In this article, the authors present microfluidic mixers containing three-dimensional (3D) geometries used to decrease mixing lengths in passive microfluidic systems. In order to create these 3D geometries, the authors use ion beam lithography and micromachining and address charging, redeposition, and stitching error effects that follow this type of fabrication. Prior to mixer fabrication, simulations were run and results were compared between a common straight mixer and two other mixers designed by the authors. The simulation results have shown that 3D geometries can generate lateral velocities and lower mixing lengths down to approximately 70 mu m. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3505128]