Chemical polishing of barium strontium titanate

Details Chemical polishing of barium strontium titanate Chemical polishing of barium strontium titanate

1994-04-07

2001-08-07

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Nongaseous phase etching of substrate

Using film of etchant between a stationary surface and a...

C216S089000, C216S100000, C216S101000, C216S108000, C252S079200, C505S410000, C505S728000

Reexamination Certificate

active

06270688

ABSTRACT:

CROSS REFERENCE TO PENDING APPLICATIONS
This application is related to an application entitled Method of Minimizing Surface Effects in Thin Ferroelectrics (TI-16728) U.S. Ser. No. 08/225,601, now U.S. Pat. No. 5,705,041 filed concurrently herewith, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to polishing of ferroelectric materials and, more specifically to polishing of perovskite materials and still more specifically to polishing of barium strontium titanate.
2. Brief Description of the Prior Art
The surfaces of ferroelectric materials and specifically barium strontium titanate have been smoothed or planarized in the prior art by a fully mechanical process wherein the surface of the material was abraded using progessively less course polishing materials or grits to abrade the surface being polished. Such polishing continued until the desired smoothness or planarity was achieved.
A problem with the above described polishing method is demonstrated in
FIG. 1
wherein there is shown a volume of barium strontium titanate
1
with a metal layer
3
thereon and an interface
5
between the metal and the BST. It can be seen that the surface of the BST
1
at and immediately below the interface
5
has numerous dislocations therein. Ferroelectric materials and specifically barium strontium titanate material with these dislocations, when used in uncooled focal plane arrays and the like, prevent the barium strontium titanate from obtaining optimal performance by causing depression of the dielectric properties and the responsivity of the material. This problem is enhanced as the thickness of the ferroelectric material decreases because the dislocation region becomes a greater percentage of the total volume.
It has been determined that these dislocations are caused by the mechanical abrading of the ferroelectric material surface. It is therefore apparent that the performance of optical arrays using ferroelectric materials will be improved if the surface of the material can be polished with a minimum of or no abrading at all. It has also been determined that polishing using typical polishing materials in a slurry or colloidal suspension, such as aluminum oxide (Al
2
O
3
) or silicon dioxide, also produces dislocations on the ferroelectric material surface and can also modify the surface chemistry of the ferroelectric material.
SUMMARY OF THE INVENTION
In accordance with the present invention, the region of dislocation is minimized at the surface of the ferroelectric material and the resulting ferroelectric material is provided with a surface region having materially fewer dislocations than were encountered by use of prior art procedures as described above.
Briefly, the ferroelectric material is initially polished by an abrading technique as in the prior art. However, the mechanical polishing terminates at a point prior to obtaining the desired smoothness, planarity and thickness with the final portion of the ferroelectric material surface being removed by a chemical polishing procedure.
The chemical polishing portion of the polishing procedure commences with a chemical polishing using an acidic solution. The acid used can be an organic acid, a mineral acid, a reducing acid, an oxidizing acid and combinations thereof. Appropriate acids which can be used in the acidic solution are perchloric acid, acetic acid (preferably glacial), nitric acid. The acid or combination of acids is combined with an oxidizing agent, preferably hydrogen peroxide and water, preferably deionized.
The polish in the form of an acidic solution is applied to the ferroelectric material surface in conjunction with a polishing wheel or the like in standard manner. The polishing surface on the polishing wheel can be absorbent and absorb polish to be deposited on the ferroelectric material surface or porous with the polish travelling therethrough to the ferroelectric material surface or in other known ways. The polishing surface can also be rigid for use with a hydroplaning polish.
The ferroelectric material is preferably but not necessarily doped in standard manner.


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