【作者】 孙宜华；

【导师】 熊惟皓； 李晨辉；

【作者基本信息】 华中科技大学 ， 材料学， 2009， 博士

【摘要】 近年来，随着液晶显示、触控面板、有机发光显示、太阳能电池等的发展，使得透明导电薄膜成为关键性材料之一。目前，常用的锡掺杂氧化铟（ITO）透明导电薄膜材料中的金属铟属于稀缺资源，开发具有透光、导电特性的“非铟”材料已成为研究的热点之一。由于氧化锌基（znO）透明导电薄膜价格较为低廉，且不具毒性，在发展上具有相当的优异性。因此，对于氧化锌薄膜材料及其制备技术的研发，引起了大家的广泛重视。为此，本论文从事了如下方面的研究：采用胶态成型加常压烧结的低成本路线开发研制超高密度的ZnO基陶瓷靶材；并采用所研制的超高密度的ZnO基陶瓷靶材进行了磁控溅射镀膜的研究；研究了不同工艺参数对薄膜性能的影响；并尝试研究制备了双层透明导电薄膜。主要结论如下：通过Zeta电位、粘度、沉降等测试，研究了添加剂含量、pH值、固含量和球磨时间对ZnO-Al₂O₃混合粉体水基悬浮液的稳定性、流动性等的影响。实验结果表明：添加聚丙烯酸（PAA）后，ZnO和Al₂O₃在pH8～10．3的碱性范围有较高Zeta电位，Zeta电位均低于-45mV。与单独添加PAA相比，同时添加聚乙二醇（PEG），ZnO和Al₂O₃的Zeta电位没有明显改变。0．2wt％的PAA为饱和吸附量。PAA为饱和吸附量时，悬浮液在pH8～10．3范围内粘度较低、稳定性较好。当pH值为9左右，PAA质量分数为0．20％时，悬浮液粘度最低、稳定性最好。可制得固相体积分数55％的悬浮液。聚乙二醇添加量的增加，使悬浮液粘度增加、稳定性下降。悬浮体的粘度随固含量的增加呈指数关系增大。球磨时间以40h为佳。XRD分析显示α-Al₂O₃颗粒均匀而稳定的分布在ZnO颗粒之间。通过优化ZnO-Al₂O₃水基悬浮液的工艺参数，注浆成型制备致密的生坯，最终烧结制得超高密度的ZnO-Al₂O₃复合陶瓷。研究了添加剂含量对生坯和烧结体的密度和强度的影响。用0．2 wt％的聚合物电解质PAA和0．2 wt％的粘结剂PEG分散，在pH9、固含量30vol％的条件下制备ZnO-Al₂O₃混合粉体水基悬浮液，注浆成型制得相对密度大于66．6％的均匀而致密的生坯，ZnO-Al₂O₃混合物生坯中颗粒均匀而致密。由于0．2wt％的PAA为ZnO-Al₂O₃混合粉体的饱和吸附量从而形成了分散性好的料浆。另一方面，添加0．2wt％PEG的生坯径向压溃强度增加到12．5MPa，有利于后续过程。在pH9、PAA和PEG的添加量均为0．2％的工艺条件下制得的生坯经1 400℃保温2h无压烧结获得几乎全致密的烧结体（相对密度大于99．7％）。添加0．3％的PAA（PAA轻微过剩），促进了烧结体的强度和密度的提高。烧结过程中α-Al₂O₃与ZnO的反应生成物为ZnAl₂O₄的尖晶石相。显微分析显示其显微结构均匀，没有异常晶粒长大和其它缺陷，铝元素均匀分布。在薄膜的制备中，基底温度的提高对于AZO薄膜导电性和透过率的提高有明显的促进作用。适当提高基底温度，增加了吸附原子的迁移能，对于薄膜结晶质量、择优取向和掺杂有利。但玻璃基底温度不宜超过450℃。基底温度达到400℃时，薄膜的电阻率达到10^-4量级，透过率到达90％以上。AZO薄膜的光学带宽均大于未掺杂ZnO薄膜的带宽（3．2eV）是由Burstein-Moss效应引起的。随着薄膜厚度的增加，晶粒尺寸增大、晶粒取向性变好、结晶质量变好，有利于电阻率的降低。可见光透过率随厚度增加逐渐下降，符合Lambert定律。当薄膜厚度较薄时，随着薄膜厚度的增加光学带宽减小是由量子尺寸效应引起的。薄膜的电阻率随靶基距的增加而增大。靶基距对薄膜透过率的影响不是十分明显，透过率的改变主要是由薄膜的厚度效应引起的。AZO薄膜电阻率随溅射功率的增加在400W范围内呈单调下降趋势。溅射功率的提高有利于结晶质量的提高和Al的掺杂。随溅射功率的增大，溅射效率得到提高，薄膜厚度增加。透过率随溅射功率的增大而下降是由于薄膜厚度效应引起的。试验中未出现180W处电阻率最小的拐点，与作者采用了超高密度的溅射靶材有关。工作气压为0．1～1．0 Pa的范围内，在不同的溅射功率下薄膜的电阻率最低值出现在一个适当的工作气压下，是由溅射原子的平均自由程和等离子气的平均原子间距之间相互协调决定的。工作气压对薄膜的透过率和光学带宽的影响不是十分显著。在200℃和400℃玻璃基底上镀膜，最低电阻率分别可达5．3×10^-4Ω．cm和1．09×10^-4Ω．cm。较高的氧分压条件下薄膜的电阻率呈数量级增大，与氧空位数量减少有关。氧分压有助于薄膜的可见光透过率的提高，与有氧分压的条件下薄膜结晶质量提高、缺陷含量减少有关。但较低的氧分压（0．1％O₂）不利于AZO薄膜的（002）择优取向。不同氧分压下光学带宽的变化可能与薄膜中的应力变化有关。加镀ZnO缓冲层有利于AZO薄膜结晶质量的提高、（002）峰的择优取向和残余应力的松弛。ZnO缓冲层对AZO薄膜的透过率影响不大，可见光平均透过率在90％左右。基底温度为250℃，分别在40mm或60mm靶基距溅射AZO薄膜，可以制备出具有较低电阻率(10^-4)和较高可见光反射率（51％）或较高电阻率(10^-3)和透过率（87％）的ITO／AZO双层膜。采用在400℃基底温度、60mm靶基距制备AZO薄膜，双层膜具有较高的可见光透过率（85～90％）和较低的电阻率(10^-4量级)。当ITO／AZO的厚度比为1：9时，得到最低的电阻率为4．89×10^-4Ω．cm。更多还原

【Abstract】 In the recent years, transparent conductive films had became one of materials inthe development of flat-panel display, plasma display panel, touch panel, OLEDdisplay, thin film solar cells and the like. Since the most important commercialmaterial for transparent conducting films nowadays is Sn-doped In₂O₃ （ITO） but themetal indium is rare resources, so the research and development of non-In materialshave attracted considerable attention in scientific research and in technologicalapplications. Recently, ZnO films have attracted interest as a transparent conductivecoating material, because the materials are consist of cheap and abundant element,non-toxic and lots of excellent characteristics. Thereby, there were aspects studied byus as follow: the ultra-density ZnO-base ceramic target were researched and developedin a low cost course of colloidal processing and pressureless sintering; the effect ofprocessing parameters on films were studied which were prepared by radio frequence（rf） with our ultra-density targets; bi-layer transparent conductive films were preparedand studied tentatively. The main concerned results and conclusions are as follow:The influences of mass fraction of additive, solid volume fraction, pH value andmilling time on the stability and fluidity of ZnO-Al₂O₃ powders aqueous suspensionwere investigated by experiments of zeta potential, viscosities and sedimentation etc. Itis found that ZnO and Al₂O₃ powders had lower zeta potential than -45 mV commonlyat pH 8-10.3 with polyacrylic acid （PAA） added. The zeta potential of ZnO and Al₂O₃had not research obviously changes adding polyethylene glycol （PEG） simultaneously,compared with only PAA added. At 0.2wt% PAA, the viscosity is lower and the slurriesare stabiler due to the saturated adsorbed amount of PAA is 0.2wt%. The lowestviscosity, the best stability and the 55% （vol. %） solids of the suspension has beenobtained when the pH value is about 9 and the mass fraction of polyacrylic acid is0.2%. The quantity of adding polyethylene glycol is increased, the viscosity ofsuspension is increased and the stability of suspension is deceased. Milling time of 40his selected as optimum in this test. XRD analysis shows that theα-Al₂O₃ particles aredistributed homogeneously among ZnO particles and are stable during process timeTo optimize the conditions of ZnO-Al₂O₃ aqueous suspensions and slip casting inorder to obtain dense green bodies and further obtain high density ZnO-Al₂O₃compound ceramics. The influences of mass fraction of additives on the fluidity ofslurries and the density and strength of green and sintered bodies were investigated.The maximum density of green bodies was 66.6% of theoretical density with compactand homogeneous green particles used 30 vol% ZnO-Al₂O₃ slurries at pH9 added0.2wt% ployelectrolytes PAA and 0.2wt% binder PEG. Since 0.2 wt% PAA could equal to the saturated adsorption amount for the ZnO-Al₂O₃ mixture powders which resultsin well dispersing slurry. On the other hand, it is advantageous to subsequent processcompare to without binders that the radial crushing strength of cast samples increasedto 12.5 MPa with 0.2% PEG added. After pressureless sintering at 1 400℃for 2 h, analmost full density body （＞99.6% TD） can be obtained at the conductions of pH9, 0.2wt% PAA and 0.2 wt% PEG. 0.3%PAA （slightly execess of PAA） added improved thestrength and density of sintered bodyies.The Al₂O₃ reacted with ZnO to form theZnAl₂O₄ spinel phase during pressureless sintering. The microstructure observationsreveal that very homogeneous materials are obtained without abnormal grain growthand free of defects and with homogeneous distribution of Al species.In the processing of film prepared, the increasing substrate temperature couldimprove conductivity and transmittance evidently due to increase the diffusivity ofadsorbed atoms to improve crystalline quality, preferred orientation and doped-level,However the temperature of glass substrate is not suitable above 450℃. When thesubstrate temperature reached 400℃, the film resistivity reached 10^-4 levels andtransmittance was above 90%. The band gaps of the AZO films are larger than theun-doped ZnO film （3.2eV） owing to Burstein-Moss effect. With the film thicknessincreasing, the gains sizes and the preferred orientation increased, the crystalline qualityand conductivity improved, but the transmittance decreased according to Lambert law.When film thickness is thinner, the band gap decreased with film thickness increasingmight be due to quanta-size effect. With the distance between target and substrate （TS）increased the resistivity of AZO film increased, which gives no evident influence oftransmittance. The change of transmittance mainly owe to the thickness effect of film.With the sputter power increased up to 400W, the resistivity of AZO filmmonotonously decreasing and film thickness increasing due to improve sputteringefficiency and the decrease of transmittance mainly owe to the thickness effect of film.Increase of sputter power improved crystalline quality and doped-level. In our study, at180W the inflexion of the minimum resistivity point is not found which might becontributed to the use of our ultra-density target. In the range of work pressure from 0.1 to1.0 Pa, the minimum resistivity of film was appeared at various work pressure withsputtering power changed which might be duo to inter-correspond between the mean freedistance of sputtered ions and the mean atom distance of plasma gas. The influence ofwork pressure on the transmittance and band gap of film is not evident in our workpressure range. The lowest resistivity of 5.3×10^-4Ω.cm and 1.48×10^-4Ω.cm could beobtained at 200℃and 400℃of substrate temperature respectively. At higher oxidepartial pressure the film resistivity increased in level of quantity due to oxide vacancydecreasing. The oxide partial pressure was improving the film transmittance to visiblelight which is relative to crystalline quality improved and the concentration of defectdecreased under oxide pressure. However the lower oxide partial pressure （0.1%O₂） is notbenefit to （002） preferred orientation. The changes of band gap of AZO film at various oxide partial pressures might be duo to the change of film stress.Adding ZnO suffer layer could improve crystalline quality and （002） preferredorientation of AZO film and depress their residual stress. The mean transmittance ofbi-layer film is about 90%, since the transmittance is not remarkably effected by ZnOsuffer. The ITO/AZO bi-layer film had higher reflectivity （up to 51%） with lowerresistivity (10^-4) or higher transmittance （87%, at below 500nm of AZO film thickness）with higher resistivity (10^-3) at 40 mm or 60 mm of TS when sputtering AZO film on250℃glass substrate respectively. The ITO/AZO bi-layer film had higher transmittance（85～90%） and lower resistivity (10^-4) when sputtering AZO film at 60 mm of TS and 400℃of glass substrate. The lowest resistivity of 4.89×10^-4Ω.cm could be obtained at 1:9 ofthe ITO/AZO thickness ratio.更多还原