Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-09-02
2001-07-24
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S765010
Reexamination Certificate
active
06265885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates in general to thin film devices and more specifically to a method, apparatus and computer program product for identifying electrostatic discharge (ESD) damage to a thin film device.
2. Description of the Related Art
Magnetic head disk drive systems are widely employed in the computer industry as a cost effective form of data storage. In a magnetic disk drive system, a magnetic recording medium, in the form of a disk, rotates at a high speed while a magnetic read/write transducer, generally referred to as a magnetic head, elevates slightly above the surface of the rotating disk. The magnetic head is attached to or formed integrally with a “slider” that is suspended over the disk on a spring-loaded support arm known as an actuator arm. As the magnetic disk is rotated at its operating speed, moving air generated by the rotating disk in conjunction with the physical design of the slider operate to lift the magnetic head allowing it to glide or elevate slightly above and over the disk surface on a cushion of air, generally referred to as an air bearing. The height at which the magnetic head elevates over the disk surface is typically only a few microinches or less and is primarily a function of the disk's rotation, the aerodynamic properties of the slider assembly and the force exerted by the spring-loaded arm.
The magnetic head typically includes a magnetoresistive (MR) transducer or sensor element electrically connected to detection circuitry. MR sensors are well known in the art and are particularly useful as read elements in magnetic transducers, especially at high data recording densities. The MR sensor generally has a resistance that modulates in response to changing magnetic fields corresponding to magnetically encoded information. The detection circuitry detects the resulting changes in resistance by passing a sense current through the MR sensor and measuring the voltage drop across the MR sensor. The detected voltage signal is then used to recover information from the magnetic disk. The MR read sensor provides a higher output signal than an inductive read head. This higher output signal results in a higher signal to noise ratio for the recording channel and consequently permits higher area density of recorded data on a magnetic disk surface.
A major problem encountered during the manufacturing and assembly of magnetic heads is the buildup of electrostatic charges on the various elements of a magnetic head or other objects that come into contact with the magnetic head and the accompanying spurious discharges of static energy generated. For example, static charges may be generated by the presence of certain materials, such as plastics, during the manufacture and subsequent handling of the magnetic heads. These charges can induce or result in electrostatic discharge. The net effect of such a discharge often damages or degrades the MR sensor in reading data correctly.
Currently, the ESD screening regimes employed in the manufacture of MR sensors are typically of two general types. One approach is to employ a sampling method wherein a number of randomly chosen MR sensors are selected and undergo a detail inspection. This approach, however, may not catch all the sensors that may have suffered ESD damage. Another method is to take a first measurement of the resistance of every sensor prior to final fabrication and a second subsequent resistance measurement of all the sensors after final fabrication. The two resistance measurements are then compared with each other to identify potential ESD damage. This method, however, requires two measurements that increase the time required to fabricate a sensor.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method, apparatus and computer program product for identifying electrostatic discharge (ESD) damage to a thin film device.
To achieve the foregoing object, and in accordance with the invention as embodied and broadly described herein, a method, apparatus and computer program product for identifying electrostatic damage to a thin film device is disclosed. The method includes (1) determining a cold resistance of the thin film device, (2) determining a hot resistance of the thin film device, (3) calculating a heating delta resistance (HDR) from the hot and cold resistances and (4) comparing the HDR to a threshold value to ascertain if the thin film device has suffered ESD damage. The HDR of the thin film device is characterized by the following relationship:
HDR=(hot resistance-cold resistance)/(cold resistance).
The present invention recognizes that there is a noticeable difference between the resulting heating delta resistance (HDR) value of a thin film device, such as MR sensor, that has suffered ESD damage from the HDR value of an undamaged device. The present invention utilizes this identified difference between the HDR values of a damaged and unaffected device to provide a more efficient and time effective screening mechanism that may be advantageously employed in, but not limited to, the manufacturing and fabrication processes of thin film devices.
In one embodiment of the present invention, the thin film device is a magnetoresistive (MR) sensor. In a related embodiment, the MR sensor is a ansitropic magnetoresistive (AMR) sensor. Alternatively, the MR sensor may be a giant magnetoresistive (GMR) sensor.
In yet another embodiment of the present invention, determining the hot resistance value of the MR sensor includes applying an operational current of the MR sensor. In an embodiment to be described in greater detail herein, the operational current ranges from about 4 milliamps to about 10 milliamps. In another related embodiment, on the other hand, determining the cold resistance of the MR sensor includes applying a current of less than 1 milliamp.
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 and scope of the invention in its broadest form.
REFERENCES:
patent: 4636724 (1987-01-01), Fukuda et al.
patent: 4823088 (1989-04-01), Fukuda
patent: 5083117 (1992-01-01), Hoigaard
patent: 5796256 (1998-08-01), Fowler et al.
patent: 6049213 (2000-04-01), Abadeer
Luo Jih-Shiuan
Smith Robert Langland
Yeh Chin-Yu
Bracewell & Patterson L.L.P.
International Business Machines - Corporation
Martin Robert B.
Metjahic Safet
Sundaram T. R.
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