Bringing in Cryogenics to Storage: Characteristics and Performance Improvement of 3D Flash Memory

We propose the storage systems incorporating 3D Flash memory in a cryogenic condition. In this paper, we investigate details of the cell characteristics and storage performance at cryogenic temperature. Several new results are obtained in addition to our previous report. (1) Countermeasures against defective mode occurrence at cryogenic temperature is analyzed. (2) The saturation current of cell transistor becomes small, but the subthreshold slope is improved by a factor of two. (3) The data retention characteristics are improved, and its lateral charge loss component is particularly small. TCAD simulations demonstrate the lateral diffusion of stored charges at cryogenic temperature is extremely suppressed and advantageous to word line pitch reductions in 3D Flash memory. (4) The endurance characteristic is improved due to the reduction of gate oxide damages caused by P/E cycle, thus the cryogenic operation allows cells to have a considerably longer lifetime. (5) Thermal simulations show that the cooling system using the liquid nitrogen reduces cross temperature effect and keeps the temperature within the device low and uniform. These results suggest bringing cryogenic cooling to the storage can significantly improve the cell characteristics and storage performance of 3D Flash memory.