Periodic Structure of Narrow FBARs Operating on SH1 Mode in LN Membrane Solidly Mounted on SiC Substrate

We propose a system of narrow FBARs with alternating voltage polarity on top electrodes on the LN platelet and a common bottom floating electrode positioned on a substrate with high acoustic velocity (SiC). This is a YBAR device that is attached to a SiC substrate. Every individual resonator radiates the bulk waves into the substrate. However, if the period of the structure is smaller than the wavelength of bulk waves in the substrate at the operation frequency, the destructive interference of the bulk waves cancels the bulk radiation in a rather long periodic structure. The amplitude of this radiation can be further reduced by optimizing the bottom electrode thickness and by introducing the additional SiO2 layer under the metal electrode. The effects of bottom metal and grooves in the piezo-layer are also studied and discussed based on simulations. Here, we present this practical YBAR-on-SiC resonator with a piezo-coupling of 25.4% and Q of ~200 at 5 GHz. It is a competitive option for potential N79 and 5G WiFi bands for sub-6G applications.