Figure 13.

Liquid-gated In₂O₃ FET-based conformal biosensors. (a) Schematic illustration of the flexible biosensor fabrication procedure. Glass substrates were coated with a thin film of PI. Next, In₂O₃ thin films were deposited over the PI via an aqueous solution-phase spin-coating procedure. The In₂O₃ thin films were then annealed at 250 °C. Interdigitating Au/Cr electrodes were patterned by photolithography. The PI films with In₂O₃ FET arrays were delaminated from the underlying glass substrates and floated in water to unroll the films. A synthetic PDMS skin replica was prepared. Thin-film, In₂O₃ FET sensors were transferred to artificial PDMS skin samples. Ultrathin PI films easily contact uneven artificial skin surfaces. (b) Conceptual images of conformally contact devices on an artificial eye for glucose sensing in tears are shown. Thin-film sensors remained in contact with the skin even during tension and relaxation. (c,d) Device performance of thin-film In₂O₃ FETs on rigid substrates and flexible artificial PDMS skin substrates is shown. After the transfer of In₂O₃ FETs to the skin replica, the devices had similar performance under liquid gating. Low voltage driving and good pinch-off characteristics were observed. Reprinted with permission from Ref. [117]. Copyright 2015 American Chemical Society.