We propose that the double barrier effect is expected to enhance the tunneling electroresistance(TER)in the ferroelectric tunnel junctions(FTJs).To demonstrate the feasibility of this mechanism,we design a model structure of Pt/BaTiO_(3)/LaAlO_(3)/Pt/BaTiO_(3)/LaAlO_(3)/Pt double barrier ferroelectric tunnel junction(DB-FTJ),which can be considered as two identical Pt/BaTiO_(3)/LaAlO_(3)/Pt single barrier ferroelectric tunnel junctions(SB-FTJs)connected in series.Based on density functional calculation,we obtain the giant TER ratio of 2.210×10^(8)%in the DB-FTJ,which is at least three orders of magnitude larger than that of the SB-FTJs of Pt/BaTiO_(3)/LaAlO_(3)/Pt,together with an ultra-low resistance area product(0.093 KΩμm^(2))in the high conductance state of the DB-FTJ.Moreover,it is possible to control the direction of polarization of the two single ferroelectric barriers separately and thus four resistance states can be achieved,making DB-FTJs promising as multi-state memory devices.
The electroresistance(ER) of La_(0.36)Pr_(0.265)Ca_(0.375)MnO_3(LPCMO) epitaxial thin film was studied under various dc currents.The current effect was compared for the unpatterned film and patterned microbridge with a width of 50 μm.The value of ER in the unpatterned LPCMO film could reach 0.54 under a 1-mA current,which is much higher than ER under 1 mA for the patterned weak phase-separated La_(0.67)Ca_(0.33)MnO_3 and La_(0.85)Sr_(0.15)MnO_3 microbridges with 50-μm width.More interestingly,for the patterned LPCMO microbridge,the maximum of ER can reach 0.6 under a small current of 100 μ.A.The results were explained by considering the coexistence of ferromagnetic metallic phase with the charge-ordered phase,and the variation of the phase separation with electric current.
The interface with a pinned dipole within the composite barrier in a ferroelectric tunnel junction(FTJ) with symmetric electrodes is investigated.Different from the detrimental effect of the interface between the electrode and barrier in previous studies,the existence of an interface between the dielectric SrTiO_3 slab and ferroelectric BaTiO_3 slab in FTJs will enhance the tunneling electroresistance(TER) effect.Specifically,the interface with a lower dielectric constant and larger polarization pointing to the ferroelectric slab favors the increase of TER ratio.Therefore,interface control of high performance FTJ can be achieved.
Micro-patterning is considered to be a promising way to analyze phase-separated manganites. We investigate resistance in micro-patterned La0.325Pr0.3Ca0.375MnO3 wires with width of 10 μm, which is comparable to the phase separation scale in this material. A reentrant of insulating state at the metal-insulator temperature Tp is observed and a giant resistance change of over 90% driven by electric field is achieved by suppression of this insulating state. This resistance change is mostly reversible, The I-V characteristics are measured in order to analyze the origin of the giant electroresistance and two possible explanations are proposed.