title: Characterization of Bi and Fe co-doped PZT capacitors for FeRAM.
abstract: Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100 °C. With this goal in mind, co-doping of thin Pb(Zr40,Ti60)O3(PZT) films with 1 at.% Bi and 1 at.% Fe was examined in order to enhance the ferroelectric properties as well as characterize the doped material. The XRD patterns of PZT-5% BiFeO3(BF) and PZT 140-nm thick films showed (111) orientation on (111) platinized Si wafers and a 30 °C increase in the tetragonal to cubic phase transition temperature, often called the Curie temperature, from 350 to 380 °C with co-doping, indicating that Bi and Fe are substituting into the PZT lattice. Raman spectra revealed decreased band intensity with Bi and Fe co-doping of PZT compared to PZT. Polarization hysteresis loops show similar values of remanent polarization, but square-shaped voltage pulse-measured net polarization values of PZT-BF were higher and showed higher endurance to repeated cycling up to 1010cycles. It is proposed that Bi and Fe are both in the +3 oxidation state and substituting into the perovskite A and B sites, respectively. Substitution of Bi and Fe into the PZT lattice likely creates defect dipoles, which increase the net polarization when measured by the short voltage pulse positive-up-negative-down (PUND) method.
authors.affiliation: Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, Japan.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Cross
authors.affiliation: R and D Center, Inostek Inc., Gyeonggi Technopark, Ansan, Korea.
authors.forename: Seung-Hyun
authors.initials: SH
authors.lastname: Kim
authors.affiliation: University of Yamanashi, 4-4-37 Takeda, Kofu, Yamanashi, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Wada
authors.affiliation: Accelrys KK, 3-3-1, Nishishinbashi, Minato-ku, Tokyo, Japan.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Chatterjee