Threshold Switching Characteristics of Te-doped Insulator Thin Films for the Application of Next-generation Non-volatile Memory

Abstract

Threshold switching (TS) characteristics of chalcogenide – abrupt increase of current when the applied electric field exceeds a critical value – has attracted wide attention since its discovery and enabled unique application (selector device) for non-volatile memory. For the TS, group VI elements such as Se or Te primarily constitute the chalcogenide alloy, but Se or Te alone cannot be used as selector device because these elements easily crystallize at room temperature. Recently, Park et al. reported Te-SbO TS selector device. In this report, unique microstructure with Te nanoclusters in insulator matrix was introduced to enhance the stability of the Te amorphous phase. In this thesis, the electrical, chemical and crystallographic properties of Te-SbO, Te-SiO2 and Te-SiN thin films are investigated and their mechanisms of TS are also analyzed. The TS mechanism of Te–SbO thin films with a unique microstructure in which a Te nanocluster is present in the SbO matrix is analyzed. During electro-forming process, amorphous Te filaments are formed between the Te nanoclusters. However, unlike conventional Ovonic threshold switching (OTS) selector devices, it has been demonstrated that the off-current flows along the filament. Numerical calculations show that the off-current is due to the trap present in the filament. We also observed changes in TS parameters through controls in the strength or volume of the filaments. Secondly, the TS of Te-SiO2 thin films has been studied. The as-deposited thin film has a microstructure in which a Te nanocluster is distributed in a SiO2 matrix. During the electro-forming process, amorphous Te filaments are formed among the Te nanoclusters and TS behaviors appear along the filaments. The Te-SiO2 thin film has a high thermal stability due to its unique microstructure, which can provide a high thermal budget for the BEOL process and is process-friendly because it is based on silicon oxide. Lastly, we also fabricated a selector device using Te-SiN thin film to investigate whether TS appears even in the case of a nitride matrix instead of an oxide matrix. The TS phenomenon was also observed in the Te-SiN thin films, and crystallographic and chemical analysis were conducted to analyze microstructure and TS mechanism. In addition, experiments were conducted to measure device specifications.