硅工艺兼容型铁电存储器的多逻辑态存储研究

发布时间：2018-03-24 04:16

本文选题：多逻辑　切入点：铁电存储器　出处：《湘潭大学》2017年博士论文

【摘要】：基于双稳态极化来存储数据的铁电存储器(FRAM)具有工作温度范围宽、读写速度快、抗疲劳、功耗低、强抗辐射性等优点,已经被应用在卫星、深空探测器等多种航天器中。但目前的FRAM仍然存在与Si工艺难兼容和存储密度过小等问题,限制了其在民用领域的应用。为促进FRAM的应用,本论文探索了在Pt及Si衬底上制备多晶铁电超薄膜的工艺,研究了制备的铁电超薄膜的铁电性能及其在多逻辑态存储的应用,并分析了多逻辑态存储机理。该研究为解决FRAM与Si工艺的兼容和存储密度低等问题提供了一种新途径,能促进FRAM的商业化应用。本论文的具体工作和相应结果如下:1.通过采用不同的制备参数来调控Pt衬底上超薄PbZr0.52Ti0.48O3(PZT)薄膜的铁电性能,从厚膜开始入手逐步实现了具有良好铁电性能的多晶PZT铁电超薄膜制备,并研究了基于PZT铁电超薄膜的Pt/PZT/Pt可翻转二极管的开关特性。通过制备参数的调制实现了具有较好电滞回线的多晶铁电超薄膜制备,当PZT薄膜厚度低于50 nm时,随薄膜厚度降低,尽管PZT超薄膜的剩余极化强度逐渐降低,但是当薄膜厚度降低至29 nm时仍保持明显的铁电性能。另外基于所制备的多晶铁电超薄膜制备了Pt/PZT/Pt可翻转二极管单元,其开关比随PZT薄膜厚度的减小而逐渐降低。当铁电薄膜的厚度薄至13 nm时,该可翻转二极管开关特性依然明显,表明超薄多晶铁电薄膜依然可应用于存储器件中。2.设计了一种铁电忆阻器存储单元,通过使用活性电极来调控铁电薄膜中的氧空位浓度,并通过电场控制氧空位的迁移距离等实现高低阻态电流的高比值。通过调控薄膜制备氧压生长了具有不同初始氧空位浓度的PZT薄膜,并制备了Ag/PZT/Pt存储单元。研究了PZT氧空位的浓度与存储单元忆阻行为的相关性。当制备氧压为10 Pa时,该单元可以实现六个逻辑态的存储;当制备氧压为20 Pa时,该单元可以实现四个逻辑态的存储,此时最高阻态和最低阻态之间的比值最高,可以达到107~108%。这些器件具有很高的开关比和良好的保持性能,用作两逻辑态存储时可以保持105 s以上,表明其在非挥发性铁电忆阻器中具有巨大的应用潜力。3.设计了一种基于ZnO:Mn/PZT复合薄膜的多逻辑态存储单元,通过逐层控制薄膜的电阻状态,开发了一种基于控制Ag离子迁移、铁电极化翻转以及氧空位迁移来实现四逻辑态存储的单元器件。研究了Ag/ZMO/PZT/Pt复合薄膜存储单元的多逻辑态存储行为,该存储单元综合了Ag/PZT(8 nm)/Pt和Ag/ZMO(20 nm)/Pt两种存储单元的阻变机理,在不同电压激励下能逐步实现Ag离子迁移、铁电极化翻转和氧空位迁移,进而实现了四逻辑态存储。该复合薄膜存储单元具有较好的重复写入性能,能在较短的时间内保持其逻辑态。该研究表明通过不同原理组合来构建新型多逻辑态存储器的设想是可行的,为新型多逻辑态存储器件研发提供了新思路。4.构建了Pt/PZT/SiOx/Si铁电隧道结单元,通过隧道结中铁电极化翻转和氧空位迁移实现了多逻辑态存储,探索了多晶铁电超薄膜应用于多逻辑态存储时与Si工艺的兼容性。在Si衬底上沉积的不同厚度PZT超薄膜具有较好的铁电性能;当使用Pt顶电极将其制备成Pt/PZT/SiOx/Si铁电隧道结单元时,其开关比随着PZT薄膜厚度的增加先增大后减小;当存储单元中PZT厚度为2.5 nm时可实现8态存储,在100 s内其各逻辑态保持性较好,且具有较好的可重复写入性能。该铁电隧道结单元的多逻辑态存储是由铁电极化翻转和氧空位迁移共同引起的。该研究结果为开发与Si工艺兼容的铁电存储器提供了新思路。5.使用BiFeO3(BFO)铁电材料来制备直接沉积在Si衬底上的多逻辑态铁电隧道结单元,研究了Pt/BFO/SiOx/Si铁电隧道结单元的存储性能,然后使用数值计算的方法对构建的存储机理模型进行了验证。研究结果表明,所制备的多逻辑态铁电隧道结单元的存储机理和可存储逻辑态的数量均与BFO薄膜的厚度相关:当采用的BFO薄膜的厚度在2 nm时,存储单元的存储行为由氧空位的迁移引起,可以实现2态存储;当厚度在3.5 nm及以上时,存储行为由氧空位和极化翻转共同引起,可以实现4态及以上的存储。所制备的BFO铁电隧道结单元保持性优于PZT铁电隧道结单元,各个逻辑态在10 min内都可以较好地保持。另外数值计算结果验证了铁电隧道结单元在不同电压激励以后引起的铁电极化翻转和氧空位迁移导致势垒高度和宽度变化的模型是正确的。该研究为开展提高与Si工艺兼容型铁电存储器的保持性能研究提供了指导。
[Abstract]:To ferroelectric memory data storage based on double steady state polarization (FRAM) has a wide range of working temperature, read and write speed, anti fatigue, low power consumption, strong radiation resistance and other advantages, has been widely used in satellite and other spacecraft in deep space probe. But the current FRAM still exists and difficult problems and compatible with Si process the storage density is too small, which limits its application in civil field. In order to promote the application of FRAM, this paper explores the process in the Pt and Si substrate preparation of polycrystalline ferroelectric film, ferroelectric properties of ferroelectric preparation of ultra thin film and its application in logic state storage, multi the logic state storage mechanism and analysis. The research provides a new way to solve the FRAM and Si process compatibility and low storage density, can promote the commercial application of FRAM. The specific work and the corresponding results are as follows: 1. by using different preparation The parameters to control the Pt substrate PbZr0.52Ti0.48O3 (PZT) ferroelectric thin film performance, from the start with the gradual implementation of the thick film ferroelectric polycrystalline PZT has good ferroelectric properties of ultra thin film, and the effects of PZT ferroelectric ultrathin films of Pt/PZT/Pt based on switching characteristics of flip diode. Modulation by preparation parameters to achieve a multi the crystal has a good ferroelectric hysteresis of the ultra thin film, when the PZT film thickness below 50 nm, with film thickness decreased, while the remnant polarization of PZT thin films decreased gradually, but when the film thickness is reduced to 29 nm is still maintaining the ferroelectric properties obviously. In polycrystalline ferroelectric prepared by super preparation of thin film Pt/PZT/Pt flip diode unit based on the switching ratio decreases with PZT film thickness decreases. When the thickness of the ferroelectric thin film thin to 13 nm, the reversible diode switching characteristics still significantly, table The ultra-thin polycrystalline ferroelectric thin films still can be applied to the memory device of the.2. design of a memristor ferroelectric storage unit by using active electrode to control the concentration of oxygen vacancy in ferroelectric thin film, and the high ratio of low resistance current through the electric field control of oxygen vacancy migration distance. By regulating the preparation of thin film oxygen the pressure to grow PZT films with different initial concentration, the Ag/PZT/Pt storage unit and prepared. The correlation of the concentration of oxygen vacancy and storage unit PZT memristive behavior. When the preparation of oxygen pressure is 10 Pa, the unit can achieve six logic state storage; when preparing oxygen pressure 20 Pa, the unit can achieve four logic state storage, the ratio between the highest and the lowest resistance resistance can reach 107~108%. the highest, these devices have very high switching ratio and maintain good performance, as the two logic states Storage can be maintained above 105 s,.3. showed that it has great potential to design a multi state logic storage unit of ZnO:Mn/PZT composite films based on ferroelectric nonvolatile memristor, the resistance state of each layer control film, developed an ion mobility control based on Ag, ferroelectric polarization reversal and oxygen to achieve the vacancy migration unit four logic States storage. Logic state storage behavior of Ag/ZMO/PZT/Pt composite film storage unit, the storage unit integrated Ag/PZT (8 nm) and /Pt Ag/ZMO (20 nm) /Pt two storage unit resistance change mechanism, to gradually realize the Ag ion migration under different excitation voltage, ferroelectric polarization flip and oxygen vacancy migration, thus achieving a four logic state storage. The composite film storage unit with repeated write performance better, can maintain its logic state in a relatively short period of time. The study on the table The idea through different combination principle to construct a new multi state memory logic is feasible, and provides a new way to construct the Pt/PZT/SiOx/Si.4. model for multi unit ferroelectric tunnel junction logic state of memory research, through the tunnel junction in the ferroelectric polarization flipping and oxygenvacancy transfer the logic state of storage, explore the polycrystalline ferroelectric ultrathin films application in logical state storage compatibility with Si technology. Different thickness of PZT thin film deposited on Si substrate with good ferroelectric properties; when using the Pt top electrode fabricated Pt/PZT/SiOx/Si ferroelectric tunnel junction unit, the on-off ratio with the increasing of PZT film thickness increases first and then decreases; when the storage unit PZT thickness of 2.5 nm can achieve 8 state storage, within 100 s of the logic state keep well, and has good performance. Many repeated write logic state of the ferroelectric tunnel junction unit. The reservoir is caused by the migration of ferroelectric polarization flip and oxygen vacancy in common. The results of this study for the development of ferroelectric memory compatible with Si technology provides a new way to use.5. BiFeO3 (BFO) ferroelectric materials prepared by direct deposition on Si substrate by multi state logic ferroelectric tunnel junction unit, the storage performance of Pt/BFO/SiOx/Si ferroelectric tunnel junction unit, then use the method of numerical calculation to verify the mechanism of storage model. The results show that the storage mechanism unit tunnel junction logic state and the number of the ferroelectric memory logic state with the thickness of BFO thin film: when the thickness of the films by BFO at 2 nm. The storage behavior of memory cell caused by the migration of oxygen vacancies, can achieve 2 state storage; when the thickness is 3.5 nm or above, common storage behavior caused by oxygen vacancies and polarization reversal, can achieve 4 state and above The storage for BFO ferroelectric tunnel junction cell prepared to maintain better than PZT ferroelectric tunnel junction unit, each logical state can be maintained within 10 min. The results are also verified by a numerical calculation of ferroelectric polarization reversal and ferroelectric tunnel junction cell caused by oxygen vacancies at different excitation voltage after migration leads to the barrier height and width variation the model is correct. The study provides guidance to maintain properties of ferroelectric memory is carried out to improve the compatibility with the Si process.

【学位授予单位】：湘潭大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TP333;TB383.2

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