Metal Oxide Thin-Film Transistors on Plastic Substrates for Entirely Flexible Analog Sensor Systems

Creating a reliable connection between our physical and the digital worlds by unobtrusively collecting data from the environment is a key to enable efficient Industry 4.0 processes or personalized healthcare solutions. In this context, truly unobtrusive sensor systems cannot be bulky and rigid, but must be lightweight, biocompatible, and have to adapt to the movement of artificial and organic surfaces. This challenge can be addressed by thin-film devices fabricated on large-area plastic substrates. However, the properties of polymeric substrates impose certain limitations such as a limited feature size and temperature resistivity influencing the fabrication and performance of the devices. Hence, the realization of unobtrusive systems requires the simultaneous optimization of mechanical and electrical device properties. Here the design and fabrication of low temperature processed amorphous Indium-Gallium-Zinc-Oxide (IGZO) based thin-film transistors (TFTs) on free-standing plastic foils is presented. The electrical DC and AC performance of such devices outperforms many other flexible technologies while the TFTs also exhibit exceptional mechanical properties. This is e.g. demonstrated by fully operational devices wrapped around a human hair. Furthermore, it will be discussed how innovative device structures, simulations, and circuit topologies can be used to realize integrated IGZO TFT based analog circuits such as amplifiers, buffers. Such circuits are essential for the onsite amplification of signals from flexible sensors. Finally, it will be shown how flexible electronics and sensors are integrated, to realize entirely flexible, front-end conditioned sensor systems for the next generation of wearables.