Effects of thermal annealing on the charge localization characteristics of HfO2/Au/HfO2 stack

To be compatible with the mainstream nano CMOS technology and to further increase the density and to reduce power consumption of non-volatile memory, high-k dielectric will become the major technology option for next generation non-volatile memory technology. To ensure the required retention time and to maintain the scalability of floating gate memory transistor, the charge store in future memory transistor should be accompanied with the high-k insolated metal or conductive clusters, islands, or nano-particles. This work proposes a simple method to fabricate high-k isolated metal cluster array. An HfO₂/Au/HfO₂ stack was first grown by using atomic layer deposition (ALD) and thermal evaporation, respectively, for HfO₂ and Au film deposition. After a high-temperature thermal annealing, a number of HfO₂-buried Au islands with diameter of about 5 to10 nm were obtained. Capacitance–voltage (C–V) measurements show that the charge storage characteristics of the Au-embedded HfO₂ structure were affected greatly by the annealing conditions. Depending on the annealing temperature (it should be governed by thickness of Au layer also), the thermal annealing may lead to the formation of Au islands/clusters, the improvement of HfO₂ blocking property as a result of defect removal, or the deterioration of the blocking property of HfO₂ due to the crystallization of HfO₂ film. Process optimization should be conducted for further improving the charge localization characteristics.