Research On Error Characteristics Modeling Of NAND Flash And Applications

As an outstanding kind of memory, NAND flash with the advantages of high density storage, low cost, low power consumption, fast reading and writing speed, has been widely applied in the field of large capacity data storage system. It is also widely used in aviation, aerospace, medical and other related fields, and gradually replace the magnetic storage device to become the main kind of memory. But the progressively development of NAND flash also reduce its reliability.The lifetime of NAND flash is highly restricted by the BER(Bit Error Rate), while ECC(Error Correcting Code) can provide only limited error correction capability to tolerate increasing bit errors. Therefore, it is very meaningful to study the NAND Flash error characteristics and related management strategies.In order to solve the problems of practical use, we analysis the error characteristics of NAND Flash. First, we acquisit experimental data through the control of the underlying hardware, then analysis the relation between BER and data storage time and P/E(Program and Erase) cycles. Based on these works, We modeled the error characteristics. On one hand, the model uses the measured data for modeling analysis, on the other hand, we compared the effectiveness of different fitting methods. Then the following two aspects are proposed accoding to the model and error characteristics.(1) In order to extend the data reliable storage time without upgrading the hardware or enhancing the ability of the ECC. In this dissertation, a novel Fixation Ratio of Error Locations Aware(FRELA) strategy is proposed. The key purpose of FRELA is to flip the corresponding bits according to the locations recorded from prior operating ECC. By virtue of the BER prediction model, the required storage space of FRELA is effectively reduced because it avoids updating the information of locations frequently.(2) In order to solve the problem of the waste of computing and redundant area consumption caused by the traditional ECC scheme. In this dissertation, an Adaptive ECC Encoding/decoding(AEE) strategy is proposed. The main idea of AEE strategy is to choose adaptive ECC for each pages in different P/E condation. In that way, AEE strategy reduces the waste of computing and redundant area consumption of OOB(Out of Band) caused by higher ECC strategy.