Cycle count storage systems
A hot count records the number of erase operations experienced by a block. The hot count is stored in an overhead data area of the block and is updated by circuits located on the same substrate as the block. Where a memory has two or more planes, each plane has circuits for updating hot counts.
1. A flash memory array comprising:
a memory chip comprising a plurality of planes, each one of the plurality of planes having dedicated row and column decoder circuits, each plane having one or more blocks, each plane of the plurality of planes having a register, each plane having an incrementing circuits, and each plane having a comparing circuit; and
a controller chip comprising a memory controller that is in communication with the memory chip, the memory controller requests the memory chip to erase one or more of the blocks;
the register for a first plane of the planes receives a hot count from a first block of the one or more blocks for the first plane, the hot count indicating the number of times the first block has been erased;
the incrementing circuit for the first plane increments the contents of the register for the first plane in response to a request from the memory controller to erase the first block; and
the comparing circuit for the first plane compares the contents of the register for the first plane with a predetermined value.
2. The memory array of claim 1 wherein the register is initialized to a non-zero number.
3. The memory array of claim 1 wherein an incremented hot count value is written back to the first block.
4. The memory array of claim 1 wherein host data stored in the first block is stored with two or more bits per memory cell and the hot count is stored with only one bit per cell.
5. The memory array of claim 1 wherein the first block includes a host data area and an overhead data area, the hot count stored in the overhead data area.
6. The memory array of claim 1 wherein the comparing circuit provides a signal to the memory controller in response to the comparing, the signal indicating that the first block is not for further use.
7. The memory array of claim 1 wherein the comparing circuit provides a signal in response to the comparing, the signal causing one or more operating conditions of the first block to be modified.
8. The memory array of claim 1 , wherein the comparing circuit for the first plane compares the contents of the register for the first plane with the predetermined value in response to the memory chip receiving the request from the memory controller to erase the first block.
9. The memory array of claim 8 , wherein the first plane further includes dedicated circuitry that reads the hot count from the first block in response to the memory chip receiving the request from the memory controller to erase the first block.
10. A NAND flash memory array having a page as the unit of programming and a block as the unit of erase, a block containing two or more pages, comprising:
a block having a host data area and an overhead data area, the overhead data area containing a hot count that records the number of times the block has been erased, the block located on a first substrate;
a comparing circuit that compares the hot count with a threshold value, the comparing circuit on the first substrate; and
a controller on a second substrate, the controller managing data storage in the memory array.
11. The NAND flash memory array of claim 10 wherein the comparing circuit is connected to a first plane of the memory array, additional planes of the memory array connected to additional comparing circuits on the first substrate.
12. The NAND flash memory of claim 10 further comprising a register on the first substrate that holds the hot count for comparing with the threshold value, the hot count incremented in the register.
13. The NAND flash memory of claim 10 wherein the host data area contains host data stored with two or more bits per memory cell and the overhead data area contains data stored with only one bit per memory cell.
14. The NAND flash memory of claim 10 wherein the comparing circuit sends a signal in response to comparing the hot count with the threshold value, the signal indicating a change at least one operating condition of the block.
15. The NAND flash memory array of claim 10 wherein:
the controller on the second substrate issues an erase command to the first substrate to request that the block be erased; and
the comparing circuit on the first substrate compares the hot count with the threshold value in response to the erase command.
16. The NAND flash memory array of claim 15 wherein the first substrate further includes dedicated circuitry that reads the hot count from the block in response to the first substrate receiving the erase command.
17. The NAND flash memory array of claim 16 , wherein the dedicated circuitry increments the hot count value and writes the incremented hot count value to the block if the hot count value does not exceed the predetermined value, and the dedicated circuitry records that the block is not for subsequent storage of data if the hot count value exceeds the predetermined value.
18. The NAND flash memory array of claim 17 , wherein the dedicated circuitry informs the controller on the second substrate that the block is not for subsequent storage of data if the hot count value exceeds the predetermined value.