STABILIZATION OF NICKEL CONDUCTIVE FILAMENT FOR IMPROVING RESISTIVE SWITCHING

Abstract

these are considered major problems in the CBRAM device. Therefore, in order to improve characteristics of CBRAM, the CF nucleation sites should be controlled during repeated switching cycles. In this dissertation, we improve the resistive switching (RS) characteristics by controlling the Ni conductive filaments (CFs) using various methods. For the first work in this dissertation, RS properties and mechanism were investigated for a Ta-layer-embedded TaOx film compared to TaOx film without a Ta layer for the application of CBRAMs. The Ta-embedded TaOx device exhibited superior switching characteristics compared to the device without a Ta layer due to a modified switching mechanism. The Ta-embedded device is regarded as a combination of two devices (Ni/TaOx/Ta and Ta/TaOx/NiSi). During the forming process, Ni CF formed over the whole combined device. However, formation and rupture of Ni CFs occurred only in the Ni/TaOx/Ta region, while Ni CFs in Ta/TaOx/NiSi were unchanged by the applied bias due to the electric field screening effect of the embedded Ta layer. The random formation of Ni CFs can be suppressed by unchanged Ni CFs in the Ta/TaOx/NiSi region because the electric field is concentrated on top of the Ni. Second, NH3 plasma treatment was utilized to enhance the RS properties. Au/Ni/TaOx/NiSi and Au/Ni/NH3 plasma-treated TaOx/NiSi resistance RAM (RRAM) devices were fabricated and the RS properties of these devices were subsequently investigated. Both RRAM devices exhibited conventional electrochemical metallization memory (ECM) behaviors. However, the NH3 plasma-treated samples exhibited improved resistance distribution compared with that of nontreated samples due to the remaining Ni conductive filaments (CF), even following a RESET process. Additionally, superior retention properties longer than 104 s were observed due to the formation of stable Ni CFs. The formation of a defect-minimized TaON layer, observed via X-ray photoelectron spectroscopy (XPS), could be the source of stability for the Ni CFs, resulting in improved device behavior for the NH3 plasma-treated samples. For the final work of dissertation, RS characteristics and reliability of Au/Ni/TaOx/NiSi and Au/Ni/TaON/NiSi CBRAM devices were investigated. To study the effect of N on RS properties, N was incorporated into the TaOx layer in some devices. The amount of N in the TaON film was adjusted by changing the N partial pressure during sputtering. The device with the N-free TaOx layer failed to operate, whereas the devices with N incorporated into this layer showed typical CBRAM operation. In addition, the CBRAM device with the higher N concentration exhibited more stable current levels and excellent retention properties.; Conventional non-volatile memory (NVM) including NAND flash memory has experienced scaling limitations under the 10 nm technology node due to charge loss tolerance and cell to cell interference. Intensive research toward the development of next-generation NVM devices such as ferroelectric random access memory (FeRAM), magnetic RAM (MRAM), phase change RAM (PCRAM), and resistance RAM (RRAM), which have the potential to replace conventional NVM, is currently underway. Among these potential solutions, RRAM has attracted particular attention due to its many advantages, including simple metal-insulator-metal (MIM) structure, fast switching speed, and excellent scalability, under the 10 nm technology node. The ReRAM device could be classified by the operation mechanism. One is anion based resistive switching memory or valence change memory (VCM). The other is cation based memory which commonly known as conductive bridge random access memory (CBRAM), programmable metallization cells (PMCs), and electrochemical metallization memory (ECM). The operation mechanism of VCM is mainly due to oxygen vacancy (Vo). However, random nucleation/growth properties of CF results in a large fluctuation of the on/off ratio and SET/RESET voltages (VSET and VRESET)