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-kappa and high-bandgap materials and their integration in oxide TFTs, with processing temperatures not exceeding 150 degrees 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 degrees C by PECVD. For instance, with Ta2O5-SiO2 as the dielectric layer, field-effect mobility of 35 cm(2)/(V-sec), close to 0 V turn-on voltage, an on/off ratio higher than 10(6), a subthreshold slope of 0.24 V/dec, and a small/recoverable threshold voltage shifts under constant current (I-D = 10 mu A) 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.