Uneven Coating Influences on Electrical Impedance of Quartz Crystal Microbalance

Abstract

High shear modulus coating material does not provide loading effect to the Quartz Crystal Microbalance sensor. The condition is met when the coating material was glassy and the layer was homogeneous. Polystyrene is considered as a glassy coating material when used on 10MHz Quartz Crystal Microbalance. Homogeneous and compact polystyrene coatings that are glassy can be obtained using the spin coating method. The film's rigid condition is shown by the sensor impedance value at the series resonance frequency after coating. However, using ultrasonic spray coatings, it was known that polystyrene films are formed not as homogeneous as when coated using spin coatings. We observed that Quartz Crystal Microbalance was damped by the polystyrene film when the coating film was not evenly distributed over the sensor surface, especially on the sensor surface above the electrode. The minimum impedance of the QCM sensor increased significantly. The unevenness of the coating causes the damping effect on the QCM sensor. The minimum sensor impedance before coating was less than 15 Ohms. When the polystyrene layer was uneven, we found that the impedance increased by more than 25 Ohms. The results showed that the distribution of polymer layers on the sensor surface is one of the important factors that must be considered to avoid the effect of damping on the sensor. The measurement results showed that the sensor has a negative mass effect.