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

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 109 cycles and improved yield in scaled devices thanks to a higher control of the layer structure and properties.