Transient processes in resistive switching memory devices at ultimate time scale down to sub-nanosecond range

The strong evolution of electronics and its rapid performance progress in the past decades call for ever faster, better scalable, more power efficient and low cost memory technology. The dominating contemporary memory types, dynamic random access memory (DRAM) and Flash, now approach the physical and technological limits beyond which no further scaling is possible. Hence, there is an urgent need for a successor technology. The redox-based resistive switching random access memory (ReRAM) is a novel memory type which is based on a two terminal device structure. The stored information is represented by the resistance of the device which can be switched between two or more different levels. The resistive switching is controlled by applying an appropriate voltage to the device, defined in amplitude and length. The findings presented up to now show a supreme performance of ReRAM. Excelling in speed, scalability, energy efficiency and endurance, ReRAM is a very promising candidate to replace both DRAM as well as Flash. In this thesis, transient processes of the resistive switching are studied at two extreme speeds: First, a slow electrocoloration of iron doped strontium titanate (Fe:STO) single crystals is investigated by means of high resolution transmission optical microscopy. The experiment makes the electro-chemical changes in the crystal visible and demonstrates the homogeneity of the redox processes at a maximum optical resolution down to 500 nm. As a model process, the electrocoloration is linked to the initial electroforming of a ReRAM cell.Second, resistive switching and kinetics of ReRAM devices are investigated. For the first time a multi-level resistive switching of tantalum oxide (TaOx) devices at sub-nanosecond times is presented and the switching kinetics on an extended time scale over 15 decades is demonstrated, performed on the same device. At the nanosecond range the switching event is determined from the pulse signal transients and the dependency of the switching time on the driving signal magnitude is shown. The ultra-fast performance of the TaOx ReRAM devices reaches the speed of the static random access memory (SRAM) but additionally benefits from the non-volatility. The write speed surpasses the concurrent DRAM and it is more than six orders of magnitude faster when compared to Flash. The presented study includes a design of the high-speed ReRAM device as well as a design and construction of a customized measurement setup.A connecting topic of this thesis is metrology. In regard of ReRAM characterization, correct measurement techniques represent a crucial prerequisite for valid results and a correct interpretation. Demonstrated testing of several commercial measurement instruments shows an incorrect operation, representing principal errors of the measurement and a potential risk for the device under test. The errors are analyzed in depth and subsequently a custom setup, optimized for the ReRAM testing, is presented