Properties and Reliability Investigation in Tellurium-Based Conductive Bridge Random Access Memory

• Main Authors: Lin, Chun-An, 林俊安
• Other Authors: Tseng, Tseung-Yuan
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/977at2

博士 === 國立交通大學 === 電子研究所 === 107 === The CBRAM devices with Tellurium as ion source are investigated in this thesis, which are categorized into three parts. In the first part, oxygen-free SiN is used as resistive layer, which prevents oxygen vacancies from being the composition of conductive filaments. Moreover, the self-diffusion of filament is limited in SiN layer, which increases the maximum working temperature in retention test. In addition, the characteristics of CBRAM with Te and TeTiW as top electrodes are compared. In the second part, high-k HfO2 as resistive layer, which is compatible with CMOS process, is used to decrease forming voltage and improve the film uniformity. Furthermore, the characteristics of CBRAM with Ta and TiW as barrier layers are compared. In the last part, because the on/off ratio of devices in the previous parts are lowered resulting from the unstable HRS resistance after several resistive switching cycles, the insertion of HfON layer effectively improves the on/off ratio under a specific switching condition. The detailed descriptions for each part are as following. In the first part, the switching properties of Te and TeTiW top electrodes (TEs) on TiW/SiN/TiN resistive switching memory devices are explored. The TeTiW TE device exhibits more favorable bipolar resistive switching behavior because of the decrease in binding energy after its use. This finding is confirmed through X-ray photoelectron spectroscopy analyses. The filament of the TeTiW TE device is metal like after forming, and the reset process corresponds with the thermal-dissolution mechanism. A physical model based on a Te filament is constructed to explain such phenomena. The TeTiW TE device provides the excellent endurance of more than 10^4 cycles, with an ON/OFF ratio of 500. The improvement can be attributed to the filament’s robustness during the forming and set processes, which prevent its diffusion even at high temperature. The device also features long retention for up to 10^4 s at 225 °C. For the second part, the impact of the barrier layer with TeTiW TE is discussed in the HfO2-based CBRAM devices. The considerable improvement of retention in the CBRAM device using TiW barrier layer is attributed to the lower amount of oxygen vacancies in the switching layer than Ta barrier, which is justified from the O1s core level in X-ray photoelectron spectroscopy analyses. Therefore, the diffusion of Te in the resistive layer of the device with the TiW barrier layer can be limited even at high temperature. The TeTiW/TiW/HfO2/TiN CBRAM device provides an excellent endurance of more than 10^4 cycles, with an ON/OFF ratio of 200. Such a device also features long retention for up to 10^4 s at 200 °C. In the last part, the memory device with dual-layer HfON/HfO2 is applied for reducing variation of read currents and enlarging the memory window. The TeTiW/Ta/HfON/HfO2/TiN device reaches 10^4 switching cycles with ON/OFF ratio of 5000.