Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-12-02
2001-06-12
Cao, Allen T. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S319000
Reexamination Certificate
active
06246553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to magnetic heads which are used to read and/or write magnetic data onto a magnetic film, and more particularly to heads using magnetoresistive materials and methods for making these heads.
2. Description of Related Art
Progress in magnetic data recording requires higher densities which in turn require increased sensitivity of the transducers (heads) used to read and write the magnetic signals. Noise reduction and protection of the heads from transient events and are important goals for the design of the heads. Many read heads operate using magnetoresistive materials, hence are called MR heads. The elements of a basic prior art MR read head with two shields are illustrated in
FIG. 1
which shows a cut away view of the layers found in one type of prior head for use in a disk drive. As is typical this head has separate structures for the read and write functions. The portion performing the write operation of the overall head is often called the write element or the write head. The write element in
FIG. 1
is an inductive head. The reading function is performed by elements which are called the MR head. A permeable magnetic layer
111
which acts as a first shield (S
1
) is deposited on an insulating layer
101
which is supported by a substrate layer (not shown). A first insulation layer
103
follows. The magnetoresistive (MR) element
114
and its leads (not shown) are deposited onto the insulation layer
103
. A second insulation layer
104
follows in effect sandwiching the MR element
114
between the two insulating layers. On top of the second insulating layer, a permeable magnetic material is deposited forming a second shield (S
2
)
222
. The elements which function together as an inductive write head include additional insulating material
107
and the induction coil
112
which is deposited in insulating layer
110
. Layer
109
acts a pole piece for the write head. The S
2
layer
222
serves a dual role by acting as the other pole piece in this particular type of head, but other designs including tape heads use separate layers for these functions.
The head of
FIG. 1
is intended for use in a disk drive, but the basic elements and functions are the same for heads intended for tape drives. Tape heads are generally constructed with the read and write elements arranged side-by-side and S
2
does not serve a dual role as a pole piece.
FIG. 2
illustrates a simplified cutaway view of the read elements in another type of prior art MR head called a ferrite head. Layer
61
is composed of ferrite with layer
61
acting as the S
1
shield and layer
65
is a magnetic or nonmagnetic closure element. Shield S
2
222
and the MR element
114
are surrounded by insulating material
67
. The MR lead
63
(which can be a conductive material such as gold) is shown connecting to the bias supply
17
. MR heads such as the type illustrated in
FIG. 2
have only one metal shield. The magnetic media travels past the gap formed by the two shields which act to block the magnetic field from the media outside of the gap. A constant dc bias current is applied to the MR element and the fluctuation in the voltage level across the MR element caused by the fluctuation of the resistance is the output signal.
FIG. 3
illustrates a simplified cutaway view of another type of prior art MR head. In this head the S
1
shield is a separate element
111
as is the S
2
shield
222
. The two shields do not need to be made from the same material. The two shields and the MR element
114
are surrounded by insulating material
67
which is deposited in several steps during the manufacturing process. The MR lead
63
is connected to the bias supply
17
as before.
There are many variations of MR head design which can be seen in prior art references such as U.S. Pat. No. 5,713,122. MR heads are currently used in disk drive systems and tape drives. Although heads in disk drives are packaged with a single read/write element pair in a unit, a tape head assembly will have a read/write element pair provided for each track in a multitrack system.
A particular noise phenomenon has been observed in data readback from magnetic tape with MR heads. In the following “MR heads” will be used to include heads using the giant magnetoresistive (GMR) effect as well the magnetoresistive effect. The output signal from the read head has been observed to contain very sharp spikes which approximate ideal pulses with very narrow width and broad spectral content. These spikes can be of either polarity and are distributed over a range of amplitudes. The output signal from a head is typically passed to a preamplifier then into an input channel which includes various filters, detectors, decoders, error correctors, etc.
The effect of the sharp spikes in the input channel signal is at least randomly dispersed, correctable single bit errors and at worst may interfere with detection of the media signal. The spikes can occur in the absence a recording signal or MR bias current, but appear to require media/head contact and relative motion.
There are schemes designed for esd protection of the elements, but these do not directly relate to the present problem. There have been proposals for and tests of heads with various schemes, such as connecting the MR shields to ground in disk heads via resistors. However, connecting the shields to ground via resistors might actually aggravate the spiking problem by building in a constant large MR-shield potential difference as the discussion below will show.
SUMMARY OF THE INVENTION
An MR head according the invention solves the head spiking problem with a charge clamp structure which provides an electrical path from a conducting shield to one or both of the MR element leads to prevent the buildup of large disruptive charges associated with the interaction of the MR element and the shield (which together can be modeled as a virtual capacitor). In one embodiment of the invention the charge clamp provides a resistive electrical path from a shield to both leads from the MR element to form a self-tracking clamp. Possible additional benefits of providing the electrical path from an MR element lead to the shield(s) include making the shield(s) more effective for EMI protection and generally protecting the MR element from high currents from other sources.
One embodiment of the invention uses a resistance connected between a lead of the MR element and an associated shield.
In another embodiment, a head with a single metal shield has a separate resistive path from the shield to each of the leads of the MR element. The two resistive paths may be implemented as a thin film structure which contacts both leads and has a central connection to the shield forming an approximately center-tapped resistor.
In another embodiment, a head with more than one conductive shield, has the shields electrically connected and then connected to one of the leads through a resistive path. Alternatively the resistance configuration can be duplicated for each shield.
In yet another embodiment, material separating the MR element and the shield is made from a material which is slightly more conductive than an insulating material to provide a resistive path for the charge.
A storage system according to the invention can include any embodiment of the MR head invention. The system's bias circuitry is connected to apply a dc bias voltage so that the S
2
shield is connected to the proper lead of the MR element. Although the invention is well suited for use in tape storage system, it can be applied in disk drives or measurement apparatus where the heads are subjected to forces which cause charges to build up between the MR element and a shield which could include contact or near-contact recording using rigid or flexible disks.
REFERENCES:
patent: 4802043 (1989-01-01), Sato et al.
patent: 4987514 (1991-01-01), Gailbreath et al.
patent: 5375022 (1994-12-01), Gill et al.
patent: 5539598 (1996-07-01), Denison et al.
patent: 5557492 (1996-09-01), Gill et al.
pat
Cao Allen T.
International Business Machines - Corporation
Knight G. Marlin
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