Juergen Steiger

High performance, stable solution-processed thin-film transistors

Most current active matrix LCDs use amorphous silicon (a-Si) thin-film transistors (TFTs) as pixel switching devices. A great disadvantage of a-Si is the limited mobility of 1cm2/Vs (volt second), which is insufficient for advanced display technologies such as 8K ultra high-definition, large-size TVs, and organic light emitting diode (OLED) displays. One promising alternative is low-temperature polysilicon, which exhibits mobility values of 100cm2/Vs. However, it is not suitable for large area fabrication because of its non-uniform crystal growth, which is why upscaling is limited.1 Solution processed metal-oxide semiconductors are good candidates to replace a-Si-based TFTs as switching devices for display applications and for large area deposition because of their high mobility, transparency, uniformity, and low manufacturing costs.2, 3 There are two specific advantages of solution-based materials, the possibility to combine different precursor systems and the direct printing of transparent amorphous oxide semiconductor (TAOS) structures (see Figure 1). However, the reliability of such metal-oxide based semiconductors is not yet satisfactory. We are working on solution processable materials for TFTs, such as semiconductor, passivation, and dielectric, which allow an increase in performance compared to a-Si, a significant lowering of process costs, and large area deposition compared to sputtering.4 This is achieved by using metal-oxide-based materials5, 6 that are deposited from solution and processed fully under ambient conditions. We prepared a stable TFT under atmospheric conditions with iXsenic S, a solution-processable product from Evonik Industries. We used iXsenic P, a solution-based hybrid polymer, as Figure 1. Transfer from state-of-the-art, vacuum-based deposition methods such as chemical vapor deposition (CVD or sputter) to advanced coating technologies in two steps. In the first step, coating technology will be combined with existing patterning technology. In the second step, photolithography can be omitted completely by means of direct printing. TAOS: Transparent amorphous oxide semiconductor.