Zhang Yulong, Sun Jianwen, Liu Huiliang, Liu Zewen
School of Integrated Circuits, Tsinghua University, Beijing 100084, China.
Institute of Telecommunication and Navigation Satellites, China Academy of Space Technology, Beijing 100094, China.
Micromachines (Basel). 2022 Jan 22;13(2):166. doi: 10.3390/mi13020166.
High-temperature processes, such as packaging and annealing, are challenges for Radio-Frequency Micro-Electro-Mechanical-Systems (RF MEMS) structures, which could lead to device failure. Coefficient of thermal expansion (CTE) mismatch and the material's creep effect affect the fabrication and performance of the MEMS, especially experiencing the high temperature. In this paper, the Thermal-Mechanical-Stress-Creep (TMSC) effect during thermal processes from room temperature (RT) to 200 °C is modeled and measured, in which an Au-cantilever-based RF MEMS switch is selected as a typical device example. A novel Isolation-Test Method (ITM) is used to measure precise TMSC variation. This method can achieve resolutions of sub-nanometer (0.5 nm) and attofarad (1 aF). There are three stages in the thermal processes, including temperature ramping up, temperature dwelling, and temperature ramping down. In different stages, the thermal-mechanical stress in anchor and cantilever, the grain growth of gold, and the thermal creep compete with each other, which result in the falling down and curling up of the cantilever. These influencing factors are decoupled and discussed in different stages. The focused ion beam (FIB) is used to characterize the change of the gold grain. This study shows the possibility of predicting the deformation of MEMS structures during different high-temperature processes. This model can be extended for material selection and package temperature design of MEMS cantilever in the further studies.
诸如封装和退火等高温工艺对射频微机电系统（RF MEMS）结构而言是挑战，这可能导致器件失效。热膨胀系数（CTE）不匹配以及材料的蠕变效应会影响MEMS的制造和性能，尤其是在经历高温时。本文对从室温（RT）到200°C的热过程中的热 - 机械 - 应力 - 蠕变（TMSC）效应进行了建模和测量，其中选择基于金悬臂梁的RF MEMS开关作为典型器件示例。一种新颖的隔离测试方法（ITM）用于测量精确的TMSC变化。该方法可实现亚纳米（0.5 nm）和阿托法拉（1 aF）的分辨率。热过程有三个阶段，包括升温、保温和降温。在不同阶段，锚定结构和悬臂梁中的热机械应力、金的晶粒生长以及热蠕变相互竞争，导致悬臂梁下降和卷曲。这些影响因素在不同阶段被解耦并进行了讨论。聚焦离子束（FIB）用于表征金晶粒的变化。本研究展示了预测不同高温过程中MEMS结构变形的可能性。该模型可在进一步研究中扩展用于MEMS悬臂梁的材料选择和封装温度设计。
