Laser Irradiation Effect Of Quartz Crystal Resonators

Quartz crystal resonators are important piezoelectric acoustic components in electronic products with complex manufacturing processes with wide applications in precise timing,frequency control,frequency selection and other fields.There are both main mode and parasitic modes in the functioning state of a resonator.If the parasitic modal frequencies are close to the main functioning mode,there will be an increase of resistance and a decrease of the quality factor.In severe cases,of the frequency jump,the resonator cannot function stably and efficiently.The traditional processing method of crystal blanks is based on the mechanical grinding to invert the quartz crystal,which can effectively suppress the parasitic modes,reduce the modal couplings,and improve the quality factor and the circuit performance parameters of the resonator.However,there are also many disadvantages such as serious pollution,complex process,longer time,inefficiency,and so on.In this study,an experimental scheme with picosecond laser processing of quartz crystals is carried out to obtain a simple,clean,and efficient method of inverted edges of crystal blanks.The subject of this paper is AT-cut quartz crystal resonators with a frequency of 40 MHz and 26 MHz.The finite element method is used to analyze the thickness-shear vibrations of 40 MHz quartz wafer.The effects of the width and depth of the beveled edges on the frequency and mode shapes of the thickness-shear vibrations are studied.The appropriate beveling parameters are selected as experimental references.The effects of picosecond laser irradiation on the performance of 40 MHz quartz crystal blanks are studied by measuring the mode shape changes of individual wafers before and after the laser irradiation.In this study,two different laser processing methods are used to invert 40 MHz quartz crystal blanks.The picosecond laser beam irradiated both ends of the quartz crystal blanks.The total energy input is limited by controlling laser parameters such as laser power and scanning time.The laser-treated wafers are processed into resonators in a production line.The performance of resonators are measured and compared with the quartz crystal resonators without inverted edge.The surface microscopic characteristics of the wafers after laser irradiation are also observed.It is found that the wafers did have an approximately inverted profile while the performance of the resonators did not change significantly.The 26 MHz quartz wafer blanks are also tested.The ablation of quartz wafers under different laser parameters is measured.The relationship between the laser parameters and the ablation depth is obtained.The shape of the26 MHz quartz wafers before and after the inverted edge are observed and measured by a micro-projector and a wafer shape analyzer.Based on the measurement,a new irradiation scheme is developed and tested.The results show that the resistance and quality factors of the laser-treated resonators are close to those of the conventional inverted process,and are superior to the resonators without inverted edge.