High-Q mechanical resonators utilizing ultra-high stressed titanium nitride films

Mechanical resonators have been employed in opto- and electromechanics for precise sensing and controlling of mechanical motions even at a quantum level. This is due to the high coherence of mechanical resonators quantified by the quality factor. In recent years, it has been shown that high tensile stress plays an important role in the high quality factor of mechanical resonators such as beams and membranes[1]. Here we demonstrate membrane resonators utilizing ultra-high stressed titanium nitride films. Our titanium nitride films have a high tensile stress exceeding 2 GPa, while silicon nitride films, which are widely used for opto- and electromechanical systems, have a tensile stress of about 1 GPa [2]. Our resonators exhibit a high quality factor of 9.2 × 10⁶ at 2 K. We found that the thermal decoherence rate estimated from our results is much lower than the typical decoherence rate of superconducting qubits, suggesting that our resonators have the potential to serve as memories to store quantum information and overcome a limitation on the coherence time of superconducting qubits, which is imposed by electrical losses. Titanium nitride films are also used for superconducting circuits with high coherence qubits [3] because of their low dielectric loss, which makes our resonators also suitable for combination with superconducting circuits.