Closely coupled micro coils with integrated flux guidance: Fabrication technology and application to proximity and magnetoelastic force sensors

A complete process technology is introduced, allowing the integrated fabrication of micro coils in transformer configurations for micro sensors. The technology makes use of UV-depth lithography, electroplating of coil conductors and soft magnetic core structures, and SU8-dielectric for embedding and planarization. It is pointed out that SU8 is especially suitable as an embedding material due to its high aspect ratio patterning capability and excellent planarization properties. Based on these properties, a novel process flow of subsequent formation of the core galvanoform becomes possible, sparing cost and time consuming dry etching of dielectric layers. The technology´s applicability is demonstrated on inductively coupled transformer sensors for distance and magnetoelastic force and torque measurements. The optimized distance sensor provides sub-micron resolution and is capable of measuring distances up to 3 mm.