The optical solution relies on the detection by organic photodetectors of the reflected infra-red light emitted by IR-LEDs directly mounted on a flex circuit, as shown in Figure 3. For this purpose, the organic semiconductor materials can be tuned to operate both in visible and near infra-red bands. Being very thin and easy to glue to other substrates such as paper, these new sensors can easily turn plastic and paper into interactive surfaces for merchandising and smart packaging solutions or to detect nearby motion. Another use case for such optical sensors is to integrate NIR emitting LEDs and organic photodiodes at the periphery of a surface so that any object left on the surface can be spotted through the detection of light path occlusion – see Figure 4. Such applications are under development for industrial products and multi-touch user interfaces and displays.
Fig. 3: Flexible proximity detection and gesture detection by
organic photodiodes (Isorg)
Because flexible and printed electronics foil sensors are easy to glue, they can easily be fitted to existing equipment. For example, Isorg is investigating the use of optical sensors for spatial spectroscopy as an in-line process control for the pharmaceutical industry. These sensors could be stuck to the windows of existing equipment. The same would apply for temperature sensor arrays used in power distribution appliances (by gluing the sensing plastic foil directly on the equipment door). Object detection sensors could find their way in logistics.
All these new developments require the cooperation of new players from the printed electronics and conventional electronics industries. System-on-foil approaches call for new substrates (PET, PEN), new attach materials (low temperature conductive glue), new conductive materials (printable copper and silver inks, TCO Transparent Conductive Organic materials) as well as new assembly and inspection equipment (pick-and-place machines, visual inspection, oven).