Novel Vertical Channel-All-Around(CAA) IGZO FETs for 2T0C DRAM with High Density beyond 4F(2) by Monolithic Stacking

For the first time, we propose a stackable vertical Channel-All-Around (CAA) IGZO FETs for high-density 4F(2) and long retention 2T0C DRAM application. The device is fabricated in a BEOL-compatible process flow where the channel and gate stack is deposited by Plasma-Enhanced Atomic Layer Deposition (PEALD). The impact of IGZO cycle ratio and plasma power on the device electrical performance are studied. An optimized 50nm-channel-length CAA IGZO FET achieved Ion >30 mu A/mu m and I-off below 1.8x10(-17)mu A/mu m at V-DS = 1V. A long retention of 300s has been experimentally verified for the CAA IGZO 2T0C-bitcell, making it a potential candidate for low-power 2TOC DRAM with ultralow refresh frequency. Finally, by monolithically stacking the vertical CAA IGZO FETs with 130nm CD to form 2T0C bit cells, we demonstrate the feasibility of the proposed BEOL-compatible 2T0C DRAM for further density scaling beyond 4F(2).