Printed capacitive touch sensors embedded in organic coatings on sheet steel

We present the first realization of printed capacitive touch buttons and touch pads integrated into the organic coatings on sheet steel. Enormous progress has been made in recent years in the field of printed electronics mostly on flexible substrates. Through the development of nanoparticle and polymer based conductive inks which can be cured at temperatures below 200°C, printing electronic structures (like organic transistors and OLEDs) on a variety of plastic substrates are possible today. In contrast to these substrates, sheet steel features a comparatively rough surface (with roughnesses in the order of ≈ 0.5 μm – 1μm) which impedes the realization of embedded electronics. Furthermore, spurious capacitances are large due to the small coating thickness (≈10 μm), i.e., the low distance between conductor and conductive substrate. In this contribution, the influence of top coat and electrode thickness (which can be neglected in traditional capacitive sensors) on touch sensor sensitivity is examined and design recommendations are derived.