Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-06-25
2001-10-02
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192200
Reexamination Certificate
active
06296741
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of making an oxide barrier layer for a spin tunnel junction and, more particularly, to implementing oxidation of a metal that forms a barrier junction without surface contamination.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotatable magnetic disk, a slider with write and read heads supported by a suspension arm above the disk and an actuator 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 to cause the slider and the write and read heads to ride on an air bearing a slight distance from the surface of the rotating disk. During rotation of the disk the write head writes magnetic bits of information to the disk and the read senses the magnetic bits from the 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.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing the aforementioned magnetic bits in circular tracks on the rotating disk.
The read head includes a sensor which senses the aforementioned magnetic bits from the rotating disk. One type of sensor is a spin tunnel junction sensor which includes an oxide barrier layer between a ferromagnetic pinned layer and a ferromagnetic free layer. The pinned layer is located on, and exchanged coupled to, an antiferromagnetic layer which pins a magnetic moment of the pinned layer in a first direction which is typically perpendicular to the ABS. The free layer has a magnetic moment which is free to rotate in response to magnetic fields from the rotating disk. A tunneling current I
T
is conducted through the spin tunnel junction sensor in a direction perpendicular to the surface planes of the layers. Because of a magnetoresistive affect between the free and pinned layers there is a change in resistance of the spin tunnel junction sensor as a function of cos &thgr;, where &thgr; is the angle between the magnetic moments of the pinned and free layers. When the magnetic moment of the free layer is parallel to the magnetic moment of the pinned layer the resistance to the tunneling current is at a minimum, and when these moments are antiparallel with respect to one another the resistance to the tunneling current is at a maximum. Accordingly, as the tunneling current I
T
is conducted through the tunnel junction sensor, an increase or decrease in the resistance of the sensor causes a change in potential in the aforementioned processing circuitry. The processing circuitry employs these potential changes to produce readback signals.
In order for the tunneling effect to work properly the oxide barrier layer must be extremely thin, such as 10 Å-20 Å thick. The barrier layer must be smooth and uniform with a low defect density and a large dielectric strength. Aluminum oxide (Al
2
O
3
) is the most commonly used barrier material. There is a strong-felt need to provide a method of making the barrier layer for a tunnel junction sensor that has the aforementioned attributes.
SUMMARY OF THE INVENTION
I investigated a sputtering deposition technique for forming barrier layers for tunnel junction sensors. In this technique a wafer substrate was placed in an ion beam sputtering chamber and aluminum oxide was sputtered on the wafer substrate to form the barrier layer with a desired thickness. At this stage the barrier layer was aluminum. The aluminum barrier layer was then subjected to oxygen which caused the aluminum to be oxidized to form aluminum oxide. An advantage of this method is that no high energy particles are involved which promotes smooth surfaces and a uniform texture of the aluminum oxide layer. The oxidation which is usually accompanied with heat may take several hours. Unfortunately, I found that the oxidation process causes the aluminum oxide barrier layer to have surface contamination. This surface contamination seriously degrades the tunnel junction effect of the sensor.
In the present invention an ion beam is directed on an aluminum target to cause aluminum atoms to be sputtered from the target and deposited on a wafer substrate. Simultaneously with depositing the aluminum atoms on the wafer substrate ionized oxygen is provided in the chamber that reacts with the aluminum atoms on the wafer substrate to form the aluminum oxide layer. In a preferred embodiment of the invention the oxygen ions are not accelerated toward the aluminum on the substrate. This eliminates any energetic particle bombardment which may deteriorate the barrier layer. The ion beam directed on the aluminum target may be implemented with a first ion beam gun which is located within the chamber. This gun ionizes a noble gas, such as argon (Ar), krypton (Kr) or xenon (Xe), and accelerates the ionized gas toward the aluminum target. A second ion beam gun located in the chamber may be employed for disassociating oxygen to produce oxygen ions which are then disseminated without acceleration within the chamber. Since a vacuum is pulled on the chamber before introduction of any gases the oxygen ions will quickly spread and envelope the aluminum atoms on the wafer substrate to form aluminum oxide. Optionally, oxygen (O
2
) gas may be introduced into the chamber through an inlet in which case the second ion beam is not used.
An object of the present invention is to provide a method of making an oxide barrier layer for a tunnel junction sensor which has smooth surfaces and a uniform texture.
Another object is to provide a method of making an aluminum oxide barrier layer for a tunnel junction sensor which has smooth surfaces, uniform texture and virtually no contamination.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.
REFERENCES:
patent: 4920094 (1990-04-01), Nogawa et al.
patent: 4923585 (1990-05-01), Krauss et al.
patent: 4994164 (1991-02-01), Bernardet et al.
patent: 5454919 (1995-10-01), Hill et al.
patent: 5650958 (1997-07-01), Gallagher et al.
patent: 5750275 (1998-05-01), Katz et al.
patent: 5768065 (1998-06-01), Ito et al.
patent: 5768071 (1998-06-01), Lin
patent: 5898547 (1999-04-01), Fontana, Jr. et al.
patent: 5962080 (1999-10-01), Tan et al.
Cantelmo Gregg
Gray Cary Ware & Freidenrich
International Business Machines - Corporation
Johnston Ervin F.
Nguyen Nam
LandOfFree
Method of making oxide barrier layer for a spin tunnel junction does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making oxide barrier layer for a spin tunnel junction, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making oxide barrier layer for a spin tunnel junction will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2573676