Whenever energy is dissipated in the form of thermal energy in a material with a thermal expansion coefficient greater than zero the material will expand and therefore forms a protrusion. In today’s read/ write heads as used in hard disk drives there are many electrical micro devices which produce thermal energy due to Joule energy dissipation. As head-to-disk spacing gets smaller and reaches sub-nanometer spacing, a careful measurement and a comprehensive understanding of Joule heating protrusions at HDI (Head-Disk Interface) becomes critical to overall HDD reliability, as well as reading and writing performance.In the past, Li [1] developed a dynamic AFM-based technique to detect protrusions that are below 1 um in lateral dimension. This size is too small for any other technique such as optical profiling due to wavelength related resolution limitations. In this paper, the AFM-based technique has been further developed in an ECS (Embedded Contact Sensor) heating scenario and detailed calibration work has been conducted to validate the AFM measurement.A piezo-electric actuator based calibration device was built and then excited by a low frequency AC signal with different voltage amplitudes. The responding piezo-electric movement was first measured by an LDV (Laser Doppler Vibrometer) on a 1 mm x 1 mm flat surface. The same piezo-electric movement was then measured on the same flat surface by the AFM-based technique mentioned above at 1&nbsp;um size lateral dimension to have a direct comparison. Furthermore, ECS protrusion results were also compared with thermo-mechanical simulations to provide a more detailed understanding of the ECS protrusion profiles. Both experimental calibration results and comparison with simulation established an accurate calibration factor between the two techniques and validated the accuracy of the AFM based protrusion measurement.&nbsp;Reference:[1] Li, Dongbo, et al. "A new AFM-based technique to detect the NFT protrusion on HAMR head."&nbsp;IEEE transactions on magnetics&nbsp;49.7 (2013): 3576-3579.

A New Method to Calibrate Protrusion Measurement on a Small Heating Device

Paper Proceedings: https://asmedigitalcollection.asme.org/ISPS/ISPS2021/volume/84799

ASME 2021 Information Storage and Processing Systems (ISPS2021)

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