Method of operating memory cell

A method of operating a memory cell, wherein the memory cell comprises a substrate having a protruding part, a top bit line located in a top portion of the protruding part, a first bottom bit line and a second bottom bit line located in the substrate respectively beside the protruding part, a word line located on the substrate and crossing over the first and second bottom bit lines, and a charge-storage layer located between the word line and the substrate,

• and wherein the memory cell has a first storage region, a second storage region, a third storage region and a fourth storage region located in the charge-storage layer, the first storage region and the second storage region are respectively adjacent to a lower portion and an upper portion of the protruding part at a side of the first bottom bit line, the third storage region and the fourth storage region are respectively adjacent to a lower portion and an upper portion of the protruding part at a side of the second bottom bit line, and the second storage region and the third storage region are regarded as a top storage region,
• the method comprising programming the top storage region of the memory cell, comprising:
• applying a first positive voltage to the word line;
• applying a second positive voltage to the top bit line;
• and
• respectively applied a bottom voltage to the first and second bottom bit lines.