A semiconductor structure comprises a reference layer of a magnetic random-access memory pillar structure, the reference layer having a first diameter, a free layer of the magnetic random-access memory pillar structure disposed over the reference layer, the free layer having a second diameter, and an electrode layer of the magnetic random-access memory pillar structure disposed over the free layer, the electrode layer having a third diameter. At least two of the first diameter, the second diameter and the third diameter are different.