Semiconductor memory device with error correction
This disclosure concerns a memory including: a first memory region including memory groups including a plurality of memory cells, addresses being respectively allocated for the memory groups, the memory groups respectively being units of data erase operations; a second memory region temporarily storing therein data read from the first memory region or temporarily storing therein data to be written to the first memory region; a read counter storing therein a data read count for each memory group; an error-correcting circuit calculating an error bit count of the read data; and a controller performing a refresh operation, in which the read data stored in one of the memory groups is temporarily stored in the second memory region and is written back the read data to the same memory group, when the error bit count exceeds a first threshold or when the data read count exceeds a second threshold.
1. A semiconductor memory device comprising:
first memory region including a plurality of memory groups including a plurality of memory cells, addresses being respectively allocated for the memory groups, the memory groups respectively being units of data erase operations;
a second memory region configured to temporarily store data read from the first memory region or to temporarily store data to be written to the first memory region;
a read counter configured to store a data read count for each memory group;
an error-correcting circuit configured to calculate an error bit count of the read data; and
a controller configured to:
if the error bit count of the read data exceeds a first threshold which is determined based on a maximum error bit count of bits correctable by the error-correcting circuit, perform a refresh operation, in which the read data stored in one of the memory groups is temporarily stored in the second memory region and is written back to the same memory group, wherein the data written back is error bit-corrected data; and
if the error bit count of the read data does not exceed a first threshold and the read count stored in the read counter exceeds a second threshold, perform a refresh operation, in which the read data stored in one of the memory groups is temporarily stored in the second memory region and is written back to the same memory group, wherein the data written back is error bit-corrected data.
2. The semiconductor memory device according to claim 1 ,
wherein a data read operation is performed on one page including a plurality of memory cells, a data erase operation is performed on one block including a plurality of pages, and the read counter stores the data read count for each block.
3. The semiconductor memory device according to claim 2 , further comprising a write counter configured to store a data write count for each memory group, wherein
the control unit changes the second threshold according to the data write count.
4. The semiconductor memory device according to claim 2 , wherein when the error bit count exceeds the first threshold and a majority of error bits changes from a first logic value to a second logic value, the second threshold is set as the data read count stored in the read counter.
5. The semiconductor memory device according to claim 1 ,
further comprising a write counter configured to store a data write count for each memory group,
wherein the control unit changes the second threshold according to the data write count.
6. The semiconductor memory device according to claim 5 , wherein when the error bit count exceeds the first threshold and a majority of error bits changes from a first logic value to a second logic value, the second threshold is set as the data read count stored in the read counter.
7. The semiconductor memory device according to claim 1 , wherein when the error bit count exceeds the first threshold and a majority of error bits changes from a first logic value to a second logic value, the second threshold is set as the data read count stored in the read counter.
8. The semiconductor memory device according to claim 1 , wherein the first memory region and the second memory region include Ferroelectric RAM, MRAM, PRAM or RRAM.
9. The semiconductor memory device according to claim 1 , wherein
the first threshold is lower than the maximum error bit count of bits correctable by the error-correcting circuit,
the second threshold is set to be equal to or lower than a read count by which read disturbance will occur.
10. A semiconductor memory device comprising
a first memory region including a plurality of memory groups including a plurality of memory cells, addresses being respectively allocated for the memory groups, the memory groups respectively being units of data erase operations;
a second memory region configured to temporarily store data read from the first memory region or configured to temporarily store data to be written to the first memory region;
an error-correcting circuit configured to calculate an error bit count of the read data;
a controller configured to perform a refresh operation, in which the read data stored in one of the memory groups is temporarily stored in the second memory region and is written back the read data to the same memory group;
a maximum value register configured to hold a maximum error bit count among error bit counts during a period from a certain refresh operation to a next refresh operation; and
a flag register configured to store flags for the memory blocks, one of the flags indicating a first read operation to the corresponding memory block after restart of a supply of power to the first memory region, when the supply of the power restarts after stop thereof, wherein
when the error bit count in the first read operation since the supply of the power to the first memory region restarts is higher than the maximum error bit count before the restart of the supply of the power, the controller executes the refresh operation.
11. The semiconductor memory device according to claim 10 , wherein the first memory region and the second memory region include Ferroelectric RAM, MRAM, PRAM or RRAM.