We investigate the ferromagnetic properties of the conducting filament (CF) nanodots formed on epitaxial BiFeO3 (BFO) thin film, which exhibit resistive switching behavior. 50-nm thick epitaxial BFO ...thin film was grown on Nb-doped SrTiO3 single crystal substrates through pulsed laser deposition. The ferroelectric microcapacitor fabricated using the epitaxial BFO thin film shows excellent ferroelectric properties with a remanent polarization of approximately 32 μC/cm2 and unipolar resistive switching behavior. CF nanodots with a diameter of approximately 16 nm are formed in the local region of the BFO thin film through conductive atomic force microscopy. Generally, ferromagnetic materials exhibit superparamagnetism, on a scale of tens of nanometers, as a result of the thermal energy of the magnetic moments. In this study, magnetic force microscopy demonstrates that the CF nanodot possesses ferromagnetism. It is suggested that exchange coupling between the CF nanodot and surrounding BFO causes the ferromagnetism of the nanodot. Our study provides new insight on the design of multistate memory cells with resistive switching and magnetic spin ordering, for application in high-density information storage media.
Resistive switching behavior has been observed mainly in transition metal oxides, particularly in the form of thin-film cells. In the present study, self-aligned, ferroelectric BiMnO3 (BMO) cubic ...nanodots on an Nb-doped SrTiO3 substrate were fabricated by pulsed laser deposition (PLD). The BMO nanodots showed the bipolar resistive switching as well as the typical piezoresponse characteristics. Significantly, H2 annealing of BMO nanodots resulted in a striking difference between the low-resistance state (LRS) and the high-resistance state (HRS) as well as a decrease in the SET and RESET voltages compared to the nonannealed BMO nanodots. We suggest that the conductive filament model is the most likely mechanism for the resistive switching in the BMO nanodots. Concentration of oxygen vacancies plays a major role in the growth of conductive paths during the H2 annealing process, leading to reduction of effective thickness in the BMO nanodots.
Polycrystalline Bi2WO6 (BWO) thin films were deposited on Pt/Ta/glass substrates by pulsed laser deposition (PLD). In this study, we comparatively investigate the influence of oxygen partial pressure ...on structural and ferroelectric properties of the BWO films. In comparison with the BWO films deposited at oxygen partial pressure of 100 and 300 mTorr, the BWO film deposited at 300 mTorr exhibits a highly a-oriented crystalline structure. The highly a-oriented polycrystalline BWO thin film shows good ferroelectric properties with a remnant polarization of about
21.5
μ
C
/
cm
2
. The piezoresponse force microscope study reveals that the highly a-oriented BWO thin film possesses larger ferroelectric domain patterns due to smaller domain wall energy.
We investigated ferroelectric properties of silver niobate (AgNbO3) thin film grown on Nb-doped SrTiO3 substrate by pulsed laser deposition. The AgNbO3 thin film exhibited room temperature ...ferroelectricity with a large remanent polarization of about 31μC/cm2 (2Pr~62μC/cm2) and fast switching behavior within 120ns. Triangular grains of AgNbO3 thin film were observed by atomic force microscopy (AFM). The piezoelectric force microscopy (PFM) study revealed that the AgNbO3 thin film had mosaic-like ferroelectric domain structure. In comparison with PbTiO3 thin films, domain size of the AgNbO3 thin films was smaller than that of PbTiO3 thin films. Based on Landau, Lifshitz, and Kittel (LLK) scaling law of the domain size versus film thickness curves, it is inferred that AgNbO3 thin films have slightly lower domain wall energy than that of PbTiO3 thin films.
•Epitaxial AgNbO3 thin film showed high remnant polarization at room temperature.•Triangular grain and mosaic-like ferroelectric domain structure were observed respectively.•Domain wall energy is discussed based on the LLK scaling law.
We report the ferroelectric properties of the epitaxial BiFeO3 (BFO) thin films grown on Nb-doped SrTiO3 substrates. The (001) and (111) BFO thin films were grown epitaxially on a single-crystalline ...(100) and (111) Nb-doped SrTiO3 substrate by pulse laser deposition, respectively. The (111) BFO film gave higher remnant polarization in the ferroelectric hysteresis loop than that of the (001) film. The (001) and (111) BFO films revealed striped and mosaic ferroelectric domain structures, respectively. The ferroelectric domain size vs. film thickness was in accordance with the scaling law of Landau, Lifshitz and Kittel. The domains of the (001) BFO film were larger than those of the (111) BFO film. This is because the (111) BFO film has a relatively large remnant polarization, even though the (111) film has a lower domain wall energy.
•Ferroelectric domain structures of epitaxial (001) and (111) BFO thin films.•Stripe and mosaic ferroelectric domain structures.•The scaling law of Landau, Lifshitz and Kittel for ferroelectric domain size vs. film thickness.
•NiO nanodots were fabricated on Nb:STO single crystal substrate by pulsed laser deposition.•Resistive switching characteristics of NiO nanodots was investigated.•Forming and SET/RESET voltages ...decreased as the thickness of NiO nanodots decreased.•As thickness of the NiO nanodots decreased, distribution of forming voltages stabilized.
High-density resistive random access memory devices benefit from the reduction in the size of memory cells to a nanoscale. As the RRAM cells become smaller and denser, more stable operation is required. In this study, resistive switching characteristics of self-assembled NiO nanodots on Nb-doped SrTiO3 substrates were examined by using conducting atomic force microscopy. For the NiO nanodot thickness of 8, 6, and 4 nm, the forming voltages were 5.43, 4.63, and 4.12 V, respectively, indicating that the forming voltage decreased as the thickness of NiO nanodots decreased. The SET and RESET voltages also decreased (2.40 and 1.21 V for 8 nm, 2.11 and 0.96 V for 6 nm, 1.86 and 0.82 V for 4 nm, respectively). In addition, as the thickness of the NiO nanodots decreased, the distribution of forming voltages stabilized. We propose that the reduction of the forming voltage distribution is related to the volume of the conductive filaments that were formed in the nanodots. The fabrication of NiO nanodots and the detailed investigation of resistive switching characteristics that depend on the size of the nanodots provide valuable insights for future NiO nanodot resistive random access memory devices.
Ferroelectric thin films find applications in numerous areas, including sensors and energy storage devices. To address the toxicity associated with thin films such as Pb(Zr,Ti)O3, developing Pb-free ...ferroelectric thin films with enhanced physical properties is necessary. Herein, the piezoelectric power generation and energy density of Sn-doped BaTiO3 (SBTO) thin films with varying Sn doping concentrations were studied. Polycrystalline SBTO thin films with Sn doping concentrations of 0%, 5%, 10%, and 15% were deposited on flexible Pt/mica substrates with a preferential (111) orientation. The SBTO thin film with a Sn doping concentration of 5% exhibited the highest remanent polarization (Pr) in the ferroelectric hysteresis loop. In contrast, the SBTO thin films with Sn doping concentrations of 10% and 15% exhibited reduced Pr owing to the formation of 90° domains. The lowest Pr was observed for the SBTO thin film with 15% Sn. With an increase in the Sn doping concentration, the piezoelectric coefficient (d33) increased due to the formation of a-domains. Owing to the high concentration of a domain, the SBTO thin film with 15% Sn exhibited the highest d33 and consequently, the highest piezoelectric power generation voltage. Moreover, the minimum Pr of the film with 15% Sn facilitated an increase in energy density and efficiency.
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