Use of Metallic Interlayers to Promote Metal/Metal Epitaxial Growth

本研究的目的是研究超薄金属夹层在多层薄膜结构中稳定界面的潜力。该研究将确定那些当在界面上沉积单层数量时可能在系统中产生突然的外延界面的金属，否则这些界面的特征是相互扩散或粗糙。与表面活性剂不同，层间材料将留在界面上，以提高化学、热和结构稳定性。与传统的扩散屏障不同，中间层应该是原子薄的，以尽量减少对器件磁性质的影响。由于目前隧道结的制造技术涉及在各种铁磁性金属（Fe, Co， Ni及其合金）上生长的Al膜的氧化，因此这些界面的结构和热稳定性将首先进行表征。然后将研究中间层对这些结构的影响。先前的研究表明，Ti, Zr，也许还有Ta有潜力在铝/过渡金属界面中作为稳定的超薄中间层。我们将研究这些磁性薄膜在氧化铝表面的结构和稳定性，无论是否有中间层。测量将利用高能离子后向散射和通道、低能电子衍射、低能离子散射和x射线光电子衍射来表征界面上有序生长或相互扩散的程度。核能级的光电子结合能将用于识别界面上的化合物形成。蒙特卡罗计算机模拟，利用嵌入原子势计算总能量，将指导结构分析。测试结构将使用那些看起来具有最稳定和突变界面的材料制造，并测量这些结构的磁开关和隧道特性。这项研究的结果将提供更好的理解，预测和生长突然外延金属/金属界面的能力。这项工作主要是针对改善薄膜磁性隧道结和巨磁阻结构中的界面，这些界面被认为是用于磁记忆或传感应用的，在这些界面中，人们认为更多的突然界面将导致具有更好的磁开关特性和更低的总电阻的器件

The objective of this research is to investigate the potential for ultrathin, metal interlayers to stabilize the interface in multilayered, thin-film structures. The research will identify those metals which when deposited in monolayer amounts at the interface make possible abrupt, epitaxial interfaces in systems that are otherwise characterized by interdiffusion or roughness. The interlayer materials, unlike surfactants, will remain at the interface to promote chemical, thermal, and structural stability. The interlayer should be atomically thin, unlike conventional diffusion barriers, to minimize the impact on any magnetic properties of the device. Since current fabrication techniques for tunnel junctions involve the oxidation of Al films grown on various ferromagnetic metals (Fe, Co, Ni, and their alloys), the structure and thermal stability of these interfaces will be characterized first. The effect of the interlayer on these structures will then be studied. Previous work suggests that Ti, Zr, and perhaps Ta have the potential for serving as stabilizing, ultrathin interlayers in aluminum/transition metal interfaces. The structure and stability of these magnetic films on oxidized Al surfaces, with and without an interlayer, will be studied. The measurements will characterize the degree of ordered growth or interdiffusion at the interface using high-energy ion backscattering and channeling, low energy electron diffraction, low-energy ion scattering, and x-ray photoelectron diffraction. Core-level photoelectron binding energies will serve to identify compound formation at the interface. Monte Carlo computer simulations, using embedded atom potentials to calculate total energies, will guide the structure analysis. Test structures will be fabricated using those materials that appear to have the most stable and abrupt interfaces, and the magnetic switching and tunneling properties of these structures will be measured. %%%The results of this research will provide a better understanding of, and ability to predict and grow abrupt epitaxial metal/metal interfaces. The work is directed primarily at improving the interfaces in thin-film magnetic tunneling junctions and giant magnetoresistive structures being considered for magnetic memory or sensing applications, where it is felt that more abrupt interfaces will result in devices with better magnetic switching characteristics and lower total resistance.***