Improved leakage and ferroelectric properties of Mn and Ti codoped BiFeO3 thin films

Abstract

Polycrystalline BiFeO 3 ͑BFO͒, Ti-doped BFO, Mn-doped BFO, and ͑Mn, Ti͒-codoped BFO ͑BFMT͒ thin films were fabricated on Pt/ SrTiO 3 ͑100͒ substrate by pulsed laser deposition. Observed leakage current behavior in those ion-doped BFO films indicated the dominance of space-charge-limited current in the high electric field region. The leakage current of the BFMT film was much reduced in relation to the other films due to the formation of deep traps. In the BFMT film, well saturated P-E hysteresis curves were observed. Remanent polarization and coercive field for maximum electric field of 2100 kV/cm were 75 C / cm 2 and 310 kV/cm, respectively. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3098408͔ Excellent ferro-/piezoelectric properties have been reported in the BiFeO 3 ͑BFO͒ thin films comparable to those of Pb͑Zr x Ti 1−x ͒O 3 , 1-3 and thus the BFO is expected as an alternative Pb-free ferro-/piezoelectric material. However, the large leakage current of BFO thin films at room temperature ͑RT͒ is known to be a serious problem, which could limit the various applications of this material.In the past several years, site-engineering technique by substitution of small amount of impurities was proposed to solve this problem, and reduced leakage current properties were reported. [4][5][6][7][8][9][10][11]15 The site-engineering technique is quite important from industrial aspects because this technique can be applied to most deposition methods. However, it is not easy to reduce the leakage current of BFO films by a single ion-doping method since the excess substitution causes an increase in leakage current in the films. 6,7 Besides, modification of electrical properties of BFO films by ion doping at Bi site is quite difficult because of the degradations in ferroelectric properties, although rare-earth elements doped at Bi site is effective to reduce the impurity phases due to bismuth and oxygen vacancies. 5,8,9 Therefore, we propose a new combination of Mn and Ti as codoping elements for Fe site of BFO thin films. In this work, we report the synthesis and characterization of ͑Mn, Ti͒-codoped BFO ͑BFMT͒ thin films by comparing with those of pure BFO, Ti-doped BFO ͑BFT͒, and Mn-doped BFO ͑BFM͒ thin films. Moreover, it is required to reduce the leakage current of BFO films in the high electric field region ͑at least more than 400 kV/cm͒ since coercive electric fields of BFO film capacitors are generally 300-500 kV/cm. Hence, we also discuss the change in conduction mechanism in the high electric field region by ion doping in the BFO thin films.BFO, BFT, BFM, and BFMT thin films were deposited on Pt-coated ͑100͒ SrTiO 3 ͑STO͒ substrates with thicknesses ranging from 220 to 240 nm, using a conventional pulsed laser deposition ͑PLD͒ system. The ceramic targets with metal compositions of Bi 1.1 FeO 3 , Bi͑Fe 0.98 Ti 0.02 ͒O 3 , Bi 1.1 ͑Fe 0.97 Mn 0.03 ͒O 3 , and Bi͑Fe 0.95 Mn 0.03 Ti 0.02 ͒O 3 were used for deposition of BFO, BFT, BFM, and BNFM films, respectively. The details of thin film fabrication were described...

Polarization-Induced Photovoltaic Effects in Nd-Doped BiFeO3 Ferroelectric Thin Films

“…Many research groups have reported that a site-engineering technique using various elements is effective to suppress the leakage current in BFO films. [11][12][13][14][15][16] We proposed (Nd,Mn)-codoped BFO (BNFM) and (Pr,Mn)-codoped BFO (BPFM), and succeeded in obtaining improved electrical properties. 14,[17][18] Recently, polarization-induced photovoltaic properties in BFO films have been reported.…”

Influences of Pr and Mn co-substitution on crystallinity and electric properties of BiFeO3 thin films

“…In the last several years, many research groups have reported that a siteengineering technique is effective to solve this problem 12) 33) because the leakage current of BFO thin films is mainly caused by the nonstoichiometric compositions or impurity phases in the film.…”

Leakage Current Properties of Cation-Substituted BiFeO3 Ceramics

“…The decreasing current density caused by Mn 3+ doping was already reported for BFO films with somewhat different behaviors. 10,25,26) That is, J values of the Mn 3+ -doped films were higher than those of undoped films in a low E region but they became smaller at higher E as a result of reduced rates of the increasing J. Mn 3+ doping in this study, however, resulted in reduced J values of the doped BFO samples even in a low E region. From a linear relationship in the log (J) vs log (E) plot for the 5%Mn 3+ -doped and undoped BFO ceramics, the slopes  in an expression J  E  were evaluated to be   1.4 and   2.4, respectively.…”