SiNx-Based Resistive Memory with Built-in Selectors

Abstract

The drastic rise of the internet of things (IoT), cloud computing, and big data centers is generating an urgent demand for high-performance/low-power memory. However, conventional charge-based memories, such as flash memory and dynamic random access memory (DRAM), are rapidly approaching their scaling limits. As an alternative, resistive switching in a dielectric film sandwiched between top and bottom electrodes (BEs) has attracted great interest for next-generation non-volatile memory applications, due to its low power consumption, fast switching time, and superb scalability down to the atomic level. Among a variety of resistance materials, silicon-based dielectrics (e.g., Si, SiOx, and SiNx) have recently drawn great deal of attention from many researchers, owing to their good compatibility to conventional Si CMOS processes. Especially, SiNx-based resistive memory shows better switching performance than the SiOx-based devices, thanks to their abundant defects. In spite of recent advances in resistive memories, some key challenges such as overshoot current and sneak current in crossbar arrays still need to be overcome. In introductory part, the advantage of silicon nitride-based RRAM with Si bottom electrode is also described. In addition, the overshoot current and sneak current path issues in cross-point RRAM are discussed and a possible soultion is also presented. In this dissertation, the self-selection SiNx-based RRAM devices are proposed and their resistive switching characterization and mechanism were discussed. Firstly, the resistive switching characteristics of SiN-based RRAM with MIS structure was investigated. The different reset transitions are observed depending on the LRS resistance. The smooth gradual reset switching offers potential application for a synaptic device in neuromorphic system. Next, the SiNx-based RRAM with tunnel barrier shows built-in nonlinearity without an additional selector device. The high selectivity in the device with tunnel barrier can be explained by the fact that the electric field depedent nonlinear carrier injection. For another approach, the diode-like resistive switching is achieved by controling dopant concentration in silicon BE. high rectification ratio (>105) between forward and reverse currents for unipolar switching mode is demonstrated. Also, the forming polarity and nonlinearity in bipolar switching mode is discussed. The high selectivity and self-rectifying characteristics of SiNx-based RRAM cell would be one of the most virtuous merits in the high-density crossbar array.