Memristors based on anionic-electronic resistive switches represent a promising alternative to transistor-based memories because of their scalability and low power consumption. To date, studies on resistive switching have focused on oxygen anionic or electronic defects leaving protonic chargecarrier contributions out of the picture despite the fact that many resistive switching oxides are well-established materials in resistive humidity sensors. Here, the way memristance is affected by moisture for the model material strontium titanate is studied. First, characterize own-processed Pt|SrTiO 3-δ |Pt bits via cyclic voltammetry under ambient conditions are thoroughly characterized. Based on the high stability of a non-volatile device structures the impact of relative humidity to the current-voltage profi les is then investigated. It is found that Pt|SrTiO 3-δ |Pt strongly modifi es the resistance states by up to 4 orders of magnitude as well as the device's current-voltage profi le shape, number of crossings, and switching capability with the level of moisture exposure. Furthermore, a reversible transition from classic memristive behavior at ambient humidity to a capacitively dominated one in dry atmosphere for which the resistive switching completely vanishes is demonstrated for the fi rst time. The results are discussed in relation to the changed Schottky barrier by adsorbed surface water molecules and its interplay with the charge transfer in the oxide.

Memristors based on mixed anionic‐electronic conducting oxides are promising devices for future data storage and information technology with applications such as non‐volatile memory or neuromorphic computing. Unlike transistors solely operating on electronic carriers, these memristors rely, in their switch characteristics, on defect kinetics of both oxygen vacancies and electronic carriers through a valence change mechanism. Here, Pt|SrTiO3‐δ|Pt structures are fabricated as a model material in terms of its mixed defects which show stable resistive switching. To date, experimental proof for memristance is characterized in hysteretic current–voltage profiles; however, the mixed anionic‐electronic defect kinetics that can describe the material characteristics in the dynamic resistive switching are still missing. It is shown that chronoamperometry and bias‐dependent resistive measurements are powerful methods to gain complimentary insights into material‐dependent diffusion characteristics of memristors. For example, capacitive, memristive and limiting currents towards the equilibrium state can successfully be separated. The memristor‐based Cottrell analysis is proposed to study diffusion kinetics for mixed conducting memristor materials. It is found that oxygen diffusion coefficients increase up to 3 × 10–15 m2s–1 for applied bias up to 3.8 V for SrTiO3‐δ memristors. These newly accessible diffusion characteristics allow for improving materials and implicate field strength requirements to optimize operation towards enhanced performance metrics for valence change memristors.

In this paper, we present a strategy to use interfacial strain in multilayer heterostructures to tune their resistive response and ionic transport as active component in an oxide-based multilayer microdot device on chip. For this, fabrication of strained multilayer microdot devices with sideways attached electrodes is reported with the material system Gd0.1Ce0.9O(2-δ)/Er2O3. The fast ionic conducting Gd0.1Ce0.9O(2-δ) single layers are altered in lattice strain by the electrically insulating erbia phases of a microdot. The strain activated volume of the Gd0.1Ce0.9O(2-δ) is investigated by changing the number of individual layers from 1 to 60 while keeping the microdot at a constant thickness; i.e., the proportion of strained volume was systematically varied. Electrical measurements showed that the activation energy of the devices could be altered by Δ0.31 eV by changing the compressive strain of a microdot ceria-based phase by more than 1.16%. The electrical conductivity data is analyzed and interpreted with a strain volume model and defect thermodynamics. Additionally, an equivalent circuit model is presented for sideways contacted multilayer microdots. We give a proof-of-concept for microdot contacting to capture real strain-ionic transport effects and reveal that for classic top-electrode contacting the effect is nil, highlighting the need for sideways electric contacting on a nanoscopic scale. The near order ionic transport interaction is supported by Raman spectroscopy measurements. These were conducted and analyzed together with fully relaxed single thin film samples. Strain states are described relative to the strain activated volumes of Gd0.1Ce0.9O(2-δ) in the microdot multilayer. These findings reveal that strain engineering in microfabricated devices allows altering the ionic conduction over a wide range beyond classic doping strategies for single films. The reported fabrication route and concept of strained multilayer microdots is a promising path for applying strained multilayer oxides as active new building blocks relevant for a broad range of microelectrochemical devices, e.g., resistive switching memory prototypes, resistive or electrochemical sensors, or as active catalytic solid state surface components for microfuel cells or all-solid-state batteries.

Resistive switches based on anionic electronic conducting oxides are promising devices to replace transistor-based memories due to their excellent scalability and low power consumption. In this study, we create a model switching system by manufacturing resistive switches based on ultrathin 5 nm, epitaxial, and grain boundary-free strontium titanate thin films with subnanometer surface roughness. For our model devices, we unveil two competing nonvolatile resistive switching processes being of different polarities: one switching in clockwise and the other in counterclockwise direction. They can be activated selectively with respect to the effective switching voltage and time applied to the device. Combined analysis of both processes with electrical DC-methods and electrochemical impedance spectroscopy reveals that the first resistive switching process is filament-based and exhibits counterclockwise bipolar resistive switching. The R(OFF)/R(ON) resistance ratio of this process is extremely stable and can be tuned in the range 5-25 depending on the switching voltage and time. Excitingly, at high electric field strength a second bipolar resistive switching process was found. This process is clockwise and, therefore, reveals the opposite polarity switching direction when compared to the first one. Both processes do not obstruct each other, consequently, stable 1, 2, or even 3 crossover current-voltage (I-V) characteristics can be addressed for the memory bits. Equivalent circuit model analysis and fitting of impedance characteristics unequivocally show for the created grain boundary free switches that the oxide's defects and its carrier distribution close to the electrode interface contribute to the resistive switching mechanism. The addressability of two sets of resistive ON and OFF states in one device through electric field strength and switching time offers exciting new operation schemes for memory devices.

high switching speed, nonvolatility, and scalability. [1] These devices were linked to the exciting concept of memristors, [2][3][4][5][6] which not only exhibit superior memory properties but are also considered to be a crucial part in neuromorphic computing hardware because of their outstanding properties, such as spike time dependent plasticity or the capability of multilevel data storage. [7] These devices consist of a simple metal|oxide|metal structure, for which in valence change memories the metal electrodes are selected to be inactive, e.g., by the choice of platinum. [8] Here, under high electrical field, typically in the range of >10 6 V m −1 , [8,9] the defects become mobile within the metal oxide and are altering the overall resistance state of the memristor. Despite the exciting switching performances reported in literature there are still many obstacles to overcome such as endurance, variability, and uniformity issues. [10] Therefore it is essential to get a better understanding of the underlying fundamentals and to unveil the defect chemistry of metal oxide-based thin films under high electrical fields at ambient conditions. In particular the role of defects, i.e., oxygen vacancies, protonic species, and electronic carriers within the metal oxide require attention as they define the final memristive characteristics. Fundamental studies on memristors predominantly address the interplay of oxygen vacancies and electronic carriers within the metal-oxide toward memristance. [11] However, contributions of protonic defects and their interplay with oxygen vacancies and electronic carriers are only rarely considered. Even though protonic defects are omnipresence in metal oxide thin films introduced either by the fabrication process and handling of the devices or through the reaction of atmospheric species like moisture during operation. Through this work we therefore focus on bipolar resistive switching valence change memories to study the role of protonic defects to memristance and its electric response for strontium titanate, SrTiO 3 .For this, we fabricate switching devices based on SrTiO 3 which is a well-suited model material and memristive oxide. The selected oxide is a mixed conductor with electronic p-type conduction at ambient conditions with a low cationic mobility when compared to the mobility of oxygen anions. [12] The cubic perovskite crystal structure of SrTiO 3 is stable over a wide Resistive switching devices based on oxides have outstanding properties, making them a promising candidate to replace today's transistor-based computer memories as non-volatile valence change memories, and can even find future application in neuromorphic computing. To date, the scientific discussion is so far mainly restricted to oxygen vacancy contributions disregarding the role of protonic defects on resistive switching. In this work, the effect of moisture and protonic contributions on resistive switching by changes in the surface to bulk ratio and oxide surface exposure of the oxide SrTiO 3 is studied. Here,...