Facile fabrication of true three-dimensional microcoils inside fused silica by a femtosecond laser

This paper presents a facile method for the fabrication of on-chip three-dimensional (3D) microcoils inside fused silica. The main fabrication process involves two steps: (1) creating 3D helical microchannels inside fused silica using an improved femtosecond laser irradiation assisted by chemical etching (FLICE) technology and (2) conductive treatment by injecting metal gallium into the helical microchannels. The high aspect ratio 3D helical microcoil was prepared inside fused silica with a diameter of 100 mu m, a length of 880 mu m and a pitch of coil of 44 mu m. The method is flexible to fabricate microcoils inside fused silica with arbitrary geometry configurations and different coil properties. This type of microcoils can be easily integrated into 'lab on a chip' (LOC) platform inside fused silica substrate.