Research On Nanocrystal Charge Trapping Memory Devices With Pseudobinary Oxides

Charge trapping memory device with SONOS structure has been considered as the promising memory device in the next generation to solve the physical limit problems of floating-gate memory device because of its low operation voltages and power consumption,good endurance and retention.Nanocrystal charge trapping memory as a new type has a large improvement of memory properties due to the mechanism of nanocrystals traps and discrete charge storage.In this work,the high-k（HfO₂）_0.4（ZrO₂）_0.6（HZO）and（Bi₂O₃）_0.4（ZrO₂）_0.6（BZO）materials were used as charge trapping layer in the unit of SONOS structure memory device,using the rapid treatment annealing（RTA）for the generation of nanocrystals,to investigate the storage capacity,charge trapping ability,energy band structure and data retention,etc.Also,the inner nanocrystals changes of charge trapping layer were investigated and the main conclusions are listed as follows:1.Design the structure of nanocrystal memory device with high-k pseudobinary oxide materials.The high-k Al₂O₃ was chosed to act as tunneling oxide layer and blocking oxide layer,and the structure of memory device was determined by p-Si/Al₂O₃/charge trapping layer/Al₂O₃/Pt.The charge trapping layers we chose high-k pseudobinary oxide materials were investigated through the binary phase diagram and XRD to analyze the various changes causing by RTA.2.Using pulse laser deposition technology,the HZO and BZO films were deposited in the design structure as charge trapping layer after confirming the conditions of deposition.The p-Si was used as a substrate to deposit multilayer structure of Al₂O₃/HZO（BZO）/Al₂O₃ to fabricate two materials memory devices,and the nanocrystals were generated by the RTA to create charge traps.3.The charge trapping characteristics of HZO and BZO devices were investiaged.The C-V measurements of HZO memory device indicated that this device had a poor charge trapping ability and the memory window was small.Although,the device showed a better memory window at high voltage,the C-V curves were not stable.Thus,the HZO memory device had low density of nanocrystals due to the high crystallization temperature,causing the hard separation of phases in HZO film.After the improvement of annealing conditions,the HZO memory device had inverse memory windows,which badly weaken the normal memory windows of HZO device.So,the HZO film as charge trapping layer to insert in nanocrystal memory device was difficult to achieve.The Bi₂O₃ material was used to replace HfO₂ to decrease the crystallization temperature of charge trapping layer.After the same annealing conditions,this BZO memory device had a large memory window at the low voltages,and the annealing conditions could be changed to mamxize the charge trapping ability of BZO device.In addition,the device with no RTA showed no memory window,which indicated the effects of nanocrystals generated in BZO film.Also,the XRD results of BZO films could prove the existence of these nanocrystals.4.The charge trapping ability and generation mechanism of charge traps in BZO memory device.The measurment results of different RTA conditions showed the various changes of BZO device properties,and this device was optimized,which displayed an excellent memory window and good retention.The XPS and HRTEM results explained the phase separation in BZO film,proved the existence of Bi₂O₃ and ZrO₂ nanocrystals and showed the changes of crystallization and oxide valence states.The VCA was used to estimate the energy band structure of BZO device and analyze the mechanism of program and erase.The measurement results of different RTA conditions also proved the effects of nanocrystals size and density on charge trapping density in BZO device.