched between two consecutive fluorite-like (Bi2O2) layers. Bi4−xLaxTi3O12 (BLT) is a more promising candidate for NvFeRAM than SBT because SBT films require high growth temperature and it shows small remanent polarization compared to BLT.3 From considerations of the structural chemistry of the Aurivillius phases, site-engineering (substitution technique) is an important factor to improve the properties of
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0116 988
J. Mater. Res., Vol. 21, No. 4, Apr 2006 http://journals.cambridge.org Downloaded: 15 Mar 2015
the materials.4 The influence of the Bi3+ site substitution by isovalent La3+, Nd3+, Pr3+, Sm3+ cations, and Ti4+ site substitution by higher valent V5+, W6+, and Mo6+ cations on the ferroelectric properties of BTO have been reported in the literature.4–9 It has been shown that the Bi-site substitution can increase the polarization as well as coercive field. However, in case of Ti-site substitution, the polarization may increase, whereas the coercive field may decrease. Ti-site substitution by higher valent cations is fu
Data Loading...
