30 Mb/mm<sup>2</sup>/layer 3D eDRAM Computing-in-Memory with Embedded BEOL Peripherals and Local Layer-wise Calibration based on First-Demonstrated Vertically-stacked CAA-IGZO 4F<sup>2</sup> 2T0C Cell
Wenjun Tang, Chuanke Chen, Jialong Liu, Chunyu Zhang, Chen Gu, Xinlv Duan, Huazhong Yang, Ling Li, Xueqing Li, Di Geng
Abstract
This paper, for the first time, reports fabricated and measured 2-layer vertically-stacked channel-all-around (CAA)-IGZO 4F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 2T0C cells. Based on this area-efficient cell structure, an ultra-dense and robust 3D eDRAM computing-in-memory (CiM) accelerator with the local-computing scheme, consisting of stacked BEOL memory arrays, BEOL multiplexing peripherals, and FEOL local layer-wise calibration, is proposed. The highlights include: 1) first fabrication and measurement of vertically-stacked CAA-IGZO 2T0C cells, with record scaled cell size as low as 0.023 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and long retention time up to 20s; 2) the 3D eDRAM CiM with embedded BEOL peripherals that realizes 1.54× higher maximum computing density than the counterpart with peripherals implemented in FEOL; 3) integrated LCU with data recovery function and readout calibration that reduces the impact of both inter-layer and intra-layer variations, achieving high accuracy up to 90% even with 20% relative variations and 8-layer stacking with 0.9× layer-wise performance decay. The measurement and evaluation results show that the proposed 3D eDRAM CiM achieves ultra-high memory and computing density up to 30 Mb/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /layer and 50 TOPS/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .