SOL GEL SPIN COATING METHODS
For sol-gel coating there are basically two methods: a spin coating method for one-sided sol-gel coating or dip coating for double-sided coating. Both sol-gel coating techniques are commonly used in manufacturing thin films. The sol-gel process is a method used to make solid materials from small molecules. Sol-gel coating is a way to create single- or multicomponent oxide coatings on glass or metals.
Static spin coating method is simply depositing a small puddle of solution on or near the center of the substrate. This can range from 1 to 10 ml depending on the viscosity of the solution and the size of the substrate to be coated. Higher viscosity and or larger substrates typically require a larger puddle to ensure full coverage of the substrate during the high speed spin step.
Dynamic spin coating method is the process of dispensing while the substrate is turning at low speed. A speed of about 500 rpm is commonly used during this step of the process. This serves to spread the fluid over the substrate and can result in less waste of resin material since it is usually not necessary to deposit as much to wet the entire surface of the substrate. This is a particularly advantageous method when the fluid or substrate itself has poor wetting abilities and can eliminate voids that may otherwise form
How do you create a sol gel?
Sol-gels are made by condensing a solution (sol) of metal oxide precursors into 3D networks. The gels are bi-phasic systems in which a continuous fluid phase fills the space inside a polymerized network. The gels can be dried in a controlled way to produce porous solids with unique thermal, mechanical, optical, and chemical properties. The early sol-gels were made of silica, by condensation of silanols (SiOH) you produced silica gels. Sol-gel processing now has become a very flexible process for materials synthesis. It is now possible to make sol gels materials from almost any transition metal, as well as make composite materials.
Spin Coater Theory
Spin coating has been used to prepare thin films for various applications. A small puddle of a fluid material onto the center of a substrate is spin coated the on substrate at high speed. Centripetal acceleration causes the formation of a thin film of material on the substrate. The film thickness depends on the solution properties such as viscosity, drying rate, percent solids, surface tension, etc. and RPM and coating time. One of the most important factors in spin coating is repeatability, as subtle variations in the parameters that define a spin-coating process can result in drastic variations in the coated film. A typical spin process consists of a dispense step in which the resin fluid is deposited onto the substrate surface, a high speed spin step to thin the fluid, and a drying step to eliminate excess solvents from the resulting film.
The spin coating methods are static spin coating, dynamic spin coating and multi rpm coating methods.
After the dispense step it is common to accelerate to a relatively high speed to thin the fluid to near its final desired thickness. Typical spin speeds for this step range from 1500-6000 rpm, depending on the properties of the fluid as well as the substrate. This step can take from 10 seconds to several minutes. The combination of spin speed and time selected for this step will generally define the final film thickness. In general, higher spin speeds and longer spin times create thinner films.
A separate drying step is sometimes added after the high speed spin step to further dry the film without substantially thinning it. This can be advantageous for thick films since long drying times may be necessary to increase the physical stability of the film before handling. Without the drying step problems can occur during handling, such as pouring off the side of the substrate when removing it from the spin bowl. A moderate spin speed will aid in drying the film without significantly changing the film thickness.
Spin speed is one of the most important factors in spin coating. The speed (rpm) affects the degree of centrifugal force applied to the resin and the turbulence of the air immediately above it. Relatively minor speed variations at this stage can result in large thickness changes. Film thickness is largely a balance between the force applied to shear the fluid resin towards the edge of the substrate and the drying rate of the resin. As the resin dries, the viscosity increases until the radial force of the spin process can no longer move the resin over the surface. At this point, the film thickness will not decrease significantly with increased spin time. All Cee® spin coating systems are specified to be repeatable to within ±0.2 rpm at all speeds.
FYTRONIX SPIN COATER
- Product Code: FYTRONIX-SPIN-COATER
- Availability: In Stock