【作者】 刘晓华；

【导师】 周大雨；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2018， 硕士

【摘要】 当前各式各样的可穿戴式、便携式甚至是可植入式器件的发展对其能量供给单元的尺寸小型化提出了更高的要求。传统储能解决方案,如超级电容器、锂电池及燃料电池等,因其较小的功率密度不适用于小型器件需要快速充放电的应用场景。静电电容器虽然具有极高的功率密度,但其较小的储能密度无法满足小型能量供给单元的储能需求。目前,提高静电电容器储能密度的最佳方案是采用以反铁电材料为介质层制备静电电容器,利用其非线性极化的特性以求在同等外加电压下获得更高的储能密度。但目前得到广泛研究的钙钛矿型反铁电材料与硅基半导体工艺不兼容,暂时无法与半导体器件集成以投入实际应用。而近年来研究发现,通过掺杂特定元素改性后的二氧化铪薄膜具备反铁电性质。由于二氧化铪材料是一种晶体管高k介质材料,具备良好的工艺兼容性。这一具备新性质材料的发现有望突破目前的技术瓶颈,成为制备高储能密度静电电容器介质材料的最佳选择。本文以掺杂浓度为6 mol%的Si掺杂HfO₂反铁电薄膜作为研究对象,通过宏观电学性能测试系统地探究这类萤石型反铁电薄膜极化特性及储能特性的外电场依赖性、温度稳定性及疲劳特性。实验表明,高场下Si掺杂HfO₂反铁电薄膜具备很高的储能密度,达到61.2 J/cm³,高于目前所报道的其他种类静电薄膜电容器的储能密度值,换算为单位质量储能密度后为1.77 Wh/kg,较目前商用静电电容器同类数值提高两个数量级。此外,实验发现温度下降导致薄膜内部非极性四方相向铁电正交相发生转变,即低温有利于正交相的稳定。作者利用一级相变理论中不同温度下四方相与正交相相对自由能的变化解释了上述实验现象。薄膜的储能特性也表现出了优异的温度稳定性。在210⁴00 K宽温度区间内,Si掺杂HfO₂反铁电薄膜的储能密度的变化范围为40.5⁵4.2 J/cm³,这与常温下数值（300 K,3.5 MV/cm电场下时为47.8 J/cm³）相比波动低于15%。在疲劳测试方面,Si掺杂HfO₂反铁电薄膜表现出了优异的疲劳耐久性,经过外加循环电场10⁹次循环,薄膜的剩余极化强度增大,最大极化强度基本不变。结合同类型铁电薄膜的实验现象,作者参考电畴反转诱发电荷注入模型对Si掺杂HfO₂反铁电薄膜的疲劳特性做出了解释。最后,本论文讨论了疲劳对薄膜储能特性的影响,发现当外加电场加载到10⁹次后,薄膜的储能密度维持在43.0 J/cm³,较初始值减小了18%,表明Si掺杂HfO₂反铁电薄膜的储能特性具备优良的疲劳耐久性。更多还原

【Abstract】 The development of a wide variety of wearable,portable and even implantable devices raises a higher demand for the size of the energy supply unit.Traditional energy storage solutions,such as supercapacitors,lithium batteries and fuel cells,are not suitable for fast charging and discharging applications for small devices because of their small power density.Although the electrostatic capacitor has very high power density,its small energy storage density cannot meet the energy storage needs of the small-size energy supply unit.At present,the best way to improve the energy storage density of the electrostatic capacitor is to use the antiferroelectric material as the dielectric layer to prepare the electrostatic capacitor because its nonlinear polarization can obtain higher energy storage density under the same applied voltage.However,the compatibility of perovskite antiferroelectrics with current silicon based semiconductor technology is temporarily unable to be put into practical application.In recent years,the doped hafnium oxide antiferroelectric film is expected to be the best choice for the preparation of high energy density electrostatic capacitor because of its high k material application background.In this paper,the 6 mol%Si doped HfO₂ antiferroelectric thin film is used as the research object.Through the electrical measurements,we investigate the dependence of the external electric field,the stability in different temperature and the fatigue properties of the energy storage properties of the fluorite-type antiferroelectric thin films systematically.The experimental results show that owing to high field induced polarization and slim double hysteresis,an extremely large ESD value of 61.2 J/cm³ is achieved at 4.5 MV/cm,which is higher than that of any other reported electrostatic capacitors.In addition,it is found that the decreased temperature leads to the transition of the nonpolar tetragonal phase to the ferroelectric orthorhombic phase,and low temperature is favorable to the stability of the orthorhombic phase.All these phenomena can be explained by the first order phase transition theory.Additionally,the energy storage properties of the films also show excellent temperature stability.In the wide temperature range of 210⁴00 K,the variation ranges of energy storage density of Si doped HfO₂ antiferroelectric thin films is 40.5⁵4.2 J/cm³,which is less than 15%of the corresponding value in room temperature（300 K,47.8 J/cm³ under 3.5 MV/cm electric field）.In the fatigue measurement,the Si doped HfO₂ antiferroelectric film shows excellent fatigue resistance.After 10⁹ cycles,the remnant polarization increases and the maximum polarization is rather stable.we partially adopt the widely recognized switching-induced charge-injection model to interpret our experimental results.Finally,the fatigue effect on the energy storage properties of the Si doped HfO₂ antiferroelectric film is discussed.It is found that the energy storage density of the film is maintained at 43 J/cm³ after bipolar field cycling up to 10⁹ cycles,which is reduced by 18%compared with the initial value.It shows that the energy storage properties of the Si doped HfO₂ antiferroelectric film have excellent endurance characteristic.更多还原