| The rapid development of the information age makes the increasing popularity of electronic products, which activates a huge memory products market and promotes the ceaseless innovation in semiconductor technology. Semiconductor technology node continues to be moved forward. However, the development of traditional Flash memory encounters obstacles with the technology nodes moving forward. Continuing to scale down the conventional memory can not guarantee the proper storage of information, so the development of the next generation of memory is imperative. The charge trapping memory(CTM) was created based on the traditional Flash memory. It can avoid the trapped charge to loss to nothing at one time due to the discrete charge storage insulated between traps and also can be scaled down as required. So it has been widely studied.At present, the development of CTM device structure is relatively mature, so most of the researches are focused on the materials. In this work, TANOS (TaN/Al2O3/Si3N4/SiO2/Si) structure were used to study some properties of the CTM device, where TaN denotes gate electrode, Al2O3 the barrier layer, Si3N4 the charge trapping layer, SiO2 the tunneling layer, Si the substrate. In this work, based on the first-principles methods and the VASP software, we studied the intrinsic defects inside Si3N4 materials and some properties of Al2O3/Si3N4 interface. This work consists of five parts. Every part is summarized as follows:The first part is an introduction, we firstly made a brief introduction for the history way of recording information so as to lead to the information storage and memory technology. Then we stated the reason to develop the CTM device and introduced the current state of the development for CTM.The second part is an overview of CTM and a description of study methods used in this work. In this part, the structure evolution and operation mechanism of CTM was narrated clearly, then the materials used to form the device were analyzed and selected. Finally, we elaborated the methods and softwares used for the part of calculation simulation and model building. And the content of the chapter was summarized as well.In the third part of this work, the storage characteristics of intrinsic defects inside Si3N4 was studied. In this part, we firstly selected five major intrinsic defects inside Si3N4 by calculating the formation energy of these defects, and then the energy band, the density of states and the bader charge were used to perform a comparison analysis for these defects. Finally, the conclusion was that the charge storage characteristics of SiN2was the best.In the fourth part, properties of Si3N4/AlO3 interface was studied. In this part, the modeling process of interface was described in detail, and structure optimization was performed as well. Two different optimization plans were carried out. Free optimization was found to be the most reasonable way of optimizing interface structure. Then the impact of O doping on interface properties was studied by calculating the density of states. The doped O can reduce the interface states, thereby improving the charge retention characteristics of the device. Finally, the charge distribution of interface system was calculated. The obtained result showed that the interface O atoms would reduce during the optimization, leading to the O deficiency.The fifth part is the summary of the work. And future prospects also were given. In the part, we made a brief outline for the work and put forward some constructive views for the future. |
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