Applications Of Piezoelectric Bimorph Beams On Micromotors And Micro Force Sensors

Piezoelectric sensors and actuators with many advantages including simple structure, fast response, high frequency, and simple driving and measuring circuits, have been extensively applied to ultrasonic devices, precision positioning, detecting of acoustics and mechanic parameters, etc. Piezoelectric biomorph beams are classic sensitive structures, and they are also multifunction platforms. Piezoelectric biomorph cantilevers have shown outstanding characteristics in displacement amplification when they are used as actuators. It can realize a relatively large displacement that stack piezoelectric units can hardly achieve. When the biomorph cantilever is used as a sensor, it also has many advantages, including good flexibility, high sensitivity, etc. This cantilever can measure a micro load by optimizing the structure and scaling down the dimensions. With the development of Microelectromechanical Systems (MEMS) technologies, micro piezoelectric biomorph beams fabricated with microfabrication techniques become more and more attractive and have more possible applications to microsensors and microactuators.In this dissertation, based on the piezoelectric bimorph cantilevers, the applicatons to piezoelectric micromotors and micro force sensors were investigated, which covers the fellowing three aspects:1. The applicaton of piezoelectric bimorph structures to piezoelectric micromotors was conducted. The structures and characteristics of piezoelectric bimorph cantilevers were studied, and the models of piezoelectric microsensors and microactuators with bimorph and unimorph structures were discussed. The elliptical movement of serial piezoelectric bimorph (serial bending arm) was analyzed and verified by experiments. The track of elliptical movement was observed using oscillograph so that the characterizaton of displacement amplification was verified. The structure of serial bending arms for piezoelectric micromotors was designed, while the driving mechanism was analyzed. Two types of prototypes with different scales and different piezoelectric serial bending arms were fabricated using precise micromachining techniques. The characteristics of the micromotors were measured, and the relationship between velocity without load, torque and driving voltage amplitude, driving frequency were tested and analyzed. The influence of pre-load and abrasion on the capability of piezoelectric micromotor was analyzed. The capability of the piezoelectric micromotors was improved, compared with other piezoelectric micromotors in the same scales. The micromotors with serial bending arms 5 mm in diameter can reach its maximumrotational velocity of 325 rpm without load, and maximum torque of 36.5μNm.2. The microfabrication techniques for piezoelectric unimorph cantilevers were investigated. The approach to deposite PZT films was studied, while various thickness of PZT films were prepared by sol-gel method on the substrate of Pt/Ti/SiO2/Si. The reason of bubbles on PZT films was analyzed and overcomed using modified annealing process. The characteristics of structure, resistance, and ferroelectrics were tested and analyzed. The results revealed that the prepared PZT films are preferentially oriented along the <111> direction, and the films have high resistance and good ferroelectricity. The patterning method of PZT films with dry etching and wet etching was conducted. The undercut was decreased using a modified wet etching process. A new ICP dry etching method, with good surface quality and satisfied etching rate, was developed. The mcirofabrication process for piezoelectric silicon microcantilevers was studied, resulting in a new modified fabrication process. Three types of of silicon-based PZT microcantilevers were fabricated successfully with this modified fabrication technique. The key techniques in the cantilever fabrication rpocess were invetigated.3. The application of the Si-based PZT piezoelectric microcantilevers to micro force measurement was studied. The dynamic model of Si-based PZT piezoelectric microcantilevers was analyzed with numerical simulation, in which the dynamic characteristics of microcantilevers were obtained. The response to microforce, applied at the free end of cantilevers, and reporise to voltage, applied on the electrodes of PZT films, were imulated with CoventorWare. The modal frequencies of the microcantilevers were extracted with modal analysis. The results of numerical caculation and FEA were in a good agreement, while the coherence and errors were studied as well. The application of the Si-based PZT piezoelectric microcantilever to micro force measurement was also studied. A piezoelectric micro force sensor, with a piezoelectric bimorph microcantilever, was investigated for the first time. The working principle of the micro force sensor was discussed. A calibration method was designed for practical applications of micro force sensors to micro robots and micromanipulation systems.