Fabrication of monocrystalline 3C–SiC resonators for MHz frequency sensors applications

Modern microelectronics and micromachining are based on crystalline silicon. The increasing demand for sensors able to operate in harsh environment, as temperature above 300 °C, high pressures, intense vibrations or corrosive liquids, has stimulated the research for alternatives to silicon. Particularly due to its superior electrical, mechanical and chemical properties, silicon carbide is a material that has attracted much attention. Some tentative of MEMS fabrication with polycrystalline or amorphous SiC have been already carried out in past but high stress in the layers and low electrical efficiency have been obtained. In this work single crystal SiC based resonators able to work at high frequencies with high quality factors have been successfully fabricated and tested. Using a novel surface micromachining process with improved CVD grown 3C–SiC layers, we have obtained suspended structure thicknesses higher than 1 μm and with vertical sidewalls clearly defined. Preliminary characterization results based on direct observation of the cantilevers resonance have shown that the resonance frequencies of these structures are 50% higher than those of equivalent Si devices. This is particularly interesting for high sensing applications. In addition, the quality factor is also increased by more than 100%, when compared with the Si counterpart. Many devices were resonated at frequencies superior to 1 MHz and the future objective will be to obtain superior frequencies with nano-devices.