Investigation of microstructural and electrical properties of composition dependent co-sputtered Hf1−xTaxO2 thin films

Abstract

Tantalum doped HfO2 gate dielectric thin films were deposited on silicon substrates using RF reactive co-sputtering by varying RF power of Ta target from 15 W to 90 W. The morphological, compositional and electrical properties of Hf1−xTaxO2 films were systematically investigated. The Ta content was found to be increased up to 21% for a Ta target power of 90 W. The evolution of monoclinic phase of Hf1−xTaxO2 was seen from XRD study upto RF power of 60 W and afterwards, the amorphous like behaviour is appeared. The featureless smooth surface with the decrease in granular morphology has been observed from FESEM micrographs of the doped films at higher RF powers of Ta. The flatband voltage is found to be shifted towards negative voltage in the capacitance–voltage plot, which was attributed to the enhancement in positive oxide charge density with rise in RF power. The interface charge density has a minimum value of 7.85 × 1011 eV−1 cm−2 for the film deposited at Ta RF power of 75 W. The Hf1−xTaxO2 films deposited at Ta target RF power of 90 W has shown lower leakage current. The high on/off ratio of the current during the set process in Hf1−xTaxO2 based memristors is found suitable for bipolar resistive switching memory device applications.