Three-dimensional memory device, manufacturing method thereof, and memory system

A memory device, comprising:

• a first stacked structure comprising first dielectric layers and first conductive layers stacked alternatively in a first direction;
• storage channel structures, each of the storage channel structures extending through the first stacked structure in the first direction and comprises a first channel layer;
• a second stacked structure on the first stacked structure and comprising second dielectric layers and second conductive layers stacked alternatively in the first direction;
• and
• select channel structures, each of the select channel structures extends through the second stacked structure in the first direction and comprises a second channel layer, wherein:
• a first storage channel structure of the storage channel structures comprises a first end and a second end opposite to the first end,
• a first select channel structure of the select channel structures comprises a third end and a fourth end opposite to the first end,
• the first end is away from the first select channel structure relative to the second end, and the third end is close to the first storage channel structure relative to the fourth end,
• the first storage channel structure and the first select channel structure overlap in the first direction,
• a diameter of the third end is smaller than a diameter of the second end, and
• a material of the second channel layer of the first select channel structure is the same as a material of the first channel layer of the first storage channel structure.