Mesa-supported, Single-crystal Microstructures Fabricated by the Surface/Bulk Micromachining Process

In fabricating microelectromechanical systems (MEMS), bulk micromachining using (100) and (110) single crystal silicon and surface micromachining using polycrystalline silicon are most commonly used. However, both micromachining methods have drawbacks, and fabricating actuating or sensing microdevices using single crystal silicon has been an active research topic in recent years. The surface/bulk micromachining (SBM) process using (111) silicon, developed by us previously, allows fabricating released structures in single crystal silicon. This paper extends the SBM process to fabricate released structures that are anchored to the substrate via mesa islands. This allows fabricating folded-type comb drive resonators. With the extension of the SBM process developed in this paper, any microstructure fabricated by the one structural polysilicon surface micromachining technique can also be fabricated in single crystal silicon.