Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
1999-09-14
2001-11-20
Faber, Alan T. (Department: 2753)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S067000, C360S046000
Reexamination Certificate
active
06320713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention generally relates to computer storage devices and in particular to magnetic read heads in computer storage devices. Still more particularly, the present invention relates to an improved method for determining MR read head resistance in computer storage devices.
2. Description of the Related Art
Manufacturers today go to great lengths to ensure that their products are of high quality, and that their operational characteristics are optimized. One group of products for which quality and reliability are of utmost importance are disk drives, which are widely utilized within computers and other devices for data storage. A disk drive, which is a type of magnetic recording device, can store vast amounts of data that can be quickly accessed.
One component of a disk drive is a magnetic transducer, referred to as a head, which is an electromagnetic device that is closely positioned to the disk to read and write data. High capacity disk drive units, which are common today, have multiple disks and multiple heads to read and write data. One type of high performance recording head is a magnetoresistive (MR) head. In order to optimize the MR head's operating point for optimum performance, it is important to first know the resistance across the MR head.
MR read heads are also used in other common storage devices, such as tape drives. The MR read head resistance is of importance for any MR read head application, including tape drives, disk drives, and others.
The measurement of the read head resistance is also important in order to ensure that the maximum power dissipation of the head is not exceeded. By knowing the resistance of the read head, more bias current can be allowed to flow through the head without exceeding the maximum power dissipation allowed in the head. More bias current means more head output, which can be very helpful in overcoming many system problems related to noise generated by the writing process.
Another advantage of measuring the head resistance to gather information relating to head wear over the life of the head while it is installed. This is possible because of the change in head resistance as a function of wear. Finally, Electrostatic Discharge (ESD) failures can be determined because a failed head will have a very high resistance.
One approach has been to assume a resistance value based upon statistical data, but manufacturing variations and the high sensitivity of the system to resistance variations can cause problems with this approach. Therefore, it is useful to measure the resistance of each head in a disk drive using a system such as controlling the biasing current applied to MR heads within a magnetic disk drive to provide optimized bias current for each head/disk/channel component combination.
At the time of manufacture, an optimized bias current for each head is ascertained and stored on the disk surface. During each subsequent power up operation the stored values are transferred to random access memory which is accessed during execution of each head switch command to apply a bias current in accordance with the optimized value to the active MR head.
One problem with this approach is that the MR resistance measurement must be accomplished at the subassembly level, before the unit is installed in the disk enclosure. For example, the resistance measurement must be completed at the MR head wafer level, the slider assembly level, or by inconvenient probing methods at the HeadStackAssembly (HSA) level (after the actuator has been assembled and just before it is merged into the disk enclosure). After the MR head, actuator and the like are merged together within the disk enclosure, the terminals of the MR head are not available for measurement without removing the unit from its enclosure, and it is impractical to extend the terminals beyond the disk enclosure because such extension can severely degrade the disk unit's file performance. Furthermore, MR resistance measurements made according to this method are time consuming and require special probes and fixtures to gain access to the MR resistance node.
For manufacturing purposes, it would be useful to protect the magnetoresistive recording heads against electrostatic discharge (ESD) with a shorting mechanism such as a solderball. In order to maximize ESD protection, the solderball should not be removed until the latest possible moment, which is just before the head is merged into the disk enclosure. However, using conventional techniques the MR resistance cannot be read until the short circuit has been removed, and measuring the resistance can be difficult once the disk drive has been installed into the disk enclosure.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved computer storage device.
It is another object of the present invention to provide an improved magnetic read head system in computer storage devices.
It is yet another object of the present invention to provide an improved method for determining MR read head resistance in computer storage devices.
The foregoing objects are achieved as is now described. A known current and resistance is used to determine a reference voltage. A variable current is then applied to the MR read head, and is adjusted to produce a voltage equal to that of the reference voltage. Then, the known current and voltage is used to determine the resistance of the MR read head.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.
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Malmberg James Ernest
Tretter Larry Leeroy
Bracewell & Patterson L.L.P.
Faber Alan T.
International Business Machines - Corporation
Klein Esther E.
Millett Douglas R.
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