Low-temperature sputtered mixtures of high-kappa 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 Ta(2)O(5) films are already amorphous, multicomponent materials such as Ta(2)O(5)-SiO(2) and Ta(2)O(5)-Al(2)O(3) allow an increase in the bandgap and the smoothness of the films, reducing their leakage current and improving (in the case of Ta(2)O(5)-SiO(2)) the dielectric/semiconductor interface properties when these dielectrics are integrated in TFTs. For HfO(2)-based dielectrics, the advantages of multicomponent materials are even clearer: while HfO(2) films present a polycrystalline structure and a rough surface, HfO(2)-SiO(2) 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 SiO(2) deposited at 400 degrees C by PECVD. For instance, with Ta(2)O(5)-SiO(2) 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 SiO(2)/HfO(2)-SiO(2)/SiO(2) are also shown, allowing a lower leakage current with lower thickness and excellent device performance.