Noise Analysis of CPP-GMR Heads with Current-Screen Layer

摘要

We investigated the head noise in current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) heads through experiments and calculations. We fabricated CPP-GMR heads having a current-screen layer (a nano-oxide layer with a confined current path) whose track width and sensor height is 80 nms. A significant increase in head noise caused by spin-torque was observed when the sensing current was negative. However, spin-torque noise was not observed at a sensing voltage of + - 120 mV when the heads had an orthogonal direction for the free and the reference layer. Therefore, spin-torque noise was not a fatal issue for current-screen-type CPP-GMR heads, regardless of whether the sensing current was positive or negative. Our calculations indicate that the head noise in the current-screen-type CPP-GMR heads is 1/6 less than that in the all-metallic type at a sensing voltage of + - 120 mV with a peak asymmetry of approx 0 percent. Even when the peak asymmetry is approx 0 percent, in the all-metallic type, the spin-torque noise is induced by the non-uniform alignment of the magnetization from the current-induced field. Accordingly, current-screen-type CPP-GMR heads have an advantage over the all-metallic type from the viewpoint of SNR.