Single crystals of the langasite family: An intriguing combination of properties promising for acoustoelectronics

The main stages of advances in acoustoelectronics and the requirements for the workhorse of acoustoelectronic devices-thermally stable high-Q piezoelectric single crystals with moderate and strong electromechanical coupling-are considered. Since 1984, the acoustic and piezoelectric properties of single-crystal complex oxides (langasite, LGS; langanite, LGN; and langatate, LGT) have been studied most extensively. The basic parameters of these crystals are superior to those of all other related crystals known to date. The material constants and basic properties of langasite single crystals are reported. The main stages of development of acoustoelectronic devices based on these crystals are described. The description begins with the development (1986) of the first LGS resonators on 128-kHz longitudinal waves intended for channel filters used in line telephone communication and ends with the development of LGS-based SAW filters for W-CDMA cellular telephony, which allows for real-time image transmission.