Bulk acoustic microwave delay lines: design, fabrication and performance

This paper presents a review of the state of the art on bulk acoustic delay lines, the main feature of which is to achieve large delays, up to 100 ¿¿s, in very small size packages. The structure uses piezoelectric thin-film transducers working at microwave frequencies (1 to 10 GHz). Basic design considerations show the range of specifications, mainly bandwidth, insertion loss and delay time, which can be reached by such devices. The fabrication process of the zinc oxide on sapphire structure is described, including thin-film deposition, impedance matching and packaging operations. We give the specifications of some typical delay lines working in transmission and reflection modes. Finally, we mention some applications of these delay lines to calibration and radar signal processing.