Chapter 6 - Magnetoresistive heads

Abstract

The introduction of magnetoresistive (MR) read heads in drives led to an increase in the annual compound growth rate of areal densities in hard disk drives. Although inductive read head technology was extended to recording densities that were never thought possible, MR heads showed a clear advantage in read signal amplitude and a demonstrated extensibility to much higher densities because of the discovery of giant magnetoresistance (GMR). The future growth in recording densities will be met by advanced MR heads and GMR heads. This chapter examines the basic principle and designs of MR heads, with an emphasis on anisotropic MR heads. The widely practicedbiasing schemes to linearize the MR sensor and to eliminate Barkhausen noise are discussed. Small signal analysis of MR sensors is also given. Reciprocity principle and transmission line model are applied to MR heads. The practical engineering issues of MR heads, such as side read asymmetry, readback nonlinearity, baseline shift, thermal asperity, and electrostatic discharge sensitivity, and MR head fabrication process are also introduced.