We Create Impossible Structures in Glass

First of all, why glass? Glass has excellent dielectric properties (low conductive losses), excellent thermal properties (thermally insulating) and is potentially very low cost. The biggest issue with glass is the difficulty of shaping it with small dimensions and high aspect ratios. Until recently, there were only a few ways to make tiny structures in glass, such as wet chemical or dry plasma etching, micromachining, and embossing. Due to its inert nature and amorphous structure, the only wet chemical etch available, hydrofluoric acid (HF), is isotropic. This results in a maximum aspect ratio (depth/width) of 0.5. Dry etching is another option and can produce higher aspect ratios, up to 8. Unfortunately, both wet and dry etching of glass are slow processes (< 1 µm hour). In the last decade or so, photo-imageable glass has been developed to the point where it can be used for 2.5D glass structures. In this method, glass is exposed to UV light through a mask and then baked to convert it to a ceramic phase, yielding a high etch selectivity in HF. This method can render aspect ratios of up to 60. However, for true 3D structures not much could be achieved – until now. Using ultra-short laser pulses from a femtosecond laser we can finally start to fabricate previously impossible structures in glass.