Memory device for applying voltages to word lines during erase operations and operating method for memory device

1 . A memory device, comprising:

a common source line;

at least one bit line; and

at least one memory string, coupled to the common source line and the at least one bit line respectively,

during an erasing operation, an erasing voltage is applied to at least one of the common source line and the at least one bit line, and a word line voltage is applied to a plurality of memory cells of the at least one memory string,

in a first period of the erasing operation, a voltage value of the erasing voltage is raised to a target voltage value, and a voltage value of the word line voltage is a first voltage value, and

in a second period after the first period of the erasing operation, the voltage value of the erasing voltage is the target voltage value, and the voltage value of the word line voltage is raised from the first voltage value to a second voltage value,

wherein a difference voltage of the first voltage value minus the second voltage value is in a range from zero to −6 volts.

2 . The memory device of claim 1 , wherein a difference voltage between the target voltage value and the first voltage value is in a range larger than 20 and less than 26 volts.

3 . The memory device of claim 1 , wherein when entering in the second period of the erasing operation, and the voltage value of the word line voltage is raised from the first voltage value to the second voltage value after a default time length.

4 . The memory device of claim 3 , wherein the default time length is larger than zero and less than 400 micro seconds.

5 . The memory device of claim 1 , wherein in the first period of the erasing operation, the voltage value of the word line voltage is decreased from an initial voltage value to the first voltage value.

6 . The memory device of claim 1 , wherein the difference voltage of the first voltage value minus the second voltage value is in a range from −3 to −4 volts.

7 . The memory device of claim 1 , wherein in the first period of the erasing operation, the first voltage value is equal to an initial voltage value.

8 . The memory device of claim 1 , wherein the first period of the erasing operation further comprises:

a first selecting signal applied to a string select transistor begins to be floated on a first time point, wherein the string select transistor is coupled between a first edge memory cell among the plurality of memory cells of the at least one memory string and the at least one bit line; and

a second selecting signal applied to a ground select transistor begins to be floated on a second time point later than the first time point, wherein the ground select transistor is coupled between a second edge memory cell among the plurality of memory cells of the at least one memory string and the common source line.

9 . The memory device of claim 8 , wherein in the second period of the erasing operation, a voltage value of the first selecting signal is higher than a voltage value of the second selecting signal.

10 . The memory device of claim 1 , wherein:

the common source line extends along a first direction,

the at least one bit line extends along a second direction and arrange along the first direction,

the plurality of memory cells of the at least one memory string arrange along a third direction, and

the first direction, the second direction and the third direction are different from each other.

11 . An operating method for a memory device, wherein the memory device comprises a common source line, at least one bit line and at least one memory string coupled to the common source line and the at least one bit line respectively, wherein the operating method comprises:

during an erasing operation, applying an erasing voltage to at least one of the common source line and the at least one bit line during the erasing operation, and applying a word line voltage to a plurality of memory cells of the at least one memory string;

in a first period of the erasing operation, raising a voltage value of the erasing voltage to a target voltage value and applying a voltage value of the word line voltage at a first voltage value, and

in a second period after the first period of the erasing operation, applying the voltage value of the erasing voltage at the target voltage value and raising the voltage value of the word line voltage from the first voltage value to a second voltage value,

wherein a difference voltage of the first voltage value minus the second voltage value is in a range from zero to −6 volts.

12 . The operating method of claim 11 , wherein a difference voltage between the target voltage value and the first voltage value is in a range larger than 20 and less than 26 volts.

13 . The operating method of claim 11 , wherein the step of raising the voltage value of the word line voltage from the first voltage value to a second voltage value comprises:

raising the voltage value of the word line voltage from the first voltage value to the second voltage value after a default time length.

14 . The operating method of claim 13 , wherein the default time length is larger than zero and less than 400 micro seconds.

15 . The operating method of claim 11 , further comprising:

decreasing the voltage value of the word line voltage from an initial voltage value to the first voltage value in the first period of the erasing operation.

16 . The operating method of claim 11 , wherein the difference voltage of the first voltage value minus the second voltage value is in a range from −3 to −4 volts.

17 . The operating method of claim 11 , wherein in the first period of the erasing operation, the first voltage value is equal to an initial voltage value.

18 . The operating method of claim 11 , wherein the first period of the erasing operation further comprising:

beginning to float a first selecting signal applied to a string select transistor on a first time point, wherein the string select transistor is coupled between a first edge memory cell among the plurality of memory cells of the at least one memory string and the at least one bit line; and

beginning to float a second selecting signal applied to a ground select transistor on a second time point later than the first time point, wherein the ground select transistor is coupled between a second edge memory cell among the plurality of memory cells of the at least one memory string and the common source line.

19 . An operating method for a memory device, wherein the memory device comprises a common source line, at least one bit line and at least one memory string coupled to the common source line and the at least one bit line respectively, wherein the operating method comprises:

during an erasing operation, applying an erasing voltage to at least one of the common source line and the at least one bit line during the erasing operation, and applying a word line voltage to a plurality of memory cells of the at least one memory string;

in a first period of the erasing operation, raising a voltage value of the erasing voltage to a target voltage value and applying a voltage value of the word line voltage at a first voltage value, and

in a second period after the first period of the erasing operation, applying the voltage value of the erasing voltage at the target voltage value and raising the voltage value of the word line voltage from the first voltage value to a second voltage value,

wherein a difference voltage of the first voltage value minus the second voltage value is in a range from −3 to −4 volts.