Redox-based nanoionic resistive memory cells are one of the most promising emerging nanodevices for future information technology with applications for memory, logic and neuromorphic computing. ...Recently, the serendipitous discovery of the link between redox-based nanoionic-resistive memory cells and memristors and memristive devices has further intensified the research in this field. Here we show on both a theoretical and an experimental level that nanoionic-type memristive elements are inherently controlled by non-equilibrium states resulting in a nanobattery. As a result, the memristor theory must be extended to fit the observed non-zero-crossing I-V characteristics. The initial electromotive force of the nanobattery depends on the chemistry and the transport properties of the materials system but can also be introduced during redox-based nanoionic-resistive memory cell operations. The emf has a strong impact on the dynamic behaviour of nanoscale memories, and thus, its control is one of the key factors for future device development and accurate modelling.
Impurities and dopants in memristive devices determine their switching kinetics, performance, and neuromorphic functionalities.
Future development of the modern nanoelectronics and its flagships ...internet of things, artificial intelligence, and neuromorphic computing is largely associated with memristive elements, offering a spectrum of inevitable functionalities, atomic level scalability, and low-power operation. However, their development is limited by significant variability and still phenomenologically orientated materials’ design strategy. Here, we highlight the vital importance of materials’ purity, demonstrating that even parts-per-million foreign elements substantially change performance. Appropriate choice of chemistry and amount of doping element selectively enhances the desired functionality. Dopant/impurity-dependent structure and charge/potential distribution in the space-charge layers and cell capacitance determine the device kinetics and functions. The relation between chemical composition/purity and switching/neuromorphic performance is experimentally evidenced, providing directions for a rational design of future memristive devices.
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.
Pr0.2Ba0.8CoO3-δ (PBCO) and Ba0.5Sr0.5Co0.5Fe0.5O3-δ (BSCF) perovskite thin film electrodes were used as model systems for testing degradation and stability during oxygen evolution reaction (OER) in ...alkaline water electrolysis. The catalyst films were prepared by chemical solution deposition (CSD) and are binder-free. Stepwise aging experiments illustrate a systematical approach to different degrees of degradation of the perovskites after defined testing cycles of cyclic voltammetry in application-near conditions. XPS and EDX characterization at each aging step enables a monitoring of the change in chemical composition during degradation. XPS analysis points to a change in the defect chemistry of PBCO during degradation. The influence of all monitored parameters on the overall electrode service lifetime is shown in a novel end of service life test (ESLT) at thin film perovskite electrodes of 100nm thickness.
Oxygen reduction and evolution have been studied with respect to the development of bifunctional air/oxygen electrode (BFE). Three groups of catalysts have been prepared: (i) Cu
x
Co
3−
x
O
4 by ...thermal decomposition of mixed nitrate and carbonate precursors; (ii) thin films of Co–Ni–Te–O and Co–Te–O were deposited by vacuum co-evaporation of Co, Ni and TeO
2 and (iii) Co
x
O
v
/ZrO
2 films were obtained by electrochemical deposition.
The electrochemical behavior of the chemically synthesized catalysts was studied on classical bilayered gas diffusion electrodes (GDEs), where the catalyst is in form of powder. The GDE catalyzed with vacuum deposited catalysts was prepared by direct deposition of the catalyst on gas-supplying layer, thus creating a ready-to-use gas diffusion electrode. Catalysts prepared electrochemically were first deposited on Ni foam and than pressed onto the gas-supplying layer.
Different catalysts deposited on classical and originally designed GDEs were compared by their electrochemical performances. Cu
0.3Co
2.7O
4 deposited on a classical bilayered GDE with loading of 50
mg
cm
−2 exhibits stable current–voltage characteristics after 200 charge–discharge cycles in a real metal hydride-air battery. The electrochemically and vacuum deposited Co
x
O
v
/ZrO
2, Co–Ni–Te–O and Co–Te–O films exhibit much higher mass activity compared to Cu
0.2Co
2.8O
4 for both oxygen reduction and evolution reactions. The difference is that the loading of electrochemically and vacuum deposited films is 0.06
mg
cm
−2 only, which is a substantial advantage from a practical viewpoint.
Lateral electrochemical metallization (ECM) cells are fabricated with a combined spacer/damascene process. The process allows the realization of nanoscale geometrical distances between the two ...electrodes independent of lithography. Such lateral ECM cells are an essential part in a reconfigurable interconnect system that may yield a strongly increased connectivity in artificial neural networks. The lateral cells show memristive properties comparable to vertical cells with switching voltages in the range of -1.5 V to 2.5 V. The influence of electrode line edge roughness on SET kinetics of such lateral cells is investigated via kinetic Monte Carlo simulations, finding a minor influence on SET time variability.
Low yttria-doped cubic zirconium oxide nitride single crystals with high nitrogen contents show unexpected high oxygen ion conductivity in a temperature range between 100°C and 300°C. The observed ...values are about two orders of magnitude higher than the conductivities for conventionally used 9.5 YSZ. This can be related to an optimal anion vacancy concentration within the oxide nitride material and the low activation energy of the vacancy-based conductivity process.
•High oxygen ion conductivity at low temperatures for Y-doped ZrON•Optimal anion vacancy concentration and low conductivity activation energy•Combination of two positive effects for improved ionic conductivity
The speed of the SET operation of a Cu/Ta2O5/Pt atomic switch from a high-resistance state to a low-resistance state was measured by transient current measurements under the application of a short ...voltage pulse. The SET time decreased exponentially with increasing pulse amplitude, reaching as low as 1 ns using moderate pulse voltages. This observation shows that oxide-based atomic switches hold potential for fast-switching memory applications. From a comparison with atomistic nucleation theory, Cu nucleation on the Pt electrode was found to be the likely rate-limiting process determining the SET time.
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