Plano-Convex Shaped Langasite Microbalances for High Temperature Applications

Piezoelectrically actuated plano-convex thickness shear mode (TSM) resonators in lanthanum gallium silicate (langasite) were fabricated. As main fabrication steps a wet etching process and a dry etching process were developed and furthermore graytone-lithography in combination with photoresist melting has been applied. The plano-convex shape is necessary to improve the Q-factor of the devices. The resulting Q-factor was up to two times higher than for simple planar resonators reaching values of more than 60,000. The special characteristics of langasite allow working temperatures of more than 700degC and a sensitive CeO₂ coating can be used for gas measurements at high temperatures.