A comprehensive theory of the spin coating technique has been reviewed and the basic principles and parameters controlling the process are clearly highlighted, which include spin speed, spin time, acceleration and fume exhaust. The process generally involves four stages: a dispense stage, substrate acceleration stage, a stage of substrate spinning at a constant rate and fluid viscous forces dominate fluid thinning behaviour and a stage of substrate spinning at a constant rate and solvent evaporation dominates the coating thinning behaviour. The study also considered some common thin film defects associated with this technique, which include comet, striation, chucks marks environmental sensitivity and edge effect and possible remedies.

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Description and theory of spin coating technique has been elaborately outlined and a spin coating machine designed and fabricated using affordable components. The system was easily built with interdisciplinary knowledge of mechanics, fluid mechanics and electronics. This equipment employs majorly three basic components and two circuit units in its operation. These include a high speed dc motor, a proximity sensor mounted at a distance of about 15 mm from a reflective metal attached to the spindle of the motor to detect every passage of the reflective metal at its front and generate pulses. The pulses are transmitted to a micro-controller which process them into rotational speed (revolution per minute) and displays it on a lead crystal display (LCD) which is also a component of the micro-controller. The circuit units are a dc power supply unit and a PWM motor speed controlling unit. The various components and circuit units of this equipment are housed in a metal casing made of an 18 gauge black metal sheet designed with a total area of 1, 529.2 cm 2. To illustrate the use of the spin-coating system, ZnO sol-gel films were prepared and characterized using SEM, XRD, UV-vis, FT-IR and RBS and the result agrees well with that obtained from standard equipment and a speed of up to 9000 RPM has been achieved.

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