Magnetic readback microscopy applied to laser-texture characterization in standard desktop disk drives

We present a variant of the magnetic-readback microscopy (MRM) technique that provides an electronic “window” into a sealed hard-drive. The analog read-back signal is probed at the preamplifier test points and is demodulated to provide local average amplitude versus time data. This data is captured repeatedly as the head is stepped by the drive servo in fractional track increments. The result looks rather like atomic force microscopy, except that the head itself is the sensing element, Z-axis sensitivity down to 2 nm and lateral resolution of the order of 1 μm can be achieved. Modified firmware of an existing disk drive allowed full servo-control in the landing zone. This was necessary to study the laser texture with the Magnetic Readback Microscope (MRM). In a sealed drive, laser-bump shape, pitch and height can be measured. We further demonstrate a technique to measure the Laser bump arrangement within the drive. We also include a comparison between MRM and Thermal Proximity Mapping (TPM) on laser bumps and thermal asperities. Finally, we report variations in M_rt caused by the laser bump annealing during certain disk manufacturing processes