Hygroscopic Nature of Solution Processed Al₂O₃ Thin Film Dielectric and Impact on Electrical Characteristics

Metal oxides are a good candidate for gate dielectrics because of their high dielectric constant and low leakage current. Solution deposition is a favorable method for thin film fabrication due to its low cost and high throughput. Here, we compare the property and stability of solution-processed Al₂O₃ and ZrO₂ films. Fourier transform infrared spectroscopy (FTIR) and electrical characterization reveal that Al₂O₃ absorbs moisture from air, while ZrO₂ remains stable with no moisture gain. This conclusion is established by comparing Al₂O₃, ZrO₂, and bilayers of Al₂O₃/ZrO₂ and ZrO₂/Al₂O₃. FTIR spectra show increased intensity in the water -OH region (3700-2500 cm^-1) when Al₂O₃ is exposed to air or purposely soaked in water. The change in surface contact potential indicates that the adsorbed water molecules’ dipoles point away from the surface. Effects of the moisture gain on electrical characteristics are studied with metal-insulator-metal capacitors and field effect transistors. Absorption of water in Al₂O₃ results in higher capacitance and dissipation at low frequencies and show a counter-clockwise hysteresis in transistor drain current vs. gate voltage curves.