原子层淀积金属氧化物阻变存储器件研究

发布时间：2018-01-08 08:37

本文关键词：原子层淀积金属氧化物阻变存储器件研究　出处：《复旦大学》2012年博士论文　论文类型：学位论文

【摘要】：随着闪存技术即将达到尺寸极限而面临无法等比例缩小的问题,一种基于材料电阻转变特性的电阻式存储器(RRAM)由于其结构简单、可缩微能力强、高速、高密度、可三维集成以及与CMOS工艺良好的兼容性等诸多优点,被研究者们广泛关注。研究已经发现了很多具有阻变特性的介质薄膜材料,然而在材料选择、制备工艺,以及器件阻变存储机理等方面还有很多问题值得探讨。为此,本文开展了系统的研究。一方面,用原子层淀积(atomic layer deposition)方法制备了多种具有阻变特性的金属氧化物介质,在材料制备、工艺优化、器件阻变存储特性、阻变微观机制上做了系统研究；另一方面,针对RRAM器件所呈现出的性能不稳定,提出了几种行之有效的优化和解决方法。本文首先研究了近期业界广泛关注的HfO2、La2O3、Nb2O5介质材料,系统探索了原子层淀积HfO2、La2O3、Nb2O5三种氧化物的工艺条件,分析了其材料特性,并制备了基于这些材料的可与CMOS工艺兼容的RRAM器件。研究表明：(1) TiN/Nb2O5/Pt/SiO2/Si结构的RRAM器件具有较低的操作电压,set电压为1.2V, reset电压为-1.2V；(2)TiN/La2O3/Pt/SiO2/Si结构的RRAM器件在1.5V时可以写入信号,-0.6V电压下擦除信号；(3)iN/Hf02/Pt/SiO2/Si结构的RRAM器件的set和reset过程发生在+3.5V和-3.5V；(4)三种RRAM器件均呈现双极性阻变特性；(5)RRAM器件的on/off(?)关比分别为50、100、1000,均呈现不错的抗噪声容限。实验证实了RRAM器件的局部熔丝(filament)导电机制,发现熔丝断裂的位置位于阳极附近,并用C-AFM直观观测到RRAM器件导电熔丝的存在。其次,论文系统研究了ALD掺杂工艺对金属氧化物RRAM存储性能的作用。独特的ALD氧化剂设计(如H2O2)可以引入过量氧掺入,使得氧空位与非键合氧的复合主导了金属氧化物的阻变特性。研究发现,在HfLaO薄膜中存在大量的非键合氧,保证了器件优异的阻变特性。基于HfLaO薄膜的RRAM器件的高低阻值比达到106以上,并在10000次重复扫描中保持稳定。同时,擦写速度也达到10ns。实验数据表明La掺入的Hf基金属氧化物介质薄膜具有优异的阻变特性,该工艺优化的器件在RRAM领域将有良好的应用前景。深入研究了温度对基于HfAlO(?)质材料的RRAM器件的影响。研究发现RRAM阻变行为与温度有密切关系,并且阻变特性能否发生存在一个关键温度值,低于此温度则阻变特性将会消失。研究表明,金属氧化物RRAM的阻变机制是由受温度影响的陷阱电荷的状态所主导,电流导致的焦耳热效应只起到辅助作用。论文通过嵌入Al2O3缓冲层,对NbAlO材料的RRAM器件性能进行了有效优化,其擦写操作可以在很低的电压(±0.8V)范围内完成,使得存储稳定性大为提升。其原因是Al2O3材料与NbAlO材料存在较大的介电常数差异,重构了RRAM器件中的电场分布：介电常数越小的区域电场强度越大。为了验证这种具有电场调制效应的叠层结构对RRAM优化的作用,我们设计了系统的实验,制备了其它三种具有Al2O3缓冲薄介质的叠层结构TaN/Al2O3/NiO/Al2O3/Pt、 TaN/AlO3/ZnO/Al2O3/Pt以及TaN/Al2O3/Pt。实验证明用这样独特堆栈结构来代替单一阻变层能够增强RRAM器件的稳定性。无论是单极性还是双极性的RRAM器件,其阻变特性均能够通过增加介电常数相对小的Al2O3电场调制层来进行优化。叠层结构具有的这种电场调制的阻变效应大大减小了RRAM器件电阻转变过程中的随机性。论文用matlab对上述结构的RRAM阻变行为进行了模拟,得到与实验数据非常吻合的阻变电流电压特性曲线,即具有电场调节作用的堆栈阻变层具有更为稳定的阻变特性。非挥发存储器件中的多值存储技术是实现海量存储的有效途径。研究表明在RRAM器件中,通过改变set过程中的钳制电流幅度(Iset)可以显著改变电阻值的大小,即可以通过这种控制set过程中的钳制电流幅度方式有效地实现器件的多值存储功能。但是钳制电流对低电阻(LRS)值的影响也明显分成两个部分：当钳制电流设置较大时,LRS阻值与Iset成线性关系,Iset越大,LRS越小；当Iset1mA时,LRS随电流Iset变化很小,Iset对LRS调制作用消失,其原因来源于测试设备的电流过冲现象,这一现象在实验中得到了验证。用嵌入金属纳米晶的方法实现了对金属氧化物RRAM阻变特性的优化。制备了TaN/Al2O3:RuNCs:Al2O3/Pt结构的RRAM器件。这种嵌入钌纳米晶的方法大大提升了氧化铝RRAM器件的阻变存储特性,其开关比保持在105以上,远远大于未嵌入纳米晶的102的数据。同时,嵌入纳米晶的RRAM器件在数据的稳定性和保持特性上都有较大提升。
[Abstract]:With flash technology will reach the size limit and can not face the scaling problem, a resistance type memory characteristic change material based on resistance (RRAM) due to its simple structure, can be a strong ability, high speed, high density, many of the advantages of three-dimensional integrated with CMOS technology and good compatibility, by researchers wide attention. Studies have found that a lot of dielectric thin film material resistance change characteristics, but in material selection, preparation process and device, resistive memory mechanism and other aspects there are many issues worthy of study. Therefore, this paper carried out a systematic study. On the one hand, using atomic layer deposition (atomic layer deposition) preparation method with a variety of metal oxide dielectric resistance change characteristics, in the material preparation, process optimization, resistive memory devices, resistive micro mechanism were studied; on the other hand, according to RRAM The performance of the parts is unstable, and several effective optimization and solutions are put forward.
La2O3 this paper studies the recent widespread concern in the industry, HfO2, Nb2O5 materials, systematically explore atomic layer deposition of HfO2, La2O3, Nb2O5 three kinds of oxide process conditions, analyzes its material properties and preparation of RRAM materials can be compatible with these devices based on CMOS technology. The research showed that: (1) RRAM TiN/Nb2O5/Pt/SiO2/Si device structure has a lower operating voltage, the set voltage is 1.2V, voltage is reset -1.2V; (2) the RRAM device TiN/La2O3/Pt/SiO2/Si can write signal in 1.5V, voltage of -0.6V erase signal; (3) set and reset RRAM devices iN/Hf02/Pt/SiO2/Si structure occurred in +3.5V and -3.5V (4; three) RRAM devices show bipolar resistive properties; (5) RRAM device on/off (?) than were 501001000, showed a good anti noise tolerance. Experiments prove that local fuse RRAM devices (filament) It is found that the position of fuse breaking is located near the anode and is intuitively observed in the presence of the conductive fuse of the RRAM device by C-AFM.
Secondly, this paper studied effects of ALD doping process on metal oxide RRAM storage performance. The unique design of ALD oxidizer (such as H2O2) can introduce excessive oxygen incorporation, the oxygen vacancy and non bonding oxygen compound leading variable characteristics of metal oxide resistance. The study found that there are a large number of non bonding oxygen in HfLaO films, the variation characteristics of the device with excellent resistance. High resistance RRAM device based on HfLaO films is more than 106, and remained stable in 10000 repeated scan. At the same time, write speed reached 10ns. the experimental data show that the Hf based metal oxide dielectric thin film La doped with varying characteristics of excellent resistance the optimization process, the device will have a good application prospect in the field of RRAM. Based on the in-depth study of the temperature on the HfAlO (?) RRAM device material. The study found that RRAM resistive behavior and temperature are closely related, and There is a critical temperature value for the occurrence of resistive characteristics. If the temperature is lower than that, the resistance characteristic will disappear. The research shows that the resistance mechanism of metal oxide RRAM is dominated by the state of trap charge affected by temperature, and the Joule heating effect caused by current plays a supplementary role only.
The embedded Al2O3 buffer layer, RRAM devices on the properties of NbAlO materials are effective optimization, the erase operation can be in low voltage (0.8V) range, the storage stability is greatly improved. The reason is that there are large differences in the dielectric constant of Al2O3 material and NbAlO material, the electric field in RRAM devices the electric field strength distribution reconstruction: dielectric constant smaller. Laminated structure in order to verify the effect of electric field modulation with RRAM optimization, we design the system experiments, the other three laminates TaN/Al2O3/NiO/Al2O3/Pt with thin Al2O3 buffer medium was prepared, and the experiment shows that this TaN/Al2O3/Pt. TaN/AlO3/ZnO/Al2O3/Pt the unique stack structure to replace the single resistive layer can enhance the stability of the RRAM device. Both unipolar or bipolar RRAM devices, the resistance change characteristics were able to Optimized by increasing the Al2O3 electric field modulation layer dielectric constant relatively small. This electric field has a laminated structure of the resistive effect greatly reduces the randomness of the RRAM resistance of the device in the transformation process. We use matlab RRAM to the structure of the variable resistance behavior simulation, have very good agreement with the experimental data. The resistive current voltage characteristic curve, which has regulating effect of electric field stack resistance variable layer has more stable resistive properties.
Non volatile memory device in multi valued storage technology is an effective way to achieve mass storage. The results indicate that in RRAM devices, by changing the holding current amplitude in the process of set (Iset) can significantly change the resistance value of the size, or through the control holding current amplitude methods during set can effectively realize the multiple devices the value of storage function. But the holding current of low resistance (LRS) value of the impact was also divided into two parts: when the holding current is high, the LRS resistance linear relationship with Iset, Iset is larger, the smaller the LRS; when Iset1mA, LRS with the current Iset change is very small, Iset to the LRS modulation effect disappeared the reason, the current source test equipment overshoot phenomenon, this phenomenon has been verified in the experiment. Using the method of embedding metal nanocrystals has been optimized on the rheological properties of metal oxide RRAM resistance. TaN/ Al2O3:RuNCs:Al2 prepared RRAM O3/Pt device structure. This method of embedding ruthenium nanocrystals greatly enhance the alumina RRAM device resistive switching characteristics, the switching ratio remained above 105, far greater than not embedded nanocrystals 102 data. At the same time, the RRAM device embedded nanocrystals have greatly improved in the stability of the data and keep the characteristics.

【学位授予单位】：复旦大学
【学位级别】：博士
【学位授予年份】：2012
【分类号】：TP333

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