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Total Ionizing Dose Effects On The State-Of-The-Art Nand Flash Memories With An Emphasis On Dosimeter Design, Preeti Kumari

Dissertations

Radiation effects are an important reliability concern for space and defense electronics, especially for non-volatile memory (NVM). State-of-the-art radiation hard NVMs have very limited capacity (in megabytes range), and high cost, making them impractical for several applications that require larger storage capacities. In this context, NAND flash memory is very attractive due to its high density (>1 tera-bytes/sq. inch) relatively low cost (<$1 per giga byte), light weight and small form factor. Hence this dissertation conducts a systematic study on the radiation effects on the commercially available off-the-shelf NAND flash memory chips. First, an experimental demonstration of radiation effects were performed on the 3-D NAND flash memory using a Co60 Gamma-ray source at Sandia National Laboratory. A significant layer-to-layer bit error variation within a physical memory block of the irradiated memory chip was observed. The possible application of these findings for the radiation-tolerant smart memory controller design were explored. Second, this dissertation evaluates a radiation induced error mitigation strategy using read-retry method. The read-retry function is typically offered in the high-density NAND memory chips to recover data once the default memory read method fails. In this work the read-retry method was applied on the irradiated 3-D NAND chip and an algorithm is proposed for its efficient implementation. Third, a systematic study was conducted on the effects of low dose gamma radiations ( 2rad(Si)/day) on high density NAND flash memory chips. The measured cumulative bit error rate (BER) over two months shows significant linear increase with exposure time and BER is independent of the prior damage. Fourth, a theoretical framework was developed to understand the total ionizing dose sensitivity of the commercial flash memory chips. The theoretical framework motivated the basic design rules for using the commercial flash memory chips as dosimeter.