First Demonstration of True 4-bit Memory with Record High Multibit Retention >10³s and Read Window >10⁵ by Hydrogen Self-Adaptive-Doping for IGZO DRAM Arrays

For the first time, we demonstrate a true 4-bit memory with a large operation margin, as well as record-long multibit retention with the largest read window in IGZO-based 2T0C DRAM. It is enabled by a low-cost oxygen-compensated hydrogen self-adaptive-doping (OHAD) method with a new theory of H self-adaptive-doping. Due to the controllable compensation for defects and enhanced source/drain doping by the OHAD method, the reduced channel carrier scattering and contact resistance are both achieved. The best-in-class devices exhibit the V TH modulated to +0.23 V and the I on boosted to 35 μA/μm, along with the smallest performance variation of σ(V TH ) = 25 mV and σ/μ(I on ) = 4%. It yields a record-high memory window >10 ⁵ and ultra-long retention of 10 ⁴ s with the largest margin, capable of the first 16-level separated current memory states for realizing a true 4-bit 2T0C DRAM cell with record-long 1000-s retention time in multibit operation.