Improving charge retention in capacitorless DRAM through material and device innovation

In this work, we report on the opportunities to enhance the retention time (RT) of an accumulation mode capacitorless DRAM (1T-DRAM) through appropriate material optimization by analyzing different semiconductor materials (Si, Ge, Si1−xGex and GaAs). It is shown that the RT can be considerably enhanced through a combination of (i) a higher bandgap material and (ii) the separation of the storage region from the conduction region. A higher bandgap (GaAs) material helps to achieve a deeper potential well, which reduces band-to-band tunneling, and thus, enhances the RT. The material optimization through GaAs and Ge-based 1T-DRAM achieves a maximum RT of ~2 s and maximum speed of ~45 ns, respectively, at a gate length of 50 nm at 85 °C. Results also indicate the trade-off between retention and speed arising out the material properties. The work quantifies the role of material and device parameters for 1T-DRAM.