Head reliability of AMR sensors based on thermal stress tests

Abstract

Head reliability of AMR sensors based on thermal stress testsTape storage drives use robust shielded anisotropic magnetoresistive (AMR) read sensors. Under normal operating conditions, changes in sensor properties are undetectable. To estimate end-of-life conditions, sensors are exposed to elevated temperatures, and changes in relevant physical parameters are measured. Then, using thermodynamic models, these measurements are extrapolated to normal operating conditions. Thermal stress experiments using elevated electrical currents for heating were conducted on AMR read sensors designed for use up to about 200 Mb/in. 2 in tape storage drives. Physical parameters that are relevant to tape-drive function include stripe resistance, AMR amplitudes and asymmetries, and stripe and shield oxidation. Changes in these parameters were measured as functions of time and temperature. The experimental results were fit to thermodynamic models, which were then used to extrapolate the observed changes to normal operating temperatures and extended times. The data shows that, at the lowest temperatures, the important processes are stripe oxidation and annealing-induced changes in magnetic characteristics. For the materials studied, the projected timeto-failure for use in a drive is greater than ten years.

Determination of the aging offset voltage of AMR sensors based on accelerated degradation test

“…However an amplitude decrease can be expected associated with degradation after a long time. These results match with the AMR amplitude changes indicated by [4].…”

“…Probably this is because the properties of the Permalloy are changing during the sensor lifetime [5]. In [4] and [5] is stated that these changes are related with the stress effect of the passivation layer on top of the Permalloy material. Therefore, because of the stress dynamics, it is possible that the offset voltage decreases in some sensors while it increases in others.…”

“…However, it is not the same regarding the offset voltage variation resulting from the aging effect [4]. The companies that produce the sensors and the reliability studies found in the literature focus on lifetime tests using acceleration test for reliability estimation.…”

Dynamic temperature rise of shielded MR sensors during simulated electrostatic discharge pulses of variable pulse width

“…Figure 10 shows a fit to the data using an Arrhenius equation: Long term (many hours) physical changes in permalloy stripes [13] from elevated temperatures and currents using Joule heat yield a significantly lower activation energy of 2 eV with a prefactor of 10 -12.4 s (for t mr of 20 nm). The long-term degradation at temperatures below 400 o C is predominately associated with electromigration [14]. Using the experimental vaues for electromigration and interdiffusion (τ 2 ), electromigration is calculated to be faster below about 600 o C while interdiffusion is faster at higher temperatures where ESD events occur.…”

A generalized equivalent temperature model in a time-varying environment

“…Wang predicted the storage life of aerospace electromagnetic relay under storage temperature 25°C -32°C based on auto-regressive and moving average model and wavelet transform model [21]. Anisotropic magnetoresistive read sensors were exposed to elevated temperatures to estimate end-of-life conditions under normal operating temperatures [5]. Huang predicted the life of tantalum capacitors under working temperature which was specified as 35°C [4].…”