Relaxed Head Media Spacing by High Resolution DDSV Reader at Multi- $hbox{Tb/in}^2$ Areal Density

摘要

At 10 $hbox{Tb/in}^2$ areal density and bit aspect ratio (BAR) of 4, the 1 T bit length is only 4 nm. By proportional scaling, it requires the head media spacing (HMS) to be around 2 nm. In such a small spacing, it is extremely hard to squeeze in the medium overcoat and lubricant for having a reliable head disk interface. This small HMS demand is mainly determined by the readback process for the reader to have large signal intensity and high signal resolution. The differential dual spin valve (DDSV) reader incorporates a metallic gap layer between the free layers of two spin valves. The opposite pinned reference layers generate the differential operation and reproduce the pulse signal from the transition of perpendicular magnetizations. With the readback resolution defined by the thicknesses of gap layer and two free layers, the DDSV reader gains more resolution than the conventional reader. Unlike conventional reader also using two shields to define signal resolution, the shields of DDSV reader is only for the elimination of inter-symbol interference. This allows the shield to shield spacing of DDSV reader to be much larger, which has smaller shunting effect and promotes the signal strength. With stronger signal intensity and higher readback resolution, the DDSV reader is able to reproduce good quality signal at much higher HMS than the conventional reader.