Percorrer por autor "Meskers, S. C. J."
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- Anomalous temperature dependence of the current in a metal-oxide-polymer resistive switching diodePublication . Gomes, Henrique L.; Rocha, Paulo R. F.; Kiazadeh, Asal; De Leeuw, Dago M.; Meskers, S. C. J.Metal-oxide polymer diodes exhibit non-volatile resistive switching. The current–voltage characteristics have been studied as a function of temperature. The low-conductance state follows a thermally activated behaviour. The high-conductance state shows a multistep-like behaviour and below 300K an enormous positive temperature coefficient. This anomalous behaviour contradicts the widely held view that switching is due to filaments that are formed reversibly by the diffusion of metal atoms. Instead, these findings together with small-signal impedance measurements indicate that creation and annihilation of filaments is controlled by filling of shallow traps localized in the oxide or at the oxide/polymer interface.
- Electroforming process in metal-oxide-polymer resistive switching memoriesPublication . Chen, Q.; Gomes, Henrique L.; Kiazadeh, Asal; Rocha, Paulo R. F.; De Leeuw, Dago M.; Meskers, S. C. J.Electroforming of an Al/Al2O3/polymer/Al esistive switching diode is reported. Electroforming is a dielectric soft-breakdown mechanism leading to hysteretic current–voltage characteristics and non–volatile memory behavior. Electron trapping occurs at early stages of electroforming. Trapping is physically located at the oxide/polymer interface. The detrapping kinetics is faster under reverse bias and for thicker oxides layers. Thermally detrapping experiments give a trap depth of 0.65 eV and a density of 5x1017 /cm2. It is proposed that the trapped electrons induce a dipole layer across the oxide. The associated electric field triggers breakdown and ultimately dictate the overall memory characteristics.
- Intrinsic and extrinsic resistive switching in a planar diode based on silver oxide nanoparticlesPublication . Kiazadeh, Asal; Gomes, Henrique L.; Rosa da Costa, Ana; Moreira, José; De Leeuw, Dago M.; Meskers, S. C. J.Resistive switching is investigated in thin-film planar diodes using silver oxide nanoparticles capped in a polymer. The conduction channel is directly exposed to the ambient atmosphere. Two types of switching are observed. In air, the hysteresis loop in the current–voltage characteristics is S-shaped. The high conductance state is volatile and unreliable. The switching is mediated by moisture and electrochemistry. In vacuum, the hysteresis loops are symmetric, N-shaped and exhibit a negative differential resistance region. The conductance states are non-volatile with good data retention, programming cycling endurance and large current modulation ratio. The switching is attributed to electroforming of silver oxide clusters.
- Lithium fluoride injection layers can form quasi-Ohmic contacts for both holes and electronsPublication . Bory, B. F.; Rocha, Paulo R. F.; Janssen, R. A. J.; Gomes, Henrique L.; de Leeuw, D. M.; Meskers, S. C. J.Thin LiF interlayers are typically used in organic light-emitting diodes to enhance the electron injection. Here, we show that the effective work function of a contact with a LiF interlayer can be either raised or lowered depending on the history of the applied bias. Formation of quasi-Ohmic contacts for both electrons and holes is demonstrated by electroluminescence from symmetric LiF/polymer/LiF diodes in both bias polarities. The origin of the dynamic switching is charging of electrically induced Frenkel defects. The current density-electroluminescence-voltage characteristics can qualitatively be explained. The interpretation is corroborated by unipolar memristive switching and by bias dependent reflection measurements. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
- Low-frequency diffusion noise in resistive-switching memories based on metal-oxide polymer structurePublication . Rocha, P. R. F.; Gomes, Henrique L.; Vandamme, L. K. J.; Chen, Q.; Kiazadeh, Asal; De Leeuw, Dago M.; Meskers, S. C. J.Low-frequency noise is studied in resistive-switching memories based on metal–oxide polymer diodes. The noise spectral power follows a 1/fγ behavior, with γ = 1 in the ohmic region and with γ = 3/2 at high bias beyond the ohmic region. The exponent γ = 3/2 is explained as noise caused by Brownian motion or diffusion of defects which induce fluctuations in diode current. The figure of merit to classify 1/f noise in thin films has an estimated value of 10−21 cm2/Ω, which is typical for metals or doped semiconductors. This value in combination with the low diode current indicates that the 1/f noise is generated in the narrow localized regions in the polymer between the contacts. The analysis unambiguously shows that the current in bistable nonvolatile memories is filamentary.
- Low-frequency noise as a diagnostic tool for OLED reliabilityPublication . Rocha, Paulo R. F.; Vandamme, L. K. J.; Meskers, S. C. J.; Gomes, Henrique L.; De Leeuw, D. M.; Van De Weijer, P.Organic light emitting diodes (OLED), either based on polymers or small molecules, suffer from early failure: an unpredictable sudden increase in current with a total loss of light output. This work addresses this problem using small-signal impedance measurements and electrical noise techniques. Robust OLEDs show a current noise spectrum proportional to 1/f. OLEDs susceptible to failure have 1/f3/2 and/or may start exhibiting a standard 1/f behavior that rapidly evolves with time (typical 30 minutes) to 1/f1.6. In addition OLEDs susceptible to early failure have a higher DC leakage. It is proposed that a combination of both measurements can be used as a diagnostic tool for OLED reliability in a production line. Insight into the physics of the degradation mechanism is also provided. Unreliable OLEDs exhibit current switching events and optical blinks at wavelengths higher than the polymer band gap electroluminescence. It is proposed that degradation is induced by the appearance of an insulating resistive switching layer. Charge recombination trough this layer is responsible for the optical and electrical blinks. © 2013 IEEE.
- Non-volatile memory device using a polymer modified nanocrystalPublication . Kiazadeh, Asal; Gomes, Henrique L.; Costa, Ana M. Rosa da; Moreira, José; De Leeuw, Dago M.; Meskers, S. C. J.Thin-film planar structures using AgCl nanocrystals embedded in a polymer blend; exhibit reliable and reproducible switching between different non-volatile conductance states. It is shown that resistive switching in these systems cannot be related with migration diffusion or aggregation of metals to form metallic filaments. This is supported by temperature-dependent measurement showing that the current in the high conductance state is thermal activated (0.6 eV).
- Opto-electronic characterization of electron traps upon forming polymer oxide memory diodesPublication . Chen, Q.; Bory, Benjamin F.; Kiazadeh, Asal; Rocha, Paulo R. F.; Gomes, Henrique L.; Verbakel, F.; De Leeuw, Dago M.; Meskers, S. C. J.Metal-insulator-polymer diodes where the insulator is a thin oxide (Al2O3) layer are electroformed by applying a high bias. The initial stage is reversible and involves trapping of electrons near the oxide/polymer interface. The rate of charge trapping is limited by electron transport through the polymer. Detrapping of charge stored can be accomplished by illuminating with light under short-circuit conditions. The amount of stored charge is determined from the optically induced discharging current transient as a function of applied voltage and oxide thickness. When the charge density exceeds 8 1017/m2, an irreversible soft breakdown transition occurs to a non-volatile memory diode.
- Planar non-volatile memory based on metal nanoparticlesPublication . Kiazadeh, Asal; Gomes, Henrique L.; Costa, Ana M. Rosa da; Rocha, P. R. F.; Chen, Q.; Moreira, José; De Leeuw, Dago M.; Meskers, S. C. J.Resistive switching properties of silver nanoparticles hosted in an insulating polymer matrix (poly(N-vinyl-2-pyrrolidone) are reported. Planar devices structures using interdigitated gold electrodes were fabricated. These devices have on/off resistance ratio as high as 103 , retention times reaching to months and good endurance cycles. Temperature-dependent measurements show that the charge transport is weakly thermal activated (73 meV) for both states suggesting that nanoparticles will not aggregate into a metallic filament.
- Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halidePublication . Bory, B. F.; Wang, J. X.; Gomes, Henrique L.; Janssen, R. A. J.; de Leeuw, D. M.; Meskers, S. C. J.Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron-hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 10(25)/m(3). The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics. (C) 2014 Author(s).