1. A method of forming a nanotube crossbar cell, the method comprising: providing a semiconductor substrate having a first opening formed thereon that defines a bottom chamber filled with a sacrificial material with a crossbar element formed over the sacrificial material of the first opening, the crossbar element comprising one of a nanotube or a nanotube ribbon, the substrate further including a second opening above the bottom chamber to define a top chamber filled with sacrificial material, the top chamber includes an extension region that extends beyond an edge of the bottom chamber; forming a roof layer on the top of the substrate so that the roof layer includes at least one aperture that exposes a portion of the sacrificial material of the extension region of the top chamber; removing the sacrificial material from the top and bottom chambers to form an open bottom chamber below the crossbar element and an open top chamber above the crossbar element; and forming a conductive plug layer that blocks the at least one aperture in the roof layer to seal the open top and bottom chambers.