MR glide inspection for hard disk defect detection

摘要

In a disk drive magnetic read/write is achieved with a magnetic head flying closely over a magnetic disk. As area 1 recording density is increased to several Gbits/In$+2$/, the dynamic flying height of the magnetic head is reduced to one $mu@-inch or less. Bumps taller than one $mu@-inch often results in head crash. Since the DLC coating on the magnetic disk surface is less than 10 nanometers in thickness, pits with depth over 10 nanometers cause damage to the magnetic layer. To prevent head crash or missing bit errors, magnetic disk surface needs to be examined for bumps taller than the dynamic flying height and pits deeper than the DLC thickness. In this paper, we report experimental results using a head with an MR sensor flying over a disk with precision bumps and pits micro-fabricated on the disk surface. Non-contact signal disturbances of the MR sensor flown over variable area square pits and bumps on the 2400 Oe media exhibit both magnetic and thermal signal characteristics. The lateral sizes of the pits and bumps obtained using the MR magnetic signal measured from a Phase Metrics MG250 tester agree well with those measured with an Atomic Force Microscope (AFM). The thermal signal characteristics of the pits and bumps are of opposite polarity, and scale in a non-linear fashion with the lateral size of the surface defects. Some preliminary experimental results involving naturally occurring surface defects and Phase Metrics' optical scatterometry tester PS5100 are also discussed for comparison purposes.