氧化石墨烯及其阻变存储器的制备和性能研究

发布时间：2018-05-06 20:51

本文选题：氧化石墨烯 + 阻变存储器　；参考：《山东大学》2012年硕士论文

【摘要】：随着信息技术的发展,高速度和高密度非易失性存储器(non-volatile random access memory, NVRAM)的发展成为一种必然趋势。传统的硅基存储器已接近其物理和工艺极限,因此,近年来各种新型的NVRAM便得到了迅速发展。其中,ReRAM具有存储密度高、功耗低、读写速度快、反复操作耐受力强、数据保持时间长、与CMOS工艺兼容、更重要的是可缩小性好(非电荷存储机制)等优点,并因此成为这些新型存储器中最有应用前景的候选者之— ReRAM单元有着简单的“三明治”(metal-insulater-metal, MIM)结构,中间绝缘阻变层的选择对器件性能起着至关重要的作用。基于GO阻变层的材料既具有有机材料成膜简单、膜层薄、成本低、可大面积溶液处理等优点,又具有无机材料器件性能好、稳定性好、寿命长等优势。因此,本文着力于研究氧化石墨烯及其阻变存储器的制备和性能研究。本论文中,首先对采用Modified Hummers'法制备的GO进行表征；其次采用旋涂工艺制备GO膜,成功制备了Al/GO/ITO ReRAM器件,并对其进行电学测试及机理分析；最后对不同退火处理下的器件进行了GO膜的表征及器件的I-V测试。本论文的研究工作及结果如下： (1)GO的制备及表征 Modified Hummers'法制备的GO在水中良好的分散性证实了GO上丰富的氧官能团。AFM数据则显示了GO的1.1nm左右的厚度及数百纳米至数微米的横向尺寸,表明了GO的完全剥离；随后的Raman光谱数据显示GO相比石墨而言有着更强的D峰和更弱的G峰,即更大的ID/IG和更小的I2D/IG,这表明了石墨烯平面上sp3平均尺寸的增加；XRD的数据显示GO有着0.93nm的层间距,证明了GO的成功插层以及石墨烯平面上sp3平均尺寸的增加；XPS分析则表明GO中含有丰富的羟基、羧基和羰基,且羟基占有很高的比重；此外,TGA测试数据显示了GO的质量随温度变化而减少的特性,进一步证实了GO中含有丰富的氧官能团。 (2) Al/GO/ITO ReRAM器件的阻变特性及机理分析 (a)阻变特性分析 Al/GO/ITO ReRAM器件在150℃退火后展现了极好的阻变特性,有着1.3V的置位电压,-2V的复位电压,约103的开关比。耐久性测试表明器件的开关比在100次循环后仍保持不变。器件的记忆时间测试则表明其有着长达104s以上的数据保存能力。此外,限制电流关系测试结果显示器件的复位电流密度和复位电压随着限制电流的增加而增加,器件的低阻态电阻随着限制电流的增加而减少。 (b)阻变机理分析电形成循环方向的机理分析表明：正向电形成循环后,器件有着稳定的低阻态和高阻态,这种结果是由于GO在电偏压下的sp3杂化和sp2杂化间的转化或表面层处的氧迁移。随后的负向电形成循环展现出了WORM的特性,我们分析这种非对称的电形成循环特性来源于器件的非对称性。 J-V特性的机理分析表明器件的J-V特性符合SCLC关系,与阻变来自于氧空位的迁移有着良好的符合度。电极单元尺寸依赖的机理分析表明：无论是高阻态还是低阻态,器件单元的电流与电极尺寸均存在着线性关系,表明器件的阻变发生在整个接触面,因此器件的机理并非sp3态与sp2态间转变的细丝机理,而是电偏压下氧官能团的迁移所引起的表面势垒的变化。 (3) GO ReRAM与退火温度的关系 (a)GO阻变层与退火温度的关系 AFM膜厚分析表明GO膜的膜厚随着退火温度的升高而减小；粗糙度分析则表明不同退火温度下的GO膜均有着良好的均匀性。Raman光谱分析表明随着退火温度的增加,GO中sp2区域平均大小逐渐增加。XRD数据表明了退火后GO中石墨结晶程度的增加,即石墨化程度的提高。XPS分析则表明C=C随着退火温度的升高而逐渐增加,对应着GO中sp2区域的增加,氧官能团的减少。 (b) GO ReRAM的性能与退火温度的关系通过对不同退火温度下器件的测试,我们发现Original Sample和Annealing150℃样品有着相同量级的开关比,而Annealing200℃和Annealing250℃样品的开关比则逐渐减少,达到10的数量级。这种开关比的变化可能来自于氧官能团的减少。
[Abstract]:With the development of information technology, the development of high speed and high-density non-volatile memory (non-volatile random access memory, NVRAM) has become an inevitable trend. The traditional silicon based memory is close to its physical and technological limits. Therefore, in recent years, various new types of NVRAM have been developed rapidly. Among them, ReRAM has a high density of storage, Low power consumption, fast reading and writing speed, strong repeated operation tolerance, long data retention time, compatible with the CMOS process, and more important is the advantages of good scalability (non charge storage mechanism) and so on, and thus become the most promising candidates in these new types of memory.
The ReRAM unit has a simple "sandwich" (metal-insulater-metal, MIM) structure. The selection of the intermediate insulation resistance layer plays a vital role in the performance of the device. The material based on the GO impedance layer has the advantages of simple film formation, thin film, low cost, large area solution treatment and so on. It also has good performance in inorganic materials. It has good stability and long life. Therefore, this paper focuses on the preparation and properties of graphene oxide and its resistive memory.
In this paper, the GO which was prepared by the Modified Hummers'method was first characterized. Secondly, the GO film was prepared by the spin coating process, and the Al/GO/ITO ReRAM device was successfully prepared. The electrical test and mechanism analysis were carried out. Finally, the characterization of the GO film and the I-V test of the devices under different annealing treatments were carried out. The results are as follows:
(1) preparation and characterization of GO
The good dispersibility of GO in water prepared by the Modified Hummers'method shows that the abundant.AFM data on GO show the thickness of 1.1nm in the GO and the transverse dimensions of several hundred nanometers to several microns, indicating the complete stripping of GO, and the subsequent Raman spectral data shows that GO has a stronger D peak and a weaker G peak than the graphite. The larger ID/IG and smaller I2D/IG show an increase in the average size of SP3 on the graphene plane, and the data of XRD show that GO has a 0.93nm interlayer space, which proves the increase of the successful intercalation of GO and the increase of the SP3 average size on the graphene plane, and XPS analysis shows that the GO contains rich hydroxyl, carboxyl and carbonyl groups, and the hydroxyl group is very high. In addition, the TGA test data show that the quality of GO decreases with temperature, which further confirms that GO is rich in oxygen functional groups.
(2) resistance variation characteristics and mechanism analysis of Al/GO/ITO ReRAM devices
Analysis of (a) resistance change characteristics
The Al/GO/ITO ReRAM device exhibits excellent resistance characteristics after annealing at 150 C, with a 1.3V setting voltage, a reset voltage of -2V, and a switching ratio of about 103.
The durability test shows that the switch ratio of the device remains unchanged after the 100 cycle. The memory time test of the device shows that the device has the data preservation capacity of more than 104s. In addition, the limiting current relation test results show that the reset current density and reset voltage increase with the increase of the Limited current, and the device has low resistivity. The resistance decreases with the increase of the limiting current.
Analysis of (b) mechanism of resistance change
The mechanism analysis of the cycle direction of electric formation shows that the device has a stable low resistance state and a high resistance state after the forward formation cycle. This result is due to the transformation of the SP3 hybrid between the GO and the SP2 hybrids under the electric bias or the oxygen migration at the surface layer. The subsequent negative electric formation cycle shows the characteristics of the WORM, and we analyze this asymmetry. The electrical forming cycle characteristics originate from the asymmetry of the device.
The mechanism analysis of J-V characteristics shows that the J-V characteristic of the device is in line with the SCLC relationship, which is in good agreement with the migration of oxygen barrier.
The mechanism analysis of the size dependence of the electrode element shows that there is a linear relationship between the current of the device unit and the size of the electrode, indicating that the device's resistance occurs at the entire contact surface, so the mechanism of the device is not the filament mechanism of the transition between the SP3 state and the SP2 state, but the migration of the oxygen functional group under the electric bias. The change of the surface barrier caused.
(3) the relationship between GO ReRAM and annealing temperature
The relationship between the (a) GO resistance layer and the annealing temperature
The AFM film thickness analysis shows that the film thickness of the GO film decreases with the increase of annealing temperature, and the roughness analysis shows that the GO films at different annealing temperatures have a good uniformity.Raman spectrum analysis. The average size of SP2 region in GO increases gradually with the increase of the annealing temperature, which indicates the degree of the graphite crystallinity in the annealed GO. The increase of the degree of graphitization by.XPS analysis shows that C=C increases with the increase of annealing temperature, which corresponds to the increase of the SP2 region in GO and the decrease of oxygen functional groups.
The relationship between the performance of (b) GO ReRAM and the annealing temperature
By testing the devices at different annealing temperatures, we found that the Original Sample and Annealing150 centigrade samples have the same magnitude of switching ratio, while the switching ratio at Annealing200 and Annealing250 degrees decreases gradually, reaching a magnitude of 10. The change of this switching ratio may come from the reduction of oxygen functional groups.

【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TP333

【参考文献】