High-Sensitivity, Skin-Attachable, and Stretchable Array of Thermo-Responsive Suspended Gate Field-Effect Transistors with Thermochromic Display

The fabrication of a skin-attachable, stretchable array of high-sensitivity temperature sensors is demonstrated. The temperature sensor consists of a single-walled carbon nanotube field-effect transistor with a suspended gate electrode of poly(N-isopropylacrylamide) (PNIPAM)-coated gold grid/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and thermochromic leuco dye. The sensor exhibits a very high sensitivity of 6.5% °C⁻¹ at temperatures between 25 and 45 °C. With increasing temperature, the suspended gate electrode bends due to the deswelling of the PNIPAM, resulting in the reduction of the air gap to increase the drain current under a constant gate voltage. At the same time, the leuco dye coated on top of the transparent gate electrode changes color to visualize changes in temperature. The 4 × 6 integrated temperature sensor array integrated using liquid metal interconnections exhibits mechanical and electrical stability under 50% biaxial stretching and allows for the spatial mapping of temperature with visual color display regardless of wrist movement while attached to the skin of the wrist. This work is expected to be widely useful in the development of skin-attachable electronics for medical and health-care monitoring.