We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown b... more We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/ Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 10(3). The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
ABSTRACT Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposit... more ABSTRACT Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposition on c-plane sapphire substrates and Schottky and Ohmic contacts have been prepared in top-top configuration. The diode current is significantly reduced after the diode has been subjected to an external magnetic field. In the reverse bias range the corresponding positive magnetoresistance is persistent and amounts to more than 1800% (50 K), 240% (30 K), and 50% (5 K). This huge magnetoresistance can be attributed to the large internal magnetic field in depleted ZnCoO with ferromagnetic exchange between stable bound magnetic polarons.
This work reports the effect of Ti diffusion on the bipolar resistive switching in Au/BiFeO3/Pt/T... more This work reports the effect of Ti diffusion on the bipolar resistive switching in Au/BiFeO3/Pt/Ti capacitor-like structures. Polycrystalline BiFeO3 thin films are deposited by pulsed laser deposition at different temperatures on Pt/Ti/SiO2/Si substrates. From the energy filtered transmission electron microscopy and Rutherford backscattering spectrometry it is observed that Ti diffusion occurs if the deposition temperature is above 600°C. The current-voltage (I-V) curves indicate that resistive switching can only be achieved in Au/BiFeO3/Pt/Ti capacitor-like structures where this Ti diffusion occurs. The effect of Ti diffusion is confirmed by the BiFeO3 thin films deposited on Pt/sapphire and Pt/Ti/sapphire substrates. The resistive switching needs no electroforming process, and is incorporated with rectifying properties which is potentially useful to suppress the sneak current in a crossbar architecture. Those specific features open a promising alternative concept for nonvolatile m...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
ABSTRACT Polycrystalline conducting, ca. 250 nm thick indium tin oxide (ITO) and indium oxide (IO... more ABSTRACT Polycrystalline conducting, ca. 250 nm thick indium tin oxide (ITO) and indium oxide (IO) films grown on SiO2/Si substrates using reactive magnetron sputtering, have been implanted with 1 and 5 at.% of Mn, followed by annealing in nitrogen or in vacuum. The effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties has been studied. The roughness of implanted films ranges between 3 and 15 nm and XRD measurements revealed a polycrystalline structure. A positive MR has been observed for Mn-implanted and post-annealed ITO and IO films. It has been interpreted by considering s-d exchange. Spectroscopic ellipsometry has been used to prove the existence of midgap electronic states in the Mn-implanted ITO and IO films reducing the transmittance below 80%.
Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO 3 /Pt structure, where a... more Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO 3 /Pt structure, where a Schottky contact and a quasi-Ohmic contact were formed at the Au/BiFeO 3 and BiFeO 3 /Pt interface, respectively. By changing the polarity of the external voltage, the Au/BiFeO 3 /Pt is switched between two stable resistance states without an electroforming process. The resistance ratio is larger than two orders of magnitude. The resistive switching is understood by the electric fieldinduced carriers trapping and detrapping, which changes the depletion layer thickness at the Au/BiFeO 3 interface.
In this work, we report the effect of FeCo atomic fraction (0.33< x&am... more In this work, we report the effect of FeCo atomic fraction (0.33< x< 0.54) and temperature on the electrical, magnetic, and tunneling magnetoresistance (TMR) properties of FeCo-Si-O granular films prepared by atom beam sputtering technique. Glancing angle x-ray ...
ABSTRACT Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by... more ABSTRACT Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.
The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investi... more The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investigated. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range from 200 to 500 °C. Two major effects are reported: (i) a large anomalous Hall effect amounting to 2 μΩ cm, and (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves coincide with the rescaled magnetization curves, a finding that is consistent with spin-dependent transport. These findings suggest that C:Co nanocomposites are promising candidates for carbon-based Hall sensors and spintronic devices.
Memristive devices are popular among neuromorphic engineers for their ability to emulate forms of... more Memristive devices are popular among neuromorphic engineers for their ability to emulate forms of spike-driven synaptic plasticity by applying specific voltage and current waveforms at their two terminals. In this paper, we investigate spike-timing dependent plasticity (STDP) with a single pairing of one presynaptic voltage spike and one post-synaptic voltage spike in a BiFeO3 memristive device. In most memristive materials the learning window is primarily a function of the material characteristics and not of the applied waveform. In contrast, we show that the analog resistive switching of the developed artificial synapses allows to adjust the learning time constant of the STDP function from 25 ms to 125 μs via the duration of applied voltage spikes. Also, as the induced weight change may degrade, we investigate the remanence of the resistance change for several hours after analog resistive switching, thus emulating the processes expected in biological synapses. As the power consump...
We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown b... more We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/ Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 10(3). The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
ABSTRACT Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposit... more ABSTRACT Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposition on c-plane sapphire substrates and Schottky and Ohmic contacts have been prepared in top-top configuration. The diode current is significantly reduced after the diode has been subjected to an external magnetic field. In the reverse bias range the corresponding positive magnetoresistance is persistent and amounts to more than 1800% (50 K), 240% (30 K), and 50% (5 K). This huge magnetoresistance can be attributed to the large internal magnetic field in depleted ZnCoO with ferromagnetic exchange between stable bound magnetic polarons.
This work reports the effect of Ti diffusion on the bipolar resistive switching in Au/BiFeO3/Pt/T... more This work reports the effect of Ti diffusion on the bipolar resistive switching in Au/BiFeO3/Pt/Ti capacitor-like structures. Polycrystalline BiFeO3 thin films are deposited by pulsed laser deposition at different temperatures on Pt/Ti/SiO2/Si substrates. From the energy filtered transmission electron microscopy and Rutherford backscattering spectrometry it is observed that Ti diffusion occurs if the deposition temperature is above 600°C. The current-voltage (I-V) curves indicate that resistive switching can only be achieved in Au/BiFeO3/Pt/Ti capacitor-like structures where this Ti diffusion occurs. The effect of Ti diffusion is confirmed by the BiFeO3 thin films deposited on Pt/sapphire and Pt/Ti/sapphire substrates. The resistive switching needs no electroforming process, and is incorporated with rectifying properties which is potentially useful to suppress the sneak current in a crossbar architecture. Those specific features open a promising alternative concept for nonvolatile m...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
ABSTRACT Polycrystalline conducting, ca. 250 nm thick indium tin oxide (ITO) and indium oxide (IO... more ABSTRACT Polycrystalline conducting, ca. 250 nm thick indium tin oxide (ITO) and indium oxide (IO) films grown on SiO2/Si substrates using reactive magnetron sputtering, have been implanted with 1 and 5 at.% of Mn, followed by annealing in nitrogen or in vacuum. The effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties has been studied. The roughness of implanted films ranges between 3 and 15 nm and XRD measurements revealed a polycrystalline structure. A positive MR has been observed for Mn-implanted and post-annealed ITO and IO films. It has been interpreted by considering s-d exchange. Spectroscopic ellipsometry has been used to prove the existence of midgap electronic states in the Mn-implanted ITO and IO films reducing the transmittance below 80%.
Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO 3 /Pt structure, where a... more Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO 3 /Pt structure, where a Schottky contact and a quasi-Ohmic contact were formed at the Au/BiFeO 3 and BiFeO 3 /Pt interface, respectively. By changing the polarity of the external voltage, the Au/BiFeO 3 /Pt is switched between two stable resistance states without an electroforming process. The resistance ratio is larger than two orders of magnitude. The resistive switching is understood by the electric fieldinduced carriers trapping and detrapping, which changes the depletion layer thickness at the Au/BiFeO 3 interface.
In this work, we report the effect of FeCo atomic fraction (0.33< x&am... more In this work, we report the effect of FeCo atomic fraction (0.33< x< 0.54) and temperature on the electrical, magnetic, and tunneling magnetoresistance (TMR) properties of FeCo-Si-O granular films prepared by atom beam sputtering technique. Glancing angle x-ray ...
ABSTRACT Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by... more ABSTRACT Ferromagnetic Ge:Mn has been fabricated by Mn implantation in intrinsic Ge wafers and by pulsed laser annealing with a pulse duration of 300 ns. Due to a segregation instability during laser annealing, Mn segregates at the liquid-solid interface and an approximately 40 nm thick Ge:Mn surface layer is strongly enriched with Mn. Plan-view images reveal a percolating Mn-rich nanonet. Hysteretic anomalous Hall effect has been observed up to 30 K, but it vanishes after etching away the 40 nm thick Mn-rich Ge:Mn surface layer. The nanonet seems to support the correlation between magnetization and hysteretic Hall resistance. Intrinsic scattering in the threads or vertices of this nanonet may lead to the observed anomalous Hall effect.
The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investi... more The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co) thin films are investigated. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range from 200 to 500 °C. Two major effects are reported: (i) a large anomalous Hall effect amounting to 2 μΩ cm, and (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves coincide with the rescaled magnetization curves, a finding that is consistent with spin-dependent transport. These findings suggest that C:Co nanocomposites are promising candidates for carbon-based Hall sensors and spintronic devices.
Memristive devices are popular among neuromorphic engineers for their ability to emulate forms of... more Memristive devices are popular among neuromorphic engineers for their ability to emulate forms of spike-driven synaptic plasticity by applying specific voltage and current waveforms at their two terminals. In this paper, we investigate spike-timing dependent plasticity (STDP) with a single pairing of one presynaptic voltage spike and one post-synaptic voltage spike in a BiFeO3 memristive device. In most memristive materials the learning window is primarily a function of the material characteristics and not of the applied waveform. In contrast, we show that the analog resistive switching of the developed artificial synapses allows to adjust the learning time constant of the STDP function from 25 ms to 125 μs via the duration of applied voltage spikes. Also, as the induced weight change may degrade, we investigate the remanence of the resistance change for several hours after analog resistive switching, thus emulating the processes expected in biological synapses. As the power consump...
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Papers by Danilo Buerger