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

Abstract

Abstract— 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 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°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 μA) 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.