Robust Monolithic 3D Carbon-Based Computing-in-SRAM With Variation-Aware Bit-Wise Data-Mapping for High-Performance and Integration Density

Bit-serial computing-in memory with SRAM cells (SRAM-CIM) enables a full set of integer and floating-point arithmetic operations and various data-intensive computations. Carbon nanotube field-effect transistors (CN-MOSFETs) with high scalability, energy-efficiency, and low process thermal budget are attractive to realize high-dense monolithic three-dimensional (M3D) SRAM-CIM. However, CN-MOSFETs possess unique process variations with asymmetric spatial correlations which can significantly influence the performance and reliability of carbon-based SRAM-CIM. In this paper, new M3D-4N4P SRAM-CIM cells with CN-MOSFETs are proposed with optimized profiles for achieving ultra-high integration density while preserving robustness of data-access and computation. Furthermore, the variation-aware bit-wise data-mapping method is proposed for enhancing the performance of carbon-based SRAM-CIM by leveraging the spatial correlations of CN-MOSFETs. By minimizing the area skew of vertically-stacked layers, the areas of proposed M3D-4N4P SRAM-CIM cells are reduced by up to 50.32% compared to the previous 6N2P SRAM-CIM cells assuming carbon nanotube transistor technology. The proposed M3D-4N4P SRAM-CIM array also achieves by up to $2.17\times $ higher throughput on arithmetic operations and 18.34% lower computing latency with 25.36% reduced energy consumptions on MAC-based benchmarks, respectively, compared to the previous 2D-6N2P SRAM-CIM array.