Albert John Wallash

Dependence of magnetoresistive head readback characteristics on sensor height

The microtrack profile and bias point of a magnetoresistive (MR) head play a fundamental role in determining the full track response. In this paper the stripe height dependence of these properties is studied. The magnetic center of the MR head is found to approach the physical center, and microtrack side slopes become steeper and more equal as the stripe height is decreased. These experimentally observed trends can be understood using a simple model based on anisotropic flux propagation in the MR sensor.

Electrostatic modeling and ESD damage of magnetoresistive sensors

The response of a thin-film sensor to the excessive current and/or voltage during an electrostatic discharge (ESD) event is studied. An unshielded magnetoresistive (MR)-like recording head structure is analyzed and modeled from the viewpoint of electrostatic theory. An electrical model for the MR head structure is proposed and used in circuit simulations to study the current flow through the thin-film resistor during a Human Body Model ESD transient. A thermal model for the thin-film resistor burnout is compared with experiment and 2D modeling of the fields and voltages are presented. Finally, Maxwells method is used to calculate the induced charge on the MR structure when a charged external conductor is present.

Reproduction of slider vibrations during head/disk interactions using PZT sensors

The use of piezoelectric lead zirconate titanate (PZT) sensors to generate plate-mode vibrations in a slider has been investigated. It is shown that individual plate modes of the slider can be excited by applying a sinusoidally varying voltage to a PZT transducer bonded to the slider. An additional square-wave input to the transducer produces asperity-hitlike vibrations in the slider. The generated signals are compared and contrasted in both the time and frequency domains with actual PZT sensor signals obtained while flying the slider over disk defects. It is concluded that slider vibrations caused by asperity hits during flying can be reproduced in the manner described. >

ESD failure mechanisms of inductive and magnetoresistive recording heads

The response of experimental thin-film recording head structures to the excessive current and voltage during an electrostatic discharge (ESD) event is studied. Inductive and magnetoresistive (MR)-like magnetic recording head structures are tested and modeled from the viewpoint of electrostatic theory. An electrical model for the shielded MR-like head structure is proposed and used in circuit simulations to study the response during Human Body Model (HBM) and Machine Model (MM) transients. A testing methodology is defined using HBM and MM ESD transients. A thermal model for thin-film resistor burnout is compared with experiment and predicts a higher failure current than is measured. Results show that the MR structure can fail due to metalization burnout or air breakdown. The HBM metalization burnout failure voltage ranged from 100 V to 300 V, while MM damage started at about 27 V. Air breakdown ranged from 550 V to 650 V.