Electronic Semiconductors, Components, Circuits, Systems C01

In this project, we work on improving the performance of organic thin-film transistors (TFTs). A central aspect is improving the carrier mobility. The highest mobilities of p‑channel organic TFTs are currently on the order of 10 cm²/Vs; those of air-stable n‑channel organic TFTs on the order of 1 cm²/Vs. Integrated circuits can in principle be fabricated using exclusively p-channel TFTs (unipolar circuits). However, complementary circuits (i.e., circuits that use p‑channel and n-channel TFTs) have the advantage of a substantially lower power consumption. Improvements in the performance of n-channel organic TFTs are thus of particular importance. We therefore collaborate with projects A01 (Bunz), A02 (Gade), A03 (Hashmi), A04 (Mastalerz) and A05 (Kivala) on the development of next-generation n-channel organic semiconductors based on N-heteropolycycles, and with projects B02 (Elstner), C06 (Zaumseil), C12 (Eggeler), C13 (Friederich) and C14 (Amirjalayer) on the development of a better understanding of the charge transport in polycrystalline thin films of organic semiconductors.

For circuits, the most important TFT-performance parameter is the transit frequency, i.e., the highest frequency at which TFTs can switch electrical signals. For most applications envisioned for organic TFTs, the transit frequency is still too low. One reason is the large contact resistance of organic TFTs; another is that organic TFTs are usually fabricated with a relatively large channel length, usually greater than 1 µm. In this project, we thus aim at a better understanding of what limits the contact resistance of organic TFTs (and at reducing it), and we plan to fabricate organic TFTs with extremely small channel lengths (≤100 nm). The goal is a substantially improved transit frequency (~100 MHz).