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- New electronic memory device concepts based on metal oxide-polymer nanostructures planer diodesPublication . Kiazadeh, Asal; Rocha, P. R. F.; Chen, Q.; Gomes, Henrique L.Nanostructure silver oxide thin films diodes can exhibit resistive switching effects. After an electroforming process the device can be programmed between a low conductance (off-state) and high conductance (on- state) with a voltage pulse and they are already being considered for non-volatile memory applications. However, the origin of programmable resistivity changes in a network of nanostructure silver oxide embedded in polymer is still a matter of debate. This work provides some results on a planer diode which may help to elucidate resistive switching phenomena in nanostructure metal oxide diodes. The XRD pattern after switching appears with different crystalline planes, plus temperature dependent studies reveal that conduction of both on and off states is weak thermal activated. Intriguing the carrier transport is the same for both on and off-states. Difference between states comes from the dramatic changes in the carrier density. The main mechanism of charge transport for on-state is tunneling. The charge transport leads to SCLC in higher voltages pulse for the off state. The mechanism will be explained based on percolation concepts.
- Resistive switching of silicon-silver thin film devices in flexible substratesPublication . Dias, C.; Leitao, D. C.; Freire, C. S. R.; H, Gomes; Cardoso, S.; Ventura, J.Novel applications for memory devices demand nanoscale flexible structures. In particular, resistive switching (RS) devices are promising candidates for wearable and implantable technologies. Here, the Pt/Si/Ag/TiW metal-insulator-metal structure was fabricated and characterized on top of flexible substrates using a straightforward microfabrication process. We also showed that these substrates are compatible with sputtering deposition. RS was successfully achieved using both commercial cellulose cleanroom paper and bacterial cellulose, and polymer (PET) substrates. The bipolar switching behavior was observed for both flat and bent (under a radius of 3.5 mm) configurations. The observed phenomenon was explained by the formation/rupture of metallic Ag filaments in the otherwise insulating Si host layer.
- 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).
- 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.
- 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.
- Switching dynamics in non-volatile polymer memoriesPublication . Verbakel, F.; Meskers, S. C. J.; Janssen, R. A. J.; Gomes, Henrique L.; van den Biggelaar, A. J. M.; De Leeuw, Dago M.The time dependence of resistive switching in metal-metal oxide-organic semiconductormetal diodes is investigated. The switching dynamics is controlled by two intrinsic time dependences. A single switching event occurs in a time scale of 400 nanoseconds, but the maximum repetitive switching between ON- and OFF-states is limited by a ‘‘dead time” of a few milliseconds. The dead time is the waiting time after programming in which a next switch is inhibited. Therefore, fast repetitive pulsing prevents the observation of non-volatile switching and limits the maximum clock rate at which these memories can be used. Understanding the origin of this dead time is crucial to future memory applications. Furthermore,the occurrence of a dead time is possibly the origin of the huge variation in the reported switching times.