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

In this work, we report a laterally coupled alternating thickness (LCAT) mode resonators operating at 3GHz with an effective electromechanical coupling coefficient (k<sup>2</sup><inf>eff</inf>) of 12.1%, using 12% scandium-doped aluminum nitride (Sc<inf>0.12</inf>Al<inf>0.88</inf>N) 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 Sc<inf>0.12</inf>Al<inf>0.88</inf>N layer, respectively, both made of molybdenum (Mo). The thickness of the top electrode layer, Sc<inf>0.12</inf>Al<inf>0.88</inf>N 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 Sc<inf>0.12</inf>Al<inf>0.88</inf>N deposited by physical vapour deposition (PVD). Electrical measurement results show that the series resonant frequency (f<inf>s</inf>) and the parallel resonant frequency (f<inf>p</inf>) are 2.96 GHz and 3.10 GHz, respectively, and the corresponding impedance at f<inf>s</inf> (R<inf>s</inf>) and impedance at f<inf>p</inf> (Rp) are 3.19 Ω and 546 Ω, respectively. Besides the high k<sup>2</sup><inf>eff</inf> of 12.1%, no spurious resonant modes are observed within a wide 1.2GHz frequency spectrum, demonstrating great potential of the reported Sc<inf>0.12</inf>Al<inf>0.88</inf>N based LCAT mode resonator in 5G duplexing solution on a single chip.

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