The Structure Principle of Xtal Oscillator

The reason why xtal oscillator has become the raw material of xtal oscillator is that it has positive (mechanical energy → electric energy) and inverse (electric energy → mechanical energy) piezoelectric effect.

If pressure is applied along the electrical axis or mechanical axis of a xtal oscillator wafer to deform the wafer, the two surfaces perpendicular to these axes will generate an electric charge. This phenomenon is called positive piezoelectric effect. If an electric field is applied to both surfaces of the xtal oscillator, the wafer will be extended or compressed in the direction of the electric axis and the mechanical axis. This phenomenon is called inverse piezoelectric effect. 

Based on this characteristic, when the xtal oscillator is placed in an alternating electric field, the volume of the xtal oscillator will be compressed or stretched periodically, thus forming the mechanical vibration of the crystal. When the frequency of the alternating electric field is equal to the inherent mechanical resonance frequency of the wafer, the mechanical vibration amplitude of the wafer is the largest, so the resonance phenomenon occurs.