Temperature-Aware Optimization Strategies For 3D Charge-Trap Flash Memory

Compared to conventional planar flash memory,advanced three-dimensional(3D)flash memory adopts charge-trap technology that can significantly enhance cell density and storage capacity.Despite these advantages,3D charge-trap flash is sensitive to temperature.Recent studies demonstrate that,the high temperature will incur both charge loss and retention degradation.This issue does not happen in two-dimensional flash memory which adopts floating gate technology.Second,current 3D charge-trap flash integrates the extra large capacity physical block,and each block contains over 1024 physical pages.The large-capacity block infrastructure will cause extra garbage collection overhead,which makes the thermal issue more complicated.In this thesis,two optimization schemes are proposed to address the temperature issue in 3D NAND flash memory.First,this thesis presents a scheme named TempLoad,a temperature-aware data allocation strategy for 3D charge-trap flash memory.TempLoad is a novel hardware and file system interface that can transparently allocate physical space based on the temperature status.TempLoad adopts several address mapping strategies to fully utilize the storage capacity and reduce the garbage collection overhead.The objective is to prevent the generation of hotspots and enhance the data integrity of 3D flash memory.Experimental results show that TempLoad can reduce the peak temperature by 28.49%,reduce the number of erase-counts by 18.77%,and reduce the uncorrectable pages by 83.71%.Second,this thesis presents a scheme named ThermAlloc.ThermAlloc permutes the allocation of physical blocks.Consecutively accessed logical blocks are distributed to different physical locations in order to prevent the accumulation of hotspots.The objective is to postpone garbage collection operations and keep the distribution of block temperature well under control.We demonstrate the viability of the proposed technique using a set of extensive experiments.Experimental results show that ThermAlloc can reduce the peak temperature by 26.94%,reduce the number of erase-counts by 46.9% and reduce average response time by 24.11%.