Integrated Circuitry Comprising A Memory Array Comprising Strings Of Memory Cells And Methods Used In Forming A Memory Array Comprising Strings Of Memory Cells

Integrated circuitry comprising a memory array comprising strings of memory cells, comprising:

• an upper stack directly above a lower stack, the lower stack comprising vertically-alternating lower-conductive-tiers and lower-insulative-tiers, the upper stack comprising vertically-alternating upper-conductive-tiers and upper-insulative-tiers;
• an upper of the lower-insulative-tiers or a lower of the upper-insulative-tiers comprising non-stoichiometric silicon dioxide having a silicon-to-oxygen atomic ratio greater than 0.5, a higher of the upper-insulative-tiers that is above said lower upper-insulative-tier comprising silicon dioxide having a silicon-to-oxygen atomic ratio less than or equal to 0.5;
• and
• channel-material strings of memory cells extending through the upper stack and the lower stack including through the non-stoichiometric silicon dioxide.

Integrated circuitry comprising a memory array comprising strings of memory cells, comprising:

• laterally-spaced memory blocks individually comprising a first vertical stack comprising alternating insulative tiers and conductive tiers, strings of memory cells comprising channel-material strings that extend through the insulative tiers and the conductive tiers, the conductive tiers individually comprising a horizontally-elongated conductive line;
• a second vertical stack aside the first vertical stack, the second vertical stack comprising an upper portion and a lower portion, the upper portion comprising alternating upper-first-insulating-tiers and upper-second-insulating-tiers of different composition relative one another, the lower portion comprising lower-first-insulating-tiers and lower-second-insulating-tiers of different composition relative one another;
• and
• an upper of the lower-second-insulating-tiers or a lower of the upper-second-insulating-tiers comprising non-stoichiometric silicon dioxide having a silicon-to-oxygen atomic ratio greater than 0.5, a higher of the upper-second-insulating-tiers that is above said lower upper-second-insulating-tier comprising silicon dioxide having a silicon-to-oxygen atomic ratio less than or equal to 0.5.