MEMS多层结构的热应力分析

Thermal stress analysis on multilayer structure of MEMS

温度载荷能够引起MEMS多层薄膜结构发生翘曲和分层等失效模式,而界面应力则是引起这些失效的直接原因。根据Suhir.E的双金属带热应力分布理论,对温度载荷作用下MEMS界面中的剪应力和剥离应力的分析表明,这两种应力随着与界面中心距离的增大呈指数增加,在界面端处达到最大值。界面应力与材料热膨胀系数和所加载温度呈线性相关,另外还与两材料层的厚度密切相关。以铜/铬组成的双层结构为例,利用Matlab数值仿真研究了界面应力与材料层厚度的关系,结果表明,界面应力与两材料层厚度比有关,当铜层和铬层厚度比为1.5时,层间剪应力和剥离应力均较小,可有效提高MEMS结构的可靠性,降低分层失效的概率。

The failure modes such as warp and delamination in MEMS multilayer structure will happen under thermal load, and the interracial stress caused by thermal load is the immediate cause to the failure modes. By using bimetal strip stress model advanced by Suhir.E, interfacial＇ shearing stress and peeling stress caused by thermal load were analyzed. The analysis shows that sheafing stress and peeling stress present exponential increatse along with the distance from centre of bonded pair, and increase sharply in the end until achieve maximum. Interracial stress is influenced linearly by difference of two material thermal expansivity and temperature loaded, and also influenced by the thickness of two material layers. Bi-layer structure composed by Cu/Cr was analyzed with Matlab on the relationship between interfaciai stress and material thickness. The result shows that the interfacial stress is influenced by the thickness ratio of two material layers. When the thickness ratio of Cu to Cr layer is 1.5, the sheafing stress and peeling stress is both small, which can reduce the probability ofdelamination failure mode.