Fully patterned p-channel SnO TFTs using transparent Al2O3 gate insulator and ITO as source and drain contacts

Abstract

SnO p-type was used as active layer to fabricate thin film transistors (TFTs) through photolithography and dry etching processes. The SnO p-type thin films (25 nm) were deposited by DC reactive sputtering with variable oxygen (O2) flow rate to then be annealed in air at 250 ◦C. Al2O3 gate dielectric (15 nm) was deposited by atomic layer deposition. Hall measurements showed p-type carrier concentration (Nh) of around 1 × 1018 cm−3 and Hall mobilities (μHall) between 0.35 and 2.64 cm2 V−1 s−1, depending on the O2 flow rate during deposition. The hole transport was dominated by variable-range hopping conduction. A change in the preferred crystalline orientation in the SnO films from (101) to (110) was associated with the increase in μHall. In addition, Raman vibrational modes at 110 and 209 cm−1 of polycrystalline SnO films showed certain dependence with the grain orientation. The SnO-based TFTs showed p-type behavior with low threshold voltages (VT) and low sub threshold swing (SS) in the range from 1.76 to 3.50 V and 1.63 to 3.24 V/dec., respectively. The TFTs mobilities in the saturation regime (μsat) were in the range of 0.12 and 1.32 cm2 V−1 s−1. The current on/off ratio (ION/IOFF) was in the order of 102, approximately. The large values of the interface trap density (DIT) contributed to the high IOFF and the low ION/IOFF of the TFTs.