Low-temperature Solution Preparation Of Zirconium Oxide Films And Thin Film Transistor Application

With the rapid development of integrated circuits,the traditional SiO₂ dielectric layer has been unable to meet the requirements of the transistor size continues to shrink.Therefore,the preparation of high-k dielectric materials that meet the requirements is the best solution to this problem.Among the many high-k materials,zirconia was chosen as the object of study because of its large bandgap（K=25）and large bandgap（Eg=7.8）.Using ultraviolet light treatment and lightwave irradiation treatment,two low-temperature annealing methods were used to adjust different UV light treatment time and lightwave irradiation treatment time.At the same time,high temperature annealing was used as an experimental comparison to study the physical structure,optical properties,and electrical properties of the dielectric layer with different annealing methods and parameters.First,the ZrOx precursor xerogel was analyzed using a thermogravimetric test,then the dielectric film phase was analyzed by X-ray diffraction,and the optical characteristics were analyzed by an ultraviolet-visible spectrophotometer.The surface morphology was analyzed by scanning electron microscopy and atomic force microscopy.The X-ray electron energy was analyzed.Spectral analysis of chemical forms and so on.Finally,a suitable semiconductor layer is deposited on the dielectric layer and a complete oxide transistor device is fabricated.When studying TFT devices,they are characterized mainly by output characteristics and transfer characteristics,and their performance is studied.ZrO₂ dielectric films were prepared from low temperature solution by UV irradiation at different times from 20 min to 80 min,and their performance characterizations were analyzed.All of the ZrO₂ thin films did not show crystallization.All of them were amorphous,and the optical transmittance was 90%higher.SEM and AFM show that the surface of the ZrO₂ thin film treated by ultraviolet light is uniform and smooth,and the roughness is as low as 0.23 nm.XPS results show that with the increase of UV treatment time,the metal oxygen content in the film increased from 50.4%to 65.4%.By preparing Si/ZrO₂/Au capacitors,we tested the dielectric properties of ZrO₂ thin films,and the leakage current density was 6.0×10-8 A/cm² at 3 MV/cm,which was four orders of magnitude lower than that of 400 ℃ annealing ZrO₂ dielectric films.At 1 KHz,the capacitance is 600 nF/cm² and the dielectric constant is 9.7.The low-temperature In2O₃/ZrO₂ TFT device prepared on this basis has good performance,the operating voltage is as low as 3 V,the mobility is 1.68 cm²/Vs,the switching ratio is 105,and the sub-threshold swing is 0.19 V/dec.These results demonstrate that UV irradiation can produce high-k zirconium oxide films and can be successfully applied to TFTs.Then we used ZrOCl₂ as the precursor solution and ZrO₂ thin films were prepared by the low-temperature solution by lightwave irradiation treatment for 5 min to 40 min.And their properties were analyzed.All ZrO₂ thin films are amorphous and have good optical transmission.With the increase of lightwave irradiation time,the bandgap width increases gradually.The band gap of the ZrO₂ dielectric films treated with 40-minute lightwave irradiation is 5.78 eV.SEM and AFM show that the lightwave irradiation treated ZrO₂ dielectric films are smooth and continuous with roughness as low as 0.30 nm.XPS analysis found that the metal oxygen content in the film increased from 47.0%to 73.0%with the increase of the lightwave irradiation time.The lightwave irradiation of ZrO₂ thin film is excellent in electrical properties.Under 3 MV/cm electric field,the leakage current of ZrO₂ dielectric film is as low as 1.3×l0-7 A/cm² for 40 min.At 100 Hz,the ZrO₂ film has a capacitance of 268.1 nF/cm² and a dielectric constant of 13.7.On this basis,a full-solution In2O₃/ZrO₂ TFT was fabricated using In2O₃ as a semiconductor layer.Due to the use of high-k dielectric materials,the operating voltage can be reduced to 3 V,the mobility can be as high as 19.4 cm²/Vs,the switching ratio as high as 6.4×105,the threshold voltage as low as 0.17 V,and the subthreshold swing of 0.09 V/dec.These results demonstrate that lightwave irradiation treatment can produce high-k zirconium oxide films and can be successfully applied to TFTs.Finally,ZrO（NO₃）₂ was used as the precursor solution,and ZrO₂ thin films were prepared by low-temperature solution lightwave irradiation treatment for 2 min to 8 min,and their properties were analyzed.When the lightwave irradiation time is less than 6 min,the ZrO₂ thin film is amorphous,and the ZrO₂ thin film begins to crystallize in 8 min.The transmittance of all ZrO₂ films was higher than 83%.SEM and AFM show that the surface of the ZrO₂ thin film is smooth and continuous with a low roughness of 0.25 nm.The XPS analysis found that the metal oxygen content in the film increased from 48.4%to 78.5%with the increase of the lightwave irradiation time.The lightwave irradiation ZrO₂ dielectric film has excellent electrical properties,and the lightwave irradiation treatment 8 min ZrO₂ dielectric film at 100 Hz,the capacitance is 296.3 nF/cm²,and the dielectric constant is 18.1.The dielectric thin film was applied to In2O₃/Zr2 TFT devices with an operating voltage as low as 3 V,a mobility as high as 24.2 cm²/Vs,a switching ratio of 6.8×1 06,a threshold voltage of 0.1 V.These results demonstrate that lightwave irradiation treatment can rapidly prepare high-k zirconium oxide films and can be successfully applied to TFTs.