Infulence Of Laser Annealing On The Performance Of Zinc Oxide Thin Film Varistors

ZnO system varistor ceramics have been extensively applied on high voltage field lightning arrester and low-voltage field circuit protection, including the power electronic devices in many field. In recent years, with the rapid development of electronic technology, electronic component integration is improving, electronic devices have been more and more sensitive to changes in voltage, because of electrostatic, surge and other factors, the probability of failure or malfunction of equipment is greatly increased, so the varistors which can not only steady the output voltage but also protect devices from over-voltages possess a widely application prospect, it also raises taller requirement to the reliability and preparation technology.In the present work, ZnO thin film varistors of high quality were prepared by RF magnetron sputtering technique with homemade target, the films were subsequently treated separately by annealing and laser annealing, summing up the above experimental research, some meaningful results are obtained.1、It can be seen that the surface was more smooth and compact when ZnO-based ceramic sputtering target was prepared at 40 MPa 、 950 ℃ compared with other preparation conditions. At this preparation conditions, he grain size was about 4-6μm,and the target was constituted with ZnO crystal phase, Bi2O3 phase and Zn2.33Sb0.67O4 spinel.2、Using Ti as the electrode material can ensure the stability of the electrode in the following annealing and laser annealing treatment. When the sputtering power is 300 W,the surface roughness of the film reaches the minimum of 18.4nm, and the surface is relatively smooth, and the obtained films are amorphous. With the increase of magnetron sputtering power, the film has a certain effect of crystallization, which is more and more obviously.3 、 Thermal annealing can prompt the amorphous thin film crystal, when theannealing temperature is above 850℃, the film grain is full, uniform and dense, and the annealing effect is better. The melting point of Bi2O3 is 825℃, in this vicinity, Bi2O3 can be dissolved, the ZnO grain boundary is formed at the rich phase, while the temperature is too high, the volatilization of Bi elements is more serious, leading to the decrease of electrical properties of the film. When the annealing temperature is 850℃,the electrical properties of the films are the best, the breakdown voltage of the sample is4.63 V, and the nonlinear coefficient is 13.89.4、The results indicate that the film irradiated by laser with moderate laser fluence and scan speed could achieve better laser annealing effects. The crystalline grains in laser irradiate zone grow up through a recrystallization process, after laser irradiation,the Bi content in the film has no obvious changes, solving the problem of Bi element’s serious volatilization in the process of annealing at high temperature. The laser fluence of 0.89J/cm2 and the scan speed of 10 mm/s are the optimal laser parameters in this experiment, and the C axis orientation of the film is the best, the breakdown voltage of the sample is 3.53 V, and the nonlinear coefficient is 18.93.