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

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 (N _h) of around 1 × 10¹⁸ cm⁻³ and Hall mobilities (μ _Hall) 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 μ _Hall. 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 (V _T) 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 (μ _sat) were in the range of 0.12 and 1.32 cm² V⁻¹ s⁻¹. The current on/off ratio (I _ON/I _OFF) was in the order of 10², approximately. The large values of the interface trap density (D _IT) contributed to the high I _OFF and the low I _ON/I _OFF of the TFTs. (paper)