Micro- and nanomechanical resonators play a prominent part in many sensing and signal processing platforms due to their capability to pervasively couple with a wide variety of physical systems. Particularly relevant is their embedding in advanced optomechanical setups, which has recently pioneered optically cooled mechanical oscillators toward the quantum regime. A frequently adopted experimental scheme exploits a thin, highly tensioned Si 3N 4 nanomembrane where the membrane's vibrations are dispersively coupled to the optical mode of a Fabry-Pérot cavity. A significant effort has been done into realizing high-quality factor membranes, considering that low mechanical loss represents a benchmark to operate in the elusive quantum regime. In this article, we compare two state-of-the-art SiN resonators, realized exploiting the dilution of the material's intrinsic dissipation and efficient solutions to fully isolate the membrane from the substrate. In particular, we examine and discuss the interplay between the edge and distributed dissipation and propose an analytical approach to evaluate the total intrinsic loss. Also, our analysis delves into the sensitivity of the devices to a point-like force and a uniform-density force field. These results provide meaningful guidelines for designing new ultra-coherent resonating devices.
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