In this work, the observations of different resistive switching polarities of epitaxial BaTiO3 (BTO) thin films fabricated by pulsed laser deposition are reported. The BTO films with various ferroelectric states and oxygen vacancy (VO) concentrations are achieved by carefully controlling the oxygen pressure during the depositions. For films with no ferroelectricity and high VO concentrations, the resistance will change from a low resistance state (LRS) to a high resistance state (HRS) during a positive voltage cycle (0 → 3 → 0 V), and from a HRS to a LRS during a negative voltage cycle (0 → −3 → 0 V). However, completely opposite RS polarity is observed for the films with weak ferroelectricity and intermediate VO concentrations. Such RS behaviors and polarity can be hardly observed or negligible for the films with good ferroelectricity and nearly free of VO. It is proposed that the unique resistance switching polarities of BTO films are attributed to the competition between the ferroelectricity and oxygen vacancy migration dynamics. Results clarify the complex RS mechanisms in the BTO films, and address the competing ferroelectricity and VO migration in modulating the RS behaviors of ferroelectric oxide‐based resistive memory devices.

The electrical conductivity, charge transport behavior, and ferroelectricity of epitaxial BaNb x Ti 1-x O 3 films (BNTO, 0.0 x 0.5) prepared by pulsed laser deposition are investigated. It is found that Nb-doping can tune the conventional insulating BaTiO 3 films from an insulating to highly conductive semiconducting or metallic state, resulting in a variation of the electrical conductivity of the BNTO films over 10 5 . For x 0.25, the charge transport is dominated by the small polaron hopping mechanism, while the charge transport for x ¼ 0.5 transits from the bipolaron to the small-polaron, and then the thermal phonon scattering mechanisms with increasing temperature. Interestingly, the piezo-force microscopy imaging reveals the presence of ferroelectricity in the properly Nb-doped conductive BNTO films (x 0.25) deposited in the presence of a small amount of oxygen (3 Â 10 À3 Pa). Our work provides additional technical roadmaps to manipulate the conductivity and charge transport behaviors in ferroelectric films, which will boost potential applications in future information storage, sensors, and photovoltaic devices. Published by AIP Publishing.Traditional ferroelectric (FE) materials are often good insulators because no free carriers for electrical conductivity are allowed due to their large band gap. While the ferroelectricity and its origins in various materials have been extensively studied and well understood, 1-4 the electrical conductivity in FE materials and in particular multiferroics as an emergent topic has been receiving attention recently, offering broad interest for potential applications. 3-5 For example, it is known that the uncharged 180 and 109 domain walls in BiFeO 3 thin films are conductive at room temperature. 6 Metallic conductivity at FE domain walls in BaTiO 3 (BTO) was also predicted and observed experimentally. 7 Dating back to the 1960s, metallic ferroelectricity as an emergent effect was first proposed and recently confirmed in LiOsO 3 , 8 while the underlying mechanism can be associated with the anisotropic unscreened Coulomb interactions. 8 These results strongly suggest that sufficient electrical conductivity may be allowed in FE materials without losing the ferroelectricity. The conductivity can originate from various charge transport mechanisms allowing different strategies for controlling the electrical conductivity and ferroelectricity. Another interesting issue is the interaction between FE polarization and carrier transport in FE films. For example, it was found that the out-of-plane resistivity of Bi 1-d FeO 3 films is closely related to the polarization-dependent interfacial barriers and charge trapping at the non-neutral domain walls with non-penetrating tail-to-tail domains. 9 This effect may be associated with the modulation of interfacial potentials by FE polarization, resulting in the ferroelectric resistive switching memory effect. 10 Given those preliminary studies, some fundamental issues yet remain unclear or under debate, such as the charge transport mechanism and...

Write‐once‐read‐many (WORM) memory behavior is often observed in polymer electret memory (PEM) devices, greatly limiting their overall performance. This paper systematically investigates the device physics of PEM devices with poly(α‐methylstyrene) as a charge trapping layer and pentacene as a semiconductor channel. The combined experiments on transistors, capacitances, and optical spectroscopy reveal that both the WORM memory behavior after negative and positive pulses and the gradual formation of memory after the continuous scanning are the results of the deficiency in minority (electrons) transport and trapping. Corresponding quantitative models are established and well explain the two‐stage, gradual trapping processes to form memory. By reducing the structural disorder and lateral channel length, ambipolar, bistable memory and much faster formation of memory window is obtained based on the same PEM device. The insights into device physics of PEM devices are expected to facilitate the design of organic, nonvolatile memory devices with high programming and erasing efficiencies.

In this work, we fabricated a high performance flash-type organic nonvolatile memory transistor, which adopted polymer-electret poly(α-methylstyrene) (PαMS) and HfO2 films as hybrid charge trapping layer (CTL). Compared with a single HfO2 or PαMS CTL structure, the hybrid HfO2/PαMS CTL structure can provide enhanced charge trapping efficiency to increase the device operation speed and reduce the leakage current to boost the device reliability. The fabricated nonvolatile organic memory transistors with the hybrid CTL shows excellent electrical properties, including low operation voltage (8 V), high speed (<10 ms), excellent data retention (on-off current ratio of 2.6 × 104 after 104 s), and good endurance (more than 2000 program/erase cycles). The present work provides useful idea for the design of future low-power consumption and highly reliable organic nonvolatile memories.

Nbdoped BaTiO 3 (BNTO) films were deposited on MgO substrates at different substrate temperatures by pulsed laser deposition. The temperature dependence of their resistivity, carrier mobility and carrier concentration were systematically investigated. It reveals that the BNTO films deposited at lower temperature show higher resistivity and lower carrier mobility, and only show semiconductor characteristics at measurement temperatures ranging from 10 to 400 K. There is a metal-semiconductor transition at about 20 K for the films grown at relatively higher temperature. The intrinsic mechanism responsible for the different charge transport behavior was revealed by microstructure studies. Low crystal quality and high density of microstructure defects, observed for BNTO films grown at low temperatures, are, in particular, massively affecting the charge transport behavior of the BNTO films. The mediated charge transport of the microstructure defects is dominated by the thermal excitation process.