Microfabrication of multi-layer glassy carbon microstructures through dye-doped negative photoresists

We report on a new technique for microfabrication of multi-layer thick microstructures consisting of a combination of glassy carbon (GC) layers alone, or layers with both GC and negative resist. In this technique, we dope a negative tone pre-cursor polymer of GC structures with a dye that will serve as an ultraviolet (UV) light blocking layer. This allows the doped negative resist layer to act—when needed—as a sacrificial layer which subsequently will enable the patterning of multiple layers of negative resists that can be pyrolyzed and turned in to GC microstructures. In this study, we demonstrate that this method offers a high yield and reliable extension of the classical carbon micro electromechanical systems process to microstructures consisting of multi-layer of GC and a combination of GC and negative resist layers. This batch process, therefore, forms a basis for a high yield and reproducible microfabrication technology for a variety of multiple layers of GC microstructures. In this study we demonstrate: (i) the optimum mixing ratio by-weight of dye and negative resist to be 1:50 (in this case, SU-8); (ii) optimized level of UV exposure needed for the dye-doped SU-8 layer to act as a sacrificial layer (1500 mJ cm⁻²); and (iii) microfabrication of a variety of thick (>250 µm) multi-layer GC and GC/SU-8 microstructures. The devices fabricated through these techniques include an accelerometer, a micromirror, a string resonator, and a microfluidic chip. (paper)