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...

Ferroelectric field-effect transistors (FeFET) based on MoS2 have recently been shown to exhibit considerable potential for use in nano sized non-volatile memory devices. Here, we demonstrated fabrication and characterization of FeFET based on MoS2 channel with vinylidene fluoride (VDF)-trifluoroethylene (TrFE) copolymer as back-gate insulator. In this device, counterclockwise hysteresis behavior was observed in the drain current–gate voltage curve, which is indicative of interaction between MoS2 carrier modulation and ferroelectric polarization switching. Furthermore, our VDF-TrFE/MoS2 FeFET exhibited only n-type behavior, a maximum linear mobility of 625 cm2/V s, a large memory window width of 16 V, and a high on/off current ratio of 8 × 105.

Nd,Mn)-cosubstituted BiFeO 3 (BFO) films with various Nd and Mn compositions were fabricated on a Pt/SrTiO 3 (100) substrate by pulsed laser deposition. X-ray diffraction patterns and atomic force microscopy images indicated that the suppression of impurity phases and a smooth surface morphology were realized by Nd substitution in the BFO films. Furthermore, by combining with Nd substitution, a small amount of Mn substitution in BFO films is effective for reducing the leakage current density by three orders of magnitude compared with that of a BFO film capacitor. The polarization vs electric field (P-E) curves showed a strong dependence of measurement frequency in the range of 0.1-2 kHz, and well-saturated P-E hysteresis loops were observed at 20 kHz at room temperature. The remanent polarization and coercive field at a maximum electric field of 1.9 MV/cm were approximately 70 mC/cm 2 and 0.32 MV/cm, respectively.

The control of the critical current density (Jc) and the junction resistance (RN) along the c axis of intrinsic Josephson junctions (IJJs) on a high-Tc superconductor is very important for applying the IJJs to electronic devices. For controlling these junction parameters, we have clarified the relationship of Jc, RN, and the carrier density in Bi2Sr2CaCu2O8+δ (Bi-2212) whiskers by changing the carrier density with an annealing process. As a result, the Jc decreased, and the RN increased systematically when the carrier density decreased. The values of Jc and RN could be controlled by a change in the carrier density.

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