Behrmann Ole, Lisec Thomas, Gojdka Björn
Fraunhofer-Institute for Silicon Technology ISIT, 25524 Itzehoe, Germany.
Micromachines (Basel). 2022 Jul 26;13(8):1178. doi: 10.3390/mi13081178.
Most current thermal MEMS use fragile structures such as thin-film membranes or microcantilevers for thermal isolation. To increase the robustness of these devices, solid thermal insulators that are compatible with MEMS cleanroom processing are needed. This work introduces a novel approach for microscale thermal isolation using porous microstructures created with the recently developed PowderMEMS wafer-level process. MEMS devices consisting of heaters on a thin-film membrane were modified with porous microstructures made from three different materials. A thermal model for the estimation of the resulting thermal conductivity was developed, and measurements for porous structures in ambient air and under vacuum were performed. The PowderMEMS process was successfully used to create microscale thermal insulators in silicon cavities at the wafer level. Measurements indicate thermal conductivities of close to 0.1 W/mK in ambient air and close to 0.04 W/mK for porous structures under vacuum for the best-performing material. The obtained thermal conductivities are lower than those reported for both glass and porous silicon, making PowderMEMS a very interesting alternative for solid microscale thermal isolation.
目前大多数热微机电系统（MEMS）采用诸如薄膜膜片或微悬臂梁等易碎结构来实现热隔离。为了提高这些器件的稳健性，需要与MEMS洁净室工艺兼容的固态热绝缘体。这项工作介绍了一种利用最近开发的粉末微机电系统（PowderMEMS）晶圆级工艺制造的多孔微结构实现微尺度热隔离的新方法。由薄膜膜片上的加热器组成的MEMS器件用三种不同材料制成的多孔微结构进行了改性。开发了一个用于估算所得热导率的热模型，并对环境空气和真空下的多孔结构进行了测量。粉末微机电系统工艺成功用于在晶圆级硅腔中制造微尺度热绝缘体。测量表明，对于性能最佳的材料，在环境空气中热导率接近0.1W/mK，在真空下多孔结构的热导率接近0.04W/mK。所获得的热导率低于玻璃和多孔硅报道的热导率，这使得粉末微机电系统成为固态微尺度热隔离的一个非常有一个非常有吸引力的替代方案。
