Flash eeprom system

• US 5,297,148 A
• Filed: 10/20/1992
• Issued: 03/22/1994
• Est. Priority Date: 04/13/1989
• Status: Expired due to Term

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SunDisk Corporation (Seagate Technology Holdings Plc)
• Inventors: Harari, Eliyahou, Mehrotra, Sanjay, Norman, Robert D.
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): HUA, LY
• Application Number:
  US07/963,838
• Time in Patent Office: 518 Days
• Field of Search: 371/10.2, 371/10.1, 371/10.3, 371/40.1, 365/200
• US Class Current: 714/710
• CPC Class Codes: G06F 11/1068 in sector programmable memories, e.g. flash disk G06F11/1072 takes precedence
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/0802 Addressing of a memory level in which the access to the desired data or data block requires associative addressing means, e.g. caches
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/0875 with dedicated cache, e.g. instruction or stack
• CPC Class Codes: G06F 12/123 with age lists, e.g. queue, most recently used [MRU] list or least recently used [LRU] list
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 2212/312 In storage controller
• CPC Class Codes: G06F 2212/7201 Logical to physical mapping or translation of blocks or pages
• CPC Class Codes: G06F 2212/7203 Temporary buffering, e.g. using volatile buffer or dedicated buffer blocks
• CPC Class Codes: G06F 2212/7205 Cleaning, compaction, garbage collection, erase control
• CPC Class Codes: G06F 2212/7207 management of metadata or control data
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0652 Erasing, e.g. deleting, data cleaning, moving of data to a wastebasket
• CPC Class Codes: G06F 3/0664 at device level, e.g. emulation of a storage device or system
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G06F 3/068 : Hybrid storage device
• CPC Class Codes: G06F 3/0688 : Non-volatile semiconductor memory arrays
• CPC Class Codes: G11C 11/5621 : using charge storage in a floating gate
• CPC Class Codes: G11C 11/5628 : Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 11/5635 : Erasing circuits
• CPC Class Codes: G11C 16/10 : Programming or data input circuits
• CPC Class Codes: G11C 16/16 : for erasing blocks, e.g. arrays, words, groups
• CPC Class Codes: G11C 16/3436 : Arrangements for verifying correct programming or erasure
• CPC Class Codes: G11C 16/344 : Arrangements for verifying correct erasure or for detecting overerased cells
• CPC Class Codes: G11C 16/3445 : Circuits or methods to verify correct erasure of nonvolatile memory cells
• CPC Class Codes: G11C 16/3454 : Arrangements for verifying correct programming or for detecting overprogrammed cells
• CPC Class Codes: G11C 16/3459 : Circuits or methods to verify correct programming of nonvolatile memory cells
• CPC Class Codes: G11C 2211/5621 : Multilevel programming verification
• CPC Class Codes: G11C 2211/5634 : Reference cells
• CPC Class Codes: G11C 2211/5643 : Multilevel memory comprising cache storage devices
• CPC Class Codes: G11C 2216/18 : Flash erasure of all the cells in an array, sector or block simultaneously
• CPC Class Codes: G11C 29/00 : Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
• CPC Class Codes: G11C 29/26 : Accessing multiple arrays G11C29/24 takes precedence
• CPC Class Codes: G11C 29/34 : Accessing multiple bits simultaneously
• CPC Class Codes: G11C 29/52 : Protection of memory contents; Detection of errors in memory contents
• CPC Class Codes: G11C 29/765 : in solid state disks
• CPC Class Codes: G11C 29/82 : for EEPROMs
• CPC Class Codes: G11C 7/1039 : using pipelining techniques, i.e. using latches between functional memory parts, e.g. row/column decoders, I/O buffers, sense amplifiers
• CPC Class Codes: G11C 8/12 : Group selection circuits, e.g. for memory block selection, chip selection, array selection

Abstract

A system of Flash EEprom memory chips with controlling circuits serves as non-volatile memory such as that provided by magnetic disk drives. Improvements include selective multiple sector erase, in which any combinations of Flash sectors may be erased together. Selective sectors among the selected combination may also be de-selected during the erase operation. Another improvement is the ability to remap and replace defective cells with substitute cells. The remapping is performed automatically as soon as a defective cell is detected. When the number of defects in a Flash sector becomes large, the whole sector is remapped. Yet another improvement is the use of a write cache to reduce the number of writes to the Flash EEprom memory, thereby minimizing the stress to the device from undergoing too many write/erase cycling.

Claims

1. A memory card connectable to a computer system, comprising

an array of electrically Erasable and Programmable Read Only Memory ("EEPROM") cells partitioned into a plurality of flash sectors,

each flash sector being a group of cells that are erasable together as a unit, and having a portion thereof reserved as redundant cells;

and

a memory controller for controlling operations of the EEPROM cells,

error detection means within said memory controller for detecting any defective cells within the array;

defect pointers, each generated by said memory controller for linking a detected defective cell'"'"'s address to that of a corresponding redundant cell substituting for the defective cells, said defect pointer being stored within the array; and

defective cell substituting means within said memory controller and responsive to said defect pointers for substituting said detected defective cell with said corresponding redundant cells.

2. The memory card as in claim 1, wherein said plurality of sectors have a portion thereof reserved as redundant sectors;

and

said EEPROM controller, upon detecting more than a predetermined number of defective cells in a sector, substitutes said sector with one of said redundant sectors.

3. The memory card as in claim 2, wherein said EEPROM controller including a circuit for implementing error correction codes for detecting and correcting errors in the operations of the EEPROM cells.

4. The memory card as in claim 1,

said memory card being compatible with a magnetic disk drive storage system and capable of substituting therefore in said computer system.