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Magnetoresistive Head with Integrated Varistor for ESD/EOS Protection

IP.com Disclosure Number: IPCOM000014696D
Original Publication Date: 2000-Apr-01
Included in the Prior Art Database: 2003-Jun-20
Document File: 1 page(s) / 32K

Publishing Venue

IBM

Abstract

Described is a magnetic recording head having a magnetoresistive read sensor combined with a layer that provides varistor action in a structure that is essentially a metal oxide varistor (MOV) to protect the magnetoresistive read element from the deleterious effects of electrostatic discharge (ESD) and electrical overstress (EOS). The novel feature of the invention is the incorporation of a MOV in an integrated fashion into the head structure by disposing it in proximity to elements of the read sensor circuit susceptible to ESD/EOS damage with minimal impact on the overall mask layout and design. Through the use of existing lead or sensor metallurgy as one electrode in contact with the layer providing varistor action, and other structures serving as grounded counter-electrodes, it is possible to shunt to ground electrical transients that would otherwise damage a sensor which is becoming increasingly ESD/EOS sensitive due to the device scaling that attends the demands of ever increasing areal recording densities. A preferred embodiment of the invention comprises a nominally 45 x 45 micron square ZnO layer, 20 microns thick, disposed under a contact stud structure of the head, and above a grounded metallic counter-electrode. Calculations based on the I-V, i. e. current-voltage, characteristic of ZnO varistors indicate that this structure would provide protection from voltage transients exceeding 2 nominally 300 mV, and sustained current densities from 0.5 mA/cm to 1.0x103 A/cm2 . This structure works in a passive, high-resistance mode under normal operation of the head; but, when a voltage transient as described above occurs, it switches on due to its highly non-linear I-V characteristic and shunts the transient to ground. An advantage of using a material with varistor action such as ZnO is that it behaves as two oppositely poled diodes in parallel clipping off both negatively and positively going transient spikes without the need of fabricating two separate discrete diodes to perform an equivalent function.[1] The location of the structure under the external contact pads of the head disposes it in an ideal location to intercept voltage transients that might appear on these pads from ESD/EOS events, which might occur due to handling, human body contact, or the build-up of triboelectric charges during processing or file-build operations. Another embodiment of the invention comprises the use of alternative materials to ZnO, which due to higher breakdown voltages would be more suitable for incorporation into other portions of the lead/sensor circuit more proximate to the sensor proper. Lower vapor pressures of some of the metals employed by these alternative metal oxides may make them more suitable for methods of fabrication that employ vacuum deposition techniques such as sputtering. Finally, the above embodiments should not be construed to preclude the use in the above structures of other varistor materials known to those skilled in the art, viz., SiC, TiO 2 , and doped variants of these, as well as ZnO doped with Bi 2 O 3 , CoO, MnO, and Sb 2 O 3 .

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Magnetoresistive Head with Integrated Varistor for ESD/EOS Protection

   Described is a magnetic recording head having a magnetoresistive read sensor
combined with a layer that provides varistor action in a structure that is
essentially a metal oxide varistor (MOV) to protect the magnetoresistive read
element from the deleterious effects of electrostatic discharge (ESD) and
electrical overstress (EOS). The novel feature of the invention is the
incorporation of a MOV in an integrated fashion into the head structure by
disposing it in proximity to elements of the read sensor circuit susceptible to
ESD/EOS damage with minimal impact on the overall mask layout and design. Through
the use of existing lead or sensor metallurgy as one electrode in contact with
the layer providing varistor action, and other structures serving as grounded
counter-electrodes, it is possible to shunt to ground electrical transients that
would otherwise damage a sensor which is becoming increasingly ESD/EOS sensitive
due to the device scaling that attends the demands of ever increasing areal
recording densities.

   A preferred embodiment of the invention comprises a nominally 45 x 45 micron
square ZnO layer, 20 microns thick, disposed under a contact stud structure of
the head, and above a grounded metallic counter-electrode. Calculations based on
the I-V, i. e. current-voltage, characteristic of ZnO varistors indicate that
this structure would provide protection from voltage transients exceeding

2nominally 300 mV, and sustained current densities from 0.5 mA/cm to 1.0x103 A/cm2
. This structure works in a passive, high-resistance mode under normal operation
of the head; but, when a voltage transient as described above occurs...