P-type Cu2O Thin Film Transistors for Active Matrix Displays: Physical Modeling and Numerical Simulation

In this paper, we present the physical modeling and numerical simulations of p-type Cu₂O TFT for the design and development of active matrix displays. In Cu₂O, the carrier transport is through copper and oxygen vacancies (<inline-formula> <tex-math notation="LaTeX">$V_{Cu}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$V_{O}$ </tex-math></inline-formula>) which are prominent defects due to their low formation energies. These defects were modeled with acceptor-like and donor-like Gaussian states. From the simulations, it was observed that the <inline-formula> <tex-math notation="LaTeX">$V_{Cu}$ </tex-math></inline-formula> significantly controls the OFF current and threshold voltage (<inline-formula> <tex-math notation="LaTeX">$V_{th}$ </tex-math></inline-formula>), while <inline-formula> <tex-math notation="LaTeX">$V_{O}$ </tex-math></inline-formula> degrades the ON current. For the analysis of device stability, both positive and negative bias stress (PBS and NBS) on Cu₂O TFT was investigated with dielectric/channel interface traps in simulations. Under NBS, a significant negative shift in the <inline-formula> <tex-math notation="LaTeX">$V_{th}$ </tex-math></inline-formula> was observed due to hole trapping from channel to dielectrics. On the contrary, during PBS, a small shift in <inline-formula> <tex-math notation="LaTeX">$V_{th}$ </tex-math></inline-formula> was observed with significant degradation in sub-threshold swing (SS) due to the deficiency of free electron and the presence of additional defects generated in Cu₂O channel as stress time increase. In addition to this effect of increase in Cu₂O channel thickness were studied where a significant amount of shift in <inline-formula> <tex-math notation="LaTeX">$V_{th}$ </tex-math></inline-formula> from −7.1 V to −6.1 V was observed as the thickness increased from 45 nm to 65 nm. Finally, the dynamic performance of Cu₂O was evaluated and found to be better for higher channel thickness in terms of holding of the output voltage. From these observations, the p-type Cu₂O TFT shall be considered for the stable and efficient pixel circuit of active matrix displays such as AMLCD.