Microelectronic devices including isolation structures protruding into upper pillar portions, and related methods and systems

A method of forming a microelectronic device, the method comprising:

• forming a stack structure comprising a vertically alternating sequence of insulative structures and conductive structures arranged in tiers;
• forming a series of pillars extending through the stack structure;
• forming at least one slit structure adjacent the series of pillars and extending through the stack structure;
• forming at least one isolation structure extending through an upper stack portion of the stack structure, the at least one isolation structure protruding into pillars of neighboring columns of pillars of the series of pillars;
• and
• forming conductive contacts in electrical communication with the pillars into which the at least one isolation structure protrudes.

A microelectronic device, comprising:

• a stack structure of vertically interleaved insulative structures and conductive structures;
• pillars, arranged in columns and extending through the stack structure, in electrical communication with conductive contacts adjacent the stack structure, each of the pillars comprising a lower pillar portion and an upper pillar portion with at least one coplanar sidewall, the lower pillar portion extending through a lower stack portion of the stack structure, the upper pillar portion extending through an upper stack portion of the stack structure;
• and
• at least one isolation structure passing between and at least partially into the upper pillar portions of the pillars of at least one neighboring pair of the columns.

An electronic system, comprising:

• an input device;
• an output device;
• a processor device operably coupled to the input device and to the output device;
• and
• a memory device operably coupled to the processor device and comprising at least one microelectronic device structure, the at least one microelectronic device structure comprising at least one elongate isolation structure extending through an upper stack portion of a stack structure of vertically interleaved insulative structures and conductive structures, the at least one elongate isolation structure at least partially overlapping lower portions of pillars of neighboring columns of a pillar array, the pillars being electrically coupled to conductive contacts of the memory device.