ZnSnO-based Oxide Semiconductors And Applications In Thin-Film Transistors

Recently,thin-film transistors(TFTs)based on metal-oxide semiconductors have attracted great attention due to the application potential in next-generation flat panel displays with large screen size,high frame rate,high resolution,and fully transparent flexible display.The amorphous silicon(a-Si)TFTs are commonly used in the active matrix-liquid crystal display(AMLCD)now.However,the mobility of a-Si TFTs is too low to meet the requirement of active-matrix organic light emitting diode display(AMOLED).Compared with ?-Si TFTs,metal-oxide-semiconductors-based TFTs have higher mobility,lower processing temperature,higher optical transparency,which makes metal oxide semiconductor TFTs more promising in the future to realize fully transparent flexible wearable display technology.Up to now,InGaZnO is one of the most promising candidates for the flat panel displays.However,indium element is rare in earth,and most of patents of InGaZnO TFTs are monopolized by western countries.It is of great significance for Chinese researchers to develop new metal-oxide-semiconductors materialsBased on the above discussion,this thesis mainly focus on ZnSnO-based oxide semiconductors,which have potential to replace InGaZnO.On the one hand,ZnSnO films and corresponding TFTs devices are prepared by pulsed laser deposition(PLD),and the effects of oxygen vacancy concentration on the electrical performance of TFTs are studied either.On the basis of previous study,we proposed a new structure of TFTs with a tunnel layer between channel and Drain/Source,and the electrical performance was studied.On the other hand,we fabricated memristors with Ge doped ZnSnO films as functional layer,and the resistance characteristics of ZnSnO-based semiconductors were studied.The thesis is carried out from following three parts are summarized as follows:1.ZnSnO films were prepared in different oxygen partial pressure by PLD.The relationship between oxygen pressure,oxygen vacancy concentration and electrical properties of TFTs was studied.It is found that the Vo concentration decrease at first,and then increase with oxygen partial pressure increasing.The corresponding ZnSnO TFTs were fabricated and electrical performances were characterized.The calculated threshold voltage,subthreshold swing,and density of interfacial trap states all increased with the rising of Vo concentration.However,the mobility of ZnSnO TFTs was related to Vo concentration and roughness of surface.When oxygen partial pressure is 6 Pa,the TFTs had a highest mobility of 23.6 cm2 V-1 s-1,Ion/Ioff of 106,threshold voltage of-1.5 V,and subthreshold swing of 0.65 V/decade.2.On the basis of bottom gate ZnSnO TFTs,a new TFT structure was redesigned.Ultrathin Al2O3 tunnel layers were deposited by atomic layer deposition on ZnSnO films.The thickness of tunnel layers can be controlled by growth cycles.When the thickness of tunnel layer is about 2 nm,the threshold voltage transfers from negative to positive.Besides,the mobility does not decrease significantly,which is superior to the mobility of Vo-suppressor-doped ZnSnO TFTs.3.Ge doped ZnSnO films were prepared by PLD,and corresponding ZnGeSnO memristors were prepared with ITO bottom electrode and Al top electrode.The electrical behavior was characterized.The ZnGeSnO memristors are with low resistance at original states.The resistance could be switched freely between high and low resistance states by appropriate positive or negative top electrode voltage.This work preliminarily explored the application of ZnSnO-based oxide semiconductors in memristors.