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At present, high internal stress in SU-8 photoresist layer has become one of the most primary problems and restricted structure stability and higher aspect ratio of SU-8 photoresist. However, the existing studies all focused on optimizing the process parameters or mask design, and could not be popularized. The purpose of this paper is to reduce the internal stress in cured SU-8 photoresist layer by ultrasonic stress relief technology. The ultrasonic stress relief mechanism in SU-8 photoresist layer was presented. Based on improved Stoney's formula, the profile mothod calculation model for SU-8 internal stress was proposed. The effect of ultrasonic stress relief on SU-8 layers was studied by experiments. Some important factors, such as amplitude of vibration, power input and relief time, were discussed. The values of internal stress before and after the ultrasonic stress relief process were compared. The research results show that the internal stress in cured SU-8 layer can be reduced effectively if the proper experimental parameters are chosen, and ultrasonic stress relief technology in nonmetal field has some practical value.ultrasonic stress relief, SU-8 photoresist layer, internal stress, profile method Citation:Du L Q, Wang Q J, Zhang X L. Reduction of internal stress in SU-8 photoresist layer by ultrasonic treatment.

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Liquid metal (LM) as the universal artificial biomimetic sensory material has attracted much interest in academic and industrial applications, such as soft robots, flexible electronics, and micro−nano devices. It remains a pivotal challenge to develop a stable and highly sensitive angle detection with a rapid response. Herein, we present an LM-based angle detection sensor. Ga-based LM is gradually injected into hollow fibers with rough internal structures, resulting in a gradient of LM content inside the fibers due to the synergistic effect of pressure drop and the fast formation of an oxide film on its surface. The LM is affected by the gravity pressure when the fiber is tilted, and the Laplace pressure on the surface of the LM continuously reaches an equilibrium state to induce the continuous deformation of the LM. The proposed sensor with highly sensitive to the tilt angle and showcases a linear relation with the tilt angle. For its advantages, this work shows a great potential application in sensor fields and opens routes for the application of electronic whiskers.