Non-volatile memory device

A non-volatile memory device, comprising at least one memory cell, wherein the at least one memory cell comprises:

• a substrate;
• an assist gate structure disposed on the substrate and comprising a gate dielectric layer;
• a tunneling dielectric layer disposed on the substrate at one side of the assist gate structure;
• a floating gate disposed on the tunneling dielectric layer and comprising:
• two first top edges opposite each other and arranged along a first direction;
• two first sidewalls opposite each other and arranged along the first direction, wherein the two first sidewalls are connected to the two first top edges respectively;
• and
• two second sidewalls opposite each other and arranged along a second direction, wherein the second direction is different from the first direction;
• an upper gate structure covering the assist gate structure and the floating gate, wherein at least one of the two first top edges of the floating gate is embedded in the upper gate structure;
• and
• a middle structure covering one of the two first sidewalls of the floating gate and opposite the assist gate structure along the first direction;
• wherein the floating gate is disposed between the middle structure and the assist gate structure, a top surface of the middle structure is level with or lower than at least one of the two first top edges of the floating gate, and the middle structure is an insulating structure or a control gate structure.