Sandisk Corporation

Western Digital Corporation

Sundisk Corporation

Zilog, Inc.

Jeffrey G Craig

John S Mangan

Kevin M Conley

Robert D Norman

Daniel C Guterman

Sanjay Mehrotra

Daniel L Auclair

Anil K Gupta

Karl M Lofgren

Jeffrey Donald Stai

Richard Albert

A non-volatile memory system is formed of floating gate memory cells arranged in blocks as the smallest unit of memory cells that are erasable together. One feature is the storage in separate blocks of the characteristics of a large number of blocks of cells in which user data is stored. These characteristics for user data blocks being accessed may, during operation of the memory system by its controller, be stored in a random access memory for ease of access and updating. A typical form of the memory system is as a card that is removably connectable with a host system but may alternatively be implemented in a memory embedded in a host system. The memory cells may be operated with multiple states in order to store more than one bit of data per cell.

Flash EEPROM system with simultaneous multiple data sector programming and storage of physical block characteristics in other designated blocks

A non-volatile memory system is formed of floating gate memory cells arranged in blocks as the smallest unit of memory cells that are erasable together. The system includes a number of features that may be implemented individually or in various cooperative combinations. One feature is the storage in separate blocks of the characteristics of a large number of blocks of cells in which user data is stored. These characteristics for user data blocks being accessed may, during operation of the memory system by its controller, be stored in a random access memory for ease of access and updating. According to another feature, multiple sectors of user data are stored at one time by alternately streaming chunks of data from the sectors to multiple memory blocks. Bytes of data in the stream may be shifted to avoid defective locations in the memory such as bad columns. Error correction codes may also be generated from the streaming data with a single generation circuit for the multiple sectors of data. The stream of data may further be transformed in order to tend to even out the wear among the blocks of memory. Yet another feature, for memory systems having multiple memory integrated circuit chips, provides a single system record that includes the capacity of each of the chips and assigned contiguous logical address ranges of user data blocks within the chips which the memory controller accesses when addressing a block, making it easier to manufacture a memory system with memory chips having different capacities. A typical form of the memory system is as a card that is removably connectable with a host system but may alternatively be implemented in a memory embedded in a host system. The memory cells may be operated with multiple states in order to store more than one bit of data per cell.

Flash EEprom system with simultaneous multiple data sector programming and storage of physical block characteristics in other designated blocks

A non-volatile memory system is formed of floating gate memory cells arranged in blocks as the smallest unit of memory cells that are erasable together. One feature is the storage in separate blocks of the characteristics of a large number of blocks of cells in which user data is stored. According to another feature, multiple sectors of user data are stored at one time by alternately streaming chunks of data from the sectors to multiple memory blocks. Yet another feature, for memory systems having multiple memory integrated circuit chips, provides a single system record that includes the capacity of each of the chips and assigned contiguous logical address ranges of user data blocks within the chips which the memory controller accesses when addressing a block, making it easier to manufacture a memory system with memory chips having different capacities.

Soft errors occur during normal use of a solid-state memory such as EEPROM or Flash EEPROM. A soft error results from the programmed threshold voltage of a memory cell being drifted from its originally intended level. The error is initially not readily detected during normal read until the cumulative drift becomes so severe that it develops into a hard error. Data could be lost if enough of these hard errors swamps available error correction codes in the memory. A memory device and techniques therefor are capable of detecting these drifts and substantially maintaining the threshold voltage of each memory cell to its intended level throughout the use of the memory device, thereby resisting the development of soft errors into hard errors.

Soft errors handling in EEPROM devices

Methods and apparatus for automatically detecting when a memory system has significantly degraded are disclosed. According to one aspect of the present invention, a method for determining a status associated with a memory system which includes a plurality of sectors includes updating a counter, comparing the counter to a threshold value, and generating an appropriate indication when comparing the counter to the threshold value yields a first result. The counter is updated each time a sector is reassigned, and indicates a number of sectors remaining in the memory system. The threshold value indicates a number of sectors which are yet to be reassigned in order for the memory system to be considered as useable, or reliable. The indication is generated when comparing the counter to the threshold value yields a first result to indicate that the memory system is substantially near a failure condition.

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Fremont, CA, United States of America

Jeffrey G Craig