| CPC H10B 43/27 (2023.02) [H01L 21/76224 (2013.01); H10D 62/115 (2025.01)] | 19 Claims |

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1. A microelectronic device, comprising:
a stack structure comprising vertically repeated tiers, the tiers individually comprising at least one insulative structure and at least one conductive structure;
a series of pillar structures extending through the stack structure, at least one of the pillar structures of the series comprising:
a lower pillar structure comprising a channel material and defining a substantially circular cross-sectional area; and
an upper pillar structure above the lower pillar structure, the upper pillar structure comprising an additional channel material and a plug structure, the plug structure comprising a conductive semiconductor material, the upper pillar structure and the plug structure thereof defining a partially-circular cross-sectional area; and
at least one isolation structure extending partially into neighboring upper pillar structures of neighboring pillar structures of the series of pillar structures.
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