Multilayer OTS Selectors Engineering for High Temperature Stability, Scalability and High Endurance

Abstract

We present the engineering of Ovonic Threshold Switching (OTS) Multilayer (ML) Selector device based on the stacking of N-doped SbSe and Ge layers. By tuning individual layers thicknesses and N content of the ML stack, we demonstrate the possibility to highly improve selector stability during integration Back-End-of-Line (BEOL) and to reduce device-to-device variability. We show how our OTS ML presents fundamental electrical characteristics that are compatible with the ones of standard bulk OTS achieved by co-sputtering technique, but enabling reliable switching operations up to 160 • C with lower variability. We study by FTIR and Raman spectroscopy the layers structure revealing the high stability achieved in OTS ML wrt bulk OTS even after 3 hours at 400 • C. In TEM/EDX analyses performed on cycled and annealed devices, we highlight the preserved integrity of the amorphous structure in OTS ML wrt bulk. Finally, OTS ML solution allows reliable endurance up to more than 10 9 cycles and improved yield in scaled devices thanks to a higher control of the layer structure and properties.

Multilayer Structure in SeAsGeSi-based OTS for High Thermal Stability and Reliability Enhancement

“…SAGS spectrum shows an evolution after annealing, which could correspond to the starting of material segregation. As shown in our previous work on SbSe-based OTS [6], the ML structure delays structural changes related to crystallization process in OTS layers. Indeed, the introduction of GeN layers in SAGS increases the Ge-Se bonds with respect to As-Se and Si-Se because of interlayer interactions leading and Ge-Se features around 190 cm 1 (and 212 cm 1 for ML) [8,11]- [13] with Ge-Ge shoulders at 300 cm 1 .…”

“…4. SAGS devices do not show functionality above 250 • C. At the same time, the leakage current (I off ) increases with operating temperature as already observed in [4,6]. The saturation voltage E m for each voltage is obtained by current vs temperature fitting (not reported) compatibly with [17] for virgin (before firing) and initialized devices (after firing).…”

“…However, AsSe-based OTS materials featuring the best high temperature stability performance are based on four or even more elements and their high complexity could lead to an intrinsic variability on their electrical parameters [4,5]. In order to address such issue, we recently demonstrated that OTS Multilayer (ML) structure is an interesting method to decrease variability without affecting the main device characteristics [6,7].…”

Material and Structural Engineering of Ovonic Threshold Switch for Highly Reliable Performance

“…[26] Lagnua et al suggested a specific multi-layered chalcogenide structure for a thermally stable OTS device. [27] The thermal stability of OTS materials can also benefit the endurance characteristics of OTS because the stability of the localized electronic traps in the amorphous chalcogenides is the most influential factor in the operation voltage distribution of an OTS and its low leakage current level. In addition, to ensure high endurance characteristics, the current overshoot (the so-called "surge current") should be considered.…”

Multilayer doped-GeSe OTS selector for improved endurance and threshold voltage stability

“…It is expected that the heterostructures of different chalcogenide can be tried to improve the performance of OTS devices, referring to the phase change heterojunction of phase change devices [19−21] . Furthermore, some reported multilayer OTS selectors were recently put forward with too much layers, which make it difficult to manufacture [21,22] . Therefore, a novel structure with simple multilayer is a new idea of device optimization and is quite necessary to be proposed.…”