A new transistor developed at the Weizmann Institute of Science in Rehovot has broken ground in microelectronics.
by Simon Griver
The new transistor has a width of 50 billionths of a meter (about one-thousandth the width of a human hair) and has an inner core of 20 billionths of a meter.
The research, which led to its production, was recently reported in Applied Physical Letters. It was conducted by a doctoral student, Shachar Richter, working with Prof. David Cahen, Dr. Yishay Manassen, and Dr. Sidney Cohen at the Weizmann Institute of Science, a world famous center for postgraduate research in physics, chemistry, the life sciences and mathematics.
In his research, Richter used atomic force microscopy, a technique in which a phonograph-like stylus probes the surface of a material, to manipulate atoms in a semiconductor. Normally, such microscopes can only shift atoms on the surface of a material, but Richter, building on earlier research by Prof. Cahen, managed to move these atoms around inside the semiconductor.
Richter achieved his results by applying a low voltage current to the semiconductor and passing a current through the material. Aided by the slight heat produced by the current, the voltage generated atoms (called dopants) which determine the materials conductivity, are propelled in a particular direction. Even though only 100 to 200 dopants were moved in this manner, this sufficed to produce a tiny transistor. It consisted of a hemispherical layer of relatively high conductivity containing the redistributed dopants, flanked on both sides by material with different conductivity.
These findings do not necessarily mean that microelectronic devices will eventually be made as small as Richters transistor. His device, however, can serve as a valuable research tool for studying the limits of miniaturization.
Richter also used the same microscope stylus, at low voltage, to map out the conductivity of this miniature structure. Richters new mapping method, scanning spreading resistance, reveals the precise path that would be taken by an electric current flowing through a transistor of this type. This new type of measurement, which was also developed
independently by Belgian researchers around the time of Richters study, promises to become an important tool for evaluating miniature electronic devices.
Funded by the Israel Science Foundation and the Minerva Foundation in Germany, the project made simple and elegant use of a chemical theory of liquids. The Rehovot researchers have in effect developed a way to predict the minimal possible size of bipolar transistors, one of the major types of transistors commonly used in microelectronics.