Fully solution-induced high performance indium oxide thin film transistors with ZrO x high-k gate dielectrics

Abstract

Solution based deposition has been recently considered as a viable option for low-cost flexible electronics. In this context, research efforts have been increasingly focused on the development of suitable solution-processed materials for oxide based transistors. In this work, we report a fully solution synthesis route, using 2-methoxyethanol as solvent, for the preparation of In₂O₃ thin films and ZrO _x gate dielectrics, as well as the fabrication of In₂O₃-based TFTs. To verify the possible applications of ZrO _x thin films as the gate dielectric in complementary metal oxide semiconductor (CMOS) electronics, fully solution-induced In₂O₃ TFTs based on ZrO₂ dielectrics have been integrated and investigated. The devices, with an optimized annealing temperature of 300 °C, have demonstrated high electrical performance and operational stability at a low voltage of 2 V, including a high μ _sat of 4.42 cm² V^-1 s^-1, low threshold voltage of 0.31 V, threshold voltage shift of 0.15 V under positive bias stress for 7200 s, and large I _on/I _off of 7.5 × 10⁷, respectively. The as-fabricated In₂O₃/ZrO _x TFTs enable fully solution-derived oxide TFTs for potential application in portable and low-power consumption electronics.

Fig. 1. Schematic diagram of solution-derived In₂O₃ and ZrO_x thin films and In₂O₃ TFTs device fabrication.

Fig. 2. XRD patterns of ZrO_x thin films as a function of annealing temperature.

Fig. 3. AFM images of the ZrO_x thin films annealed at (a) 300 °C, (b) 400 °C, (c) 500 °C, (d) 600 °C.

Fig. 4. Optical transmittances of ZrO_x thin films annealed at different temperatures. The insets above and below display the band gap energy values of these ZrO_x films and photographs of bare glass and as-processed ZrO_x thin films annealed at various temperatures, respectively.

Fig. 5. Annealing temperature dependent refractive index (a) and fitting packing density (b) for solution-derived ZrO₂ thin films.

Fig. 6. XPS spectra of O 1s (a) and Zr 3d peaks (c) for ZrO_x thin films as a function of annealing temperature. (b) Semiquantitative analyses of the oxygen component for the corresponding ZrO_x thin films. (d) Si 2p XPS core-level spectra of Si/ZrO_x gate stacks annealed at different temperatures.

Fig. 7. (a) Areal capacitance and (b) leakage current density of the ZrO_x dielectric thin films annealed at various temperatures.

Fig. 8. (a) Schematic illustration of the bottom-gate and top-contact In₂O₃/SiO₂ TFTs. (b) and (c) Output and transfer characteristics of the In₂O₃/SiO₂TFTs.

Fig. 9. Output and transfer characteristics of the In₂O₃/ZrO_x TFTs.

Fig. 10. (a) Transfer curves of 300 °C-annealed In₂O₃/ZrO_x TFT under PBS with a VG value of 2 V for 7200 s. (b) The V_TH shift as a function of stress time. The inset shows the time dependence of ΔV_TH in the In₂O₃ TFT with an ZrO_x gate dielectric under the bias-stress of 1 V. (c) The energy band diagram of the 300 °C-annealed In₂O₃/ZrO_x TFT under PBS.