A three-dimensional (3D) NAND memory device includes a substrate, a staircase region including a first stack and a second stack, a barrier structure extending vertically through the first stack and laterally separating the first stack from the second stack, and a through array contact extending vertically through the first stack to the substrate. The first stack is disposed on the substrate and includes first and second dielectric layers arranged alternately in a vertical direction. The second stack is disposed on the substrate and includes conductor layers and third dielectric layers arranged alternately in the vertical direction. The barrier structure has an unclosed shape.