Evaluation of Y2O3 gate insulators for a-IGZO thin film transistors

In this work, Y 2 O 3 was evaluated as a gate insulator for thin film transistors fabricated using an amorphous InGaZnO 4 (a-IGZO) active layer. The properties of Y 2 O 3 were examined as a function of various processing parameters including plasma power, chamber gas conditions, and working pressure. The leakage current density for the Y 2 O 3 film prepared under the optimum conditions was observed to be -3.5 x 10 ―9 A/cm 2 at an electric field of 1 MV/cm. The RMS roughness of the Y 2 O 3 film was improved from 1.6 nm to 0.8 nm by employing an ALD (Atomic Layer Deposition) HfO 2 underlayer. Using the optimized Y 2 0 3 deposition conditions, thin film transistors (TFTs) were fabricated on a glass substrate. The important TFT device parameters of the on/off current ratio, sub-threshold swing, threshold voltage, and electric field mobility were measured to be 7.0 x 10 7 , 0.18 V/dec, 1.1 V, and 3.3 cm 2 /Vs, respectively. The stacked insulator consisting of Y 2 O 3 /HfO 2 was highly effective in enhancing the device properties.