Study of physical causes of intermodulation distortions in HFF crystal resonators

The paper is devoted to experimental study of non-linearity of HFF crystal units and its influence on the quartz filter intermodulations. On statistical treatment of the measurement data the regression coefficients linking the crystal parameters non-linearity with the intermodulation level have been defined. The origin of the crystal non-linearity was explored through standard fabrication process stages. It was deduced that a main source of the non-linearity most probably arises during the electrodes deposition as the film imperfections creating some flicking capacitance and resistance depending of crystal vibration amplitude. Some ways of reduction of the crystal non-linearity are proposed and discussed in the paper.