界面合金化控制柔性Al/PI薄膜应力的研究

针对航天器用MEMS热控百叶窗存在的柔性薄膜应力问题, 开展界面合金化控制薄膜应力技术研究. 通过给柔性Al/PI薄膜体系添加中间层Sn, 使其合金化, 使晶格产生膨胀畸变, 来引入相反的应力与已经存在的本征压应力相抗衡, 可获得低表观应力的薄膜. 用SEM和EDS剖面分析验证了Sn原子发生了明显的扩散现象, 形成了Al-Sn合金层. 这种方法可作为控制薄膜应力的一种新的技术手段.

Study on controlling the stress in flexible Al/PI film by interface alloying

Micro-eletromechanical system (MEMS) thermal-control shutters for spacecraft are fabricated by using the flexible Al/PI film, because of its light mass, no brittleness and withstanding severe mechanical environment (mechanical environment adaptability) in space. But the stress in the film would be able to bend the shutters too much to fabricate shutter array. Therefore, how to control the thin film stress is an important problem and it is necessary for flat shutters to take some measure to remove or reduce the thin film stress. This internal stress in the thin film formed intricately during the deposition process would make the film exhibit macroscopic compressive stress. So it is difficult to control the thin film stress micro-mechanically, but macro-mechanically. According to the results of the current study, the controlling technology of thin stress is commonly applicable to rigid substrates. In this paper, the flexible Al/PI film may be controlled by interface alloying. We put forward a way of adding Sn layer to the flexible Al/PI film, which makes Al/Sn interface to be alloyed as a measure to control the stress. In the alloy phase, lattice expansion and distortion results in the emergence of transverse shearing stress. The intrinsic compressive stress can be canceled out by the transverse shearing stress and the apparent stress in the films decreases consequently. The Sn atoms diffusion behaviour is proved to form Al-Sn alloying layer by SEM and EDS. This method can be used as a new technology of controlling thin film stress.