Top-gate In–Al–Zn–O thin film transistor based on organic poly(methyl methacrylate) dielectric layer

In this paper, we report a top-gate amorphous In–Al–Zn–O (a-IAZO) thin film transistor (TFT) based on dip-coated poly(methyl methacrylate) (PMMA) dielectric layer and investigate PMMA thickness influence on a-IAZO TFT performance. A thinner PMMA gate dielectric can cumulate more charges per unit area and induce more electron carriers, resulting in increasing of on-state current of TFT. Moreover, it is found that a TFT with the thinner PMMA gate dielectric contains less trap states at a-IAZO/PMMA interface due to decreased surface roughness with thinner PMMA dielectric, which is essential for reducing the capture of electron carriers in the process of electron transport. Therefore, the on/off current ratio (I_on/off), saturated mobility (μ_sat) and subthreshold gate swing (SS) of device improved with the PMMA thickness decreased from 610 to 280 nm. Furthermore, experimental results show that the PMMA thickness plays an important role on controlling the threshold voltage (V_th) and adjusting the operating mode of device, thus influencing on the power dissipation. Overall, the TFT with a 390-nm-thick PMMA dielectric layer exhibits the adequate operating mode (enhancement mode) and the high electrical performance (a high μ_sat of 21.42 cm²/Vs, a small SS of 0.46 V/decade, a close-to-zero V_th of 0.12 V, and I_on/off of more than10⁴).