| 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. |
PDF Full Text Request