Infineon Technologies AG (Germany) inventors divulge carbon nanotube arrays for sensor and microelectronic applications and a simpler method for producing carbon nanotube arrays with controlled directional growth in U.S. Patent 7,635,867.
According to Infineon inventors Andrew Graham, Franz Hofmann, Johannes Kretz; (Munchen, DE), Franz Kreupl, Richard Luyken and Wolfgang Rosner, they have solved the problem of providing a spatially well defined array of planar-oriented nanotubes needed for microelectronic applications and sensors.
The method for producing a nanotube array has a number of advantages. Geometrically ordered structures of nanotubes in a planar arrangement can be produced by a combination of semiconductor technology nanostructuring techniques and a technique for growing nanotubes. The individual steps of the method are based on proven, standardized semiconductor technology processes. Therefore, there is no need to develop new installations for carrying out the method according to the invention for producing the nanotube array. This saves time and costs.
A major advantage of the Infineon method according to the inventors, is in the fact that the pore geometry can be controlled means that the production of nanotubes can be precisely predetermined with regard to dimensions and direction of growth. The cross-sectional area of a nanotube is fixed by the dimension of the uncovered catalyst surface, since the nanotube growth can only start from a catalytically active material.
The preferred direction of growth of a nanotube is predetermined simply by the normal vector of the uncovered catalyst surface and is additionally stabilized by the electrically insulating layers arranged on both sides of the catalyst layer. This provides the nanotube with mechanical guidance during its growth, with the result that the nanotube grows in a predeterminable direction parallel to the surface of the substrate.
If a nanotube is allowed to grow on this surface of the catalyst layer, the direction of growth is predetermined by the geometry of the arrangement. The direction of growth of the carbon nanotube is perpendicular to the uncovered surface of the catalyst layer. Therefore, the direction of growth of the nanotube is horizontal, i.e. the nanotube grows in a direction which is parallel to the surface of the substrate. The first and second electrically insulating layers projecting beyond the catalyst layer on both sides mechanically guide the growth of the nanotube, with the result that the growth takes place in the horizontal direction parallel to the surface of the substrate. Since the direction of growth can be predetermined by the geometry of the pores, it is possible to achieve a defined structure of carbon nanotubes. This high degree of structural definition is advantageous when the nanotube array is being coupled to conventional silicon microelectronics.
A further advantage is that the nanotube array provides individual nanotubes rather than tufts of nanotubes with diameters in the region of 50 nm, as in the prior art. The periodic provision of pores also makes it possible to achieve a periodic array of nanotubes. In this respect, it should be emphasized that the size of the pores can be selected to be sufficiently small for only a single nanotube to grow in or from a pore.
Infineon’s nanotube array has a substrate, a catalyst layer, which includes one or more sub-regions, on the surface of the substrate and at least one nanotube arranged on the surface of the catalyst layer, parallel to the surface of the substrate. The at least one nanotube is arranged parallel to the surface of the substrate such that it results in a planar arrangement of at least one nanotube. The nanotube array is suitable for coupling to conventional silicon microelectronics.
It is possible for a nanotube array to be electronically coupled to macroscopic semiconductor electronics. Furthermore, the nanotube array may have an electrically insulating layer between the substrate and the catalyst layer. This electrically insulating layer preferably has a topography which is such that the at least one nanotube rests on the electrically insulating layer at its end sections and is uncovered in its central section.
