Write frequency dependence of popcorn noise in GMR heads

Abstract

Popcorn noise of integrated inductive write/GMR read heads was characterized at various write currents and frequencies. The popcorn noise count tends to increase with write current and peaks at a certain frequency. This was attributed to heating-cooling cycles of heads induced by the write current, which rolls off with frequency. In fact, it was observed that write current heating peaks around the same frequency. The heating is caused by Joule heating of writer coils and eddy current loss of the writer core. A larger popcorn count was observed if the heat diffusion path is restrained, for example, by unloading heads from the media surface. The clock frequency at which the popcorn noise peaks is higher when tested with a pseudo-random write pattern instead of a single frequency pattern. Potential impact of high data rate and write current rise time of preamplifiers is discussed.