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(Zr 40 , Ti 60 )O 3 (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% BiFeO 3 (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 10 10 cycles. 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.

Phase-formation, microstructure, and piezoelectric/dielectric properties of BiYO3-doped Pb(Zr0.53Ti0.47)O3 for piezoelectric energy harvesting devices

“…Many investigations have been conducted to obtain piezoelectric ceramics with a high d 33 value and small K 33 T [17][18][19]. From considerations of ionic radii, it is probable that bismuth (Bi) and yttria (Y) ions occupy the Pb site, and that charge compensation will take place by the creation of Pb vacancies in the lattice, which facilitate the movement of the domain wall so as to improve the piezoelectric and dielectric properties [20][21][22][23][24][25]. It was reported that the substitution of Bi in PZT increased sinterability, retarded grain growth, and decreased grain size [22][23][24].…”

“…From considerations of ionic radii, it is probable that bismuth (Bi) and yttria (Y) ions occupy the Pb site, and that charge compensation will take place by the creation of Pb vacancies in the lattice, which facilitate the movement of the domain wall so as to improve the piezoelectric and dielectric properties [20][21][22][23][24][25]. It was reported that the substitution of Bi in PZT increased sinterability, retarded grain growth, and decreased grain size [22][23][24]. In addition, it was also reported that a uniform grain size distribution with decreasing grain size yielded a large P r and a small leakage current in Y-doped PZT materials [20,21,25].…”

Growth of BiFeO3/SrTiO3 artificial superlattice structure by RF sputtering

“…A PUND (positive-up negative-down) polarization test is a powerful tool to probe the ferroelectric behavior of a ferroelectric material; the transient current estimated with PUND is related to the leakage current of a ferroelectric material [47][48][49][50][51]. 1C showed a small transient current, less than 0.02 mA, which is as small as in the previous work of BFO single layer measured at low temperature (93 K) [48].…”

Recent progress on piezoelectric energy harvesting: structures and materials

“…As the Fe 2 O 3 doped into PZT ceramics can effectively create defect dipoles and increase the net polarization [67], Yoon et al [68] [70]. Later, they selected the alkaline-earth metal ion of Sr 2+ which has the same valence as Pb 2+ to optimize the electrical properties of PZN-PZT ceramics.…”