Sensitivity Enhancing And Parallel Detection Technique With Self-Sensing Piezoelectric MicroSensors

Piezoelectric PZT (Lead Zirconate Titanate) microcantilever, sensitive to nano-scale deflection, has been successfully used as self-sensing probes in SPM systems since 1990s. PZT film with high piezoelectric constant and electromechanical coupling coefficient, which is the key material of self-sensing and self-actuated piezoelectric microsensors, has shown the potential in constructing compact parallel detection systems such as ultra-high-density storage, parallel-fabrication plasma devices, et al. However, the preparation of high quality PZT thin film is rather time-consuming, which limits its mass production and commercial application. As the self-sensing function of piezoelectric microsensors is based on the detection of piezoelectric charge output of the PZT layer, it is necessary to enchance the sensitivity of miniaturized piezoelectric microsensors. Additionally, the difference between microsensors makes it difficult to realize parallel-driving and parallel-measuring. Therefore, we focused on the sensitivity enchancing and parallel detection technique with piezoelectric microsensors, and research on the rapid preparation of high quality PZT thin film, the fabrication of piezoelectric microsensors with optimized parameters, parallel detection technique of weak piezoelectric signal.To enchance the performance of piezoelectric microsensors, the properties of PZT thin film and the parameters in fabrication should be enhanced and optimized. Perovskite LaNiO₃ film was introduced as the seed layer in PZT film preparation with rapid heat treatment. The relationship between sensitivity and structure parameters of piezoelectric microsensors was concluded from the basic microcantilever theory. The processing parameters in fabrication were studied. Differential charge amplifiers were modified for parallel detection. Self-sensing and self-actuated piezoelectric PZT microcantilever array for parallel-detection mass sensors with pictogram sensitivity was realized.The research work of this dissertation can be summarized as follows: (1) Fast preparation of high performance PZT film and fabrication of PZT film based micro devices. Perovskite conductive oxide LNO films were prepared by Sol-Gel mothed as the seed layer to induce the growth of preferred (100) orientation of PZT films and reduce (111) orientation. Finally the acquired PZT films have good dielectric and piezoelectric property. Problems in the fabrication of PZT thin film based devices were presented, and key factors were emphasized.(2) Detection and measurement of weak signals. Signal characteristics of high resonance frequency PZT cantilevers are analyzed with the theory of piezoelectric micro-cantilevers. Differential charge amplifier is used to extract and amplify the weak signal. Key factors that influencing the output of the amplifier are analyzed. By choosing appropriate operational amplifier chips and adding adjustable resistance and capacitance in the circuit, phase error is eliminated.(3) Piezoelectric micro-sensor based resonant mass sensors array. To increase detection efficiency, parallel working system is contructed with the self-sensing and self-actuating PZT cantilevers. A number of key issues are investigated such as working mode, parallel exciting and parallel sensing mothed, probe-sample approach method and position adjustment. Additionally, micro piezoelectric PZT cantilevers working in liquid environment have been investigated.(4) The fabrication and optimization of PZT thin film actuators. PZT thin film based deformable mirror actuators are analyzed. While miniaturized, it is optimized in deformable and driving ability. Mathematical model of piezoelectric all-fiber phase modulator was improved and effect of piezoelectric coefficient d₃₁ was calculated. It is applied to the optimization of structure parameters of the modulator. Sol-ESD method is applied to prepare PZT thin films on the surface of optical fiber. It is suitable for nonplanar PZT thin film fabrication.