Preparation And Study Of Li-or Mn-doped ZnO Piezoelectric Thin Films

Zinc Oxide (ZnO) is a classic II -VI semiconductor material with a wide direct band-gap of 3.3 eV at room temperature. It has been extensively applied in piezoelectricity conversion, solar cell, gas sensor, UV detector, lighting displayer, integrated device etc. for its excellent physical properties. In this thesis, the preparation and characteristic of ZnO thin films with and without doping for piezoelectric sensor were investigated.In this work, ZnO piezoelectric thin films were prepared by sol-gel method on Pt/Ti/SiO₂/Si substrates. Dopant source were LiCl, Li₂CO₃ and Mn(CH₃COO)₂, repetitively. X-ray diffraction(XRD), Atom force microscopy(AFM), X-ray photoelectron spectroscopy (XPS) and Current-Voltage(I-V) were adopted to characterize ZnO thin films. It was revealed that c-orientation of undoped films was affected by both drying and annealing temperatures, and the latter was more remarkable. The resistivity of ZnO thin films after doping Li⁺ and Mn²+ was rapidly increased. Doping of Li₂CO₃ decreased the annealing temperature for forming c-axis orientation from 600℃ to 550℃　, compared with undoped and LiCl-doped ZnO thin films. Co-doped ZnO thin films possessed preferred c-axis orientation, good stoichiometry ratio and quite high resistivity when annealed at both 600℃ and 550℃. The annealing temperature range of preferred c-axis orientation was much wider for Mn-doped ZnO thin films.The influence of the technical parameter, such as doping concentration and annealing temperature on the c-axis orientation, morphology, stoichiometry and resistivity of ZnO thin films were thoroughly discussed through undoped, Li⁺-doped and Mn²+-doped ZnO thin films in this thesis. The performance of ZnO thin films abtained in this work can basically meet the requirement for piezoelectric sensor. The characteristic of ZnO piezoelectric films was improved by doping and the reason for it was analyzed.