Ultra-low CTE-mismatch of 3C-SiC-on-Si thin films for high temperature MEMS applications

Abstract

In this paper, we demonstrate the impact of controlled gas flow changes with alternative supply deposition on the CTE-mismatch of 3C-SiC-Si heterostructures using LPCVD. Especially for MEMS systems it is of great interest to overcome the working temperature limitations given by classic Si applications. Silicon carbide, among other things, is known for its outstanding thermal properties. Thus, replacing or combining Si with SiC in key positions can increase the range of applications. However, the well-known issue of the CTE-mismatch of up to 31 % at 900 °C is impeding this promising progress. With our tailored polycrystalline 3C-SiC thin films it is possible to control the CTE-mismatch resulting in values as low as 3.8 % at 900 °C. For demonstration purposes, we applied two 3C-SiC thin films with significant differently CTEs to micromachined 3C-SiC/Si-MEMS micro hotplate (µHP) structures. Using tailored platinum micro heaters for thermal excitation, the deflection of the µHPs was measured. Hereby µHPs with a lower CTE-mismatch showed on average 3.6 times less deflection amplitudes for the same applied heating power. Theoretical considerations of the impact of the platinum on the total deflections are also provided. We emphasize the potential for MEMS applications, as either the thermal stress can be reduced, or the working temperature of such devices can be significantly increased without causing damaging malfunctions of the device.