Preparation Of Gallium Oxide Particles And High-density Targets

Due to its excellent optical and electronic properties,IGZO semiconductor channel layer has become one of the most promising oxide active layer after a-Si and low temperature p-Si,showing the great commercial application in the next generation of transparent,flexible,ultra-thin display field.Recently,the synthesis of high-qualityβ-Ga₂O₃particles which are used as the raw material of fabricating IGZO still remains a challenge.In this paper,Ga₂O₃ particles were firstly synthesized by a simple direct precipitation technique.The effects of the aging time,the aging temperature,the molar concentration of Ga³⁺and pH value in the reactant on the phase structure,morphology and size of the as-prepared samples were systematically investigated.The as-prepared particles were characterized by XRD,SEM,TG-DSC,TEM and Laser diffraction particle size analyzer,respectively,and the possible growth mechanism of the typical Ga₂O₃ particles was proposed.Based on the study,the as-prepared monodispersedβ-Ga₂O₃ micro-ellipsoid particles（E-G）,β-Ga₂O₃ micro-rods particles（R-G）and as-received commercialβ-Ga₂O₃particles（C-G）were used as the raw materials to fabricate theβ-Ga₂O₃ green bodies by die pressing and subsequent cold isostatic pressing,respectively.These compacts were sintered at different temperatures in air.The effects of theβ-Ga₂O₃ micro-particles with different morphology and size and the sintering parameters on the densification behavior and microstructural evolution of ceramic targets were studied in detail.The main results are as follows:（1）The uniformly sized and monodispersedβ-Ga₂O₃ crystalline micro-particles have been successfully synthesized through a controlled precipitation technique.The monoclinic phase of as-preparedβ-Ga₂O₃ was independent on the reaction conditions.However,these reaction parameters had an important effect on the morphology and size ofβ-Ga₂O₃ particles.（2）It was important condition to keep the aging time of 3 h or over for the preparation ofβ-Ga₂O₃ micro-particles with the uniform size and monodisperse.The aging temperature played a significant role in the preparation of monodispersedβ-Ga₂O₃ layered-structures.As the aging temperature increases from 30°C to 70°C,the morphology of the preparedβ-Ga₂O₃ particles was changing from the ellipsoids to the rods.When the aging temperature was fixed at 70°C,the molar concentration of Ga³⁺did not affect the morphology of the preparedβ-Ga₂O₃ particles.However,as the molar concentration of Ga³⁺increases,the size of monodispersedβ-Ga₂O₃ rods appeared to increase first and then decrease.The pH value had a vital influence on the morphology and size of the as-prepared Ga₂O₃ samples.When the pH value was lower,the obtained particles were irregular morphology;when the pH value was higher,the obtained particles had the longer aspect ratio.（3）Ostwald ripening and oriented attachment growth mechanism of the uniformly hierarchicalβ-Ga₂O₃ crystals were proposed.Owing to the higher temperature providing greater activity for the formed crystalline nuclei,the hierarchicalβ-Ga₂O₃ micro-rods were obtained at 70°C,while theβ-Ga₂O₃ micro-ellipsoids were acquired at 30°C.（4）The main peak（-202）of E-G and R-G ceramics sintered at elevated temperature,ascribed to the lowest surface energy of the（-202）crystal surface.Compared with C-G,the monodispersed E-G and R-G had higher sintering activity with a more uniform particle size and a smaller aspect ratio and the densification temperature of as-preparedβ-Ga₂O₃ was reduced by over 100°C.Under the lower temperature,the high-density targets were obtained using the as-prepared Ga₂O₃ particles with uniform size as the raw materials.Furthermore,the highest density of E-G ceramics was 5.96 g/cm³ sintered at 1400°C,and the relative density was 99.7%.Differential densification led to the lower density of C-G ceramics.Due to a higher sintering activity,E-G and R-G ceramics had larger grains than those of C-G ceramics sintered at the same temperature.The sintering temperature had an obvious effect on the microstructure and weight losses of sintered Ga₂O₃ ceramics.