Deposition and characterization of threshold-switching Ge-Sb-Bi-Te and Si-As-Te thin films for the application of next-generation non-volatile memory

Abstract

endurance test using 200 ns-long pulse showed little degradation of the device performance after 1,000 times of ON-OFF switching. Suppression of the leakage current by serial connection of TiO2 unipolar memory and Si-As-Te threshold-switching thin film was observed, which indicates that Si-As-Te threshold switch is a promising candidate for selector devices of crossbar array of resistive switching memory.

thermal engineering of phase change material by substitutional doping.

Amorphous Si-As-Te thin films were sputter-deposited to make threshold switch for selector devices of crossbar array of resistive switching memory. Bi-directional flow of current is possible in threshold switch, which is required for selector device of bipolar resistive switching memory. Instead of Ge and Sb used for phase-changing chalcogenides, Si and As are used for threshold-switch application because bonding enthalpy of Si-Te and As-Te are larger than that of Ge-Te and Sb-Te (bonding enthalpy: Si-Te 38.5 kcal/mol, As-Te 32.7 kcal/mol, Ge-Te 35.5 kcal/mol, and Sb-Te 31.6 kcal/mol). Higher thermal stability of Si-As-Te enabled the construction of stable threshold switch

Threshold-switching of chalcogenide – abrupt decrease of resistance when the applied electric field exceeds a critical value – has attracted wide attention since its discovery and enabled unique application for non-volatile memory. For the threshold switching, group VI elements such as Se or Te primarily constitute the chalcogenide alloy, but Se or Te alone cannot be used for non-volatile memory because these elements easily crystallizes at room temperature. To enhance the stability of the amorphous phase, group IV and V elements are added to cross-link the atomic network within amorphous phase. In this thesis, group IV and V elements are varied for different application of chalcogenides

Ge, Sb, and Bi for phase change memory and Si and As for threshold-switch application.

Bi is added to Ge2Sb2Te5 – the most intensely studied material for phase change memory – by cosputtering Bi2Te3 and Ge2Sb2Te5 compound targets to incorporate Bi atoms in Ge/Sb sites of Ge2Sb2Te5. This study revealed that incorporated Bi increased the crystallization speed of both amorphous and liquid phase. This was attributed to the decrease of the activation energy of crystallization and reduction of the thermal conductivity by doping Bi to Ge2Sb2Te5. It is suggested that Bi-doped Ge2Sb2Te5 shows a guideline for the development of future phase change memory