Investigation for the Feasibility of High-Mobility Channel in 3D NAND Memory

As the number of stacked layers in 3D NAND flash memory increases, the cell current for reading scheme is continuously decreased. The purpose of this paper is to study the integration of alternative channel materials with electron mobility higher than poly-Si (e.g., SiGe, InGaAs) in 3D NAND, as a feasible approach to improve current conduction and to enable further-scaling for future 3D NAND generations. Meanwhile, the industrial-relevant "Macaroni" channel geometry can also be applied in this new type of memory device for better gate controllability and higher cell drive current. A series of simulations are performed with Sentaurus TCAD to clarify the advantages of high-mobility channel materials in 3D NAND. It has been confirmed from the simulation results that the drive-current (Id) reduction for 3D NAND with high-mobility channel is much lower than that for counterpart with poly-Si channel as the number of memory stacked layer increases. Meanwhile, the variation of threshold voltage (Vth) and sub-threshold swing (SS) for high-mobility channel is also small. Therefore, the introduction of high-mobility channel material can be regarded as an effective and practical solution to enable further scaling for future 3D NAND generations with a channel-hole diameter down to 50 nm.