Memory device including vertical channel structure
Provided is a memory device with a vertical channel structure. The memory device includes a memory cell array including a plurality of memory cells and a plurality of string selection lines, a negative charge pump configured to generate a bias voltage of a negative level, to be applied to at least one of the plurality of string selection lines, and a control logic circuit configured to apply, for a first period, a prepulse voltage to at least one unselected string selection line among the plurality of string selection lines excluding a selected string selection line to which a memory cell selected from among the plurality of memory cells is connected and thereafter apply the bias voltage to the at least one unselected string selection line so as to perform a read operation on the selected memory cell.
1. A memory device comprising:
a memory cell array including a plurality of memory cells and a plurality of string selection lines;
a negative charge pump configured to generate a bias voltage of a negative level, to be applied to at least one of the plurality of string selection lines; and
a control logic circuit configured to apply, for first period, a prepulse voltage to at least one unselected string selection line among the plurality of string selection lines excluding a selected string selection line to which a memory cell selected from among the plurality of memory cells is connected, and thereafter apply the bias voltage to the at least one unselected string selection line so as to perform a read operation on the selected memory cell.
2. The memory device of claim 1 , further comprising:
a substrate including a first word line cut region and a plurality of string selection line cut regions, and
wherein a level of the bias voltage is based on whether the at least one unselected string selection line is provided in an edge region adjacent to the first word line cut region or a center region between the plurality of string selection line cut regions.
3. The memory device of claim 2 , wherein
the negative charge pump is configured to generate a first bias voltage and a second bias voltage,
the control logic circuit is configured to apply the first bias voltage to a first unselected string selection line in the edge region and apply the second bias voltage to a second unselected string selection line in the center region, and
the second bias voltage is less than the first bias voltage.
4. The memory device of claim 3 , wherein
the negative charge pump is further configured to generate a third bias voltage and a fourth bias voltage,
the center region comprises a first center region spaced a first distance from the first word line cut region and a second center region spaced a second distance from the first word line cut region, wherein the second distance is greater than the first distance
the control logic circuit is further configured to apply the third bias voltage to a third unselected string selection line in the first center region, and apply the fourth bias voltage to a fourth unselected string selection line in the second center region, and
the third bias voltage is less than or equal to the second bias voltage, and the fourth bias voltage is less than the third bias voltage.
5. The memory device of claim 1 , wherein the negative charge pump is further configured to generate a plurality of voltages that reduce gradually from a ground voltage to the bias voltage.
6. The memory device of claim 1 , further comprising:
a row decoder, the row decoder including,
a signal line decoder configured to receive a bias voltage control signal and the bias voltage, and the signal line decoder configured to output the bias voltage in response to the bias voltage control signal; and
a pass transistor connected to one of the at least one unselected string selection line and the signal line decoder.
7. The memory device of claim 6 , wherein the pass transistor comprises a triple well type field-effect transistor (FET) including a deep well and a pocket well provided in the deep well and biased to a negative level voltage.
8. The memory device of claim 1 , wherein the prepulse voltage has a positive level.
9. The memory device of claim 2 , wherein the memory cell array further comprises a plurality of word lines stacked on the substrate in a vertical direction and connected to the plurality of memory cells.
10. A memory device for performing a read operation on a selected memory cell, the memory device comprising:
a memory cell array including a plurality of memory cells and a plurality of string selection lines;
a negative charge pump configured to generate a bias voltage of a negative level, to be applied to an unselected string selection line among the plurality of string selection lines excluding a string selection line to which the selected memory cell of the plurality of memory cells is connected; and
a row decoder configured to apply a prepulse voltage to the unselected string selection line for a first period and thereafter apply the bias voltage thereto for a second period.
11. The memory device of claim 10 , wherein
the row decoder comprises
a signal line decoder; and
a pass transistor configured to connect the signal line decoder and the unselected string selection line,
the signal line decoder comprises
a first transistor configured to be turned off in the second period to block connection between at least one transistor and the pass transistor; and
a second transistor configured to be turned on in the second period to apply the bias voltage to the pass transistor, and
the at least one transistor is configured to apply the prepulse voltage to the pass transistor in the first period.
12. The memory device of claim 11 , wherein each of the first transistor and the second transistor comprises a triple well type field-effect transistor (FET) including a deep well and a pocket well provided in the deep well and biased to a negative level voltage.
13. The memory device of claim 12 , wherein the negative charge pump is further configured to
apply the bias voltage to a drain of the second transistor; and
apply a first voltage of a negative level to the pocket well of each of the first transistor and the second transistor.
14. The memory device of claim 10 , wherein
the row decoder comprises
a signal line decoder; and
a pass transistor configured to connect the signal line decoder and the unselected string selection line, and
the signal line decoder comprises
a first transistor configured to be turned on in the first period to apply the prepulse voltage to the pass transistor; and
a pull-up transistor and a pull-down transistor each configured to apply the bias voltage to the pass transistor in the second period and connected in series between a first input pin and a ground node.
15. The memory device of claim 14 , wherein each of the first transistor, the pull-up transistor and the pull-down transistor comprises a triple well type field-effect transistor (FET) including a deep well and a pocket well provided in the deep well and biased to a negative level voltage.
16. The memory device of claim 15 , wherein the negative charge pump is further configured to
apply the bias voltage to the first input pin; and
apply a first voltage of a negative level to the pocket well of each of the first transistor, the pull-up transistor, and the pull-down transistor.
17. A memory device comprising:
a memory cell array comprising
a first word line cut region and a second word line cut region;
a plurality of string selection line cut regions between the first and second word line cut regions; and
a plurality of vertical channel structures between the first word line cut region and the plurality of string selection line cut regions, between the second word line cut region and the plurality of string selection line cut regions, and between adjacent string selection line cut regions among the plurality of string selection line cut regions; and
a control logic circuit configured to
apply a prepulse voltage to a first string selection line and a second string selection line connected to a plurality of unselected memory cells so as to perform a read operation on a selected memory cell,
divide the plurality of vertical channel structures into first vertical channel structures and second vertical channel structures according to a distance to an adjacent word line cut region among the first and second word line cut regions, and
apply different voltages to the first string selection line connected to the first vertical channel structures and the second string selection line connected to the second vertical channel structures after application of the prepulse voltage.
18. The memory device of claim 17 , wherein the control logic circuit is further configured to apply different bias voltages of a negative level to the first string selection line and the second string selection line.
19. The memory device of claim 18 , wherein a distance to the adjacent word line cut region from the first vertical channel structures is longer than a distance to the adjacent word line cut region from the second vertical channel structures, and
a first bias voltage applied to the first string selection line is less than a second bias voltage applied to the second string selection line.
20. The memory device of claim 19 , wherein a first prepulse operation performance time for applying the prepulse voltage to the first string selection line is longer than a second prepulse operation performance time for applying the prepulse voltage to the second string selection line.