Abstract: A planar diode sputtering source employs an anode and a generally concave cathode. The interior surfaces of the cathode include an outer portion providing a lip for protecting a surrounding cooling jacket from sputtering, a middle portion configured to optimize the average match between the surface thereof with a surrounding magnetic field for long useful life, and an inner portion. The middle and outer portion are faired together to minimize localized target erosion leading to premature target depletion or failure. The inner portion joins the middle portion with surface tangents meeting at an angle which minimizes local erosion at this juncture.