A method for manufacturing a memory device may include obtaining a substrate structure that includes a substrate, an oxide material layer positioned on the substrate, a polysilicon material layer positioned on the oxide material layer, a first control gate and a second control gate positioned on the polysilicon material layer, and an offset oxide layer positioned between the first control gate and the second control gate. The method may further include the following steps: removing, using the offset oxide layer as a first mask, a portion of the polysilicon material layer for forming a polysilicon structure that includes a first step structure; forming a masking oxide layer on the offset oxide layer; removing, using the masking oxide layer as a second mask, a portion of the polysilicon structure for forming a floating gate polysilicon member that includes the first step structure and a second step structure.