Memory array including memory cell strings and method for forming memory array including memory cell strings

The invention relates to a memory array comprising strings of memory cells and a method for forming a memory array comprising strings of memory cells. A memory array including strings of memory cells includes laterally spaced memory blocks individually including a vertical stack including alternating insulating layers and conductive layers over a conductor layer. A string of memory cells includes a string of channel material extending through the insulating layer and the conductive layer. The channel material string is electrically coupled directly to a conductor material of the conductor layer. The insulating layer immediately above a lowermost one of the conductive layers includes a lower first insulating material and an upper second insulating material above an upper first insulating material. The upper second insulating material has a different composition than the lower first insulating material. Intermediate material is laterally between laterally adjacent memory blocks and longitudinally along the memo