Development and characterization of flexible and stretchable substrates with integrated sensors

Stretchable electronics are already affected by mechanical stresses due to their application. These electronics must be designed accordingly and securely anchored in the substrate material through a suitable manufacturing process to follow these expansions. For this purpose, a transfer process from meandering microstructures to extra soft silicone is chosen. The bond between both is achieved by a special linker molecule. If further components, like sensor chips, are integrated into such stretchable systems, particular attention must be paid to the load on the chip, its electrical connections and the intersection from chip to substrate. Due to a cover layer of silicone on the chip, on the one hand, the stress on this intersection can be reduced and on the other hand, the chip can be protected from being pushed out of the substrate and against environmental influences. The chips themselves have to be flexible to adapt to the externally given deformations. Therefore, chips are thinned by grinding processes to a few tens of microns and thus become flexible. But strains of the overall system still lead to mechanical stress in the chip, which can cause strong signal changes of the sensor output values. Such effects can be eliminated by optimizing the chip geometry or stacking of two identical sensors and applying an appropriate algorithm. Both approaches are demonstrated on capacitive CMOS pressure sensors. The algorithm of the second approach compares the stress-dependent measuring values with a stressless sensor output value and creates a compensation equation out of this. Thus, not only mechanical stress due to elongation of the entire system, but also any undesired influences on the sensor output values can be compensated. An application as an artificial skin points out further challenges in integrating stretchable electronics and sensor chips into systems