All printed smart sensor paves way for touchless keyboards

In a study published in Advanced Materials, a team led by Martin Zirkl at the Institute of Surface Technologies and Photonics in Weiz, have focused on developing an easy to manufacture smart sensor. The device was printed from only five organic links – a polymer sensor, a conductive polymer, a conductive carbon paste, a polymer electrolyte and a photoresist polymer. To produce an integrated sensor, transistor and display on the same flexible substrate, a mixture of screen printing and inkjet printing was used. According to Zirkl, the sensor combines both piezoelectric and pyroelectric qualities, so changes in temperature or pressure generate charges which give rise to a voltage. This voltage controls a transistor which amplifies the sensor signal and this response is then outputted on a flexible electrochromic display. The test unit that the researchers produced consisted of multiple sensor spots, linked up to a numeric display via a transistor. The piezoelectric sensing abilities were tested by applying pressure on the sensor spots, and the pyroelectric properties were tested both by shining a laser pointer onto a sensor spot and by moving a finger in front of the sensor spots. All three of these stimuli correctly activated the display. Zirkl discovered that the pyroelectric sensor could even detect simple gestures and could sense heat from the human body at distances up to 20cm. A similar sensor network with the same functionality has also been developed, but using a more traditional manufacturing approach - spin on processes and physical vapour deposition. However, when comparing the performance of the two sensor arrays, it was found that the printed sensor performed even better than the traditionally manufactured device.