Memory device with fail search and redundancy
View Patent ↗An automatic redundancy system may exploit an existing microprocessor management system on chip for carrying out autonomously, without communicating with an external testing machine, the operations of: writing data in the memory array according to one or more pre-established test patterns, verifying data successively read from the memory array, and substituting failed elements of the memory array with equivalent redundancy structures. A logic structure may detect and store memory array failures upstream of the output data path. Thereby, data collection relating to failures may be accomplished more quickly and without any interaction with the testing machine apart from communicating the end of the execution of the redundancy process.
1. A memory device comprising:
a fail block to verify and store addresses of failed memory cells of an array of memory cells during execution of a test algorithm, said fail block comprising
a logic gate having a first input coupled to an output of a sense amplifier, and a second input to receive an expected logic value according to the test algorithm, and
a resettable bistable circuit to store information of the failed memory cells and coupled to said logic gate;
a pattern block to be input with addresses of memory cells generated by an internal address counter and to output, based on a pattern for testing an integrity of said array of memory cells, command flags for programming the addressed memory cell to a microcontroller and the expected logic value to the second input of said logic gate; and
a redundancy block coupled to and interacting with said microcontroller to substitute redundant memory cells for the failed memory cells or to generate a non-redundancy flag.
2. The memory device according to claim 1 wherein said resettable bistable circuit comprises a latch.
3. The memory device according to claim 1 wherein said redundancy block is to implement rules where columns comprising failed memory cells detected during the execution of the test algorithm are mapped onto available redundancy columns of said array of memory cells.
4. The memory device according to claim 1 wherein said array of memory cells comprises a reserved sector being inaccessible by a user and on which mapping data of columns comprising failed memory cells are permanently written.
5. The memory device according to claim 1 wherein said microcontroller comprises a read only memory; and wherein the test algorithm is programmed in said read only memory for managing the memory device.
6. The memory device according to claim 1 wherein said array of memory cells is organized in sectors; and wherein the memory cells of said array of memory cells are located by a row and a column address.
7. The memory device according to claim 1 further comprising:
supply pads, a clock signal pad, a chip enabling command pad, a write enabling command pad, and pads for input/output enabling command, input address, and output memory data; and wherein the memory device is to interact with an electric wafer sort (EWS) test machine to implement the substitution of the redundant memory cells or to generate the non-redundancy flag only through said supply pads, said clock signal pad, said chip enabling command pad, said write enabling command pad, and said pads for input/output enabling command, input address, and output memory data.
8. The memory device according to claim 1 wherein said array of memory cells comprises a FLASH array of memory cells.
9. A FLASH memory device comprising:
an array of FLASH memory cells;
a microcontroller to manage erase, program, erase verify, program verify, and read operations of data in said array of FLASH memory cells;
a logic circuit to verify and store addresses of failed FLASH memory cells during execution of a test algorithm and comprising
a logic gate to detect a discrepancy between an expected logic value according to the test algorithm and a value of a respective FLASH memory cell, the discrepancy indicating the respective FLASH memory cell comprises a failed FLASH memory cell, and
a latch coupled to an output of said logic gate to store an indication of the failed FLASH memory cell;
a pattern logic circuit to be input with the addresses of failed FLASH memory cells and to output, based on a pattern for testing an integrity of said array of FLASH memory cells, command flags to program the addressed FLASH memory cell sent to said microcontroller and the expected logic value applied to an input of said logic circuit; and
a redundancy logic circuit coupled to said microcontroller to substitute for columns comprising failed FLASH memory cells or to generate a non-redundancy flag.
10. The FLASH memory device according to claim 9 wherein said redundancy logic circuit is to implement rules where columns comprising failed FLASH memory cells detected during the execution of the test algorithm are mapped onto available redundancy columns of said array of FLASH memory cells.
11. The FLASH memory device according to claim 9 wherein said array of FLASH memory cells comprises a reserved sector being inaccessible by a user and on which mapping data of the columns comprising failed FLASH memory cells are permanently written.
12. The FLASH memory device according to claim 9 wherein said microcontroller comprises a read only memory; and wherein the test algorithm is programmed in said read only memory for managing the FLASH memory device.
13. The FLASH memory device according to claim 9 wherein said array of FLASH memory cells is organized in sectors; and wherein the FLASH memory cells of said array of FLASH memory cells are located by a row and a column address.
14. The FLASH memory device according to claim 9 further comprising
supply pads, a clock signal pad, a chip enabling command pad, a write enabling command pad, and pads for input/output enabling command, input address, and output memory data; and wherein the FLASH memory device is to interact with an electric wafer sort (EWS) test machine to implement the substitution for columns comprising failed FLASH memory cells or to generate the non-redundancy flag only through said supply pads, said clock signal pad, said chip enabling command pad, said write enabling command pad, and said pads for input/output enabling command, input address, and output memory data.
15. A method comprising:
writing a test pattern into an array of memory cells;
detecting failed memory cells by determining discrepancies between values stored in the memory cells and respective expected logic values based upon a testing algorithm and the test pattern;
storing addresses of the failed memory cells;
outputting, based on the test pattern, command flags to a microcontroller to program addressed memory cells;
outputting, based on the test pattern, the expected logic value of addressed memory cells; and
autonomously, within the memory device, substituting redundant memory cells for the failed memory cells or generating a non-redundancy flag.
16. The method according to claim 15 further comprising
implementing rules where columns comprising failed memory cells detected during an execution of the test algorithm are mapped onto available redundancy columns of the array of memory cells.
17. The method according to claim 15 wherein the array of memory cells comprises a reserved sector being inaccessible by a user; and the method further comprises
writing onto the reserved sector a mapping data of columns comprising the failed memory cells.
18. The method according to claim 15 wherein the microcontroller comprises a read only memory; and the method further comprises
programming the test algorithm in the read only memory for managing the memory device.