Two- and three-dimensional microcoil fabrication process for three-axis magnetic sensors on flexible substrates

Abstract

This work presents a fabrication process validation for planar and 3D microcoils (microsolenoids) as three-axis magnetic sensors. The devices are elaborated on flexible substrates (Kapton ® and Peek ®) to allow its location as close as possible to the surface to be characterized. The fabrication process is based on copper micromoulding. For planar microcoils, the process implements only one step of micromoulding: photolithography of a 18 μm thick photoresist and copper growth by electrodeposition through the patterned photoresist. Matrices of 1–80 turns planar microcoils with an external size of less than 2 mm, a thickness of 5–15 μm, a width of 5–20 μm and 5–10 μm track spacing have been realized. For microsolenoids, the process, more original, implements only two steps of micromoulding. The second one uses a 3D photolithography process of a 18 μm thick photoresist and a copper electrodeposition with an overflow technique. The fabricated microsolenoids are comprised of 10 or 13 wires whose sizes are 30 μm in length, 18 μm in height and 8 or 10 μm in width and spacing. The electrical tests show high values of inductance for planar devices (up to 1 μH) and values of about 1 nH for microsolenoids. For both types of devices the Q-factors are about 20.