  At reduced dimensionality, Coulomb interactions play a crucial role in
determining device properties. While such interactions within the same carbon
nanotube have been shown to have unexpected properties, device integration and
multi-nanotube devices require the consideration of inter-nanotube
interactions. We present calculations of the characteristics of planar carbon
nanotube transistors including interactions between semiconducting nanotubes
and between semiconducting and metallic nanotubes. The results indicate that
inter-tube interactions affect both the channel behavior and the contacts. For
long channel devices, a separation of the order of the gate oxide thickness is
necessary to eliminate inter-nanotube effects. Because of an exponential
dependence of this length scale on dielectric constant, very high device
densities are possible by using high-k dielectrics and embedded contacts.
