Investigation of Bipolar Resistive Switching Characteristics of Si3N4-based RRAM with MIS Structure

Abstract

New memories such as phase change RAM (PRAM), magnetoresistive RAM (MRAM) and resistive RAM (RRAM) are expected to replace Si-based DRAM and NAND Flash faced with technical and physical limits. RRAM is a strong candidate for high density and low power application because of its simple structure, CMOS compatibility, scalability and applicability of 3D structure and MLC operation. However, unsolved some critical issues such as the leakage currents at crossbar array, high operating current and poor uniformity are an obstacle for commercialization in market. Recently, RRAM using transition metal oxides (TMO) such as HfO2, TaO2 shows excellent resistive switching characteristics such as high endurance (>109), fast writing speed (<10 ns), scalability (<10 nm). However, other resistive materials can be potential candidates when having comparative advantage and finding their suitable applications. Nitride-based RRAM have been recently reported with good endurance and retention and fast switching speed. In this thesis, Si3N4-based RRAM with metal-insulator-silicon (MIS) was fabricated in respect to high density, mass production issues and new applications. MIS structure has an advantage of integrating with a selector such as diode or transistor without bottom electrode (BE) using metal which must require deposition and patterning. And, Ti as top electrode (TE) is used to avoid noble metals such as Pt, Au, and Ru which are expensive and hard to etch. Low pressure chemical vapor deposition (LPCVD) is used for deposition of Si3N4. LPCVD is suitable for vertical 3D stacking due to good step coverage for high density. The switching mechanism of this memory structure is explained by fitting in double logarithmic scale and temperature dependency. HRS and LRS are well agreement with SCLC (Space charge limited current). Forming-free behavior that is originated from thin thickness of switching layer is useful to low operation switching. And, self-compliance is observed by restriction of parasitic resistance without an external current limiter. Also, multi-level storage ability is demonstrated for potential of MLC operation for high density. Distinct set and reset transition that are gradually modulated by controlling voltage stop and compliance current can be used to employ MLC operation. Finally, the potentiating and depressing of the current are performed by pulse and DC voltage mode for neuromorphic systems as new applications.