Low-temperature sputtered mixtures of high-κ and high bandgap dielectrics for GIZO TFTs

— This paper discusses the properties of sputtered multicomponent amorphous dielectrics based on mixtures of high-κ and high-bandgap materials and their integration in oxide TFTs, with processing temperatures not exceeding 150°C. Even if Ta2O5 films are already amorphous, multicomponent materials such as Ta2O5—SiO2 and Ta2O5—Al2O3 allow an increase in the bandgap and the smoothness of the films, reducing their leakage current and improving (in the case of Ta2O5—SiO2) the dielectric/semiconductor interface properties when these dielectrics are integrated in TFTs. For HfO2- based dielectrics, the advantages of multicomponent materials are even clearer: while HfO2 films present a polycrystalline structure and a rough surface, HfO2—SiO2 films exhibit an amorphous structure and a very smooth surface. The integration of the multicomponent dielectrics in GIZO TFTs allows remarkable performance, comparable with that of GIZO TFTs using SiO2 deposited at 400°C by PECVD. For instance, with Ta2O5—SiO2 as the dielectric layer, field-effect mobility of 35 cm2/(V-sec), close to 0 V turn-on voltage, an on/off ratio higher than 106, a subthreshold slope of 0.24 V/dec, and a small/recoverable threshold voltage shifts under constant current (ID= 10 μA) stress during 24 hours are achieved. Initial results with multilayers of SiO2/HfO2—SiO2/SiO2 are also shown, allowing a lower leakage current with lower thickness and excellent device performance.