The ability to produce complex surface geometries at the micro-scale is sought after for potential applications in controlling the wettability and adhesion of surfaces, developing cell and tissue engineering scaffolds, and engineering high-performance composite materials.
Existing methods for fabricating 3D microstructures can be categorized into parallel processes such as interference and inclined exposure lithography, and serial processes typically used for prototyping, such as direct laser write lithography and focused ion beam milling. Parallel processes benefit from high throughput, but are typically limited to producing large arrays of relatively simple structures, while the serial processes can create a wide range of geometry but have comparatively low throughput. This invention provides a novel microfabrication technique that overcomes this trade-off by enabling large-area fabrication of freeform carbon nanotube (CNT) microstructures.
In CNTs grown using chemical vapor deposition (CVD), the growth rate depends on the substrate material used. When a single CNT feature is grown partially on SiO2 and partially on TiN, the differential growth rates induce internal stresses that result in a curved feature. The curvature of such a feature can be finely tuned by varying how much of it is grown on each substrate material.
The microfabrication process detailed in this invention begins with two photolithography steps. The first of these creates a patterned SiO2 layer on TiN substrate. Subsequently, CNT growth catalyst is selectively deposited onto the patterned SiO2-TiN sublayer to control the location of CNT features. Finally, CNT growth is induced through a CVD process. The Inventors have demonstrated that this process is capable of producing 3D CNT structures with a range of complex geometries. The geometry and mechanical properties of these CNT structures can be independently modified through a variety of post-processing steps such as capillary forming and conformal coating, making this process well-aligned with the principle of hierarchical design.
- Produces microstructures with freeform 3D geometry with high uniformity
- Enables high throughput compared to existing 3D microfabrication processes
- Allows independent control of geometry and mechanical properties