**4.2 Microfabrication of PTFE**

PTFE microfabrication is difficult to achieve. It is impossible to fabricate this material through wet etching with chemicals (acids and alkali) used in numerous microfabrication techniques, such as lithography, because of its excellent chemical resistance. Additionally, when the temperature is increased above the melting point of PTFE (327°C), the viscosity becomes too high for moulding. Moreover, laser ablation, which has been widely used in recent years as an effective tool for direct microfabrication, is also difficult. Because the first absorption band of PTFE is near 160 nm, where little light is absorbed by the UV to infrared (IR) domain, ablation processing using a laser with this domain is not possible. Most laser processing of PTFE is not laser ablation but rather thermal processing, which causes a deformation in structure surfaces. Therefore, lasers with narrower wavelengths, such as vacuum ultraviolet (VUV) pulsed-lasers or ultrashort pulsed-lasers, are used for microfabrication of PTFE. However, the aspect ratio of the structures that can be fabricated is very small, generally <1. For these reasons, laser ablation was developed, replacing lasers with SR light.
