Microelectronic devices, memory devices, and electronic systems

A memory device, comprising:

• a stack structure comprising conductive structures vertically interleaved with insulative structures;
• strings of memory cells vertically extending through the stack structure;
• a source structure vertically underlying the stack structure and coupled to the strings of memory cells;
• conductive plug structures vertically overlying and in electrical communication with the strings of memory cells, at least one of the conductive plug structures comprising:
• a first portion having a substantially uniform horizontal width across a vertical height thereof;
• and
• a second portion underlying and unitary with the first portion and having variable horizontal widths across a vertical height thereof, the second portion comprising:
• a largest horizontal width at a vertical position most proximate to the first portion;
• and
• a smallest horizontal width at an additional vertical position most proximate to the strings of memory cells;
• and
• digit line structures vertically overlying and in electrical communication with the conductive plug structures.

An electronic system, comprising:

• a processor device operably connected to an input device and an output device;
• and
• a memory device operably connected to the processor device and comprising:
• a stack structure comprising conductive material and insulative material vertically alternating with the conductive material;
• strings of memory cells vertically extending through the stack structure;
• a source structure vertically underlying the stack structure and in electrical communication with the strings of memory cells;
• digit lines vertically overlying the stack structure;
• conductive contact structures vertically overlying the stack structure and coupling the strings of memory cells to the digit lines, the conductive contact structures individually comprising:
• a first portion having a substantially uniform horizontal cross-sectional area across an entire vertical dimension thereof;
• and
• a second portion underlying and unitary with the first portion and having a non-uniform horizontal cross-sectional area across an entire vertical dimension thereof;
• and
• control logic circuitry vertically underlying the source structure and in electrical communication with the strings of memory cells.