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A hard, uniform coating of A12O3 can be formed on A1Mg disks by anodization. Co-planar servo patterns of A1 imbedded in A12O3 can also be formed by selective anodization.
English (United States)
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Aluminum Anodization for Low Defects and Capacitive Servo Disks
A hard, uniform coating of A12O3 can be formed on A1Mg disks by
anodization. Co-planar servo patterns of A1 imbedded in A12O3 can also be
formed by selective anodization.
A planar coat of A13O3 can be obtained by the following process
steps: 1. Diamond-turn or polish the A1Mg disk. 2. Evaporate or sputter 500 to 2500 angstroms of Nb or Hf,
Ti, Ta (or any of the class of refractive metals). 3. Evaporate or sputter 1 to 5 microns of A1. 4. Anodize the evaporated A1 in oxalic acid, sulfuric
acid, or similar organic acid at room temperature (RT)
and 20 to 30 VDC applied (until current nearly stops
flowing). Anodization will stop at the Nb, Ta, Hf,
etc. interface. 5. Rinse the disk with water and then seal the pores and
level the surface in boiling water.
Since pure A1 is being anodized, not A1Mg, there will be very few pits or
imperfections. Anodization will stop at the level of the refractory metal.
For formation of capacitive servo disks by selective
anodization, the process proceeds as follows: 1. Diamond-turn or polish the A1Mg disk surface. 2. Evaporate or sputter 500 to 2500 angstroms Ta, Nb, Hf,
or other refractory metal. 3. Evaporate or sputter 1 to 5 microns of A12, preferably
at RT to give a small grain.
a) Optionally: Sputter or evaporate
approximately 0.2 to 0.5 micron of Schott
glass or S102 .
b) Optionally: Blanket anodize A1 approximately
0.2-micron deep over the whole surface. Dry
and bake. 4. Apply Shipley photoresist and bake at approximately 100
to 110oC to provide good adhesion. 5. Expose the desired capacitive servo pattern (areas