Production issues in using Silicon Dioxide films for temperature compensated Bulk and Surface Acoustic Wave devices

In this paper, production oriented aspects of using Silicon Dioxide (SiO₂) films in manufacturing of Temperature Compensated Bulk Acoustic Wave (BAW)/ Film Bulk Acoustic Resonator (FBAR) [1], [2] and Surface Acoustic Wave (SAW) devices have been presented. SiO₂ has been used to obtain low Temperature Coefficient (TempCo) in acoustic wave devices for more than three decades [3]. One of the big issues is that depending on the method of deposition and the amount of times SiO₂ is exposed to the ambient environment [4], it can significantly alter temperature compensating properties of the film as well as etch rate in a thickness trimming process with focused Ion Beam. Plasma Enhanced Chemical Vapor Deposition (PECVD), RF diode and RF magnetron depositions with in-situ thickness trimming and capping layers were tested on the temperature compensated FBAR and SAW structures. Repeatability of the results was tested with different amount of time before processing steps. Best results were obtained using RF diode sputtered SiO₂ with in-situ trimming process [5] and in-situ aluminum nitride (AlN) sputtered capping layer.