TCAD Based Study of String Current Variability in 3D NAND Flash Memory
Mrinmoy Mahapatra, Prathamesh Ganesh Kekarjawlekar, K. Akshay · 2025
3D NAND memory has become indispensable for high-density data storage, offering superior scalability and cost-efficiency. However, with shrinking memory cell sizes and increasing cell densities, precise control over fabrication parameters is crucial for optimal performance in advanced memory applications. The variability in string current is a significant concern for device performance and reliability. This paper employs Technology Computer-Aided Design (TCAD) simulations to investigate the impact of the dimensional variations on the string current, which subsequently alters the critical electrical properties of 3D NAND flash memory cells. We investigate variations in cell spacing, tunneling and blocking oxide thickness and channel thickness, that result due to process variations during etching, deposition and lithography. Our study assesses the impact of these factors on critical performance metrics, including on-current$({I}_{{on}})$, threshold voltage$({V}_{{th}})$, maximum trans-conductance value$({G}_{{m}})$and sub-threshold slope (SS) of memory cells. The results indicate that changes in the plug depth have a negligible effect on the electrical parameters, while variations in cell spacing have a significant impact on these metrics. Under a worst-case 20% process variation in all dimensions,${I}_{{on}}, {V}_{{th}}, {G}_{{m}}$and SS deviate by approximately 78%, 21%, 38% and 14%, respectively. These results emphasize the need for precise fabrication control and variability-aware design to maintain the reliability and efficiency of high-density 3D NAND memory in advanced applications.