Error detection/correction and fault detection/recovery – Pulse or data error handling – Memory testing
Reexamination Certificate
1999-01-06
2001-04-10
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Memory testing
C360S031000
Reexamination Certificate
active
06216242
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the field of rigid magnetic disc drives, and more particularly, but not by way of limitation, to a test head configuration which is capable of both disc media magnetic certification and thermal asperity detection.
Disc drives of the type known as “Winchester” disc drives or hard disc drives are well known in the industry. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent to the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path.
As the physical size of disc drives has decreased historically, the physical size of many of the disc drive components has also decreased to accommodate this size reduction. Similarly, the density of the data recorded on the magnetic media has been greatly increased. In order to accomplish this increase in data density, significant improvements in both the recording heads and recording media have been made.
For instance, the first rigid disc drives used in personal computers had a data capacity of only 10 megabytes, and were in the format commonly referred to in the industry as the “full height, 5¼″ format. Disc drives of the current generation typically have a data capacity of over a gigabyte (and frequently several gigabytes) in a 3½″ package which is only one fourth the size of the full height, 5¼″ format or less. Even smaller standard physical disc drive package formats, such as 2½″ and 1.8″, have been established. In order for these smaller envelope standards to gain market acceptance, even greater recording densities must be achieved.
The recording heads used in disc drives have evolved from monolithic inductive heads to composite inductive heads (without and with metal-in-gap technology) to thin-film heads fabricatd using semi-conductor deposition techniques to the current generation of thin-film heads incorporating inductive write and magneto-resistive (MR) read elements. This technology path was necessitated by the need to continuously reduce the size of the gap in the head used to record and recover data, since such a gap size reduction was needed to reduce the size of the individual bit domain and allow greater recording density.
Since the reduction in gap size also meant that the head had to be closer to the recording medium, the quest for increased data density also lead to a parallel evolution in the technology of the recording medium. The earliest Winchester disc drives included discs coated with “particulate” recording layers. That is, small particles of ferrous oxide were suspended in a non-magnetic adhesive and applied to the disc substrate. With such discs, the size of the magnetic domain required to record a flux transition was clearly limited by the average size of the oxide particles and how closely these oxide particles were spaced within the adhesive matrix. The smoothness and flatness of the disc surface was also similarly limited. However, since the size of contemporary head gaps allowed data recording and retrieval with a head flying height of twelve microinches (0.000012 inches) or greater, the surface characteristics of the discs were adequate for the times.
Disc drives of the current generation incorporate heads that fly at nominal heights of only about 2.0&mgr;″, and products currently under development will reduce this flying height to 1.5&mgr;″ or less. Obviously, with nominal flying heights in this range, the surface characteristics of the disc medium must be much more closely controlled than was the case only a short time ago.
Industry demands for increasing data storage capacity are being met by increases in the areal density with which data are stored on the disc surfaces. The areal density of a disc drive product is defined as the mathematical product of the linear density (or number of bits recorded along the length of the data track), typically defined as “bits per inch”, and the track density, measured radially across the disc and defined in “tracks per inch”.
In order to increase the areal density at the current industry rate of approximately 60% per year, the track density is constantly being increased, and in order to accomplish this, the width of the operational read/write heads has steadily decreased, with current disc drive products incorporating heads having a width of 2.0 microns, 1.5 microns or less. It will be apparent to one of skill in the art that the decrease in track width leads, in turn, to a decrease in the size of an allowable disc media defect.
Each disc is statistically tested at the component level before being assembled into a disc drive. Magnetic defects are tested for in a process called “certification testing”. During the disc certification process, a selected test signal is written to the disc and then read back. If the amplitude of the recovered signal falls below a predetermined level, a defect is recorded. Allowable defects are typically on the order of 33% of the intended track width. As the track widths decrease, so, too, does the size of allowable defects. With a 2.0 micron product track width, the allowable defect size is 0.7 microns. As the product track width decreases to 1.5 microns, the allowable defect size will be less than 0.5 microns.
The heads used to perform disc certification testing are referred to as “certification heads”. During current certification testing, the certification heads cover nominally 35% of the disc surface. As the allowable defect size decreases, the width of the certification heads must also decrease accordingly, and the test time needed to maintain 35% coverage of the disc surface increases proportionally. As the time to certify each disc increases, the throughput of each individual test unit does down, in turn
Chung Phung M.
Heller III Edward P.
Seagate Technology LLC
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