Phase and mass relationship of the QCM sensor coated with rigid thin film

Quartz crystal microbalance (QCM) is a type of very high sensitivity mass sensing device, its sensitivity can be characterized by either frequency shift or phase shift. The main effect inducing this characteristic is the mass effect. That is to say, when the sensing surface of the device is perturbed by adding a thin film of or a mass layer, the resonant frequency will change, and so do the corresponding phase. A classical quantitative equation relating resonant frequency to added mass of the film was first derived by Sauerbrey, it reveals that frequency decrease proportional to the mass that was added to the surface of the QCM. In this paper, a new method called phase response analysis method(PRAM) is proposed to study the relation between phase shift and mass change of a rigid thin film coated on QCM from the point of physical view. It is a new way to describe the mass change that coated on the surface of the QCM quantitatively. It is a simple mathematic model and might be useful in some phase controlled sensor array systems. Numerically calculated results of this model show that there has a linear relationship between the phase shift and mass change. Meanwhile, the high fundamental frequency and small surface area can improve sensitivity. The principle of phase shift measurement and corresponding measurement system is also discussed.