Study On The Hydrogen-doping And Design Of Bilayer Structure In Metal Oxide Thin-film Transistors

In recent years,transparent flexible display devices are in a process of extremely rapid development,and further increase the performance requirements of thin film transistor,which as a key switching element.Oxide semiconductor especially for amorphous oxide semiconductor?AOS?,as the most mainstream TFTs active channel layer material,is one of the most potential material to replace traditional a-Si:H,which have many remarkable advantages,such as high mobility,good mechanical flexibility,high optical transparency,simple low temperature fabricated process.In this paper,for the current amorphous oxide semiconductors such as ZnO,In₂O₃ and InGaZnO,the related devices are prepared by rf magnetron sputtering,and the hydrogen doping effect are explored and the double-dual structure are designed.The specific contents are as follows:Firstly,ZnO,In₂O₃ and InGaZnO TFTs were prepared by magnetron sputtering,and hydrogen plasma treatment were performed,with the treatment time varying from 0 to 12 min.When the treatment time increased from 0 min to 5 min,the threshold voltage of ZnO:H-TFTs were continuously skewed to the left and decreased from 1.1 V to-23.4 V.When the treatment time increased to more than 8 min,the device could not be turned off.When the treatment time increased from 0 min to 12 min,the mobility of ZnO:H-TFTs increased from 3.8 cm²/Vs to14.3 cm²/Vs.When the treatment time increased from 0 min to 9 min,the threshold voltage of InGaZnO:H-TFTs kept drifting to the left and decreased from 0.1 V to-27.1 V.When the treatment time increased to more than 10 min,the device could not be cut off.However,different from the ZnO-TFTs,when the treatment time increased from 0 min to 12 min,the mobility of InGaZnO:H-TFT decreased from 26.0 cm²/Vs at 0 min and achieve to the maximum36.6 cm²/Vs at 3 min.However,when the time was increased to 12min,the device could not be turned off.In₂O₃-TFTs are different from ZnO-TFTs and InGaZnO-TFTs.With the continuous increase of treatment time,the transfer characteristic curve moves firstly to the left and then to the right,and the on state current of the device firstly increasing and then decreasing.When the treatmet time increased from 0 min to 6 min,the threshold voltage of the device continued to deviate to the left,from-4.5 V to-35.2 V,and the mobility increased from 35.0 cm²/Vs to 55.9cm²/Vs.When the treatment time continued to increase,the threshold voltage of the device increased from-35.2 V to-19.2 V,and the mobility decreased from 55.9 cm²/Vs to 30.8 cm²/VsSecondly,InGaZnO/In₂O₃ TFTs with high mobility were fabricated by magnetron sputtering at room temperature.Firstly,we studied the effect of different thickness combination and thin film deposition sequence on the performance of bilayer device,and we achieve the InGaZnO?5 nm?/In₂O₃?20 nm?TFTs with best electrical performance,with high mobility of64.4 cm²/Vs,SS of 204 mV/dec,switch 2.5×10⁷ and?V_TH of 1.8 V.In addition,after using high-k gate insulator?HfO₂ and Si₃N₄?,the thin film transistor have a high mobility of 67.5cm²/Vs and 79.1 cm²/Vs,respectively,and the SS of the device achieve further improvement,85 mV/dec and 92 mV/dec,respectively.Then,we studied the electrical properties of InGaZnO and In₂O₃ monolayer devices grown at different substrate temperatures.The completely different trends in the electrical properties of the two devices indicate that the different defect types dominat in the two materials.Therefore,we proposed the defect self-compensation effect between InGaZnO and In₂O₃ thin films.In order to verify this mechanism,we firstly obtained consistent simulation results through SILVACO/Atlas system,and carried out simulation on the device according to DFT calculation,and observed the formation of In-O bond.Then we used X-ray photoelectron spectroscopy to analyzes the InGaZnO?5 nm?,InGaZnO?5 nm?/In₂O₃?2nm?and InGaZnO?5 nm?/In₂O₃?5 nm?O 1 s spectrum,with In₂O₃ film thickness increased from 2 nm to 5 nm,the continuous decrease of oxygen vacancy and the increase of M-O bonds mean the existence of defects self-compensation effect;Finally,Low Frequency Noise analysis further verified that the decreases of average defect density.Finally,ZnO/In₂O₃,Al₂O₃/In₂O₃ and Ga₂O₃/In₂O₃ TFTs were fabricated and their electrical properties were studied.The mobility of ZnO/In₂O₃,Al₂O₃/In₂O₃ and Ga₂O₃/In₂O₃ TFTs were improved in different degrees,which were 46.2 cm²/Vs,55.4 cm²/Vs and 47.5 cm²/Vs,respectively.The threshold voltage is-2.3 V,-6.8 V and 0.2 V respectively.In ZnO/In₂O₃ TFTs,the Fermi level of In₂O₃ is higher than that of ZnO,which leads to the migration of ZnO electrons to In₂O₃.As a result,the electron depletion at the ZnO/In₂O₃ contact interface and the formation of the built-in electric field in ZnO thin film reduce the resistivity of In₂O₃ and lead to the deviation of threshold voltage while increasing the mobility.A 2D electron channel is formed when Al₂O₃ and In₂O₃ come into contact.The O atoms in In₂O₃ break away from Al₂O₃and causes cluster self-doping,which result in the semi-metallization of In₂O₃,thus increasing the on state current and making the threshold voltage negative.When Ga₂O₃ layer and In₂O₃layer come into contact,In₂O₃ has a very low energy level compensation?⁰.27 eV?compared with Ga₂O₃,which leads to the carrier injection of In₂O₃ layer into Ga₂O₃,thus increasing the conductivity of the device and enhancing its performance.