This article presents the development of single-nanometer magnetic tunnel junctions (MTJs) with high data retention and high-speed capabilities for spin-transfer torque magnetoresistive random access memory (STT-MRAM). The researchers used a multilayered CoFeB/MgO structure as the free layer, allowing independent control of shape and interfacial anisotropies. This design enables the MTJs to meet the requirements of both high-data retention and high-speed switching. The MTJs were fabricated down to 2.0 nm in diameter, achieving high data retention (over 10 years) and high-speed switching (10 ns or below) in sub-5-nm MTJs. The study shows that by engineering the number of CoFeB/MgO interfaces and/or CoFeB thicknesses, the performance of the MTJs can be tailored for specific applications. The results demonstrate that the proposed MTJs have the potential for high-performance and high-density STT-MRAM. The study also discusses the challenges of scaling down MTJs and the importance of balancing retention and switching speed in different applications. The findings suggest that optimizing the interfacial and shape anisotropies can improve the performance of MTJs for both high-data retention and high-speed switching. The research provides a design guideline for fabricating ultra-small MTJs used in a wide variety of applications.This article presents the development of single-nanometer magnetic tunnel junctions (MTJs) with high data retention and high-speed capabilities for spin-transfer torque magnetoresistive random access memory (STT-MRAM). The researchers used a multilayered CoFeB/MgO structure as the free layer, allowing independent control of shape and interfacial anisotropies. This design enables the MTJs to meet the requirements of both high-data retention and high-speed switching. The MTJs were fabricated down to 2.0 nm in diameter, achieving high data retention (over 10 years) and high-speed switching (10 ns or below) in sub-5-nm MTJs. The study shows that by engineering the number of CoFeB/MgO interfaces and/or CoFeB thicknesses, the performance of the MTJs can be tailored for specific applications. The results demonstrate that the proposed MTJs have the potential for high-performance and high-density STT-MRAM. The study also discusses the challenges of scaling down MTJs and the importance of balancing retention and switching speed in different applications. The findings suggest that optimizing the interfacial and shape anisotropies can improve the performance of MTJs for both high-data retention and high-speed switching. The research provides a design guideline for fabricating ultra-small MTJs used in a wide variety of applications.