Back-End-of-Line Compatible InSnO/ZnO Heterojunction Thin-Film Transistors With High Mobility and Excellent Stability

We examine low-temperature fabricated InSnO/ZnO (ITO/ZnO) heterojunction thin-film transistors (TFTs) with high mobility and excellent stability. The effects of ITO thickness (0, 2, 4, 6, and 8 nm) on performance of the ITO/ZnO TFTs are studied. For the devices with a 6-nm ITO layer, a field-effect mobility ( $\mu _{\mathrm{FE}}$ ) of 55.50 cm ² /Vs, a subthreshold swing (SS) of 113.22 mV/decade, a turn-on voltage ( $\text{V}_{\mathrm{ON}}$ ) of −3 V, and an on/off current ratio ( $\text{I}_{\mathrm{ON}}/\text{I}_{\mathrm{OFF}}$ ) over 10 ⁷ are obtained. Besides, the devices demonstrate excellent stability with a threshold voltage shift of 0.68 and −0.25 V under the positive and negative gate-bias stress, respectively. Operation mode of the ITO/ZnO TFTs is analyzed. The results show that potential well at ITO/ZnO heterointerface forms electronic accumulation, which is beneficial to improve the $\mu _{\mathrm{FE}}$ of the ITO/ZnO TFTs. Our work promotes applications of the oxide TFTs to back-end-of-line (BEOL) circuits.