3-STAR: A Super-steep switching, Stackable, and Strongly Reliable Transistor Array RAM for Sub-10nm DRAM and beyond

A novel capacitor-less DRAM, named 3-STAR (A Super-steep switching, Stackable, and Strongly reliable Transistor Array RAM), is proposed, and investigated for the first time. The proposed device has vertical channel transistor (VCT) structure with gate-all-around (GAA) type of three gate stacks and is characterized by having poly-Si channel and trap layer between gate dielectric ( G
ox
) and channel. Our results show super steep switching (subthreshold slope < 1 mV/dec), excellent memory window (MW > 2V), good retention (t
R
> 100sec at 85°C) and endurance (> 10
¹⁰
) behaviors without any degradation. Trap layer is a key element because it has deep trap energy level, and it makes dramatically extend the lifetime of the base charge (Q
base
) stored in trap layer. Therefore, the retention characteristics and MW are greatly improved. Since it protects G ox from deterioration, endurance characteristics is also extremely improved. In case of adding tunnel oxide (T
ox
) between trap layer and poly Si, dual operation (DRAM mode, and NVM mode) is possible depending on the bias operating conditions because the Q
base
can be stored only in poly Si or stored both poly Si and trap layer. 3-STAR is a promising next DRAM device and can also be extended to new applications such as a neuromorphic area thanks to its dual mode and steep switching characteristics.