OFES e-Skin

The skin is our largest organ; it is a gateway between the brain and the rest of the world. The human skin consists of an integrated, stretchable network of sensors for detection of tactile and thermal stimuli, allowing us to move within our environment safely and effectively. Now imagine a device, an electronic skin (e-skin) that perfectly conforms to the human skin and could communicate whats going on outside and inside your body. It might inform surgeons, provide alerts when your body is about to fall ill, or even diagnose diseases inside another human being, simply through the sense of touch and temperature. Significant progress in the development and advancement of e-skin has been achieved in recent years, thus paving the way for applications like robots with soft grippers and all round perception, wearable and textile electronics such as multi-sensitive gloves for healthcare as well as free-form objects of variable formats with smart, interactive and sensitive surfaces. The majority of the recently developed sensor arrays are electrically controlled by passive matrix addressing, which cannot prevent low contrast ratio and crosstalk effect. Therefore, active circuitry is inevitable to unambiguously address a large number of sensors. In most solutions this is realized by integrating in each pixel an addressing transistor to the sensor which generally requires complex and expensive manufacturing processes. In the project (OFES e-Skin) a multi-functional e-skin based on a network of organic field effect sensors on ultrathin and thus conformable substrates will be developed by using innovative concepts, geometries and materials. The key-point in this project is the integration of organic transistors and polymer sensors in a field-effect sensor device for simultaneous detection of pressure, strain and temperature thus forming the basic unit of a sensor network with high integration density and signal-to-noise ratio due to a minimization of the area consumption and the number of wirings and crossings. A second, optionally floating, gate is used for addressing the individual pixels and poling of the ferroelectric thus enabling a cross-talk free active-matrix sensor network. Additionally, the second gate architecture offers the opportunity to harvest electrical energy. The combination of energy harvesting and sensing represents a breakthrough in self- sustaining sensor skins. A large-area multi-modal e-skin with simultaneous energy harvesting and sensing functionality has not been realized so far. Finally, the flexible field-effect sensor matrix should be used as smart sensor patch (placed on the humans left breast) for simultaneously detecting ECG parameters such as (respiratory rate, heart rate and their variability) and temperature of the skin surface. A precise detection of respiration and heart rate is substantial for medical diagnostics.

Health is a very precious commodity, as we experience every day and especially in these times shaken by a pandemic. Continuous recording of health status through diagnostic techniques that combine high wearing comfort with high reliability, accuracy and cost-effectiveness is therefore very desirable. In this context, an ultraflexible solution of a wireless medical patches for continuous monitoring of vital parameters was developed within this project. The ultraflexibility is due to the very low overall thickness (only 2.5 m in total, 1/3 of a conventional cling film) of the sensors on a substrate only 1 m thick, and it guarantees high wearing comfort, high sensitivity, and superior component reliability. Our health patch solution not only includes this radically reduced layer thickness, but also new material combinations, novel device concepts and new integration principles (multi-stack transducers on 3D curved surfaces). The compact wireless healthcare monitoring device with high wearing comfort is capable of early detection of lifestyle-related diseases such as heart disease, signs of stress state, sleep apnea syndrome and the like and could pave the way towards imperceptible point-of-care diagnostics at home. Besides vital parameter detection these sensors can also be used to produce electrical energy (by converting (bio-) mechanical energy, such as body movement, in electrical energy). An energy harvesting device based on these ultrathin sensors and combined with ultraflexible electronic (some parts) and storage elements was realized. A second task in this project was the development of a sensor network with organic transistors for addressing the individual pixels to enable a cross-talk free active-matrix sensor network. Additionally innovative sensor devices for simultaneous detection of pressure, strain and temperature were investigated. Since the presented ultrathin energy harvesting and sensing devices (sensor network) can be conformably attached to various objects or to the human body, opportunities for many potential 'self-sustaining' applications that range from robotics, artificial e-skin and wearable electronics to biomedical applications are opened up.