Compensation method to achieve uniform programming speed of flash memory devices
View Patent ↗Systems and methodologies are provided herein for increasing operation speed uniformity in a flash memory device. Due to the characteristics of a typical flash memory array, memory cells in a memory array may experience distributed substrate resistance that increases as the distance of the memory cell from an edge of the memory array increases. This difference in distributed substrate resistance can vary voltages supplied to different memory cells in the memory array depending on their location, which can in turn cause non-uniformity in the speed of high voltage operations on the memory array such as programming. The systems and methodologies provided herein reduce this non-uniformity in operation speed by providing compensated voltage levels to memory cells in a memory array based at least in part on the location of each respective memory cell. For example, a compensated operation voltage can be provided that is higher near the center of the memory array and lower near an edge of the memory array, thereby lessening the effect of distributed substrate resistance and providing increased operation speed uniformity throughout the memory array.
1. A system that facilitates performing a high voltage operation in a flash memory device, comprising:
a memory array having a plurality of wordlines, each wordline coupled to a plurality of memory cells;
a high voltage pump that generates at least one operation voltage for the high-voltage operation and transfers the at least one operation voltage to the memory array; and
a compensation component that adjusts the voltage generated by the high voltage pump based as a function of distance between a location of a wordline in the memory array coupled to one or more memory cells on which the high voltage operation is to be performed and an edge of the memory array.
2. The system of claim 1 , wherein the high voltage operation is a programming operation.
3. The system of claim 2 , wherein the compensation component adjusts the at least one operation voltage upward if the wordline in the memory array coupled to one or more memory cells on which the programming operation is to be performed is located near an edge of the memory array, thereby increasing programming speed on the one or more memory cells.
4. The system of claim 2 , wherein the compensation component adjusts the at least one operation voltage downward if the wordline in the memory array coupled to one or more memory cells on which the programming operation is to be performed is located near the center of the memory array, thereby decreasing programming speed on the one or more memory cells.
5. The system of claim 1 , wherein the memory array includes an x-decoder for transferring a first operation voltage to a wordline in the memory array and a y-decoder for transferring a second operation voltage to a memory cell in each wordline in the memory array.
6. The system of claim 5 , wherein the y-decoder transfers the second operation voltage to one of a source of a memory cell in each wordline in the memory array and a drain of a memory cell in each wordline in the memory array.
7. The system of claim 5 , wherein the memory array further includes bitlines that connect a memory cell coupled to each wordline in the memory array and the y-decoder transfers a second operation voltage to a bitline in the memory array.
8. The system of claim 7 , wherein the high voltage operation is performed on a plurality of memory cells that share a common wordline in the memory array by keeping the x-decoder stationary to provide the first operation voltage to the common wordline and switching the y-decoder to sequentially provide the second operation voltage to bitlines in the memory array that are connected to the plurality of memory cells.
9. The system of claim 1 , wherein one or more adjacent wordlines in the memory array are divided into wordline groups and the compensation component adjusts the operation voltage generated by the high voltage pump based on the location of a wordline group in the memory array containing one or more memory cells on which the high voltage operation is performed.
10. The system of claim 1 , further comprising an address sequencer that receives an address for each of the one or more memory cells on which the high voltage operation is performed.
11. A method of performing a high voltage operation in a flash memory device, comprising:
receiving address information corresponding to a location of one or more memory cells in a memory array;
calculating one or more compensated operation voltages based at least in part on the location of the one or more memory cells in the memory array in relation to one or more edges of the memory array;
generating the one or more compensated operation voltages; and
transferring the one or more compensated operation voltages to the one or more memory cells in the memory array.
12. The method of claim 11 , wherein the high voltage operation is a programming operation.
13. The method of claim 12 , wherein the calculating includes determining a wordline in the memory array on which each of the one or more memory cells is respectively located.
14. The method of claim 13 , wherein the calculating further includes at least one of increasing a standard programming voltage to be transferred to a memory cell located on a wordline near an edge of the memory array, thereby increasing programming speed on the memory cell; and decreasing a standard programming voltage to be transferred to a memory cell located on a wordline near the center of the memory array, thereby decreasing programming speed on the memory cell.
15. The method of claim 12 , wherein the calculating further includes grouping one or more adjacent wordlines into wordline groups and determining the wordline group in which each of the one or more memory cells is respectively located.
16. The method of claim 15 , wherein the calculating further includes:
assigning two or more wordline groups located at opposing edges of the memory array a predetermined maximum programming voltage;
assigning one or more wordline groups located at the center of the memory array a predetermined minimum programming voltage; and
assigning each wordline group between the edges and the center of the memory array an intermediate programming voltage between the maximum programming voltage and the minimum programming voltage such that a first intermediate programming voltage corresponding to a first wordline group is lower than a second intermediate programming voltage corresponding to a second wordline group that is located closer to an edge of the array than the first wordline group.
17. The method of claim 11 , wherein the compensated operation voltages include at least one of a wordline voltage, a source voltage, and a drain voltage.
18. A system for performing a high voltage operation in a flash memory device, comprising:
means for receiving address information corresponding to a location of one or more memory cells in a memory array;
means for generating a high voltage for the high voltage operation;
means for compensating the high voltage based at least in part on a distance from the one or more memory cells in the memory array to a center wordline of the memory array; and
means for transferring the high voltage to the one or more cells in the memory array.
19. The system of claim 18 , wherein the high voltage operation is a programming operation.
20. The system of claim 18 , wherein the high voltage is one of a wordline voltage, a source voltage, and a drain voltage.