Fabrication and characterization of polycrystalline SiC resonators

This paper presents the development of polycrystalline 3C silicon carbide (polySiC) lateral resonant devices, which are fabricated by a three-mask surface micromachining process using silicon dioxide (SiO₂), polysilicon, and nickel (Ni) as the isolation, sacrificial, and contact metallization layers, respectively. The polySiC resonators are packaged for operation in high temperature environments using ceramic-based materials and nickel wirebonding procedures. Device operation is successfully demonstrated over <10^-5-760 torr and 22-950°C pressure and temperature ranges, respectively. Quality factors (Qs) of >100 000 at <10^-5 torr and resonant frequency drifts of <18 ppm/h under continuous operation are achieved using an scanning electron microscope (SEM) setup. Device resonant frequency varies nonlinearly with increasing operating temperature. Finite element modeling reveals that this variation resulted from the interplay between the Young´s modulus of polySiC and induced stresses, which occur due to mismatch in thermal expansion coefficients of the polySiC film and the underlying silicon (Si) substrate.