Semiconductor memory device, erasing method and programing method thereof
A semiconductor memory device, an erasing method and a programming method are provided. The semiconductor memory device includes a memory array, which includes a plurality of NAND strings; a page buffer/sensing circuit, which is connected to the NAND strings of the memory array through bit lines and outputs whether the NAND strings include failures; and a detecting circuit, which is connected to the plurality of page buffer/sensing circuits and detects a number of the failures among the NAND strings of a selected block. The block is determined to be usable when the number of the failures among the NAND strings detected by the detecting circuit is less than or equal to a fixed number, and the block is determined to be unusable as a bad block when the number of the failures exceeds the fixed number.
1. An erasing method of semiconductor storage device, comprising steps of:
applying an erasing pulse to a selected block;
detecting a number of failures among NAND strings of the selected block when the selected block is unqualified in an erasing verification and a number of times of applying the erasing pulse reaches a predetermined number of times; and
completing the erasing in a state of the selected block to be usable when the number of the failures among the NAND strings is less than or equal to a fixed number, and managing the selected block to be unusable as a bad block when the number of the failures exceeds the fixed number.
2. The erasing method of semiconductor storage device according to claim 1 wherein the fixed number is less than or equal to a number of bits correctable through an error checking/correcting process.
3. A programming method of semiconductor storage device, comprising steps of:
detecting a number of failures among NAND strings of a selected block;
determining a permissible number of unqualified bits in a programming verification based on the number of the failures among the NAND strings being detected;
applying a programming pulse to a selected page of the selected block; and
performing the programming verification on the selected page based on the permissible number of unqualified bits,
wherein the programming verification is determined as suspectedly qualified when the selected page having a number of bits with programming failure less than or equal to the permissible number of unqualified bits.
4. The programming method of semiconductor storage device according to claim 3 , wherein the permissible number of unqualified bits is less than or equal to a number of bits correctable through an error checking/correcting process.
5. The programming method of semiconductor storage device according to claim 3 , wherein the permissible number of unqualified bits correspondingly decreases when the number of the failures among the NAND strings increases.
6. The programming method of semiconductor storage device according to claim 3 , wherein the step of detecting the number of the failures among the NAND strings of the selected block comprises: performing a step of reverse reading, wherein the step of reverse reading is to read by applying a voltage from a common source line of the selected block to the NAND strings.
7. The programming method of semiconductor storage device according to claim 3 , wherein the programming method further comprises: performing an error checking/correcting process on data to be programmed, and
correcting an error caused by the failures among the NAND strings through the error checking/correcting process when reading the data.
8. A semiconductor storage device, comprising:
a memory array, comprising a plurality of NAND strings;
a plurality of output circuits, connected to the NAND strings of the memory array through a bit line, and outputting whether the NAND strings include failures;
a detecting circuit, connected to the plurality of the output circuits, and detecting a number of the failures among the NAND strings of a selected block; and
an erasing circuit, for erasing the selected block, wherein when the selected block is unqualified in an erasing verification and a number of times of applying an erasing pulse reaches a predetermined number of times, the erasing circuit completes the erasing in a state of the selected block to be usable when the number of the failures among the NAND strings is less than or equal to a fixed number, and the erasing circuit manages the selected block to be unusable as a bad block when the number of the failures exceeds the fixed number.
9. The semiconductor storage device according to claim 8 , wherein the detecting circuit comprises: a first circuit, generating a plurality of detection voltages corresponding to whether the NAND strings include the failures outputted by the plurality of the output circuits; a second circuit, generating a reference voltage; and a comparison circuit, comparing the detection voltages with the reference voltage, and the comparison circuit detecting the number of the failures among the NAND strings connected to the plurality of the output circuits.
10. The semiconductor memory device according to claim 8 , wherein the semiconductor memory device further comprises a reverse reading circuit for performing a reverse reading on the plurality of NAND strings of the selected block by applying a voltage from a common source line of the selected block to the NAND strings and applying a verification voltage to all pages of the selected block, wherein the plurality of output circuits outputs whether the NAND strings include the failures based on a read result of the reverse reading circuit.
11. The semiconductor storage device according to claim 8 , wherein the semiconductor memory device further comprises a programming circuit for programming a selected page of the selected block, and
the programming circuit performing a programming verification on the selected page based on a permissible number of unqualified bits, wherein the permissible number of unqualified bits is set based on the number of the failures among the NAND strings detected by the detecting circuit.
12. The semiconductor storage device according to claim 11 , wherein the semiconductor memory device further comprises an error checking/correcting circuit for performing an error checking/correcting process on data to be programmed and data read from the memory array, wherein the permissible number of unqualified bits is less than or equal to a number of bits correctable by the error checking/correcting circuit.
13. The semiconductor storage device according to claim 8 , wherein the plurality of output circuits comprises a page buffer/sensing circuit.