Characterization of ZnO/DLC/Si SAW devices using FCVA-produced DLC films

Surface acoustic wave (SAW) filters were fabricated using a multilayer structure of ZnO/diamond-like carbon (DLC)/Si and frequency response characteristics were analyzed. DLC films were deposited with varying preparation conditions (substrate bias, deposition time, and N₂ doping flow rate). The sp³ fraction, thickness, surface roughness, and resistivity of DLC films were measured as a function of deposition conditions. The center frequency of SAW devices with DLC-buffer was measured to be about 575 MHz, which was much higher than that (340 MHz) of ZnO/Si(100) SAW devices. The variation of center frequencies of DLC-buffer SAW devices showed almost the same trend as that of sp³ fractions of DLC films. By decreasing the thickness of DLC buffer layers, higher electro-mechanical coupling coefficient (K_eff²), lower insertion loss (IL), and larger side-lobe rejection (SLR) levels were obtained.