US Patent 11355177 Vertical memory device

A memory device includes: a first memory cell mat that includes first multi-layer level sub word lines positioned over a substrate; a second memory cell mat that is laterally spaced apart from the first memory cell mat and includes second multi-layer level sub word lines; a first sub word line driver circuit that is positioned underneath the first memory cell mat; and a second sub word line driver circuit that is positioned underneath the second memory cell mat, wherein the first sub word line driver circuit is positioned underneath ends of the first multi-layer level sub word lines, and the second sub word line driver circuit is positioned underneath ends of the second multi-layer level sub word lines.