Mechanisms of crystallization of CoFeB-based TMR stacks under laser annealing

激光退火下 CoFeB 基 TMR 叠层的结晶机制

• 批准号: 282193534
• 负责人: Professor Dr. Alexander Horn
• 金额: --
• 依托单位: Zentrum für Mikrotechnologien (ZfM)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/282193534?language=en
• 关键词: Mechanisms; crystallization; CoFeB; based; TMR

CoFeB/MgO based layer stacks have been extensively investigated as model systems for understanding spin-dependent phenomena and the tunneling magnetoresistance (TMR) effect, as well as due to their suitability for applications such as magnetic recording media, sensors, or microwave sources for communication applications. Such devices rely on a crucial thermal treatment, necessary to maximize the TMR ratio by ensuring the crystallization of the layers, together with an appropriate boron migration, as well as setting the reference magnetization through the exchange bias (EB) effect. Whereas this can be done via standard vacuum annealing in the presence of a magnetic field, a laser-based approach presents several advantages. In particular, the EB can be set locally, allowing to establish different reference magnetization directions across a single wafer and therefore to implement multidimensional magnetic field sensors with minimum magnetic hysteresis. For this purpose, a profound understanding of the changes of the thin film structural properties induced by the laser irradiation, including crystallization of the layers and diffusion mechanisms, is required. With this proposal, this laser based procedure will be introduced as a tool to induce structural modifications of CoFeB single layers, as well as CoFeB layers integrated in complex layer systems such as, for instance, magnetic tunnel junctions. The challenges underlying the characterization of the thin films involved in TMR devices will be addressed by combining ellipsometric and magneto-optical spectroscopy techniques, which have been proven in our previous work to be extremely sensitive to structural changes, too. The in-situ optical characterization of the layers during the laser annealing process, along with simulations toward the temperature dynamics of the irradiation, will furthermore allow to parameterize in detail a model of the heat transfer dynamics of the laser annealing on these thin films. Finally, a comprehensive investigation comparing oven and laser annealing, bridging the gap between continuous plane layer systems and completely microfabricated TMR devices, will be performed, to acquire the applicability of laser annealing for local enhancement of the TMR device response. This will be done in the context of the structural properties responsible for setting the EB and to obtain large TMR yields in a rather small temperature window and opposing dependencies with regard to crystallization and diffusion.

基于COFEB/MGO的层堆栈已被广泛研究为用于了解自旋依赖性现象和隧道磁磁性（TMR）效应的模型系统，以及由于它们适用于诸如磁记录媒体，传感器或微波源的通信应用程序的应用。此类设备依赖于至关重要的热处理，这是通过确保层结晶以及适当的硼迁移以及通过交换偏置（EB）效应设置参考磁化来确保层的结晶而最大化TMR比。尽管这可以通过在磁场的存在下通过标准真空退火来完成，但基于激光的方法具有多种优势。特别是，可以在本地设置EB，从而允许在单个晶圆上建立不同的参考磁化方向，从而实现具有最小磁性磁滞的多维磁场传感器。为此，需要对激光照射引起的薄膜结构特性的变化（包括层的结晶和扩散机制）的深刻理解。通过此提案，将引入基于激光的程序作为诱导COFEB单层结构修饰的工具，以及集成在复杂层系统中的COFEB层，例如磁性隧道连接。通过结合椭圆测量和磁光谱技术，将解决参与TMR设备涉及的薄膜表征的挑战，这些技术在我们以前的工作中已经证明了这对结构变化非常敏感。在激光退火过程中，层的原位光学表征以及朝向辐照温度动力学的模拟将允许在这些薄膜上进行激光退火的热传递动力学的模型进行参数化。最后，将进行一项比较烤箱和激光退火的全面研究，将连续平面系统之间的间隙和完全微观的TMR设备桥接，以获取激光退火以局部增强TMR设备响应的适用性。这将在负责设置EB的结构特性的背景下完成，并在相当小的温度窗口中获得大型TMR产量，并且在结晶和扩散方面相反。