Nathan Curland

Characterization of the Reader Width Using the Micro-Track Test in Perpendicular Recording

Micro-track test is a valuable tool used to characterize the electrical reader width in perpendicular recording. The test is based on trimming both sides of a track written with a single tone and followed by a cross-track scan of the remaining track. The reader cross-track profile or read sensitivity function is characterized by a narrow band measurement of the read-back signal as a function of cross-track position. With increasing track density, the signal amplitude decreases due to incomplete media saturation and to an increase in the off-track noise due to percolation and opposite polarity media saturation. These effects cause a lump at the edge of the micro-track profile that changes the width of the profile (MT10 and MT50). Micro-magnetic analysis indicates that the off-track demagnetization field creates a track-edge section in the media with opposite polarity relative to the originally written track. This section is coherent with the main track and decreases the read-back signal during the scan of the micro-track. Consequently, the shape of the cross-track read sensitivity function becomes distorted, causing a reduction in MT10 and a side lump. The solution to this problem is to increase the amplitude of the micro-track read-back signal by reduced trimming and by the use of a higher density (KFCI) in the main track that minimizes the off-track demagnetization field. These test improvements are shown to preserve the integrity of the micro-track profile and to enable an accurate measurement of MT10 and MT50. Optimizing reader and writer widths in perpendicular recording requires an accurate measurement of these parameters.

Measuring and understanding write width and off-track as a function of linear density in perpendicular recording

Multiple techniques have been developed and used to characterize the width of a written track in perpendicular recording. This work investigates written tracks using the WPE (write plus erase) test based on writing the main track at a given density and trimming both sides of the track multiple times with another density. The edge of the original track, after each trimming step, is characterized by a narrow band measurement of the read-back signal as a function of cross-track position. The use of a narrow band filter improves the test SNR and helps separate the track into 2 sections: A good region (track center) and a degraded region (track edge). Test and micro-magnetic analysis were used under multiple linear densities for the main track and for the trimming tracks. The results indicate that the WPE value decreases as the density increased between 200 kfci and 1500 kfci. For densities lower than 200 kfci and higher than 1500 kfci, the WPE value does not change significantly. When the main track was fixed...

Integrating an MR head into a peak detection channel

Integrating an MR head into a peak detection channel requires the engineer to deal with basic differences between MR and thin film heads. These differences result from nonlinear sensor response, separate write and read elements, and having an active element at the ABS. A simple model for flux superposition can adequately address nonlinear effects and be used for equalization design. Timing budgets can be developed which demonstrate the dominance of media noise for present day systems. Single threshold qualification can handle most current system requirements, Separate read/write elements mean that more attention needs to be paid to offtrack equalization design and head dimensional tolerancing. An active element at the ABS requires better control of the head-disc potential and leakage currents. >

Design and performance of a recessed thin film inductive transducer

An improved inductive transducer is achieved by placing the coil and the majority of the transducer body into a recessed alumina basecoat. Process advantages of a recessed over planar structure includes lower top pole topography, improved pole trim capability, and improved top pole composition uniformity. Coil and photoresist processing in a recessed cavity allows for multiple layers with lower resistance without increasing transducer Permalloy path length. Recessed trimmed design performance has increased efficiency with higher amplitude and a narrower pulse width along with improved overwrite compared to planar untrimmed transducers. The recessed basecoat design is explained, and compared to planar transducers using modeling and performance results.