In this paper, novel piezoelectric microbalance biosensors using single crystal lead zinc niobate-lead titanate (PZN-PT) and lead magnesium niobate-lead titanate (PMN-PT) are presented. The PZN-PT/ PMN-PT materials exhibit extremely high piezoelectric coefficients and other desirable properties for biosensors, supposed to be a superior substitution for the conventional quartz crystal with the improved performance. . These biosensors provide rapid and minute quantitative target detection by monitoring the change in resonance frequency of the crystal probe. With the geometrical variations, various prototypes are compared with conventional quartz crystal microbalances (QCM). The superiority of the materials over conventional quartz crystal is demonstrated experimentally in terms of sensitivity. In addition, we examine the feasibility of ultra miniaturization of the PZN-PT based biosensor by fabricating freestanding single crystal films of the PZN-PT and patterning micro-scale biosensors with ion milling and argon-ion laser-induced etching technique. A fabricated prototype sensor utilizing the material in a thin film form has a size of 300x100x7um<sup>3</sup>.
A smart cantilever structure using single-crystal relaxor ferroelectric material is presented. The smart cantilever possesses both sensing and actuation capabilities, embedded in a monomorph and resulting in a smart structure. Single crystal relaxor ferroelectric materials (1-x)Pb(Zn<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3-x</sub>PbTiO<sub>3</sub> (PZN-PT) and (1-x)Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3-x</sub>PbTiO<sub>3</sub> (PMN-PT) are ideal for actuator and sensor applications since they exhibit very high piezoelectric coefficients. We separately pattern interdigitated electrodes on the top and bottom surfaces of a single crystal cantilever beam. The interdigitated electrode design results in an electric field- gradient that after poling not only induces flapping actuation but also, simultaneously, allows us to detect internally or externally induced stresses. As a monolithic actuator integrated with a sensor, it has potential applications in various Micro-Electro-Mechanical Systems (MEMS), Scanning Probe Microscopy (SPM) and Near-field Scanning Optical Microscopy (NSOM). We fabricate monomorph prototypes and characterize their performance in terms of actuation displacement and sensing capabilities, respectively. Finally, an active vibration control experiment was successfully conducted by using the smart cantilever structure.
A novel design of an atomic force microscope (AFM) with a (1-x)Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3-x</sub>PbTiO<sub>3</sub> (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.
In this paper, we report an innovative depth-sensing nanoindenter using a lead zirconium titanate (PZT) stack actuator. The conventional nanoindenter requires two sensors and closed-loop controls for precise loading or positioning due to inherent high hysteresis and creep characteristics of the PZT actuators. On the other hand, we have shown that an open-loop positioning control scheme using a single displacement sensor can be used for nanoindentation. The developed control scheme compensates for the hysteresis and creep errors of PZT actuators. By adopting the single-sensor open-loop control, the overall system structure can be simplified and a robust control environment can be achieved. In addition, a high positioning repeatability was achieved by using a flexure type mainframe with a high preload applied to the PZT actuator. To verify the system performance, we conducted the standard indentation tests on a fused quartz sample, and the results were compared with those from a commercial nanoindenter. Besides the basic nanoindentation functions, the developed system also has the capability for surface imaging through a scanning function. The pre-indentation scanning capability proved to be a very useful method for positioning the tip in the desired indentation location. Similarly, post-indentation scanning allows for visualization of the indentation marks after the tests.