First Principles Study Of The Electrical Properties Of IGZO Materials Under Mechanical Strain

IGZO-TFTs play an important role in the field of display technology,with high mobility,high switching current ratio,uniformity and stability,and can produce large-area,high-resolution,high refresh rate and low-power display panels.With the development of flexible display technology,IGZO materials have a broader application prospect.However,the threshold voltage shift occurs when IGZO-TFTs are bent under mechanical strain,which leads to degradation of device performance.Experiments show that mechanical strain causes oxygen vacancy defects in IGZO materials,which affects device performance,but its specific physical mechanism is still unclear.The first-principles calculation based on density functional theory has an extremely important application in computational materials science.This paper uses the first-principles calculation to theoretically demonstrate the trend of strain-induced IGZO material properties change,and explores the physical mechanism it produces.In order to obtain more reliable calculation results,the calculation algorithm based on zinc oxide material is studied.The innovative shell-LDA/GGA+U-1/2 algorithm is compared with some existing methods,and because it is more reasonable,accurate,and efficient,have become the main calculation methods in this paper.IGZO materials have various structures due to different chemical ratios.After analysis,the atomic interlaced InGaZnO₄ with a calculated band gap of 3.29 eV is used as the basic structure of this study.At the same time,it is verified that the oxygen vacancy defect is the main donor of electron carriers in n-type-InGaZnO₄,which has a significant effect on the material properties.The amorphous InGaZnO₄ was constructed by first-principles molecular dynamics.It is found that the band gap value of the amorphous structure is reduced to 2.45 eV,which is consistent with the experimental phenomenon.The calculated defect level of oxygen vacancy defect of amorphous InGaZnO₄ is combined with the conduction band,and the impurity is completely ionized.The character of InGaZnO₄ crystal,oxygen vacancy defect of InGaZnO₄ crystal and InGaZnO₄ amorphous structure under the mechanical strain have been researched.The anisotropy of crystal c and b axial is taken into account,and the band gap value,impurity ionization energy and carrier mobility are analyzed.In general,when the influence of other factors is not considered,the threshold voltage of IGZO-TFTs will be decreased significantly under the tensile strain,and the threshold voltage swing will be increased significantly,which is consistent with the experimental phenomenon;the threshold voltage of IGZO-TFTs will be increased under compressive stress slightly,and the threshold voltage swing will be decreased,which is inconsistent with the experimental phenomenon.However,the research in this paper shows that when InGaZnO₄ is transformed from a defect-free structure to an oxygen vacancy defect structure,the carrier concentration will increase significantly,and the carrier mobility will be greatly reduced.The combination of the experiment conclusion that mechanical strain causes IGZO crystal to generate oxygen vacancy defects and the calculation results in this paper,can not only confirm the experimental phenomenon that the threshold voltage is decreased and the threshold voltage swing is increased under the action of compressive strain,but also explain the confused experimental phenomenon that the change under compressive strain is insignificant compared with that under the tensile strain.These conclusions make the research of this paper have great reference value.