A typical method of top-down fabrication includes photolithography to define the geometry of channels on a substrate wafer. The geometry is created by several thin-film deposition and etching steps to form trenches. The substrate wafer is then bonded to another wafer to seal the trenches and form channels. Other technologies to fabricate nano-channels include surface micromachining with sacrificial layers, nano-imprinting lithography, and soft-lithography.