Figure 3: Transparent TFTs transferred on polyimide foil.

(a) Transparent TFTs have been fabricated by replacing metals with transparent ITO (Scale bar, 100 μm). (b) The devices are transferred on a polyimide foil. After the transfer wrinkles are observed in the ITO layer. The wrinkles were not present in the case of Ti/Au metallization (Fig. 2b) and they are due to built-in stress in the ITO film. (c) Devices bent to 10 mm (ε=0.25%). (d) Devices bent to 6 mm (ε=0.4%). (e) Transfer characteristic (V_DS=0.1, 5 V) of a W/L=280 μm/60 μm transparent TFT, which is measured on Si, flat on polyimide after transfer and then bent to 10 and 6 mm (tensile strain parallel to the channel). Higher strain levels provoke cracks and delamination of the ITO. (f) Output characteristics for V_GS=1, 1.5, 2 V of the device shown in e. (g–i) The transfer yield is about 50% (10 devices out of 20 work after transfer). The most remarkable changes, after the transfer, are observed in the increase of the gate leakage, I_G, ((i) plot in logarithmic scale) and of the off-current, I_off, ((h) plot in logarithmic scale). Threshold voltage, V_TH, remains, instead, stable and average mobility, μ, is of about 16 cm² V⁻¹s⁻¹, which is lower than the Ti/Au metallization because of the increased contact resistance. Errors bars in the plots indicate the s.d.