Algorithm for charge loss reduction and Vt distribution improvement
View Patent ↗Methods and systems for accurately programming or erasing one or more memory cells on a selected wordline of a memory device are provided. In one embodiment, the memory device comprises a memory array, a threshold voltage measuring component configured to measure a threshold voltage of each memory cell on the selected wordline of the memory array, and an average threshold voltage determining component configured to determine an average threshold voltage result uniquely associated with the selected wordline, based on the measured threshold voltages. The memory device is configured to program one or more of the memory cells to a predefined program level relative to the determined average threshold voltage, or to erase memory cells of the selected wordline to the determined average threshold voltage. The method is particularly useful for multi-level flash memory cells to reduce charge loss while improving data reliability and Vt distributions of the programmed element states.
1. A method of programming or erasing one or more memory cells on a wordline of a memory array, the method comprising:
providing one or more unprogrammed memory cells on a selected wordline to be programmed or erased;
initially measuring a threshold voltage (Vt) uniquely associated with the selected wordline for each of the one or more memory cells on the selected wordline;
determining an average threshold voltage Vt(avg) uniquely associated with the selected wordline based on the measured threshold voltages, before programming or erasing the one or more memory cells; and
programming one or more of the memory cells of the selected wordline to a predefined program level uniquely associated with the determined average threshold voltage Vt(avg) uniquely associated with the selected wordline; or
erasing one or more of the memory cells of the selected wordline to the determined average threshold voltage Vt(avg).
2. The method of claim 1 , wherein the one or more memory cells comprise multi-level flash memory cells, individually comprising element-pairs having two physical bits per memory cell and two or more program levels and a blank level, the levels comprising three or more data levels corresponding to three or more threshold voltages.
3. The method of claim 1 , wherein the one or more memory cells comprise multi-level memory cells having two or more of the predefined program levels.
4. The method of claim 3 , wherein determining the average threshold voltage Vt(avg) uniquely associated with the selected wordline based on the measured threshold voltages, comprises:
determining an average threshold voltage uniquely associated with the selected wordline based on the measured threshold voltage of each memory cell for the selected wordline, comprising:
a) selecting a wordline to be programmed or erased;
b) selecting one or more of the unprogrammed memory cells on the selected wordline to be programmed or erased;
c) measuring a threshold voltage (Vt) for each memory cell on the selected wordline; and
d) determining an average threshold voltage uniquely associated with the selected wordline by averaging the measured threshold voltages uniquely associated with the selected wordline.
5. The method of claim 1 , wherein the predefined program level uniquely associated with the selected wordline comprises one of a plurality of program levels utilized by the one or more memory cells, and wherein the plurality of program levels individually comprise a predetermined voltage offset from the determined average threshold voltage.
6. The method of claim 5 , wherein the predefined program level is applied to each memory cell during a program verify operation of the memory array.
7. The method of claim 5 , wherein programming one or more of the memory cells of the selected wordline to the predefined program level uniquely associated with the determined average threshold voltage Vt(avg) uniquely associated with the selected wordline, comprises:
a) selecting a wordline to be programmed;
b) selecting one or more of the unprogrammed memory cells on the selected wordline to be programmed;
c) selecting a program level from the plurality of program levels individually comprising a respective program voltage; and
d) applying pulses of the program voltage to the one or more memory cells until each of the one or more memory cells generally correspond to the selected program level for the selected wordline.
8. The method of claim 1 , wherein determining the average threshold voltage Vt(avg) uniquely associated with the selected wordline based on the measured threshold voltages, comprises:
averaging the measured threshold voltages (Vt) uniquely associated with the selected wordline for each of the one or more memory cells on the selected wordline.
9. A method of programming or erasing one or more memory cells on a wordline of a memory array, the method comprising:
providing one or more unprogrammed memory cells on a selected wordline to be programmed or erased; and
programming one or more of the memory cells of the selected wordline to a predefined program level uniquely associated with the determined average threshold voltage Vt(avg) uniquely associated with the selected wordline, comprising:
programming one or more of the memory cells to the predefined program level offset from the predetermined average threshold voltage Vt(avg) uniquely associated with the selected wordline, until each memory cell generally corresponds to the respective predefined program level.
10. The method of claim 9 , wherein erasing one or more of the memory cells of the selected wordline to the predetermined average threshold voltage Vt(avg), comprises:
erasing one or more memory cells of the selected wordline to the predetermined average threshold voltage Vt until each of the one or more memory cells generally correspond to the average threshold voltage Vt for the selected wordline.
11. A method of programming or erasing one or more memory cells on a wordline of a memory array, the method comprising:
providing one or more unprogrammed memory cells on a selected wordline to be programmed or erased;
measuring a threshold voltage (Vt) uniquely associated with the selected wordline for each of the one or more memory cells on the selected wordline;
determining an average threshold voltage Vt(avg) uniquely associated with the selected wordline based on the measured threshold voltages;
determining a program verify level uniquely associated with the selected wordline and the determined average threshold voltage Vt(avg); and
programming one or more of the memory cells of the selected wordline to a predefined program level uniquely associated with the determined program verify level uniquely associated with the selected wordline; or
erasing one or more of the memory cells of the selected wordline to the determined program verify level.
12. The method of claim 11 , wherein the predefined program verify level comprises one of a program verify voltage and a program verify current, and wherein the determined program verify level comprises one of an average program verify voltage and an average program verify current.
13. The method of claim 11 , wherein the one or more memory cells comprise multi-level flash memory cells, comprising element-pairs individually having two or more program levels and a blank level, the levels comprising three or more data levels corresponding to three or more threshold voltages.
14. The method of claim 13 , wherein the determined program verify level is used for verifying one of the three or more threshold voltages and data levels of each memory cell during a program verify operation.
15. The method of claim 11 , wherein the one or more memory cells comprise multi-level memory cells having two or more predefined program levels.
16. The method of claim 15 , wherein determining the program verify level uniquely associated with the selected wordline and the determined average threshold voltage Vt(avg), comprises:
a) selecting a wordline to be programmed or erased;
b) selecting one or more of the unprogrammed memory cells on the selected wordline to be programmed or erased;
c) measuring a threshold voltage (Vt) for each memory cell on the selected wordline; and
d) determining an average threshold voltage uniquely associated with the selected wordline by averaging the measured threshold voltages uniquely associated with the selected wordline.
e) determining a program verify level uniquely associated with the selected wordline and the determined average threshold voltage based on a predetermined voltage offset from the determined average threshold voltage.
17. The method of claim 16 , wherein programming one or more of the memory cells to the predefined program level relative to the determined program verify level for the selected wordline, comprises:
a) selecting a program level from the two or more predefined program levels and a respective determined program voltage; and
b) applying pulses of the program voltage to the one or more memory cells until each of the one or more memory cells generally correspond to the program voltage for the selected wordline.
18. The method of claim 11 , wherein the predefined program level comprises one of a plurality of program levels utilized by the one or more memory cells.
19. The method of claim 11 , wherein programming one or more of the memory cells of the selected wordline to the predefined program level uniquely associated with the determined program verify level uniquely associated with the selected wordline, comprises:
programming one or more of the memory cells to a predefined program level that is offset from the determined program verify level for the selected wordline, until each memory cell generally corresponds to the predefined program level, wherein the predefined program level comprises one of a plurality of program levels and respective threshold voltages having a respective offset from the predetermined average threshold voltage.
20. The method of claim 11 , wherein erasing the one or more memory cells of the selected wordline to the determined program verify level, comprises:
erasing one or more of the memory cells of the selected wordline to the program verify level until each of the one or more memory cells generally correspond to the program verify level for the selected wordline.
21. A memory device, comprising:
a memory array comprising a multi-bit flash memory, comprising one or more unprogrammed memory cells on a selected wordline of the memory array, the multi-bit flash memory cells individually comprising element-pairs having two physical bits per memory cell and two or more program levels and a blank level per memory cell, the levels comprising three or more data levels corresponding to three or more threshold voltages;
a threshold voltage measuring component configured to measure a threshold voltage (Vt) uniquely associated with the selected wordline for the one or more memory cells on the selected wordline; and
an average threshold voltage determining component configured to determine an average threshold voltage Vt(avg) uniquely associated with the selected wordline based on the measured threshold voltages on the selected wordline of the memory array;
wherein the memory device is configured to program or erase the one or more memory cells on the selected wordline of the memory array;
wherein the memory device is configured to
program one or more of the memory cells of the selected wordline to a predefined program level uniquely associated with the determined average threshold voltage Vt(avg) uniquely associated with the selected wordline; or
erase one or more of the memory cells of the selected wordline to the determined average threshold voltage Vt(avg).
22. The memory device of claim 21 , wherein the predefined program level comprises one of a plurality of program levels utilized by the one or more memory cells, and wherein the plurality of program levels individually comprise a predetermined voltage offset from the determined average threshold voltage.
23. An electronic device, comprising:
a user input configured to allow a user to input data;
a user output configured to output data to a user;
a central processing unit (CPU) operatively coupled to the user input and the user output and configured to receive and process the user input and to output the user output; and
a memory operatively coupled to the CPU and configured to receive data from and send data to the CPU, the memory comprising a memory array, a threshold voltage measuring component, and an average threshold voltage determining component, the memory configured to program or erase one or more memory cells on a selected wordline of the memory array, wherein the memory, comprises:
a memory array;
a threshold voltage measuring component configured to measure a threshold voltage (Vt) uniquely associated with a selected wordline for one or more memory cells on the selected wordline; and
an average threshold voltage determining component configured to determine an average threshold voltage Vt(avg) uniquely associated with the selected wordline based on the measured threshold voltages on the selected wordline of the memory array; and
wherein the memory is configured to
program one or more of the memory cells of the selected wordline to a predefined program level uniquely associated with the determined average threshold voltage Vt(avg) uniquely associated with the selected wordline; or
erase one or more of the memory cells of the selected wordline to the determined average threshold voltage Vt(avg).
24. The device of claim 23 , the electronic device comprising at least one of a communication device, Personal Data Assistant (PDA), cell phone, memory stick, flash drive device, video camcorder, voice recorder, USB flash drive, fax machine, flash memory, laptop, computer, scanner, MP3player, digital camera, home video game console, hard drive and memory card.
25. The device of claim 23 , wherein the one or more memory cells of the memory array comprise multi-level flash memory cells comprising element-pairs, individual memory elements of the element-pairs having two or more program levels and a blank level, the levels comprising three or more data levels corresponding to three or more threshold voltages.