Three-Dimensional Microfabrication by Two-Photon Lithography
- PDF / 1,453,753 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 55 Downloads / 179 Views
Three-Dimensional Microfabrication by Two-Photon Lithography Da Yang, Shalin J. Jhaveri, and Christopher K. Ober Abstract The controlled formation of submicrometer-scale structures in three dimensions is of increasing interest in many applications. Not intended to produce the smallest structures, but instead aimed at complex topographies, two-photon lithography is an intrinsic 3D lithography technique that enables the fabrication of structures difficult to access by conventional single-photon processes with far greater spatial resolution than other 3D microfabrication techniques. By tightly focusing a femtosecond laser beam into a resin, subsequent photo-induced reactions such as polymerization occur only in the close vicinity of the focal point, allowing the fabrication of a 3D structure by directly writing 3D patterns. The current research effort in two-photon lithography is largely devoted to the design and synthesis of high-efficiency photoinitiators and sensitizers, as well as the development of new materials and systems. This article provides an overview of the progress in two-photon processes for the formation of complex images and the development of patterned structures. Keywords: microfabrication, lithography.
Introduction Technological advances in the diverse fields of, for example, microfluidics, photonics, and tissue engineering require the development of three-dimensional (3D) structuring capabilities at the scale of a few nanometers. New technologies based on conventional optical lithography, such as laser rapid prototyping, have been developed for 3D microfabrication. However, single-photon absorption, used in standard photolithographic techniques, is a 2D process. In such processes, the 3D structures required for more complex devices are built up layer by layer via consecutive lithographic steps. With a spatial resolution of greater than 10 µm, such processes clearly cannot satisfy the requirement for submicrometer feature sizes in device fabrication. Two-photon lithography based on twophoton absorption (TPA) is an intrinsic 3D lithography that has broad potential for
976
constructing 3D structures (Figure 1). The TPA process depends on the nonlinear absorbance of certain chromophores that will simultaneously absorb two photons of radiation to produce photochemical reactions that mimic that of radiation of twice the energy. The advantage of this process is that outside the focal point, the incident light is below the absorbance threshold and passes through the reaction material. Yet by tightly focusing a femtosecond laser beam into the resin, subsequent photo-induced reactions such as polymerization occur only in close proximity to the focal point, allowing the fabrication of a 3D structure by directly writing 3D patterns by sample scanning. The extent of TPA depends quadratically on excitation intensity; therefore, TPA is confined to a focal volume of the order of the cube of the excitation wavelength. For many processes, in practice, structures on the
order of 250 nm can be created. Highnumeri
Data Loading...
