Over the last 15 years or so magnetron sputtering systems have undergone considerable development. In a "conventional" magnetron a higher substrate ion bombardment, the number of ions hitting the substrate during coating (vital for hard dense coatings) can only be achieved by increasing the power to the target or decreasing the distance from the target. To overcome this problem the unbalanced magnetron was developed.

An unbalanced magnetron possesses stronger magnets on the outside resulting in the expansion of the plasma away from the surface of the target towards the substrate to be coated considerably increasing the substrate ion bombardment.

Figure 5. An unbalanced magnetron, the outer North poles are stronger than the inner South poles therefore the field lines stretch further into the vacuum chamber

With the development of the unbalanced magnetron the substrate ion current that could be achieved and therefore the quality of the coatings increased dramatically but more was to come with the development of multimagnetron geometry with magnetic field linkage. The magnets within the magnetrons are arranged such that alternating poles are next to each other resulting in the linkage of field lines. This prevents electrons escaping to the chamber walls resulting in much higher ion current densities and dense, hard well adhered coatings.