Sol-Gel PMMA-ZrO₂ Hybrid Layers as Gate Dielectric for Low-Temperature ZnO-Based Thin-Film Transistors

We report a simple sol-gel process for the deposition of poly(methyl methacrylate) (PMMA)-ZrO₂ organic-inorganic hybrid films at low temperature and studied their properties as a function of the molar ratios of the precursors in the hybrid sol-gel solution, which included zirconium propoxide as the inorganic (zirconia) source, methyl methacrylate as the organic source, and 3-trimethoxy-silyl-propyl-methacrylate (TMSPM) as the coupling agent to enhance the compatibility between the organic and inorganic phases. The hybrid thin-film deposition was done on glass slide substrates by the dip-coating method. After deposition, the films were heat-treated at 100 °C for 24 h. The analysis of the hybrid films included Fourier transform infrared spectroscopy to identify their chemical groups and thermogravimetric analysis to determine the content of their organic and inorganic components. In addition, capacitance-voltage (C-V) and current-voltage (I-V) curves in metal-insulator-metal structures, using gold as metal contacts, were measured to find the dielectric constant and leakage current of the PMMA-ZrO₂ hybrid films. Finally, because of their adequate dielectric characteristics, single hybrid layers were deposited on indium tin oxide-coated glass substrates and were tested as gate dielectric in thin-film transistors (TFTs), using sputtered ZnO layers as the semiconductor active channel. We measured the output electrical response and transfer characteristics of these hybrid dielectric gate-based devices and determined their main electrical parameters as a function of the TMSPM content in the hybrid dielectric gate layer. The better TFT electrical behavior presents field effect mobility of 0.48 cm²/V s, low threshold voltage of 3.3 V, and on/off current ratio of 10⁵, and it was obtained by using PMMA-ZrO₂ with 0.3 TMSPM content as the gate dielectric layer. The values obtained for the electrical parameters show that PMMA-ZrO₂ hybrid films are quite suitable for dielectric gate applications in TFTs.