High Performance Thin Film Transistors Based On New Semiconductor Materials And Hot-pressing Sintering Targets

Since the 21 st century,the metal oxide thin film transistors(MO-TFT)as the backplane of flat panel display,has developed rapidly,owning to its low cost,high mobility and large area uniformity.Channel materials plays a decisive role at TFT,which magnetron sputtering method is the most widely used,high-quality target for the sputtering film quality is particularly important.Magnetron sputtering is the most wide deposition method for channel layer,and high quality target is the key factors to improve the quality of sputtering film.With the progress of display technology to high-definition,large-scale,develop new oxide semiconductor layer material,preparae oxide target,and thereby fabricate high mobility,outstanding stability TFT is urgent priority.In this paper,using Indium-zinc-oxide(IZO)target as the starting point,the oxide targets were prepared by hot-pressing sintering methods,using mixed ZnO and In2O3(20,50,63 wt.%)as raw materials,then fabricated TFT by magnetron sputtering with above sintered target.Study effect of sintering process or the In2O3 content on IZO targets and TFT,and improve the performance of IZO TFT through process optimization.The target performance of 20 wt.% In2O3 indicates that increased the sintering temperature and prolonged the sintering time is beneficial to improve the density of the target.It was showed that proper high density target can improve the performance of the TFT.It could be seen clearly post-annealing,adjustment of channel layer thickness and sputtering with amount of oxygen could optimize the performance of 50 wt.% In2O3 content TFT,to achieve the maximum mobility of 36.40 cm2/(V.s-1).In the wake of increase of In2O3 content,IZO target has entered the sintering stage with sintering temperature of 900 oC,the density at low density level and gradually reduced,but the corresponding TFT' mobility increased.In2O3 content was too high could lead to more carrier concentration,Von serious negative drift,so 50% In2O3 TFT owned the best TFT performance,and made annealing temperature down to 300 oC for requirements of ultra-high-definition display,also verified the feasibility of preparing high mobility TFT with low density targets.The TFT prepared by above targets have good semiconductor properties,uniformity and stability,and overcome some of the inherent limitations of IZO,and realize the integration of target and TFT process,which opens up a new thinking for MO-TFT.Then,neodymium(Nd)doped IZO new channel layer was fabricated for TFT.It was found that Nd element distributed uniformly in the whole NIZO film,which revealed nano crystalline structure,implying that Nd was incorporated into the IZO lattice rather than segregated as clusters.As the annealing temperature increased,the turn-on voltage(Von)of the NIZO TFT became more and more negative.It could be seen that only with small amount of Nd(~ 1%)doping could make NIZO TFT exhibited lower sub-threshold swing(SS)and less Von shift than IZO TFT,as the annealing temperature increased.Furthermore,the carrier concentration of NIZO could be drastically reduced.In-depth studies showed that the Nd element can be used as superior oxygen binder,inhibit oxygen vacancy and control carrier concentration due to the low electronegativity(~ 1.1)and strong Nd-O bond energy(703 kj / mol).The NIZO TFT annealed at 300 oC owned the best performance,a saturation mobility of 22.7 cm2V-1s-1,with excellent electrical stability.Simultaneously solved the thorny problems that the carrier concentration of IZO system is too high to suppress and lower mobility IGZO TFT.