NBN Superconducting Electrodes for Cryogenic Lamb Wave Resonators on Lithium Niobate with Enhanced Quality Factor

This work presents a So mode Lamb wave resonator (L WR) on the lithium niobate (LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) platform. Niobium nitride (NbN) was utilized as the superconducting electrode material to reduce the electrode loss and increase the quality factor (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex>) of the resonator at cryogenic temperature. During the fabrication, a novel process was developed to avoid the corrosion of NbN by XeF 2 upon release. In the cryogenic temperature test, we observed a significant increase in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex> value of the device below 10 K. For further analysis, a unique modified Butterworth-Van Dyke (MBVD) model was used to fit the test results at different temperatures. The electrode loss, which is the Rs value in the model, is extremely close to 0 at superconducting temperature. This achievement is remarkable for future applications in emerging hybrid quantum networks that integrate phonons and qubits.