二氧化钛薄膜的阻变性能优化研究

发布时间：2018-02-27 14:44

本文关键词： 阻变存储器氧化钛阻变的物理特性掺杂氧化钛薄膜电极工程　出处：《湘潭大学》2016年硕士论文　论文类型：学位论文

【摘要】：在过去的几十年中,因为高速/高存储密度的非易失性存储器(NVMs)的出现,信息技术的持续发展从而使得我们的计算机能具有强大的处理能力。但是,传统的非易失性存储器(例如闪存)的器件尺寸将会在不远的将来达到技术的物理极限。为了解决这个问题,研究者们提出了一些新型的非易失性存储器的概念。基于新型材料的下一代非易失性存储器的候选,有相变存储器、铁电存储器、磁存储器以及阻变存储器(RRAM)。在这些存储器中,基于某一些材料的电阻转换效应的阻变存储器得到了十分广泛关注,这是由于它的结构简单、功耗低、开关比高、擦写速度快、保持时间长以及与半导体工艺兼容等优点。许多多晶态和非晶态的过渡金属氧化物(TMOs)均被应用于阻变存储器中,其中包括了TiO2、ZrO2、ZnO和Hf O2等。而基于氧化钛的阻变存储器,其电阻转换机制是较为清晰:TinO2n-1(即所谓的Magnéli相)导电细丝的形成和断裂。因此,我们选择了氧化钛薄膜的阻变存储器作为研究的重点,具体工作内容如下:(1)从理论上,建立了氧化钛阻变器件的导电模型,并利用第一性原理计算了器件掺杂前后的氧空位生成能和导电细丝能带图,对器件的电学性能进行了理论分析。(2)利用溶胶-凝胶法在Pt/Ti/SiO2/Si的衬底上制备了氧化钛的薄膜,并利用相应的手段对其进行了微观结构的表征。随后,我们运用Keithley 4200-SCS半导体参数分析仪测试了Pt/TiO2/Pt器件的电学性能,发现Pt/TiO2/Pt器件存在单、双极阻变特性共存的现象并且还需要一个电初始化过程。电阻转换的阈值电压和高阻态阻值的分布较为分散,需要进一步的提升器件的稳定性。(3)利用溶胶-凝胶法合成了P型离子(La)与N型离子(Fe)掺杂的氧化钛薄膜,并且对比了它们的阻变性能。与未掺杂氧化钛器件相比,La、Fe离子掺杂的阻变器件的阻变性都能得到明显改善,包括将低了Set的电压、提高了转换电压和高阻态时的稳定性。尤其是La掺杂器件,阻变性能的改进更为突出。这是由于La离子掺杂能够使氧化钛薄膜内氧空位生成增多。此外,关于掺杂引起的氧化钛薄膜内氧空位生成能的降低,我们通过实验验证了理论计算的结果及导电细丝能带图的结果。(4)此外,我们还探究了将La离子掺杂的氧化钛阻变存储器的Pt顶电极换为Ag作为顶电极所造成的影响,在其中金属Ag扮演者导电细丝这一重要角色。与Pt作为顶电极的结构相比,Ag/TiO2:La/Pt系统中阻变参数的均匀性得到了显著改善,例如转换电压及高、低阻态阻值。当重复循环扫描100次后,,由于器件的损耗较大,器件的阻变性能消失。
[Abstract]:In the last few decades, with the advent of high speed / high density nonvolatile memory (NVMs), the continued development of information technology has enabled our computers to have powerful processing power. In order to solve this problem, the device size of traditional nonvolatile memory (such as flash memory) will reach the physical limit of technology in the near future. Researchers have proposed some new concepts of nonvolatile memory. Candidates for the next generation of nonvolatile memory based on new materials include phase change memory, ferroelectric memory, magnetic memory, and resistive memory. Resistive memory based on resistive conversion effect of some materials has been paid more and more attention because of its simple structure, low power consumption, high switching ratio, and fast writing speed. Many transition metal oxide (TMOs) of polycrystalline and amorphous states are used in resistive memory, including TIO _ 2o _ 2ZrO _ 2 ZnO and HF _ 2, and resistive memory based on titanium oxide. The mechanism of resistance conversion is the formation and fracture of the conductive filament of: TinO2n-1 (so called Magn 茅 li phase). Therefore, we choose the resistive memory of titanium oxide film as the focus of the research, and the specific work is as follows: 1) theoretically. The conductive model of titanium oxide resistive device is established. The oxygen vacancy formation energy and the energy band diagram of conductive filament before and after doping are calculated by the first principle. The electrical properties of the device were theoretically analyzed. (2) Titanium oxide thin films were prepared on Pt/Ti/SiO2/Si substrates by sol-gel method, and their microstructure was characterized by corresponding means. We have tested the electrical properties of Pt/TiO2/Pt devices by using Keithley 4200-SCS semiconductor parameter analyzer, and found that there is a single Pt/TiO2/Pt device. The coexistence of bipolar resistance and the need for an electrical initialization process. The distribution of threshold voltage and high resistance resistance values for resistance conversion is more dispersed. In order to improve the stability of the device, the doped titanium oxide films were synthesized by sol-gel method. Compared with the undoped titanium oxide devices, the resistive properties of these devices are improved obviously, including the reduction of the voltage of Set. The conversion voltage and the stability of high resistance state are improved, especially for La doped devices. This is due to the increase of oxygen vacancies in titanium oxide films due to the doping of La ions. With regard to the decrease of oxygen vacancy formation energy in titanium oxide films caused by doping, we have verified the theoretical results and the results of the band diagram of conductive filaments by experiments. In addition, We also investigated the effect of changing the Pt top electrode of La ion doped titanium oxide resistance memory into Ag as the top electrode. In which Ag plays an important role in conducting filament. Compared with Pt as the top electrode, the uniformity of resistance parameters in Ag / TIO _ 2: La / Pt system has been significantly improved, such as the conversion voltage and the high conversion voltage. Low resistance state resistance. After 100 cycles of repeated cyclic scanning, the resistance performance of the device will disappear due to the large loss of the device.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TP333

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