Unipolar resistive switching in planar Pt/BiFeO3/Pt structure

This work was supported by the NASA EPSCoR Grant # NNX13AB22A. Financial support to various researchers from IFN-NSF grant # EPS 1002410 (RSK, DB, YS and BRW) is gratefully acknowledged. S. K. is thankful to UGC, India for a Raman fellowship under Indo-US 21st century knowledge initiatives (No:5-53/2013(I.C)).We report unipolar resistive switching suitable for nonvolatile memory applications in polycrystalline BiFeO3 thin films in planar electrode configuration with non-overlapping Set and Reset voltages, On/Off resistance ratio of similar to 10(4) and good data retention (verified for up to 3,000 s). We have also observed photovoltaic response in both high and low resistance states, where the photocurrent density was about three orders of magnitude higher in the low resistance state as compared to the high resistance state at an illumination power density of similar to 100 mW/cm(2). Resistive switching mechanisms in both resistance states of the planar device can be explained by using the conduction filament (thermo-chemical) model. (C) 2015 Author(s).Publisher PDFPeer reviewe

Microwave dielectric properties of Ti-substituted Bi2 (Zn 2/3Nb4/3)O7 pyrochlores at cryogenic temperatures

Monoclinic pyrochlore ceramic Bi2Zn2/3−x/3Nb4/3−2x/3TixO7 (M–BZN) with x=0–0.4 is synthesized and the structure and microwave cryogenic properties are scrutinized. The dielectric constant (ɛ') and loss tangent (tanδ) of these ceramics are measured at a frequency of 3 GHz and temperature range of 15–300 K. With an increase in x value from 0 to 0.4, the dielectric constant and dielectric loss tangent of the investigated materials increase from 70 to 114 and 0.009 to 0.061, respectively. The Ti-substituted ceramics show an increase in dielectric constant with temperature, and the loss tangent shows a peak around 200 K. The peak in the dielectric loss tangent becomes more prominent with an increase of Ti content. The temperature where the dielectric loss tangent peak appears is found to be decreasing slightly with an increase of titanium doping. The observed dielectric characteristics of the titanium-doped M–BZN ceramics are attributed to the presence of the relaxation in these materials, originating from the disorder caused by the Ti4+ substitution

Enhanced resistive switching in forming-free graphene oxide films embedded with gold nanoparticles deposited by electrophoresis

Forming-free resistive random access memory (ReRAM) devices having low switching voltages are a prerequisite for their commercial applications. In this study, the forming-free resistive switching characteristics of graphene oxide (GO) films embedded with gold nanoparticles (Au Nps), having an enhanced on/off ratio at very low switching voltages, were investigated for non-volatile memories. The GOAu films were deposited by the electrophoresis method and as-grown films were found to be in the low resistance state; therefore no forming voltage was required to activate the devices for switching. The devices having an enlarged on/off ratio window of ~106 between two resistance states at low voltages (<1 V) for repetitive dc voltage sweeps showed excellent properties of endurance and retention. In these films Au Nps were uniformly dispersed over a large area that provided charge traps, which resulted in improved switching characteristics. Capacitance was also found to increase by a factor of ~10, when comparing high and low resistance states in GOAu and pristine GO devices. Charge trapping and de-trapping by Au Nps was the mechanism responsible for the improved switching characteristics in the films

Holmium hafnate : an emerging electronic device material

Financial support from DOE Grant No. DE-FG02-08ER46526 is acknowledged. S.P.P. is grateful to NSF for financial assistance under Grant No. NSF-EFRI RESTOR #1038272. Y.S. is thankful to IFN-NSF for doctoral fellowship under NSF-RII-0701525 grant.We report structural, optical, charge transport, and temperature properties as well as the frequency dependence of the dielectric constant of Ho2Hf2O7 (HHO) which make this material desirable as an alternative high-k dielectric for future silicon technology devices. A high dielectric constant of similar to 20 and very low dielectric loss of similar to 0.1% are temperature and voltage independent at 100 kHz near ambient conditions. The Pt/HHO/Pt capacitor exhibits exceptionally low Schottky emission-based leakage currents. In combination with the large observed bandgap Eg of 5.6 eV, determined by diffuse reflectance spectroscopy, our results reveal fundamental physics and materials science of the HHO metal oxide and its potential application as a high-k dielectric for the next generation of complementary metal-oxide-semiconductor devices.Publisher PDFPeer reviewe

Enhanced resistive switching in forming-free graphene oxide films embedded with gold nanoparticles deposited by electrophoresis

Forming-free resistive random access memory (ReRAM) devices having low switching voltages are a prerequisite for their commercial applications. In this study, the forming-free resistive switching characteristics of graphene oxide (GO) films embedded with gold nanoparticles (Au Nps), having an enhanced on/off ratio at very low switching voltages, were investigated for non-volatile memories. The GOAu films were deposited by the electrophoresis method and as-grown films were found to be in the low resistance state; therefore no forming voltage was required to activate the devices for switching. The devices having an enlarged on/off ratio window of ~106 between two resistance states at low voltages (<1 V) for repetitive dc voltage sweeps showed excellent properties of endurance and retention. In these films Au Nps were uniformly dispersed over a large area that provided charge traps, which resulted in improved switching characteristics. Capacitance was also found to increase by a factor of ~10, when comparing high and low resistance states in GOAu and pristine GO devices. Charge trapping and de-trapping by Au Nps was the mechanism responsible for the improved switching characteristics in the films