MOHOS-type memory performance using HfO2 nanoparticles as charge trapping layer and low temperature annealing

In this work, HfO2 nanoparticles (np-HfO2) are embedded within a spin-on glass (SOG)-based oxide matrix and used as a charge trapping layer in metal–oxide–high-k–oxide–silicon (MOHOS)-type memory applications. This charge trapping layer is obtained by a simple sol–gel spin coating method after using different concentrations of np-HfO2 and low temperature annealing (down to 425 °C) in order to obtain charge–retention characteristics with a lower thermal budget. The memoryʹs charge trapping characteristics are quantized by measuring both the flat-band voltage shift of MOHOS capacitors (writing/erasing operations) and their programming retention times after charge injection while correlating all these data to np-HfO2 concentration and annealing temperature. Since a large memory window has been obtained for our MOHOS memory, the relatively easy injection/annihilation (writing/erasing) of charge injected through the substrate opens the possibility to use this material as an effective charge trapping layer. It is shown that by using lower annealing temperatures for the charge trapping layer, higher densities of injected charge are obtained along with enhanced retention times. In conclusion, by using np-HfO2 as charge trapping layer in memory devices, moderate programming and retention characteristics have been obtained by this simple and yet low-cost spin-coating method.