Chromium oxide – A novel sacrificial layer material for MEMS/NEMS and micro/nanofluidic device fabrication

Abstract

Free standing membranes for fluidic devices typically require long etching times due to the slow, diffusion limited exchange of etchant and etch products when large etch distances are involved. In these cases, high etch selectivity is required between the sacrificial and channel-wall materials. Here, we introduce chromium oxide, Cr2O3, as a versatile sacrificial layer material for the fabrication of microfluidic and nanofluidic channels. Chromium oxide has many desirable attributes as a sacrificial layer: it can be deposited by sputtering to form stress-controlled films, it adheres well to both metal and dielectric surfaces, it is resistant to most acids and bases, but etches rapidly in standard chromium etchants, and has minimal tendencies to react with other commonly used materials. In addition, typical chromium etchants are highly selective to materials commonly used in microfabricated systems. To fully explore the process characteristics of this material we performed a comprehensive set of experiments to quantify its behavior in ways relevant to its use in device fabrication. The results presented in this paper will provide a starting point to optimize Cr2O3 for fabrication of fluidic devices.