User-interactive electronic skin for instantaneous pressure visualization

Abstract

Electronic skin (e-skin) presents a network of mechanically flexible sensors that can conformally wrap irregular surfaces and spatially map and quantify various stimuli 1-12 . Previous works on e-skin have focused on the optimization of pressure sensors interfaced with an electronic readout, whereas user interfaces based on a human-readable output were not explored. Here, we report the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels. In this system, organic light-emitting diodes (OLEDs) are turned on locally where the surface is touched, and the intensity of the emitted light quantifies the magnitude of the applied pressure. This work represents a system-on-plastic 4,13-17 demonstration where three distinct electronic componentsthin-film transistor, pressure sensor and OLED arrays-are monolithically integrated over large areas on a single plastic substrate. The reported e-skin may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices.Although both passive 6,8,12 and active-matrix 1,2,5,9 designs can be used for enabling the predicted user-interactive e-skins, the active-matrix design is advantageous as it minimizes signal crosstalk and thereby offers better spatial resolution and contrast, and a faster response. In the active-matrix backplane circuitry, each pixel is controlled by a thin-film transistor (TFT) that acts as a switch for addressing either current-or voltage-driven devices. Here, we incorporate the active-matrix design into the e-skin by using semiconductor-enriched nanotubes 18 as the channel material of the TFTs. Carbon nanotube networks are proven to be a promising material platform for high-performance TFTs (refs 9,17,19-21) with high current drives needed for switching OLEDs (ref. 22). A schematic structure of a pixel of the user-interactive e-skin with an integrated TFT, OLED and pressure sensor is depicted in Fig. 1a. Each pixel in the active-matrix consists of a nanotube TFT with the drain connected to the anode of an OLED. The OLED uses a simple bilayer structure 23 and the colour of the emitted light is controlled by using different emissive layer materials (details in the Methods). In this work, red, green, blue and yellow colours are demonstrated. On top of the OLEDs, a pressure-sensitive rubber 1,5,24,25 (PSR) is laminated, which is in electrical contact with the cathode (that is, top contact) of the OLED at each pixel. The top surface of the PSR is coated with a conductive silver ink to act as the ground contact. Here, the conductivity of the PSR increases by an applied pressure 1,5,24,25 in the underlying OLED turning on. As illustrated in Fig. 1b, the single-pixel circuitry is integrated into an active-matrix array. The resulting system-on-plastic provides a touch user interface, allowing the pressure profile to be...

Two-dimensional flexible nanoelectronics

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Solution‐Processed Bilayer Dielectrics for Flexible Low‐Voltage Organic Field‐Effect Transistors in Pressure‐Sensing Applications

“…Over the past decade, electronic skin (e‐skin) has been developed as a viable technology to mimic temperature, humidity, pressure, and strain sensing of human skin 1, 2, 3. As a basic part of e‐skin, pressure sensors are attracting growing attention because they can detect tiny pressure change by converting an external force to electrical or other recognized signals 4, 5.…”

Highly deformable liquid-state heterojunction sensors

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