Design of a compact atomic force microscope to enhance scanning speed

A novel design of an atomic force microscope (AFM) with a (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal scanner and a self-sensing cantilever is presented in this paper. The piezoelectric scanner and the self-sensing cantilever are integrated into a small-sized all-in-one structure with a microscope objective focused on the tip. The Z-scanner consists of two parallel PMN-PT unimorphs. This design can minimize the rotation and the sideways deflection at the sensing tip. The XY-scanner consists of two perpendicular small rods of PMN-PT. In this design, each PMN-PT rod serves as an actuator as well as a flexure because of the elastic property of the single crystal material. Under this configuration, the XY scanner can guarantee a fully decoupled planar scanning motion without positioning sensors and a sophisticated closed-loop control mechanism which is required for a XY scanner with conventional piezoelectric tubes. Furthermore, by adopting a self-sensing MEMS cantilever, the AFM design is simplified by discarding various optical sensing components. The attached objective offers fast visible inspection and rough positioning of the tip for measurement setups. We used a digital signal processor (DSP) based control scheme to achieve fast control speeds of the AFM. We also used LABVIEW for a flexible programming environment. We conducted finite-element analyses to characterize the dynamic performance of the AFM system. The system showed a high frequency band due to the small inertia of the moving part with relatively rigid structure. In addition, various scanning tests were performed to demonstrate that the system is capable of providing near video images.