Signal-to-noise optimization in narrow vertical and horizontal giant magnetoresistent head sensors (abstract)

Abstract

An analysis was performed on the optimum distance that vertical or horizontal M–R sensors should extend into a read head gap in order to optimize the signal-to-noise ratio of the amplified signal excluding media noise. The optimum distance depends on the decay length of the signal flux in the gap, sensor resistance, lead resistance, equivalent resistance of the amplifier, gap uniformity, sensor width, signal field sensitivity of the average sensor permeability, and bias field magnitudes. To a first approximation for typical values of the parameters, the optimum distance ranges from 1 to 2.5 times the decay length in the gap. Vertical sensors were found to utilize more effectively a nonuniform gap because the magnetic material can extend under the rear contact. The magnetization at the back edge of a horizontal sensor is essentially pinned by demagnetizing fields. Because sensor current densities are typically high, a 100 °C operating temperature was assumed. Also, because run length limited codes are used, the 1/f noise contribution of the GMR material was not considered in the calculations.