A memory device includes a well, a poly layer, a dielectric layer, an alignment layer and an active area. The poly layer is formed above the well. The dielectric layer is formed above the poly layer. The alignment layer is formed on the dielectric layer, used to receive an alignment layer voltage and substantially aligned with the dielectric layer in a projection direction. The active area is formed on the well. The dielectric layer is thicker than the alignment layer. A first overlap area of the poly layer and the active area is smaller than a second overlap area of the poly layer and the dielectric layer excluding the first overlap area.