Reduction of the Frequency-Temperature Shift of Piezoelectric Resonators by Mechanical Stress

A method is described which allows a reduction of the frequency-temperature shift of piezoelectric crystals by the use of bimetal elements applying temperature-dependent pressure to selected spots on the circumference of the resonator disk. A decrease in the frequency change from ±15 to ±1 parts per million can be achieved for the AT cut of quartz over a wide temperature range by using one pair of bimetallic elements for the upper and one pair for the lower temperature range. This is accomplished without any increase in the resonance resistance of the crystal. Equations and curves are developed which enable one to obtain the optimum parameters of the bimetallic elements for a given frequency-temperature curve of the crystal. An experimental device, and results achieved with it under various conditions are described in detail. It is expected that in many cases this technique will make power- and space-consuming crystal ovens unnecessary.