Affiliations: [a] Test Optimization to Drive Laboratory, Seagate
Technology (Thailand), Nakornratchasrima, Thailand | [b] School of Engineering and Technology, Asian Institute
of Technology, Pathumthani, Thailand | [c] Information Technology Group, Faculty of Science,
Thaksin University, Phatalung, Thailand
Abstract: We did an experimental study to examine head instabilities and noise
of tunneling magnetoresistance (TMR) sensors using in high-density
perpendicular recording systems. It found that the instability signatures on
the transfer curves could be categorized into two groups; permanent magnet/free
layer (PM/FL) failure and synthetic antiferromagnetic layers/antiferromagnetic
layer (SAF/AFM) failure. The thermal-mechanical stress from the adaptive flying
height (AFH) heater as well as head-disk interaction potentially degrades PM
resulting in the reduction of the FL stabilizing field, therefore TMR ratio and
signal increases. The non-uniformity of PM remnant magnetization and the
switching of PM grains especially near the edge potentially degrade the biasing
field. Scanning electron microscope images of these weak heads show rough
surface and scratches close to the active area of read sensor. The deep
scratches by particles in the head-disk interaction and shallow scratches by
the slider lapping process is a potential cause to degrade PM. In another
group, the thermal-mechanical stress from AFH heater potentially reduces the
exchange-bias field and thermal stability of SAF/AFM layers allowing partial
flipping of SAF edge magnetization, consequently it induces voltage
fluctuations and hysteresis loops in the transfer curves.
Keywords: Adaptive flying height, head-disk interaction, thermal-mechanical stress, head instabilities
