There is an increased interest in the Conductive Bridge Random Access Memory (CBRAM) and Resistive Random Access Memory (RRAM) because of their excellent scaling potential, low power consumption, high switching speed, good retention and endurance properties. Although, various mechanisms have been proposed to explain the switching behavior in CBRAM devices, i.e. metal ion migration and subsequent formation and rupture of conductive filament, formation of conductive path via oxygen ion transport etc, there are still many aspects of these mechanisms that are little understood or are being disputed. This work probes the details of the switching mechanisms on a new level and asks questions like: 1) How is the formation of nanofilament affected by various degrees of Cu diffusion stopping power of the inert electrode? To answer this question, resistive switches with very thin Cu layers covering the Pt electrode were fabricated and analyzed. 2) How does a limited source of active ions impact the formation and rupture of nanofilaments? To answer this question, new samples with limited Cu supply were fabricated and analyzed. 3) What is the mechanism of nanofilament formation in Pt/TaOx/Pt resistive switches where the active copper electrode is removed and replaced by inert Pt electrode. 4) What are the most suitable conditions (material structure of the device and operation conditions) to set and reset multi nanofilaments? This work summarizes the current status of analysis of the data obtained while attempting to explain interesting phenomena like volatile switching and multiple filament formation experienced by modifying the switch structures. / Master of Science

Emerging memory technologies are being intensively investigated for extending Moore\'s law in the next decade. The conductive bridge random access memory (CBRAM) is one of the most promising candidates. CBRAM shows unique nanoionics-based filamentary switching mechanism. Compared to flash memory, the advantages of CBRAM include excellent scalability, low power consumption, high OFF-/ON-state resistance ratio, good endurance, and long retention. Besides the nonvolatile memory applications, resistive switching devices implement the function of memristor which is the fourth basic electrical component. This research presents the characterization and modeling of Cu/TaOx/Pt resistive switching devices. Both Cu and oxygen vacancy nanofilaments can conduct current according to the polarity of bias voltage. The volatile resistive switching phenomenon has been observed on Cu/TaOx/delta-Cu/Pt devices and explained by a flux balancing model. The resistive devices are also connected in series and in anti-parallel manner. These circuit elements are tested for chaotic neural circuit. The quantum conduction has been observed in the I-V characteristics of devices, evidencing the metallic contact between the nanofilament and electrodes. The model of filament radial growth has been developed to explain the transient I-V relation and multilevel switching in the metallic contact regime. The electroforming/SET and RESET processes have been simulated according to the mechanism of conductive filament formation and rupture and validated by experimental results. The Joule and Thomson heating effects have also been investigated for the RESET processes. / Ph. D.