Preparation And Performance Research Of High-k Oxide Thin Film Transistors

Thin film transistors?TFT?are widely used in flat panel display technologies because of their simple structure and excellent performance.Metal oxide semiconductors are considered as the most promising semiconductor material for flat panel displays because of their outstanding physical properties.With the continuous improvement of integration level for integrated circuit,the TFT keeps getting smaller;looking for high dielectric constant materials to replace traditional silicon dioxide is a very effective way to increase the integration of integrated circuits.The way of increasing the dielectric constant instead of reducing the thickness of the insulating layer,not only can suppress leakage current,but also meet the requirement of scaling down for TFT.Now,high manufacturing costs and complex manufacturing processes are still a problem to be solved for flat panel display.It is still necessary to develop the fabrication technology of high performance TFTs with low cost and large area.Solution preparation technique?sol-gel and ink-jet printing technologies?are considered as the promising fabrication technologies of high performance TFTs with low cost and large area for the future selection.In this dissertation,the high dielectric constant ytterbium oxide thin films were prepared by solution method.The effects of different annealing temperature on the physical and electrical performances of as-deposited ytterbium oxide thin films were studied,and an indium oxide thin film transistor was fabricated based on ytterbium oxide dielectric thin film.The performance of the TFTs based on as-deposited ytterbium oxide thin films were also studied and discussed.The optimized In₂O₃/Yb₂O₃ TFT exhibits high electrical performances,including operating voltage of 3 V,field-effect mobility of 4.98cm²V^-1s^-1,on/off current ratio of¹0⁶,and subthreshold swing of 70 mV/decade,respectively.The optimized In₂O₃/Yb₂O₃ TFT also shows good dynamic switching characteristics.The inverter composed of the optimized In₂O₃/Yb₂O₃ TFT reveals excellent inverting performance;it has a gain of 10.6 and a noise margin of 1.05 V at a supply voltage of 4 V,showing its potential for the applications in multistage circuits.This experiment demonstrates the feasibility of the fabrication of ytterbium oxide thin films and the related TFTs by solution method.In addition,this dissertation researched a new method for preparation of hafnium oxide dielectric films and indium-free Zn-Sn metal oxide semiconductor films by solution method.After effectively removing the chloride ion contained in the precursor solution by the redox reaction,the quality of the prepared film was improved and the annealing temperature was reduced.The performance of the ZnSnO/HfO₂ TFT prepared by this method has been greatly improved,such as the high field-effect mobility of 13.2cm²/V^-1s^-1,the low subthreshold swing of 70 mV/dec,and the low operating voltage of 2V.Finally,the high-performance ZnSnO/HfO_x TFT is applied to a resistor-loaded inverter,which also exhibits excellent switching response performance.The inverter has a gain of11 at supply voltage of 2.5 V,and the inverter also exhibits good dynamic inverting characteristic.Through a series of experiments and analysis,it has been proved that the addition of perchloric acid solution is feasible and effective for removing chloride ions and reducing the fabrication temperature of thin films.It is speculated that this method can be also applied to fabricat other high-quality metal oxide semiconductor films or dielectric films and related devices for chlorine salts based materials.