Considerations for high data rate recording with thin-film heads

Abstract

Much higher data rates are inevitable as efforts are made to increase linear density and reduce rotational latency in rigid disk drives. Thin film heads have attributes which make them very attractive for high data rates. This paper looks at the significance of head inductance and eddy currents in limiting field rise times. Poor rise times can cause severe distortion and loss of performance at high data rates. A simple reluctance model is developed to explore the relationship between the geometry of a head and its inductance. The model is extended to include the effects of eddy currents and to allow the frequency dependent efficiency (hence the field rise time) to be calculated. Based on this rise time a geometric model is used to calculate the positions of the recorded transitions and the resulting transition-shift distortion. Experimental results at transition separations down to 6 ns reveal a strong write current dependency which is not seen in the model. This dependence is, however, clearly seen in a simple domain wall model which implicitly includes magnetic saturation. Transition shift distortion can be mitigated by the use of precompensation. It is found possible to successfully recover data at 180 Mbit/s using a conventional thin-film head. © 1990 IEEE