Application of langasite crystals in monolithic filters operating in shear modes

The piezoelectric material langasite (La₃Ga₅SiO₁₄) is discussed. The techniques of growing langasite crystals and the influence of different methods of charge preparation on the piezoelectric properties of the grown material are described. The difference in properties of crystals grown along crystallophysic Z- and Y-axes is explained. Data on anisotropy of elastic wave velocities and on piezoelectric constants and their temperature dependencies vs. orientation with respect to crystallophysic axes are presented for piezoelectric substrates operating in the thickness shear mode. Experimental results coincide well with theoretical data. Monolithic filters have been designed operating in shear mode over the frequency range from 5 MHz to 18.5 MHz. Filters operating at 5 MHz, 10.7 MHz, and 18.5 MHz have been manufactured as a result. The frequency-temperature characteristics and aging of filters operating over the temperature range from -60°C to +85°C are investigated. A comparison of monolithic quartz crystal and langasite crystal filters is given. The technology for manufacture of langasite elements and monolithic filters is described