High-Precision and Rapid Direct Laser Writing Using a Liquid Two-Photon Polymerization Initiator

Abstract

Two-photon polymerization based direct laser writing (DLW) is an emerging micronano 3D fabrication technology wherein two-photon initiators (TPIs) are a key component in photoresists. Upon exposure to a femtosecond laser, TPIs can trigger the polymerization reaction, leading to the solidification of photoresists. In other words, TPIs directly determine the rate of polymerization, physicochemical properties of polymers, and even the photolithography feature size. However, they generally exhibit extremely poor solubility in photoresist systems, severely inhibiting their application in DLW. To break through this bottleneck, we propose a strategy to prepare TPIs as liquids via molecular design. The maximum weight fraction of the as-prepared liquid TPI in photoresist significantly increases to 2.0 wt %, which is several times higher than that of commercial 7-diethylamino-3-thenoylcoumarin (DETC). Meanwhile, this liquid TPI also exhibits an excellent absorption cross section (64 GM), allowing it to absorb femtosecond laser efficiently and generate abundant active species to initiate polymerization. Remarkably, the respective minimum feature sizes of line arrays and suspended lines are 47 and 20 nm, which are comparable to that of the-state-of-the-art electron beam lithography. Besides, the liquid TPI can be utilized to fabricate various high-quality 3D microstructures and manufacture large-area 2D devices at a considerable writing speed (1.045 m s −1 ). Therefore, the liquid TPI would be one of the promising initiators for micronano fabrication technology and pave the way for future development of DLW.

Push–Pull Carbazole-Based Dyes: Synthesis, Strong Ultrafast Nonlinear Optical Response, and Effective Photoinitiation for Multiphoton Lithography

“…Thanks to their strong optical nonlinearities, traditional MPL-based 3D printing has successfully achieved high-resolution features of submicrometers . Moreover, more recent studies have demonstrated ongoing advancements in MPL technology, achieving feature sizes below 100 nm. − However, many research groups that assess the effectiveness of PIs by determining TPA cross sections using high-repetition rate (as, e.g., MHz) femtosecond (fs) laser sources have led to the erroneous conclusion that a high cross section is not responsible for high efficiency. − Primarily, under such experimental conditions, unwanted thermal effects inevitably manifest, obscuring pure electronic response contributions to the NLO response . As a result, erroneous extremely large values of the TPA cross section have been reported.…”

Two-photon polymerization lithography for imaging optics

“…However, its speed is naturally slow, necessitating faster scanning or multibeam approaches for large-scale fabrication. Therefore, to transition from laboratory research to industrial applications, mass production becomes imperative, which can be achieved through the development of extreme sensitive photoresists [245,246] and high-speed TPL technologies [247,248]. Various scanning schemes, including single beam writing with stage scanning, galvanometer scanning, rotating mirror scanning, or acousto-optic deflector (AOD) scanning, have been explored to increase speed.…”

A Computational Evaluation of Minimum Feature Size in Projection Two-Photon Lithography for Rapid Sub-100 nm Additive Manufacturing

“…Approaches for increasing the throughput include increasing the scanning speed of serial writing, parallelizing the writing, and combining the previous two approaches [ 21 , 22 , 23 , 24 ]. It is noteworthy that recent studies have demonstrated high scanning speeds up to and exceeding 1 m s −1 with serial TPL [ 25 , 26 , 27 , 28 , 29 ]. However, the printing of 3D structures with sub-100 nm feature sizes has not yet been demonstrated at these high speeds.…”