Fabrication method for grating‐mode‐type SAW resonator used in voltage‐controlled oscillator: optimum shape for electrode fingers and investigation of accurate process techniques

Abstract

AbstractAn optimum electrode finger shape is obtained for the grating‐mode‐type SAW resonator on a 15° YX‐LiNbO3 with a large relative bandwidth used for a high‐C/N broadband VCO. Spurious responses by Rayleigh wave need to be suppressed completely in the SAW resonator. Its impedance characteristics are extremely sensitive to the variations of electrode finger linewidth and film thickness. The specifications for the film thickness and linewidth of the electrode finger are derived by simulation and experiment. It is demonstrated that the electrode finger film thickness of h/λ0 = 0.1325 and the relative electrode finger linewidth ratio of L/(L+S} = 0.575 are standard and their deviations need to be controlled accurately in fabrication. Assuming applications to industrial wireless terminals at 170 and 420 MHz, process accuracy enhancement is discussed so that the electrode finger specifications are satisfied. In the present SAW resonator with a thick electrode finger, an antireflection film is introduced in the photoresist process. Al‐Cu alloy is used for the electrode fingers to produce an excellent impedance characteristic. The VCO using the present SAW resonator satisfies the specifications of the above wireless terminals. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(9): 11–20, 2001