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Environmental Impact And Improvement Mechanism Of Bias-stress Stability Of Amorphous Oxide Semiconductor Thin Film Transistors

Posted on:2020-12-26Degree:MasterType:Thesis
Country:ChinaCandidate:Y ZhouFull Text:PDF
GTID:2428330620460015Subject:Electronic science and technology
Abstract/Summary:PDF Full Text Request
Amorphous indium gallium zinc oxide thin film transistors?a-IGZO TFTs?are considered to replace the conventional silicon-based TFTs and drive next-generation flat panel displays?FPDs?because of their good electrical properties.However,they still have many stability issues to be solved,especially the physical mechanism and improvement method of their bias-stress stability.Therefore,the positive gate bias voltage?PGBS?stability was in-depth studied in this paper.We analyzed the impact factors of relative humidity on the PGBS stability and studied how the passivation layers improved the bias-stress stability of a-IGZO TFTs.First,we systematically tested the PGBS stability of the a-IGZO TFT devices at different relative humidity?RH?.The results show that the ambient humidity significantly affected the bias-stress stability of the devices.When the RH reached 50%,the threshold voltage shift became the largest value of 15 V and the bias stability of the TFT was worst.We believe that this phenomenon was mainly due to the comprehensive influences of the ambient atmosphere around the a-IGZO TFTs.Accordingly,we established a low-high humidity?LHH?model to explain the role of the ambient atmosphere:for the low RH,the moisture-assisted oxygen adsorption dominated,causing a positive shift in the threshold voltage;for the high RH,the direct direct moisture adsorption was dominant,causing a negative shift in the threshold voltage.Therefore,the threshold voltage shift increased from 5 V to 11.5 V and then dropped to4.5 V when the RH increased from 10%to 90%.Secondly,SiO2 or Al2O3 films with different thicknesses were used to passivate the a-IGZO TFTs,making the devices more stable during PGBS tests.With the increase in the passivation layer thickness,the PGBS stability of a-IGZO TFTs improved due to their stronger barrier effect.When the passivation layer thickness was larger than the characteristic length,nearly no threshold voltage shift occurred,indicating that the ambient atmosphere effect rather than the charge trapping dominated the PGBS instability of a-IGZO TFTs in this study.The SiO2 PV layers showed a better improvement effect than the Al2O3 because the former had a smaller characteristic length?5 nm?than that of the Al2O3 PV layers?10 nm?.
Keywords/Search Tags:Amorphous InGaZnO, thin film transistor, positive gate bias stress, passivation layer, characteristic length
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