Title : Fabrication of multilayer high-? dielectric thin films using deep ultraviolet annealing approach
A photochemical activation method for a solution-processed multi-layer metal oxide semiconductors is proposed in this project for high performance thin film transistors (TFTs) applications. This ultra-fast, simple and cost effective annealing method utilizes ultraviolet light of sufficient energy to be absorbed by the transparent metal oxide layer and provides the sufficient energy for sol-gel condensation in ambient air. On the other hand, the deployment of multi-layer gate dielectric configuration is desirable as it improves the capacitance between the gate electrode and the channel layer, which enhances the subthreshold slope and reduces the operating voltage. Hence, configuration of both single and multilayer high-k gate dielectric will be used to estimate the performance of solution-processed metal oxide thin films with deep UV-annealing technique. The performance of the fabricated metal oxide capacitors was optimized according to the number and order of dielectric layers in four different multilayers configurations: a) thin films of pure yttrium oxide Y2O3, b) pure hafnium oxide HfO2, c) alternating layers of HfO2/Y2O3 (HfO2 at the bottom) and d) Y2O3/HfO2 (Y2O3 at the bottom). The electrical and optical analysis for various thin films were investigated to assess the performance of the devices. We have found that the average transmittance of 10 layers of Y2O3 film was over 98% in the visible range while it decreases to 75% for HfO2 films within the same range. However, for the other two dielectric films that were prepared alternately between Y2O3 and HfO2 layers, the transmittance was above 90% for HfO2/Y2O3 and around 85% for Y2O3/HfO2. The electrical properties of films were analyzed by capacitance-voltage (C-V) and current -voltage (I-V) measurements. It was found that the dielectric films with alternative configuration of HfO2/Y2O3 yielded the lowest leakage current 1.49 10-9A at an applied voltage of 1 volt and had a dielectric constant of 9.22 at 100 KHz. This provides particular and compelling possibilities in constituting low-temperature process for applications where the thermal budget becomes a crucial necessity.