Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2001-11-21
2003-04-29
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C360S031000
Reexamination Certificate
active
06556006
ABSTRACT:
BACKGROUND
1. Field
The inventor's disclosure generally relates to disk drives and more particularly to a method and system for detecting electrostatic noise of magneto-resistive heads in hard disk drive assemblies.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of information. The information is recorded on concentric tracks on either surface of one or more magnetic recording disks. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads. The read/write heads must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
Dual element transducers are increasingly utilized in hard disk drives because they are lighter than single element transducers. Dual element transducers include a single write element and a separate read element which is constructed from a magneto-resistive material. Such dual element transducers are commonly referred to as magneto-resistive (“MR”) heads and the read elements of such heads are often referred to as GMR/MR sensors. More recently, heads have been constructed using alternating magnetic and nonmagnetic films thereby drastically increasing their resistivity. Such heads are generally known as giant magneto-resistive (“GMR”) heads.
Along with the desire to improve head design, there is also a desire to decrease the failure rate of the hard disk drives. While such failures occur for a variety of reasons, one cause is GMR/MR head instability, particularly head instability associated with electrostatic discharge. Such electrostatic discharge manifests as popping noise and may similarly be caused by a variety of conditions, such as junction permanent-magnet insufficiency or dielectric breakdown of the insulting layer between the conducting sensor stripes.
One problem with detecting popping noise in a GMR/MR head is that different causes of popping noise manifest as different types of popping noise. For example, popping noise manifested as amplitude spikes may be caused by GMR/MR internal design flaws, while popping noise manifested as an unstable baseline not correlated to a signal may be caused by dielectric breakdown. Finally, heads which exhibit unstable baselines correlated to a signal may be caused by junction-induced instability.
One problem in the art is that it is difficult to detect these different types of popping noise using a single simple method. Thus, there is a need in the art for a single improved method that is capable of detecting different types of popping noise.
BRIEF SUMMARY
The inventor discloses a method and system for detecting defective heads. In one embodiment, the method comprising erasing a track on a disk, said disk including a plurality of tracks, reading said track with a head, determining a first signal amplitude at a first frequency using a first current supplied to said head, and determining a second signal amplitude at said first frequency using a second current supplied to said head. The method further comprises determining a first noise measure, said first noise measure to be a function of said first signal amplitude and said second signal amplitude, and identifying said head as having a first defect type where said first noise measure is greater than a first amplitude threshold.
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Cho Keung Youn
Kao Andrew
Li Zhaohui
Aiello Jeffrey P.
Irell & Manella LLP
Samsung Electronics Co,. Ltd.
Snow Walter E.
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