Sub-Micrometer 3D Printing with 3D Ice Lithography

Additive manufacturing or 3D printing has become an important tool due to its ability to directly produce complex 3D structures. Many 3D printing techniques are currently available, ranging from large-scale concrete printing to sub-micrometer printing to create scaffolds for cell growth. Recently, numerous efforts have been geared toward developing 3D printing techniques or tools capable of building micro or even nanometer-scale 3D structures. The ability to directly produce 3D structures on this scale is crucial to a lot of industries and scientific fields, such as microelectronics, microbiology, and biomedical among others.

In this PhD project, we are developing a novel 3D printing tool and technique capable of producing structures with resolution less than 1 micrometer, based on the previous development on ice lithography (IL) with organic ice resist. The process is called 3D Ice Lithography (3DIL), due to IL step being used to build sub-micrometer 3D structure layer-by-layer.

In this process, liquid nitrogen is used to cool down the process stage to cryogenic conditions (~ -190 °C), inside a vacuum environment. Using the very cold stage, we freeze a thin layer of ice made of organic materials. The thin layer of organic ice is then exposed to a focused electron beam (e-beam) that we control to follow a specific pattern. On the area that was exposed by e-beam, the organic ice is reacted into crosslinked structure that stays stable in room temperature. This becomes the building block of our 3D structure. These two steps are then repeated, adding a stack of ice and crosslinked structures one layer at a time. By controlling the e-beam exposure pattern, we can arrange the crosslinked structures into a complete 3D structure, with a resolution of less than 1 μm. After the entire 3D structure is completed, we bring the stage back to room temperature. The remaining organic ice is evaporated, and leaving only a micro-3D
structure.

To implement the above process, we designed a new instrument that is capable of processing user input in the form of g-code file, which is also used widely in other 3D printing process. We tested the performance of the new instrument using nonane as the precursor. An optimization process was also performed to discover the optimum printing parameters for 3DIL with nonane to achieve sub-micrometer resolution. With the optimized process, we demonstrated the 3DIL printing capability to produce microfluidic device, and photonic crystals among others. Lastly, we also investigated the compatibility of 3DIL process with organometallic precursors.