Memory arrays comprising strings of memory cells and methods used in forming a memory array comprising strings of memory cells

Abstract

A memory array comprising strings of memory cells comprises an upper stack above a lower stack. The lower stack comprises vertically-alternating lower conductive tiers and lower insulative tiers. The upper stack comprises vertically-alternating upper conductive tiers and upper insulative tiers. An intervening tier is vertically between the upper and lower stacks. The intervening tier is at least predominantly polysilicon and of different composition from compositions of the upper conductive tier and the upper insulative tier immediately-above the intervening tier and of different composition from compositions of the lower conductive tier and the lower insulative tier immediately-below the intervening tier. Channel-material strings of memory cells extend through the upper stack, the intervening tier, and the lower stack. Other structures and methods are disclosed.