The inversion field-effect transistor is the basic device of modern microelectronics and is nowadays used more than a billion times on every state-of-the-art computer chip. In the future, this rigid technology will be complemented by flexible electronics produced at extremely low cost. Organic field-effect transistors have the potential to be the basic device for flexible electronics, but still need much improvement. In particular, despite more than 20 years of research, organic inversion mode transistors have not been reported so far. Here we discuss the first realization of organic inversion transistors and the optimization of organic depletion transistors by our organic doping technology. We show that the transistor parameters—in particular, the threshold voltage and the ON/OFF ratio—can be controlled by the doping concentration and the thickness of the transistor channel. Injection of minority carriers into the doped transistor channel is achieved by doped contacts, which allows forming an inversion layer.

No abstract

We present an optimized approach for the deposition of Al2O3 (as a model secondary material) coating into high aspect ratio (≈180) anodic TiO2 nanotube layers using the atomic layer deposition (ALD) process. In order to study the influence of the diffusion of the Al2O3 precursors on the resulting coating thickness, ALD processes with different exposure times (i.e., 0.5, 2, 5, and 10 s) of the trimethylaluminum (TMA) precursor were performed. Uniform coating of the nanotube interiors was achieved with longer exposure times (5 and 10 s), as verified by detailed scanning electron microscopy analysis. Quartz crystal microbalance measurements were used to monitor the deposition process and its particular features due to the tube diameter gradient. Finally, theoretical calculations were performed to calculate the minimum precursor exposure time to attain uniform coating. Theoretical values on the diffusion regime matched with the experimental results and helped to obtain valuable information for further optimization of ALD coating processes. The presented approach provides a straightforward solution toward the development of many novel devices, based on a high surface area interface between TiO2 nanotubes and a secondary material (such as Al2O3).

The thermal atomic layer deposition of TiO2 from Cp*Ti(OMe)3 and ozone was studied in a 300 mm wafer reactor by quadrupole mass spectrometry (QMS). The deposited thin films were analyzed by X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), grazing incident X-ray diffraction, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The XRR and XPS measurements revealed that nearly stoichiometric TiO2 films were grown in a self-limiting growth mode. The growth per cycle increased from 0.22 Å at 235 °C to 0.29 Å at 330 °C. Films deposited on titanium nitride showed an anatase crystal structure, while films deposited on ruthenium crystallized in the rutile phase. The ToF-SIMS analysis indicated that the carbon contamination reduced to very low levels at a deposition temperature of 295 °C. The QMS studies revealed the release of MeOH during the precursor pulse. CO2 and H2O were released during the ozone pulse at a process pressure of 7 mbar. At a pressure of 3 × 10−3 mbar, the release of the Cp* ligand and the remaining OMe ligands during the ozone pulse could be observed. It was demonstrated that QMS studies can be used in a 300 mm reactor at very low pressures to study the process chemistry.