Abstract
The effect of a transparent conductive oxide (TCO) buffer layer on the insulator matrix and on the resistive switching process in the metal/TiO2/TCO/metal assembly was studied depending on the material of the TCO (ITO-(In2O3)0.9(SnO2)0.1 or SnO2 or ZnO). For the first time electro-physical studies and near edge x-ray absorption fine structure (NEXAFS) studies were carried out jointly and at the same point of the sample, providing direct experimental evidence that the switching process strongly influences the lowest unoccupied bands and the local atomic structure of the TiO2 layers. It was established that a TCO layer in a metal/TiO2/TCO/metal assembly is an additional source of oxygen vacancies for the TiO2 film. The RL (RH) states are achieved presumably with the formation (rupture) of the electrically conductive path of oxygen vacancies. Inserting an Al2O3 thin layer between the TiO2 and TCO layers to some extent restricts the processes of migration of the oxygen ions and vacancies, and does not allow the anti-clockwise bipolar resistive switching in a Au/TiO2/Al2O3/ITO/Au assembly. The greatest value of the ratio RH/RL is observed for the assembly with a SnO2 buffer layer that will provide the maximum set of intermediate states (recording analog data) and increase the density of information recording in this case.
Highlights
Relentless downscaling of microelectronic devices had already brought the size of their critical parts to the range of few nanometers and continues to challenge scientists and technologists
Detailed analysis of the switching process in metal/TiO2(20nm)/SnO2/metal assembly shows that resistive switching from one state to another state in this structure occurs only by changing the polarity of the applied voltage and under conditions of a strong electric field applied to the TiO2 layer (~ 1MV/cm)
Taking into account a high concentration of oxygen vacancies in transparent-conductive-oxide (TCO) layers we have assumed that TCO layer in metal/TiO2/TCO/metal assembly could be an additional source of oxygen vacancies for TiO2 film
Summary
Relentless downscaling of microelectronic devices had already brought the size of their critical parts to the range of few nanometers and continues to challenge scientists and technologists. Developing nanoscale memory-bit cells [1,2] for non-volatile random access memory (NVRAM) is one key technological step now. Among the many candidates for the next-generation non-volatile memory based on a non-charge mechanism, resistance-switching random access memory (RRAM) has attracted attention as an essential step towards new era of non-Boolean neuromorphic computing [3,4]. As follows from [5] the memristor with memristance M provides a functional dependence between flux φ and charge qdφ =Mdq. In special case when M is itself a function of the charge, other words, the resistance of the material depends on the charge passing through it a new circuit functions such as resistive switching are opened
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