Strain investigation of PECVD passivation layer for ferroelectric domain wall random access memory

Ferroelectric domain-wall random access memory (DWRAM), based on the utilization of highly conductive domain walls in insulating ferroelectric LiNbO3 (LNO) single-crystal thin films, holds great promise for the future of memory storage. The ability to scale this technology up in a crossbar architecture means that it has the otential to surpass the storage density capabilities of commercial ferroelectric random access memory devices. Nevertheless, the passivation layer in the vertically integrated structure (VIS) architecture is critical because it affects many vital parameters of the memory such as retention, on/off current ratio, reliability, etc. Therefore, a detailed strain investigation of silicon nitride and silicon dioxide fabricated by plasma-enhanced chemical vapor deposition (PECVD) is presented. Furthermore, the effect of residual strain on the electrical properties of LNO DW cells was investigated. The results indicated that a monolayer of SiO2 or Si3N4 is not a good choice for the insulating layer because of the undesirable passivation caused by defects and residual strain. Hence, a Si3N4/SiO2 composite passivation layer is proposed, which not only solves the residual strain problem but also ensures good insulation performance. Finally, a crossbar array of DW memory cells with an on/off current ratio greater than 104 was fabricated using the Si3N4/SiO2 composite dielectric layer, demonstrating good uniformity and retention. This work validates the feasibility of high-density integration of LNO domain wall memories and provides a foundation for selecting passivation layers in the VIS architecture.