Influence of wafer symmetry on the dynamic parameters of rectangular plates

During the manufacture of rectangular resonators, we have shown the necessity of accurately determining the acceptable tolerances for surface flatness and parallelism of the raw material, in this case an AT cut wafer 38.1/spl times/38.1 mm. To this end, we have investigated the dynamic parameter variations of finished units as a function of different levels of surface parallelism. Initially the wafers are plane-parallel, hence we introduced a change of parallelism by chemical etching. Different evolutions of impedance, inductance, Q-factor and unwanted modes in relation to the main mode due to the angular error caused by loss of parallelism in both directions X and Z are discussed.