Piezoelectric resonators having a lateral field excited SC cut quartz crystal element

摘要

SC cut crystal resonators having lateral field excitation are disclosed. An SC cut quartz crystal blank is a doubly rotated Y cut which has the very valuable characteristic that its resonance frequency is stable while under stress, either from temperature gradients or from shock and vibration. Because of the threefold symmetry of quartz, and since the SC cut is rotated 22 degrees about the Z axis, there is a Y axis only about 8 degrees from the surface of an SC cut plate. A lateral field directed along or near this axis strongly excites the C mode and very weakly excites the B mode, if at all. The electrodes generating the lateral field are placed on the same major surface of an SC cut quartz crystal disc element and shaped to place the strongest field in the center of the disc element. This has been found to strongly couple to the C mode and suppress all other modes including the B mode and satellite C modes. Spectral purity and Q are enhanced thereby. Also, since the electrodes are disposed on only one major surface of the disc, the other major surface is unencumbered and available for frequency adjustment. The angle which the field forms with the Z' axis determines the relative degree of coupling of the B and C modes. At an angle of about +110° , optimal coupling is obtained for the C mode while the B mode is substantially suppressed. At about +160°, optimal suppression of the B mode is obtained while coupling of the C mode remains strong. At about + 60°, approximately equal coupling of the B and C modes is obtained.