A typical microprocessor integrates a large number (greater than a hundred million) of small (less than 100 nanometers) electronic parts, but the miniaturized systems of the future will also need to incorporate photonic, mechanical, chemical, and even biological devices. The semiconductor industry has had impressive success in producing integrated electronics, but it has been decidedly less successful at mass-manufacturing multifunctional microsystems, partly because the processes used to make different components are incompatible. A major question for engineers is what manufacturing process can mass-produce useful multifunctional, miniature systems. The conventional approach to making engineered products is unlikely to yield a satisfying answer.
The most complex functional systems are found in the biological world. Nature is full of machines with trillions of nanoscale components all working in harmony. The complexity and sophistication of biological machines–in terms of the number of parts, the variety of materials used, and the diversity of functions performed–is far beyond what any microfabrication or nanofabrication can achieve.
These advanced biological machines are mass-produced in a way that is fundamentally different from the way we produce products such as microprocessors, automobiles, or airplanes today. In nature, components “self-assemble” to yield complex functional systems. Inspired in part by this observation, a number of research groups are working to enlist self-assembly as a method for producing functional products across size scales. The hope is to create a new paradigm in mass manufacturing in which self-assembly replaces assembly of parts one by one. We believe that, in principle, it is possible to “grow” an integrated circuit, a biomedical sensor, or a display.
To get a system to self-assemble from the bottom up, you have to address a few key issues: how the parts are made, how they are induced to recognize and bind to each other in the correct fashion, and how the assembly process can be controlled and streamlined. Chemical synthesis can readily produce a large number of nanoscale “parts” such as quantum dots or molecules that are designed to perform specific functions. And researchers can take advantage of specific covalent bonds or supramolecular bonds such as DNA hybridization or protein-inorganic surface interactions to program the self-assembly process.
Our group has investigated these methods as a way to produce hybrid organic-inorganic transistors and photonic waveguides. Solid-state microfabrication is another technique for producing parts for self-assembly. The parts are fabricated separately, released, and then induced to self-assemble. Our group has used this approach to construct high-performance silicon circuits on plastic.
This revolutionary manufacturing method offers many opportunities. Growing machines may not be as far-fetched as it once seemed.
Babak A. Parviz is an assistant professor of electrical engineering at the University of Washington. He is also a member of this year’s TR35.