Over 12% of Coupling Coefficient Demonstrated by 3GHz Sc0.12Al0.88N Based Laterally Coupled Alternating Thickness (LCAT) Mode Resonators

Abstract

In this work, we report a laterally coupled alternating thickness (LCAT) mode resonators operating at 3GHz with an effective electromechanical coupling coefficient (k²eff) of 12.1%, using 12% scandium-doped aluminum nitride (Sc0.12Al0.88N) as the piezoelectric layer. The top and bottom electrodes are formed by patterning two groups of interdigitated electrodes (IDEs) on the top and bottom surface of the Sc0.12Al0.88N layer, respectively, both made of molybdenum (Mo). The thickness of the top electrode layer, Sc0.12Al0.88N layer, and the bottom electrode layer is 0.1μm, 0.7μm, and 0.2μm, respectively. The designed resonator is fabricated by in-house 200mm piezoelectric platform, with the Sc0.12Al0.88N deposited by physical vapour deposition (PVD). Electrical measurement results show that the series resonant frequency (fs) and the parallel resonant frequency (fp) are 2.96 GHz and 3.10 GHz, respectively, and the corresponding impedance at fs (Rs) and impedance at fp (Rp) are 3.19 Ω and 546 Ω, respectively. Besides the high k²eff of 12.1%, no spurious resonant modes are observed within a wide 1.2GHz frequency spectrum, demonstrating great potential of the reported Sc0.12Al0.88N based LCAT mode resonator in 5G duplexing solution on a single chip.