Writing Process Induced Media Noise Measurement

Writing processes can cause extra medium noise, which is the dominant noise in the perpendicular recording system. This work describes the methodology of using averaging methods to measure the writer footprints and its noise profiles, which are recorded at different writing currents on a Spin-stand. Two different commercial heads have been used for the evaluation. The test is performed on a 2.5 inch commercial disc at the middle diameter (MD) location, rotating at 5400 RPM spindle speed, and at 0 skew angle. The center track is DC erased over an AC erased background and then recorded with a repetitive footprint data pattern and an alignment data pattern. Multiple revolution averaging and down track footprint averaging are used to retrieve the noise free footprint profile of the writer. Using the noise free footprint profile, the statistical characteristics of noise can be derived from the individual noisy footprint which shows the media noise characteristics induced by writing process. Using footprint and noise profile data, signal to noise ratio (SNR) for regions near the trailing edge of the writer profile are calculated and suggests that the ideal writing condition for writer A and B to be 55 and 25 mA respectively.