Robust Free-Standing Nano-Thin SiC Membranes Enable Direct Photolithography for MEMS Sensing Applications

This work presents fabrication of micro structures on sub–100 nm SiC membranes with a large aspect ratio up to 1:3200. Unlike conventional processes, this approach starts with Si wet etching to form suspended SiC membranes, followed by micro-machined processes to pattern free-standing microstructures such as cantilevers and micro bridges. This technique eliminates the sticking or the under-etching effects on free-standing structures, enhancing mechanical performance which is favorable for MEMS applications. In addition, post-Si-etching photography also enables the formation of metal electrodes on free standing SiC membranes to develop electrically-measurable devices. To proof this concept, the authors demonstrate a SiC pressure sensor by applying lithography and plasma etching on released ultrathin SiC films. The sensors exhibit excellent linear response to the applied pressure, as well as good repeatability. The proposed method opens a pathway for the development of self-sensing free-standing SiC sensors.