专利名称：Multi-bit-per-cell flash EEPROM memory
with refresh
发明人：Hock C. So,Sau C. Wong申请号：US11101938申请日：20050407公开号：US07170781B2公开日：20070130
专利附图：
摘要：A multibit-per-cell non-volatile memory divides the suitable threshold voltagesof memory cells into ranges corresponding to allowed states for storage of data andranges corresponding to forbidden zones indicating a data error. A read process in
accordance automatically checks whether a threshold voltage is in a forbidden zone. In analternative embodiment, a refresh process includes reprogramming the thresholdvoltage into an allowed state. In the case of a flash memory, a refresh reads a sector ofthe memory and saves corrected data from the sector in a buffer or another sector. Thecorrected data from the buffer or other sector can be written back in the original sector,or the corrected data can be left in the other sector with addresses of the original sectorbeing mapped to the other sector. Refresh process for the non-volatile memory can beperform in response to detecting a threshold voltage in a forbidden zone, as part of apower-up procedure for the memory, or periodically with a period on the order of days,weeks, or months. As a further aspect, the allowed states correspond to gray codeddigital values so that allowed states that are adjacent in threshold voltage correspond tomultibit values that differ in only a single bit. Error detection and correction codes can beused to identify data errors and generate corrected data for refresh operations.
申请人：Hock C. So,Sau C. Wong
地址：Redwood City CA US,Hillsborough CA US
国籍：US,US
代理机构：Parsons Hsue & de Runtz LLP
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