Readback Resolution of Differential Dual CPP Spin Valve Reader

The readback resolution of conventional CPP spin valve reader is mainly determined by the shield to shield spacing and partially affected by the head media spacing change. As the linear density grows continuously, the bit length will be reduced to sub-10 nm or even sub-5 nm in the future. In such, the shield to shield spacing has to be below 20 nm or even 10 nm. It gradually becomes not feasible to squeeze all the functional layers used by current reader, such as: AFM layer, SAF, tunnel barrier, free layer, and capping layer, in such a small spacing. The differential dual spin valve (DDSV) read head is one of the new reader structures that can provide better readback resolution. This work studied the sensitivity function of DDSV reader without and with shields, then, identified the waveform characteristics of readback signal at different head media spacing (HMS) and gap layer (GL) thickness. The readback resolution of DDSV reader is mainly determined by the thickness of the gap layer between the two free layers. The two shields are still necessary for the DDSV reader in order to have the free layers picking up more localized media flux. The shield to shield spacing at 35 nm helps to constrain the free layers to pick up media flux mainly from ±5 nm region.