16 - Resistive switching characteristics of TiO2 thin films for nonvolatile memory applications

Abstract

The resistive random-access memory (RRAM) is an emerging memory device which possesses both the capabilities of inherent memory and computation primarily due to its nonvolatile nature, low operational power, ultra-fast switching speed, and high density to overcome fundamental limitations of von Neumann computer architecture. TiO2 due to excellent compatibility with existing CMOS technology is a potential material for resistive switching. Although well studied, a clear understanding of switching mechanisms in TiO2 and its consequences on other switching parameters such as switching power, switching times, switching variability, etc., are poorly understood. In this chapter, resistive switching characteristics of TiO2 thin films for nonvolatile memory applications have been reviewed. In case of TiO2-based RRAM devices with noble metal electrode such as Au/TiO2/Pt, unipolar resistive switching with initial electroforming process was observed. The transient characteristics of Au/TiO2/Pt devices revealed reset and set switching times ∼250μs and 180ns, respectively. The significant decrease in reset switching time up to 400ns by applying high-amplitude voltage pulse was explained on the basis of a self-accelerated thermal dissolution of conducting filaments. In contrast, low-power, high-speed, and 3-bit multilevel bipolar resistance switching operation was observed in TiO2 when copper was used as counterelectrode. Low programming voltages ≤1V along with low reset current ∼10μA and fast switching time of ∼250ns resulted in ultra-low energy (∼pJ) memory operation of Cu/TiO2/Pt devices. Multibit resistive switching with eight distinct and nonoverlapping resistance states was obtained in Cu/TiO2/Pt devices by controlling compliance current during the set process. TiO2-based RRAM devices with fast and reliable resistive switching at low operating power can be promising future memory applications.