Semiconductor memory device including multiple conductive line layers

1. A semiconductor memory device, comprising:

a plurality of memory cells on a substrate, each of the plurality of memory cells including an access transistor and a pull-down transistor;

a first line layer on the memory cells, the first line layer including a power line, a first lower landing pad, and a second lower landing pad;

a second line layer on the first line layer, the second line layer including a ground line having an opening and an upper landing pad in the opening, the opening surrounding the upper landing pad when viewed in a plan view, the ground line including a pair of first segments and a pair of second segments that define the opening, each of the first segments extending in a second direction and having a first width in a first direction intersecting the second direction, each of the second segments extending in the first direction and having a second width in the second direction, the first width being greater than the second width; and

a third line layer including a word line on the second line layer,

wherein the ground line is electrically connected through the first lower landing pad to a terminal of the pull-down transistor, and

wherein the word line is electrically connected through the upper landing pad and the second lower landing pad to a terminal of the access transistor,

wherein the power line vertically overlaps a corresponding one of the first segments, and

wherein a via between the first lower landing pad and a corresponding one of the second segments is spaced apart from the corresponding one of the first segments.

2. The semiconductor memory device of claim 1 , wherein

the first line layer further includes a bit line, and

the bit line and the power line extend parallel to each other in the first direction.

3. The semiconductor memory device of claim 2 , wherein

the first lower landing pad and the second lower landing pad are adjacent to the bit line, and

the first lower landing pad and the second lower landing pad are arranged in the first direction.

4. The semiconductor memory device of claim 1 , wherein at least a portion of the upper landing pad vertically overlaps the second lower landing pad.

5. The semiconductor memory device of claim 1 , wherein the upper landing pad includes a pair of upper landing pads in the opening.

6. The semiconductor memory device of claim 1 , wherein

the ground line has a plurality of openings, and

the ground line is a mesh-typed conductive structure.

7. The semiconductor memory device of claim 1 , further comprising:

a fourth line layer including an upper word line on the third line layer,

wherein the word line and the upper word line are electrically connected to each other.

8. A semiconductor memory device, comprising:

a plurality of memory cell transistors on a substrate;

a first line layer on the memory cell transistors; and

a second line layer on the first line layer,

wherein the first line layer includes a bit line, a power line, a first lower landing pad, and a second lower landing pad,

wherein the second line layer includes a ground line having a plurality of openings,

wherein the ground line includes a pair of first segments that extend in a second direction and a pair of second segments that extend in a first direction intersecting the second direction,

wherein each of the openings is defined by the pair of first segments and the pair of second segments,

wherein a width in the first direction of each first segment of the pair of first segments is greater than a width in the second direction of each second segment of the pair of second segments,

wherein the second line layer further includes a via between the first lower landing pad and a corresponding one of the second segments,

wherein the ground line has electrical connection through the via and the first lower landing pad to a terminal of a first memory transistor of the memory cell transistors,

wherein the power line vertically overlaps a corresponding one of the first segments, and

wherein the via is spaced apart from the corresponding one of the first segments.

9. The semiconductor memory device of claim 8 , wherein

the semiconductor memory device includes a third line layer on the second line layer, and

the third line layer includes a word line that is electrically connected through an upper landing pad, which is included in the second line layer and provided in a corresponding one of openings, and the second lower landing pad to a terminal of a second memory transistor of the memory cell transistors.

10. The semiconductor memory device of claim 8 , wherein

the first lower landing pad is a lower ground line,

the bit line, the power line, and the lower ground line extend parallel to each other, and

the ground line is electrically connected through the lower ground line to the terminal of the first memory transistor.

11. A semiconductor memory device, comprising:

a plurality of memory cells on a substrate, each of the memory cells including a plurality of memory transistors; and

a first line layer, a second line layer, and a third line layer sequentially stacked on the memory cells,

wherein the first line layer includes a bit line, a power line, and a first lower landing pad,

wherein the second line layer includes a ground line having an opening and an upper landing pad in the opening, the ground line including a pair of first segments and a pair of second segments that define the opening, each of the first segments extending in a second direction and having a first width in a first direction intersecting the second direction, each of the second segments extending in the first direction and having a second width in the second direction, the first width being greater than the second width,

wherein the opening surrounds the upper landing pad when viewed in a plan view,

wherein the third line layer includes a word line,

wherein the word line is electrically connected through the upper landing pad and the first lower landing pad to a terminal of a first memory transistor of the memory transistors,

wherein the power line vertically overlaps a corresponding one of the first segments, and

wherein a via between the first lower landing pad and a corresponding one of the second segments is spaced apart from the corresponding one of the first segments.

12. The semiconductor memory device of claim 11 , wherein

the first line layer includes a second lower landing pad, and

the ground line is electrically connected through the second lower landing pad to a terminal of a second memory transistor of the memory transistors.

13. The semiconductor memory device of claim 11 , wherein

the first line layer includes a lower ground line, and

the ground line is electrically connected through the lower ground line to a terminal of a second memory transistor of the memory transistors.

14. The semiconductor memory device of claim 11 , wherein the first memory transistor is an access transistor of a static random access memory (SRAM) cell.