Advances in MEMS Sensors Based on Two-Photon Polymerization 3D Printing (Invited)

Significance Two-photon polymerization three-dimensional (3D) printing technology, which leverages optical nonlinear effects,femtosecond laser ultrashort pulses, and extremely high peak intensities, has revolutionized material processing. By meticulously focusing the laser within a transparent photoresist and inducing multiphoton absorption in both time and space, the abovementioned technology enables the additive manufacturing of photonic devices, micro/nano-mechanical structures, microfluidic devices, and other 3D polymeric micro-nano structures. Two-photon polymerization 3D printing technology is a promising tool for realizing innovative applications of MEMS (microelectromechanical system) sensors. Progress The combination of two-photon polymerization lithography and 3D printing enables a precise polymerization reaction between monomers at a specific point in both time and space. By integrating 3D printing technology, intricate 3D structures can be realized at micro- and nano-scales. Performing two-photon polymerization under the threshold effect based on ultrafast laser processing overcomes the diffraction limit, thus resulting in exceptional resolutions for 3D microstructure printing at the micro- and nanoscales.Femtosecond laser two-photon polymerization 3D printing technology has yielded remarkable results in various fields, such as optical metamaterial manufacturing, micro-optical device production, shape-memory polymer development, the fabrication of micro-nano mechanical structures, the creation of micro-nano fluid devices, and the construction of biological microstructure frameworks.Recently, MEMS sensor manufacturing has demonstrated significant breakthroughs in terms of temperature sensing, humidity detection, mechanical analysis, and biochemistry exploration via the utilization of diverse functional materials via 3D printing and the design of intricate sensor structures with fine precision. These advancements have significantly propelled the development of MEMS sensors, particularly with the simultaneous adoption of photonics technologies, which have facilitated the emergence of optical MEMS sensors based on microscopic structures (as exemplified by optical fiber sensors). Consequently, the concept of "optical fiber laboratory" has advanced to a new stage. Conclusions and Prospects This paper provides a comprehensive review of the background, research significance, development history, development trends, basic principles, and most recent progress associated with two-photon polymerization 3D printing technology. Focusing on two-photon polymerization 3D printing MEMS sensors, this paper presents an updated review of the advancements realized in four areas: temperature, humidity, mechanical, and biochemistry sensing. By leveraging the optical nonlinear effect, ultrafine laser processing can overcome the diffraction limit and trigger the polymerization of material molecules inside a substrate. This enables two-photon polymerization 3D printing and thus the flexible creation of complex micro- and nano-structures with diverse functionalities, which presents significant implications for MEMS devices in optoelectronics, photonics,chemistry, and biomedicine. Over the recent two decades since the inception of two-photon polymerization 3D printing, researchers have continuously developed advanced photosensitive materials and processing technologies that further enhance structural resolution while reducing costs. Two-photon polymerization 3D printing creates new possibilities for MEMS design. In the future, two-photon polymerization 3D printing is anticipated to be used in MEMS devices, thus facilitating the development of more advanced sensors.MEMS devices with enhanced performance are expected to improve the sensitivity and detection limits of MEMS sensors, thereby promoting their miniaturization, intelligence, and integration.