Capacitorless 3D DRAM

Author: EIS Release Date: Jan 10, 2022

Capacitorless  indium-gallium-zinc-oxide (IGZO DRAM is a suitable candidate for realizing high-density 3D DRAM, says Imec.

 

Imec has developed  a fully 300mm BEOL compatible IGZO-based capacitorless DRAM cell with >103s retention and unlimited (>1011) endurance.

 

These results were obtained after selecting the most optimal integration scheme for the single IGZO transistors, i.e., a gate-last integration scheme with buried oxygen tunnel and self-aligned contacts.

 

The implementation of a buried oxygen tunnel in combination with an anneal in O2 ambient was proven to reduce the oxygen-vacancy concentration in the IGZO channel without impacting the series resistance at source and drain region – leading to larger on-current and lower off-current.

 

With this architecture, the gate length of the IGZO TFT could be scaled down to an unprecedented 14nm, while still preserving >100s retention.

 

The retention at small gate length could be further optimized by controlling the threshold voltage (Vt) through equivalent oxide thickness (EOT) scaling, by contact resistance improvement and by reducing the IGZO layer thickness.

 

When the latter thickness is reduced to 5nm, the oxygen tunnel and anneal step in O2 can even be omitted – leading to a much-simplified integration approach.