CNFET-Based High Throughput SIMD Architecture

Carbon nanotube field effect transistor (CNFET), using the carbon nanotubes (CNTs) as the material for conducting, is a promising alternative of CMOS technology to overcome the “power wall” issue. Recently, a microprocessor solely based on CNFETs was fabricated and demonstrated, which is a big step forward to the industrial practice. However, CNFETs are inherently subject to much larger process variation or manufacturing defects; thereby it may cause significant design cost to build high performance processors. This is exacerbated in the large register file (RF) architectures widely used in single instruction multiple data (SIMD) architectures, e.g., general public utilities style processors, where the number of critical paths are multiplied by the SIMD width and thread count. In this paper, we seek cost-effective approaches to address the issues by judiciously exploiting the strong asymmetric spatial correlation in the variation unique to the CNFET fabrication process. This paper presents a microarchitectural model to characterize CNFET delay variation and malfunction, under which we show that the RF organizations coupled with the architectural schemes are critical to the performance and power consumption of the SIMD processor. Therefore, we propose several architectural techniques to mitigate the performance degradation and the impact of CNT metallization, leveraging the distinctive CNFET characteristics and the unique features in the SIMD processors. Experimental results verify the effectiveness of the proposed techniques and demonstrate the great opportunity offered by this new device technology.