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by Neil Graf
Without question, the transistor ranks among the most important devices used to develop the technology that surrounds us in our everyday lives, such as radios, TVs, and computers.
A transistor is a three-terminal solid-state device that acts as an on-off switch. Transistors have many important applications, including producing the current, voltage, and power gains of signals; coupling circuits of differing impedance levels; and manipulating signals in the frequency domain.
The transistor was invented December 23, 1947, by a trio of scientists—experimentalist Walter Brattain and theoreticians William Shockley and John Bardeen—who shared the 1956 Nobel prize in physics for the invention.
Although the first transistor was developed at Bell Labs, New Jersey, the history behind its invention has a rich and venerable connection to the Minnesota. Brattain earned his doctorate from the University in 1929, and Bardeen was on the University faculty from 1938 to 1941. After spending World War II at the U.S. Naval Ordinance Laboratory, Bardeen considered returning to the University's physics department, but decided to accept a position at Bell Labs.
The invention of the transistor sparked what many would call "a solid-state electron device revolution." This revolution was in large part made possible by "Moore's Law."
In 1965, Gordon Moore, then chairman of Intel, predicted that the number of transistors per silicon chip would double every year for at least the following two decades. To date, Moore's Law has been uncannily accurate. Currently, a 2.2 GHz Pentium 4 microprocessor holds approximately 55 million transistors on a silicon chip slightly larger than one square inch.
One might ask, "What is the limit of the density of transistors that can be put on a silicon wafer?" Answers may differ, but the density limit may be reached as soon as 2010. However, nanotechnology—typically defined as any technology dealing with structures smaller than 100 nanometers—will likely come to the rescue.
Nanotechnology's role
A group of IT faculty is conducting research aimed at using nanometer-sized single crystal silicon particles to improve the manufacture of electronic devices such as computer chips.
To fabricate nanotransistors for this project, the researchers synthesize controlled-diameter spherical silicon particles in a silane (SiH4) plasma. The particles are extracted from the plasma chamber and put through a series of postprocessing steps to acquire various properties. Then they are deposited at predetermined sites on a wafer using electrostatic techniques.
The nanoparticles can be used to make transistors and various single electron devices. A unique feature of this approach is that chips can be built on any kind of substrate plus they can freely mix different kinds of single crystal materials. Steve Campbell, professor of electrical engineering and director of IT's Microtechnology Laboratory, says we might someday see high-performance computers woven into clothing or built on a contact lens.
Transistors are built with nano-particles using electron beam lithography, a process in which a focused beam of electrons strikes the surface of the substrate coated with a thin film called a resist. When the wafer is put in a chemical developer solution, areas on which electrons were deposited are removed, leaving the desired structure.
Looking ahead
Using electron beam lithography, it's possible to create physical structures with very precise dimensions and shapes—such as an image of the University logo—composed of lines 1,000 times smaller than a human hair.
Thanks to nanotechnology, the capacity to make electronic devices increasingly small, intricate, and complex will no doubt continue for many years. The applications for such atomic-size electronic devices are countless, and the possibilities of this burgeoning field of science seem limited only by the imagination.
Whatever the future may bring in the form of nanotechnological advances, it would be hard to argue that this technology will not affect people and the planet in dramatic ways. One can expect to see nanotechnology bring out the best in scientists and engineers across the globe as they make the world a more hospitable place by increasing the quality of life and standard of living.
As Campbell says, "The previously unimaginable world we live in today, with streaming video, laptops, PDAs and cell phones, was brought about by microtechnology innovations. There is every reason to believe that nanotechnology will provide at least as many changes to our lives that we cannot yet foresee."
FOR MORE INFORMATION:
www.rohm.co.jp/en/transistor/what1.html
www.thestudy.qc.ca/students/History/Transistors/Links.html
