Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-08-09
2003-02-25
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06525913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a read head with sunken prefill insulation for preventing lead to shield shorts and maintaining planarization and, more particularly, to first and second prefill insulation layers which are located in first and second recesses in a first shield layer on each side of a read sensor.
2. Description of the Related Art
The heart of a computer is an assembly is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Magnetic heads are constructed in rows and columns on a wafer by sputter deposition of various material layers and photolithography steps for masking the layers and forming them into desired shapes. In the formation of the read head portion of the magnetic head assembly a first shield layer and a first read gap layer are deposited on the wafer followed by deposition of multiple layers of the read sensor. A bilayer photoresist is then formed to cover all of the MR sensor material layer except for first and second openings located at first and second sites for first and second hard bias and lead layers which are to be connected to first and second edges of the MR sensor. Ion milling is then implemented to remove the sensor material within the first and second openings all the way down to the first read gap layer with a slight overmill of the first read gap layer to ensure that all of the sensor material has been removed. Hard bias material and lead layer material is then sputter deposited after which the bilayer photoresist is removed leaving first and second hard bias and lead layers connected to first and second side edges of a partially completed sensor. These series of steps define the track width of the read head which directly relates to the storage capacity of the rotating magnetic disk which will be discussed in more detail hereinafter.
Next, a bilayer photoresist mask is formed to cover the first and second hard bias and lead layers just deposited as well as the sensor with a back edge of the photoresist defining a location for the back edge of the MR sensor. Ion milling is again implemented which removes all of the sensor material except for the partially completed sensor which now has a defined front and back edge. A second read gap layer and a second shield layer are then formed followed by various sputter deposition steps and photolithography to form the write head. The wafer is then diced into rows of magnetic head assemblies after which each row is lapped to form the air bearing surface (ABS) of each magnetic head in the row. The row of magnetic heads is then diced into individual magnetic head assemblies for mounting on the aforementioned suspension and placement in a magnetic disk drive.
The storage capability of the magnetic disk depends, in part, upon the areal density of the read head which is a product of the track width density and the linear density of the read head. The track width density is expressed as tracks per inch (TPI) along the width of the magnetic disk and linear density is expressed as bits per inch (BPI) along the track of the magnetic disk. There is a strong-felt need to decrease the track width of the read head in order to increase the storage capacity of the. magnetic disk, which can be expressed as gigabits per square inch. For a one gigabit per square inch capacity the track width of the read head should be 0.75 to 0.80 &mgr;m, for a 40 gigabit per square inch capacity the track width of the read head should be 0.35 to 40 &mgr;m and for a 100 gigabit per square inch capacity the track width of the read head should be 0.18 to 0.20 &mgr;m. With a decreased track width it becomes more important to accurately define the location of the first and second hard bias and lead layers at their connection to the MR sensor, as well as forming sharper junctions at these connections. In order to accurately locate the lead to sensor junction with a sharp connection it is important that the first read gap layer be planarized across the wafer so that a light exposure step of the photoresist for patterning is accomplished without shadows which are caused by steps or high profiles of the first read gap layer near the lead to sensor junction sites.
The linear bit density of the read head is determined by the spacing between the first and second shield layers of the read head. This spacing is dependent upon the thicknesses of the first and second read gap layers as well as the thickness of the sensor. A typical thickness of the read sensor is about 400 Å, a typical thickness of the hard bias layer is about 150 Å and a typical thickness of the lead layer is about 600 Å. Accordingly, with a 400 Å thick sensor the first and second hard bias and lead layers will project 350 Å above a top surface of the read sensor on each side of the sensor assuming that the first read gap layer is planar. The higher profile of the first and second hard bias and lead layers on each side of the read sensor requires the second read gap layer be formed on first and second steps with a dip down on the sensor therebetween. When the second read gap layer is sputter deposited onto the wafer the thickness of the second read gap layer portions on the upwardly sloping surfaces of the steps will be less than the second read gap layer portions which are flat on each side of the steps. The thinner second read gap layer portions on the steps increase the risk of pin holes which cause a shorting between the lead layers and the second shield layer. In spite of these problems there is a strong-felt need to reduce the thicknesses of the first and second read gap layers so as to increase the linear bit density of the read head. For a 1 gigabit per square inch capacity a typical thickness of each of the first and second read gap layers is 500 to 600 Å, for a 40 gigabit per square inch capacity a typical thickness of these layers is 150 Å and for a 100 gigabit per square inch capacity a typical thickness of these layers is 10 Å. It should be noted that it is not practical to reduce the thickness of the first and second lead layers because such a reduction will increase a parasitic resistance of the lead layers which competes with the resistance of the sensor.
A prior art teaching for decreasing the thickness of the first read gap layer without the risk of shorts is set forth in commonly assigned U.S. Pat. No. 5,568,335 which is incorporated by reference herein. In this patent first and second prefill insulation layers are deposited on the first shield layer on each side of the MR sensor followed by formation of the first read gap layer. The first and second prefill layers provide extra insulation between the first and second hard bias and lead layers and the first shield layer so as to lower the risk of shorting between the first and second hard bias and lead layers and the first shield layer. However, because of the profile each of the first and second prefill insulation layers they must be kept at least 10 &mgr;m away from the side wall sites of the read sensor so that the formation of the first and second hard bias and lead layers at their junctions to the first and second side edges of the M
Emilio Santini Hugo Alberto
Mauri Daniele
International Business Machines - Corporation
Johnston Ervin F.
Saber Paik
Tupper Robert S.
Watko Julie Anne
LandOfFree
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