GTRCiM: Generic Temperature-Resilient Subthreshold-FeFET Based Compute-in-Memory
Compute-in-memory (CiM) offers a promising solution to the hardware challenges faced in artificial intelligence (AI) and the Internet of Things (IoT), particularly in tackling the ”memory wall” problem. By leveraging nonvolatile memory (NVM) devices arranged in a crossbar structure, CiM efficiently accelerates multiply-accumulate (MAC) computations, which are essential for neural networks and various AI models. Emerging NVM, i.e., Ferroelectric FET (FeFET), is a particularly appealing choice for constructing ultra-low-power CiM arrays due to its CMOS compatibility, voltage-driven write/read mechanisms and high ION/IOFF ratio. Operating FeFETs in the subthreshold region, i.e., subthreshold-FeFETs, further reduces power, but introduces vulnerability to temperature drift, leading to potential accuracy degradation. In this paper, we present subthreshold-FeFET based temperature-resilient 2T-1FeFET and 2FeFET-1T CiM cell designs that address the temperature vulnerability. These two cells leverage feedback mechanisms to minimize the output current fluctuations caused by temperature drift. We further propose GTRCiM, a novel generic temperature-resilient CiM design that accommodates both our proposed CiM cells and other typical FeFET based cells while maintaining ultra-low-power consumption with subthreshold-FeFETs. By incorporating an additional column of the CiM array as a reference, and leveraging the temperature-resilient cell design, GTRCiM compensates for the effects of temperature drift, as temperature affects both arrays uniformly. We integrate the proposed GTRCiM array with typical 1FeFET-1R, and our proposed 2T-1FeFET, 2FeFET-1T cells and validate that GTRCiM enhances the temperature resilience with our proposed cells and even the temperature vulnerable 1FeFET-1R cell. Benchmarking results at system level using the NeuroSim framework show that our proposed GTRCiM array integrated with subthreshold-FeFET based 1FeFET-1R cells achieves 28.09 TOPS/W energy efficiency, surpassing existing CiM designs while maintaining sufficient temperature resilience.