【作者】 刘建科；

【导师】 王秀峰；

【作者基本信息】 陕西科技大学 ， 材料物理与化学， 2014， 博士

【摘要】 氧化锌（ZnO）的禁带宽度很大，激子束缚能力强，具有很高的电导率，因此在半导体电阻材料、太阳能材料以及荧光材料等方面均有广泛地应用。ZnO做为电阻材料其电阻特性主要表现形式为压敏电阻和线性电阻。ZnO做为线性电阻时，其伏安特性（I-V）为线性，材料是一种多晶半导体，非线性系数相当小，电阻温度系数为正，通流能力很强，同时电阻率可调范围较大。其机理是因为晶粒与晶界之间的接触为欧姆特性。它的主要应用领域是现代电力-电子技术中的电流断路器，释能电阻器、点接地电阻器以及无感测量电阻装置等。ZnO压敏电阻是一种以ZnO为主体的多晶半导体陶瓷，经过典型的电子陶瓷工艺制成，同时掺杂了多种金属氧化物。在ZnO压敏电阻击穿区内，压敏电阻两端所加的电压大于其压敏电压，ZnO具有压敏特性的主要原因是隧道击穿电子机理。其主要应用领域是高压稳压电路中，如电视机视放管、高压真空开关以及卫星地面接收站等。本文研究掺杂对ZnO电阻特性的影响，在以下方面做出了创造性成果：（1）ZnO薄膜的制备采用射频磁控溅射法分别在玻璃衬底和塑料衬底（对苯二甲酸乙二醇酯PET）上分别对掺铝的氧化锌进行沉积，形成厚度在200nm左右的透明导电薄膜（AZO）。实验结果表明：薄膜厚度均匀。PET衬底和玻璃衬底上，AZO薄膜的方阻分别为45/sq和19/sq，透光率均达90%以上。这说明，在制备AZO薄膜时，柔性衬底可以代替硬质衬底，其应用能够使电子器件更加微型化、集成化、智能化。研究表明，这种方法制备的ZnO薄膜满足对其电阻特性研究的条件，且对ZnO薄膜的改性研究提供了技术支持。（2）研究发现：ZnO掺杂碱土或金属氧化物氧化镁、氧化钛、氧化铝（MgO，TiO2，Al2O3）后，经SEM、XRD、EDS测试以及电性能参数的测定，可大幅提高线性电阻的能量密度，降低非线性系数。结果表明：掺入MgO对ZnO线性电阻的性能影响很大，使ZnO晶粒内部的电子气压强随温度的升高而下降，直接导致阻温系数显著增加；当MgO掺杂量达到7wt%时，线性电阻的能量密度高达812J/cm3，非线性系数为1.12，阻温系数为正，并且达到3.4×10-4/℃；掺杂TiO2可以大幅度提高基体的致密度和晶粒的均匀性，从而显著地影响其能量密度，当有7wt%的TiO2掺入到ZnO线性电阻时，其能量密度可以达到780J/cm3；掺杂Al2O3则能改变尖晶石的生成方式以及生成量，减小线性电阻颗粒的晶粒尺寸，降低晶界势垒高度，对ZnO线性电阻的非线性系数与电阻率也有很大的影响。当Al2O3掺杂量达到9wt%时，电阻率达到285.24·cm，非线性系数低至1.17。（3）研究发现：ZnO掺杂稀土氧化物（Y2O3、La2O3）可以使基体颗粒的分布更加均匀，能大幅降低ZnO线性电阻的非线性系数，并提高电阻率的稳定性。当Y2O3、La2O3的掺杂量分别为0.25mol%、0.5mol%时，线性电阻的能量密度分别达到809J/cm3、812J/cm3，非线性系数分别达到1.14和1.12，电阻温度系数分别达到2.7×10-4/℃和3.4×10-4/℃。（4）研究发现：ZnO中掺杂Y2O3和Pr6O11可以显著影响其压敏特性，较大幅度提高非线性系数和压敏电压。同时，烧结制度对其性能也有影响。通过SEM、XRD和EDS等性能测试，结果可以看出，Y2O3和Pr6O11的引入，改变了尖晶石的生成方式，细化了压敏电阻的颗粒尺寸，同时稀土元素在ZnO晶界钉扎，抑制晶粒的生长，使晶体微观结构更加均匀。此外，在烧结过程中，稀土氧化物能增加施主浓度，增加ZnO晶体中的的自由电子浓度，从而使填隙的Zn2+浓度下降和传质能力下降，抑制了ZnO晶粒的生长。但是，Y2O3是施主掺杂，提供大量的施主电子，降低了ZnO的肖特基势垒，能使非线性系数减小，进而使漏电流增大，因此在该方面对提高ZnO压敏电阻的电学性能不利。研究表明：当Pr6O11掺杂量为3.37wt%，烧成温度为1150°C时，压敏电阻的电学性能最佳，且漏电流很小，仅为0.4μA，非线性系数达到44，压敏电压达到340V/mm。（5）研究发现：掺杂ZnO的制备工艺对其线性电阻的微观结构和电学性能也有较大影响。控制好烧结温度和降温速率，能制备出能量密度高，阻温系数小，非线性系数小，以及均匀性高的ZnO线性电阻。基于前面掺杂TiO2改善ZnO线性电阻的配方，①对添加剂进行不同方法的处理，同时改善烧结制度，当添加剂在1100℃条件下煅烧2小时，线性电阻的能量密度达到821J/cm3，非线性系数达到1.10，且阻温系数为正，达到3.94×10-4/℃。同时，电阻率为792·cm，电阻率的稳定性达到56.4%；②添加剂经过适当的煅烧温度和降温处理可以降低反应活化能，提高粉料的活性，从而提高原料的分散性，使微观颗粒分布更加均匀，进而优化ZnO线性电阻的电性能参数，当烧成温度在1320℃到1360℃之间，降温速率在100℃/h左右时，线性电阻的电性能参数相对最佳。当控制烧结温度为1340℃，降温速率为100℃/h，经测试可知，能量密度达到825J/cm3，非线性系数达到1.10，阻温系数达到4.01×10-4/℃，同时电阻率为790·cm，电阻率的稳定性为57.4%。ZnO无论作为透明导电薄膜，压敏电阻还是线性电阻，均与ZnO的六角纤锌矿结构密切相关。对于线性电阻和压敏电阻，主要与ZnO的晶粒尺寸，晶界势垒等因素相关。控制晶界的成分，或尖晶石的数量及生成方式可以有效地控制ZnO电阻的非线性系数，势垒高度以及能量密度等性质，从而决定ZnO线性电阻和压敏电阻中在不同领域中的应用。更多还原

【Abstract】 Zinc Oxide (ZnO),with very big band gap and the strong exciton bindingcapability, have high conductance.There are widely used in semiconductormaterials, solar energy materials and fluorescent materials and so on. ZnO can beas resistance materials, mainly about linear resistance ceramics and varistors.As a linear resistance, the volt ampere characteristic (I-V) of ZnO is alinear, it is a polycrystalline semiconductor with very small nonlinear coefficientand the positive resistance temperature coefficient, so its flow passagecomponent is very significant, and its resistivity have large tuning range,theresean is ohmic contact for grain and grain boundary.The application fieldmainly inlude current circuit breaker of modern power electronic technology,energy release resistor,the contactless measurement of resistance and so on.ZnO varistor is a polycrystalline semiconductor ceramics made mainly withZnO as the main body by electronic ceramics typical process, simultaneouslydoped with various metal oxides. At ZnO varistor breakdown region, the varistorvoltage on both ends of the varistor voltage is greater than the varistorvoltage.The main reason ZnO as a varistor is tunneling electron mechanism.Themain field of application is high voltage stabilizing circuit, such as the TVtube,high voltage vacuum switch and satellite ground receiving station.This paper studies the effect of ZnO doping on the electrical resistance,made creative achievements as the following aspects:(1)The preparation of ZnO thin filmsBy RF magnetron sputtering, Zinc Oxide were deposited respectively onaluminum doped in the glass substrate and the plastic substrate, the formation ofabout200nm in thickness of the transparent conductive film (AZO). Theexperimental results show that the film thickness is uniform. The sheetresistances of the films deposited on glass and PET substrates were19/sq and45/sq respectively, and their visible transmittances both were>90%. Thisshows that the hard substrate can be replaced by flexible substrate in preparing AZO thin film, its application in electronic devices can make devices moreminiaturization, integration and intelligent.Our research shows that, ZnO thinfilms prepared by this method satisfy the resistance characteristics of conditions,which provides technical support for the ZnO films modified study.(2)This study found that ZnO doped alkaline earth metal oxides or MagnesiumOxide, Titanium oxide, Alumina (MgO, TiO2, Al2O3), can greatly improve thelinear resistance energy density and reduce the nonlinear coefficient,which havemeasured by SEM, XRD, EDS test and electric performance parameters.Research results show that: MgO-doped have greatly influences on the ZnOlinear resistor, and the electron gaspressure inside the ZnO grains strongly decreases with the temperatureincreasing, which directly lead to resistance temperature coefficient significantlyincreased; When the MgO concentration is7wt%, the linear resistance of highenergy density up to812J/cm3, The nonlinear coefficient is1.12, resistancetemperature coefficient is positive, and reached3.4×10-4/℃; The TiO2–dopedcan greatly improve the uniformity of density and grain of matrix, thussignificantly affect its energy density; When the TiO2is doped with7wt%intothe ZnO linear resistor, its energy density can reach780J/cm3; Al2O3-doped canchange the formation of spinel, decreases the grain sizeof linear resistiveparticles and reduce the grain boundary barrier height, which have greatinfluence for the nonlinear coefficient and resistivity of ZnO linear resistor.When the Al2O3concentration reached9wt%, resistivity reached285.24Ω·cm,the nonlinear coefficient is below1.17.(3) The results show that ZnO doped rare earth oxides (Y2O3, La2O3) canmake the distribution of matrix particles more evenly,reduce the nonlinearcoefficient of ZnO linear resistor significantly, and improve the stability ofelectrical resistivity. As the doping amount of Y2O3and La2O3get0.25mol%and0.5mol%respectively, the energy density of ZnO linear resistance are809J/cm3and812J/cm3, the nonlinear coefficient were1.14and1.12and theresistance-temperature coefficient get2.7×10-4/℃and3.4×10-4/℃respectively.(4) The results suggest that ZnO doped with Y2O3and Pr6O11cansignificantly affect the varistor characteristics, increase the nonlinear coefficientgreatly and the varistor voltage. At the same time, the sintering system also has influence on its performance. After tested by the SEM, XRD and EDS weretested, the results show that:withthe introduction of Y2O3and Pr6O11, the wayof the formation of spinel changed; the varistor particle size become small,,thegrain growth is restrained with rare earth elements in the ZnO grain boundarypinning, and the crystal microstructure is more uniform. In addition, in theprocess of sintering, rare earth oxides can increase the donor concentration andincrease the concentration of free electrons in ZnO crystal, which made bothinterstitial concentrations of Zn2+and the mass transfer ability decreased andinhibit the growth of ZnO grains. However, the doped Y2O3was as a donordoping to provide a large number of electronic, resulting in reduction of Schottkybarrier, which reduces the nonlinear coefficient, increases leakage current andagainst for improving the electrical properties of ZnO varistor. When thesintering temperature was1150°C and the doping of Pr6O11was3.37wt%, thevaristor electrical performance is the best, and the leakage current is very small,only0.4μ A, nonlinear coefficient reaches44, the varistor voltage up to340V/mm.(5) The results show that doped ZnO preparation process had a great influenceon the linear resistor microstructure and electrical properties. Well control ofsintering temperature and cooling rate can prepare ZnO with characteristics ofhigh energy density, small resistance temperature coefficient, small nonlinearcoefficient and high uniformity. Baed TiO2-doped technology improved linearresistance formula of ZnO,①method for processing different additive, andimprove the sintering system, When the additive in the condition of1100℃calcination of2hours, the linear resistance and energy density reached to821J/cm3, the nonlinear coefficient is1.10, and the resistance temperaturecoefficient is positive, reached3.94×10-4/℃. At the same time, the resistivity is792cm, the stability of electrical resistivity reached56.4%.②The additive aftersuitable calcining temperature and cooling treatment can reduce the reactionactivation energy, improving powder activity, so that improve the dispersion ofraw materials, the micro-particle distribution is more uniform, and thenoptimization the electric performance parameters of ZnO linear resistor. Whenthe firing temperature is in1320℃to1360℃, the cooling rate at100℃around/h, the electric performance parameters of linear resistance relative to the best. When the sintering temperature is1340℃, the cooling rate of100℃/h, the testresults show that energy density reached825J/cm3, nonlinear coefficient reached1.10, resistance temperature coefficient is4.01×10-4/℃. At the same time,resistivity is790cm, the stability of electrical resistivity of57.4%.ZnO ceramic could be used in transparent conducting thin films, varistorsand linear resistances, which is closely related to its hexagonal wurtzite structure.As varistors and linear resistances, which mainly associated with the grain sizeof ZnO and the grain boundary barrier factors.We can control the nonlinearcoefficient, grain boundary barrier and energy density of ZnO resistance byadjusting the constituent of grain boundary, or the number of spinel and theproducing way of spinel. According to these properties, we can apply ZnO aslinear resistor or the varistor in different fields.更多还原