## 3 Results  
### Electrical Characterization  
Figure 2 reports the typical output and transfer characteristic curves of the fabricated device on the different kinds of substrate mentioned in the Materials and Methods section. Polyethylene terephthalate (PET) has been considered for its high transparency as a conventional substrate for initial process setup and optimization. A standard thickness of 175 \(\upmu\)m was considered, thus giving a significant flexibility to fabricated devices. A total number of 50 OFETs were fabricated and tested in five different batches, with a process reliability of 98% (one device in 50 short-circuited). Typical output and transfer characteristic curves are reported in Figure 2a,b, respectively. Devices can operate at gate-to-source (V\({}_{\text{GS}}\)) and drain-to-source (V\({}_{\text{DS}}\)) not exceeding 3 V in absolute value, with a threshold voltage around 0 V. From the output characteristic curves, it is possible to observe that a good current stability in saturation regime has been obtained, as well as a significant field-effect current modulation. From the linear regime, no significant contact resistance effects can be observed. These elements suggest that ideal charge carrier injection conditions have been obtained, as well as the ideal insulator-semiconductor interface. This is also confirmed by the negligible hysteresis that can be observed from transfer characteristic curves, both in linear and saturation regime. Interestingly enough, the gate-to-source current (I\({}_{\text{GS}}\), from now on leakage current) is in the range of 10\({}^{-10}\) A, thus demonstrating that a very good insulation of the gate electrode was obtained with a Parylene C layer thin enough (around 250 nm) to ensure the capacitance per unit are suitable for low-voltage operation. The sub-threshold current, which mainly depends on leakage current, is therefore in the same order of magnitude; this could be further reduced by decreasing the gate dielectric thickness in order to enhance gate coupling, but this may affect the process reliability and leakage current. Nonetheless, an on/off current ratio of 104 is obtained, although a limited aspect ratio was designed. The assessed fabrication process was then transferred onto ultra-conformable, 700-nm-thick Parylene C substrates, thus obtaining the thinnest, all-organic transparent OFET reported in the literature to the best of our knowledge. According to the procedure described in [PERSON] et al., [11] Parylene C was deposited over 175-\(\upmu\)m-thick PET carrier substrates, previously coated with a soap solution. The amphoteric molecules of the soap reduce the adhesion of Parylene C to substrates, thus making its mechanical peel-off possible in dry conditions after the fabrication process is completed. This property made the transfer of the substrate from the carrier substrate to the final support easier than wet peel-off and recovery from the surface of the liquid, and also ensured the absence of solvent residues. Thirty devices were fabricated in this configuration on two different batches; in this case, only two devices (one per batch) were not functioning, thus maintaining the reliability of the process at above 93%. Representative characteristic curves, shown in Figure 2c,d, show that the overall electrical characteristics are comparable to those obtained over standard PET substrates. A slightly larger (but still negligible) hysteresis is noticeable; it is also qualitatively evident that mobility is slightly lower than those obtained on PET, as channel conductance (the slope of the linear regime in output characteristic curves) is lower. These results may be justified by the larger roughness of the Parylene C substrate, due to the non-perfect uniformity of the amphoteric molecule layer deposited on the carrier substrate.