Metal-Oxide-Semiconductor Structure with Au Nanocrystals for Charge Storage

In this work, Metal-Oxide-Semiconductor structure with Au nanocrystals formed by chemical redundant method for charge storage is fabricated. Scanning Electron Microscopy and Transmission Electron Microscope are utilized to characterize the structure of fabricated devices. In the characterization of memory performance, we use high frequency capacitance-voltage (C-V) measurement to measure the memory window for comparing the storage capacity and charging efficiency. On the other hand, through the time dependent variation of device capacitance measured under fixed voltage, the effective charge loss rate can be calculated to compare the retention regarding the stored charge of devices. In the first part of study on our devices, the devices with different structure parameters including the density of Au nanocrystals, the temperatures of post-deposition-anneal (PDA) process, and the thickness of tunnel oxide are measured to compare the effects of different structures. From the results of measurements, the effects of different structures are discussed and the optimized parameters of our devices are found. In the second part of our study, the effect of PDA process is further studied. Different devices with/without PDA process are fabricated and their current-voltage (I-V) characteristics at various temperatures are measured. The measured I-V curves are then fitted with appropriate conduction mechanisms to calculate the ratio of currents caused by different mechanisms. By comparing the ratios of different conduction currents, we found that PDA process can reduce defects and traps in oxide and suppress the leakage current, at the same time, make the leakage current converged and limited. The fitting parameters in different conduction mechanisms are also compared. We found that through PDA process the trap density is decreased to enhance the confinement of stored charge in Au nanocrystal. Besides, the results indicate that the PDA process can also suppress the leakage current attributed to the hopping of electrons from one traps to another.