Local self-boosting method of flash memory device and program method using the same
Provided is a local self-boosting method of a flash memory device including at least one string having memory cells respectively connected to wordlines. The local self-boosting method includes forming a potential well at a channel of the string and forming potential walls at the potential well to be disposed at both sides of a channel of a selected one of the memory cells. The channel of the selected memory cell is locally limited by the potential walls and boosted when a program voltage is applied to the selected memory cell.
1. A local self-boosting method of a flash memory device including at least one string having memory cells respectively connected to wordlines, the local self-boosting method comprising:
forming a potential well at a channel of the at least one string, forming the potential well includes driving the wordlines with a first pass voltage; and
forming potential walls at the potential well to be disposed at both sides of a channel of a selected one of the memory cells, forming potential walls includes driving at least one wordline adjacent respectively to both sides of a wordline connected to the selected memory cell with a second pass voltage that is lower than the first pass voltage, wherein:
the channel of the selected memory cell is locally limited by the potential walls and boosted when a program voltage is applied to the selected memory cell, application of the program voltage to the selected memory cell starting after driving of the at least one wordline with the second pass voltage has started.
2. The local self-boosting method as claimed in claim 1 , wherein the first and second pass voltages are within a pass voltage window.
3. The local self-boosting method as claimed in claim 1 , wherein the at least one wordline adjacent respectively to both sides of a wordline connected to the memory cell is driven with the second pass voltage after the other wordlines are driven with the second pass voltage and before the wordline connected to the selected memory cell is driven with a program voltage.
4. The local self-boosting method as claimed in claim 1 , wherein forming the potential well and forming potential walls are performed simultaneously.
5. The local self-boosting method as claimed in claim 1 , wherein the selected memory cell is a memory cell to be program-inhibited.
6. The local self-boosting method as claimed in claim 1 , wherein a potential of a channel of the string does not change when the selected memory cell is a memory cell to be programmed.
7. A program method of a flash memory device including at least one string having memory cells respectively connected to wordlines, the program method comprising:
driving the wordlines with a first pass voltage to form a potential well at a channel of the at least one string;
driving at least one wordline adjacent respectively to both sides of a selected one of the wordlines with a second pass voltage that is lower than the first pass voltage, to form potential walls at the potential well to be disposed at both sides of a channel of a selected one of the memory cells, the channel of the selected memory cell being locally limited by the potential walls; and
driving the selected wordline with a program voltage such that the channel of the selected memory cell is boosted when the program voltage is applied to the selected memory cell, application of the program voltage to the selected memory cell starting after driving of the at least one wordline with the second pass voltage has started.
8. The program method as claimed in claim 7 , wherein the first pass voltage is higher than the second pass voltage.
9. The program method as claimed in claim 8 , wherein the first and second pass voltages are within a pass voltage window.
10. The program method as claimed in claim 7 , wherein a memory cell connected to the selected wordline is a memory cell to be program-inhibited.
11. A program method of a flash memory device including at least one string having memory cells respectively connected to wordlines, the program method comprising:
driving the wordlines with a first pass voltage to form a potential well at a channel of the at least one string;
driving at least one wordline adjacent respectively to both sides of a selected one of the wordlines and other wordlines, except the selected wordline, with a second pass voltage that is lower than the first pass voltage, to form potential walls at the potential well to be disposed at both sides of a channel of a selected one of the memory cells, the channel of the selected memory cell being locally limited by the potential walls; and
driving the selected wordline with a program voltage such that the channel of the selected memory cell is boosted when the program voltage is applied to the selected memory cell, application of the program voltage to the selected memory cell starting after driving of the at least one wordline with the second pass voltage has started.
12. The program method as claimed in claim 11 , wherein the first pass voltage is lower than the second pass voltage.
13. The program method as claimed in claim 11 , wherein, when two wordlines respectively adjacent to both sides of the selected wordline are driven with the first pass voltage, one wordline just adjacent respectively to both sides of the selected wordline is driven with the second pass voltage before the selected wordline is driven with the program voltage.
14. A flash memory device, comprising:
at least one string having memory cell respectively connected to wordlines; and
a control logic configured to control voltage to be supplied to the wordlines during a program operation, wherein:
the control logic controls voltages of the wordlines such that the program operation is performed in a local self-boosting manner including forming a potential well at a channel of the string and forming potential walls at the potential well to be disposed at both sides of a channel of a selected one of the memory cells, forming the potential well including driving the wordlines with a first pass voltage, and forming potential walls including driving at least one wordline adjacent respectively to both sides of a wordline connected to the selected memory cell with a second pass voltage that is lower than the first pass voltage, and
the channel of the selected memory cell is locally limited by the potential walls such that the channel of the selected memory cell is boosted when a program voltage is applied to the selected memory cell during the program operation when application of the program voltage to the selected memory cell started after driving of the at least one wordline with the second pass voltage had started.