Low-voltage organic thin film transistors with solution processed hafnium oxide and polymer dielectrics

Low-voltage pentacene-based organic thin film transistors (OTFTs) are fabricated with solution-process hafnium oxide (HfO₂) as gate dielectric layer. The dielectric high-k HfO₂ film was deposited from the sol-gel solution prepared by dissolving HfCl₄(98%, Sigma-Aldrich) in ethanol at a proper concentration. We have investigated the effects of the insulating layer on device. As a result, the device with only HfO₂ gate dielectric exhibited a good performance with a threshold voltage of -0.88 V, a sub-threshold swing of 1.12 V/dec, and a high field-effect mobility of 1×10^-3 cm²/Vs. After employing a very thin PMMA film onto HfO₂, the performance of the devices with bilayer dielectrics shows a great improvement. The mobility of these OTFTs can be further boost up to 1.2×10^-2 cm²/Vs, and the sub-threshold swing reduced to 0.77 V/dec and the drain current on/off ratio increased almost 7 times. The PMMA insulator buffer layer can also effectively reduce gate leakage current. The results demonstrate that an appropriate polymer buffer layer is a favorable way to improve the performance of the OTFTs with good electrical stability.