Lydia Baril

Degradation of GMR and TMR recording heads using very short duration ESD transients

Electrostatic discharge (ESD) testing results for giant magnetoresistive (GMR) and tunneling magnetoresistive (TMR) recording heads using a direct charged device model (D-CDM) tester are reported for the first time. The D-CDM is intended to replicate the ESD event produced by metal-to-metal contact discharge that occurs as a charged component discharges to another object at a different electrostatic potential. This discharge, through a very short path to ground, corresponds to an extremely fast (<1 ns wide), high-amplitude current transient. The D-CDM tester produces a transient by first charging the device itself and then grounding the device with a mercury relay. The ESD testing was done in situ with a quasi-static tester (QST) on GMR recording heads. Resistance, amplitude, asymmetry, and transfer curves were recorded after each ESD event. D-CDM physical failure voltages are much lower (4-5 V) than the ones obtained with the human body model (HBM) (25-30 V). Magnetic failure threshold can be even lower. We also report some D-CDM damage on TMR recording heads.

Electromagnetic field induced degradation of magnetic recording heads in a GTEM cell

A gigahertz transverse electromagnetic mode (GTEM) cell was used to apply a controlled RF electric field to magnetic recording assemblies. The resistance and magnetic properties of the giant magnetoresistive (GMR) and tunneling MR (TMR) sensors were measured before and after exposure to the electric field. No degradation in GMR sensor properties was observed for pulsed field strengths up to 40 V/m for the standard assembly configuration. However, severe resistance and magnetic damage was observed when an additional 7 cm long wire was attached to the input of the GMR sensor. It is concluded that it is important to understand and measure the radiated immunity failure level for extremely ESD sensitive devices like magnetic recording assemblies.

Thermal Effects and Self-Heating Time Constant for GMR Recording Heads

An understanding of the temperature of the GMR reader element used in disk drives during operating and non-operating condition is critical to optimize its performance. Self-heating and/or external heat sources will cause an increase in the temperature of the GMR sensor. In this work we concentrate on the self-heating effect due to bias current. Experiments that monitored the resistance change during very short current pulses showed that state-of-the-art GMR sensors have an extremely short time-constant that is less than 2 ns. This work is applicable to the current transients that the GMR head experiences during electrical crosstalk, electrostatic discharge and thermal asperities.Copyright