System, method, and apparatus for detecting signal-to-noise ratio decay in perpendicular magnetic recording

Abstract

A magnetic test module runs on a spin stand to detect amplitude decay and noise evolution at the same time. Signal-to-noise ratio (SNR) decay is directly measured. The recording performance is correlated better with SNR instead of signal only. The thermal stability of the system is evaluated more accurately with this SNR decay method. A heater is placed under the media disk, and a remote sensing thermometer and temperature controller form a subsystem to set up desired environmental temperature. The heater creates a heated band and the read / write head flies above the heated band. The temperature control system may be removed when SNR decay measurement is performed under room temperature.

Description

BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] The present invention relates in general to perpendicular magnetic recording in disk drives and, in particular, to an improved system, method, and apparatus for detecting signal-to-noise ratio decay in perpendicular magnetic recording. [0003] 2. Description of the Related Art [0004] Thermal decay due to the “superparamagnetic effect” in longitudinal magnetic recording is becoming a significant concern as the rate of areal density increases rapidly. In the past, substantial effort was devoted to characterizing media thermal decay and understanding the impact of media decay on the ultimate recording performance. Precise and quantitative prediction of media thermal decay lifetime was commonly believed to be an important task. In the prior art, amplitude or magnetization versus time was measured, then the decay rate was determined in percentage decrease per decade of log(time). [0005] Perpendicular magnetic recording (PMR) has...

AI Technical Summary

Benefits of technology

[0012] In one embodiment, the aged signal and test signal are interleaved on the same written track. Write gate and read gate features are used to control the sequence of aged magnetic bits and test magnetic bits. The aged magnetic bits also act as a reference signal to eliminate the adverse effects of thermal drift and sensitivity change mentioned above.

[0014] In order to measure SNR decay, the noise evolution is measured at the same time of detecting signal decay. A spectrum analyzer is implemented into the spin stand to measure the noise in frequency domain. Integrated noise can be obtained when a frequency sweep is performed. One can monitor this integrated noise as a function of time. Frequency sweep and noise integration is a long process and takes much more time than detecting the aged / test signal. The data-taking efficiency can be improved by properly selecting noise samples and constructing noise sensitivity to define integrated noise as a quantity for monitoring noise evolution.

Problems solved by technology

Media that may exhibit a significant amount of signal decay after several years of recording are not practically useful.

It poses a challenge to reliably measure extremely small changes of the recorded signals because of thermal drift and sensitivity changes of the transducer of the recording head.

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