Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-08-25
2002-02-05
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06344952
ABSTRACT:
FIELD OF INVENTION
The present invention relates to magnetic recording heads. More particularly, the present invention relates to magnetic recording heads having conductive shields.
BACKGROUND OF INVENTION
The requirements for providing magnetic tape drives with higher data storing capacities have lead to the development of multi-track storage techniques in which a number of read elements are aligned with a number of write elements. The aligned read and write elements are bound in essentially identical read and write element pairs. The elements in each pair are placed in a distant opposition to each other such that each track of the magnetic tape is accessed by a read element and a distant write element.
The read elements conventionally contain magnetoresistive sensors fabricated by the use of thin film fabrication techniques as described in the related application. The magneto-resistive sensors are characterized by a resistance that changes in response to an external magnetic field from data stored on a magnetic tape. Each thin film magnetoresistive sensor is typically positioned in between two magnetically permeable shields. The shields guide stray magnetic fields away from the magneto-resistive element. The shields are typically thin film deposited adjacent to the magneto-resistive sensor. These thin film shields are typically electrically conductive.
The conductive shields and the magneto-resistive sensor and its contacts form a capacitor, which has a capacitance dependent on the area extension and the insulating material between the shields and the magneto-resistive sensor. During the operation of the tape drive, the magnetic recording tape is moved over the head, which is comprised of the read and write elements. The movement of the tape over the head can result in an electrical charge accumulating on the conductive shields. Such a charging process is often referred to as tribocharging. The capacitor is sometimes discharged suddenly by a transient conductive path between the magneto-resistive sensor and the shield due, e.g., to an interaction with the tape. Although, the build up of the charge on the shields tends to be slow, and therefore not disruptive, studies show that the discharge can take place abruptly, e.g. within less than 1 nanosecond. During discharge, up to 50% of the stored charge may flow through the magneto-resistive sensor itself, thus appearing as a data signal. The amplitude of such spurious signals has been predicted to be approximately 0.1 to 3 millivolts per volt of stored charge potential difference between the shield and the magneto-resistive sensor. Tribocharging potentials can reach several, if not 10s of volts. The resulting noise pulses when this charge discharges can be up to 10 mV or more in peak amplitude, a signal that is often larger than the magneto-resistive signal itself. Since the pulses are only a few nanoseconds in duration, this process may produce single bit errors in the channel.
Previous attempts have been made to prevent the charge buildup by making a short circuit connection between the magneto-resistive sensor and the shields. Unfortunately, such a permanent short circuit makes magneto-resistive elements having ductile shields more susceptible to another noise phenomenon often referred to as “telegraph noise” (TGN). The TGN is due to intermittent connections between the magnetoresistive element and the shields, e.g. caused by the presence of ductile shield material in the insulating gap between the MR sensor and the shields. The presence of a permanent electrical short to the contact on one side of the sensor makes intermittent completion of the short circuit due to conductive bridging of the shield much more likely.
Therefore, there exists a need for a magnetic tape drive with a magnetoresistive read element that is resistant to tribocharging and without unduly increasing susceptibility to telegraph noise.
OBJECTS AND ADVANTAGES
It is a primary object of the present invention to provide magnetoresistive read element that is resistive to tribocharging and telegraph noise. It is another object of the present invention to provide tape drive employing such a magneto-resistive read element.
SUMMARY OF THE INVENTION
The disadvantages of the prior art are overcome by the present invention of a read element comprising a magneto-resistive sensor electrically connected to first and second leads and at least one electrically conductive magnetic shield proximate the magneto-resistive sensor. A resistor is electrically connected to the conductive magnetic shield and to one or more of the first and second leads. The resistor is disposed between the first and second leads. The resistor continuously discharges electric charge that would otherwise build up on the conductive magnetic shield. The resistor typically has a resistance that is large enough to protect against noise due to intermittent electrical shorting by the conductive magnetic shield and small enough to prevent a build-up of electric charge on the shield. The resistance may be between about 10 k&OHgr; and about 200 k&OHgr;. In one embodiment of the invention, the resistor is comprised of tantalum. The resistor is typically a thin film resistor disposed in substantially the same substrate plane as the magneto-resistive sensor. In a particular embodiment of the invention, the resistor is a serpentine thin film resistor that has been deposited in substantially the same substrate plane as the magneto-resistive sensor.
The read element may further comprise a second magnetic shield located adjacent the magneto-resistive sensor such that the magneto-resistive element is disposed between the first and second magnetic shields. The second shield may comprise a ferrite material, which is typically not electrically conductive. Alternatively, the second shield may comprise an electrically conductive material. When the second shield is electrically conductive, like the first shield, the resistor may be connected to the first and second shields.
The read element may be fabricated by a method according to an embodiment of the invention. According to the method, the magneto-resistive sensor, first and second conductive contacts and one or more resistors are formed on a first insulating layer. A conductive magnetic shield is formed over a second insulating layer, which is formed over the magneto resistive read element such that the resistor or resistors electrically connect to the shield. The first insulating layer may be deposited over another shield that may also be electrically connected to the resistor.
Embodiments of read elements of the present invention find use in magnetic tape drives. Such a tape drive typically includes a read head that incorporates one or more read elements of the type described above. The tape drive typically includes some means for moving a tape over the read elements.
REFERENCES:
patent: 5465186 (1995-11-01), Bajorek et al.
patent: 5539598 (1996-07-01), Denison et al.
patent: 5557492 (1996-09-01), Gill et al.
patent: 6081409 (2000-06-01), Hughbanks et al.
patent: 6160688 (2000-12-01), Okumura
Biskeborn Robert Glenn
Chen Tsung Yuan
Doscher Michael J.
Jarratt James Devereaux
Koeppe Peter V.
Cao Allen
International Business Machines - Corporation
Lumen Intellectual Property Services Inc.
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