The Litho-to-Nano link

Linking in a one-to-one fashion features with separation below the lithographic limit to lithographically defined contacts. If the availability of nanofabrication techniques is fundamental to establish nanotechnology, no less vital is the integration of the nanostructures with higher-level structures. As emphasized in a scholium to [129], “the difficulties in communication between the nanoworld and the macroworld represent a central issue in the development of nanotechnology.” This is particularly true in the case of hybrid silicon-molecular devices, wherein once the crossbar structure is formed, it is necessary to link it to the embedding conventional CMOS circuitry [130]. The importance of addressing nanoscale elements in arrays goes beyond the area of memories and will be critical to the realization of other integrated nanosystems such as chemical or biological sensors, electrically driven nanophotonics, or even quantum computers. In the following analysis, however, attention will be confined to the problem of addressing, by means of externally accessible lithographic contacts, nanoscopic crosspoints in a sublithographic crossbar. The practical exploitation of the functionalized crossbar requires that once this structure has been prepared, it must be linked to conventional silicon circuitry. This is a difficult task because the current conventional CMOS circuits at the forefront of the technology are characterized by a feature size of 45 nm (half pitch) whereas crossbars can now on be prepared with a pitch of, say, 30 nm.