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topic 770

Anodizing a thinfilm deposited on alumina


Q. I need to deposit a 50-500 um alumina layer on the 0.5 um metal pattern deposited on 1 mm thick alumina substrate (2 x 2 inch or 4 x 4 inch). Would anodizing or another technique work?

Andy Peczalski


A. Andy

I assume the metal pattern on the ceramic is aluminum, not sure if the 0.5 um dimension refers to trace width or thickness.

In any event 2 possibilities come to mind, one is chemical vapor deposition; the other is "barrier layer anodizing" (if you have a continuous pattern) this is the process used to make aluminum capacitors. I don't recall too many details I think a boric acid type electrolyte is used. But try checking the literature.

Paul Stransky
- Putnam, Connecticut


A. Andy, this is what is my understanding of what you are talking about. You have 1 mm thick alumina substrates on which you have metal patterns (lines) that are 0.5 micron wide. You need 50 to 500 micron alumina layer (insulator) on the pattern.

My questions are, what type of metal is patterned and how thick is it? If you have a 10 micron thick aluminum line, you cannot expect 50 micron thick aluminum oxide growing out of it using conventional anodizing. Also, I hope you are not trying to pattern the top layer too.

Paul Stransky is right, you need a CVD or a PVD method. CVD may be too high temp method for your application. The alternative might be sputtering (plasma PVD) alumina.

Mandar Sunthankar
- Fort Collins, Colorado


A. Andy, try ceramic paints. I've used alumina #903HP from Cutronics, NY. No heat treatment.

Andrew Verstak
- Richmond,Virginia


A. After writing the letter above, I realized that sputtering may be too slow for growing a >50 micron coating of alumina. I have no idea what CVD can do as far as throughput. There may be a solution that is going to take some research if no one has done it yet. It is relatively straightforward to produce thick aluminum coatings with vacuum evaporation. This coating may then be anodized.

Mandar Sunthankar
- Fort Collins, Colorado


A. Andy,

A 50-500 micron thick ceramic coating can be applied by plasma (thermal) spraying. It can also be done by Chemical Vapor Deposition (CVD) but this requires high temperature processing. Ceramic paints that are fired on can also be used though they have a glass binder material.

Donald M. Mattox
Society of Vacuum Coaters
Albuquerque, New Mexico

Ed. note:
            Mr. Mattox is
            the author of -->


A. I have a new process called Keronite. It is a plasma electrolytic oxidation process converting the surface aluminium into Alumina in situ. 50 µm layer takes about 1 hour. Very hard surface too. Best wishes

Robert Altham
- Cambridge, England

December 22, 2008

A. Hi Andy. Plasma electrolytic oxidation (PEO) is also known as "spark anodizing" or microarc oxidation (MAO). You may wish to see letter 44269 and letter 685 for an introduction. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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