The Future of Nanotechnologies in Computing (Part 2)
Nano-devices
The development of VSLI computer systems over the last few decades has mainly been led by the development of the CMOS chip (Neimier et al 2000). This has proved to be a very successful method of building computer systems, which is still conforming to the implied rules of Moore’s Law, which can be seen in Figure 4. However, the refinement of the silicon transistor may well reach its limits within the next decade with top speeds of around 10-15GHz (Beckett and Jennings 2002). This means that the development of nano-scale electronics and system architectures is becoming increasingly important.
Figure 4 – Diagram illustrating Moore’s Law (Intel).
Most of the nanotechnologies that are currently in use are knows as ‘passive nanostructures’. Passive nanostructures are nano-scale materials; they do not in themselves do anything, but can be used to build other nano-devices or inserted into other larger materials to change their physical properties. Passive nanostructures are already well understood and are produced in bulk for use within many commercial products (Winters 2005). This is only the first stage in the development of nanotechnologies. There will be another three stages of development before nanotechnologies can be exploited to their full (The NanoTechnology Group Inc 2006). The next stage is ‘active nanostructures’. These have only become commercially viable in the last couple of years in devices such as computer processors (Winters 2005). Active nanostructures are devices that perform some kind of processing or action, such as a semi-conductor. Active nanostructures are currently used commercially, but are also still in development so they can be improved and their full potential harnessed. The third generation will be complex nanostructures (Winters 2005). These will involve using different combinations of active and passive nanostructures to create simple devices and machines. These are still very much in research and development and are not yet used commercially. The fourth stage of development will be molecular nano-systems. The development of these systems will require all the previous stages to be well developed and a good understanding of nano-system biology will be required as these systems will in effect be synthetic biology (The NanoTechnology Group Inc 2006).
Development Techniques
There are two approaches to the way nanotechnologies can be developed. These are top-down and bottom-up. When using the top-down approach devices are constructed by removing material from larger entities, such as semi-conductors. Very complex structures can be made, such as microprocessors, using this process (Lundstorm 2002). Most current computer chip technologies that reach the nano-scale are achieved with a top-down approach, but increasingly new techniques are being used to converge bottom-up and top-down production techniques.
The bottom-up approach involves building devices up atom by atom. This technique is also known as molecular nanotechnology. As was mentioned earlier molecular nanotechnology will be the fourth stage and the ultimate goal in the development of nanotechnologies. These will use the forces of nature to ‘self assemble’ nanostructures (Lundstorm 2002). The self assembling properties of biological systems, such as DNA, can be used to control the organisation of entities such as carbon nano-tubes, which may lead to the ability to ‘grow’ parts of an integrated circuit, rather than having to rely on expensive ‘top-down’ techniques (Institute of Nanotechnology 2006).
As the development of bottom-up techniques improve they will no doubt be integrated with top-down techniques and will probably some day replace most top-down production techniques. This is because the lithography of top-down techniques is very complex and expensive; however as bottom-up techniques develop they should be self-assembling which will greatly reduce the cost of constructing nano-devices.
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