A convection freeze sublimation (CFS) method was developed to release silicon nitride strings with a high aspect ratio and high tensile stress, which are widely applied as electromechanical resonators. This method is cost-efficient and easy to operate for its implementation at atmospheric pressure and no vacuum or cryogenic equipment is needed. The CFS system is composed of cyclohexane, nitrogen gas, a freezer and a drying chamber. Cyclohexane with low surface tension (24.38 mN m−1) and high phase transition temperature (6.5 °C) was chosen as the medium in the CFS method. Nitrogen gas was introduced into the drying chamber to facilitate the sublimation of solid cyclohexane by enhancing heat convection at the solid–air interface. A convective mass transfer model was calculated to quantitatively analyze the influence of convective parameters on the sublimation rate. The silicon nitride string array were successfully released with the aid of 3 ml min−1 flow of nitrogen gas. However, when the nitrogen flow rate exceeded 6 ml min−1, the strings adhered in some points because solid cyclohexane is prone to melt instead of sublimating under excessive heat introduced by nitrogen gas. Furthermore, a finite element model was built to explore the influence of different outlet parameters on the magnitude and uniformity of flow field on the surface of solid cyclohexane. To evaluate the mechanical property of the released string, we measured the natural frequency of a single string and confirmed the influence of tensile stress on its natural frequency. The results showed that the CFS method is able to serve as a general tool for ultra-weak structure releasing, which makes this method applicable in fields such as optomechanics and metamaterials.

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