Evidence for Pseudocapacitance and Faradaic Charge Transfer in High-Mobility Thin-Film Transistors with Solution-Processed Oxide Dielectrics

In developing low-power electronics, low-voltage transistors have been intensively investigated. One of the most important findings is that some high-k oxide gate dielectrics can lead to remarkable enhancement of apparent mobility in thin-film transistors (TFTs), which is not clearly understood. Here, we investigate InO_x TFTs with solution-processed AlO_x dielectrics. At very low frequencies (<1 Hz), the AlO_x films feature strong voltage-dependent capacitance. Also, cyclic voltammograms show clear features of surface-controlled Faradaic charge transfer. The two independent experiments both point to the formation of pseudocapacitance, which is similar to the mechanism behind some supercapacitors. A physical model including charge transfer is established to describe ion distribution. The charge transfer is probably related to residual hydrogens, as revealed by secondary-ion mass spectroscopy. The results provide direct evidence of the formation of pseudocapacitance in TFTs with high apparent mobilities and advance the understanding of mechanisms, measurements, and applications of such TFTs for low-power electronics.