Micro/nanoscale electronics assembly: where are we? Where do we go from here?
Article Type: Viewpoint From: Assembly Automation, Volume 30, Issue 3
Recent estimates by international research institutes suggest that by the year 2015, $1 trillion worth of products worldwide will incorporate nanotechnology in key functional components. Of this amount, nanoelectronics– including semiconductors, nanotransistors, ultra capacitors, nanostorage and nanosensors – will amount to $300 billon. Nanoscale electronics devices have received a great deal of attention due to their small size and versatility relative to conventional microelectronic chips. They will have a major impact on information processing, storage and transmission technologies by continuing or surpassing Moore’s law of doubling data storage and processing capacities every 18 months.
Assembly tasks consist of two basic categories: part mating and part joining. Assembly of micro and nano devices needs to address these two issues. Mass production of nanoscale electronics is a challenging task. Can current semiconductor manufacturing technology be applied or will new methods need to be invented? What are the critical issues that may prohibit automated assembly?What are possible solutions?
So where are we?
Top down. Refers to creation of small devices such as nanoelectronic devices based on a larger template such as a wafer. Current semiconductor fabrication equipment can produce devices smaller than 100 nm,such as the magnetoresistance-based hard drive heads described on the US National Nanotechnology Initiative web site (www.nano.gov/html/facts/appsprod.html). The challenge is to further reduce the size of devices produced to less than 100 nm and to double the size of data storage every 18 months. Research has successfully demonstrated use of Atomic Force Microscope (AFM) tips to deposit chemicals (<10 nm) upon the surface of a desired pattern. Focused ion beams(FIB) can then be used to directly remove or deposit materials (<5 nm) onto a desired pattern template. Although these are significant achievements, the process is still very time consuming and costly and is not designed for mass production. Similarly, although excellent nanojoining processes been developed using lasers, electronic ion beams, ultrasound and resistance welding, the equipment is designed for laboratory – not industry – environments.
Bottom up. Typically refers to the arrangement of nanomaterials into a complex assembly. The materials may be atoms or molecules. Common approaches include self-assembly, chemical synthesis and direct (sometimes called positional) assembly. Self-assembly refers to the spontaneous organization of molecules or objects into well-defined aggregates via non-covalent interactions (or forces). Self-assembly techniques, such as use of a DNA structure as a carrier template to assemble nanomaterials, have received much attention. These assemblies can generally be fabricated in large quantities. However, the functional properties (such as electrical and catalytic) of these structures have not yet been fully studied and understood. Moreover, reliable methods for interconnecting these structures to form larger networked structures (such as integrated circuits) have not yet been developed.
Where do we go from here?
Learning from nature. Studies have shown that using AFMs to arrange large quantities of nanoparticles into desired patterns is difficult and time-consuming. Molecular biology-based approaches, such as use of DNA structures, exhibit the capability of self-assembly of large quantities of nanomaterial into patterns. Understanding how self-assembly takes place and how to control self-assembly to form desired patterns and provide desired functions is an important and challenging agenda. In addition, understanding how to interconnect these structures to form larger networked structures (such as integrated circuits) is another challenging task.
Man-made versus natural. Semiconductor materials have been the primary ingredient for manufacturing integrated circuits. The fabrication process and equipment are a modern marvel of technology. Natural approaches,such as use of DNA structures, allow self-assembly by providing a lock-and-key recognition mechanism. Understanding how to take advantage of the strengths of various materials is an interesting and promising area for exploration. Such understanding would bring us a step closer to successful and cost-effective mass assembly of large quantities of nanoelectronics.
Top-down, bottom-up and self-assembly. One of the most costly manufacturing processes is patterning and prospects for cost reductions for top-down methods are not encouraging. Progress is being made in the use of self-assembly for block co-polymers to achieve increasingly complex features. For example, it appears that self-assembly methods provide improvements in line-edge roughness relative to top-down methods of patterning. IBM has reported experimental use of limited forms of self-assembly in a pre-production facility;however, much research is needed to provide an adequate foundation for the utilization of directed self-assembly in mainstream production of integrated circuits. Perhaps, an appropriate goal for the use of self-assembly in nanoelectronics manufacturing is to approach the very high assembly speed, very high complexity and very low energy costs of assembly that is observed in living organisms.
In summary, much progress has been made, but there is much territory yet to explore. Given that 20 countries worldwide have set nanotechnology as a research priority and many researchers are devoting energy into this field (over 1,200 universities and 1,050 organizations), as reported in the 2006 European Commission DG Research Nano S&T report (http://cordis.europa.eu/nanotechnology/),it is obvious that the future is bright and progress will be significant.
Sheng-Jen “Tony” HsiehBased at the Texas A&M University, College Station, Texas, USA
