Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Reexamination Certificate
2002-05-28
2004-05-04
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
C324S699000, C324S713000, C029S603090, C360S317000
Reexamination Certificate
active
06731110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to data storage systems and, in particular, to magneto-resistive sensors. More particularly, the present invention relates to a magneto-resistive device having a built-in test structure and a method for determining resistance and track width of a magneto-resistive transducer.
2. Description of the Related Art
A thin film MR head employs a magneto-resistive (MR) transducer for reading information signals from a moving magnetic medium, such as a rotating magnetic disk. Conductive leads are employed for connecting the MR sensor to externally located read pads and a sense current is applied to the MR transducer via the read pads. Magnetic fields from the magnetic medium cause resistance changes in the MR transducer that, in turn, cause potential changes across the read pads which are sensed by a detector, such as a differential amplifier. The output of the detector is the readback signal.
Shields employed in the MR transducer prevent destructive interference of the magnetic field from adjacent transitions in the media (a.k.a. ISI or intersymbol interference). Accordingly, the MR transducer and the conductive leads are sandwiched between first and second insulation gap layers and the first and second gap layers are sandwiched between first and second shield layers. The MR device, which comprises the MR transducer, literally “flies” with respect to a rotating magnetic disk, supported by a thin cushion of air that the disk moves between the disk and a air bearing surface (ABS) of the MR transducer. The thin cushion of air is commonly referred to as an “air bearing”. The air bearing provides a first force which is counterbalanced by a second force from a suspension which carries the MR device. The counterbalance can be designed to provide a very small distance (“flying height”) between the ABS and the rotating disk, such as 0.075 microns. With this arrangement the MR device can read information from each circular track on a rotating magnetic disk with high resolution.
Generally, the combined inductive write transducer and MR read transducer are formed from adjacent layers of material on a wafer substrate so as to read and write on the same track. The fabrication of the devices generally comprises a sequence of deposition and etching steps with the MR transducer formed first, and the inductive write transducer formed on top of the MR transducer. The MR transducer typically comprises a magneto-resistive stripe and two conductive leads on either side thereof. The stripe height is a critical feature and is determined by the height defining edge, which is the bottom edge of the stripe. The inductive transducer typically includes a bottom pole, an insulating layer, half an electrical coil, an insulating layer, a top pole, an insulating layer and the other half of the coil. The coil halves are interconnected by means of vias, and the coil and the two conductive leads of the MR transducer are connected to terminals by means of vias. The inductive transducer poles are narrowed to a very narrow pole tip having a precisely controlled width, or throat, the width of which defines the recorded track width.
Typically, rows of transducers are deposited simultaneously on the wafer substrate using conventional process methods. The wafer substrate may be a hard ceramic material which is used to form disk sliders or tape modules, with the transducers deposited thereon. The substrate is then cut into rows of sliders in a side-by-side relationship with the pole tips of the inductive write transducers and the MR stripes of the MR read transducers extending to an edge of the substrate row. The row edge is then lapped to the optimum dimensions of throat height and stripe height.
With stripe height ranges below 0.100 um and 0.20 um mean expected in the near future, MR devices are becoming more difficult to fabricate. The ability to control wafer process and disposition with ever increasing requirements are also adding to the complexity and difficulty of fabricating the MR devices. For example, to accommodate the reduction in stripe heights, the MR devices track width requirements will have to controlled to less than 10% against track values of less than 0.30 um.
Accordingly, what is needed in the art are more direct and improved methods for assessing key performance related process variation. More particularly, what is needed in the art is an improved MR device with a built-in test structure that will allow for more direct measurement and efficient monitoring of the MR device's characteristics.
SUMMARY OF THE INVENTION
To address the above discussed deficiencies in the prior art, and in accordance with the invention as embodied and broadly described herein, a magneto-resistive device with a built-in test structure is disclosed. The magneto-resistive device includes a slider having first and second lower termination pads and first and second upper termination pads. A first conductive trace element electrically couples the first lower termination pad to the first upper termination pad and a second conductive trace element electrically couples the second lower termination pad to the second upper termination pad. The magneto-resistive device also includes a magneto-resistive transducer deposited on the slider and the resistance of the magneto-resistive transducer is obtained by passing an electrical current between the first and second lower termination pads and measuring a voltage across the first and second upper termination pads.
In another advantageous embodiment, the present invention discloses a method for determining a track width of a magneto-resistive transducer included on a slider on a wafer substrate, where the wafer substrate has at least first and second sliders. Each of the first and second sliders also includes first and second lower and upper termination pads and the magneto-resistive transducers associated with the first and second sliders have different stripe heights, e.g., 3.0 and 5.0 um. The method includes electrically coupling, on each slider, the first lower termination pads with the first upper termination pad and the second lower termination pad with the second upper termination pad. The total resistance, i.e., transducer resistance and lead resistances, of each of the first and second magneto-resistive transducers is determined by driving a current through the first and second upper termination pads of each transducer and measuring the resultant potential difference across the first and second upper termination pads of the respective transducer. Following which, the transducer resistances of the first and second magneto-resistive transducers are determined by passing a current through the first and second lower termination pads and measuring a voltage across the first and second upper termination pads. Subsequently, the track width of the first and second magneto-resistive transducers are computed utilizing the following relationship:
MRW=[
(
Dh
) (
MRS
3) (
MRS
5)]/[
Rs
(
MRS
3
−MRS
5)],
where MRW is the track width, Dh is the delta of the stripe heights of the magneto-resistive transducers, MRS3 is the resistance of the first magneto-resistive transducer, MRS5 is the resistance of the second magneto-resistive transducer and RB is a sheet resistance of the wafer substrate.
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit
Bracewell & Patterson L.L.P.
International Business Machines - Corporation
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