The influence of two different ohmic electrodes (W and Ta) on the resistive switching characteristics of TaO x -based resistive random access memory (ReRAM) devices has been studied. Consistently, ...higher resistance OFF states have been observed with the W-ohmic electrode under the same operational conditions for all reset stop voltages (V reset-stop ) during both the dc and ac measurements. The deeper reset for samples with W-electrode is attributed to the less negative Gibbs-free energy of W-oxide compared with Ta-oxide, resulting in easier re-oxidation of the filament through oxygen exchange with the W-electrode. The higher R OFF /R ON (>10 3 ) with the W-electrode enables 3-bit multilevel cell operation in the Pt/W/TaO x /Pt ReRAM device. An excellent retention for these eight states is demonstrated at 125°C for 10 4 s. Furthermore, the TaO x ReRAM device with both the electrodes shows high endurance up to 10 6 cycles based on two states.
The utilization of bipolar-type memristive devices for the realization of synaptic connectivity in neural networks strongly depends on the ability of the devices for analog conductance modulation ...under application of electrical stimuli in the form of identical voltage pulses. Typically, filamentary valence change mechanism (VCM)-type devices show an abrupt SET and a gradual RESET switching behavior. Thus, it is challenging to achieve an analog conductance modulation during SET and RESET. Here, we show that analog as well as binary conductance modulation can be achieved in a Pt/HfO2/TiOx/Ti VCM cell by varying the operation conditions. By analyzing the switching dynamics over many orders of magnitude and comparing to a fully dynamic switching model, the origin of the two different switching modes is revealed. SET and RESET transition show a two-step switching process: a fast conductance change succeeds a slow conductance change. While the time for the fast conductance change, the transition time, turns out to be state-independent for a specific voltage, the time for the slow conductance change, the delay time, is highly state-dependent. Analog switching can be achieved if the pulse time is a fraction of the transition time. If the pulse time is larger than the transition time, the switching becomes probabilistic and binary. Considering the effect of the device state on the delay time in addition, a procedure is proposed to find the ideal operation conditions for analog switching.
Micro solid oxide fuel cells (μ-SOFC) were manufactured with perovskite type proton conductors on silicon substrates and with structured Pt-grid electrodes. In order to miniaturize the μ-SOFCs and to ...shorten the ion path through the electrolyte, the thin film proton conductors were only ~510nm thick. The thin films consist of 10mol% yttrium-doped BaZrO3 (BZY10) and they were deposited by means of chemical solution deposition (CSD). CSD was applied, because it represents a highly attractive fabrication method, considering the relatively low investment costs and flexibility with regard to stoichiometry. The backsides of the μ-SOFCs on the substrates were opened by wet chemical and plasma etching to form the freestanding membranes. The completed μ-SOFCs resist up to a temperature of 450°C. Their electrical properties, such as permittivity, and resistivity were investigated. By means of electrochemical impedance spectroscopy (EIS) in the temperature range of 100°C to 450°C, the resistivity properties and the activation energies of the model μ-SOFC were studied with humid hydrogen in nitrogen at the anode and different oxygen partial pressures at the cathode. The results provide a clear hint for a dominating protonic defect transport mechanism in the electrolyte. In the 450°C measurement, the model μ-SOFCs reached an open circuit voltage of 600mV with 100% oxygen at the cathode and humid hydrogen in nitrogen at the anode.
•Low cost fabrication of Y:BaZrO3 (BZY) films by chemical solution deposition (CSD)•Fully crystalline BZY thin films at temperatures as low as 900°C•The obtained activation energy of ~0.4eV indicates a dominating proton transport.•Micromachining and CSD enabled the fabrication of a model μ-solid oxide fuel cell.•Proof of concept by measurement of an open circuit voltage at the BZY membrane
The oxygen evolution reaction (OER) during alkaline water electrolysis is the bottleneck of water splitting. Perovskite materials have been particularly proposed as good and economically reasonable ...electrocatalysts for the OER, showing promise and advantages with respect to classic metallic electrodes. However, the degradation of perovskites during catalysis limits their service lifetime. Recently, the material BaCo0.98Ti0.02O3−δ:Co3O4 was shown to be electrocatalytically and chemically stable during water electrolysis even under industrially relevant conditions. The lifetime of this perovskite-based system is prolonged by a factor of 10 in comparison to that of Pr0.2Ba0.8CoO3−δ and is comparable to that of industrially applied electrodes. Here we report on the degradation kinetics of several OER catalysts at room temperature, comparatively studied by monitoring the oxygen evolution at microelectrodes. A decrease in the reaction rate within a maximum of 60 s is observed, which is related to chemical and/or structural changes at the oxide surface.
Recently, the sneak-path obstacle in passive crossbar arrays has been overcome by the invention of complementary resistive switches (CRSs) consisting of two bipolar antiserially connected memristive ...elements. Here, we demonstrate the vertical integration of CRS cells based on Cu/SiO 2 /Pt bipolar resistive switches. CRS cells were fabricated and electrically characterized, showing high resistance ratios (R off /R on >; 1500) and fast switching speed (<; 120 μs). The results are one step further toward the realization of high-density passive nanocrossbar-array-based gigabit memory devices.
•Novel Direct-Metal-Laser-Sintered (DMLS) Aluminium Heat Exchangers (HEX).•DMLS HEX filled with Phase Change Materials (PCM) for Li-Ion cells isothermalisation.•Different operating conditions tested ...by changing cell cycles and boundary conditions.•Cells isothermalisation improved by PCM DMLS HEX compared to natural convection.
Operating Li-Ion cells at adverse temperatures can lead to performance decrease and faster ageing effect. A thermal management system (TMS) designed to guarantee the cells isothermal condition is therefore necessary. Phase Change Materials (PCM) can form part of an efficient TMS based on passive cooling. However, when Li-Ion cells are exposed to extreme electrical regimes, PCMs cannot recover all of the latent heat due to their low thermal conductivity. This study experimentally investigates the isothermal performance of PCMs integrated with Direct-Metal-Laser-Sintered (DMLS) aluminium heat exchangers (HEX) as a passive TMS. The DMLS HEXs are employed to enhance the equivalent thermal conductivity of the TMS and thermally connect the Li-Ion cell to the PCM. The TMS performance is evaluated in terms of cell average surface temperature and temperature uniformity. Single and consecutive cycles at different discharge rates are imposed to simulate intermittent and constant loads. To assess the TMS sensitivity to the thermal boundary conditions, the HEX is either insulated or surrounded by the ambient air. Under single discharge cycles, the cell temperature rise and temperature disuniformity decrease using the PCM HEX in both thermal boundary conditions compared to relying on air natural convection. Under consecutive cycles, the temperature rise is minimised when the PCM HEX is not insulated. These results show that PCMs show great potential as a passive TMS for a variety of Li-Ion cells’ operating conditions. However, the optimisation of the PCM-TMS design is found to be case-dependent.
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