Microcantilever-based mass sensors: working at higher modes against reducing the dimensions

Enhanced sensitivity and quality factor of microcantilever (MC)-based mass sensors when working at higher modes and reducing the dimensions are compared. By analysing the out-of-plane vibration signals recorded using an atomic force microscopy head, seven unique modes of a low spring constant MC are identified and mode shapes are assigned with the help of finite element method simulations. Polymer coating on the MC is applied by a precise dip coating setup and shift in frequency because of added mass is used to estimate the mass sensitivity. Similar measurements were also carried out for different dimensions of MC. The authors found that mass sensitivity increases with increase of eigenvalue (lambda(2)(n)) and decreasing dimensions (T/L-2) where T is thickness and L is length of MC. Although mass sensitivity was found to enhance by either method, quality factor was found to decrease at higher modes after the addition of polymer mass.