Zno Thin Films And Acoustic Sensor Structure Simulation

Zinc oxide (ZnO) is an important piezoelectric material. It has many advantages such as low cost, nontoxic, ease to form single crystal films and preferential oriented films, compatible to semicondutor technology and integratable to miniature devices. In the past 20 years, the deposition processing of ZnO thin films and its piezoelectric properties were intensely studied. In recent years, much attention has been paid to novel miniature piezoelectric devices which based on piezoelectric thin film technology and MEMS technology.In this thesis, ZnO thin films were prepared on sillcon substrates by RF sputtering as well as by reactive DC magnetron sputtering. The deposition parameters such as substrate temperature, sputtering power, sputtering time, total pressure, the ratio of Ar to oxygen, and heat treatment temperature were systematically studied. The films were characterized by X-ray diffraction. The results showed that the ZnO thin films prepared by RF sputtering under a wide processing"window"were highly c-axis preferential grown. In the XRD spectrum, only ZnO (002) peak existed, other peaks were absent. However, ZnO films prepared by reactive sputtering showed weak (100) and (110) peaks. The sizes of the grains ZnO prepared by RF sputtering were in the range of 40 to 60 nm observed by atomic force microscope. The optimal deposition conditions of RF sputtering are: substrate temperature 400℃, 20%O2, power 120W, sputtering time 150 minutes. The films prepared by RF sputtering were annealed in air at 500-700℃for 2 hours. Rocking curve tests were performed on the annealed films. The results showed that the FWHM of the rocking curves decreased with the increasing temperature. It indicated that the oritation of the films was enhanced under high temperature. The piezoelectric stress coefficient e33 was also increased slightly with the increasing temperature.The static, modal and harmonic analysises of the ZnO cantilever piezoelectric acoustic micro-sensors were simulated by using the finite element analysis software ANSYS9.0. The results showed that the maximal voltage genenrated in the cantilever was 16.4 mV induced by 1Pa acoustic pressure; the first–order inherent frequency of the sensor was 12.379 KHz, the relationship curve between induced voltage and dynamic pressure frequency was obtained by harmonic analysis from 1kHz to 30kHz, the maximal voltage is 0.25V when the frequency is 12kHz. Through simulating, the effects of cantilever parameters on the sensitivity and resonator modals were presented in this paper. The simulation results showed that the length of cantilever is the main factor to influence the sensitivity and working stability of the sensors among all the structure parameters.