Preparation Of Aluminum Oxide Thin Films By Sol-gel Process And Application In Transistors

The wide application of liquid crystal display in our daily life promotes the constant upgrading of transistor materials.As an ideal material to replace the traditional dielectric layer,the high-k dielectric materials provides infinite possibilities for the development of LCD technology.Alumina(Al2O3)has high dielectric constant(k=9.0)and large band gap(Eg=8.7 eV).It is one of the most promising high-k dielectric materials.However,conventional Al2O3 films are usually deposited by vacuum methods such as atomic layer deposition and chemical vapor deposition,although high quality dielectric thin films can be obtained,but the cost of preparation is higher.In this paper,a low-cost sol-gel process was used to prepare Al2O3 dielectric layer.The effects of annealing temperature on Al2O3 dielectric thin films were investigated.The InZnO thin film transistor(IZO/Al2O3 TFT)was prepared,and the performance of the device was characterized by the output characteristic curve and the transfer characteristic curve.At the same time,a new low-temperature lightwave irradiation was developed to prepared Al2O3 dielectric layer.Finally,lightwave irradiation was applied to the preparation of ZnO thin films.Firstly,we prepared Al2O3 dielectric layer by sol-gel process,and studied the the structure and properties of Al2O3 dielectric layer annealed at 300-600 0C.All Al2O3 dielectric layers were amorphous and smooth,without cracks or pores.The optical transmittance of Al2O3 dielectric layers in the visible light range was higher than 95%,and the bandgap increased as the annealing temperature increased.XPS results shown that increased the annealing temperature can effectively promoted the formation of metal oxygen and reduced the content of combined oxygen.The leakage current of Al2O3 annealed at 600 ℃ is 3.9×10-7 A/cm2 at 3 MV/cm,the capacitance at 1 KHz is 101.1 nF/cm2,and the dielectric constant is 8.2.The mobility of the InZnO/Al2O3 TFT prepared is 7.23 cm2-1s-1,the Ion/Ioff is 3.05×106,the VTH is 1.32 V.These properties indicated that the high-k Al2O3 thin films prepared by sol-gel process can be successfully applied in transistors.In order to reduce the preparation temperature of Al2O3 thin films,we prepared Al2O3 thin films by lightwave irradiation instead of the traditional high temperature annealing.Within 10-40 min of lightwave irradiation,The Al2O3 film did not crystallize and had a good surface morphology.The optical transmittance of Al2O3 dielectric layers was high,and the band gap becomed larger as time increased.The XPS results shown that the metal oxygen increased and the combined oxygen decreasesd with the increased of time.The leakage currents of Al2O3 thin film obtained by lightwave irradiation for 40 min at 3 MV/cm was 5.60×10-8 A/cm2.The capacitance at 1 KHz was 158.1 nF/cm2,and the dielectric constants was 7.8.These results demonstrated that lightwave irradiation can prepared high-k Al2O3 dielectric layer.Finally,we prepared ZnO thin films by lightwave irradiation using zinc nitrate.When the lightwave irradiation time was less than 5 min,the ZnO crystal was not completely formed and the film surface was uneven.Prolonging the lightwave irradiation time,making ZnO film smoothness and increasing the Zn-O bond.In addition,Increased lightwave irradiation time causes a "redshift" in the absorption limit of ZnO,leading to a smaller band gap.Compared with the traditional high-temperature annealing,the ZnO film obtained by lightwave irradiation has less combined oxygen content and more uniform grains.This means that lightwave irradiation is a great potential annealing method with highly efficiency and energy-saving.