Research On TFT Memory Based On Channel Characteristics Of InGaZnO

With the development of technology,people have higher requirements for the portability and small size of the panel,and the In Ga Zn O Thin Film Transistors(IGZO-TFTs)memory has made it more suitable for the display module and the storage module.Small physical size limits,greater integration.At the same time,it also features high resolution,high refresh rate and low power consumption.For the IGZO-TFTs memory,there is sometimes a phenomenon of threshold voltage drift,which leads to degradation of device performance.In addition,the prepared IGZO has different atomic ratios due to the difference in the preparation process and the experimental conditions.However,devices using different atomic ratios of IGZO as the channel may have different electrical characteristics,so it is necessary to study IGZO with different element ratios.This paper combines the first-principles calculation software VASP with the device property simulation software Silvaco to analyze the electrical characteristics and laws of IGZO-TFTs memory from the microscopic level and macroscopic characteristics.Firstly,for IGZO materials,due to the characteristics of their quaternary compounds,they have different configurations.In this paper,the virtual crystal approximation model is compared with the traditional atomic interlacing model and the column interleaving model to calculate the structure after optimization.,energy band,density of states,effective mass,and carrier concentration.It is found that the virtual crystal approximation model is not much different from the traditional atomic interlaced and column interleaved models in terms of structure,energy band and density of states.Under the premise of the same number of atoms,the system of the unit cell of the virtual crystal approximation model is always smaller than the other two models,which means that the virtual crystal approximation model has a more stable structure.Therefore,in the subsequent research,the virtual crystal approximation model will be adopted as the basic structure of IGZO.Secondly,by modifying the parameters of the virtual crystal approximation model,three kinds of IGZO materials,In3Ga4Zn2O12,In3Ga3Zn3O12 and In3Ga2Zn4O12,are discussed.Similarly,the VASP software was used to calculate the structure,energy density,effective mass,and carrier concentration of the three.The calculation results show that with the increase of Ga content,the system can always become larger,and the energy band is also increased from 2.9 e V to 3.5 e V,which is in line with the theoretical results.The unit cell with the ratio of In3Ga3Zn3O12 has the smallest volume,presumably due to the imbalance of Ga and Zn content,which weakens the symmetry of the unit cell,weakens the interaction force between atoms,and thus increases the unit cell volume..In addition,oxygen vacancy defects are the main carrier sources of n-type semiconductor IGZO.The oxygen vacancy defects of IGZO with different element ratios are also calculated.By comparing the defect energy bands,it can be found that in In3Ga2Zn4O12,oxygen vacancy defects are The shallow level exists,while in In3Ga3Zn3O12 and In3Ga4Zn2O12,the oxygen vacancy defect exists as a deep level.In addition,the defect formation energy of the three is calculated.The defect formation energy of In3Ga3Zn3O12 is found to be the smallest,which also confirms the influence of unit cell symmetry on the stability of the system.Finally,three different TFT memory structures are discussed on the Silvaco software.After comparison,the bottom gate memory was selected as the basic structure for subsequent research.Based on the bottom gate structure,the IGZO material parameters of different atomic ratios were imported into Silvaco by modifying the material parameters and comparing their electrical properties.It is found that for the band gap of IGZO,the threshold voltage of the device will shift positively with the increase of the forbidden band width;for the effective mass of electrons,it mainly affects the on-state current of the device,and the relationship between them is inverse;An increase in the peak density of the defect state causes a negative shift in the threshold voltage.Changes in the defect level position also affect the device's threshold voltage and subthreshold slope.Comparing the material properties and the electrical properties of the device,it was found that the TFT memory with the atomic ratio of IGZO of In:Zn:Ga:O=1:1:1:4 has the best characteristics.These conclusions make the work of this paper have certain reference value.