Authors: M. Pozzi, A.J. Harris, J.S. Burdess, K.K. Lee and R. Cheung
Affilation: Newcastle University, United Kingdom
Pages: 65 - 68
Keywords: cubic silicon carbide, 3C-SiC, MEMS, micro-electro-mechanical-systems, residual stress, temperature dependency of Young’s modulus, temperature coefficient of Young’s modulus, TCYM, harsh environment
Silicon carbide (SiC) is widely recognised as the leading candidate to replace silicon in Micro Electro-Mechanical Systems (MEMS) devices operating in harsh environments. The superiority of SiC over Si as regards mechanical, chemical and electronic properties is well documented. Yet, SiC is not so well understood as Si. In this work, test devices in SiC are designed, fabricated and evaluated between room temperature (RT) and 600 C. The active material is a cubic poly SiC layer deposited on a poly-Si layer which is separated from the Si substrate by a thermal oxide. Cantilevers and bridges are excited either mechanically or electrostatically. Their resonance frequency is measured by Laser Doppler Velocimetry and used to derive the Young’s modulus and residual stress in the heteroepitaxial layer (330±45 GPa and 200±20MPa, respectively). The temperature coefficient of Young’s modulus is found to be -53±2 ppm/K in the range RT to ~300 C, while an analytical expression is given for the temperature dependency of the Young’s modulus between RT and 500 C. The residual tensile stress is found to depend on temperature in a complex manner.