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Spin Coating

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Spin Coating

Usually deployed in R&D and pilot scale systems spin coating is a common technique used to apply uniform thin films to flat substrates. Usually an excess amount of a solution is dispensed onto the substrate, which is then rotated at high speeds in order to spread the fluid uniformly by centrifugal force.

 

Rotation is continued while the fluid spins off the edges of the substrate, until the desired thickness of the film is achieved. The applied solvent is usually volatile and simultaneously evaporates. The achievable film thickness is a function of angular spinning speed, solid material content of the solution and the type of solvent.

 

Once spin-coating is complete, the plate is typically placed onto a hotplate (heated to somewhere between 80°C to 160°C) for several seconds or minutes to initially evaporate residual solvent and solidify the coating.

 

Depending on the layer thickness and the solvent the substrate is then baked-out for several hours, or typically overnight, in a convection or vacuum oven, at a temperature high enough to sufficiently remove the remaining solvent. Some materials are more difficult to coat than others.

 

Most often poor quality, hazy, or "Mura defect" coatings are the result of moisture absorption due to environmental humidity. Strict control over the laboratory environment is the best way to improve coating quality, so the integration of spin coaters into gloveboxes or generally into inert gas equipment is preferable so that the sample does not have a chance to absorb moisture.

 

For more demanding processes one should consider having the spin coater integrated into an inert, laminar flow enclosure to eliminate the disadvantageous effects of moisture and particles. Major advantages of this technique are cost-efficiency, a limited set of process parameters to be controlled, low maintenance, ease of operation and adaptability to a variety of different processes.

 

However spin coating reaches its limits when material usage and coating of large areas comes into consideration. Due to the process nature about 90% to 95 % of the feed material is spun off the substrate and is withdrawn from the process bowl as waste material. Especially in OLED applications where the active materials constitute a significant cost factor alternative coating solutions should be considered.

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