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

Abstract

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 ( $V_{Cu}$ and $V_{O}$ ) 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 $V_{Cu}$ significantly controls the OFF current and threshold voltage ( $V_{th}$ ), while $V_{O}$ 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 $V_{th}$ was observed due to hole trapping from channel to dielectrics. On the contrary, during PBS, a small shift in $V_{th}$ 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 $V_{th}$ 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.

Keywords

• Cuprous oxide (Cu₂O)
• density of states (DOS)
• thin film transistors (TFTs)
• negative bias stress (NBS)
• positive bias stress (PBS)
• and dynamic response